Modern Measurements of Uranium Decay Rates

NASA Astrophysics Data System (ADS)

Parsons-Moss, T.; Faye, S. A.; Williams, R. W.; Wang, T. F.; Renne, P. R.; Mundil, R.; Harrison, M.; Bandong, B. B.; Moody, K.; Knight, K. B.

2015-12-01

It has been widely recognized that accurate and precise decay constants (λ) are critical to geochronology as highlighted by the EARTHTIME initiative, particularly the calibration benchmarks λ235U and λ238U. [1] Alpha counting experiments in 1971[2] measured λ235U and λ238U with ~0.1% precision, but have never been independently validated. We are embarking on new direct measurements of λ235U, λ238U, λ234Th, and λ234U using independent approaches for each nuclide. For the measurement of λ235U, highly enriched 235U samples will be chemically purified and analyzed for U concentration and isotopic composition by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). Thin films will be electrodeposited from these solutions and the α activity will be measured in an α-γ coincidence counting apparatus, which allows reduced uncertainty in counting efficiency while achieving adequate counting statistics. For λ238U measurement we will measure ingrowth of 234Th in chemically purified, isotopically enriched 238U solutions, by quantitatively separating the Th and allowing complete decay to 234U. All of the measurements will be done using MC-ICP-MS aiming at 0.05% precision. This approach is expected to result in values of λ238U with less than 0.1% uncertainty, if combined with improved λ234Th measements. These will be achieved using direct decay measurements with an E-ΔE charged particle telescope in coincidence with a gamma detector. This system allows measurement of 234Th β-decay and simultaneous detection and identification of α particles emitted by the 234U daughter, thus observing λ234U at the same time. The high-precision λ234U obtained by the direct activity measurements can independently verify the commonly used values obtained by indirect methods.[3] An overarching goal of the project is to ensure the quality of results including metrological traceability in order to facilitate implementation across diverse disciplines. [1] T.M. Harrison et al., (2015) It's About Time:Opportunities and Challenges for U.S. Geological Survey. Institute of Geophysics and Planetary Physics Publication 6539, University of California, Los Angeles [2] A. H. Jaffey et al., Physical Review C, 4, 5, (1971), 1889-1906 [3] H. Cheng et al., Chemical Geology, 169, (2000), 17-33

Concentration and characteristics of depleted uranium in water, air and biological samples collected in Serbia and Montenegro.

PubMed

Jia, Guogang; Belli, Maria; Sansone, Umberto; Rosamilia, Silvia; Gaudino, Stefania

2005-09-01

During the Balkan conflicts, in 1995 and 1999, depleted uranium (DU) rounds were employed and were left in the battlefield. Health concern is related to the risk arising from contamination of the environment with DU penetrators and dust. In order to evaluate the impact of DU on the environment and population in Serbia and Montenegro, radiological surveys of DU in water, air and biological samples were carried out over the period 27 October-5 November 2001. The uranium isotopic concentrations in biological samples collected in Serbia and Montenegro, mainly lichens and barks, were found to be in the range of 0.67-704 Bqkg(-1) for (238)U, 0.48-93.9 Bqkg(-1) for (234)U and 0.02-12.2 Bqkg(-1) for (235)U, showing uranium levels to be higher than in the samples collected at the control sites. Moreover, (236)U was detectable in some of the samples. The isotopic ratios of (234)U/(238)U showed DU to be detectable in many biological samples at all examined sites, especially in Montenegro, indicating widespread ground-surface DU contamination, albeit at very low level. The uranium isotopic concentrations in air obtained from the air filter samples collected in Serbia and Montenegro were found to be in the range of 1.99-42.1 microBqm(-3) for (238)U, 0.96-38.0 microBqm(-3) for (234)U, and 0.05-1.83 microBqm(-3) for (235)U, being in the typical range of natural uranium values. Thus said, most of the air samples are DU positive, this fact agreeing well with the widespread DU contamination detected in the biological samples. The uranium concentrations in water samples collected in Serbia and Montenegro were found to be in the range of 0.40-21.9 mBql(-1) for (238)U, 0.27-28.1 mBql(-1) for (234)U, and 0.01-0.88 mBql(-1) for (235)U, these values being much lower than those in mineral water found in central Italy and below the WHO guideline for drinking water. From a radiotoxicological point of view, at this moment there is no significant radiological risk related to these investigated sites in terms of possible DU contamination of water, air and/or plants.

U isotopes distribution in the Lower Rhone River and its implication on radionuclides disequilibrium within the decay series.

PubMed

Zebracki, Mathilde; Cagnat, Xavier; Gairoard, Stéphanie; Cariou, Nicolas; Eyrolle-Boyer, Frédérique; Boulet, Béatrice; Antonelli, Christelle

2017-11-01

The large rivers are main pathways for the delivery of suspended sediments into coastal environments, affecting the biogeochemical fluxes and the ecosystem functioning. The radionuclides from 238 U and 232 Th-series can be used to understand the dynamic processes affecting both catchment soil erosion and sediment delivery to oceans. Based on annual water discharge the Rhone River represents the largest river of the Mediterranean Sea. The Rhone valley also represents the largest concentration in nuclear power plants in Europe. A radioactive disequilibrium between particulate 226 Ra (p) and 238 U (p) was observed in the suspended sediment discharged by the Lower Rhone River (Eyrolle et al. 2012), and a fraction of particulate 234 Th was shown to derive from dissolved 238 U (d) (Zebracki et al. 2013). This extensive study has investigated the dissolved U isotopes distribution in the Lower Rhone River and its implication on particulate radionuclides disequilibrium within the decay series. The suspended sediment and filtered river waters were collected at low and high water discharges. During the 4-months of the study, two flood events generated by the Rhone southern tributaries were monitored. In river waters, the total U (d) concentration and U isotopes distribution were obtained through Q-ICP-MS measurements. The Lower Rhone River has displayed non-conservative U-behavior, and the variations in U (d) concentration between southern tributaries were related to the differences in bedrock lithology. The artificially occurring 236 U was detected in the Rhone River at low water discharges, and was attributed to the liquid releases from nuclear industries located along the river. The ( 235 U/ 238 U) (d) activity ratio (=AR) in river waters was representative of the 235 U natural abundance on Earth. The ( 226 Ra/ 238 U) (p) AR in suspended sediment has indicated a radioactive disequilibrium (average 1.3 ± 0.1). The excess of 234 Th in suspended sediment =( 234 Th xs(p) ) was apparent solely at low water discharges. The activity of 234 Th xs(p) was calculated through gamma measurements and ranged from unquantifiable to 56 ± 14 Bq kg -1 . The possibility of using 234 Th as a tracer for the suspended sediment dynamics in large Mediterranean river was then discussed. Copyright © 2017 Elsevier Ltd. All rights reserved.

Variations in the uranium isotopic compositions of uranium ores from different types of uranium deposits

NASA Astrophysics Data System (ADS)

Uvarova, Yulia A.; Kyser, T. Kurt; Geagea, Majdi Lahd; Chipley, Don

2014-12-01

Variations in 238U/235U and 234U/238U ratios were measured in uranium minerals from a spectrum of uranium deposit types, as well as diagenetic phosphates in uranium-rich basins and peraluminous rhyolites and associated autunite mineralisation from Macusani Meseta, Peru. Mean δ238U values of uranium minerals relative to NBL CRM 112-A are 0.02‰ for metasomatic deposits, 0.16‰ for intrusive, 0.18‰ for calcrete, 0.18‰ for volcanic, 0.29‰ for quartz-pebble conglomerate, 0.29‰ for sandstone-hosted, 0.44‰ for unconformity-type, and 0.56‰ for vein, with a total range in δ238U values from -0.30‰ to 1.52‰. Uranium mineralisation associated with igneous systems, including low-temperature calcretes that are sourced from U-rich minerals in igneous systems, have low δ238U values of ca. 0.1‰, near those of their igneous sources, whereas uranium minerals in basin-hosted deposits have higher and more variable values. High-grade unconformity-related deposits have δ238U values around 0.2‰, whereas lower grade unconformity-type deposits in the Athabasca, Kombolgie and Otish basins have higher δ238U values. The δ234U values for most samples are around 0‰, in secular equilibrium, but some samples have δ234U values much lower or higher than 0‰ associated with addition or removal of 234U during the past 2.5 Ma. These δ238U and δ234U values suggest that there are at least two different mechanisms responsible for 238U/235U and 234U/238U variations. The 234U/238U disequilibria ratios indicate recent fluid interaction with the uranium minerals and preferential migration of 234U. Fractionation between 235U and 238U is a result of nuclear-field effects with enrichment of 238U in the reduced insoluble species (mostly UO2) and 235U in oxidised mobile species as uranyl ion, UO22+, and its complexes. Therefore, isotopic fractionation effects should be reflected in 238U/235U ratios in uranium ore minerals formed either by reduction of uranium to UO2 or chemical precipitation in the form of U6+ minerals. The δ238U values of uranium ore minerals from a variety of deposits are controlled by the isotopic signature of the uranium source, the efficiency of uranium reduction in the case of UO2 systems, and the degree to which uranium was previously removed from the fluid, with less influence from temperature of ore formation and later alteration of the ore. Uranium isotopes are potentially superb tracers of redox in natural systems.

236U measurement with accelerator mass spectrometry at CIAE

NASA Astrophysics Data System (ADS)

Wang, Xianggao; Jiang, Shan; He, Ming; Dong, Kejun; Wang, Wei; Li, Chaoli; He, Guozhu; Li, Shizhuo; Gong, Jie; Lu, Liyuan; Wu, Shaoyong

2010-07-01

236U is a long-lived radioactive isotope which is produced principally by thermal neutron capture on 235U. 236U may be potentially applied in geological research and nuclear safeguards. Accelerator mass spectrometry is presently the most sensitive technique for the measurement of 236U and a measurement method for long-lived heavy ion 236U has been developed. The set-up uses a dedicated injector and the newly proposed 208Pb 16O2- molecular ions for the simulation of 236U ion transport. A sensitivity of lower than 10 -10 has been achieved for the isotopic ratio 236U/ 238U in present work.

Depleted and enriched uranium exposure quantified in former factory workers and local residents of NL Industries, Colonie, NY USA.

PubMed

Arnason, John G; Pellegri, Christine N; Moore, June L; Lewis-Michl, Elizabeth L; Parsons, Patrick J

2016-10-01

Between 1958 and 1982, NL Industries manufactured components of enriched (EU) and depleted uranium (DU) at a factory in Colonie NY, USA. More than 5 metric tons of DU was deposited as microscopic DU oxide particles on the plant site and surrounding residential community. A prior study involving a small number of individuals (n=23) indicated some residents were exposed to DU and former workers to both DU and EU, most probably through inhalation of aerosol particles. Our aim was to measure total uranium [U] and the uranium isotope ratios: (234)U/(238)U; (235)U/(238)U; and (236)U/(238)U, in the urine of a cohort of former workers and nearby residents of the NLI factory, to characterize individual exposure to natural uranium (NU), DU, and EU more than 3 decades after production ceased. We conducted a biomonitoring study in a larger cohort of 32 former workers and 99 residents, who may have been exposed during its period of operation, by measuring Total U, NU, DU, and EU in urine using Sector Field Inductively Coupled Plasma - Mass Spectrometry (SF-ICP-MS). Among workers, 84% were exposed to DU, 9% to EU and DU, and 6% to natural uranium (NU) only. For those exposed to DU, urinary isotopic and [U] compositions result from binary mixing of NU and the DU plant feedstock. Among residents, 8% show evidence of DU exposure, whereas none shows evidence of EU exposure. For residents, the [U] geometric mean is significantly below the value reported for NHANES. There is no significant difference in [U] between exposed and unexposed residents, suggesting that [U] alone is not a reliable indicator of exposure to DU in this group. Ninety four percent of workers tested showed evidence of exposure to DU, EU or both, and were still excreting DU and EU decades after leaving the workforce. The study demonstrates the advantage of measuring multiple isotopic ratios (e.g., (236)U/(238)U and (235)U/(238)U) over a single ratio ((235)U/(238)U) in determining sources of uranium exposure. Copyright © 2016 Elsevier Inc. All rights reserved.

Recent Developments in MC-ICP-MS for Uranium Isotopic Determination from Small Samples.

NASA Astrophysics Data System (ADS)

Field, P.; Lloyd, N. S.

2016-12-01

V002: Advances in approaches and instruments for isotope studies Session ID#: 12653 Recent Developments in MC-ICP-MS for Uranium Isotopic Determination from small samples.M. Paul Field 1 & Nicholas S. Lloyd. 1 Elemental Scientific Inc., Omaha, Nebraska, USA. field@icpms.com 2 Thermo Fisher Scientific, Hanna-Kunath-Str. 11, 28199 Bremen, Germany. nicholas.lloyd@thermofisher.com Uranium isotope ratio determination for nuclear, nuclear safeguards and for environmental applications can be challenging due to, 1) the large isotopic differences between samples and 2) low abundance of 234U and 236U. For some applications the total uranium quantities can be limited, or it is desirable to run at lower concentrations for radiological protection. Recent developments in inlet systems and detector technologies allow small samples to be analyzed at higher precisions using MC-ICP-MS. Here we evaluate the combination of Elemental Scientific apex omega desolvation system and microFAST-MC dual loop-loading flow-injection system with the Thermo Scientific NEPTUNE Plus MC-ICP-MS. The inlet systems allow for the automated syringe loading and injecting handling of small sample volumes with efficient desolvation to minimize the hydride interference on 236U. The highest ICP ion sampling efficiency is realized using the Thermo Scientific Jet Interface. Thermo Scientific 1013 ohm amplifier technology allows small ion beams to be measured at higher precision, offering the highest signal/noise ratio with a linear and stable response that covers a wide dynamic range (ca. 1 kcps - 30 Mcps). For nanogram quantities of low enriched and depleted uranium standards the 235U was measured with 1013 ohm amplifier technology. The minor isotopes (234U and 236U) were measured by SEM ion counters with RPQ lens filters, which offer the lowest detection limits. For sample amounts ca. 20 ng the minor isotopes can be moved onto 1013 ohm amplifiers and the 235U onto standard 1011 ohm amplifier. To illustrate the application a set of solutions from environmental particles [1] were analyzed, the use of precise three isotope ratio plots allows for source attribution with increased confidence. [1] Lloyd et al. 2009, J. Anal. At. Spectrom., 24(6), 752-758.

The Effect of U-234 Content on the Neutronic Behavior of Uranium Systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Busch, Robert D.; Bledsoe, Keith C

2011-01-01

When analyzing uranium systems, the usual rule of thumb is to ignore the U-234 by assuming that it behaves neutronically like U-238. Thus for uranium systems, the uranium is evaluated as U-235 with everything else being U-238. The absorption cross section of U-234 is indeed qualitatively very similar to that of U-238. However, thermal absorption cross section of U-234 is about 100 times that of U-238. At low U-235 enrichments, the amount of U-234 is quite small so the impact of assuming it is U-238 is minimal. However, at high enrichments, the relative ratio of U-234 to U-238 is quitemore » large (maybe as much as 1 to 5). Thus, one would expect that some effect of using the rule of thumb might be seen in higher enriched systems. Analyses were performed on three uranium systems from the set of Benchmarks [1]. Although the benchmarks are adequately characterized as to the U-234 content, often, materials used in processing are not as well characterized. This issue may become more important with the advent of laser enrichment processes, which have little or no effect on the U-234 content. Analytical results based on the relationship of U-234 activity to that of U-235 have shown good predictive capability but with large variability in the uncertainties [2]. Rucker and Johnson noted that the actual isotopics vary with enrichment, design of the enrichment cascade, composition of the feed material, and on blending of enrichments so there is considerable uncertainty in the use of models to determine isotopics. Thus, it is important for criticality personnel to understand the effects of variation of U-234 content in fissile systems and the impact of different modeling assumptions in handling the U-234. Analyses were done on LEU, IEU and HEU benchmarks from the International Handbook. These indicate that the effect of ignoring U-234 in HEU metal systems is non-conservative while it seems to be conservative for HEU solution systems. The magnitude of change in k-effective was as high as 0.4%, which has implications on selection of administrative margins and the determination of the upper subcriticality limit.« less

Rapid Method for Sodium Hydroxide Fusion of Asphalt ...

EPA Pesticide Factsheets

Technical Brief--Addendum to Selected Analytical Methods (SAM) 2012 Rapid method developed for analysis of Americium-241 (241Am), plutonium-238 (238Pu), plutonium-239 (239Pu), radium-226 (226Ra), strontium-90 (90Sr), uranium-234 (234U), uranium-235 (235U) and uranium-238 (238U) in asphalt roofing material samples

Increasing the Accuracy in the Measurement of the Minor Isotopes of Uranium: Care in Selection of Reference Materials, Baselines and Detector Calibration

NASA Astrophysics Data System (ADS)

Poths, J.; Koepf, A.; Boulyga, S. F.

2008-12-01

The minor isotopes of uranium (U-233, U-234, U-236) are increasingly useful for tracing a variety of processes: movement of anthropogenic nuclides in the environment (ref 1), sources of uranium ores (ref 2), and nuclear material attribution (ref 3). We report on improved accuracy for U-234/238 and U-236/238 by supplementing total evaporation protocol TIMS measurement on Faraday detectors (ref 4)with multiplier measurement for the minor isotopes. Measurement of small signals on Faraday detectors alone is limited by noise floors of the amplifiers and accurate measurement of the baseline offsets. The combined detector approach improves the reproducibility to better than ±1% (relative) for the U-234/238 at natural abundance, and yields a detection limit for U-236/U-238 of <0.2 ppm. We have quantified contribution of different factors to the uncertainties associated with these peak jumping measurement on a single detector, with an aim of further improvement. The uncertainties in the certified values for U-234 and U-236 in the uranium standard NBS U005, if used for mass bias correction, dominates the uncertainty in their isotopic ratio measurements. Software limitations in baseline measurement drives the detection limit for the U-236/U-238 ratio. This is a topic for discussion with the instrument manufacturers. Finally, deviation from linearity of the response of the electron multiplier with count rate limits the accuracy and reproducibility of these minor isotope measurements. References: (1) P. Steier et al(2008) Nuc Inst Meth(B), 266, 2246-2250. (2) E. Keegan et al (2008) Appl Geochem 23, 765-777. (3) K. Mayer et al (1998) IAEA-CN-98/11, in Advances in Destructive and Non-destructive Analysis for Environmental Monitoring and Nuclear Forensics. (4) S. Richter and S. Goldberg(2003) Int J Mass Spectrom, 229, 181-197.

Image segmentation for uranium isotopic analysis by SIMS: Combined adaptive thresholding and marker controlled watershed approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Willingham, David G.; Naes, Benjamin E.; Heasler, Patrick G.

A novel approach to particle identification and particle isotope ratio determination has been developed for nuclear safeguard applications. This particle search approach combines an adaptive thresholding algorithm and marker-controlled watershed segmentation (MCWS) transform, which improves the secondary ion mass spectrometry (SIMS) isotopic analysis of uranium containing particle populations for nuclear safeguards applications. The Niblack assisted MCWS approach (a.k.a. SEEKER) developed for this work has improved the identification of isotopically unique uranium particles under conditions that have historically presented significant challenges for SIMS image data processing techniques. Particles obtained from five NIST uranium certified reference materials (CRM U129A, U015, U150, U500more » and U850) were successfully identified in regions of SIMS image data 1) where a high variability in image intensity existed, 2) where particles were touching or were in close proximity to one another and/or 3) where the magnitude of ion signal for a given region was count limited. Analysis of the isotopic distributions of uranium containing particles identified by SEEKER showed four distinct, accurately identified 235U enrichment distributions, corresponding to the NIST certified 235U/238U isotope ratios for CRM U129A/U015 (not statistically differentiated), U150, U500 and U850. Additionally, comparison of the minor uranium isotope (234U, 235U and 236U) atom percent values verified that, even in the absence of high precision isotope ratio measurements, SEEKER could be used to segment isotopically unique uranium particles from SIMS image data. Although demonstrated specifically for SIMS analysis of uranium containing particles for nuclear safeguards, SEEKER has application in addressing a broad set of image processing challenges.« less

Actinides in deer tissues at the rocky flats environmental technology site.

PubMed

Todd, Andrew S; Sattelberg, R Mark

2005-11-01

Limited hunting of deer at the future Rocky Flats National Wildlife Refuge has been proposed in U.S. Fish and Wildlife planning documents as a compatible wildlife-dependent public use. Historically, Rocky Flats site activities resulted in the contamination of surface environmental media with actinides, including isotopes of americium, plutonium, and uranium. In this study, measurements of actinides [Americium-241 (241Am); Plutonium-238 (238Pu); Plutonium-239,240 (239,240Pu); uranium-233,244 (233,234U); uranium-235,236 (235,236U); and uranium-238 (238U)] were completed on select liver, muscle, lung, bone, and kidney tissue samples harvested from resident Rocky Flats deer (N = 26) and control deer (N = 1). In total, only 17 of the more than 450 individual isotopic analyses conducted on Rocky Flats deer tissue samples measured actinide concentrations above method detection limits. Of these 17 detects, only 2 analyses, with analytical uncertainty values added, exceeded threshold values calculated around a 1 x 10(-6) risk level (isotopic americium, 0.01 pCi/g; isotopic plutonium, 0.02 pCi/g; isotopic uranium, 0.2 pCi/g). Subsequent, conservative risk calculations suggest minimal human risk associated with ingestion of these edible deer tissues. The maximum calculated risk level in this study (4.73 x 10(-6)) is at the low end of the U.S. Environmental Protection Agency's acceptable risk range.

Applications of New Synthetic Uranium Reference Materials for Geochemistry Research (Invited)

NASA Astrophysics Data System (ADS)

Richter, S.; Weyer, S.; Alonso, A.; Aregbe, Y.; Kuehn, H.; Eykens, R.; Verbruggen, A.; Wellum, R.

2009-12-01

For many applications in geochemistry research isotope ratio measurements play a significant role. In geochronology isotope abundances of uranium and its daughter products thorium and lead are being used to determine the age and history of various samples of geological interest. For measuring the isotopic compositions of these elements by mass spectrometry, suitable isotope reference materials are needed to validate measurement procedures and to calibrate multi-collector and ion counting detector systems. IRMM is a recognized provider for nuclear isotope reference materials to the nuclear industry and nuclear safeguards authorities, which are also being applied widely for geochemical applications. The preparation of several new synthetic uranium reference materials at IRMM during the recent five years has provided significant impacts on geochemical research. As an example, the IRMM-074 series of gravimetrically prepared uranium mixtures for linearity testing of secondary electron multipliers (SEMs) has been applied for the redetermination of the secular equilibrium 234U/238U value and the 234U half-life by Cheng et al (2009). Due to the use of IRMM-074, results with smaller uncertainties were obtained, which are shifted by about 0.04% compared to the commonly used values published earlier by Cheng et al. in 2000. This has a significant impact for U isotope measurements in geochemistry.. As a further example, the new double spike IRMM-3636 with a 233U/236U ratio of 1:1 and an expanded uncertainty as low as 0.016% (coverage factor k=2, 95% confidence level) was prepared gravimetrically. This double spike allows internal mass fractionation correction for high precision 235U/238U ratio measurements of close to natural samples. Using the new double spike IRMM-3636, the 235U/238U ratios for several commonly used natural U standard materials from NIST/NBL and IRMM, such as e.g. NBS960 (=NBL CRM-112a), NBS950a,b and IRMM-184, have been re-measured with improved precision and accuracy. The (preliminary) result of 137.836(23) for the 238U/235U ratio of NBS960, measured using the new gravimetrically prepared 233U/236U-Double Spike IRMM-3636, is deviating by -0.032% from the well-known and widely used consensus value of 137.88. For the consensus value no uncertainty has ever been assigned, but it is outside the uncertainty limits of the new measurement result. The re-measured 238U/235U ratio of 137.689(22) of IRMM-184 agrees quite well with the certified value of 137.697(41), the calculated difference is only -0.006(34)% which is insignificant. The results for both NBS960 and IRMM-184, obtained using multi-dynamic TIMS at IRMM and using high efficiency MC-ICPMS at the University of Frankfurt, agree well with each other. As a conclusion, the IRMM-3636 Double Spike has been successfully applied for measurements of important uranium isotopic standards like NBS960 and IRMM-184, with improved uncertainties at the level of 0.016%.

Neutron Capture Cross Sections and Gamma Emission Spectra from Neutron Capture on 234,236,238U Measured with DANCE

NASA Astrophysics Data System (ADS)

Ullmann, J. L.; Mosby, S.; Bredeweg, T. A.; Couture, A. J.; Haight, R. C.; Jandel, M.; Kawano, T.; O'Donnell, J. M.; Rundberg, R. S.; Vieira, D. J.; Wilhelmy, J. B.; Wu, C.-Y.; Becker, J. A.; Chyzh, A.; Baramsai, B.; Mitchell, G. E.; Krticka, M.

2014-05-01

A new measurement of the 238U(n, γ) cross section using a thin 48 mg/cm2 target was made using the DANCE detector at LANSCE over the energy range from 10 eV to 500 keV. The results confirm earlier measurements. Measurements of the gamma-ray emission spectra were also made for 238U(n, γ) as well as 234,236U(n, γ). These measurements help to constrain the radiative strength function used in the cross-section calculations.

Analysis of reaction cross-section production in neutron induced fission reactions on uranium isotope using computer code COMPLET.

PubMed

Asres, Yihunie Hibstie; Mathuthu, Manny; Birhane, Marelgn Derso

2018-04-22

This study provides current evidence about cross-section production processes in the theoretical and experimental results of neutron induced reaction of uranium isotope on projectile energy range of 1-100 MeV in order to improve the reliability of nuclear stimulation. In such fission reactions of 235 U within nuclear reactors, much amount of energy would be released as a product that able to satisfy the needs of energy to the world wide without polluting processes as compared to other sources. The main objective of this work is to transform a related knowledge in the neutron-induced fission reactions on 235 U through describing, analyzing and interpreting the theoretical results of the cross sections obtained from computer code COMPLET by comparing with the experimental data obtained from EXFOR. The cross section value of 235 U(n,2n) 234 U, 235 U(n,3n) 233 U, 235 U(n,γ) 236 U, 235 U(n,f) are obtained using computer code COMPLET and the corresponding experimental values were browsed by EXFOR, IAEA. The theoretical results are compared with the experimental data taken from EXFOR Data Bank. Computer code COMPLET has been used for the analysis with the same set of input parameters and the graphs were plotted by the help of spreadsheet & Origin-8 software. The quantification of uncertainties stemming from both experimental data and computer code calculation plays a significant role in the final evaluated results. The calculated results for total cross sections were compared with the experimental data taken from EXFOR in the literature, and good agreement was found between the experimental and theoretical data. This comparison of the calculated data was analyzed and interpreted with tabulation and graphical descriptions, and the results were briefly discussed within the text of this research work. Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.

Plutonium age dating reloaded

NASA Astrophysics Data System (ADS)

Sturm, Monika; Richter, Stephan; Aregbe, Yetunde; Wellum, Roger; Mayer, Klaus; Prohaska, Thomas

2014-05-01

Although the age determination of plutonium is and has been a pillar of nuclear forensic investigations for many years, additional research in the field of plutonium age dating is still needed and leads to new insights as the present work shows: Plutonium is commonly dated with the help of the 241Pu/241Am chronometer using gamma spectrometry; in fewer cases the 240Pu/236U chronometer has been used. The age dating results of the 239Pu/235U chronometer and the 238Pu/234U chronometer are scarcely applied in addition to the 240Pu/236U chronometer, although their results can be obtained simultaneously from the same mass spectrometric experiments as the age dating result of latter. The reliability of the result can be tested when the results of different chronometers are compared. The 242Pu/238U chronometer is normally not evaluated at all due to its sensitivity to contamination with natural uranium. This apparent 'weakness' that renders the age dating results of the 242Pu/238U chronometer almost useless for nuclear forensic investigations, however turns out to be an advantage looked at from another perspective: the 242Pu/238U chronometer can be utilized as an indicator for uranium contamination of plutonium samples and even help to identify the nature of this contamination. To illustrate this the age dating results of all four Pu/U clocks mentioned above are discussed for one plutonium sample (NBS 946) that shows no signs of uranium contamination and for three additional plutonium samples. In case the 242Pu/238U chronometer results in an older 'age' than the other Pu/U chronometers, contamination with either a small amount of enriched or with natural or depleted uranium is for example possible. If the age dating result of the 239Pu/235U chronometer is also influenced the nature of the contamination can be identified; enriched uranium is in this latter case a likely cause for the missmatch of the age dating results of the Pu/U chronometers.

206Pb-230Th-234U-238U and 207Pb-235U geochronology of Quaternary opal, Yucca Mountain, Nevada

USGS Publications Warehouse

Neymark, Leonid A.; Amelin, Yuri V.; Paces, James B.

2000-01-01

U–Th–Pb isotopic systems have been studied in submillimeter-thick outermost layers of Quaternary opal occurring in calcite–silica fracture and cavity coatings within Tertiary tuffs at Yucca Mountain, Nevada, USA. These coatings preserve a record of paleohydrologic conditions at this site, which is being evaluated as a potential high-level nuclear waste repository. The opal precipitated from groundwater is variably enriched in 234U (measured 234U/238U activity ratio 1.124–6.179) and has high U (30–313 ppm), low Th (0.008–3.7 ppm), and low common Pb concentrations (measured 206Pb/204Pb up to 11,370). It has been demonstrated that the laboratory acid treatment used in this study to clean sample surfaces and to remove adherent calcite, did not disturb U–Th–Pb isotopic systems in opal. The opal ages calculated from 206Pb∗/238U and 207Pb∗/235U ratios display strong reverse discordance because of excess radiogenic 206Pb∗ derived from the elevated initial 234U. The data are best interpreted using projections of a new four-dimensional concordia diagram defined by 206Pb∗/238U, 207Pb∗/235U, 234U/238Uactivity, and 230Th/238Uactivity. Ages and initial 234U/238U activity ratios have been calculated using different projections of this diagram and tested for concordance. The data are discordant, that is observed 207Pb∗/235U ages of 170 ± 32 (2σ) to 1772 ± 40 ka are systematically older than 230Th/U ages of 34.1 ± 0.6 to 452 ± 32 ka. The age discordance is not a result of migration of uranium and its decay products under the open system conditions, but a consequence of noninstantaneous growth of opal. Combined U–Pb and 230Th/U ages support the model of slow mineral deposition at the rates of millimeters per million years resulting in layering on a scale too fine for mechanical sampling. In this case, U–Pb ages provide more accurate estimates of the average age for mixed multiage samples than 230Th/U ages, because ages based on shorter-lived isotopes are nonlinearly biased by younger mineral additions. Use of the combined U–Th–Pb technique to date Yucca Mountain Quaternary opals significantly extends the age range beyond that of the 230Th/U dating method and shows that selected fracture pathways in the unsaturated zone felsic tuffs of Yucca Mountain have been active throughout the Quaternary.

Geochemistry of speleothem records from southern Illinois: Development of (234U)/(238U) as a proxy for paleoprecipitation

USGS Publications Warehouse

Zhou, Juanzuo; Lundstrom, C.C.; Fouke, B.; Panno, S.; Hackley, K.; Curry, B.

2005-01-01

Natural waters universally show fractionation of uranium series (U-series) parent-daughter pairs, with the disequilibrium between 234U and 238U (234U)/(238U) commonly used as a tracer of groundwater flow. Because speleothems provide a temporal record of geochemical variations in groundwater precipitating calcite, (234U)/(238U) variations in speleothems provide a unique method of investigating water-rock interaction processes over millennium time scales. We present high precision Thermal Ionization Mass Spectrometric (TIMS) U-series analyses of speleothems and drip waters from Fogelpole Cave in southern Illinois. Data from all speleothems from the cave show an inverse correlation between (234U)/(238U) and U concentration, following the pattern observed in groundwaters globally. Within a 65-cm-long stalagmite, concordant 234U-238 U-230Th and 235U-231Pa ages for 5 samples indicate accurate chronology from 78.5 ka to 30 ka. Notably, (234U)/(238U)o which differs from most speleothems by having (234U)/(238U)o <1, positively correlates with speleothem growth rate. We generalize this to the observation that speleothems globally show (234U)/ (238U)o deviating farther from secular equilibrium at lower growth rates and approaching secular equilibrium at higher grow rates. Based on the Fogelpole observations, we suggest that groundwater (234U)/(238U) is controlled by the U oxidation state, the U concentration of the water and the fluid velocity. A transport model whereby U-series nuclides react and exchange with mineral surfaces can reproduce the observed trend between growth rate and (234U)/(238U)o. Based on this result, we suggest that (234U)/(238U)o in speleothems may record changes in hydrologic flux with time and thus could provide a useful proxy for long term records of paleoprecipitation. ?? 2005 Elsevier B.V. All rights reserved.

Depleted and enriched uranium exposure quantified in former factory workers and local residents of NL Industries, Colonie, NY USA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arnason, John G.

Background: Between 1958 and 1982, NL Industries manufactured components of enriched (EU) and depleted uranium (DU) at a factory in Colonie NY, USA. More than 5 metric tons of DU was deposited as microscopic DU oxide particles on the plant site and surrounding residential community. A prior study involving a small number of individuals (n=23) indicated some residents were exposed to DU and former workers to both DU and EU, most probably through inhalation of aerosol particles. Objectives: Our aim was to measure total uranium [U] and the uranium isotope ratios: {sup 234}U/{sup 238}U; {sup 235}U/{sup 238}U; and {sup 236}U/{supmore » 238}U, in the urine of a cohort of former workers and nearby residents of the NLI factory, to characterize individual exposure to natural uranium (NU), DU, and EU more than 3 decades after production ceased. Methods: We conducted a biomonitoring study in a larger cohort of 32 former workers and 99 residents, who may have been exposed during its period of operation, by measuring Total U, NU, DU, and EU in urine using Sector Field Inductively Coupled Plasma - Mass Spectrometry (SF-ICP-MS). Results: Among workers, 84% were exposed to DU, 9% to EU and DU, and 6% to natural uranium (NU) only. For those exposed to DU, urinary isotopic and [U] compositions result from binary mixing of NU and the DU plant feedstock. Among residents, 8% show evidence of DU exposure, whereas none shows evidence of EU exposure. For residents, the [U] geometric mean is significantly below the value reported for NHANES. There is no significant difference in [U] between exposed and unexposed residents, suggesting that [U] alone is not a reliable indicator of exposure to DU in this group. Conclusions: Ninety four percent of workers tested showed evidence of exposure to DU, EU or both, and were still excreting DU and EU decades after leaving the workforce. The study demonstrates the advantage of measuring multiple isotopic ratios (e.g., {sup 236}U/{sup 238}U and {sup 235}U/{sup 238}U) over a single ratio ({sup 235}U/{sup 238}U) in determining sources of uranium exposure. - Highlights: • Biomonitoring study of residents and former workers exposed to DU in Colonie NY. • Urine (99 residents+32 former workers) analyzed for depleted uranium (DU). • DU detected in 84% of workers and 8% of residents >30 years after plant closed. • Enriched uranium detected in 6% of former workers based on isotope ratios.« less

Radiogenic isotopic approaches for quantifying radionuclide transport (Invited)

NASA Astrophysics Data System (ADS)

Maher, K.; Depaolo, D. J.; Singleton, M. J.; Christensen, J. N.; Conrad, M. E.

2009-12-01

Naturally occurring variations in the isotopic compositions of U and Sr provide unique opportunities for assessing the fate and transport of radionuclides at field-scale conditions. When coupled with reactive transport models, U and Sr isotopes may also provide additional constraints on the rates of sediment-fluid or sediment-waste interactions. Such isotopic approaches can be useful for sites where subsurface characterization is complicated by a lack of accessibility or the presence of substantial heterogeneity. In addition, a variety of quantitative modeling approaches of different complexity can be used to evaluate experimentally determined parameters for radionuclide mobility at the field-scale. At the Hanford Site in eastern Washington, 87Sr/86Sr and 234U/238U ratios have been used to quantify the residence time of Sr and U in the unsaturated zone, the long-term background infiltration rate through the unsaturated zone, and to assess the influence of enhanced wastewater discharge on the regional unconfined aquifer. As a result of different processing techniques or due to interactions between caustic waste and the natural sediment, waste plumes may also inherit isotopic fingerprints (e.g. 234U/238U, 235U/238U, 236U/238U; δ15N & δ18O of nitrate) that can be used to resolve multiple sources of contamination. Finally, enriched isotopic tracers can be applied to experimental manipulations to assess the retardation of a variety of contaminants. Collectively this isotopic data contributes unique perspectives on both the hydrologic conditions across the site and the mobility of key radionuclides. Predicting the long-term fate and transport of radionuclides in the environment is often challenging due to natural heterogeneity and incomplete characterization of the subsurface, however detailed analysis of isotopic variations can provide one additional means of characterizing the subsurface.

Method for radioactivity monitoring

DOEpatents

Umbarger, C. John; Cowder, Leo R.

1976-10-26

The disclosure relates to a method for analyzing uranium and/or thorium contents of liquid effluents preferably utilizing a sample containing counting chamber. Basically, 185.7-keV gamma rays following .sup.235 U alpha decay to .sup.231 Th which indicate .sup.235 U content and a 63-keV gamma ray doublet found in the nucleus of .sup.234 Pa, a granddaughter of .sup.238 U, are monitored and the ratio thereof taken to derive uranium content and isotopic enrichment .sup.235 U/.sup.235 U + .sup.238 U) in the liquid effluent. Thorium content is determined by monitoring the intensity of 238-keV gamma rays from the nucleus of .sup.212 Bi in the decay chain of .sup.232 Th.

Developing 226Ra and 227Ac age-dating techniques for nuclear forensics to gain insight from concordant and non-concordant radiochronometers

DOE PAGES

Kayzar, Theresa M.; Williams, Ross W.

2015-09-26

The model age or ‘date of purification’ of a nuclear material is an important nuclear forensic signature. In this study, chemical separation and MC-ICP-MS measurement techniques were developed for 226 Ra and 227Ac: grand-daughter nuclides in the 238U and 235U decay chains respectively. The 230Th- 234U, 226Ra- 238U, 231Pa- 235U, and 227Ac- 235U radiochronometers were used to calculate model ages for CRM-U100 standard reference material and two highly-enriched pieces of uranium metal from the International Technical Working Group Round Robin 3 Exercise. In conclusion, the results demonstrate the accuracy of the 226Ra- 238U and 227Ac- 235U chronometers and provide informationmore » about nuclide migration during uranium processing.« less

Developing 226Ra and 227Ac age-dating techniques for nuclear forensics to gain insight from concordant and non-concordant radiochronometers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kayzar, Theresa M.; Williams, Ross W.

The model age or ‘date of purification’ of a nuclear material is an important nuclear forensic signature. In this study, chemical separation and MC-ICP-MS measurement techniques were developed for 226 Ra and 227Ac: grand-daughter nuclides in the 238U and 235U decay chains respectively. The 230Th- 234U, 226Ra- 238U, 231Pa- 235U, and 227Ac- 235U radiochronometers were used to calculate model ages for CRM-U100 standard reference material and two highly-enriched pieces of uranium metal from the International Technical Working Group Round Robin 3 Exercise. In conclusion, the results demonstrate the accuracy of the 226Ra- 238U and 227Ac- 235U chronometers and provide informationmore » about nuclide migration during uranium processing.« less

Background reduction in 236U/238U measurements

NASA Astrophysics Data System (ADS)

Buompane, Raffaele; De Cesare, Mario; De Cesare, Nicola; Di Leva, Antonino; D'Onofrio, Antonio; Fifield, L. Keith; Fröhlich, Michaela; Gialanella, Lucio; Marzaioli, Fabio; Sabbarese, Carlo; Terrasi, Filippo; Tims, Stephen; Wallner, Anton

2015-10-01

The measurements of actinide isotopic ratios, in particular 236U/238U, in environmental samples requires high sensitivity. In particular, special effort must be devoted to the suppression of interfering nuclides, such as 235,238U, when measuring 236U. At the AMS facility of CIRCE, isotopic ratios down to ∼10-10 are currently measured using a gas E - ΔE detector. In order to push this limit lower towards natural levels, a time-of-flight system is used, featuring a micro-channel plate start detector and a Si stop detector. As the mass resolution of the latter is limited by the layout, an attempt to reduce the abundant isotope interference by other means has been undertaken. In this study, we report preliminary results on the characterization of the presence of molecular interferences when using UO-, UC- and UC2- as injected molecular ions. In particular the possibility to stabilize the current yield from carbide cathodes has been investigated: it was found that the best cathode preparation procedure is obtained pressing U salts baked at 800 °C mixed with graphite and Al powder. Moreover, the 238U background in 236U measurements is strongly reduced injecting UC- ions, as verified using a time-of-flight detection system. On the other hand, 235U interference is larger with respect to UO- injection, but this increase is smaller than expected on the basis of abundances of 13C and 17O in UC and UC2 molecules on one side and UO, on the other.

Determination of uranium isotopic composition and 236U content of soil samples and hot particles using inductively coupled plasma mass spectrometry.

PubMed

Boulyga, S F; Becker, J S

2001-07-01

As a result of the accident at the Chernobyl nuclear power plant (NPP) the environment was contaminated with spent nuclear fuel. The 236U isotope was used in this study to monitor the spent uranium from nuclear fallout in soil samples collected in the vicinity of the Chernobyl NPP. Nuclear track radiography was applied for the identification and extraction of hot radioactive particles from soil samples. A rapid and sensitive analytical procedure was developed for uranium isotopic ratio measurement in environmental samples based on double-focusing inductively coupled plasma mass spectrometry (DF-ICP-MS) with a MicroMist nebulizer and a direct injection high-efficiency nebulizer (DIHEN). The performance of the DF-ICP-MS with a quartz DIHEN and plasma shielded torch was studied. Overall detection efficiencies of 4 x 10(-4) and 10(-3) counts per atom were achieved for 238U in DF-ICP-QMS with the MicroMist nebulizer and DIHEN, respectively. The rate of formation of uranium hydride ions UH+/U+ was 1.2 x 10(-4) and 1.4 x 10(-4), respectively. The precision of short-term measurements of uranium isotopic ratios (n = 5) in 1 microg L(-1) NBS U-020 standard solution was 0.11% (238U/235U) and 1.4% (236U/238U) using a MicroMist nebulizer and 0.25% (235U/238U) and 1.9% (236U/P38U) using a DIHEN. The isotopic composition of all investigated Chernobyl soil samples differed from those of natural uranium; i.e. in these samples the 236U/238U ratio ranged from 10(-5) to 10(-3). Results obtained with ICP-MS, alpha- and gamma-spectrometry showed differences in the migration properties of spent uranium, plutonium, and americium. The isotopic ratio of uranium was also measured in hot particles extracted from soil samples.

Determination of U isotope ratios in sediments using ICP-QMS after sample cleanup with anion-exchange and extraction chromatography.

PubMed

Zheng, Jian; Yamada, Masatoshi

2006-01-15

The determination of uranium is important for environmental radioactivity monitoring, which investigates the releases of uranium from nuclear facilities and of naturally occurring radioactive materials by the coal, oil, natural gas, mineral, ore refining and phosphate fertilizer industries, and it is also important for studies on the biogeochemical behavior of uranium in the environment. In this paper, we describe a quadrupole ICP-MS (ICP-QMS)-based analytical procedure for the accurate determination of U isotope ratios ((235)U/(238)U atom ratio and (234)U/(238)U activity ratio) in sediment samples. A two-stage sample cleanup using anion-exchange and TEVA extraction chromatography was employed in order to obtain accurate and precise (234)U/(238)U activity ratios. The factors that affect the accuracy and precision of U isotope ratio analysis, such as detector dead time, abundance sensitivity, dwell time and mass bias were carefully evaluated and corrected. With natural U, a precision lower than 0.5% R.S.D. for (235)U/(238)U atom ratio and lower than 2.0% R.S.D. for (234)U/(238)U activity ratio was obtained with less than 90 ng uranium. The developed analytical method was validated using an ocean sediment reference material and applied to an investigation into the uranium isotopic compositions in a sediment core in a brackish lake in the vicinity of U-related nuclear facilities in Japan.

High-precision determination of {sup 234}U/{sup 238}U activity ratios in natural waters and carbonates by ICPMS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ketterer, M.E.; Khourey, C.J.

1998-12-31

A method has been developed for precise measurement of {sup 234}U/{sup 238}U activity ratios in natural waters and carbonates using quadrupole inductively coupled plasma mass spectrometry. A recovery of 80--85% of seawater U is achieved by Fe(III) coprecipitation followed by extraction chromatography with a supported dipentyl pentane phosphonate material; 90--95% of U is recovered from carbonates, which are dissolved in HNO{sub 3} and subjected to the same extraction chromatographic preparation. Isotopic measurements are made via recirculating pneumatic nebulization of small volumes of solutions containing 0.5--5 mg/L U. {sup 234}U/{sup 235}U is measured as a proxy for determination of {sup 234}U/{supmore » 238}U; iridium is added to sample solutions and the ion ratio {sup 191}Ir{sup 40}Ar{sup +}/{sup 193}Ir{sup 40}Ar{sup +} is measured for internal mass discrimination correction {sup 234}U/{sup 238}U activity ratios in the range 1.143--1.154 are observed for 13 seawater and contemporary corals, in agreement with the established marine {sup 234}U/{sup 238}U activity ratio. For samples sizes of 5--25 {micro}g U, ICPMS uncertainties of {+-} 0.2--0.5% relative, 2{theta} standard error, approach those obtained for < 0.1 {micro}g U by thermal ionization mass spectrometry. Measurements of {sup 234}U/{sup 238}U activity ratios in bottled waters, Lake Erie surface waters, mollusk fossils, and fertilizers are also demonstrated.« less

Bomb fall-out 236U as a global oceanic tracer using an annually resolved coral core

PubMed Central

Winkler, Stephan R.; Steier, Peter; Carilli, Jessica

2012-01-01

Anthropogenic 236U (t½=23.4 My) is an emerging isotopic ocean tracer with interesting oceanographic properties, but only with recent advances in accelerator mass spectrometry techniques is it now possible to detect the levels from global fall-out of nuclear weapons testing across the water column. To make full use of this tracer, an assessment of its input into the ocean over the past decades is required. We captured the bomb-pulse of 236U in an annually resolved coral core record from the Caribbean Sea. We thereby establish a concept which gives 236U great advantage – the presence of reliable, well-resolved chronological archives. This allows studies of not only the present distribution pattern, but gives access to the temporal evolution of 236U in ocean waters over the past decades. PMID:23564966

238U/235U determinations of some commonly used reference materials and U-bearing accessory minerals (Invited)

NASA Astrophysics Data System (ADS)

Condon, D.; Noble, S.; McLean, N.; Bowring, S. A.

2009-12-01

We have determined 238U/235U ratios for a suite of commonly used natural (CRM 112a, SRM 950a, HU-1) and synthetic (IRMM 184 and CRM U500) uranium reference materials in addition to several U-bearing accessory phases (zircon and monazite) by thermal ionisation mass-spectrometry (TIMS) using the IRMM 3636 233U-236U double spike to accurately correct for mass fractionation. The 238U/235U values for the natural uranium reference materials differ, by up to 0.1%, from the widely used ‘consensus’ value (137.88) with all having 238U/235U values less than 137.88. Similarly, initial 238U/235U data from zircon and monazite yield 238U/235U values that are lower than the ‘consensus’ value. The data obtained from U-bearing minerals is used to assess how the uncertainty in the 238U/235U ratio contributes to the systematic discordance observed in 238U/206Pb and 235U/207Pb dates (Mattinson, 2000; Schoene et al., 2006) which has traditionally been wholly attributed to error in the U decay constants. The 238U/235U determinations made on the synthetic reference materials yield results that are considerably more precise and accurate than the certified values (0.02% vs. 0.1% for CRM U500). The calibration of isotopic tracers used for U-daughter geochronology that are partially based upon these reference materials, and the resultant age determinations, will benefit from increased accuracy and precision. Mattinson, J.M., 2000. Revising the “gold standard”—the uranium decay constants of Jaffey et al., 1971. Eos Trans. AGU, Spring Meet. Suppl., Abstract V61A-02. Schoene B., Crowley J.L., Condon D.C., Schmitz M.D., Bowring S.A., 2006, Reassessing the uranium decay constants for geochronology using ID-TIMS U-Pb data. Geochimica et Cosmochimica Acta 70: 426-445

Non-destructive determination of uranium, thorium and 40K in tobacco and their implication on radiation dose levels to the human body.

PubMed

Landsberger, S; Lara, R; Landsberger, S G

2015-11-01

The naturally occurring radionuclides of (235)U, (238)U and (232)Th and their daughter products are a potential major source of anthropogenic radiation to tobacco smokers. Often overlooked is the presence of (40)K in tobacco and its implication to radiation dose accumulation in the human body. In this study, these three radiation sources have been determined in four typical US cigarettes using neutron activation analysis (NAA). The NAA reactions of (238)U(n,γ)(239)U, (232)Th(n,γ)(233)Th and (41)K(n,γ)(42)K were used to determine (235)U, (238)U and (232)Th and (40)K, respectively. The activity of (238)U can easily be determined by epithermal NAA of the (238)U(n,γ)(239)U reaction, and the activity of (235, 234)U can easily be deduced. Using isotopic ratios, the activity due to (40)K was found by the determined concentrations of (41)K (also by epithermal neutrons) in the bulk material. Each gram of total potassium yields 30 Bq of (40)K. The annual effective dose for smokers using 20 cigarettes per day was calculate to be 14.6, 137 and 9 μSv y(-1) for (238,235,) (234)U, (232)Th and (40)K, respectively. These values are significantly lower that the dose received from (210)Po except for (232)Th. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Neutron-Induced Fission Cross Section Measurements for Full Suite of Uranium Isotopes

NASA Astrophysics Data System (ADS)

Laptev, Alexander; Tovesson, Fredrik; Hill, Tony

2010-11-01

A well established program of neutron-induced fission cross section measurement at Los Alamos Neutron Science Center (LANSCE) is supporting the Fuel Cycle Research program (FC R&D). The incident neutron energy range spans energies from sub-thermal energies up to 200 MeV by measuring both the Lujan Center and the Weapons Neutron Research center (WNR). Conventional parallel-plate fission ionization chambers with actinide deposited foils are used as a fission detector. The time-of-flight method is implemented to measure neutron energy. Counting rate ratio from investigated and standard U-235 foils is translated into fission cross section ratio. Different methods of normalization for measured ratio are employed, namely, using of actinide deposit thicknesses, normalization to evaluated data, etc. Finally, ratios are converted to cross sections based on the standard U-235 fission cross section data file. Preliminary data for newly investigated isotopes U-236 and U-234 will be reported. Those new data complete a full suite of Uranium isotopes, which were investigated with presented experimental approach. When analysis of the new measured data will is completed, data will be delivered to evaluators. Having data for full set of Uranium isotopes will increase theoretical modeling capabilities and make new data evaluations much more reliable.

Determination of extremely low (236)U/(238)U isotope ratios in environmental samples by sector-field inductively coupled plasma mass spectrometry using high-efficiency sample introduction.

PubMed

Boulyga, Sergei F; Heumann, Klaus G

2006-01-01

A method by inductively coupled plasma mass spectrometry (ICP-MS) was developed which allows the measurement of (236)U at concentration ranges down to 3 x 10(-14)g g(-1) and extremely low (236)U/(238)U isotope ratios in soil samples of 10(-7). By using the high-efficiency solution introduction system APEX in connection with a sector-field ICP-MS a sensitivity of more than 5,000 counts fg(-1) uranium was achieved. The use of an aerosol desolvating unit reduced the formation rate of uranium hydride ions UH(+)/U(+) down to a level of 10(-6). An abundance sensitivity of 3 x 10(-7) was observed for (236)U/(238)U isotope ratio measurements at mass resolution 4000. The detection limit for (236)U and the lowest detectable (236)U/(238)U isotope ratio were improved by more than two orders of magnitude compared with corresponding values by alpha spectrometry. Determination of uranium in soil samples collected in the vicinity of Chernobyl nuclear power plant (NPP) resulted in that the (236)U/(238)U isotope ratio is a much more sensitive and accurate marker for environmental contamination by spent uranium in comparison to the (235)U/(238)U isotope ratio. The ICP-MS technique allowed for the first time detection of irradiated uranium in soil samples even at distances more than 200 km to the north of Chernobyl NPP (Mogilev region). The concentration of (236)U in the upper 0-10 cm soil layers varied from 2 x 10(-9)g g(-1) within radioactive spots close to the Chernobyl NPP to 3 x 10(-13)g g(-1) on a sampling site located by >200 km from Chernobyl.

Development of a “Fission-proxy” Method for the Measurement of 14-MeV Neutron Fission Yields at CAMS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gharibyan, Narek

2016-10-25

Relative fission yield measurements were made for 50 fission products from 25.6±0.5 MeV alpha-induced fission of Th-232. Quantitative comparison of these experimentally measured fission yields with the evaluated fission yields from 14-MeV neutron-induced fission of U-235 demonstrates the feasibility of the proposed fission-proxy method. This new technique, based on the Bohr-independence hypothesis, permits the measurement of fission yields from an alternate reaction pathway (Th-232 + 25.6 MeV α → U-236* vs. U-235 + 14-MeV n → U-236*) given that the fission process associated with the same compound nucleus is independent of its formation. Other suitable systems that can potentially bemore » investigated in this manner include (but are not limited to) Pu-239 and U-237.« less

Measuring Uranium Decay Rates for Advancement of Nuclear Forensics and Geochronology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Parsons-Davis, Tashi

Radioisotopic dating techniques are highly valuable tools for understanding the history of physical and chemical processes in materials related to planetary sciences and nuclear forensics, and rely on accurate knowledge of decay constants and their uncertainties. The decay constants of U-238 and U-235 are particularly important to Earth science, and often the measured values with lowest reported uncertainties are applied, although they have not been independently verified with similar precision. New direct measurements of the decay constants of U-238, Th-234, U-235, and U-234 were completed, using a range of analytical approaches. An overarching goal of the project was to ensuremore » the quality of results, including metrological traceability to facilitate implementation across diverse disciplines. This report presents preliminary results of these experiments, as a few final measurements and calculations are still in progress.« less

Ground water contamination with (238)U, (234)U, (235)U, (226)Ra and (210)Pb from past uranium mining: cove wash, Arizona.

PubMed

Dias da Cunha, Kenya Moore; Henderson, Helenes; Thomson, Bruce M; Hecht, Adam A

2014-06-01

The objectives of the study are to present a critical review of the (238)U, (234)U, (235)U, (226)Ra and (210)Pb levels in water samples from the EPA studies (U.S. EPA in Abandoned uranium mines and the Navajo Nation: Red Valley chapter screening assessment report. Region 9 Superfund Program, San Francisco, 2004, Abandoned uranium mines and the Navajo Nation: Northern aum region screening assessment report. Region 9 Superfund Program, San Francisco, 2006, Health and environmental impacts of uranium contamination, 5-year plan. Region 9 Superfund Program, San Franciso, 2008) and the dose assessment for the population due to ingestion of water containing (238)U and (234)U. The water quality data were taken from Sect. "Data analysis" of the published report, titled Abandoned Uranium Mines Project Arizona, New Mexico, Utah-Navajo Lands 1994-2000, Project Atlas. Total uranium concentration was above the maximum concentration level for drinking water (7.410-1 Bq/L) in 19 % of the water samples, while (238)U and (234)U concentrations were above in 14 and 17 % of the water samples, respectively. (226)Ra and (210)Pb concentrations in water samples were in the range of 3.7 × 10(-1) to 5.55 × 102 Bq/L and 1.11 to 4.33 × 102 Bq/L, respectively. For only two samples, the (226)Ra concentrations exceeded the MCL for total Ra for drinking water (0.185 Bq/L). However, the (210)Pb/(226)Ra ratios varied from 0.11 to 47.00, and ratios above 1.00 were observed in 71 % of the samples. Secular equilibrium of the natural uranium series was not observed in the data record for most of the water samples. Moreover, the (235)U/(total)U mass ratios ranged from 0.06 to 5.9 %, and the natural mass ratio of (235)U to (total)U (0.72 %) was observed in only 16 % of the water samples, ratios above or below the natural ratio could not be explained based on data reported by U.S. EPA. In addition, statistical evaluations showed no correlations among the distribution of the radionuclide concentrations in the majority of the water samples, indicating more than one source of contamination could contribute to the sampled sources. The effective doses due to ingestion of the minimum uranium concentrations in water samples exceed the average dose considering inhalation and ingestion of regular diet for other populations around the world (1 μSv/year). The maximum doses due to ingestion of (238)U or (234)U were above the international limit for effective dose for members of the public (1 mSv/year), except for inhabitants of two chapters. The highest effective dose was estimated for inhabitants of Cove, and it was almost 20 times the international limit for members of the public. These results indicate that ingestion of water from some of the sampled sources poses health risks.

Extended optical model for fission

DOE PAGES

Sin, M.; Capote, R.; Herman, M. W.; ...

2016-03-07

A comprehensive formalism to calculate fission cross sections based on the extension of the optical model for fission is presented. It can be used for description of nuclear reactions on actinides featuring multi-humped fission barriers with partial absorption in the wells and direct transmission through discrete and continuum fission channels. The formalism describes the gross fluctuations observed in the fission probability due to vibrational resonances, and can be easily implemented in existing statistical reaction model codes. The extended optical model for fission is applied for neutron induced fission cross-section calculations on 234,235,238U and 239Pu targets. A triple-humped fission barrier ismore » used for 234,235U(n,f), while a double-humped fission barrier is used for 238U(n,f) and 239Pu(n,f) reactions as predicted by theoretical barrier calculations. The impact of partial damping of class-II/III states, and of direct transmission through discrete and continuum fission channels, is shown to be critical for a proper description of the measured fission cross sections for 234,235,238U(n,f) reactions. The 239Pu(n,f) reaction can be calculated in the complete damping approximation. Calculated cross sections for 235,238U(n,f) and 239Pu(n,f) reactions agree within 3% with the corresponding cross sections derived within the Neutron Standards least-squares fit of available experimental data. Lastly, the extended optical model for fission can be used for both theoretical fission studies and nuclear data evaluation.« less

In-beam spectroscopy of the k π=0- bands in230 236U

NASA Astrophysics Data System (ADS)

Zeyen, P.; Ackermann, B.; Dämmrich, U.; Euler, K.; Grafen, V.; Günther, C.; Herzog, P.; Marten-Tölle, M.; Prillwitz, B.; Tölle, R.; Lauterbach, Ch.; Maier, H. J.

1987-12-01

The K π=0- bands in even uranium nuclei were studied in the compound reactions231Pa( p, 2 n)230U,230, 232Th( α,2 n)232, 234U and236U( d, pn)236U. In-beam γ-rays were measured in coincidence with conversion-electrons, which were detected with an iron-free orange spectrometer. The negative-parity levels are observed up to intermediate spins ( I<13-). In addition, the 1- and 3- levels in230U were confirmed by a decay study with an isotope separated230Pa source. For the heavier isotopes ( A≥232) the properties of the K π=0- bands (energies and γ-branchings) are consistent with a vibrational character of these bands. For230U the K π=0- band lies at rather low energy ( E(1-)=367 keV), and the level spacings within this band are very similar to those of the isotones228Th and226Ra, which might indicate the onset of a stable octupole deformation.

Determining the isotopic compositions of uranium and fission products in radioactive environmental microsamples using laser ablation ICP-MS with multiple ion counters.

PubMed

Boulyga, Sergei F; Prohaska, Thomas

2008-01-01

This paper presents the application of a multicollector inductively coupled plasma mass spectrometer (MC-ICP-MS)--a Nu Plasma HR--equipped with three ion-counting multipliers and coupled to a laser ablation system (LA) for the rapid and sensitive determination of the 235U/238U, 236U/238U, 145Nd/143Nd, 146Nd/143Nd, 101Ru/(99Ru+99Tc) and 102Ru/(99Ru+99Tc) isotope ratios in microsamples collected in the vicinity of Chernobyl. Microsamples with dimensions ranging from a hundred mum to about 1 mm and with surface alpha activities of 3-38 mBq were first identified using nuclear track radiography. U, Nd and Ru isotope systems were then measured sequentially for the same microsample by LA-MC-ICP-MS. The application of a zoom ion optic for aligning the ion beams into the ion counters allows fast switching between different isotope systems, which enables all of the abovementioned isotope ratios to be measured for the same microsample within a total analysis time of 15-20 min (excluding MC-ICP-MS optimization and calibration). The 101Ru/(99Ru+99Tc) and 102Ru/(99Ru+99Tc) isotope ratios were measured for four microsamples and were found to be significantly lower than the natural ratios, indicating that the microsamples were contaminated with the corresponding fission products (Ru and Tc). A slight depletion in 146Nd of about 3-5% was observed in the contaminated samples, but the Nd isotopic ratios measured in the contaminated samples coincided with natural isotopic composition within the measurement uncertainty, as most of the Nd in the analyzed samples originates from the natural soil load of this element. The 235U/238U and 236U/238U isotope ratios were the most sensitive indicators of irradiated uranium. The present work yielded a significant variation in uranium isotope ratios in microsamples, in contrast with previously published results from the bulk analysis of contaminated samples originating from the vicinity of Chernobyl. Thus, the 235U/238U ratios measured in ten microsamples varied in the range from 0.0073 (corresponding to the natural uranium isotopic composition) to 0.023 (corresponding to initial 235U enrichment in reactor fuel). An inverse correlation was observed between the 236U/238U and 235U/238U isotope ratios, except in the case of one sample with natural uranium. The heterogeneity of the uranium isotope composition is attributed to the different burn-up grades of uranium in the fuel rods from which the microsamples originated.

Constraining the calculation of U 234 , 236 , 238 ( n , γ ) cross sections with measurements of the γ -ray spectra at the DANCE facility

DOE PAGES

Ullmann, J. L.; Kawano, T.; Baramsai, B.; ...

2017-08-31

The cross section for neutron capture in the continuum region has been difficult to calculate accurately. Previous results for 238 U show that including an M 1 scissors-mode contribution to the photon strength function resulted in very good agreement between calculation and measurement. Our paper extends that analysis to 234 , 236 U by using γ -ray spectra measured with the Detector for Advanced Neutron Capture Experiments (DANCE) at the Los Alamos Neutron Science Center to constrain the photon strength function used to calculate the capture cross section. Calculations using a strong scissors-mode contribution reproduced the measured γ -ray spectramore » and were in excellent agreement with the reported cross sections for all three isotopes.« less

Connecting the U-Th and U-Pb Chronometers: New Algorithms and Applications

NASA Astrophysics Data System (ADS)

McLean, N. M.; Smith, C. J. M.; Roberts, N. M. W.; Richards, D. A.

2016-12-01

The U-Th and U-Pb geochronometers are important clocks for separate intervals of the geologic timescale. U-Th dates exploit disequilibrium in the 238U intermediate daughter isotopes 234U and 230Th, and are often used to date corals and speleothems that are zero age through 800 ka. The U-Pb system relies on secular equilibrium decay of 238U to 206Pb and 235U to 207Pb over longer timescales, and can be used to date samples from <1 Ma to 4.5 Ga. Disequilibrium plays a role in young U-Pb dates, but only as a nuisance correction. Both chronometers can produce dates with uncertainties <0.1% near the center of their applicable age ranges, but become less precise at their intersection, when the 238U decay chain approaches secular equilibrium and there has been little time for ingrowth of radiogenic Pb. However, if measurements or assumptions about both chronometers can be made, then they can be combined into a single, more informed date. Coupling the datasets can improve their precision and accuracy and help interrogate the assumptions that underpin each. Working with this data is difficult for two reasons. The Bateman equations are long and cumbersome for U decay chains that include 238U, 234U, 230Th, 226Ra, 206Pb and 235U, 231Pa, and 207Pb. Also, Pb measurements often comprise varying amounts of radiogenic Pb from locally heterogeneous U concentrations mixed with varying amounts of common Pb. At present there is no established, flexible computational framework to combine information from measurements and/or assumptions of these parameters, and no way to visualize and interpret the results. We present new algorithms to quickly and accurately solve the system of differential equations defined by both of the uranium decay chains and the linear regression through the U-Pb isochron. The results are illustrated on a new concordia diagram, where the concordia curve is determined by measured and/or assumed U-series disequilibrium and can have unfamiliar topologies. We demonstrate this approach using data collected by solution and laser ablation ICPMS on carbonates with measurable 230Th and 234U disequilibrium, measurable disequilibrium for only 234U, and when only assumptions can be made about initial U-series disequilibrium. Potential applications include refining chronologies at ca. 1 Ma, an important period in Earth history.

Isolation and Puification of Uranium Isotopes for Measurement by Mass-Spectrometry (233, 234, 235, 236, 238U) and Alpha Spectrometry (232U)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marinelli, R; Hamilton, T; Brown, T

2006-05-30

This report describes a standardized methodology used by researchers from the Center for Accelerator Mass Spectrometry (CAMS) (Energy and Environment Directorate) and the Environmental Radiochemistry Group (Chemistry and Materials Science Directorate) at the Lawrence Livermore National Laboratory (LLNL) for the full isotopic analysis of uranium from solution. The methodology has largely been developed for use in characterizing the uranium composition of selected nuclear materials but may also be applicable to environmental studies and assessments of public, military or occupational exposures to uranium using in-vitro bioassay monitoring techniques. Uranium isotope concentrations and isotopic ratios are measured using a combination of Multimore » Collector Inductively Coupled Plasma Mass Spectrometry (MC ICP-MS), Accelerator Mass Spectrometry (AMS) and Alpha Spectrometry.« less

Airborne Plutonium and non-natural Uranium from the Fukushima DNPP found at 120 km distance a few days after reactor hydrogen explosions.

PubMed

Shinonaga, Taeko; Steier, Peter; Lagos, Markus; Ohkura, Takehisa

2014-04-01

Plutonium (Pu) and non-natural uranium (U) originating from the Fukushima Daiichi Nuclear Power Plant (FDNPP) were identified in the atmosphere at 120 km distance from the FDNPP analyzing the ratio of number of atoms, following written as n(isotope)/n(isotope), of Pu and U. The n((240)Pu)/n((239)Pu), n((241)Pu)/n((239)Pu), n((234)U)/n((238)U), n((235)U)/n((238)U) and n((236)U)/n((238)U) in aerosol samples collected before and after the FDNPP incident were analyzed by accelerator mass spectrometry (AMS) and inductively coupled plasma mass spectrometry (ICPMS). The activity concentrations of (137)Cs and (134)Cs in the same samples were also analyzed by gamma spectrometry before the destructive analysis. Comparing the time series of analytical data on Pu and U obtained in this study with previously reported data on Pu, U, and radioactive Cs, we concluded that Pu and non-natural U from the FDNPP were transported in the atmosphere directly over a 120 km distance by aerosol and wind within a few days after the reactor hydrogen explosions. Effective dose of Pu were calculated using the data of Pu: (130 ± 21) nBq/m(3), obtained in this study. We found that the airborne Pu contributes only negligibly to the total dose at the time of the incident. However the analytical results show that the amount of Pu and non-natural U certainly increased in the environment after the incident.

^235U(n,xnγ) Excitation Function Measurements Using Gamma-Ray Spectroscopy at GEANIE

NASA Astrophysics Data System (ADS)

Younes, W.; Becker, J. A.; Bernstein, L. A.; Archer, D. E.; Stoyer, M. A.; Hauschild, K.; Drake, D. M.; Johns, G. D.; Nelson, R. O.; Wilburn, S. W.

1998-04-01

The ^235U(n,xn) cross sections (where x<=2) have previously been measured at several incident neutron energies. In particular, the ^235U(n,2n) cross section has been measured(J. Frehaut et al.), Nucl. Sci. Eng. 74,29 (1980). reliably up to peak near E_n≈ 11 MeV, but not along the tail which is predicted by some(M.B. Chadwick, private communication.) codes to yield significant (e.g. >= 10% of peak) cross section out to E_n≈ 30 MeV. We have measured gamma-ray spectra resulting from ^235U(n,xn) as a function of neutron energy in the range 1 MeV <~ En <~ 200 MeV using the GEANIE spectrometer at the LANSCE/WNR ``white'' neutron source. We will present excitation functions for the de-excitation gamma rays in ^234,235U compared to predictions from the Hauser-Feshbach-preequilibrium code GNASH(M.B. Chadwick and P.G. Young, Los Alamos Report No. LA-UR-93-104, 1993.).

High-Resolution Inductively Coupled Plasma Optical Emission Spectrometry for (234)U/(238)Pu Age Dating of Plutonium Materials and Comparison to Sector Field Inductively Coupled Plasma Mass Spectrometry.

PubMed

Krachler, Michael; Alvarez-Sarandes, Rafael; Rasmussen, Gert

2016-09-06

Employing a commercial high-resolution inductively coupled plasma optical emission spectrometry (HR-ICP-OES) instrument, an innovative analytical procedure for the accurate determination of the production age of various Pu materials (Pu powder, cardiac pacemaker battery, (242)Cm heat source, etc.) was developed and validated. This undertaking was based on the fact that the α decay of (238)Pu present in the investigated samples produced (234)U and both mother and daughter could be identified unequivocally using HR-ICP-OES. Benefiting from the high spectral resolution of the instrument (<5 pm) and the isotope shift of the emission lines of both nuclides, (234)U and (238)Pu were selectively and directly determined in the dissolved samples, i.e., without a chemical separation of the two analytes from each other. Exact emission wavelengths as well as emission spectra of (234)U centered around λ = 411.590 nm and λ = 424.408 nm are reported here for the first time. Emission spectra of the isotopic standard reference material IRMM-199, comprising about one-third each of (233)U, (235)U, and (238)U, confirmed the presence of (234)U in the investigated samples. For the assessment of the (234)U/(238)Pu amount ratio, the emission signals of (234)U and (238)Pu were quantified at λ = 424.408 nm and λ = 402.148 nm, respectively. The age of the investigated samples (range: 26.7-44.4 years) was subsequently calculated using the (234)U/(238)Pu chronometer. HR-ICP-OES results were crossed-validated through sector field inductively coupled plasma mass spectrometry (SF-ICPMS) analysis of the (234)U/(238)Pu amount ratio of all samples applying isotope dilution combined with chromatographic separation of U and Pu. Available information on the assumed ages of the analyzed samples was consistent with the ages obtained via the HR-ICP-OES approach. Being based on a different physical detection principle, HR-ICP-OES provides an alternative strategy to the well-established mass spectrometric approach and thus effectively adds to the quality assurance of (234)U/(238)Pu age dates.

Measurements of natural uranium concentration and isotopic composition with permil-level precision by inductively coupled plasma-quadrupole mass spectrometry

NASA Astrophysics Data System (ADS)

Shen, Chuan-Chou; Lin, Huei-Ting; Chu, Mei-Fei; Yu, Ein-Fen; Wang, Xianfeng; Dorale, Jeffrey A.

2006-09-01

A new analytical technique using inductively coupled plasma-quadrupole mass spectrometry (ICP-QMS) has been developed that produces permil-level precision in the measurement of uranium concentration ([U]) and isotopic composition (δ234U) in natural materials. A 233U-236U double spike method was used to correct for mass fractionation during analysis. To correct for ratio drifting, samples were bracketed by uranium standard measurements. A sensitivity of 6-7 × 108 cps/ppm was generated with a sample solution uptake rate of 30 μL/min. With a measurement time of 15-20 min, standards of 30-ng uranium produced a within-run precision better than 3‰ (±2 R.S.D.) for δ234U and better than 2‰ for [U]. Replicate measurements made on standards show that a between-run reproducibility of 3.5‰ for δ234U and 2‰ for [U] can be achieved. ICP-QMS data of δ234U and [U] in seawater, coral, and speleothem materials are consistent with the data measured by other ICP-MS and TIMS techniques. Advantages of the ICP-QMS method include low cost, easy maintenance, simple instrumental operation, and few sample preparation steps. Sample size requirements are small, such as 10-14 mg of coral material. The results demonstrate that this technique can be applied to natural samples with various matrices.

Age of the moon: An isotopic study of uranium-thorium-lead systematics of lunar samples

USGS Publications Warehouse

Tatsumoto, M.; Rosholt, J.N.

1970-01-01

Concentrations of U, Th, and Pb in Apollo 11 samples studied are low (U. 0.16 to 0.87; Th, 0.53 to 3.4; Pb, 0.29 to 1.7, in ppm) but the extremely radiogenic lead in samples allows radiometric dating. The fine dust and the breccia have a concordant age of 4.66 billion years on the basis of 207Pb/206Pb, 206Pb/238U, 207Pb/235U, and 208Pb/232Th ratios. This age is comparable with the age of meteorites and with the age generally accepted for the earth. Six crystalline and vesicular samples are distinctly younger than the dust and breccia. The 238U/235U ratio is the same as that in earth rocks, and 234U is in radioactive equilibrium with parent 238U.

Formation of the 50-Year Element 94 from Deuteron Bombardment of U{sup 238}

DOE R&D Accomplishments Database

Kennedy, J. W.; Perlman, M. L.; Segre, E.; Wahl, A. C.

1942-06-01

It has been shown by bombardment with deuterons of a sample of U{sup 238}, greatly depleted in U{sup 235} and U{sup 234}, that the 50-year 94 activity and 2.0 day 93 activity are formed in approximately the same yield as with the natural mixture of uranium isotopes. The activities are thus shown to arise from the U{sup 238} nucleus, and from considerations of the energy of the compound nucleus (U{sup 238} + d).

Fission cross section of 239Th and 232Th relative to 235U

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meadows, J. W.

1979-01-01

The fission cross sections of /sup 230/Th and /sup 232/Th were measured relative to /sup 235/U from near threshold to near 10 MeV. The weights of the thorium samples were determined by isotopic dilution. The weight of the uranium deposit was based on specific activity measurements of a /sup 234/U-/sup 235/U mixture and low geometry alpha counting. Corrections were made for thermal background, loss of fragments in the deposits, neutron scattering in the detector assembly, sample geometry, sample composition and the spectrum of the neutron source. Generally the systematic errors were approx. 1%. The combined systematic and statistical errors weremore » typically 1.5%. 17 references.« less

Validation of Hansen-Roach library for highly enriched uranium metal systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wenz, T.R.; Busch, R.D.

The Hansen-Roach 16-group cross-section library has been validated for use in pure uranium metal systems by modeling the Godiva critical assembly using the neutronics transport theory code ONEDANT to perform effective multiplication factor (k{sub eff}) calculations. The cross-section library used contains data for 118 isotopes (34 unique elements), including the revised cross sections for {sup 235}U and {sup 238}U. The Godiva critical assembly is a 17.4-cm sphere composed of 93.7 wt% {sup 235}U, 1.0 wt% {sup 234}U, and 5.3 wt% {sup 238}U with an effective homogeneous density of 18.7 g/cm{sup 3}.

Evaluating the potential of the MegaSIMS for nuclear forensics

NASA Astrophysics Data System (ADS)

Boehnke, P.; McKeegan, K. D.; Coath, C. D.; Hutcheon, I. D.; Steele, R. C.; Harrison, M.

2013-12-01

Nuclear forensics investigates the illicit movement of nuclear materials. Measurements of uranium isotopic compositions are an important key as they permit provenance tracing and determination of intended use. Traditional secondary ion mass spectrometers (SIMS) are incapable of resolving 235UH from 236U due to the high mass resolving power (MRP ~38,000) needed, significantly limiting their ability to accurately measure 236U/235U, particularly for highly enriched uranium. This limitation can significantly inhibit the ability to establish details about enrichment processes. The MegaSIMS is a unique combination of SIMS and accelerator mass spectrometry (AMS) and allows for molecular interference free measurements, while retaining the spatial resolution and ease of sample preparation common in SIMS analyses. The instrument was primarily designed to measure the oxygen isotope composition of the solar wind [1] and its capability for measuring high mass elements has not been evaluated previously. We evaluated the potential of the MegaSIMS by measuring 236U/235U without hydride interference. While preliminary results show abundance sensitivity of ~E-9 and an MRP of ~1,200 at the high mass side of 238 amu, precision is limited by the detector geometry and slow magnet switching. Future work will include developing electrostatic peak switching as well as refining the measurement precision and abundance sensitivity of the MegaSIMS for nuclear forensics. [1] McKeegan, Kallio, Heber, Jarzebinski, Mao, Coath, Kunihiro, Wiens, Nordholt, Moses Jr., Reisenfeld, Jurewicz, and Burnett, 2011. Science. 332, 1528-1532.

Enhanced techniques for the measurement of ultra-low level (pg and fg) actinide analysis by ICP-MS for forensic and geologic applications

NASA Astrophysics Data System (ADS)

Pollington, A. D.; Kinman, W.; Hanson, S. K.

2014-12-01

Recent advances in mass spectrometry have led to an improved ability to measure high precision isotope ratios at increasingly low analyte concentrations. Combining techniques for enhanced ionization with better counting of small ion beams, we routinely measure isotope ratios on 100's of pg uranium samples and ≤10 pg plutonium samples with relative standard deviations of 1‰ on major isotope ratios and 10‰ on minor ratios achievable. With slightly larger samples (≤1 ng total U), these precisions can be as low as 0.01‰ (10 ppm) and 1‰ respectively. These techniques can be applied to both nuclear forensics questions where only a small amount of sample is available, as well as geologic questions such as U-Pb or U-Th disequilibrium geochronology from either single small crystals, or microsampled domains from within a heterogeneous sample. The analytical setup is a Cetac Aridus II desolvating nebulizer interfaced with a ThermoScientific Neptune Plus equipped with a jet-type sample cone and x-type skimmer cone. The combination of the desolvating nebulizer with the enhanced cone setup leads to an increase in sensitivity on the order of 10x that of a standard glass spray chamber (~1000V/ppm U). The Neptune Plus is equipped with 9 Faraday cups and 5 electron multipliers (two behind RPQ energy filters for improved abundance sensitivtiy). This allows for the simultaneous collection of all isotopes of either U or Pu with a combination of Faraday cups (e.g., 235U and 238U) and electron multipliers (e.g., 234U and 236U) with other configurations also available (e.g., 235U and 238U can instead be measured on electron multipliers in small samples). As sample sizes get small, the contributions from environmental blanks, as well as interfering species, become increasing concerns. In this study, we will present data on efforts to minimize the contribution of environmental U using scaled down chemical procedures as well as the effect of polyatomic species on the precision and accuracy of actinide isotope measurements and what procedures can be applied to minimize interferences.

Isotopic evidence for reductive immobilization of uranium across a roll-front mineral deposit

DOE PAGES

Brown, Shaun T.; Basu, Anirban; Christensen, John N.; ...

2016-05-20

We use uranium (U) isotope ratios to detect and quantify the extent of natural U reduction in groundwater across a roll front redox gradient. Our study was conducted at the Smith Ranch-Highland in situ recovery (ISR) U mine in eastern Wyoming, USA, where economic U deposits occur in the Paleocene Fort Union formation. To evaluate the fate of aqueous U in and adjacent to the ore body, we investigated the chemical composition and isotope ratios of groundwater samples from the roll-front type ore body and surrounding monitoring wells of a previously mined area. The 238U/ 235U of groundwater varies bymore » approximately 3‰ and is correlated with U concentrations. Fluid samples down-gradient of the ore zone are the most depleted in 238U and have the lowest U concentrations. Activity ratios of 234U/ 238U are ~5.5 up-gradient of the ore zone, ~1.0 in the ore zone, and between 2.3 and 3.7 in the down-gradient monitoring wells. High-precision measurements of 234U/ 238U and 238U/ 235U allow for development of a conceptual model that evaluates both the migration of U from the ore body and the extent of natural attenuation due to reduction. We find that the premining migration of U down-gradient of the delineated ore body is minimal along eight transects due to reduction in or adjacent to the ore body, whereas two other transects show little or no sign of reduction in the down-gradient region. Lastly, these results suggest that characterization of U isotopic ratios at the mine planning stage, in conjunction with routine geochemical analyses, can be used to identify where more or less postmining remediation will be necessary.« less

Neutron-Induced Fission Measurements at the Dance and Lsds Facilities at Lanl

NASA Astrophysics Data System (ADS)

Jandel, M.; Bredeweg, T. A.; Bond, E. M.; Chadwick, M. B.; Couture, A.; O'Donnell, J. M.; Fowler, M. M.; Haight, R. C.; Hayes-Sterbenz, A. C.; Rundberg, R. S.; Rusev, G. Y.; Ullmann, J. L.; Vieira, D. J.; Wilhelmy, J. B.; Wu, C. Y.; Becker, J. A.; Alexander, C. W.; Belier, G.

2014-09-01

New results from neutron-induced fission measurements performed at the Detector for Advanced Neutron Capture Experiments (DANCE) and Lead Slowing Down Spectrometer (LSDS) are presented. New correlated data on promptfission γ-ray (PFG) distributions were measured using the DANCE array for resonant neutron-induced fission of 233U, 235U and 239Pu. The deduced properties of PFG emission are presented using a simple parametrization. An accurate knowledge of fission γ-ray spectra enables us to analyze the isomeric states of 236U created after neutron capture on 235U. We briefly discuss these new results. Finally, we review details and preliminary results of the challenging 237U(n,f) cross section measurement at the LSDS facility.

Uranium isotopes in well water samples as drinking sources in some settlements around the Semipalatinsk Nuclear Test Site, Kazakhstan.

PubMed

Yamamoto, Masayoshi; Tomita, Junpei; Sakaguchi, Aya; Ohtsuka, Yoshihito; Hoshi, Masaharu; Apsalikov, Kazbek N

Radiochemical results of U isotopes ( 234 U, 235 U and 238 U) and their activity ratios are reported for well waters as local sources of drinking waters collected from the ten settlements around the Semipalatinsk Nuclear Test Site (SNTS), Kazakhstan. The results show that 238 U varies widely from 3.6 to 356 mBq/L (0.3-28.7 μg/L), with a factor of about 100. The 238 U concentrations in some water samples from Dolon, Tailan, Sarzhal and Karaul settlements are comparable to or higher than the World Health Organization's restrictive proposed guideline of 15 μg (U)/L. The 234 U/ 238 U activity ratios in the measured water samples are higher than 1, and vary between 1.1 and 7.9, being mostly from 1.5 to 3. The measured 235 U/ 238 U activity ratios are around 0.046, indicating that U in these well waters is of natural origin. It is probable that the elevated concentration of 238 U found in some settlements around the SNTS is not due to the close-in fallout from nuclear explosions at the SNTS, but rather to the intensive weathering of rocks including U there. The calculated effective doses to adults resulting from consumption of the investigated waters are in the range 1.0-18.7 μSv/y. Those doses are lower than WHO and IAEA reference value (100 μSv/y) for drinking water.

Certification of the Uranium Isotopic Ratios in Nbl Crm 112-A, Uranium Assay Standard (Invited)

NASA Astrophysics Data System (ADS)

Mathew, K. J.; Mason, P.; Narayanan, U.

2010-12-01

Isotopic reference materials are needed to validate measurement procedures and to calibrate multi-collector ion counting detector systems. New Brunswick Laboratory (NBL) provides a suite of certified isotopic and assay standards for the US and international nuclear safeguards community. NBL Certified Reference Material (CRM) 112-A Uranium Metal Assay Standard with a consensus value of 137.88 for the 238U/235U ratio [National Bureau of Standards -- NBS, currently named National Institute for Standards and Technology, Standard Reference Material (SRM) 960 had been renamed CRM 112-A] is commonly used as a natural uranium isotopic reference material within the earth science community. We have completed the analytical work for characterizing the isotopic composition of NBL CRM 112-A Uranium Assay Standard and NBL CRM 145 (uranyl nitrate solution prepared from CRM 112-A). The 235U/238U isotopic ratios were characterized using the total evaporation (TE) and the modified total evaporation (MTE) methods. The 234U/238U isotope ratios were characterized using a conventional analysis technique and verified using the ratios measured in the MTE analytical technique. The analysis plan for the characterization work was developed such that isotopic ratios that are traceable to NBL CRM U030-A are obtained. NBL is preparing a certificate of Analysis and will issue a certificate for Uranium Assay and Isotopics. The results of the CRM 112-A certification measurements will be discussed. These results will be compared with the average values from Richter et al (2010). A comparison of the precision and accuracy of the measurement methods (TE, MTE and Conventional) employed in the certification will be presented. The uncertainties in the 235U/238U and 234U/238U ratios, calculated according to the Guide to the Expression of Uncertainty in Measurements (GUM) and the dominant contributors to the combined standard uncertainty will be discussed.

The 238U/235U isotope ratio of the Earth and the solar system: Constrains from a gravimetrically calibrated U double spike and implications for absolute Pb-Pb ages

NASA Astrophysics Data System (ADS)

Weyer, Stefan; Noordmann, Janine; Brennecka, Greg; Richter, Stephan

2010-05-01

The ratio of 238U and 235U, the two primordial U isotopes, has been assumed to be constant on Earth and in the solar system. The commonly accepted value for the 238U/235U ratio, which has been used in Pb-Pb dating for the last ~ 30 years, was 137.88. Within the last few years, it has been shown that 1) there are considerable U isotope variations (~1.3‰) within terrestrial material produced by isotope fractionation during chemical reactions [1-3] and 2) there are even larger isotope variations (at least 3.5‰) in calcium-aluminum-rich inclusions (CAIs) in meoteorites that define the currently accepted age of the solar system [4]. These findings are dramatic for geochronology, as a known 238U/235U is a requirement for Pb-Pb dating, the most precise dating technique for absolute ages. As 238U/235U variations can greatly affect the reported absolute Pb-Pb age, understanding and accurately measuring variation of the 238U/235U ratio in various materials is critical, With these new findings, the questions also arises of "How well do we know the average U isotope composition of the Earth and the solar system?" and "How accurate can absolute Pb-Pb ages be?" Our results using a gravimetrically calibrated 233U/236U double spike IRMM 3636 [5] indicate that the U standard NBL 950a, which was commonly used to define the excepted "natural" 238U/235U isotope ratio, has a slightly lower 238U/235U of 137.836 ± 0.024. This value is indistinguishable from the U isotope compositions for NBL 960 and NBL112A, which have been determined by several laboratories, also using the newly calibrated U double spike IRMM 3636 [6]. These findings provide new implications about the average U isotope composition of the Earth and the solar system. Basalts display a very tight range of U isotope variations (~0.25-0.32‰ relative to SRM 950a). Their U isotope composition is also very similar to that of chondrites [4], which however appear to show a slightly larger spread. Accepting terrestrial basalts to be the best representation of the U isotope composition of the Earth and the solar system, and the new 238U/235U for SRM 950a of 137.836, this would result in an average 238U/235U for the Earth and the solar system of ~ 137.80. The effect of a revised 238U/235U ratio on Pb-Pb ages is age dependent. It results in an age overestimation of ~0.8 Ma for the age of the solar system and up to 1.5 Ma for very young material (with bulk Earth U isotope composition). [1] Stirling, C.H., Andersen, M.B., Potter, E.-K., et al. (2007) EPSL 264, 208-225; [2] Weyer, S., Anbar, A. D., Gerdes, A., et al. (2008) GCA 72, 345-359. [3] Bopp, C.H., Lundstrom, C.C., Johnsons, T.M., Glessner, J.G. (2009) Geology 37, 611-614. [4] Brennecka, G.A., Weyer, S., Wadhwa, et al. (2010) Science, 327, p. 449. [5] Richter, S., Alonzo-Munoz, A., Eykens, R., et al. (2008) IJMS 269, 145-148. [6] Richter, S., et al. EGU meeting 2010.

Natural radionuclide mobility and its influence on U-Th-Pb dating of secondary minerals from the unsaturated zone at Yucca Mountain, Nevada

USGS Publications Warehouse

Neymark, L.A.; Amelin, Y.V.

2008-01-01

Extreme U and Pb isotope variations produced by disequilibrium in decay chains of 238U and 232Th are found in calcite, opal/chalcedony, and Mn-oxides occurring as secondary mineral coatings in the unsaturated zone at Yucca Mountain, Nevada. These very slowly growing minerals (mm my-1) contain excess 206Pb and 208Pb formed from excesses of intermediate daughter isotopes and cannot be used as reliable 206Pb/238U geochronometers. The presence of excess intermediate daughter isotopes does not appreciably affect 207Pb/235U ages of U-enriched opal/chalcedony, which are interpreted as mineral formation ages. Opal and calcite from outer (younger) portions of coatings have 230Th/U ages from 94.6 ?? 3.7 to 361.3 ?? 9.8 ka and initial 234U/238U activity ratios (AR) from 4.351 ?? 0.070 to 7.02 ?? 0.12, which indicate 234U enrichment from percolating water. Present-day 234U/238U AR is ???1 in opal/chalcedony from older portions of the coatings. The 207Pb/235U ages of opal/chalcedony samples range from 0.1329 ?? 0.0080 to 9.10 ?? 0.21 Ma, increase with microstratigraphic depth, and define slow long-term average growth rates of about 1.2-2.0 mm my-1, in good agreement with previous results. Measured 234U/238U AR in Mn-oxides, which pre-date the oldest calcite and opal/chalcedony, range from 0.939 ?? 0.006 to 2.091 ?? 0.006 and are >1 in most samples. The range of 87Sr/86Sr ratios (0.71156-0.71280) in Mn-oxides overlaps that in the late calcite. These data indicate that Mn-oxides exchange U and Sr with percolating water and cannot be used as a reliable dating tool. In the U-poor calcite samples, measured 206Pb/207Pb ratios have a wide range, do not correlate with Ba concentration as would be expected if excess Ra was present, and reach a value of about 1400, the highest ever reported for natural Pb. Calcite intergrown with opal contains excesses of both 206Pb and 207Pb derived from Rn diffusion and from direct ??-recoil from U-rich opal. Calcite from coatings devoid of opal/chalcedony contains 206Pb and 208Pb excesses, but no appreciable 207Pb excesses. Observed Pb isotope anomalies in calcite are explained by Rn-produced excess Pb. The Rn emanation may strongly affect 206Pb-238U ages of slow-growing U-poor calcite, but should be negligible for dating fast-growing U-enriched speleothem calcite.

Radioisotope dilution analyses of geological samples using 236U and 229Th

USGS Publications Warehouse

Rosholt, J.N.

1984-01-01

The use of 236U and 229Th in alpha spectrometric measurements has some advantages over the use of other tracers and measurement techniques in isotope dilution analyses of most geological samples. The advantages are: (1) these isotopes do not occur in terrestrial rocks, (2) they have negligible decay losses because of their long half lives, (3) they cause minimal recoil contamination to surface-barrier detectors, (4) they allow for simultaneous determination of the concentration and isotopic composition of uranium and thorium in a variety of sample types, and (5) they allow for simple and constant corrections for spectral inferences, 0.5% of the 238U activity is subtracted for the contribution of 235U in the 236U peak and 1% of the 229Th activity is subtracted from the 230Th activity. Disadvantages in using 236U and 229Th are: (1) individual separates of uranium and thorium must be prepared as very thin sources for alpha spectrometry, (2) good resolution in the spectrometer system is required for thorium isotopic measurements where measurement times may extend to 300 h, and (3) separate calibrations of the 236U and 229Th spike solution with both uranium and thorium standards are required. The use of these tracers in applications of uranium-series disequilibrium studies has simplified the measurements required for the determination of the isotopic composition of uranium and thorium because of the minimal corrections needed for alpha spectral interferences. ?? 1984.

DETERMINATION AND DOSE CONTRIBUTION OF URANIUM ISOTOPES AND 210Po ACTIVITY CONCENTRATIONS OF NATURAL SPRING WATERS IN THE PROVINCE OF GRANADA, SPAIN.

PubMed

Milena-Pérez, A; Piñero-García, F; Expósito-Suárez, V M; Mantero, J; Benavente, J; Ferro-García, M A

2018-03-01

The activity concentrations of alpha-emitters comprising isotopes of uranium (238, 234, 235U) and polonium (210Po) were measured using alpha-particle spectrometry in natural spring waters in the province of Granada, Spain. These water are consumed by the population of the zone who live in villages. This is almost half of the population of the whole region. Mean values of activity concentrations found are 42.61 ± 2.66; 49.55 ± 3.03; 1.64 ± 0.28 and 1.74 ± 0.15 mBq L-1 for 238U, 234U, 235U and 210Po, respectively. Finally, the radiological impact of the analysed waters has been determined, in terms of the estimation of the committed annual effective dose due to the ingestion of the water. The assessment has been carried out for five age groups with the aim to cover all the population. The calculated annual effective doses are observed to be below the prescribed dose limit of 100 μSv y-1 recommended by WHO.

The use of secondary ion mass spectrometry in forensic analyses of ultra-small samples

NASA Astrophysics Data System (ADS)

Cliff, John

2010-05-01

It is becoming increasingly important in forensic science to perform chemical and isotopic analyses on very small sample sizes. Moreover, in some instances the signature of interest may be incorporated in a vast background making analyses impossible by bulk methods. Recent advances in instrumentation make secondary ion mass spectrometry (SIMS) a powerful tool to apply to these problems. As an introduction, we present three types of forensic analyses in which SIMS may be useful. The causal organism of anthrax (Bacillus anthracis) chelates Ca and other metals during spore formation. Thus, the spores contain a trace element signature related to the growth medium that produced the organisms. Although other techniques have been shown to be useful in analyzing these signatures, the sample size requirements are generally relatively large. We have shown that time of flight SIMS (TOF-SIMS) combined with multivariate analysis, can clearly separate Bacillus sp. cultures prepared in different growth media using analytical spot sizes containing approximately one nanogram of spores. An important emerging field in forensic analysis is that of provenance of fecal pollution. The strategy of choice for these analyses-developing host-specific nucleic acid probes-has met with considerable difficulty due to lack of specificity of the probes. One potentially fruitful strategy is to combine in situ nucleic acid probing with high precision isotopic analyses. Bulk analyses of human and bovine fecal bacteria, for example, indicate a relative difference in d13C content of about 4 per mil. We have shown that sample sizes of several nanograms can be analyzed with the IMS 1280 with precisions capable of separating two per mil differences in d13C. The NanoSIMS 50 is capable of much better spatial resolution than the IMS 1280, albeit at a cost of analytical precision. Nevertheless we have documented precision capable of separating five per mil differences in d13C using analytical spots containing less than 300 picograms of bacteria. Perhaps the most successful application of SIMS for forensic purposes to date is in the field of nuclear forensics. An example that has been used by laboratories associated with the International Atomic Energy Agency is the examination of environmental samples for enriched uranium particles indicative of clandestine weapons production activities.. The analytical challenge in these types of measurements is to search complex environmental matrices for U-bearing particles which must then be analyzed for 234U, 235U, and 236U content with high precision and accuracy. Older-generation SIMS instruments were hampered by small geometries that made resolution of significant interferences problematic. In addition, automated particle search software was proprietary and difficult to obtain. With the development of new search software, the IMS 1280 is capable of searching a sample in a matter of hours, flagging U-bearing particles for later analyses, and providing a rough 235U content. Particles of interest can be revisited for high precision analyses, and all U-isotopes can be measured simultaneously in multicollector mode, dramatically improving analysis time and internal precision. Further, the large geometry of the instrument allows complete resolution of isobaric interferences that have traditionally limited SIMS analyses of difficult samples. Examples of analyses of micron-sized standard particles indicate that estimates of 235U enrichment can be obtained with an external relative precision of 0.1% and 234U and 236U contents can be obtained with a relative precision of less than 1%. Analyses of 'real' samples show a dramatic improvement in the data quality obtained compared with small-geometry SIMS instruments making SIMS the method of choice for these high-profile samples when accurate, precise, and rapid results are required.

Comparison of Grab, Air, and Surface Results for Radiation Site Characterization

NASA Astrophysics Data System (ADS)

Glassford, Eric Keith

2011-12-01

The use of proper sampling methods and sample types for evaluating sites believed to be contaminated with radioactive materials is necessary to avoid misrepresenting conditions at the site. This study was designed to investigate if the site characterization, based upon uranium contamination measured in different types of samples, is dependent upon the mass of the sample collected. A bulk sample of potentially contaminated interior dirt was collected from an abandoned metal processing mill that rolled uranium between 1948 and 1956. The original mill dates from 1910 and has a dirt floor. The bulk sample was a mixture of dirt, black and yellow particles of metal dust, and small fragments of natural debris. Small mass (approximately 0.75 grams (g)) and large mass (approximately 70g) grab samples were prepared from the bulk sample material to simulate collection of a "grab" type sample. Air sampling was performed by re-suspending a portion of the bulk sample material using a vibration table to simulate airborne contamination that might be present during site remediation. Additionally, samples of removable contaminated surface dust were collected on 47 mm diameter filter paper by wiping the surfaces of the exposure chamber used to resuspend the bulk material. Certified reference materials, one containing a precisely known quantity of U 3O8 and one containing a known quantity of natural uranium, were utilized to calibrate the gamma spectrometry measurement system. Non-destructive gamma spectrometry measurements were used to determine the content of uranium-235 (235U) at 185 keV and 143 keV, thorium-234 (234Th) at 63 keV, and protactinium-234m (234mPa) at 1001 keV in each sample. Measurement of natural uranium in small, 1 g samples is usually accomplished by radiochemical analysis in order to measure alpha particles emitted by 238U, 235U, and 234U. However, uranium in larger bulk samples can also be measured non-destructively using gamma spectrometry to detect the low energy photons from 234Th and 234mPa, the short-lived decay products of 238U, and 235U. Two sided t-tests and coefficient of variation were used to compare sampling types. The large grab samples had the lowest calculated coefficient of variation results for activity and atom percentage. The wipe samples had the highest calculated coefficient of variation of mean specific activity (dis/sec/g) for all three energies. The air filter samples had the highest coefficient of variation calculation for mean atom percentage, for both uranium isotopes examined. The data indicated that the large mass sample was the most effective at characterizing the rolling mill radioactive site conditions, since this would indicate which samples had the smallest variations compared to the mean. Additionally, measurement results of natural uranium in the samples indicate that the distribution of radioactive contamination at the sampling location is most likely non-homogeneous and that the size of the sample collected and analyzed must be sufficiently large to insure that the analytical results are truly representative of the activity present.

Practical issues in discriminating between environmental and occupational sources in a uranium urinalysis bioassay program

DOE Office of Scientific and Technical Information (OSTI.GOV)

Long, M.P.; Carbaugh, E.H.; Fairrow, N.L.

1994-11-01

Workers at two Department of Energy facilities, the Pantex Plant in Texas and the Hanford Site in Washington, are potentially exposed to class Y depleted or natural uranium. Since trace amounts of uranium are naturally present in urine excretion, site bioassay programs must be able to discern occupational exposure from naturally occurring uranium exposure. In 1985 Hanford established a 0.2-{mu}g/d environmental screening level for elemental uranium in urine; the protocol was based on log-normal probability analysis of unexposed workers. A second study of background uranium levels commenced in 1990, and experiences in the field indicated that there seemed to bemore » an excessive number of urine samples with uranium above the screening level and that the environmental screening level should be reviewed. Due to unforeseen problems, that second study was terminated before the complete data could be obtained. Natural uranium in rock (by weight, 99.27% {sup 288}U, 0.72% {sup 235}U, and 0.006% {sup 234}U) has approximately equal activity concentrations of {sup 238}U and {sup 234}U. Earlier studies, summarized by the U.S. Environmental Protection Agency in 51 FR 32068, have indicated that {sup 234}U (via {sup 234}Th) has a greater environmental mobility than {sup 238}U and may well have a higher concentration in ground water. By assuming that the {sup 238}U-to {sup 234}U ratio in the urine of nonoccupationally exposed persons should reflect the ratio of environmental levels, significant occupational exposure to depleted uranium would shift that ratio in favor of {sup 238}U, allowing use of the ratio as a co-indicator of occupational exposure in addition to the isotope-specific screening levels. This approach has been adopted by Pantex. The Pacific Northwest Laboratory is studying the feasibility of applying this method to the natural and recycled uranium mixtures encountered at Hanford. The Hanford data included in this report represent work-in-progress.« less

Depth distributions of uranium-236 and cesium-137 in the Japan/East Sea; toward the potential use as a new oceanic circulation tracer

NASA Astrophysics Data System (ADS)

Sakaguchi, A.; Kadokura, A.; Steier, P.; Takahashi, Y.; Shizuma, K.; Yamamoto, M.

2012-04-01

137Cs (T1/2=30.2 y) has been spread all over the world as a fission product of atmospheric nuclear weapons tests in the 1960s. This nuclide has been used as a powerful tool for oceanography due to the well-defined origin and conservative behaviour in water . However, the number of atoms has decayed already to one thirds compared with its initial levels, and it will become more difficult to measure. In this situation, we focus on 236U (T1/2=2.342-107 y) as a candidate for a new isotopic tracer for oceanography. The detection of 236U in the environment has become possible only recently, by the development of measuring techniques with high sensitivity based on AMS. Our group showed that global fallout from bomb tests contains 236U, which might be produced as nuclear reactions of 235U(n,γ) and/or 238U(n,3n). So 236U has been therefore globally distributed in the surface environment. Thus, 236U has a similar potential as a tracer for environmental dynamics as 137Cs, especially for oceanography. In this study, a comprehensive attempt was made to measure the concentration of 236U in marine samples such as water, suspended solid and bottom sediments to clarify the environmental behaviour of this isotope. Furthermore, the discussion of the circulation of deep and bottom water in "Miniature Ocean", the Japan Sea, has been attempted. Bottom sediments (4 sites) and seawater samples (7 sites) were collected from the Japan Sea. The sediment core was cut into 1 cm segments from the surface to 5 cm in depth within a few hours after the sampling. About 20 L of seawater samples were collected from some depths in each site, and immediately after the sampling, the water was filtered with 0.45 μm pore-size membrane-filters. After the appropriate pre-treatment for each sample, uranium isotope and 137Cs were measured with AMS and Ge-detector, respectively. 236U was successfully detected for all seawater samples, and 236U/238U atom ratios in seawater were in the range of (0.19-1.75)-10-9. The dissolved 236U concentration showed a subsurface maximum and decreased steeply with depth. The minimum value was found at a depth of 2500 m and bottom (about 3000 m in depth) in the northern and the southern areas, respectively. These profiles are markedly different from that of natural 238U which is nearly constant over the depth, suggesting that 236U has not yet reached steady state. For the SS sample, 236U could not be detected in significant levels. The total 236U inventory of the water column was estimated at 1012-1013 atom/m2. This value is nearly the same as the global fallout level (17.8-1012 atom/m2). 236U was also found in the bottom sediments, and the inventory was about 1/40 compared with that in water column. All above characters are comparable with 137Cs which is anthropogenic conservative nuclide in ocean. Actually, the diffusion coefficients for both nuclides show the nearly same value. The detail discussion including the circulation of deep-water in the Japan Sea will be given in our presentation.

Neutrons as Party Animals: An Analogy for Understanding Heavy-Element Fissility

NASA Astrophysics Data System (ADS)

Reed, B. Cameron

2012-12-01

I teach a general education class on the history of nuclear physics and the Manhattan Project. About halfway through the course we come to the discovery of fission and Niels Bohr's insight that it is the rare isotope of uranium, U-235, which fissions under slow-neutron bombardment as opposed to the much more common U-238 isotope. As an "explanation" of the differing responses of the two isotopes to bombarding neutrons, I use the known (measured) masses of the various isotopes involved to compute the energies released upon neutron capture and then compare them to the fission barriers of the "compound" nuclei so formed (U-236 and U-239). The energy released in the (neutron + U-235) reaction exceeds the fission barrier by about one million electron-volts (1 MeV), while that for the (neutron + U-238) case falls about 1.6 MeV short. (The fission barriers are respectively about 5.7 and 6.5 MeV.)

U-isotopes and (226)Ra as tracers of hydrogeochemical processes in carbonated karst aquifers from arid areas.

PubMed

Guerrero, José Luis; Vallejos, Ángela; Cerón, Juan Carlos; Sánchez-Martos, Francisco; Pulido-Bosch, Antonio; Bolívar, Juan Pedro

2016-07-01

Sierra de Gádor is a karst macrosystem with a highly complex geometry, located in southeastern Spain. In this arid environment, the main economic activities, agriculture and tourism, are supported by water resources from the Sierra de Gádor aquifer system. The aim of this work was to study the levels and behaviour of some of the most significant natural radionuclides in order to improve the knowledge of the hydrogeochemical processes involved in this groundwater system. For this study, 28 groundwater and 7 surface water samples were collected, and the activity concentrations of the natural U-isotopes ((238)U, (235)U and (234)U) and (226)Ra by alpha spectrometry were determined. The activity concentration of (238)U presented a large variation from around 1.1 to 65 mBq L(-1). Elevated groundwater U concentrations were the result of oxidising conditions that likely promoted U dissolution. The PHREEQC modelling code showed that dissolved U mainly existed as uranyl carbonate complexes. The (234)U/(238)U activity ratios were higher than unity for all samples (1.1-3.8). Additionally, these ratios were in greater disequilibrium in groundwater than surface water samples, the likely result of greater water-rock contact time. (226)Ra presented a wide range of activity concentrations, (0.8 up to about 4 × 10(2) mBq L(-1)); greatest concentrations were detected in the thermal area of Alhama. Most of the samples showed (226)Ra/(234)U activity ratios lower than unity (median = 0.3), likely the result of the greater mobility of U than Ra in the aquifer system. The natural U-isotopes concentrations were strongly correlated with dissolution of sulphate evaporites (mainly gypsum). (226)Ra had a more complex behaviour, showing a strong correlation with water salinity, which was particularly evident in locations where thermal anomalies were detected. The most saline samples showed the lowest (234)U/(238)U activity ratios, probably due to fast uniform bulk mineral dissolution, which would minimize the impact of solubility-controlled fractionation processes. Furthermore, the high bulk dissolution rates promoted greater groundwater (226)Ra/(234)U ratios because the Ra has a comparatively much greater mobility than U in saline conditions. Copyright © 2016 Elsevier Ltd. All rights reserved.

Uranium Isotopes in Calcium Carbonate: A Possible Proxy for Paleo-pH and Carbonate Ion Concentration?

NASA Astrophysics Data System (ADS)

Chen, X.; Romaniello, S. J.; Herrmann, A. D.; Wasylenki, L. E.; Anbar, A. D.

2015-12-01

Natural variations of 238U/235U in marine carbonates are being explored as a paleoredox proxy. However, in order for this proxy to be robust, it is important to understand how pH and alkalinity affect the fractionation of 238U/235U during coprecipitation with calcite and aragonite. Recent work suggests that the U/Ca ratio of foraminiferal calcite may vary with seawater [CO32-] concentration due to changes in U speciation[1]. Here we explore analogous isotopic consequences in inorganic laboratory co-precipitation experiments. Uranium coprecipitation experiments with calcite and aragonite were performed at pH 8.5 ± 0.1 and 7.5 ± 0.1 using a constant addition method [2]. Dissolved U in the remaining solution was periodically collected throughout the experiments. Samples were purified with UTEVA resin and 238U/235U was determined using a 233U-236U double-spike and MC-ICP-MS, attaining a precision of ± 0.10 ‰ [3]. Small but resolvable U isotope fractionation was observed in aragonite experiments at pH ~8.5, preferentially enriching heavier U isotopes in the solid phase. 238U/235U of the dissolved U in these experiments can be fit by Rayleigh fractionation curves with fractionation factors of 1.00002 - 1.00009. In contrast, no resolvable U isotope fractionation was detected in an aragonite experiment at pH ~7.5 or in calcite experiments at either pH. Equilibrium isotope fractionation among dissolved U species is the most likely mechanism driving these isotope effects. Our quantitative model of this process assumes that charged U species are preferentially incorporated into CaCO3 relative to the neutral U species Ca2UO2(CO3)3(aq), which we hypothesize to have a lighter equilibrium U isotope composition than the charged U species. According to this model, the magnitude of U isotope fractionation should scale with the fraction of the neutral U species in the solution, in agreement with our experimental results. These findings suggest that U isotope variations in abiotic CaCO3 reflect changes in aqueous U(VI) speciation, which are in turn a function of carbonate ion chemistry and pH. Hence, the door is opened to the development of a possible 238U/235U proxy for the carbonate ion system. [1] DeCarlo et al., (2015), GCA, 162,151-165. [2] Reeder et a., (2001), GCA, 65, 3491-3503. [3] Weyer et al., (2008) GCA 72, 345-359.

Study of uranium oxidation states in geological material.

PubMed

Pidchenko, I; Salminen-Paatero, S; Rothe, J; Suksi, J

2013-10-01

A wet chemical method to determine uranium (U) oxidation states in geological material has been developed and tested. The problem faced in oxidation state determinations with wet chemical methods is that U redox state may change when extracted from the sample material, thereby leading to erroneous results. In order to quantify and monitor U redox behavior during the acidic extraction in the procedure, an analysis of added isotopic redox tracers, (236)U(VI) and (232)U(IV), and of variations in natural uranium isotope ratio ((234)U/(238)U) of indigenous U(IV) and U(VI) fractions was performed. Two sample materials with varying redox activity, U bearing rock and U-rich clayey lignite sediment, were used for the tests. The Fe(II)/Fe(III) redox-pair of the mineral phases was postulated as a potentially disturbing redox agent. The impact of Fe(III) on U was studied by reducing Fe(III) with ascorbic acid, which was added to the extraction solution. We observed that ascorbic acid protected most of the U from oxidation. The measured (234)U/(238)U ratio in U(IV) and U(VI) fractions in the sediment samples provided a unique tool to quantify U oxidation caused by Fe(III). Annealing (sample heating) to temperatures above 500 °C was supposed to heal ionizing radiation induced defects in the material that can disturb U redox state during extraction. Good agreement between two independent methods was obtained for DL-1a material: an average 38% of U(IV) determined by redox tracer corrected wet chemistry and 45% for XANES. Copyright © 2013 Elsevier Ltd. All rights reserved.

Pu 236 ( n , f ) , Pu 237 ( n , f ) , and Pu 238 ( n , f ) cross sections deduced from ( p , t ) , ( p , d ) , and ( p , p ' ) surrogate reactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hughes, R. O.; Beausang, C. W.; Ross, T. J.

2014-07-01

The Pu 236(n,f), Pu 237(n,f) and Pu 238(n,f) cross sections have been inferred by utilizing the surrogate ratio method. Targets of Pu 239 and U 235 were bombarded with 28.5-MeV protons, and the light ion recoils, as well as fission fragments, were detected using the STARS detector array at the K150 Cyclotron at the Texas A&M cyclotron facility. The (p, tf) reaction on Pu 239 and U 235 targets was used to deduce the σ (Pu 236(n,f))/σ(U 232(n,f)) ratio, and the Pu 236(n,f) cross section was subsequently determined for En=0.5–7.5 MeV. Similarly, the (p,df) reaction on the same two targetsmore » was used to deduce the σ(Pu 237(n,f))/σ(U 233(n,f)) ratio, and the Pu 237(n,f) cross section was extracted in the energy range En=0.5–7 MeV. The Pu 238(n,f) cross section was also deduced by utilizing the (p,p') reaction channel on the same targets. There is good agreement with the recent ENDF/B-VII.1 evaluated cross section data for Pu 238(n,f) in the range En=0.5–10.5 MeV and for Pu 237(n,f) in the range En=0.5–7 MeV; however, the Pu 236(n,f) cross section deduced in the present work is higher than the evaluation between 2 and 7 MeV.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eppich, Gary R.; Williams, Ross W.; Gaffney, Amy M.

Here, age dating of nuclear material can provide insight into source and suspected use in nuclear forensic investigations. We report here a method for the determination of the date of most recent chemical purification for uranium materials using the 235U- 231Pa chronometer. Protactinium is separated from uranium and neptunium matrices using anion exchange resin, followed by sorption of Pa to an SiO 2 medium. The concentration of 231Pa is measured by isotope dilution mass spectrometry using 233Pa spikes prepared from an aliquot of 237Np and calibrated in-house using the rock standard Table Mountain Latite and the uranium isotopic standard U100.more » Combined uncertainties of age dates using this method are 1.5 to 3.5 %, an improvement over alpha spectrometry measurement methods. Model ages of five uranium standard reference materials are presented; all standards have concordant 235U- 231Pa and 234U- 230Th model ages.« less

Action levels for airborne uranium in the workplace: chemical and radiological assessments.

PubMed

Leggett, R W; Meck, R A

2018-06-01

A method is described for deriving two levels of action-an investigation level (IL) and an immediate action level (IAL)-for different forms and mixtures of the natural uranium (U) isotopes 234 U, 235 U, and 238 U in air in the workplace. An IL indicates the need to confirm the validity of moderately elevated measurements of airborne U and adequacy of confinement controls and determine whether work limitations are appropriate. An IAL indicates that safeguards should be put into place immediately, including removal of workers from further exposure until conditions are acceptable. Derivations of ILs and IALs are based on latest radiation protection guidance, information on chemical toxicity of U, and biokinetic models for U. An action level (IL or IAL) is the more restrictive of two derived values, the action level based on U as a chemical hazard and the action level based on U as a radiation hazard.

Polyatomic interferences on high precision uranium isotope ratio measurements by MC-ICP-MS: Applications to environmental sampling for nuclear safeguards

DOE PAGES

Pollington, Anthony D.; Kinman, William S.; Hanson, Susan K.; ...

2015-09-04

Modern mass spectrometry and separation techniques have made measurement of major uranium isotope ratios a routine task; however accurate and precise measurement of the minor uranium isotopes remains a challenge as sample size decreases. One particular challenge is the presence of isobaric interferences and their impact on the accuracy of minor isotope 234U and 236U measurements. Furthermore, we present techniques used for routine U isotopic analysis of environmental nuclear safeguards samples and evaluate polyatomic interferences that negatively impact accuracy as well as methods to mitigate their impacts.

Uranium beam characterization at CIRCE for background and contamination determinations.

PubMed

De Cesare, M; De Cesare, N; D'Onofrio, A; Fifield, L K; Gialanella, L; Terrasi, F

2015-09-01

The Accelerator Mass Spectrometry (AMS) is the most sensitive technique, compared either to the Inductively Coupled Plasma (ICP-MS) or Thermal Ionization (TI-MS) mass spectrometer, for the actinide (e.g. (236)U, (x)Pu isotopes) measurements. They are present in environmental samples at the ultra trace level since atmospheric tests of Nuclear Weapons (NWs) performed in the past, deliberate dumping of nuclear waste, nuclear fuel reprocessing, on a large scale, and operation of Nuclear Power Plants (NPPs), on a small scale, have led to the release of a wide range of radioactive nuclides in the environment. At the Center for Isotopic Research on Cultural and Environmental heritage (CIRCE) in Caserta, Italy, an upgraded actinide AMS system, based on a 3-MV pelletron tandem accelerator, has been developed and routinely operated. At CIRCE a charge state distribution as a function of terminal voltage, the beam emittance, measured in the 20° actinides dedicated beam line, as well as the energy and position validation of the U ions were performed in order to determine the best measurement conditions. A (236)U/(238)U isotopic ratio background level of about 5×10(-12) or 3×10(-13), depending on the Time of Flight-Energy (TOF-E) configurations, as well as the spatial distribution of the (235)U, (238)U interferences ions and a (236)U contamination mass of about 0.5 fg have been determined. Copyright © 2015 Elsevier Ltd. All rights reserved.

Environmental characterization and radio-ecological impacts of non-nuclear industries on the Red Sea coast.

PubMed

El Mamoney, M H; Khater, Ashraf E M

2004-01-01

The Red Sea is a deep semi-enclosed and narrow basin connected to the Indian Ocean by a narrow sill in the south and to the Suez Canal in the north. Oil industries in the Gulf of Suez, phosphate ore mining activities in Safaga-Quseir region and intensified navigation activities are non-nuclear pollution sources that could have serious radiological impacts on the marine environment and the coastal ecosystems of the Red Sea. It is essential to establish the radiological base-line data, which does not exist yet, and to investigate the present radio-ecological impact of the non-nuclear industries to preserve and protect the coastal environment of the Red Sea. Some natural and man-made radionuclides have been measured in shore sediment samples collected from the Egyptian coast of the Red Sea. The specific activities of 226Ra and 210Pb (238U) series, 232Th series, 40K and 137Cs (Bq/kg dry weight) were measured using gamma ray spectrometers based on hyper-pure germanium detectors. The specific activities of 210Po (210Pb) and uranium isotopes (238U, 235U and 234U) (Bq/kg dry weight) were measured using alpha spectrometers based on surface barrier (PIPS) detectors after radiochemical separation. The absorbed radiation dose rates in air (nGy/h) due to natural radionuclides in shore sediment and radium equivalent activity index (Bq/kg) were calculated. The specific activity ratios of 228Ra/226Ra, 210Pb/226Ra, 226Ra/238U and 234U/238U were calculated for evaluation of the geo-chemical behaviour of these radionuclides. The average specific activity of 226Ra (238U) series, 232Th series, 40K and 210Pb were 24.7, 31.4, 427.5 and 25.6 Bq/kg, respectively. The concentration of 137Cs in the sediment samples was less than the lower limit of detection. The Red Sea coast is an arid region with very low rainfall and the sediment is mainly composed of sand. The specific activity of 238U, 235U and 234U were 25.3, 2.9 and 25.0 Bq/kg. The average specific activity ratios of 226Ra/228Ra, 210Pb/226Ra and 234U/238U were 1.67, 1.22 and 1.0, respectively. The relationship between 226Ra/228Ra activity ratio and sample locations along the coastal shoreline indicates the increase of this ratio in the direction of the Shuqeir in the north and Safaga in the south where the oil exploration and phosphate mining activities are located. These activities may contribute a high flux of 226Ra. The concentration and distribution pattern of 226Ra in sediment can be used to trace the radiological impact of the non-nuclear industries on the Red Sea coast.

Reaction paths and host phases of uranium isotopes (235U; 238U), Saanich Inlet

NASA Astrophysics Data System (ADS)

Amini, M.; Holmden, C. E.; Francois, R. H.

2009-12-01

In recent times, Uranium has become increasingly the focus of stable isotope fractionation studies. Variations in 238U/235U have been reported as a result of redox reactions [1,2] from the nuclear field shift effect [3], and a mass-dependent, microbially-mediated, kinetic isotope effect [4]. The 238U/235U variability caused by changes in environmental redox conditions leads to an increase in the 238U/235U ratios of the reduced U species sequestered into marine sediments. This points to U isotope variability as a new tool to study ancient ocean redox changes. However, the process by which reduced sediments become enriched in the heavy isotopes of U is not yet known, and hence the utility of 238U/235U as a redox tracer remains to be demonstrated. In order to further constrain sedimentary U enrichment and related isotope effect, we are investigating U isotopic compositions of water samples and fresh surface sediment grab samples over a range of redox conditions in the seasonally anoxic Saanich Inlet, on the east coast of Vancouver Island. U was sequentially extracted from sediments in order to characterize specific fractions for their isotopic composition. The measurements were carried out by MC-ICPMS using 233U/236U-double spike technique. The data are reported as δ238U relative to NBL 112a with a 238U/235U ratio of 137.88 (2sd). External precision is better than 0.10‰ (2sd). Fifteeen analyses of seawater yielded δ238U of -0.42±0.08‰ (2sd). The results for the water samples indicate a homogenous δ238U value throughout the Saanich Inlet water column that matches the global seawater signature. All of the water samples from above and below average -0.42±0.05‰ (2sd). In contrast, a plankton net sample yielded a distinctly different, (about 0.5‰ lighter) isotope value. Bacterial reduction experiments [4] have also shown isotope enrichment factors of about -0.3‰. In addition, metal isotope fractionation occurs during adsorption with the light isotope being preferentially adsorbed [5]. Whether plankton mediated chemical reduction or scavenging causes this fractionation will be further investigated by leaching experiments on sediment trap samples. By contrast, weak acidic leachates (at pH 6) of suboxic bottom sediments, tend towards higher δ238U values. For oxic sediments, U contents of this fraction were below detection limit. Stronger leaching at pH 3 removed most of the uranium from suboxic and oxic sediments. For oxic sediments, this fraction yields the seawater δ238U signature, while the U released from the suboxic sample is about 0.2‰ heavier. This matches the value for previously reported bulk analyses of suboxic sediments [1] implying that the reduced sedimentary U is released by this treatment,. Major and trace element analyses and XRD patterns will help relating this fraction to a specific mineral or reactive phase. [1] Weyer et al. (2007) GCA 72, 345-399. [2] Stirling et al. (2007) EPSL 264, 208-225. [3] Schauble (2007) GCA 71, 2170-2189. [4] Rademacher et al. (2006) Environ. Sci. Technol. 40,6943-6948. [5] Wasylenki (2009) GCA A1419.

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2013-09-16

.... 234 of October 1, 1999, Delegation of Authority No. 236-3 of August 28, 2000 (and, as appropriate.... Department of State (telephone: 202- 632-6467). The mailing address is U.S. Department of State, SA-5, L/PD...

234U/238U evidence for local recharge and patterns of groundwater flow in the vicinity of Yucca Mountain, Nevada, USA

USGS Publications Warehouse

Paces, J.B.; Ludwig, K. R.; Peterman, Z.E.; Neymark, L.A.

2002-01-01

Uranium concentrations and 234U/238U ratios in saturated-zone and perched ground water were used to investigate hydrologic flow and downgradient dilution and dispersion in the vicinity of Yucca Mountain, a potential high-level radioactive waste disposal site. The U data were obtained by thermal ionization mass spectrometry on more than 280 samples from the Death Valley regional flow system. Large variations in both U concentrations (commonly 0.6-10 ??g 1-1) and 234U/238U activity ratios (commonly 1.5-6) are present on both local and regional scales; however, ground water with 234U/238U activity ratios from 7 up to 8.06 is restricted largely to samples from Yucca Mountain. Data from ground water in the Tertiary volcanic and Quaternary alluvial aquifers at and adjacent to Yucca Mountain plot in 3 distinct fields of reciprocal U concentration versus 234U/238U activity ratio correlated to different geographic areas. Ground water to the west of Yucca Mountain has large U concentrations and moderate 234U/238U whereas ground water to the east in the Fortymile flow system has similar 234U/238U, but distinctly smaller U concentrations. Ground water beneath the central part of Yucca Mountain has intermediate U concentrations but distinctive 234U/238U activity ratios of about 7-8. Perched water from the lower part of the unsaturated zone at Yucca Mountain has similarly large values of 234U/238U. These U data imply that the Tertiary volcanic aquifer beneath the central part of Yucca Mountain is isolated from north-south regional flow. The similarity of 234U/238U in both saturated- and unsaturated-zone ground water at Yucca Mountain further indicates that saturated-zone ground water beneath Yucca Mountain is dominated by local recharge rather than regional flow. The distinctive 234U/238U signatures also provide a natural tracer of downgradient flow. Elevated 234U/238U in ground water from two water-supply wells east of Yucca Mountain are interpreted as the result of induced flow from 40 a of ground-water withdrawal. Elevated 234U/238U in a borehole south of Yucca Mountain is interpreted as evidence that natural downgradient flow is more likely to follow southerly paths in the structurally anisotropic Tertiary volcanic aquifer where it becomes diluted by regional flow in the Fortymile system.

NBL CRM 112-A: A new certified isotopic composition

NASA Astrophysics Data System (ADS)

Thomas, R. B.; Essex, R. M.; Mason, P.

2007-12-01

NBL CRM 112-A Uranium Metal Assay Standard is commonly used as a natural uranium isotopic reference material within the earth science mass spectrometry community. The metal is from the same parent material as NBS SRM 960, the uranyl nitrate solution, CRM 145, and the high-purity uranyl nitrate solution CRM 145-B. Because CRM 112-A has not yet been certified for isotopic composition, it has been assumed that this material has a natural 235U/238U (0.0072527), and the δ234U has been determined by measurement (e.g. -37.1‰; Cheng et al., 2000). These values have been widely used to calibrate the concentration of spikes and standards, and to correct measurements for instrument or mass bias. New, preliminary, isotopic measurements on CRM 145 and CRM 112-A performed at New Brunswick Laboratory suggest that these reference materials have a slightly lower 235U/238U and δ234U than have been commonly used. If this is the case, then data using the accepted values may be slightly biased. The significance of this bias will depend on the uncertainty of the measurement, how the CRM 112-A data is used to correct measurement data, the cited values that were used to correct the data, and the final certified values of the CRM. This fall, New Brunswick Laboratory is certifying the isotopic composition of the CRM 112-A metal using high precision thermal ionization mass spectrometry techniques. Upon completion of certification, the new CRM 112- A standard with certified isotopic ratios will provide the earth science community with a well characterized and traceable reference for calibrating and correcting their mass spectrometry measurement systems.

Simultaneous determination of the quantity and isotopic ratios of uranium in individual micro-particles by isotope dilution thermal ionization mass spectrometry (ID-TIMS).

PubMed

Park, Jong-Ho; Choi, Eun-Ju

2016-11-01

A method to determine the quantity and isotopic ratios of uranium in individual micro-particles simultaneously by isotope dilution thermal ionization mass spectrometry (ID-TIMS) has been developed. This method consists of sequential sample and spike loading, ID-TIMS for isotopic measurement, and application of a series of mathematical procedures to remove the contribution of uranium in the spike. The homogeneity of evaporation and ionization of uranium content was confirmed by the consistent ratio of n((233)U)/n((238)U) determined by TIMS measurements. Verification of the method was performed using U030 solution droplets and U030 particles. Good agreements of resulting uranium quantity, n((235)U)/n((238)U), and n((236)U)/n((238)U) with the estimated or certified values showed the validity of this newly developed method for particle analysis when simultaneous determination of the quantity and isotopic ratios of uranium is required. Copyright © 2016 Elsevier B.V. All rights reserved.

Radiative neutron capture cross section from 236U

NASA Astrophysics Data System (ADS)

Baramsai, B.; Jandel, M.; Bredeweg, T. A.; Bond, E. M.; Roman, A. R.; Rusev, G.; Walker, C. L.; Couture, A.; Mosby, S.; O'Donnell, J. M.; Ullmann, J. L.; Kawano, T.

2017-08-01

The 236U(n ,γ ) reaction cross section has been measured for the incident neutron energy range from 10 eV to 800 keV by using the Detector for Advanced Neutron Capture Experiments (DANCE) γ -ray calorimeter at the Los Alamos Neutron Science Center. The cross section was determined with the ratio method, which is a technique that uses the 235U(n ,f ) reaction as a reference. The results of the experiment are reported in the resolved and unresolved resonance energy regions. Individual neutron resonance parameters were obtained below 1 keV incident energy by using the R -matrix code sammy. The cross section in the unresolved resonance region is determined with improved experimental uncertainty. It agrees with both ENDF/B-VII.1 and JEFF-3.2 nuclear data libraries. The results above 10 keV agree better with the JEFF-3.2 library.

78 FR 27470 - Culturally Significant Objects Imported for Exhibition Determinations: “Shaping Power: Luba...

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2013-05-10

....), Delegation of Authority No. 234 of October 1, 1999, and Delegation of Authority No. 236-3 of August 28, 2000... mailing address is U.S. Department of State, SA-5, L/PD, Fifth Floor (Suite 5H03), Washington, DC 20522...

Natural and man-made radioactivity in soils and plants around the research reactor of Inshass.

PubMed

Higgy, R H; Pimpl, M

1998-12-01

The specific radioactivities of the U-series, 232Th, 137Cs and 40K were measured in soil samples around the Inshass reactor in Cairo, using a gamma-ray spectrometer with a HpGe detector. The alpha activity of 238U, 234U and 235U was measured in the same soil samples by surface barrier detectors after radiochemical separation and the obtained results were compared with the specific activities determined by gamma-measurements. The alpha-activity of 238Pu, 239+240Pu, 241Am, 242Cm and 244Cm was measured after radiochemical separation by surface barrier detectors for both soil and plant samples. Then beta-activity of 241Pu was measured using liquid scintillation spectrometry.

Student Flow Simulation for the Consolidated Navy Electronic Warfare School.

DTIC Science & Technology

1982-07-01

WLR-1 201 202 203 204 205 USN 6YO AN/SLQ-32 206 207 208 209 210 USN 6YO AN/SLQ-17 211 212 213 214 215 JSN 6YO AN/WLR-8 216 217 218 219 220 uSN 4YO AN...WLR-I 221 222 2?3 224 225 JSN 4YO AN/SLQ-32 226 227 228 229 230 UrN 4YO AN/SLQ-17 231 232 233 234 235 USN 4YO AN/WLR-8 236 237 238 2 9 240 JSN 3X6 AN...USN 6YO 1 ASSIGN node ASS3 (after CDP 3C) USN 4YO 2 GOON node N3 USN 3X6 3 GOON node N3 USN Late Conv. 4 GOON node N3 Fit. Returnee 6 Introduced in the

(234)U/(238)U signatures associated with uranium ore bodies: part 1 Ranger 3.

PubMed

Lowson, Richard T; McIntyre, Mark G

2013-04-01

The Ranger 3 ore body is an early Proterozoic U ore body in the Alligator Rivers U province, Northern Territory, Australia. It has surface expression with a redox front located between 30 and 50 m below the surface. The ground water U concentration and (234)U/(238)U AR signature in the top 10 m of the weathered zone are reported for 357 samples collected over 4 wet seasons, at 5 depths, along a transect in-line with the hydraulic gradient and along the centre line of the ore body and its associated dispersion halo. The results show that the weathered zone displays a general U isotope feature for this type of ore body with the (234)U/(238)U AR for the ground water and amorphous phase of the solid matrix being less than 1. The ground water (234)U/(238)U AR is independent of the annual monsoonal climate and depth within the range surface to 10 m. In the vicinity of the U ore body the ground water (234)U/(238)U AR is 0.75 and is very similar to the (234)U/(238)U AR of the amorphous phase of the solid (0.76). The (234)U/(238)U ARs of the amorphous phase and ground water rise and separate to values of 0.88 and 1.02 at the end of the transect. The rise and separation in (234)U/(238)U AR are interpreted as evidence that the source of the U in the ground water is from the water-soluble sub-phase of the amorphous phase and that the ground water flow is too fast to allow the processes occurring across the solid-water interface to reach chemical equilibrium. The data set is a robust characterisation of the coarse and fine detail of the (234)U/(238)U AR signature in the weathered zone of U ore bodies. Copyright © 2012 Elsevier Ltd. All rights reserved.

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2013-05-28

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78 FR 56767 - Culturally Significant Objects Imported for Exhibition Determinations: “Cercle et Carré and the...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-09-13

... of Authority No. 234 of October 1, 1999, Delegation of Authority No. 236-3 of August 28, 2000, and... mailing address is U.S. Department of State, SA-5, L/PD, Fifth Floor (Suite 5H03), Washington, DC 20522...

Field Application of 238U/235U Measurements To Detect Reoxidation and Mobilization of U(IV).

PubMed

Jemison, Noah E; Shiel, Alyssa E; Johnson, Thomas M; Lundstrom, Craig C; Long, Philip E; Williams, Kenneth H

2018-03-20

Biostimulation to induce reduction of soluble U(VI) to relatively immobile U(IV) is an effective strategy for decreasing aqueous U(VI) concentrations in contaminated groundwater systems. If oxidation of U(IV) occurs following the biostimulation phase, U(VI) concentrations increase, challenging the long-term effectiveness of this technique. However, detecting U(IV) oxidation through dissolved U concentrations alone can prove difficult in locations with few groundwater wells to track the addition of U to a mass of groundwater. We propose the 238 U/ 235 U ratio of aqueous U as an independent, reliable tracer of U(IV) remobilization via oxidation or mobilization of colloids. Reduction of U(VI) produces 238 U-enriched U(IV), whereas remobilization of solid U(IV) should not induce isotopic fractionation. The incorporation of remobilized U(IV) with a high 238 U/ 235 U ratio into the aqueous U(VI) pool produces an increase in 238 U/ 235 U of aqueous U(VI). During several injections of nitrate to induce U(IV) oxidation, 238 U/ 235 U consistently increased, suggesting 238 U/ 235 U is broadly applicable for detecting mobilization of U(IV).

(234)U/(238)U signatures associated with uranium ore bodies: part 2 Manyingee.

PubMed

Lowson, Richard T; McIntyre, Mark G

2013-04-01

The Manyingee ore body is a roll-front U ore body located at depth in the Cretaceous sandstone sediments of a Proterozoic palaeo valley. It is located in a confined aquifer. The aquifer is recharged 4 km upstream by the Ashburton River. Groundwater samples were collected at and up to 4.7 km downstream of the ore body. The ground water (234)U/(238)U activity ratios (AR) were elevated to 1.86 in the vicinity of the ore body and then declined to 1.06 over the 4.7 km transect. The elevated (234)U/(238)U ARs are attributed to selective leaching of (234)U sites by oxidising waters, with α recoil as a necessary precursor to produce activated (234)U sites. Direct ejection into another phase following α recoil is considered to be a minor contributor to (234)U -(238)U disequilibrium in this environment. The profile is considered to be typical of the (234)U/(238)U AR profile at and down gradient of the redox front of a U ore body. Crown Copyright © 2012. Published by Elsevier Ltd. All rights reserved.

(234)U/(238)U signatures associated with uranium ore bodies: part 3 Koongarra.

PubMed

Lowson, Richard T

2013-04-01

The Koongarra ore body is an early Proterozoic U ore body in the Alligator Rivers U province, Northern Territory, Australia. It has surface expression with a redox front located ∼30 m below the surface. The (234)U/(238)U activity ratios (AR) for the ground water and the amorphous phase of the solid have been analysed for the ore zone and dispersion halo as a function of depth. The results display a (234)U/(238)U AR signature with depth which may be common to all U ore bodies. The (234)U/(238)U AR is depressed below secular equilibrium in the weathered material above the redox front; rises significantly above secular equilibrium in the vicinity of the redox front; and is followed by a gradual decrease with depth below the redox front. The amplitude of the profile is a function of local conditions. A model is proposed for the signature in which oxidising waters preferentially leach the (234)U sites at the redox front due to preconditioning of the (234)U sites by α recoil during the decay of (23)(8)U to (23)(4)U. Mass balance requires the solid material left behind the redox front to have a (234)U/(238)U AR reduced below 1. Local second order effects may be superimposed on the signature. The signature may have application to calibrating scenarios for nuclear waste repositories, assisting in understanding historical climates, economic evaluation of U ore bodies and U exploration. Copyright © 2012 Elsevier Ltd. All rights reserved.

Uranium-234 anomalies in authigenic uranium as a new oxygenation proxy in the Southern Ocean

NASA Astrophysics Data System (ADS)

Hayes, C. T.; Severmann, S.; Anderson, A.

2016-12-01

Authigenic uranium (aU) is a sensitive indicator for suboxic conditions in marine pore waters that has been used to reconstruct past oxygenation conditions or organic matter export. aU suffers, however, from possible post-depositional remobilization or "burn-down" when the depth of the oxygenation front in the sediments undergoes rapid changes. In terms of isotope composition, the 234U/238U activity ratio, or δ234U in per mil notation, of authigenic U will reflect the isotope ratio in seawater (147‰) which has been relatively stable (within 15‰) for at least one ocean residence time of U (about 400 kyr). The δ234U ratio in bulk marine sediments should then reflect the mixture of the seawater ratio and the ratio of detrital U (0‰ or somewhat negative). In careful analysis of bulk δ234U over a peak in aU from Southern Ocean core ODP-1094, I found ratios higher than seawater (up to 250‰), not explainable by isotope mixing of known sources. I propose a new diagenetic effect in which a partial reoxidation of an aU emplacement can cause 234U that has been alpha-recoiled from in-situ 238U decay to diffuse into the aU emplacement. This means that with aU records that may be slightly altered by reoxidation, careful tracking of δ234U will allow proper identification of the depth/size of the original aU emplacement. Therefore, δ234U of aU is a more robust redox tracer than elemental proxies alone. In this presentation, I will recount the evidence for this assertion and lay out future research targets.

Seawater 234U/238U recorded by modern and fossil corals

NASA Astrophysics Data System (ADS)

Chutcharavan, Peter M.; Dutton, Andrea; Ellwood, Michael J.

2018-03-01

U-series dating of corals is a crucial tool for generating absolute chronologies of Late Quaternary sea-level change and calibrating the radiocarbon timescale. Unfortunately, coralline aragonite is susceptible to post-depositional alteration of its primary geochemistry. One screening technique used to identify unaltered corals relies on the back-calculation of initial 234U/238U activity (δ234Ui) at the time of coral growth and implicitly assumes that seawater δ234U has remained constant during the Late Quaternary. Here, we test this assumption using the most comprehensive compilation to date of coral U-series measurements. Unlike previous compilations, this study normalizes U-series measurements to the same decay constants and corrects for offsets in interlaboratory calibrations, thus reducing systematic biases between reported δ234U values. Using this approach, we reassess (a) the value of modern seawater δ234U, and (b) the evolution of seawater δ234U over the last deglaciation. Modern coral δ234U values (145.0 ± 1.5‰) agree with previous measurements of seawater and modern corals only once the data have been normalized. Additionally, fossil corals in the surface ocean display δ234Ui values that are ∼5-7‰ lower during the last glacial maximum regardless of site, taxon, or diagenetic setting. We conclude that physical weathering of U-bearing minerals exposed during ice sheet retreat drives the increase in δ234U observed in the oceans, a mechanism that is consistent with the interpretation of the seawater Pb-isotope signal over the same timescale.

Extreme fractionation of 234U 238U and 230Th 234U in spring waters, sediments, and fossils at the Pomme de Terre Valley, southwestern Missouri

USGS Publications Warehouse

Szabo, B. J.

1982-01-01

Isotopic fractionation as great as 1600% exists between 234U and 238U in spring waters, sediments, and fossils in the Pomme de Terre Valley, southwestern Missouri. The activity ratios of 234U 238U in five springs range from 7.2 to 16 in water which has been discharged for at least the past 30,000 years. The anomalies in 234U 238U ratio in deep water have potential usefulness in hydrologic investigations in southern Missouri. Clayey units overlying the spring bog sediments of Trolinger Spring are enriched in 230Th relative to their parent 234U by as much as 720%. The results indicate that both preferential displacement via alpha recoil ejection and the preferential emplacement via recoiling and physical entrapment are significant processes that are occurring in the geologic environment. ?? 1982.

Fractionation of 238U/235U by reduction during low temperature uranium mineralisation processes

NASA Astrophysics Data System (ADS)

Murphy, Melissa J.; Stirling, Claudine H.; Kaltenbach, Angela; Turner, Simon P.; Schaefer, Bruce F.

2014-02-01

Investigations of ‘stable’ uranium isotope fractionation during low temperature, redox transformations may provide new insights into the usefulness of the 238U/235U isotope system as a tracer of palaeoredox processes. Sandstone-hosted uranium deposits accumulate at an oxidation/reduction interface within an aquifer from the low temperature reduction of soluble U(VI) complexes in groundwaters, forming insoluble U(IV) minerals. This setting provides an ideal environment in which to investigate the effects of redox transformations on 238U/235U fractionation. Here we present the first coupled measurements of 238U/235U isotopic compositions and U concentrations for groundwaters and mineralised sediment samples from the same redox system in the vicinity of the high-grade Pepegoona sandstone-hosted uranium deposit, Australia. The mineralised sediment samples display extremely variable 238U/235U ratios (herein expressed as δUCRM145238, the per-mil deviation from the international NBL standard CRM145). The majority of mineralised sediment samples have δUCRM145238 values between -1.30±0.05 and 0.55±0.12‰, spanning a ca. 2‰ range. However, one sample has an unusually light isotopic composition of -4.13±0.05‰, which suggests a total range of U isotopic variability of up to ca. 5‰, the largest variation found thus far in a single natural redox system. The 238U/235U isotopic signature of the mineralised sediments becomes progressively heavier (enriched in 238U) along the groundwater flow path. The groundwaters show a greater than 2‰ variation in their 238U/235U ratios, ranging from δUCRM145238 values of -2.39±0.07 to -0.71±0.05‰. The majority of the groundwater data exhibit a clear systematic relationship between 238U/235U isotopic composition and U concentration; samples with the lowest U concentrations have the lowest 238U/235U ratios. The preferential incorporation of 238U during reduction of U(VI) to U(IV) and precipitation of uranium minerals leaves the groundwaters enriched in 235U, resulting in a progressive shift in 238U/235U towards lighter values in the aqueous phase as U is removed. These data can be modelled by a closed system Rayleigh fractionation model, with a fractionation factor (α, representing the 238U/235U composition of the groundwater relative to the solid uranium minerals) ranging from ∼0.9996 to 1.0000, with the majority of datapoints ranging from α values of 0.9998 to 0.9999. The sense and magnitude of the results of this study imply that 238U/235U fractionation is likely to be controlled by volume-dependent nuclear field shift effects during the reduction of U(VI) to U(IV) during mineralisation processes. These findings support the use of the 238U/235U isotopic system as a tracer to constrain the nature and timing of palaeoredox conditions.

Empirical calibration of uranium releases in the terrestrial environment of nuclear fuel cycle facilities.

PubMed

Pourcelot, Laurent; Masson, Olivier; Saey, Lionel; Conil, Sébastien; Boulet, Béatrice; Cariou, Nicolas

2017-05-01

In the present paper the activity of uranium isotopes measured in plants and aerosols taken downwind of the releases of three nuclear fuel settlements was compared between them and with the activity measured at remote sites. An enhancement of 238 U activity as well as 235 U/ 238 U anomalies and 236 U are noticeable in wheat, grass, tree leaves and aerosols taken at the edge of nuclear fuel settlements, which show the influence of uranium chronic releases. Further plants taken at the edge of the studied sites and a few published data acquired in the same experimental conditions show that the 238 U activity in plants is influenced by the intensity of the U atmospheric releases. Assuming that 238 U in plant is proportional to the intensity of the releases, we proposed empirical relationships which allow to characterize the chronic releases on the ground. Other sources of U contamination in plants such as accidental releases and "delayed source" of uranium in soil are also discussed in the light of uranium isotopes signatures. Copyright © 2017 Elsevier Ltd. All rights reserved.

Influence of glacial meltwater on global seawater δ234U

NASA Astrophysics Data System (ADS)

Arendt, Carli A.; Aciego, Sarah M.; Sims, Kenneth W. W.; Das, Sarah B.; Sheik, Cody; Stevenson, Emily I.

2018-03-01

We present the first published uranium-series measurements from modern Greenland Ice Sheet (GrIS) runoff and proximal seawater, and investigate the influence of glacial melt on global seawater δ234U over glacial-interglacial (g-ig) timescales. Climate reconstructions based on closed-system uranium-thorium (U/Th) dating of fossil corals assume U chemistry of seawater has remained stable over time despite notable fluctuations in major elemental compositions, concentrations, and isotopic compositions of global seawater on g-ig timescales. Deglacial processes increase weathering, significantly increasing U-series concentrations and changing the δ234U of glacial meltwater. Analyses of glacial discharge from GrIS outlet glaciers indicate that meltwater runoff has elevated U concentrations and differing 222Rn concentrations and δ234U compositions, likely due to variations in subglacial residence time. Locations with high δ234U have the potential to increase proximal seawater δ234U. To better understand the impact of bulk glacial melt on global seawater δ234U over time, we use a simple box model to scale these processes to periods of extreme deglaciation. We account for U fluxes from the GrIS, Antarctica, and large Northern Hemisphere Continental Ice Sheets, and assess sensitivity by varying melt volumes, duration and U flux input rates based on modern subglacial water U concentrations and compositions. All scenarios support the hypothesis that global seawater δ234U has varied by more than 1‰ through time as a function of predictable perturbations in continental U fluxes during g-ig periods.

The Application of 238U/235U as a Redox-Proxy for Past Ocean Chemistry

NASA Astrophysics Data System (ADS)

Andersen, M. B.; Westermann, S.; Bahniuk, A.; Vasconcelos, C.; McKenzie, J. A.; Föllmi, K. B.; Vance, D.

2014-12-01

The recent discovery of significant variation in 238U/235U caused by redox change at the surface Earth has led to its use to extract information on the oxygenation state of ancient oceans from marine sediments [e.g. 1]. Recent studies have focused on improving the understanding of the 238U/235U signature in modern marine carbonates [2] and black shales [3] to improve the robustness of this tracer. To further advance its use we have focused on improving our understanding of 238U/235U systematics in modern dolomite, another commonly occurring rock-type in the geological record, before turning to 238U/235U signatures in ancient sediments. The measured dolomite samples, precipitated in modern environments of coastal hypersaline lagoons in Brazil, all exhibit 238U/235U values that deviate from the seawater composition [3]. Observed values are both lighter (ca. 130 ppm; as also observed in dolomite from tidal-ponds on Bahamas [2]) and heavier (50-180 ppm). These distinct 238U/235U values for different dolomite-precipitates likely attest to the particular formation style, as well as early diagenetic processes. We use such modern settings to discuss the utility of 238U/235U in ancient sediments, the singularity of any observed 238U/235U signal, its relation to global ocean chemistry and potential diagenetic overprinting. These constraints are then used to evaluate a well-preserved marine carbonate section [4] and published black shale 238U/235U data [1], both deposited during the Oceanic Anoxic Event 2 (93 Ma). We discuss the capabilities of both the carbonate and black shale section for retaining information on the 238U/235U composition in the ocean during OAE 2. [1] Montoya-Pino et al. (2010) Geology, 38, 315-318 [2] Romaniello et al. (2013) 362, 305-316 [3] Andersen et al. (2014) EPSL, 400, 184-194 [4] Westermann et al. (2010) Cret. Res., 31, 500-514

Migration behavior of naturally occurring radionuclides at the Nopal I uranium deposit, Chihuahua, Mexico

NASA Astrophysics Data System (ADS)

Prikryl, James D.; Pickett, David A.; Murphy, William M.; Pearcy, English C.

1997-04-01

Oxidation of pyrite at the Nopal I uranium deposit, Peña Blanca district, Chihuahua, Mexico has resulted in the formation of Fe-oxides/hydroxides. Anomalous U concentrations (i.e. several hundred to several thousand ppm) measured in goethite, hematite, and amorphous Fe-oxyhydroxides in a major fracture that crosscuts the deposit and the absence of U minerals in the fracture suggest that U was retained during secondary mineral growth or sorbed on mineral surfaces. Mobilization and transport of U away from the deposit is suggested by decreasing U concentrations in fracture-infilling materials and in goethite and hematite with distance from the deposit. Greater than unity {234U}/{238U} activity ratios measured in fracture-infilling materials indicate relatively recent ( < 1 Ma) U uptake from fluids that carried excess 234U. Systematic decreases in {234U}/{238U} activity ratios of fracture materials with distance from the deposit suggest a multistage mobilization process, such as remobilization of U from 234U-enriched infill minerals or differential or diminished transport of U-bearing solutions containing excess 234U.

Seasonal variations of natural radionuclides, minor and trace elements in lake sediments and water in a lignite mining area of North-Western Greece.

PubMed

Noli, Fotini; Tsamos, Panagiotis

2018-05-01

The radiological and chemical pollution of a cluster of four lakes in a lignite mining area of North-Western Greece was investigated using a variety of analytical techniques. Alpha spectrometry was applied to measure the activity concentrations of the uranium radioisotopes (U-234, U-235, and U-238) in waters. The mass activities of U-238, Th-232, and K-40 in sediments were measured by high-resolution gamma spectrometry. Furthermore, the determination of the minor and trace elements was carried out by instrumental neutron activation analysis (INAA) in both water and sediments samples, respectively. Pollution levels were also evaluated by calculating enrichment factors (EFs), contamination factors (CFs) and pollution load index (PLI). The data were discussed taking into account several parameters such as the distance from the pollution source, temperature, and location and showed that the environmental impact in this region could not be considered as negligible. The deviation of the isotopic ratio of U-234/U-238 from the equilibrium value indicated waters with intensive dissolution of uranium. The activity values in both waters and sediments found to be low in cool periods and increased in warm periods. Moreover, the concentrations of the elements U, Zn, and Fe were raised in water samples indicating possible pollution as well as the CFs and PLI denoted accumulation in the sediments and moderate to severe contamination for Zn and Cr in some cases.

Dissolution behaviour of 238U, 234U and 230Th deposited on filters from personal dosemeters.

PubMed

Becková, Vera; Malátová, Irena

2008-01-01

Kinetics of dissolution of (238)U, (234)U and (230)Th dust deposited on filters from personal alpha dosemeters was studied by means of a 26-d in vitro dissolution test with a serum ultrafiltrate simulant. Dosemeters had been used by miners at the uranium mine 'Dolní Rozínka' at Rozná, Czech Republic. The sampling flow-rate as declared by the producer is 4 l h(-1) and the sampling period is typically 1 month. Studied filters contained 125 +/- 6 mBq (238)U in equilibrium with (234)U and (230)Th; no (232)Th series nuclides were found. Half-time of rapid dissolution of 1.4 d for (238)U and (234)U and slow dissolution half-times of 173 and 116 d were found for (238)U and (234)U, respectively. No detectable dissolution of (230)Th was found.

31 CFR 540.315 - Uranium-235 (U235).

Code of Federal Regulations, 2013 CFR

2013-07-01

... 31 Money and Finance:Treasury 3 2013-07-01 2013-07-01 false Uranium-235 (U235). 540.315 Section... FOREIGN ASSETS CONTROL, DEPARTMENT OF THE TREASURY HIGHLY ENRICHED URANIUM (HEU) AGREEMENT ASSETS CONTROL REGULATIONS General Definitions § 540.315 Uranium-235 (U235). The term uranium-235 or U235 means the fissile...

31 CFR 540.315 - Uranium-235 (U235).

Code of Federal Regulations, 2012 CFR

2012-07-01

... 31 Money and Finance:Treasury 3 2012-07-01 2012-07-01 false Uranium-235 (U235). 540.315 Section... FOREIGN ASSETS CONTROL, DEPARTMENT OF THE TREASURY HIGHLY ENRICHED URANIUM (HEU) AGREEMENT ASSETS CONTROL REGULATIONS General Definitions § 540.315 Uranium-235 (U235). The term uranium-235 or U235 means the fissile...

31 CFR 540.315 - Uranium-235 (U235).

Code of Federal Regulations, 2014 CFR

2014-07-01

... 31 Money and Finance:Treasury 3 2014-07-01 2014-07-01 false Uranium-235 (U235). 540.315 Section... FOREIGN ASSETS CONTROL, DEPARTMENT OF THE TREASURY HIGHLY ENRICHED URANIUM (HEU) AGREEMENT ASSETS CONTROL REGULATIONS General Definitions § 540.315 Uranium-235 (U235). The term uranium-235 or U235 means the fissile...

31 CFR 540.315 - Uranium-235 (U235).

Code of Federal Regulations, 2011 CFR

2011-07-01

... 31 Money and Finance:Treasury 3 2011-07-01 2011-07-01 false Uranium-235 (U235). 540.315 Section... FOREIGN ASSETS CONTROL, DEPARTMENT OF THE TREASURY HIGHLY ENRICHED URANIUM (HEU) AGREEMENT ASSETS CONTROL REGULATIONS General Definitions § 540.315 Uranium-235 (U235). The term uranium-235 or U235 means the fissile...

31 CFR 540.315 - Uranium-235 (U235).

Code of Federal Regulations, 2010 CFR

2010-07-01

... 31 Money and Finance: Treasury 3 2010-07-01 2010-07-01 false Uranium-235 (U235). 540.315 Section... FOREIGN ASSETS CONTROL, DEPARTMENT OF THE TREASURY HIGHLY ENRICHED URANIUM (HEU) AGREEMENT ASSETS CONTROL REGULATIONS General Definitions § 540.315 Uranium-235 (U235). The term uranium-235 or U235 means the fissile...

Development and application of mass spectrometric techniques for ultra-trace determination of 236U in environmental samples-A review.

PubMed

Bu, Wenting; Zheng, Jian; Ketterer, Michael E; Hu, Sheng; Uchida, Shigeo; Wang, Xiaolin

2017-12-01

Measurements of the long-lived radionuclide 236 U are an important endeavor, not only in nuclear safeguards work, but also in terms of using this emerging nuclide as a tracer in chemical oceanography, hydrology, and actinide sourcing. Depending on the properties of a sample and its neutron irradiation history, 236 U/ 238 U ratios from different sources vary significantly. Therefore, this ratio can be treated as an important fingerprint for radioactive source identification, and in particular, affords a definitive means of discriminating between naturally occurring U and specific types of anthropogenic U. The development of mass spectrometric techniques makes it possible to determine ultra-trace levels of 236 U in environmental samples. In this paper, we review the current status of mass spectrometric approaches for determination of 236 U in environmental samples. Various sample preparation methods are summarized and compared. The mass spectrometric techniques emphasized herein are thermal ionization mass spectrometry (TIMS), inductively coupled plasma mass spectrometry (ICP-MS) and accelerator mass spectrometry (AMS). The strategies or principles used by each technique for the analysis of 236 U are described. The performances of these techniques in terms of abundance sensitivity and detection limit are discussed in detail. To date, AMS exhibits the best capability for ultra-trace determinations of 236 U. The levels and behaviors of 236 U in various environmental media are summarized and discussed as well. Results suggest that 236 U has an important, emerging role as a tracer for geochemical studies. Copyright © 2017 Elsevier B.V. All rights reserved.

A search for isotopic anomalies in uranium. [in chondritic meteorites and terrestrial basalt

NASA Technical Reports Server (NTRS)

Chen, J. H.; Wasserburg, G. J.

1980-01-01

The U-238/U-235 ratios for nine bulk chondritic meteorites and a terrestrial basalt were measured. The total range in U-238/U-235 determined for both total meteorites and for acid leaches was from 137.2 terrestrial U. The typical errors in a single determination are plus or minus 6 per thousand (2 sigma m) for a 2 ng U sample from a chondrite. Taking the extreme values of delta U-235 for each measurement the maximum amount of excess U-235 that can be allowed to be present ranges from 200 million to 2 billion atoms per gram of bulk meteorite. These results do not support the claims of variations in U-238/U-235 at the percentage levels or number of excess U-235 atoms in some of the same meteorites as reported by several other previous workers.

Uranium-234 anomalies in corals older than 150,000 years

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bard, E.; Fairbanks, R.G.; Zindler, A.

1991-08-01

The authors present new precise U-Th ages of well-preserved coral specimens collected from the island of Barbados, West Indies, and the atoll of Mururoa, French Polynesia. Their new data confirm the ages attributed to oxygen isotope stage 7 in the framework of the Milankovitch theory. By using thermal ionization mass spectrometry (TIMS), it is also possible to quantify precisely the [sup 234]U/[sup 238]U ratios in corals. Samples older than 150 kyr B.P. are shown to be characterized by significant excesses of [sup 234]U relative to the uranium isotopic composition expected if the corals grew in present-day sea water. Assuming thatmore » the [sup 230]Th-ingrowth ages are accurate, these anomalies translate into high initial [sup 234]U/[sup 238]U ratios: about 1.2 at 200 kyr and up to 1.5 at about 450 kyr B.P. They propose that the anomalies result from both diagenetic addition and replacement of U and possibly from global changes in the [sup 234]U/[sup 238]U composition of the sea water through time. The [sup 234]U anomalies cast doubt on the accuracy of the classical [sup 230]Th-ingrowth dating method in old corals, and in particular for the use of measured [sup 234]U/[sup 238]U ratios alone to date corals older than 150 kyr.« less

Excess of (236)U in the northwest Mediterranean Sea.

PubMed

Chamizo, E; López-Lora, M; Bressac, M; Levy, I; Pham, M K

2016-09-15

In this work, we present first (236)U results in the northwestern Mediterranean. (236)U is studied in a seawater column sampled at DYFAMED (Dynamics of Atmospheric Fluxes in the Mediterranean Sea) station (Ligurian Sea, 43°25'N, 07°52'E). The obtained (236)U/(238)U atom ratios in the dissolved phase, ranging from about 2×10(-9) at 100m depth to about 1.5×10(-9) at 2350m depth, indicate that anthropogenic (236)U dominates the whole seawater column. The corresponding deep-water column inventory (12.6ng/m(2) or 32.1×10(12) atoms/m(2)) exceeds by a factor of 2.5 the expected one for global fallout at similar latitudes (5ng/m(2) or 13×10(12) atoms/m(2)), evidencing the influence of local or regional (236)U sources in the western Mediterranean basin. On the other hand, the input of (236)U associated to Saharan dust outbreaks is evaluated. An additional (236)U annual deposition of about 0.2pg/m(2) based on the study of atmospheric particles collected in Monaco during different Saharan dust intrusions is estimated. The obtained results in the corresponding suspended solids collected at DYFAMED station indicate that about 64% of that (236)U stays in solution in seawater. Overall, this source accounts for about 0.1% of the (236)U inventory excess observed at DYFAMED station. The influence of the so-called Chernobyl fallout and the radioactive effluents produced by the different nuclear installations allocated to the Mediterranean basin, might explain the inventory gap, however, further studies are necessary to come to a conclusion about its origin. Copyright © 2016 Elsevier B.V. All rights reserved.

Vertical distribution of 236U in the North Pacific Ocean.

PubMed

Eigl, R; Steier, P; Sakata, K; Sakaguchi, A

2017-04-01

The first extensive study on 236 U in the North Pacific Ocean has been conducted. The vertical distribution of 236 U/ 238 U isotopic ratios and the 236 U concentrations were analysed on seven depth profiles, and large variations with depth were found. The range of 236 U/ 238 U isotopic ratios was from (0.09 ± 0.03) × 10 -10 to (14.1 ± 2.2) × 10 -10 , which corresponds to 236 U concentrations of (0.69 ± 0.24) × 10 5 atoms/kg and (119 ± 21) × 10 5 atoms/kg, respectively. The variations in 236 U concentrations could mainly be attributed to the different water masses in the North Pacific Ocean and their formation processes. Uranium-236 inventories on the water column of each sampling station were calculated and varied between (3.89 ± 0.08) × 10 12 atoms/m 2 and (7.03 ± 0.50) × 10 12 atoms/m 2 , which is lower than in former studies on comparable latitudes in the North Atlantic Ocean and the Sea of Japan. The low inventories of 236 U found for the North Pacific Ocean in this study can be explained by the lack of additional input sources of artificial radionuclides, apart from global and regional/local fallout. This study expands the use of 236 U as oceanographic circulation tracer to yet another ocean basin and shows that this isotope can be used for tracing circulation patterns of water masses in the Pacific Ocean. Copyright © 2016 Elsevier Ltd. All rights reserved.

Constraining the calculation of 234,236,238U (n ,γ ) cross sections with measurements of the γ -ray spectra at the DANCE facility

NASA Astrophysics Data System (ADS)

Ullmann, J. L.; Kawano, T.; Baramsai, B.; Bredeweg, T. A.; Couture, A.; Haight, R. C.; Jandel, M.; O'Donnell, J. M.; Rundberg, R. S.; Vieira, D. J.; Wilhelmy, J. B.; Krtička, M.; Becker, J. A.; Chyzh, A.; Wu, C. Y.; Mitchell, G. E.

2017-08-01

The cross section for neutron capture in the continuum region has been difficult to calculate accurately. Previous results for 238U show that including an M 1 scissors-mode contribution to the photon strength function resulted in very good agreement between calculation and measurement. This paper extends that analysis to U,236234 by using γ -ray spectra measured with the Detector for Advanced Neutron Capture Experiments (DANCE) at the Los Alamos Neutron Science Center to constrain the photon strength function used to calculate the capture cross section. Calculations using a strong scissors-mode contribution reproduced the measured γ -ray spectra and were in excellent agreement with the reported cross sections for all three isotopes.

Sharpening the U-Th Chronometer: Progress and Outlook

NASA Astrophysics Data System (ADS)

McLean, N. M.; Condon, D. J.; Henderson, G. M.; Richards, D. A.; Noble, S.; Mason, A.

2013-12-01

Uranium is incorporated into a variety of natural materials when they form, including carbonates like speleothems and corals. The two most abundant naturally occurring uranium isotopes, 238U and 235U, decay to 206Pb and 207Pb over long timescales with half-lives of 4.5 and 0.7 billion years respectively, but transition through several intermediate daughter isotopes with shorter half-lives first. Fractionation between these daughter isotopes, including 234U, 230Th, and 231Pa, and their parent isotopes, followed by their time-dependent return to secular equilibrium over the course of up to ~800 kyr, forms the basis for U-series geochronology, and allows speleothems and corals to be precisely dated. These carbonates often additionally incorporate chemical and isotopic signatures (e.g., trace elements, δ18O and δ13C) from the environment in which they form, and thus are some of the best dated paleoclimate archives, offering clues about past and future conditions for life on Earth. Over the past decade, the analytical precision of U-series isotope measurements has improved dramatically, largely due to the steadily increasing sensitivity of multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). Analytical uncertainties in U-Th dates now approach or are better than 0.1% (2σ), for instance ×100 years for a speleothem or coral that is 130 kyr old (Cheng et al., 2013). However, the accuracy of U-series dates also depends on the accuracy of tracer calibrations, reference solutions and data reduction protocols, which has not kept pace in many laboratories. This means that dates measured in different labs, while impressively precise, may not be directly comparable. To address issues of inter-laboratory bias and improve the accuracy and inter-comparability of U-Th dates, we have instigated work in three related directions. First, we report on the mixing of three synthetic U-Th age solutions, created by combining high-purity mono-isotopic solutions to mimic the isotopic composition of commonly analyzed materials. These age solutions will form the basis for an inter-laboratory comparison and serve as international reference materials for assessing long-term reproducibility. Second is the creation of several U-Th gravimetric solutions, which can be used to calibrate the mixed 229Th-236U×233U tracers used in the community without having to rely on materials assumed to be in secular equilibrium. Tracers calibrated against these solutions, and therefore U-Th dates measured with these tracers, will be fully metrologically traceable. Finally, we report progress on and important considerations in developing data reduction and uncertainty propagation protocols for calculating U-Th dates and constructing and interpreting U-Th age models. Reference: Cheng et al. (2013) EPSL 371-372, 82-91

A low initial abundance of 247Cm in the early solar system and implications for r-process nucleosynthesis

NASA Astrophysics Data System (ADS)

Stirling, Claudine H.; Halliday, Alex N.; Potter, Emma-Kate; Andersen, Morten B.; Zanda, Brigitte

2006-11-01

The short-lived nuclide 247Cm is produced by r-process nucleosynthesis. When the presolar nebula formed, 247Cm became isolated from r-process production and its abundance diminished as a result of radioactive decay. Given its short half-life of only ˜ 16 million years, 247Cm is presently extinct, but its former presence should be detectable as small variations in 235U/ 238U in primitive meteoritic material, provided Cm was chemically fractionated from U at the time these solid objects formed. The magnitude of U isotopic anomalies in meteorites can thus be used to elucidate the timing and character of the last r-process nucleosynthetic event for input into models describing the formation and evolution of the early solar system. Here we report coupled U isotopic determinations and Nd/U proxy measurements for Cm/U in a series of acid-etched leachates and mineral assemblages extracted from meteorites containing primitive phases expected to show strong Cm-U fractionations. Using multiple-collector ICPMS, we are able to determine 235U/ 238U with 2 σ analytical uncertainties of ± 1 epsilon (1 epsilon = 1 part in 10,000) on sample sizes consisting of < 3 ng of 238U and < 20 pg of 235U. A double-spiking procedure using a mixed 236U- 233U spike was employed to allow instrumental mass fractionation to be reliably corrected internally and at high precision. Uranium isotopic results for almost 40 different phases show no resolvable deviations in 235U/ 238U from the chondritic value, at the ˜ 1-2 epsilon level. These data supplement our previous observations for a suite of bulk meteorite samples [C.H. Stirling, A.N. Halliday, D. Porcelli, In search of live 247Cm in the early solar system, Geochim. Cosmochim. Acta 69 (2005) 1059-1071] and provide evidence for a solar system initial 247Cm/ 235U of < 8 × 10 - 5 . Such a low value is difficult to explain without a long time-scale of ˜ 2.3 × 10 8 years between the last actinide producing r-process event and the formation of the solar system. As such it is difficult to reconcile with a model of actinide production in the same r-process forming event as 182Hf with a half-life of 8.9 My [G.J. Wasserburg, M. Busso, R. Gallino, Abundances of actinides and short-lived nonactinides in the interstellar medium: Diverse supernova sources for the r-processes, Astrophys. J. 466 (1996) L109-L113]. The alternative models of 182Hf production via a neutron-rich fast s-process, occurring, for example, in the helium burning shell in a 25 solar mass star during explosive nucleosynthesis [G.J. Wasserburg, M. Busso, R. Gallino, Abundances of actinides and short-lived nonactinides in the interstellar medium: Diverse supernova sources for the r-processes, Astrophys. J. 466 (1996) L109-L113], or via a distinct r-process event that is separate from actinide production [G.J. Wasserburg, M. Busso, R. Gallino, K.M. Nollet, Short-lived nuclei in the early solar system: Possible AGB sources, Nucl. Phys. A (in press)], may provide a viable explanation. However, further studies are also required to assess the veracity of Cm-U systematics, which are critically dependent on the suitability of using Nd and the light rare earth elements (LREEs) as a chemical proxy for Cm.

DETERMINATION OF REPORTABLE RADIONUCLIDES FOR DWPF SLUDGE BATCH 7B (MACROBATCH 9)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Crawford, C. L.; Diprete, D. P.

The Waste Acceptance Product Specifications (WAPS) 1.2 require that “The Producer shall report the inventory of radionuclides (in Curies) that have half-lives longer than 10 years and that are, or will be, present in concentrations greater than 0.05 percent of the total inventory for each waste type indexed to the years 2015 and 3115”. As part of the strategy to comply with WAPS 1.2, the Defense Waste Processing Facility (DWPF) will report for each waste type, all radionuclides (with half-lives greater than 10 years) that have concentrations greater than 0.01 percent of the total inventory from time of production throughmore » the 1100 year period from 2015 through 3115. The initial listing of radionuclides to be included is based on the design-basis glass as identified in the Waste Form Compliance Plan (WCP) and Waste Form Qualification Report (WQR). However, it is required that this list be expanded if other radionuclides with half-lives greater than 10 years are identified that may meet the greater than 0.01% criterion for Curie content. Specification 1.6 of the WAPS, International Atomic Energy Agency (IAEA) Safeguards Reporting for High Level Waste (HLW), requires that the ratio by weights of the following uranium and plutonium isotopes be reported: U-233, U-234, U-235, U-236, U-238, Pu-238, Pu-239, Pu-240, Pu-241, and Pu- 242. Therefore, the complete set of reportable radionuclides must also include this set of U and Pu isotopes. The DWPF is receiving radioactive sludge slurry from HLW Tank 40. The radioactive sludge slurry in Tank 40 is a blend of the heel from Sludge Batch 7a (SB7a) and Sludge Batch 7b (SB7b) that was transferred to Tank 40 from Tank 51. The blend of sludge in Tank 40 is also referred to as Macrobatch 9 (MB9). This report develops the list of reportable radionuclides and associated activities as a function of time. The DWPF will use this list and the activities as one of the inputs for the development of the Production Records that relate to radionuclide inventory. This work was initiated through Technical Task Request (TTR) HLW-DWPF-TTR-2011-0004; Rev. 0 entitled Sludge Batch 7b Qualification Studies. Specifically, this report details results from performing Subtask II, Item 2 of the TTR and, in part, meets Deliverable 6 of the TTR. The work was performed following the Task Technical and Quality Assurance Plan (TTQAP), SRNL-RP-2011-00247, Rev. 0 and Analytical Study Plan (ASP), SRNL-RP-2011-00248, Rev. 0. In order to determine the reportable radionuclides for SB7b (MB9), a list of radioisotopes that may meet the criteria as specified by the Department of Energy’s (DOE) WAPS was developed. All radioactive U- 235 fission products and all radioactive activation products that could be in the SRS HLW were considered. In addition, all U and Pu isotopes identified in WAPS 1.6 were included in the list. This list was then evaluated and some isotopes were excluded from the projection calculations. Based on measurements and analytical detection limits, 27 radionuclides have been identified as reportable for DWPF SB7b as specified by WAPS 1.2. The WCP and WQR require that all of the radionuclides present in the Design Basis glass be considered as the initial set of reportable radionuclides. For SB7b, all of the radionuclides in the Design Basis glass are reportable except for three radionuclides: Pd-107, Cs-135, and Th-230. At no time during the 1100- year period between 2015 and 3115 did any of these three radionuclides contribute to more than 0.01% of the radioactivity on a Curie basis. Two additional uranium isotopes (U-235 and -236) must be added to the list of reportable radionuclides in order to meet WAPS 1.6. All of the Pu isotopes (Pu-238, -239, -240, -241, and -242) and other U isotopes (U-233, -234, and -238) identified in WAPS 1.6 were already determined to be reportable according to WAPS 1.2 This brings the total number of reportable radionuclides for SB7b to 29. The radionuclide measurements made for SB7b are similar to those performed in the previous SB7a MB8 work. Some method development/refinement occurred during the conduct of these measurements, leading to lower detection limits and more accurate measurement of some isotopes than was previously possible. Improvement in the analytical measurements will likely continue, and this in turn should lead to improved detection limit values for some radionuclides and actual measurements for still others.« less

Determination Of Reportable Radionuclides For DWPF Sludge Batch 7B (Macrobatch 9)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Crawford, C. L.; DiPrete, D. P.

The Waste Acceptance Product Specifications (WAPS) 1.2 require that “The Producer shall report the inventory of radionuclides (in Curies) that have half-lives longer than 10 years and that are, or will be, present in concentrations greater than 0.05 percent of the total inventory for each waste type indexed to the years 2015 and 3115”. As part of the strategy to comply with WAPS 1.2, the Defense Waste Processing Facility (DWPF) will report for each waste type, all radionuclides (with half-lives greater than 10 years) that have concentrations greater than 0.01 percent of the total inventory from time of production throughmore » the 1100 year period from 2015 through 3115. The initial listing of radionuclides to be included is based on the design-basis glass as identified in the Waste Form Compliance Plan (WCP) and Waste Form Qualification Report (WQR). However, it is required that this list be expanded if other radionuclides with half-lives greater than 10 years are identified that may meet the greater than 0.01% criterion for Curie content. Specification 1.6 of the WAPS, International Atomic Energy Agency (IAEA) Safeguards Reporting for High Level Waste (HLW), requires that the ratio by weights of the following uranium and plutonium isotopes be reported: U-233, U-234, U-235, U-236, U-238, Pu-238, Pu-239, Pu-240, Pu-241, and Pu-242. Therefore, the complete set of reportable radionuclides must also include this set of U and Pu isotopes. The DWPF is receiving radioactive sludge slurry from HLW Tank 40. The radioactive sludge slurry in Tank 40 is a blend of the heel from Sludge Batch 7a (SB7a) and Sludge Batch 7b (SB7b) that was transferred to Tank 40 from Tank 51. The blend of sludge in Tank 40 is also referred to as Macrobatch 9 (MB9). This report develops the list of reportable radionuclides and associated activities as a function of time. The DWPF will use this list and the activities as one of the inputs for the development of the Production Records that relate to radionuclide inventory. This work was initiated through Technical Task Request (TTR) HLW-DWPF-TTR-2011-0004; Rev. 0 entitled Sludge Batch 7b Qualification Studies. Specifically, this report details results from performing Subtask II, Item 2 of the TTR and, in part, meets Deliverable 6 of the TTR. The work was performed following the Task Technical and Quality Assurance Plan (TTQAP), SRNL-RP-2011-00247, Rev. 0 and Analytical Study Plan (ASP), SRNL-RP-2011-00248, Rev. 0. In order to determine the reportable radionuclides for SB7b (MB9), a list of radioisotopes that may meet the criteria as specified by the Department of Energy’s (DOE) WAPS was developed. All radioactive U-235 fission products and all radioactive activation products that could be in the SRS HLW were considered. In addition, all U and Pu isotopes identified in WAPS 1.6 were included in the list. This list was then evaluated and some isotopes were excluded from the projection calculations. Based on measurements and analytical detection limits, 27 radionuclides have been identified as reportable for DWPF SB7b as specified by WAPS 1.2. The WCP and WQR require that all of the radionuclides present in the Design Basis glass be considered as the initial set of reportable radionuclides. For SB7b, all of the radionuclides in the Design Basis glass are reportable except for three radionuclides: Pd-107, Cs-135, and Th-230. At no time during the 1100-year period between 2015 and 3115 did any of these three radionuclides contribute to more than 0.01% of the radioactivity on a Curie basis. Two additional uranium isotopes (U-235 and -236) must be added to the list of reportable radionuclides in order to meet WAPS 1.6. All of the Pu isotopes (Pu-238, -239, -240, -241, and -242) and other U isotopes (U-233, -234, and -238) identified in WAPS 1.6 were already determined to be reportable according to WAPS 1.2 This brings the total number of reportable radionuclides for SB7b to 29. The radionuclide measurements made for SB7b are similar to those performed in the previous SB7a MB8 work. Some method development/refinement occurred during the conduct of these measurements, leading to lower detection limits and more accurate measurement of some isotopes than was previously possible. Improvement in the analytical measurements will likely continue, and this in turn should lead to improved detection limit values for some radionuclides and actual measurements for still others.« less

Certified reference materials for radionuclides in Bikini Atoll sediment (IAEA-410) and Pacific Ocean sediment (IAEA-412).

PubMed

Pham, M K; van Beek, P; Carvalho, F P; Chamizo, E; Degering, D; Engeler, C; Gascó, C; Gurriaran, R; Hanley, O; Harms, A V; Herrmann, J; Hult, M; Ikeuchi, Y; Ilchmann, C; Kanisch, G; Kis-Benedek, G; Kloster, M; Laubenstein, M; Llaurado, M; Mas, J L; Nakano, M; Nielsen, S P; Osvath, I; Povinec, P P; Rieth, U; Schikowski, J; Smedley, P A; Suplinska, M; Sýkora, I; Tarjan, S; Varga, B; Vasileva, E; Zalewska, T; Zhou, W

2016-03-01

The preparation and characterization of certified reference materials (CRMs) for radionuclide content in sediments collected offshore of Bikini Atoll (IAEA-410) and in the open northwest Pacific Ocean (IAEA-412) are described and the results of the certification process are presented. The certified radionuclides include: (40)K, (210)Pb ((210)Po), (226)Ra, (228)Ra, (228)Th, (232)Th, (234)U, (238)U, (239)Pu, (239+240)Pu and (241)Am for IAEA-410 and (40)K, (137)Cs, (210)Pb ((210)Po), (226)Ra, (228)Ra, (228)Th, (232)Th, (235)U, (238)U, (239)Pu, (240)Pu and (239+240)Pu for IAEA-412. The CRMs can be used for quality assurance and quality control purposes in the analysis of radionuclides in sediments, for development and validation of analytical methods and for staff training. Copyright © 2015 Elsevier Ltd. All rights reserved.

UDATE1: A computer program for the calculation of uranium-series isotopic ages

USGS Publications Warehouse

Rosenbauer, R.J.

1991-01-01

UDATE1 is a FORTRAN-77 program with an interface for an Apple Macintosh computer that calculates isotope activities from measured count rates to date geologic materials by uranium-series disequilibria. Dates on pure samples can be determined directly by the accumulation of 230Th from 234U and of 231Pa from 235U. Dates for samples contaminated by clays containing abundant natural thorium can be corrected by the program using various mixing models. Input to the program and file management are made simple and user friendly by a series of Macintosh modal dialog boxes. ?? 1991.

Activity disequilibrium between 234U and 238U isotopes in natural environment.

PubMed

Boryło, Alicja; Skwarzec, Bogdan

The aim of this work was to calculate the values of the 234 U/ 238 U activity ratio in natural environment (water, sediments, Baltic organisms and marine birds from various regions of the southern Baltic Sea; river waters (the Vistula and the Oder River); plants and soils collected near phosphogypsum waste heap in Wiślinka (Northern Poland) and deer-like animals from Northern Poland. On the basis of the studies it was found that the most important processes of uranium geochemical migration in the southern Baltic Sea ecosystem are the sedimentation of suspended material and the vertical diffusion from the sediments into the bottom water. Considerable values of the 234 U/ 238 U are characterized for the Vistula and Oder Rivers and its tributaries. The values of the 234 U/ 238 U activity ratio in different tissues and organs of the Baltic organisms, sea birds and wild deer are varied. Such a large variation value of obtained activity ratios indicates different behavior of uranium isotopes in the tissues and organisms of sea birds and wild animals. This value shows that uranium isotopes can be disposed at a slower or faster rate. The values of the 234 U/ 238 U activity ratio in the analyzed plants, soils and mosses collected in the vicinity of phosphogypsum dumps in Wiślinka are close to one and indicate the phosphogypsum origin of the analyzed nuclides. Uranium isotopes 234 U and 238 U are not present in radioactive equilibrium in the aquatic environment, which indicates that their activities are not equal. The inverse relationship is observed in the terrestrial environment, where the value of the of the 234 U/ 238 U activity ratio really oscillates around unity.

Depth profile of 236U/238U in soil samples in La Palma, Canary Islands

PubMed Central

Srncik, M.; Steier, P.; Wallner, G.

2011-01-01

The vertical distribution of the 236U/238U isotopic ratio was investigated in soil samples from three different locations on La Palma (one of the seven Canary Islands, Spain). Additionally the 240Pu/239Pu atomic ratio, as it is a well establish tool for the source identification, was determined. The radiochemical procedure consisted of a U separation step by extraction chromatography using UTEVA® Resin (Eichrom Technologies, Inc.). Afterwards Pu was separated from Th and Np by anion exchange using Dowex 1x2 (Dow Chemical Co.). Furthermore a new chemical procedure with tandem columns to separate Pu and U from the matrix was tested. For the determination of the uranium and plutonium isotopes by alpha spectrometry thin sources were prepared by microprecipitation techniques. Additionally these fractions separated from the soil samples were measured by Accelerator Mass Spectrometry (AMS) to get information on the isotopic ratios 236U/238U, 240Pu/239Pu and 236U/239Pu, respectively. The 236U concentrations [atoms/g] in each surface layer (∼2 cm) were surprisingly high compared to deeper layers where values around two orders of magnitude smaller were found. Since the isotopic ratio 240Pu/239Pu indicated a global fallout signature we assume the same origin as the probable source for 236U. Our measured 236U/239Pu value of around 0.2 is within the expected range for this contamination source. PMID:21481502

The uranium-isotopic composition of Saharan dust collected over the central Atlantic Ocean

NASA Astrophysics Data System (ADS)

Aciego, Sarah M.; Aarons, Sarah M.; Sims, Kenneth W. W.

2015-06-01

Uranium isotopic compositions, (234U/238U)activity , are utilized by earth surface disciplines as chronometers and source tracers, including in soil science where aeolian dust is a significant source to the total nutrient pool. However, the (234U/238U)activity composition of dust is under characterized due to material and analytical constraints. Here we present new uranium isotope data measured by high precision MC-ICP-MS on ten airborne dust samples collected on the M55 trans-Atlantic cruise in 2002. Two pairs of samples are presented with different size fractions, coarse (1-30 μm) and fine (<1 μm), and all samples were processed to separate the water soluble component in order to assess the controls on the (234U/238U)activity of mineral aerosols transported from the Sahara across the Atlantic. Our results indicate (234U/238U)activity above one for both the water soluble (1.13-1.17) and the residual solid (1.06-1.18) fractions of the dust; no significant correlation is found between isotopic composition and travel distance. Residual solids indicate a slight dependance of (234U/238U)activity on particle size. Future modeling work that incorporates dust isotopic compositions into mixing or isotopic fractionation models will need to account for the wide variability in dust (234U/238U)activity .

A Record of Uranium-Series Transport in Fractured, Unsaturated Tuff at Nopal I, Sierra Peña Blanca, Chihuahua, Mexico

NASA Astrophysics Data System (ADS)

Denton, J.; Goldstein, S. J.; Paviet, P.; Nunn, A. J.; Amato, R. S.; Hinrichs, K. A.

2015-12-01

In this study we utilize U-series disequilibria measurements to investigate mineral fluid interactions and the role fractures play in the geochemical evolution of an analogue for a high level nuclear waste repository, the Nopal I uranium ore deposit. Samples of fracture-fill materials have been collected from a vertical drill core and surface fractures. High uranium concentrations in these materials (12-7700 ppm) indicate U mobility and transport from the deposit in the past. U concentrations generally decrease with horizontal distance away from the ore deposit but show no trend with depth. Isotopic activity ratios indicate a complicated geochemical evolution in terms of the timing and extent of actinide mobility, possibly due to changing environmental (redox) conditions over the history of the deposit. 234U/238U activity ratios are generally distinct from secular equilibrium and indicate some degree of open system U behavior during the past 1.2 Ma. However, calculated closed system 238U-234U-230Th model ages are generally >313 ka and >183 ka for the surface fracture and drill core samples respectively, suggesting closed system behavior for U and Th over this most recent time period. Whole rock isochrons drawn for the drill core samples show that at two of three depths fractures have remained closed with respect to U and Th mobility for >200 ka. However, open system behavior for U in the last 350 ka is suggested at 67 m depth. 231Pa/235U activity ratios within error of unity suggest closed system behavior for U and Pa for at least the past 185 ka. 226Ra/230Th activity ratios are typically <1 (0.7-1.2), suggesting recent (<8 ka) radium loss and mobility due to ongoing fluid flow in the fractures. Overall, the mainly closed system behavior of U-Th-Pa over the past ~200 ka provides one indicator of the geochemical immobility of these actinides over long time-scales for potential nuclear waste repositories sited in fractured, unsaturated tuff.

U-Pb ages of uraniferous opals and implications for the history of beryllium, fluorine, and uranium mineralization at Spor Mountain, Utah

USGS Publications Warehouse

Ludwig, K. R.; Lindsey, D.A.; Zielinski, R.A.; Simmons, K.R.

1980-01-01

The U-Pb isotope systematics of uraniferous opals from Spor Mountain, Utah, were investigated to determine the suitability of such material for geochronologic purposes, and to estimate the timing of uranium and associated beryllium and fluorine mineralization. The results indicate that uraniferous opals can approximate a closed system for uranium and uranium daughters, so that dating samples as young as ???1 m.y. should be possible. In addition, the expected lack of initial 230Th and 231Pa in opals permits valuable information on the initial 234U/238U to be obtained on suitable samples of ???10 m.y. age. The oldest 207Pb/235U apparent age observed, 20.8 ?? 1 m.y., was that of the opal-fluorite core of a nodule from a beryllium deposit in the Spor Mountain Formation. This age is indistinguishable from that of fission-track and K-Ar ages from the host rhyolite, and links the mineralization to the first episode of alkali rhyolite magmatism and related hydrothermal activity at Spor Mountain. Successively younger ages of 13 m.y. and 8-9 m.y. on concentric outer zones of the same nodule indicate that opal formed either episodically or continuously for over 10 m.y. Several samples of both fracture-filling and massive-nodule opal associated with beryllium deposits gave 207Pb/235U apparent ages of 13-16 m.y., which may reflect a restricted period of mineralization or perhaps an averaging of 21- and <13-m.y. periods of opal growth. Several samples of fracture-filling opal in volcanic rocks as young as 6 m.y. gave 207Pb/235U ages of 3.4-4.8 m.y. These ages may reflect hot-spring activity after the last major eruption of alkali rhyolite. ?? 1980.

Observations of 231Pa/ 235U disequilibrium in volcanic rocks

NASA Astrophysics Data System (ADS)

Pickett, David A.; Murrell, Michael T.

1997-04-01

We present here the first survey of ( 231Pa/ 235U) ratios in volcanic rocks; such measurements are made possible by new mass spectrometric techniques. The data place new constraints on the timing and extent of magma source and evolutionary processes, particularly due to the sensitivity of the 231Pa- 235U pair and its intermediate time scale ( 231Pat 1/2 = 33 ky). ( 231Pa/ 235U) is found to vary widely, from 0.2 in carbonatites to 1.1-2.9 in basalts and 0.9-2.2 in arcs. Substantial Pa enrichment is nearly ubiquitous, suggestive of the relative incompatibility of Pa, qualitatively consistent with available partitioning data. The level of 231Pa- 235U disequilibrium typically far exceeds that of 230Th- 238U and is comparable to 226Ra- 230Th. The high ( 231Pa/ 235U) ratios in MORB and other basalts reflect a large degree of discrimination between two incompatible elements, posing challenges for modelling of melt generation and migration. Fundamental differences in ( 231Pa/ 235U) among different basaltic environments are likely related to contrasts in melting zone conditions (e.g., melting rate). Strong ( 231Pa/ 235U) disequilibria in continental basalts, for which ( 230Th/ 238U) disequilibria are small or absent, demonstrate that Pa-U fractionation is possible in both garnet and spinel mantle stability fields. In arcs, correlation of ( 231Pa/ 235U) and ( 230Th/ 238U) is consistent with U enrichment via slab-derived fluids, a process which is additional to the still dominant Pa enrichment. An important new constraint is provided by the observation that the near-equilibrium ( 230Th/ 238U) common to arcs and continental basalts is not typically accompanied by near-equilibrium ( 231Pa/ 235U), arguing against the influence of long magma history, crustal material, or equilibrium mantle sources in affecting decay-series ratios. Small sample sets from two silicic centers illustrate: (1) recent, rapid U enrichment in the magma chamber (El Chichón); and (2) the failure of substantial magma H 2O-CO 2 degassing to effect U-Th-Pa fractionation (Mono Craters).

Study of 236U/238U ratio at CIRCE using a 16-strip silicon detector with a TOF system

NASA Astrophysics Data System (ADS)

De Cesare, M.; De Cesare, N.; D'Onofrio, A.; Gialanella, L.; Terrasi, F.

2015-04-01

Accelerator Mass Spectrometry (AMS) is presently the most sensitive technique for the measurement of long-lived actinides, e.g. 236U and xPu isotopes. A new actinide AMS system, based on a 3-MV pelletron tandem accelerator, is operated at the Center for Isotopic Research on Cultural and Environmental Heritage (CIRCE) in Caserta, Italy. In this paper we report on the procedure adopted to increase the 236U abundance sensitivity as low as possible. The energy and position determinations of the 236U ions, using a 16-strip silicon detector have been obtained. A 236U/238U isotopic ratio background level of about 2.9×10-11 was obtained, summing over all the strips, using a Time of Flight-Energy (TOF-E) system with a 16-strip silicon detector (4.9×10-12 just with one strip).

Testing the concept of drift shadow at Yucca Mountain, Nevada

USGS Publications Warehouse

Paces, J.B.; Neymark, L.A.; Ghezzehei, T.; Dobson, P.F.

2006-01-01

If proven, the concept of drift shadow, a zone of reduced water content and slower ground-water travel time beneath openings in fractured rock of the unsaturated zone, may increase performance of a proposed geologic repository for high-level radioactive waste at Yucca Mountain, To test this concept under natural-flow conditions present in the proposed repository horizon, isotopes within the uranium-series decay chain (uranium-238, uranium-234, and thorium-230, or 238U-234U-230Th) have been analyzed in samples of rock from beneath four naturally occurring lithophysal cavities. All rock samples show 234U depletion relative to parent 238U indicating varying degrees of water-rock interaction over the past million years. Variations in 234U/238U activity ratios indicate that depletion of 234U relative to 238U can be either smaller or greater in rock beneath cavity floors relative to rock near cavity margins. These results are consistent with the concept of drift shadow and with numerical simulations of meter-scale spherical cavities in fractured tuff. Differences in distribution patterns of 234U/ 238U activity ratios in rock beneath the cavity floors are interpreted to reflect differences in the amount of past seepage into lithophysal cavities, as indicated by the abundance of secondary mineral deposits present on the cavity floors.

Measurement of the 234U(n, f ) cross-section with quasi-monoenergetic beams in the keV and MeV range using a Micromegas detector assembly

NASA Astrophysics Data System (ADS)

Stamatopoulos, A.; Kanellakopoulos, A.; Kalamara, A.; Diakaki, M.; Tsinganis, A.; Kokkoris, M.; Michalopoulou, V.; Axiotis, M.; Lagoyiannis, A.; Vlastou, R.

2018-01-01

The 234U neutron-induced fission cross-section has been measured at incident neutron energies of 452, 550, 651 keV and 7.5, 8.7, 10 MeV using the 7Li ( p, n) and the 2H( d, n) reactions, respectively, relative to the 235U( n, f ) and 238U( n, f ) reference reactions. The measurement was performed at the neutron beam facility of the National Center for Scientific Research "Demokritos", using a set-up based on Micromegas detectors. The active mass of the actinide samples and the corresponding impurities were determined via α-spectroscopy using a surface barrier silicon detector. The neutron spectra intercepted by the actinide samples have been thoroughly studied by coupling the NeuSDesc and MCNP5 codes, taking into account the energy and angular straggling of the primary ion beams in the neutron source targets in addition to contributions from competing reactions ( e.g. deuteron break-up) and neutron scattering in the surrounding materials. Auxiliary Monte Carlo simulations were performed making combined use of the FLUKA and GEF codes, focusing particularly on the determination of the fission fragment detection efficiency. The developed methodology and the final results are presented.

Towards A Modern Calibration Of The 238U/235U Paleoredox Proxy: Apparent Uranium Isotope Fractionation Factor During U(VI)-U(IV) Reduction In The Black Sea

NASA Astrophysics Data System (ADS)

Rolison, J. M.; Stirling, C. H.; Middag, R.; Rijkenberg, M. J. A.; De Baar, H. J. W.

2015-12-01

The isotopic compositions of redox-sensitive metals, including uranium (U), in marine sediments have recently emerged as powerful diagnostic tracers of the redox state of the ancient ocean-atmosphere system. Interpretation of sedimentary isotopic information requires a thorough understating of the environmental controls on isotopic fractionation in modern anoxic environments before being applied to the paleo-record. In this study, the relationship between ocean anoxia and the isotopic fractionation of U was investigated in the water column and sediments of the Black Sea. The Black Sea is the world's largest anoxic basin and significant removal of U from the water column and high U accumulation rates in modern underlying sediments have been documented. Removal of U from the water column occurs during the redox transition of soluble U(VI) to relatively insoluble U(IV). The primary results of this study are two-fold. First, significant 238U/235U fractionation was observed in the water column of the Black Sea, suggesting the reduction of U induces 238U/235U fractionation with the preferential removal of 238U from the aqueous phase. Second, the 238U/235U of underlying sediments is related to the water column through the isotope fractionation factor of the reduction reaction but is influenced by mass transport processes. These results provide important constraints on the use of 238U/235U as a proxy of the redox state of ancient oceans.

Distribution of uranium and thorium in groundwater of arid climate region

NASA Astrophysics Data System (ADS)

Murad, Ahmed; Alshamsi, Dalal; Aldahan, Ala; Hou, Xiaolin

2014-05-01

Uranium, thorium and their decay products are the most common radionuclides in groundwater in addition to potassium-40. Once groundwater is used for drinking, domestic and irrigation purposes, the radionuclides will then pose environmental and health related hazard originating from radioactivity and toxicity. In the investigation presented here, assessment of 238U, 235U and 232Th concentrations in groundwater across of the United Arab Emirates (UAE) is evaluated in terms of quality and sources. The region is dominated by arid climate conditions and radioactivity assessment of groundwater is essential for safe use of groundwater. Furthermore, the results were linked to data from other arid regions and worldwide. Groundwater samples (total dissolved solids,TDS, 142.5 mg L-1 to 12770 mg L-1) from 67 different wells were collected across geomorphologically different areas and most of the wells are actively used for agriculture. The aquifers are recent sand dunes, Quaternary (3 million years to present) sediments, and older carbonate rocks (230-10 million years). The 235U, 238U and 232Th measurements were carried out using ICP-MS system equipped with an Xt-skimmer cone and a concentric nebulizer under hot plasma conditions. Concentrations of 235U, 238U and 232Th range at (0.125-508.4) ng L-1, (25.81-69237) ng L-1 and (0.236-2529) ng L-1, respectively. Apparently, most 235U, 238U, 232Th concentrations in the sampled groundwater are below the WHO proposed permissible level of 60000 ng/L for total uranium (1 Bq L-1 for 235U and 10 Bq L-1 for 238U) and 5000 ng L-1 (1Bq L-1) for 232Th. A few samples show high concentrations of uranium that are associated with high TDS values and occur within interbedded limestones and shales aquifer. Comparison with worldwide groundwater data suggests that 238U concentration is highest in the arid regions groundwater where the recharge to aquifers is relatively low. The situation for 232Th concentrations seems less affected by climatic conditions, most likely is related to its less solubility in water compared to uranium. We calculated the accumulated TU and 232Th concentration in the irrigation water annually to estimate the cumulative concentrations after twenty years on specific agricultural areas. The TU and 232Th are expected not to reach more than 1.14 x 10-3 g (1.14 mg) and 4.32 x 10-6 g (4.32 μg) respectively after twenty years if the daily irrigation is at its maximum amount (10 m3). Despite these obtained values of concentrations in irrigation water, the transfer of uranium and thorium into crop is not readily and it is expected that only a tiny fraction of the element end into the body. However, further research is needed to quantify the dietary exposures in the UAE with detailed data from crops and consumers.

234U— 238U— 230Th— 232Th systematics in saline groundwaters from central Missouri

NASA Astrophysics Data System (ADS)

Banner, Jay L.; Wasserburg, G. J.; Chen, James H.; Moore, Clyde H.

1990-12-01

Saline groundwaters with 4.7 to 26‰ total dissolved solids were sampled from springs and artesian wells in Mississippian and Ordovician carbonates and sandstones in central Missouri. U—Th isotopic variations provide a means of evaluating processes of water-rock interaction and fluid mixing and estimating the time scales of element transport. Recently developed mass spectrometric techniques are used to make isotopic measurements on small-volume groundwater samples (0.1-4 l) with high precision (e.g., < ±5% for 234U/ 238U activity ratios). The groundwaters have a wide range of 238U concentrations, 50 × 10 -12 to 200 × 10 -12 g/g; 234U/ 234U activity ratios, 2.15-16.0; 232Th concentrations, 0.10 × 10 -12 to 33 × 10 -12 g/g; and 230Th concentrations, 0.91 × 10 -17 to 26 × 10 -17 g/g. Unfiltered and filtered (0.4 μm, 0.1 μm) aliquots of a saline sample have the same isotopic composition and concentration of U, indicating that 234U and 238U occur almost entirely as dissolved species. The concentration of 232Th is up to seven times lower in filtered vs. unfiltered aliquots, indicating that 232Th is predominantly associated with particulates in the groundwaters. In contrast, most of the 230Th is in solution. Previous geochemical studies indicate that: (1) the saline waters originated as meteoric recharge and evolved through halite dissolution, reactions with silicates and saline-dilute mixing processes during a long-distance flow history; and (2) interaction with limestone and dolomite aquifer rocks in central Missouri has been limited. A consistent relationship between U/Ca and 234U/ 238U activity ratio is observed in the groundwaters and provides constraints on the U/Ca ratios and 234U/ 238U activity ratios of end-member reservoirs and on the processes of isotopic exchange in this water-rock system. Model calculations that simulate (1) saline-dilute groundwater mixing and (2) limited extents of dissolution of carbonate aquifer minerals by the groundwaters can account for the variations in U/Ca, 234U/ 238U and 18O/ 16O in the suite of water samples. The model calculations demonstrate that dissolved U isotopic compositions can be a sensitive indicator of water-rock interaction, which in turn limits the usefulness of 234U— 238U disequilibria for groundwater age determinations. The concentration of dissolved 230Th in the groundwaters is (1) two to three orders of magnitude below 230Th— 234U equilibrium activity levels, and (2) significantly in excess of concentrations estimated for the supply of Th to solution via desorption and dissolution. A model involving the derivation of the excess 230Th from the in situ decay of dissolved 234U in the groundwaters indicates the operation of an adsorption mechanism on the time scale of 10-10 3 years. The results reported here may have broader application to the assessment and management of hazardous chemical species in natural environments.

Using 238U/235U ratios to understand the formation and oxidation of reduced uranium solids in naturally reduced zones

NASA Astrophysics Data System (ADS)

Jemison, N.; Johnson, T. M.; Druhan, J. L.; Davis, J. A.

2016-12-01

Uranium occurs in groundwater primarily as soluble and mobile U(VI), which can be reduced to immobile U(IV), often observed in sediments as uraninite. Numerous U(VI)-contaminated sites, such as the DOE field site in Rifle, CO, contain naturally reduced zones (NRZ's) that have relatively high concentrations of organic matter. Reduction of heavy metals occurs within NRZ's, producing elevated concentrations of iron sulfides and U(IV). Slow, natural oxidation of U(IV) from NRZ's may prolong U(VI) contamination of groundwater. The reduction of U(VI) produces U(IV) with a higher 238U/235U ratio. Samples from two NRZ sediment cores recovered from the Rifle site revealed that the outer fringes of the NRZ contain U(IV) with a high 238U/235U ratio, while lower values are observed in the center . We suggest that as aqueous U(VI) was reduced in the NRZ, it was driven to lower 238U/235U values, such that U(IV) formed in the core of the NRZ reflects a lower 238U/235U. Two oxidation experiments were conducted by injecting groundwater containing between 14.9 and 21.2 mg/L dissolved O2 as an oxidant into the NRZ. The oxidation of U(IV) from this NRZ increased aqueous U(VI) concentrations and caused a shift to higher 238U/235U in groundwater as U(IV) was oxidized primarily on the outer fringes of the NRZ. In total these observations suggest that the stability of solid phase uranium is governed by coupled reaction and transport processes. To better understand various reactive transport scenarios we developed a model for the formation and oxidation of NRZ's utilizing the reactive transport software CrunchTope. These simulations suggest that the development of isotopically heterogeneous U(IV) within NRZ's is largely controlled by permeability of the NRZ and the U(VI) reduction rate. Oxidation of U(IV) from the NRZ's is constrained by the oxidation rate of U(IV) as well as iron sulfides, which can prevent oxidation of U(IV) by scavenging dissolved oxygen.

75 FR 54692 - Culturally Significant Objects Imported for Exhibition Determinations: “Miró: The Dutch Interiors”

Federal Register 2010, 2011, 2012, 2013, 2014

2010-09-08

..., notice was published on page 48736 of the Federal Register (volume 75, number 154) of determination made.... 2681, et seq.; 22 U.S.C. 6501 note, et seq.), Delegation of Authority No. 234 of October 1, 1999, and Delegation of Authority No. 236-3 of August 28, 2000, I hereby determine that the additional object to be...

High resolution isotopic analysis of U-bearing particles via fusion of SIMS and EDS images

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tarolli, Jay G.; Naes, Benjamin E.; Garcia, Benjamin J.

Image fusion of secondary ion mass spectrometry (SIMS) images and X-ray elemental maps from energy-dispersive spectroscopy (EDS) was performed to facilitate the isolation and re-analysis of isotopically unique U-bearing particles where the highest precision SIMS measurements are required. Image registration, image fusion and particle micromanipulation were performed on a subset of SIMS images obtained from a large area pre-screen of a particle distribution from a sample containing several certified reference materials (CRM) U129A, U015, U150, U500 and U850, as well as a standard reference material (SRM) 8704 (Buffalo River Sediment) to simulate particles collected on swipes during routine inspections ofmore » declared uranium enrichment facilities by the International Atomic Energy Agency (IAEA). In total, fourteen particles, ranging in size from 5 – 15 µm, were isolated and re-analyzed by SIMS in multi-collector mode identifying nine particles of CRM U129A, one of U150, one of U500 and three of U850. These identifications were made within a few percent errors from the National Institute of Standards and Technology (NIST) certified atom percent values for 234U, 235U and 238U for the corresponding CRMs. This work represents the first use of image fusion to enhance the accuracy and precision of isotope ratio measurements for isotopically unique U-bearing particles for nuclear safeguards applications. Implementation of image fusion is essential for the identification of particles of interests that fall below the spatial resolution of the SIMS images.« less

First study on 236U in the Northeast Pacific Ocean using a new target preparation procedure for AMS measurements.

PubMed

Eigl, R; Steier, P; Winkler, S R; Sakata, K; Sakaguchi, A

2016-10-01

We succeeded in obtaining the depth profile of 236 U for a sampling station in the Northeast Pacific Ocean using only one litre of seawater sample from each depth. For this purpose, a new procedure was developed that allowed for the preparation of accelerator mass spectrometry targets for trace uranium using only 100 μg of iron carrier material. The 236 U concentrations in water samples from the Northeast Pacific Ocean showed large variations from (9.26 ± 0.42) × 10 6 atoms/kg at 60 m depth to (0.08 ± 0.02) × 10 6 atoms/kg at a depth of 3000 m. The high 236 U concentrations in surface water reflect the input of 236 U by global and local fallout from nuclear weapons tests. The low 236 U concentrations in seawater from 1500 m and below are an indicator for the low vertical diffusion of surface water to deeper layers in the North Pacific Ocean. The total inventory of 236 U on the water column was (8.35 ± 0.23) × 10 12 atoms/m 2 , which is lower compared to those of other ocean regions solely affected by global fallout on comparable latitudes. This study represents the first dataset for 236 U in the Pacific Ocean and shows the possibility of downsizing sample volumes which may help in future applications of 236 U as tracer for large ocean areas. Copyright © 2016 Elsevier Ltd. All rights reserved.

A modern framework for the interpretation of 238U/235U in studies of ancient ocean redox

NASA Astrophysics Data System (ADS)

Andersen, M. B.; Romaniello, S.; Vance, D.; Little, S. H.; Herdman, R.; Lyons, T. W.

2014-08-01

The abundance and isotope composition of redox sensitive elements in ancient sediments are increasingly used to understand the past ocean's geochemical state and the oxygenation history of the Earth. The redox transition of uranium (U) from soluble U+6 to relatively insoluble U+4 and its subsequent incorporation into reduced sediments has been used to deduce the redox state of the oceans in the past. Furthermore, recent analytical improvements have revealed significant 238U/235U fractionation during this redox transition, offering the potential for U isotopes to act as a redox proxy. However, the development of U isotopes as a geochemical tracer requires that U isotope systematics associated with redox changes, are well-characterized. This study focuses on U isotopes in recent sediments from the two largest modern anoxic ocean basins, the Black Sea and the Cariaco Basin, with the aim of advancing our understanding of the U isotope systematics in reducing marine environments. These anoxic sediments have high U accumulation rates and high 238U/235U ratios relative to seawater, in general agreement with a process that accumulates reduced U with a heavy isotopic composition. Using Al and Ca concentrations to correct for detrital and biogenic carbonate-bound U, we estimate the reduced authigenic U accumulated in the sediments and its 238U/235U. These results highlight the importance of isotopic mass balance constraints during diffusive transport and reaction of U from seawater and through pore-water, affecting the observed 238U/235U in sediments. Using these constraints, the average percentages of U depletion from top to bottom of the water column can be estimated, assuming batch-removal of U into anoxic sediments in a restricted basin. Using this framework, 238U/235U in modern anoxic sediments from the Black Sea imply U depletions in the water column of ∼30%, which is close to the observed ∼40% U depletion in the modern Black Sea water column at these depths. Similar U depletion in the water column is estimated from anoxic sediment samples of the Cariaco Basin. These recent anoxic sediments provide a basis for interpreting authigenic 238U/235U in ancient sediments. In particular, such analyses may offer insights, based on mass balance relationships, into whether particular ancient sediments were deposited in an open ocean or restricted basin. As such, this approach may provide key insight into the controls on local versus ocean-scale redox and, in that light, constraints the capacity of other proxies to capture global signals for anoxia/euxinia.

Mass and abundance 236U sensitivities at CIRCE

NASA Astrophysics Data System (ADS)

De Cesare, M.; De Cesare, N.; D'Onofrio, A.; Fifield, L. K.; Gialanella, L.; Terrasi, F.

2015-10-01

The actinides (e.g. 236U and xPu isotopes) are present in environmental samples at the ultra trace level since atmospheric tests of NWs (Nuclear Weapons) performed in the past, deliberate dumping of nuclear waste, nuclear fuel reprocessing, on a large scale and operation of NPPs (Nuclear Power Plants) on a small scale have led to the release of a wide range of radioactive nuclides in the environment. Their detection requires the most sensitive AMS (Accelerator Mass Spectrometry) techniques and at the Center for Isotopic Research on Cultural and Environmental heritage (CIRCE) in Caserta, Italy, an upgraded actinide AMS system, based on a 3-MV pelletron tandem accelerator, has been operated. In this paper the progress made in order to push the 236U mass sensitivity and 236U/238U isotopic ratio down to the natural levels is reported. A uranium contamination mass of about 0.05 μg and a 236U/238U isotopic ratio sensitivities at the level of 3.2 × 10-13 are presently achievable.

Radiochronometry in the CMX-4 Exercise-Draft

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kristo, M. J.; Williams, R.; Gaffney, A. M.

In a recent international exercise, 10 international nuclear forensics laboratories successfully performed radiochronometry on 3 low-enriched uranium oxide samples, providing 12 analytical results using 3 different parent-daughter pairs serving as independent chronometers. The vast majority of the results were consistent with one another and consistent with the known processing history of the materials. In general, for these particular samples, mass spectrometry gave more accurate and more precise analytical results than decay counting measurements. In addition, the concordance of the 235U- 231Pa and 234U- 230Th chronometers confirmed the validity of the age dating assumption, increasing our confidence in the resulting conclusions.

Heterogeneity in the 238U/235U Ratios of Angrites.

NASA Astrophysics Data System (ADS)

Tissot, F.; Dauphas, N.; Grove, T. L.

2016-12-01

Angrites are differentiated meteorites of basaltic composition, of either volcanic or plutonic origin, that display minimal post-crystallization alteration, metamorphism, shock or impact brecciation. Because quenched angrites cooled very rapidly, all radiochronometric systems closed simultaneously in these samples. Quenched angrites are thus often used as anchors for cross-calibrating short-lived dating methods (e.g., 26Al-26Mg) and the absolute dating techniques (e.g, Pb-Pb). Due to the constancy of the 238U/235U ratio in natural samples, Pb-Pb ages have long been calculated using a "consensus" 238U/235U ratio, but the discovery of resolvable variations in the 238U/235U ratio of natural samples, means that the U isotopic composition of the material to date also has to be determined in order to obtain high-precision Pb-Pb ages. We set out (a) to measure at high-precision the 238U/235U ratio of a large array of angrites to correct their Pb-Pb ages, and (b) to identify whether all angrites have a similar U isotopic composition, and, if not, what were the processes responsible for this variability. Recently, Brennecka & Wadhwa (2012) suggested that the angrite-parent body had a homogeneous 238U/235U ratio. They reached this conclusion partly because they propagated the uncertainties of the U isotopic composition of the various U double spikes that they used onto the final 238U/235U ratio the sample. Because this error is systematic (i.e., it affects all samples similarly), differences in the δ238U values of samples corrected by the same double spike are better known than one would be led to believe if uncertainties on the spike composition are propagated. At the conference, we will present the results of the high-precision U isotope analyses for six angrite samples: NWA 4590, NWA 4801, NWA 6291, Angra dos Reis, D'Orbigny, and Sahara 99555. We will show that there is some heterogeneity in the δ238U values of the angrites and will discuss the possible processes by which different angrite samples can acquire different U isotopic compositions. The U isotope data will then be used to correct Pb-Pb ages of angrites estimated using an assumed 238U/235U ratio. These ages will be used to discuss the degree of concordance between short-lived nuclides systems and the absolute Pb-Pb clock in early Solar System materials.

Process for producing enriched uranium having a .sup.235 U content of at least 4 wt. % via combination of a gaseous diffusion process and an atomic vapor laser isotope separation process to eliminate uranium hexafluoride tails storage

DOEpatents

Horton, James A.; Hayden, Jr., Howard W.

1995-01-01

An uranium enrichment process capable of producing an enriched uranium, having a .sup.235 U content greater than about 4 wt. %, is disclosed which will consume less energy and produce metallic uranium tails having a lower .sup.235 U content than the tails normally produced in a gaseous diffusion separation process and, therefore, eliminate UF.sub.6 tails storage and sharply reduce fluorine use. The uranium enrichment process comprises feeding metallic uranium into an atomic vapor laser isotope separation process to produce an enriched metallic uranium isotopic mixture having a .sup.235 U content of at least about 2 wt. % and a metallic uranium residue containing from about 0.1 wt. % to about 0.2 wt. % .sup.235 U; fluorinating this enriched metallic uranium isotopic mixture to form UF.sub.6 ; processing the resultant isotopic mixture of UF.sub.6 in a gaseous diffusion process to produce a final enriched uranium product having a .sup.235 U content of at least 4 wt. %, and up to 93.5 wt. % or higher, of the total uranium content of the product, and a low .sup.235 U content UF.sub.6 having a .sup.235 U content of about 0.71 wt. % of the total uranium content of the low .sup.235 U content UF.sub.6 ; and converting this low .sup.235 U content UF.sub.6 to metallic uranium for recycle to the atomic vapor laser isotope separation process.

Process for producing enriched uranium having a {sup 235}U content of at least 4 wt. % via combination of a gaseous diffusion process and an atomic vapor laser isotope separation process to eliminate uranium hexafluoride tails storage

DOEpatents

Horton, J.A.; Hayden, H.W. Jr.

1995-05-30

An uranium enrichment process capable of producing an enriched uranium, having a {sup 235}U content greater than about 4 wt. %, is disclosed which will consume less energy and produce metallic uranium tails having a lower {sup 235}U content than the tails normally produced in a gaseous diffusion separation process and, therefore, eliminate UF{sub 6} tails storage and sharply reduce fluorine use. The uranium enrichment process comprises feeding metallic uranium into an atomic vapor laser isotope separation process to produce an enriched metallic uranium isotopic mixture having a {sup 235} U content of at least about 2 wt. % and a metallic uranium residue containing from about 0.1 wt. % to about 0.2 wt. % {sup 235} U; fluorinating this enriched metallic uranium isotopic mixture to form UF{sub 6}; processing the resultant isotopic mixture of UF{sub 6} in a gaseous diffusion process to produce a final enriched uranium product having a {sup 235}U content of at least 4 wt. %, and up to 93.5 wt. % or higher, of the total uranium content of the product, and a low {sup 235}U content UF{sub 6} having a {sup 235}U content of about 0.71 wt. % of the total uranium content of the low {sup 235}U content UF{sub 6}; and converting this low {sup 235}U content UF{sub 6} to metallic uranium for recycle to the atomic vapor laser isotope separation process. 4 figs.

Use of integral experiments for the assessment of a new 235U IRSN-CEA evaluation

NASA Astrophysics Data System (ADS)

Ichou, Raphaëlle; Leclaire, Nicolas; Leal, Luiz; Haeck, Wim; Morillon, Benjamin; Romain, Pascal; Duarte, Helder

2017-09-01

The Working Party on International Nuclear Data Evaluation Co-operation (WPEC) subgroup 29 (SG 29) was established to investigate an issue with the 235U capture cross-section in the energy range from 0.1 to 2.25 keV, due to a possible overestimation of 10% or more. To improve the 235U capture crosssection, a new 235U evaluation has been proposed by the Institut de Radioprotection et de Sûreté Nucléaire (IRSN) and the CEA, mainly based on new time-of-flight 235U capture cross-section measurements and recent fission cross-section measurements performed at the n_TOF facility from CERN. IRSN and CEA Cadarache were in charge of the thermal to 2.25 keV energy range, whereas the CEA DIF was responsible of the high energy region. Integral experiments showing a strong 235U sensitivity are used to assess the new evaluation, using Monte-Carlo methods. The keff calculations were performed with the 5.D.1 beta version of the MORET 5 code, using the JEFF-3.2 library and the new 235U evaluation, as well as the JEFF-3.3T1 library in which the new 235U has been included. The benchmark selection allowed highlighting a significant improvement on keff due to the new 235U evaluation. The results of this data testing are presented here.

Evaluation of Uranium-235 Measurement Techniques

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaspar, Tiffany C.; Lavender, Curt A.; Dibert, Mark W.

2017-05-23

Monolithic U-Mo fuel plates are rolled to final fuel element form from the original cast ingot, and thus any inhomogeneities in 235U distribution present in the cast ingot are maintained, and potentially exaggerated, in the final fuel foil. The tolerance for inhomogeneities in the 235U concentration in the final fuel element foil is very low. A near-real-time, nondestructive technique to evaluate the 235U distribution in the cast ingot is required in order to provide feedback to the casting process. Based on the technical analysis herein, gamma spectroscopy has been recommended to provide a near-real-time measure of the 235U distribution inmore » U-Mo cast plates.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ullmann, J. L.; Kawano, T.; Baramsai, B.

The cross section for neutron capture in the continuum region has been difficult to calculate accurately. Previous results for 238 U show that including an M 1 scissors-mode contribution to the photon strength function resulted in very good agreement between calculation and measurement. Our paper extends that analysis to 234 , 236 U by using γ -ray spectra measured with the Detector for Advanced Neutron Capture Experiments (DANCE) at the Los Alamos Neutron Science Center to constrain the photon strength function used to calculate the capture cross section. Calculations using a strong scissors-mode contribution reproduced the measured γ -ray spectramore » and were in excellent agreement with the reported cross sections for all three isotopes.« less

Calorimetric low temperature detectors for low-energetic heavy ions and their application in accelerator mass spectrometry

NASA Astrophysics Data System (ADS)

Kraft-Bermuth, S.; Andrianov, V. A.; Bleile, A.; Echler, A.; Egelhof, P.; Kiseleva, A.; Kiselev, O.; Meier, H. J.; Meier, J. P.; Shrivastava, A.; Weber, M.; Golser, R.; Kutschera, W.; Priller, A.; Steier, P.; Vockenhuber, C.

2009-10-01

The energy-sensitive detection of heavy ions with calorimetric low temperature detectors was investigated in the energy range of E =0.1-1 MeV/amu, commonly used for accelerator mass spectrometry (AMS). The detectors used consist of sapphire absorbers and superconducting aluminum transition edge thermometers operated at T ˜1.5 K. They were irradiated with various ion beams (C13,A197u,U238) provided by the VERA tandem accelerator in Vienna, Austria. The relative energy resolution obtained was ΔE /E=(5-9)×10-3, even for the heaviest ions such as U238. In addition, no evidence for a pulse height defect was observed. This performance allowed for the first time to apply a calorimetric low temperature detector in an AMS experiment. The aim was to precisely determine the isotope ratio of U236/U238 for several samples of natural uranium, U236 being known as a sensitive monitor for neutron fluxes. Replacing a conventionally used detection system at VERA by the calorimetric detector enabled to substantially reduce background from neighboring isotopes and to increase the detection efficiency. Due to the high sensitivity achieved, a value of U236/U238=6.1×10-12 could be obtained, representing the smallest U236/U238 ratio measured at the time. In addition, we contributed to establishing an improved material standard of U236/U238, which can be used as a reference for future AMS measurements.

High-Resolution Triple Resonance Autoionization of Uranium Isotopes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schumann, Philipp G.; Wendt, K; Bushaw, Bruce A.

2005-11-01

The near-threshold autoionization (AI) spectrum of uranium has been investigated by triple-resonance excitation with single-mode continuous lasers. Spectra were recorded over the first {approx}30 cm-1 above the first ionization limit at a resolution of 3x10-4 cm 1 using intermediate states with different J values (6, 7, 8) to assign AI level total angular momentum JAI = 5 to 9. Resonances with widths ranging from 8 MHz to 30 GHz were observed; the strongest ones have JAI = 9 and widths of {approx} 60 MHz. Hyperfine structures for 235U and isotope shifts for 234,235U have been measured in the two intermediatemore » levels and in the final AI level for the most favorable excitation path. These measurements were performed using aqueous samples containing sub-milligram quantities of uranium at natural isotopic abundances, indicating the potential of this approach for trace isotope ratio determinations.« less

Uranium and its decay products in samples contaminated with uranium mine and mill waste

NASA Astrophysics Data System (ADS)

Benedik, L.; Klemencic, H.; Repinc, U.; Vrecek, P.

2003-05-01

The routine determination of the activity concentrations of uranium isotopes (^{238}U, ^{235}U and ^{234}U), thorium isotopes (^{212}Th, ^{230}TI, and ^{228}Th), ^{231}Pa, ^{226}Ra, ^{210}Pb and ^{210}Po in the environment is one of the most important tasks in uranium mining areas. Natural radionuclides contribute negligibly to the extemal radiation dose, but in the case of ingestion or inhalation can represent a very serious hazard. The objective of this study was to determine the activities of uranium and its decay products ^{230}Th, ^{231}Pa, ^{226}Ra, ^{210}Pb and ^{210}Po in sediments and water below sources of contamination (uranium mine, disposal sites and individual inflows) using gamma and alpha spectrometry, beta counting, the liquid scintillation technique and radiochemical neutron activation analysis.

First application of calorimetric low-temperature detectors in accelerator mass spectrometry

NASA Astrophysics Data System (ADS)

Kraft, S.; Andrianov, V.; Bleile, A.; Egelhof, P.; Golser, R.; Kiseleva, A.; Kiselev, O.; Kutschera, W.; Meier, J. P.; Priller, A.; Shrivastava, A.; Steier, P.; Vockenhuber, C.

2004-03-01

For the first time, calorimetric low-temperature detectors were applied in accelerator mass spectrometry, a well-known method for determination of very small isotope ratios with high sensitivity. The aim of the experiment was to determine with high accuracy the isotope ratio of 236U/238U for several samples of natural uranium, 236U being known as a sensitive monitor for neutron flux. Measurements were performed at the VERA tandem accelerator at Vienna, Austria. The detectors consist of sapphire absorbers and superconducting transition edge thermometers operated at T≈ 1.5 K. The relative energy resolution obtained for 17.39 MeV 238U is ΔE/E=4-9×10-3, depending on the experimental conditions. This performance enabled to substantially reduce background from neighbouring isotopes and to increase the detection efficiency. Due to the high sensitivity achieved, a value of 236U/238U=6.5×10-12 could be obtained, representing the smallest 236U/238U ratio measured until now.

Biogeochemical aspects of uranium mineralization, mining, milling, and remediation

USGS Publications Warehouse

Campbell, Kate M.; Gallegos, Tanya J.; Landa, Edward R.

2015-01-01

Natural uranium (U) occurs as a mixture of three radioactive isotopes: 238U, 235U, and 234U. Only 235U is fissionable and makes up about 0.7% of natural U, while 238U is overwhelmingly the most abundant at greater than 99% of the total mass of U. Prior to the 1940s, U was predominantly used as a coloring agent, and U-bearing ores were mined mainly for their radium (Ra) and/or vanadium (V) content; the bulk of the U was discarded with the tailings (Finch et al., 1972). Once nuclear fission was discovered, the economic importance of U increased greatly. The mining and milling of U-bearing ores is the first step in the nuclear fuel cycle, and the contact of residual waste with natural water is a potential source of contamination of U and associated elements to the environment. Uranium is mined by three basic methods: surface (open pit), underground, and solution mining (in situ leaching or in situ recovery), depending on the deposit grade, size, location, geology and economic considerations (Abdelouas, 2006). Solid wastes at U mill tailings (UMT) sites can include both standard tailings (i.e., leached ore rock residues) and solids generated on site by waste treatment processes. The latter can include sludge or “mud” from neutralization of acidic mine/mill effluents, containing Fe and a range of coprecipitated constituents, or barium sulfate precipitates that selectively remove Ra (e.g., Carvalho et al., 2007). In this chapter, we review the hydrometallurgical processes by which U is extracted from ore, the biogeochemical processes that can affect the fate and transport of U and associated elements in the environment, and possible remediation strategies for site closure and aquifer restoration.This paper represents the fourth in a series of review papers from the U.S. Geological Survey (USGS) on geochemical aspects of UMT management that span more than three decades. The first paper (Landa, 1980) in this series is a primer on the nature of tailings and radionuclide mobilization from them. The second paper (Landa, 1999) includes coverage of research carried out under the U.S. Department of Energy’s Uranium Mill Tailings Remedial Action Program (UMTRA). The third paper (Landa, 2004) reflects the increased focus of researchers on biotic effects in UMT environs. This paper expands the focus to U mining, milling, and remedial actions, and includes extensive coverage of the increasingly important alkaline in situ recovery and groundwater restoration.

Distribution of naturally occurring radionuclides (U, Th) in Timahdit black shale (Morocco).

PubMed

Galindo, C; Mougin, L; Fakhi, S; Nourreddine, A; Lamghari, A; Hannache, H

2007-01-01

Attention has been focused recently on the use of Moroccan black oil shale as the raw material for production of a new type of adsorbent and its application to U and Th removal from contaminated wastewaters. The purpose of the present work is to provide a better understanding of the composition and structure of this shale and to determine its natural content in uranium and thorium. A black shale collected from Timahdit (Morocco) was analyzed by powder X-ray diffraction and SEM techniques. It was found that calcite, dolomite, quartz and clays constitute the main composition of the inorganic matrix. Pyrite crystals are also present. A selective leaching procedure, followed by radiochemical purification and alpha-counting, was performed to assess the distribution of naturally occurring radionuclides. Leaching results indicate that 238U, 235U, 234U, 232Th, 230Th and 228Th have multiple modes of occurrence in the shale. U is interpreted to have been concentrated under anaerobic conditions. An integrated isotopic approach showed the preferential mobilization of uranium carried by humic acids to carbonate and apatite phases. Th is partitioned between silicate minerals and pyrite.

Fission Product Yields of 233U, 235U, 238U and 239Pu in Fields of Thermal Neutrons, Fission Neutrons and 14.7-MeV Neutrons

NASA Astrophysics Data System (ADS)

Laurec, J.; Adam, A.; de Bruyne, T.; Bauge, E.; Granier, T.; Aupiais, J.; Bersillon, O.; Le Petit, G.; Authier, N.; Casoli, P.

2010-12-01

The yields of more than fifteen fission products have been carefully measured using radiochemical techniques, for 235U(n,f), 239Pu(n,f) in a thermal spectrum, for 233U(n,f), 235U(n,f), and 239Pu(n,f) reactions in a fission neutron spectrum, and for 233U(n,f), 235U(n,f), 238U(n,f), and 239Pu(n,f) for 14.7 MeV monoenergetic neutrons. Irradiations were performed at the EL3 reactor, at the Caliban and Prospero critical assemblies, and at the Lancelot electrostatic accelerator in CEA-Valduc. Fissions were counted in thin deposits using fission ionization chambers. The number of fission products of each species were measured by gamma spectrometry of co-located thick deposits.

A COMPREHENSIVE STUDY OF THE NEUTRON ACTIVATION ANALYSIS OF URANIUM BY DELAYED-NEUTRON COUNTING

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dyer, F.F.; Emery, J.F.; Leddicotte, G.W.

The method of neutron activation analysis of U by delayed-neutron counting was investigated in order to ascertain if the method would be suitable for routine application to such analyses. It was shown that the method can be used extensively and routinely for the determination of U. Emphasis was placed on the determination of U in the types of sample materials encountered in nuclear technology. Determinations of U were made on such materials as ores, granite, sea sediments, biological tissue, graphite, and metal alloys. The method is based upon the fact that delayed neutrons are emitted from fission products from themore » interaction of neutrons with U/sup 235/. Since the U/sup 235/ component of U undergoes most of the fissions when a sample is in a neutron flux, the method is predominately one for the determination of U/sup 235/. The total U in a sample or the isotopic composition of the U in a sample can be determined provided there is a prior knowledge of one of these quantities. The U/sup 235/ content of a test sample is obtained by comparing its delayed-neutron count to that obtained with a comparator sample containing a known quantity of U/sup 235/. (auth)« less

Uranium 238U/235U isotope ratios as indicators of reduction: Results from an in situ biostimulation experiment at Rifle, Colorado, USA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bopp IV, C.J.; Lundstrom, C.C.; Johnson, T.M.

2010-02-01

The attenuation of groundwater contamination via chemical reaction is traditionally evaluated by monitoring contaminant concentration through time. However, this method can be confounded by common transport processes (e.g. dilution, sorption). Isotopic techniques bypass the limits of concentration methods, and so may provide improved accuracy in determining the extent of reaction. We apply measurements of {sup 238}U/{sup 235}U to a U bioremediation field experiment at the Rifle Integrated Field Research Challenge Site in Rifle, Colorado (USA). An array of monitoring and injection wells was installed on a 100 m{sup 2} plot where U(VI) contamination was present in the groundwater. Acetate-amended groundwatermore » was injected along an up-gradient gallery to encourage the growth of dissimilatory metal reducing bacteria (e.g. Geobacter species). During amendment, U concentration dropped by an order of magnitude in the experiment plot. We measured {sup 238}U/{sup 235}U in samples from one monitoring well by MC-ICP-MS using a double isotope tracer method. A significant {approx}1.00{per_thousand} decrease in {sup 238}U/{sup 235}U occurred in the groundwater as U(VI) concentration decreased. The relationship between {sup 238}U/{sup 235}U and concentration corresponds approximately to a Rayleigh distillation curve with an effective fractionation factor ({alpha}) of 1.00046. We attribute the observed U isotope fractionation to a nuclear field shift effect during enzymatic reduction of U(VI){sub (aq)} to U(IV){sub (s)}.« less

Natural and artificial radionuclides in a marine core. First results of 236U in North Atlantic Ocean sediments.

PubMed

Villa-Alfageme, M; Chamizo, E; Santos-Arévalo, F J; López-Gutierrez, J M; Gómez-Martínez, I; Hurtado-Bermúdez, S

2018-06-01

There are very few data available of 236 U in marine sediment cores. In this study we present the results from the first oceanic depth profile of 236 U in a sediment core sampled in the North Atlantic Ocean, at the PAP site (4500 m depth, Porcupine Abyssal Plain (PAP) site, 49°0' N, 16°30' W). Additionally, the sediment core was radiologically characterized through the measurement of anthropogenic 137 Cs, 239 Pu, 240 Pu, 129 I and 14 C and natural 210 Pb, 40 K and 226 Ra. The measured 236 U concentrations decrease from about 90·10 6  at g -1 at the seafloor down to 0.5·10 6  at g -1 at 6 cm depth. They are several orders of magnitude lower than the reported values for soils from the Northern Hemisphere solely influenced by global fallout (i.e. from 2700·10 6 to 7500·10 6  at g -1 ). 236 U/ 238 U atom ratios measured are at least three orders of magnitude above the estimated level for the naturally occurring dissolved uranium. The obtained inventories are 1·10 12  at m -2 for 236 U, 80 Bq m -2 for 137 Cs, 45 Bq m -2 for 239+240 Pu and 2.6·10 12  at m -2 for 129 I. Atomic ratios for 236 U/ 239 Pu, 137 Cs/ 236 U and 129 I/ 236 U, obtained from the inventories are 0.036, 0.11 and 2.5 respectively. Concentration profiles show mobilization probably due to bioturbation from the abundant detritivore holothurian species living at the PAP site sea-floor. The range of 236 U, 137 Cs, 239+240 Pu and 129 I values, inventories and ratios of these anthropogenic radionuclides are more similar to the values due to fall-out than values from a contribution from the Nuclear Fuel Reprocessing Plants dispersed to the south-west of the North Atlantic Ocean. However, signs of an additional source are detected and might be associated to the nuclear wastes dumped on the Eastern North Atlantic Ocean. Copyright © 2017 Elsevier Ltd. All rights reserved.

Analysis and application of heavy isotopes in the environment

NASA Astrophysics Data System (ADS)

Steier, Peter; Dellinger, Franz; Forstner, Oliver; Golser, Robin; Knie, Klaus; Kutschera, Walter; Priller, Alfred; Quinto, Francesca; Srncik, Michaela; Terrasi, Filippo; Vockenhuber, Christof; Wallner, Anton; Wallner, Gabriele; Wild, Eva Maria

2010-04-01

A growing number of AMS laboratories are pursuing applications of actinides. We discuss the basic requirements of the AMS technique of heavy (i.e., above ˜150 amu) isotopes, present the setup at the Vienna Environmental Research Accelerator (VERA) which is especially well suited for the isotope 236U, and give a comparison with other AMS facilities. Special emphasis will be put on elaborating the effective detection limits for environmental samples with respect to other mass spectrometric methods. At VERA, we have carried out measurements for radiation protection and environmental monitoring ( 236U, 239,240,241,242,244Pu), astrophysics ( 182Hf, 236U, 244Pu, 247Cm), nuclear physics, and a search for long-lived super-heavy elements ( Z > 100). We are pursuing the environmental distribution of 236U, as a basis for geological applications of natural 236U.

Determination of 235U/238U Ratio on Urine by ICP-MS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Collins, L; Gobaleza, A; Langston, R

2011-10-19

LLNL Internal Dosimetry Program - The new procedure satisfies the requirement to determine {sup 235}U/{sup 238}U ratio in bioassay urine samples. MDA - The L{sub C} and MDA{sub 95} for {sup 235}U are well below the required detection limit of 0.00035 {mu}g/L. Turn around time - Analysis of 10 samples plus 2 QCs can be completed in one work day (8 hours).

Measurement of the^ 235U(n,n')^235mU Integral Cross Section in a Pulsed Reactor

NASA Astrophysics Data System (ADS)

Vieira, D. J.; Bond, E. M.; Belier, G.; Meot, V.; Becker, J. A.; Macri, R. A.; Authier, N.; Hyneck, D.; Jacquet, X.; Jansen, Y.; Legrendre, J.

2009-10-01

We will present the integral measurement of the neutron inelastic cross section of ^235U leading to the 26-minute, E*=76.5 eV isomer state. Small samples (5-20 microgm) of isotope-enriched ^235U were activated in the central cavity of the CALIBAN pulsed reactor at Valduc where a nearly pure fission neutron spectrum is produced with a typical fluence of 3x10^14 n/cm^2. After 30 minutes the samples were removed from the reactor and counted in an electrostatic-deflecting electron spectrometer that was optimized for the detection of ^235mU conversion electrons. From the decay curve analysis of the data, the 26-minute ^235mU component was extracted. Preliminary results will be given and compared to gamma-cascade calculations assuming complete K-mixing or with no K-mixing.

238U and 235U isotope fractionation upon oxidation of uranium-bearing rocks by fracture waters

NASA Astrophysics Data System (ADS)

Chernyshev, I. V.; Golubev, V. N.; Chugaev, A. V.; Mandzhieva, G. V.

2016-10-01

The variations in 238U/235U values accompanying mobilization of U by fracture waters from uranium-bearing rocks, in which U occurs as a fine impregnation of oxides and silicates, were studied by the high-precision (±0.07‰) MC-ICP-MS method. Transition of U into the aqueous phase in the oxidized state U(VI) is accompanied by its isotope fractionation with enrichment of dissolved U(VI) in the heavy isotope 238U up to 0.32‰ in relation to the composition of the solid phases. According to the sign, this effect is consistent with the tendency of the behavior of 238U and 235U upon interaction of river waters with rocks of the catchment areas [11] and with the effect observed during oxidation of uraninite by the oxygen-bearing NaHCO3 solution [12].

First measurements of (236)U concentrations and (236)U/(239)Pu isotopic ratios in a Southern Hemisphere soil far from nuclear test or reactor sites.

PubMed

Srncik, M; Tims, S G; De Cesare, M; Fifield, L K

2014-06-01

The variation of the (236)U and (239)Pu concentrations as a function of depth has been studied in a soil profile at a site in the Southern Hemisphere well removed from nuclear weapon test sites. Total inventories of (236)U and (239)Pu as well as the (236)U/(239)Pu isotopic ratio were derived. For this investigation a soil core from an undisturbed forest area in the Herbert River catchment (17°30' - 19°S) which is located in north-eastern Queensland (Australia) was chosen. The chemical separation of U and Pu was carried out with a double column which has the advantage of the extraction of both elements from a relatively large soil sample (∼20 g) within a day. The samples were measured by Accelerator Mass Spectrometry using the 14UD pelletron accelerator at the Australian National University. The highest atom concentrations of both (236)U and (239)Pu were found at a depth of 2-3 cm. The (236)U/(239)Pu isotopic ratio in fallout at this site, as deduced from the ratio of the (236)U and (239)Pu inventories, is 0.085 ± 0.003 which is clearly lower than the Northern Hemisphere value of ∼0.2. The (236)U inventory of (8.4 ± 0.3) × 10(11) at/m(2) was more than an order of magnitude lower than values reported for the Northern Hemisphere. The (239)Pu activity concentrations are in excellent agreement with a previous study and the (239+240)Pu inventory was (13.85 ± 0.29) Bq/m(2). The weighted mean (240)Pu/(239)Pu isotopic ratio of 0.142 ± 0.005 is slightly lower than the value for global fallout, but our results are consistent with the average ratio of 0.173 ± 0.027 for the southern equatorial region (0-30°S). Copyright © 2014 Elsevier Ltd. All rights reserved.

Meta-analysis of depleted uranium levels in the Middle East region.

PubMed

Bešić, Larisa; Muhović, Imer; Mrkulić, Fatima; Spahić, Lemana; Omanović, Ammar; Kurtovic-Kozaric, Amina

2018-06-08

Since the first widespread use of depleted uranium in military in the 1991 Gulf War, the so-called "Gulf War Syndrome" has been a topic of ongoing debate. However, a low number of reliable scientific papers demonstrating the extent of possible contamination as well as its connection to the health status of residents and deployed veterans has been published. The authors of this study have therefore aimed to make a selection of data based on strict inclusion and exclusion criteria. With the goal of clarifying the extent of DU contamination after the Gulf Wars, previously published data regarding the levels of DU in the Middle East region were analyzed and presented in the form of a meta-analysis. In addition, the authors attempted to make a correlation between the DU levels and their possible effects on afflicted populations. According to results observed by comparing 234 U/ 238 U and 235 U/ 238 U isotopic activity ratios, as well as 235 U/ 238 U mass ratios in air, water, soil and food samples among the countries in the Middle East region, areas indicating contamination with DU were Al Doha, Manageesh and Um Al Kwaty in Kuwait, Al-Salman, Al-Nukhaib and Karbala in Iraq, Beirut in Lebanon and Sinai in Egypt. According to these data, no DU contamination was observed in Algeria, Israel, Afghanistan, Oman, Qatar, Iran, and Yemen. Due to the limited number of reliable data on the health status of afflicted populations, it was not possible to make a correlation between DU levels and health effects in the Middle East region. Copyright © 2018. Published by Elsevier Ltd.

Uranium from German Nuclear Power Projects of the 1940s— A Nuclear Forensic Investigation

PubMed Central

Mayer, Klaus; Wallenius, Maria; Lützenkirchen, Klaus; Horta, Joan; Nicholl, Adrian; Rasmussen, Gert; van Belle, Pieter; Varga, Zsolt; Buda, Razvan; Erdmann, Nicole; Kratz, Jens-Volker; Trautmann, Norbert; Fifield, L Keith; Tims, Stephen G; Fröhlich, Michaela B; Steier, Peter

2015-01-01

Here we present a nuclear forensic study of uranium from German nuclear projects which used different geometries of metallic uranium fuel.3b,d, 4 Through measurement of the 230Th/234U ratio, we could determine that the material had been produced in the period from 1940 to 1943. To determine the geographical origin of the uranium, the rare-earth-element content and the 87Sr/86Sr ratio were measured. The results provide evidence that the uranium was mined in the Czech Republic. Trace amounts of 236U and 239Pu were detected at the level of their natural abundance, which indicates that the uranium fuel was not exposed to any major neutron fluence. PMID:26501922

European roe deer antlers as an environmental archive for fallout (236)U and (239)Pu.

PubMed

Froehlich, M B; Steier, P; Wallner, G; Fifield, L K

2016-01-01

Anthropogenic (236)U and (239)Pu were measured in European roe deer antlers hunted between 1955 and 1977 which covers and extends beyond the period of intensive nuclear weapons testing (1954-1962). The antlers were hunting trophies, and hence the hunting area, the year of shooting and the approximate age of each animal is given. Uranium and plutonium are known to deposit in skeletal tissue. Since antler histology is similar to bone, both elements were expected in antlers. Furthermore, roe deer shed their antlers annually, and hence antlers may provide a time-resolved environmental archive for fallout radionuclides. The radiochemical procedure is based on a Pu separation step by anion exchange (Dowex 1 × 8) and a subsequent U purification by extraction chromatography using UTEVA(®). The samples were measured by Accelerator Mass Spectrometry at the VERA facility (University of Vienna). In addition to the (236)U and (239)Pu concentrations, the (240)Pu/(239)Pu isotopic ratios were determined with a mean value of 0.172 ± 0.023 which is in agreement with the ratio of global fallout (∼0.18). Rather high (236)U/(238)U ratios of the order of 10(-6) were observed. These measured ratios, where the (236)U arises only from global fallout, have implications for the use of the (236)U/(238)U ratio as a fingerprint for nuclear accidents or releases from nuclear facilities. Our investigations have shown the potential to use antlers as a temporally resolved archive for the uptake of actinides from the environment. Copyright © 2015 Elsevier Ltd. All rights reserved.

U-Pb ages of secondary silica at Yucca Mountain, Nevada: Implications for the paleohydrology of the unsaturated zone

USGS Publications Warehouse

Neymark, L.A.; Amelin, Y.; Paces, J.B.; Peterman, Z.E.

2002-01-01

Uranium, Th and Pb isotopes were analyzed in layers of opal and chalcedony from individual mm- to cm-thick calcite and silica coatings at Yucca Mountain, Nevada, USA, a site that is being evaluated for a potential high-level nuclear waste repository. These calcite and silica coatings on fractures and in lithophysal cavities in Miocene-age tuffs in the unsaturated zone (UZ) precipitated from descending water and record a long history of percolation through the UZ. Opal and chalcedony have high concentrations of U (10 to 780 ppm) and low concentrations of common Pb as indicated by large values of 206Pb/204Pb (up to 53,806), thus making them suitable for U-Pb age determinations. Interpretations of U-Pb isotope systems in opal samples at Yucca Mountain are complicated by the incorporation of excess 234U at the time of mineral formation, resulting in reverse discordance of U-Pb ages. However, the 207PB/235U ages are much less affected by deviation from initial secular equilibrium and provide reliable ages of most silica deposits between 0.6 and 9.8 Ma. For chalcedony subsamples showing normal age discordance, these ages may represent minimum times of deposition. Typically, 207Pb/235U ages are consistent with the microstratigraphy in the mineral coating samples, such that the youngest ages are for subsamples from outer layers, intermediate ages are from inner layers, and oldest ages are from innermost layers. 234U and 230Th in most silica layers deeper in the coatings are in secular equilibrium with 238U, which is consistent with their old age and closed system behavior during the past -0.5 Ma. The ages for subsamples of silica layers from different microstratigraphic positions in individual calcite and silica coating samples collected from lithophysal cavities in the welded part of the Topopah Spring Tuff yield slow long-term average growth rates of 1 to 5 mm/Ma. These data imply that the deeper parts of the UZ at Yucca Mountain maintained long-term hydrologic stability over the past 10 Ma. despite significant climate variations. U-Pb ages for subsamples of silica layers from different microstratigraphic positions in individual calcite and silica coating samples collected from fractures in the shallower part of the UZ (welded part of the overlying Tiva Canyon Tuff) indicate larger long-term average growth rates up to 23 mm/Ma and an absence of recently deposited materials (ages of outermost layers are 3-5 Ma.). These differences between the characteristics of the coatings for samples from the shallower and deeper parts of the UZ may indicate that the nonwelded tuffs (PTn), located between the welded parts of the Tiva Canyon and Topopah Spring Tuffs, play an important role in moderating UZ flow.

Uranium isotope ratios of Muonionalusta troilite and complications for the absolute age of the IVA iron meteorite core

NASA Astrophysics Data System (ADS)

Brennecka, Gregory A.; Amelin, Yuri; Kleine, Thorsten

2018-05-01

The crystallization ages of planetary crustal material (given by basaltic meteorites) and planetary cores (given by iron meteorites) provide fiducial marks for the progress of planetary formation, and thus, the absolute ages of these objects fundamentally direct our knowledge and understanding of planet formation and evolution. The lone precise absolute age of planetary core material was previously obtained on troilite inclusions from the IVA iron meteorite Muonionalusta. This previously reported Pb-Pb age of 4565.3 ± 0.1 Ma-assuming a 238U/235U =137.88-only post-dated the start of the Solar System by approximately 2-3 million years, and mandated fast cooling of planetary core material. Since an accurate Pb-Pb age requires a known 238U/235U of the sample, we have measured both 238U/235U and Pb isotopic compositions of troilite inclusions from Muonionalusta. The measured 238U/235U of the samples range from ∼137.84 to as low as ∼137.22, however based on Pb and U systematics, terrestrial contamination appears pervasive and has affected samples to various extents for Pb and U. The cause of the relative 235U excess in one sample does not appear to be from terrestrial contamination or the decay of short-lived 247Cm, but is more likely from fractionation of U isotopes during metal-silicate separation during core formation, exacerbated by the extreme U depletion in the planetary core. Due to limited Pb isotopic variation and terrestrial disturbance, no samples of this study produced useful age information; however the clear divergence from the previously assumed 238U/235U of any troilite in Muonionalusta introduces substantial uncertainty to the previously reported absolute age of the sample without knowledge of the 238U/235U of the sample. Uncertainties associated with U isotope heterogeneity do not allow for definition of a robust age of solidification and cooling for the IVA core. However, one sample of this work-paired with previous work using short-lived radionuclides-suggests that the cooling age of the IVA core may be significantly younger than previously thought. This work indicates the metallic cores of protoplanetary bodies solidified no earlier than the first ∼5-10 million years of the Solar System.

Chronology of Pu isotopes and 236U in an Arctic ice core.

PubMed

Wendel, C C; Oughton, D H; Lind, O C; Skipperud, L; Fifield, L K; Isaksson, E; Tims, S G; Salbu, B

2013-09-01

In the present work, state of the art isotopic fingerprinting techniques are applied to an Arctic ice core in order to quantify deposition of U and Pu, and to identify possible tropospheric transport of debris from former Soviet Union test sites Semipalatinsk (Central Asia) and Novaya Zemlya (Arctic Ocean). An ice core chronology of (236)U, (239)Pu, and (240)Pu concentrations, and atom ratios, measured by accelerator mass spectrometry in a 28.6m deep ice core from the Austfonna glacier at Nordaustlandet, Svalbard is presented. The ice core chronology corresponds to the period 1949 to 1999. The main sources of Pu and (236)U contamination in the Arctic were the atmospheric nuclear detonations in the period 1945 to 1980, as global fallout, and tropospheric fallout from the former Soviet Union test sites Novaya Zemlya and Semipalatinsk. Activity concentrations of (239+240)Pu ranged from 0.008 to 0.254 mBq cm(-2) and (236)U from 0.0039 to 0.053 μBq cm(-2). Concentrations varied in concordance with (137)Cs concentrations in the same ice core. In contrast to previous published results, the concentrations of Pu and (236)U were found to be higher at depths corresponding to the pre-moratorium period (1949 to 1959) than to the post-moratorium period (1961 and 1962). The (240)Pu/(239)Pu ratio ranged from 0.15 to 0.19, and (236)U/(239)Pu ranged from 0.18 to 1.4. The Pu atom ratios ranged within the limits of global fallout in the most intensive period of nuclear atmospheric testing (1952 to 1962). To the best knowledge of the authors the present work is the first publication on biogeochemical cycles with respect to (236)U concentrations and (236)U/(239)Pu atom ratios in the Arctic and in ice cores. Copyright © 2013 Elsevier B.V. All rights reserved.

Transatlantic Regulatory Cooperation: Background and Analysis

DTIC Science & Technology

2008-10-22

Damien Geradin, “Regulatory Co - opetition ,” Journal of International Economic Law (2000), 235-255, p. 236. 15 Transatlantic Policy Network (TPN), Completing... co -chairs (ministerial-level appointees with cabinet rank) from each side, as well as a number of EU Commissioners and U.S. Cabinet Members for the...broad ranging policy areas covered in the Framework. Currently, the co -chairs are Daniel Price, Assistant to the President for International Economic

Estimated Marine Residence Times for Drowned Barbadian Paleoreefs

NASA Astrophysics Data System (ADS)

Mey, J. L.

2008-12-01

Fossil corals are used to estimate past sea level and also to calibrate 14C ages with the aid of U-Th and U-Pa dating methods. These coral fossils have often been subaerially exposed and thus are affected by diagenesis during their initial interaction with fresh water. In an effort to understand when such disequilibria in fossil coral reefs occurred, we have quantified our 'dissolution-cum-adsorption' model (Mey, 2008) for the uranium series disequilibria using a geometrical construction, based on the evolution of the activities in a 230Th/238U versus 234U/238U diagram for closed versus open systems. The traditional age equations for the uranium-series with excess daughters have been used to construct a relationship between (i) the angles of the equal age lines in the 230Th/238U versus 234U/238U activity diagrams, and (ii) the quantified angles of the regressed lines of several uranium series disequilibria trends from Barbados. Our results indicate that the severity of the Barbados uranium series disequilibria is not only explained by 234U and 230Th addition, but may also reflect a loss of 238U through dissolution of coral skeletal structure. The net effect is 238U removal, whereas 234U and 230Th remain; thus, the disequilibria for the extant coral increase the excess daughters' ratio. Our results further indicate that the activity of 234U is reduced (compared to 230Th), as would be expected in regard to the lower mobility of trapped 230Th. It is proposed that the major dissolution that caused the uranium series disequilibria occurred during one relatively short-lived event when the paleoreefs experienced the very first freshwater exposure. During this event, the diagenetic potential was at its maximum for redistribution of the uranium series; this then caused the 234U and the 230Th to behave in a systematic way, resulting in linear trends. The linear trends in the open system uranium series were set early, as shown in the 230Th/238U versus 234U/238U activity diagrams. The timing of the first exposure of the freshwater in the reefs is calculated based on the results of our new model. From the relationship between, (i) dissolution, (ii) in-grown 230Th, and (iii) excess 234U, we derived that the 60,000 old Marine Isotope stage 3 (MIS 3) reef was exposed to freshwater 36-38,000 years after growth in the marine environment. We have calculated these 'marine residence times' for the MIS 3 5a, 5c, 5e, 6.0, 7a and 7c reefs; our results correspond with the duration of the sea level high stand in each of the stages. References: Mey, J. L., (2008) The Uranium Series Diagenesis and the Morphology of Drowned Barbadian Paleoreefs, PhD dissertation, 325pp: Graduate Center, City University of New York, New York.

234U/238U isotope data from groundwater and solid-phase leachate samples near Tuba City Open Dump, Tuba City, Arizona

USGS Publications Warehouse

Johnson, Raymond H.; Horton, Robert J.; Otton, James K.; Ketterer, Michael K.

2012-01-01

This report releases 234U/238U isotope data, expressed as activity ratios, and uranium concentration data from analyses completed at Northern Arizona University for groundwater and solid-phase leachate samples that were collected in and around Tuba City Open Dump, Tuba City, Arizona, in 2008.

Concentrations of selected radionuclides and their spatial distribution in marine sediments from the northwestern Gulf, Kuwait.

PubMed

Uddin, Saif; Behbehani, Montaha

2018-02-01

This study focuses on creating a baseline for 40 K, 210 Pb, 137 Cs, 90 Sr, 226 Ra, 228 Ra, 238 U, 235 U, 234 U, 239+240 Pu and 238 Pu in marine sediments in the northwestern Gulf. The respective measured concentration ranges were 386-489, 32.3-48.8, 1.5-2.9, 4.53-5.42, 18.3-23.1, 18.8-23.0, 22.3-30.5, 0.99-1.33, 25.6-34.8, 0.30-0.93, and 0.0008-0.00018Bqkg -1 . The levels of these radionuclides are generally comparable to values reported for other marine waters in the northern hemisphere. The 137 Cs activity in the Gulf sediments offshore Kuwait is an order of magnitude lower compared to sediments from northeastern Iran. Other than that finding, no hot spots were observed in sediments adjacent to power and desalination plants, oil and gas industrial activities or wastewater treatment facilities. These data will serve as a baseline to gauge possible future inputs of radionuclides in the northern Gulf. The calculated average ratio of 235 U/ 238 U activity in the area is in agreement with the reported figure of the natural uranium ratio, suggesting the absence of depleted uranium (DU) at all the stations. The low concentration of 239+240 Pu suggests that there is no significant source of plutonium except that from atmospheric fallout from weapon testing and possible dry deposition via long-range dust transport. Copyright © 2017 Elsevier Ltd. All rights reserved.

Theoretical Model for Volume Fraction of UC, 235U Enrichment, and Effective Density of Final U 10Mo Alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Devaraj, Arun; Prabhakaran, Ramprashad; Joshi, Vineet V.

2016-04-12

The purpose of this document is to provide a theoretical framework for (1) estimating uranium carbide (UC) volume fraction in a final alloy of uranium with 10 weight percent molybdenum (U-10Mo) as a function of final alloy carbon concentration, and (2) estimating effective 235U enrichment in the U-10Mo matrix after accounting for loss of 235U in forming UC. This report will also serve as a theoretical baseline for effective density of as-cast low-enriched U-10Mo alloy. Therefore, this report will serve as the baseline for quality control of final alloy carbon content

Potential effects of alpha-recoil on uranium-series dating of calcrete

USGS Publications Warehouse

Neymark, L.A.

2011-01-01

Evaluation of paleosol ages in the vicinity of Yucca Mountain, Nevada, at the time the site of a proposed high-level nuclear waste repository, is important for fault-displacement hazard assessment. Uranium-series isotope data were obtained for surface and subsurface calcrete samples from trenches and boreholes in Midway Valley, Nevada, adjacent to Yucca Mountain. 230Th/U ages of 33 surface samples range from 1.3 to 423 thousand years (ka) and the back-calculated 234U/238U initial activity ratios (AR) are relatively constant with a mean value of 1.54 ± 0.15 (1σ), which is consistent with the closed-system behavior. Subsurface calcrete samples are too old to be dated by the 230Th/U method. U-Pb data for post-pedogenic botryoidal opal from a subsurface calcrete sample show that these subsurface calcrete samples are older than ~ 1.65 million years (Ma), old enough to have attained secular equilibrium had their U-Th systems remained closed. However, subsurface calcrete samples show U-series disequilibrium indicating open-system behavior of 238U daughter isotopes, in contrast with the surface calcrete, where open-system behavior is not evident. Data for 21 subsurface calcrete samples yielded calculable 234U/238U model ages ranging from 130 to 1875 ka (assuming an initial AR of 1.54 ± 0.15, the mean value calculated for the surface calcrete samples). A simple model describing continuous α-recoil loss predicts that the 234U/238U and 230Th/238U ARs reach steady-state values ~ 2 Ma after calcrete formation. Potential effects of open-system behavior on 230Th/U ages and initial 234U/238U ARs for younger surface calcrete were estimated using data for old subsurface calcrete samples with the 234U loss and assuming that the total time of water-rock interaction is the only difference between these soils. The difference between the conventional closed-system and open-system ages may exceed errors of the calculated conventional ages for samples older than ~ 250 ka, but is negligible for younger soils.

Radionuclide Transport in Fracture-Granite Interface Zones

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Q; Mori, A

In situ radionuclide migration experiments, followed by excavation and sample characterization, were conducted in a water-conducting shear zone at the Grimsel Test Site (GTS) in Switzerland to study diffusion paths of radionuclides in fractured granite. In this work, we employed a micro-scale mapping technique that interfaces laser ablation sampling with inductively coupled plasma-mass spectrometry (LA/ICP-MS) to measure the fine-scale (micron-range) distribution of actinides ({sup 234}U, {sup 235}U, and {sup 237}Np) in the fracture-granite interface zones. Long-lived {sup 234}U, {sup 235}U, and {sup 237}Np were detected in flow channels, as well as in the adjacent rock matrix, using the sensitive, feature-basedmore » mapping of the LA/ICP-MS technique. The injected sorbing actinides are mainly located within the advective flowing fractures and the immediately adjacent regions. The water-conducting fracture studied in this work is bounded on one side by mylonite and the other by granitic matrix regions. These actinides did not penetrate into the mylonite side as much as the relatively higher-porosity granite matrix, most likely due to the low porosity, hydraulic conductivity, and diffusivity of the fracture wall (a thickness of about 0.4 mm separates the mylonite region from the fracture) and the mylonite region itself. Overall, the maximum penetration depth detected with this technique for the more diffusive {sup 237}Np over the field experimental time scale of about 60 days was about 10 mm in the granitic matrix, illustrating the importance of matrix diffusion in retarding radionuclide transport from the advective fractures. Laboratory tests and numerical modeling of radionuclide diffusion into granitic matrix was conducted to complement and help interpret the field results. Measured apparent diffusivity of multiple tracers in granite provided consistent predictions for radionuclide transport in the fractured granitic rock.« less

^2^3^8U/^2^3^5U Ratios of Anagrams: Angrites and Granites

NASA Astrophysics Data System (ADS)

Tissot, F. L. H.; Dauphas, N.

2012-03-01

We report ^2^3^8U/^2^3^5U ratios of five angrites and give the corresponding Pb-Pb ages of D'Orbigny and Angra Dos Reis. The U-isotopic composition of terrestrial granites (I, S, and A types) is also assessed to determine the influence of the protolith.

Determination of 238u/235u, 236u/238u and uranium concentration in urine using sf-icp-ms and mc-icp-ms: an interlaboratory comparison.

PubMed

Parrish, Randall R; Thirlwall, Matthew F; Pickford, Chris; Horstwood, Matthew; Gerdes, Axel; Anderson, James; Coggon, David

2006-02-01

Accidental exposure to depleted or enriched uranium may occur in a variety of circumstances. There is a need to quantify such exposure, with the possibility that the testing may post-date exposure by months or years. Therefore, it is important to develop a very sensitive test to measure precisely the isotopic composition of uranium in urine at low levels of concentration. The results of an interlaboratory comparison using sector field (SF)-inductively coupled plasma-mass spectrometry (ICP-MS) and multiple collector (MC)-ICP-MS for the measurement of uranium concentration and U/U and U/U isotopic ratios of human urine samples are presented. Three urine samples were verified to contain uranium at 1-5 ng L and shown to have natural uranium isotopic composition. Portions of these urine batches were doped with depleted uranium (DU) containing small quantities of U, and the solutions were split into 100 mL and 400 mL aliquots that were subsequently measured blind by three laboratories. All methods investigated were able to measure accurately U/U with precisions of approximately 0.5% to approximately 4%, but only selected MC-ICP-MS methods were capable of consistently analyzing U/U to reasonable precision at the approximately 20 fg L level of U abundance. Isotope dilution using a U tracer demonstrates the ability to measure concentrations to better than +/-4% with the MC-ICP-MS method, though sample heterogeneity in urine samples was shown to be problematic in some cases. MC-ICP-MS outperformed SF-ICP-MS methods, as was expected. The MC-ICP-MS methodology described is capable of measuring to approximately 1% precision the U/U of any sample of human urine over the entire range of uranium abundance down to <1 ng L, and detecting very small amounts of DU contained therein.

Dispersion of the Neutron Emission in U{sup 235} Fission

DOE R&D Accomplishments Database

Feynman, R. P.; de Hoffmann, F.; Serber, R.

1955-01-01

Equations are developed which allow the calculation of the average number of neutrons per U{sup235} fission from experimental measurements. Experimental methods are described, the results of which give a value of (7.8 + 0.6){sup ?} neutrons per U{sup 235} thermal fission.

Prompt neutron emission and energy balance in 235U(n,f)

NASA Astrophysics Data System (ADS)

Göök, Alf; Hambsch, Franz-Josef; Oberstedt, Stephan

2017-09-01

Investigations of prompt fission neutron (PFN) emission are of importance in understanding the fission process in general and the sharing of excitation energy among the fission fragments in particular. Experimental activities at JRC-Geel on PFN emission in response to OECD/NEA nuclear data requests is presented in this contribution. The focus lies on on-going investigations of PFN emission from the reaction 235U(n,f) in the region of the resolved resonances taking place at the GELINA facility. For this reaction strong fluctuations of fission fragment mass distributions and mean total kinetic energy have been observed as a function of incident neutron energy in the resonance region. In addition, fluctuations of prompt neutron multiplicities have also been observed. The goal of the present study is to verify the current knowledge of PFN multiplicity fluctuations and to study correlations with fission fragment properties. The experiment employs a scintillation detector array for neutron detection, while fission fragment properties are determined via the double kinetic energy technique using a position sensitive twin ionization chamber. Results on PFN multiplicity correlations with fission fragment properties from the present study show significant differences compared to earlier studies on this reaction, induced by thermal neutrons. Specifically, the total kinetic energy dependence of the neutron multiplicity per fission shows an inverse slope FX1TKE/FX2ν approximately 35% weaker than observed in earlier studies of thermal neutron induced fission on 235U. The inverse slope is related to the energy carried away per emitted neutron and is, thereby, closely connected to the energy balance of the fission reaction. The present result should have strong impact on the modeling of both prompt neutron and prompt γ-ray emission in fission of the 236U compound nucleus.

The timing of high sea levels over the past 200,000 years

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gallup, C.D.; Edwards, R.L.; Johnson, R.G.

1994-02-11

The [sup 230]Th ages and [sup 234]U/[sup 238]U ratios were determined for Barbados corals that grew during periods of high sea level within the last 200,000 years. The similarity of the initial [sup 234]U/[sup 238]U ratios of some of the corals to the modern marine value suggests that these samples are pristine and that the marine [sup 234]U/[sup 238]U ratio 83,000 and 200,000 years ago was within 2 per mil of the modern value. The accuracies of the [sup 230]Th ages are evaluated on the basis of the [sup 234]U/[sup 238]U values and a model of the behavior of uraniummore » and thorium isotopes during diagenesis. For the last three interglacial and two intervening interstadial periods, sea level peaked at or after peaks in summer insolation in the Northern Hemisphere. This overall pattern supports the idea that glacial-interglacial cycles are caused by changes in Earth's orbital geometry. The sea-level drop at the end of the penultimate interglacial, the last interglacial, and a subsequent interstadial period lagged behind the decrease in insolation by 5,000 to 10,000 years.« less

Radiation Doses to Members of the U.S. Population from Ubiquitous Radionuclides in the Body: Part 1, Autopsy and In Vivo Data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Watson, David J.; Strom, Daniel J.

This paper is part one of a three-part series investigating annual effective doses to residents of the United States from intakes of ubiquitous radionuclides, including radionuclides occurring naturally, radionuclides whose concentrations are technologically enhanced, and anthropogenic radionuclides. This series of papers explicitly excludes intakes from inhaling 222Rn, 220Rn, and their short-lived decay products; it also excludes intakes of radionuclides in occupational and medical settings. The goal of part one of this work was to review, summarize, and characterize all published and some unpublished data for U.S. residents on ubiquitous radionuclide concentrations in tissues and organs. Forty-five papers and reports weremore » obtained and their data reviewed, and three data sets were obtained via private communication. The 45 radionuclides of interest are the 238U series (14 nuclides), the actinium series (headed by 235U; 11 nuclides), and the 232Th series (11 nuclides); primordial radionuclides 87Rb and 40 K; cosmogenic and fallout radionuclides 14C and 3H; and purely anthropogenic radionuclides 137Cs-137mBa, 129I, and 90Sr-90Y. Measurements judged to be relevant were available for only 15 of these radionuclides: 238U, 235U, 234U, 232Th, 230Th, 228Th, 228Ra, 226Ra, 210Pb, 210Po, 137Cs, 87Rb, 40K, 14C, and 3H. Recent and relevant measurements were not available for 129I and 90Sr-90Y. A total of 11,714 radionuclide concentration measurements were found in one or more tissues or organs from 14 States. Data on age, sex, geographic locations, height, and weight of subjects were available only sporadically. Too often authors did not provide meaningful values of uncertainty of measurements so that variability in data sets is confounded with measurement uncertainty. The following papers detail how these shortcomings are overcome to achieve the goals of the three-part series.« less

IAEA CIELO Evaluation of Neutron-induced Reactions on 235U and 238U Targets

DOE PAGES

Capote, R.; Trkov, A.; Sin, M.; ...

2018-02-01

Evaluations of nuclear reaction data for the major uranium isotopes 238U and 235U were performed within the scope of the CIELO Project on the initiative of the OECD/NEA Data Bank under Working Party on Evaluation Co-operation (WPEC) Subgroup 40 coordinated by the IAEA Nuclear Data Section. Both the mean values and covariances are evaluated from 10 -5 eV up to 30 MeV. The resonance parameters of 238U and 235U were re-evaluated with the addition of newly available data to the existing experimental database. The evaluations in the fast neutron range are based on nuclear model calculations with the code EMPIRE–3.2more » Malta above the resonance range up to 30 MeV. 235U(n,f), 238U(n,f), and 238U(n,γ) cross sections and 235U(n th,f) prompt fission neutron spectrum (PFNS) were evaluated within the Neutron Standards project and are representative of the experimental state-of-the-art measurements. The Standards cross sections were matched in model calculations as closely as possible to guarantee a good predictive power for cross sections of competing neutron scattering channels. 235U(n,γ) cross section includes fluctuations observed in recent experiments. 235U(n,f) PFNS for incident neutron energies from 500 keV to 20 MeV were measured at Los Alamos Chi-Nu facility and re-evaluated using all available experimental data. While respecting the measured differential data, several compensating errors in previous evaluations were identified and removed so that the performance in integral benchmarks was restored or improved. Covariance matrices for 235U and 238U cross sections, angular distributions, spectra and neutron multiplicities were evaluated using the GANDR system that combines experimental data with model uncertainties. Unrecognized systematic uncertainties were considered in the uncertainty quantification for fission and capture cross sections above the thermal range, and for neutron multiplicities. Evaluated files were extensively benchmarked to ensure good performance in reactor calculations and fusion-related systems. New comprehensive evaluations show excellent agreement with available differential data and integral performance better than current evaluated data libraries, and represent a step forward in a quest for better nuclear data for applications.« less

IAEA CIELO Evaluation of Neutron-induced Reactions on 235U and 238U Targets

NASA Astrophysics Data System (ADS)

Capote, R.; Trkov, A.; Sin, M.; Pigni, M. T.; Pronyaev, V. G.; Balibrea, J.; Bernard, D.; Cano-Ott, D.; Danon, Y.; Daskalakis, A.; Goričanec, T.; Herman, M. W.; Kiedrowski, B.; Kopecky, S.; Mendoza, E.; Neudecker, D.; Leal, L.; Noguere, G.; Schillebeeckx, P.; Sirakov, I.; Soukhovitskii, E. S.; Stetcu, I.; Talou, P.

2018-02-01

Evaluations of nuclear reaction data for the major uranium isotopes 238U and 235U were performed within the scope of the CIELO Project on the initiative of the OECD/NEA Data Bank under Working Party on Evaluation Co-operation (WPEC) Subgroup 40 coordinated by the IAEA Nuclear Data Section. Both the mean values and covariances are evaluated from 10-5 eV up to 30 MeV. The resonance parameters of 238U and 235U were re-evaluated with the addition of newly available data to the existing experimental database. The evaluations in the fast neutron range are based on nuclear model calculations with the code EMPIRE-3.2 Malta above the resonance range up to 30 MeV. 235U(n,f), 238U(n,f), and 238U(n,γ) cross sections and 235U(nth,f) prompt fission neutron spectrum (PFNS) were evaluated within the Neutron Standards project and are representative of the experimental state-of-the-art measurements. The Standards cross sections were matched in model calculations as closely as possible to guarantee a good predictive power for cross sections of competing neutron scattering channels. 235U(n,γ) cross section includes fluctuations observed in recent experiments. 235U(n,f) PFNS for incident neutron energies from 500 keV to 20 MeV were measured at Los Alamos Chi-Nu facility and re-evaluated using all available experimental data. While respecting the measured differential data, several compensating errors in previous evaluations were identified and removed so that the performance in integral benchmarks was restored or improved. Covariance matrices for 235U and 238U cross sections, angular distributions, spectra and neutron multiplicities were evaluated using the GANDR system that combines experimental data with model uncertainties. Unrecognized systematic uncertainties were considered in the uncertainty quantification for fission and capture cross sections above the thermal range, and for neutron multiplicities. Evaluated files were extensively benchmarked to ensure good performance in reactor calculations and fusion-related systems. New comprehensive evaluations show excellent agreement with available differential data and integral performance better than current evaluated data libraries, and represent a step forward in a quest for better nuclear data for applications.

IAEA CIELO Evaluation of Neutron-induced Reactions on 235U and 238U Targets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Capote, R.; Trkov, A.; Sin, M.

Evaluations of nuclear reaction data for the major uranium isotopes 238U and 235U were performed within the scope of the CIELO Project on the initiative of the OECD/NEA Data Bank under Working Party on Evaluation Co-operation (WPEC) Subgroup 40 coordinated by the IAEA Nuclear Data Section. Both the mean values and covariances are evaluated from 10 -5 eV up to 30 MeV. The resonance parameters of 238U and 235U were re-evaluated with the addition of newly available data to the existing experimental database. The evaluations in the fast neutron range are based on nuclear model calculations with the code EMPIRE–3.2more » Malta above the resonance range up to 30 MeV. 235U(n,f), 238U(n,f), and 238U(n,γ) cross sections and 235U(n th,f) prompt fission neutron spectrum (PFNS) were evaluated within the Neutron Standards project and are representative of the experimental state-of-the-art measurements. The Standards cross sections were matched in model calculations as closely as possible to guarantee a good predictive power for cross sections of competing neutron scattering channels. 235U(n,γ) cross section includes fluctuations observed in recent experiments. 235U(n,f) PFNS for incident neutron energies from 500 keV to 20 MeV were measured at Los Alamos Chi-Nu facility and re-evaluated using all available experimental data. While respecting the measured differential data, several compensating errors in previous evaluations were identified and removed so that the performance in integral benchmarks was restored or improved. Covariance matrices for 235U and 238U cross sections, angular distributions, spectra and neutron multiplicities were evaluated using the GANDR system that combines experimental data with model uncertainties. Unrecognized systematic uncertainties were considered in the uncertainty quantification for fission and capture cross sections above the thermal range, and for neutron multiplicities. Evaluated files were extensively benchmarked to ensure good performance in reactor calculations and fusion-related systems. New comprehensive evaluations show excellent agreement with available differential data and integral performance better than current evaluated data libraries, and represent a step forward in a quest for better nuclear data for applications.« less

Computer program FPIP-REV calculates fission product inventory for U-235 fission

NASA Technical Reports Server (NTRS)

Brown, W. S.; Call, D. W.

1967-01-01

Computer program calculates fission product inventories and source strengths associated with the operation of U-235 fueled nuclear power reactor. It utilizes a fission-product nuclide library of 254 nuclides, and calculates the time dependent behavior of the fission product nuclides formed by fissioning of U-235.

10 CFR 150.11 - Critical mass.

Code of Federal Regulations, 2013 CFR

2013-01-01

... uranium enriched in the isotope U-235 in quantities not exceeding 350 grams of contained U-235; uranium-233 in quantities not exceeding 200 grams; plutonium in quantities not exceeding 200 grams; or any... not exceed the limitation and are within the formula, as follows: (175 (grams contained U-235/350)+(50...

10 CFR 150.11 - Critical mass.

Code of Federal Regulations, 2011 CFR

2011-01-01

... uranium enriched in the isotope U-235 in quantities not exceeding 350 grams of contained U-235; uranium-233 in quantities not exceeding 200 grams; plutonium in quantities not exceeding 200 grams; or any... not exceed the limitation and are within the formula, as follows: (175 (grams contained U-235/350)+(50...

10 CFR 150.11 - Critical mass.

Code of Federal Regulations, 2010 CFR

2010-01-01

... uranium enriched in the isotope U-235 in quantities not exceeding 350 grams of contained U-235; uranium-233 in quantities not exceeding 200 grams; plutonium in quantities not exceeding 200 grams; or any... not exceed the limitation and are within the formula, as follows: (175 (grams contained U-235/350)+(50...

10 CFR 150.11 - Critical mass.

Code of Federal Regulations, 2014 CFR

2014-01-01

... uranium enriched in the isotope U-235 in quantities not exceeding 350 grams of contained U-235; uranium-233 in quantities not exceeding 200 grams; plutonium in quantities not exceeding 200 grams; or any... not exceed the limitation and are within the formula, as follows: (175 (grams contained U-235/350)+(50...

10 CFR 150.11 - Critical mass.

Code of Federal Regulations, 2012 CFR

2012-01-01

... uranium enriched in the isotope U-235 in quantities not exceeding 350 grams of contained U-235; uranium-233 in quantities not exceeding 200 grams; plutonium in quantities not exceeding 200 grams; or any... not exceed the limitation and are within the formula, as follows: (175 (grams contained U-235/350)+(50...

Radioactivity in three species of eastern Mediterranean jellyfish.

PubMed

Mamish, S; Al-Masri, M S; Durgham, H

2015-11-01

Activity concentrations of (137)Cs, (40)K, (210)Po, (210)Pb, (234)U and (238)U were determined in umbrella and oral arms of three widely distributed jellyfish species; namely Rhopilema nomadica Galil, 1990, Aurelia aurita Linne, 1758 and Aequorea forskalea Péron & Lesueur, 1810 collected from February 2011 to January 2012 in four sampling locations along the Syrian coast (Eastern Mediterranean Sea). The results have shown significant variations in radionuclides activity concentrations amongst the species. The average activity concentrations of (40)K, (210)Po, (210)Pb, (234)U and (238)U in the umbrella of R. nomadica species were higher than the average activity concentrations in the umbrella of A. aurita species by about 3.2, 1.4, 1.8, 3.2 and 3.2 folds, and A. forskalea species by about 45.5, 15.4, 19, 7.4 and 7.6 folds, respectively. The average activity concentrations of (40)K, (210)Po, (210)Pb, (234)U and (238)U in oral arms of R. nomadica species were higher than the average activity concentrations in oral arms of A. aurita species by about 3.8, 1.7, 1.9, 2.8 and 2.9 folds, respectively. (137)Cs activity concentrations were below the detection limit in all measured samples. In addition, activity concentrations of (137)Cs, (40)K, (210)Po, (210)Pb, (234)U and (238)U were also determined in 44 surface seawater samples and the activity concentrations ranged between 10.6 and 11.9 Bq l(-1) for (40)K, 1.1 and 1.4 mBq l(-1) for (210)Po, 0.5 and 0.7 mBq l(-1) for (210)Pb, 40.8 and 44.5 mBq l(-1) for (234)U, and 36.9 and 38.4 mBq l(-1) for (238)U, while (137)Cs activity concentrations were below the detection limit in all measured samples. Moreover, the umbrella and oral arms readily accumulated (40)K, (210)Po, (210)Pb, (234)U and (238)U above ambient seawater levels in the sequence of (210)Po > (210)Pb > (4) K > (234)U and (238)U. Concentration ratio (CR) values were relatively high for (210)Po and (210)Pb and reached 10(3) and 10(2), respectively for the jellyfish R. nomadica species compared to A. aurita and A. forskalea species. Therefore, R. nomadica can be used as biomonitor for these two radionuclides in the Eastern Mediterranean Sea. However, the obtained data can be considered the first reported baseline values for radioactivity in jellyfish. Copyright © 2015 Elsevier Ltd. All rights reserved.

The geochemistry of uranium and thorium isotopes in the Western Desert of Egypt

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dabous, A.A.

1994-11-01

The concentrations of {sup 238}U, {sup 234}U, {sup 232}Th, and {sup 228}Th have been measured in the groundwaters of the Bahariya and Farafra oases of the Western Desert of Egypt. These waters are characterized by normal amounts of U, but unusually high concentrations of Th. The pattern of variation of the parent isotopes, {sup 238}U and {sup 232}Th, as well as the daughter isotopes, {sup 234}U, {sup 230}Th, and {sup 228}Th, is systematic within and between the two oases. From the unusually consistent distribution of the {sup 234}U/{sup 238}U activity ratios one can conclude that the samples from both oasesmore » are representative of a two-component mixing system. One component, characterized by low U content and a high {sup 234}U/{sup 238}U activity ratio, is typical of deep artesian systems and probably represents flowthrough water derived from the Nubian highlands to the south. The second component is characterized by a greater U concentration and a low activity ratio. This signature is hypothesized as being derived by leaching of downward infiltrating water during pluvial times. The source of the U may be the uraniferous phosphate strata that overly the sandstone aquifer in both oasis areas. Higher Th values are associated with the artesian flow component of the mixing system and suggests that Th-bearing minerals may be abundant in the Nubian sandstone aquifer. The distribution of {sup 230}Th and {sup 228}Th in the water samples supports this interpretation.« less

Uranium from German Nuclear Power Projects of the 1940s--A Nuclear Forensic Investigation.

PubMed

Mayer, Klaus; Wallenius, Maria; Lützenkirchen, Klaus; Horta, Joan; Nicholl, Adrian; Rasmussen, Gert; van Belle, Pieter; Varga, Zsolt; Buda, Razvan; Erdmann, Nicole; Kratz, Jens-Volker; Trautmann, Norbert; Fifield, L Keith; Tims, Stephen G; Fröhlich, Michaela B; Steier, Peter

2015-11-02

Here we present a nuclear forensic study of uranium from German nuclear projects which used different geometries of metallic uranium fuel. Through measurement of the (230)Th/(234)U ratio, we could determine that the material had been produced in the period from 1940 to 1943. To determine the geographical origin of the uranium, the rare-earth-element content and the (87)Sr/(86)Sr ratio were measured. The results provide evidence that the uranium was mined in the Czech Republic. Trace amounts of (236)U and (239)Pu were detected at the level of their natural abundance, which indicates that the uranium fuel was not exposed to any major neutron fluence. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Compendium of energy-dependent sensitivity profiles for the TRX-2 thermal lattice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tomlinson, E.T.; Lucius, J.L.; Drischler, J.D.

1978-03-01

Energy-dependent sensitivity profiles for five responses calculated for the TRX-2 thermal lattice with the ORNL sensitivity code system FORSS are presented here both in graphical form and in SENPRO format. The responses are the multiplication factor, k/sub eff/; the ratio of epithermal-to-thermal captures in /sup 238/U, /sup 28/rho; the ratio of epithermal-to-thermal fissions in /sup 235/U, /sup 25/delta; the ratio of fissions in /sup 238/U to fissions in /sup 235/U, /sup 28/delta; and the ratio of captures in /sup 238/U to fissions in /sup 235/U, CR. A summary table of the total sensitivities is also presented.

Seasonal progression of uranium series isotopes in subglacial meltwater: Implications for subglacial storage time

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arendt, Carli A.; Aciego, Sarah M.; Sims, Kenneth W. W.

The residence time of subglacial meltwater impacts aquifer recharge, nutrient production, and chemical signals that reflect underlying bedrock/substrate, but is inaccessible to direct observation. We report the seasonal evolution of subglacial meltwater chemistry from the 2011 melt season at the terminus of the Athabasca Glacier, Canada. We also measured major and trace analytes and U-series isotopes for twenty-nine bulk meltwater samples collected over the duration of the melt season. This dataset, which is the longest time-series record of ( 234U/ 238U) isotopes in a glacial meltwater system, provides insight into the hydrologic evolution of the subglacial system during active melting.more » Meltwater samples, measured from the outflow, were analyzed for ( 238U), ( 222Rn) and ( 234U/ 238U)activity, conductivity, alkalinity, pH and major cations. Subglacial meltwater varied in [238U] and (222Rn) from 23 to 832 ppt and 9 to 171 pCi/L, respectively. Activity ratios of ( 234U/ 238U) ranged from 1.003 to 1.040, with the highest ( 238U), ( 222Rn) and ( 234U/ 238U)activity values occurring in early May when delayed-flow basal meltwater composed a significant portion of the bulk melt. Furthemore, from the chemical evolution of the meltwater, we posit that the relative subglacial water residence times decrease over the course of the melt season. This decrease in qualitative residence time during active melt is consistent with prior field studies and model-predicted channel switching from a delayed, distributed network to a fast, channelized network flow. As such, our study provides support for linking U-series isotopes to storage lengths of meltwater beneath glacial systems as subglacial hydrologic networks evolve with increased melting and channel network efficiency.« less

Seasonal progression of uranium series isotopes in subglacial meltwater: Implications for subglacial storage time

DOE PAGES

Arendt, Carli A.; Aciego, Sarah M.; Sims, Kenneth W. W.; ...

2017-07-31

The residence time of subglacial meltwater impacts aquifer recharge, nutrient production, and chemical signals that reflect underlying bedrock/substrate, but is inaccessible to direct observation. We report the seasonal evolution of subglacial meltwater chemistry from the 2011 melt season at the terminus of the Athabasca Glacier, Canada. We also measured major and trace analytes and U-series isotopes for twenty-nine bulk meltwater samples collected over the duration of the melt season. This dataset, which is the longest time-series record of ( 234U/ 238U) isotopes in a glacial meltwater system, provides insight into the hydrologic evolution of the subglacial system during active melting.more » Meltwater samples, measured from the outflow, were analyzed for ( 238U), ( 222Rn) and ( 234U/ 238U)activity, conductivity, alkalinity, pH and major cations. Subglacial meltwater varied in [238U] and (222Rn) from 23 to 832 ppt and 9 to 171 pCi/L, respectively. Activity ratios of ( 234U/ 238U) ranged from 1.003 to 1.040, with the highest ( 238U), ( 222Rn) and ( 234U/ 238U)activity values occurring in early May when delayed-flow basal meltwater composed a significant portion of the bulk melt. Furthemore, from the chemical evolution of the meltwater, we posit that the relative subglacial water residence times decrease over the course of the melt season. This decrease in qualitative residence time during active melt is consistent with prior field studies and model-predicted channel switching from a delayed, distributed network to a fast, channelized network flow. As such, our study provides support for linking U-series isotopes to storage lengths of meltwater beneath glacial systems as subglacial hydrologic networks evolve with increased melting and channel network efficiency.« less

Quantification of 235U and 238U activity concentrations for undeclared nuclear materials by a digital gamma-gamma coincidence spectroscopy.

PubMed

Zhang, Weihua; Yi, Jing; Mekarski, Pawel; Ungar, Kurt; Hauck, Barry; Kramer, Gary H

2011-06-01

The purpose of this study is to investigate the possibility of verifying depleted uranium (DU), natural uranium (NU), low enriched uranium (LEU) and high enriched uranium (HEU) by a developed digital gamma-gamma coincidence spectroscopy. The spectroscopy consists of two NaI(Tl) scintillators and XIA LLC Digital Gamma Finder (DGF)/Pixie-4 software and card package. The results demonstrate that the spectroscopy provides an effective method of (235)U and (238)U quantification based on the count rate of their gamma-gamma coincidence counting signatures. The main advantages of this approach over the conventional gamma spectrometry include the facts of low background continuum near coincident signatures of (235)U and (238)U, less interference from other radionuclides by the gamma-gamma coincidence counting, and region-of-interest (ROI) imagine analysis for uranium enrichment determination. Compared to conventional gamma spectrometry, the method offers additional advantage of requiring minimal calibrations for (235)U and (238)U quantification at different sample geometries. Crown Copyright © 2011. Published by Elsevier Ltd. All rights reserved.

Monte Carlo analysis of TRX lattices with ENDF/B version 3 data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hardy, J. Jr.

1975-03-01

Four TRX water-moderated lattices of slightly enriched uranium rods have been reanalyzed with consistent ENDF/B Version 3 data by means of the full-range Monte Carlo program RECAP. The following measured lattice parameters were studied: ratio of epithermal-to-thermal $sup 238$U capture, ratio of epithermal- to-thermal $sup 235$U fissions, ration of $sup 238$U captures to $sup 235$U fissions, ratio of $sup 238$U fissions to $sup 235$U fissions, and multiplication factor. In addition to the base calculations, some studies were done to find sensitivity of the TRX lattice parameters to selected variations of cross section data. Finally, additional experimental evidence is afforded bymore » effective $sup 238$U capture integrals for isolated rods. Shielded capture integrals were calculated for $sup 238$U metal and oxide rods. These are compared with other measurements. (auth)« less

On the Search for Nuclear Resonance Fluorescence Signatures of 235U and 238U above 3 MeV

DOE Office of Scientific and Technical Information (OSTI.GOV)

Warren, Glen A.; Caggiano, Joseph A.; Bertozzi, William

Nuclear resonance fluorescence is a physical process that provides an isotope-specific signature that could be used for the identification and characterization of materials. The technique involves the detection of prompt discrete-energy photons emitted from a sample that is exposed to MeV-energy photons. Potential applications of the technique range from detection of high explosives to characterization of special nuclear materials such as 235U. Pacific Northwest National Laboratory and Passport Systems have collaborated to conduct a pair of measurements to search for a nuclear resonance fluorescence response of 235U above 3 MeV and of 238U above 5 MeV using an 8 gmore » sample of highly enriched uranium and a 90 g sample of depleted uranium. No new signatures were observed. The minimum detectable integrated cross section for 235U is presented.« less

On the Search for Nuclear Resonance Fluorescence Signatures of 235U and 238U above 3 MeV

DOE Office of Scientific and Technical Information (OSTI.GOV)

Warren, Glen A.; Caggiano, Joseph A.; Bertozzi, William

Abstract–Nuclear resonance fluorescence is a physical process that provides an isotope-specific signature that could be used for the identification and characterization of materials. The technique involves the detection of prompt discrete-energy photons emitted from a sample that is exposed to photons in the MeV energy range. Potential applications of the technique range from detection of high explosives to characterization of special nuclear materials such as 235U. Pacific Northwest National Laboratory and Passport Systems have collaborated to conduct a a pair of measurements to search for a nuclear resonance fluorescence response of 235U above 3 MeV and of 238U above 5more » MeV using an 8 g sample of highly enriched uranium and a 90 g sample of depleted uranium. No new signatures were observed. The minimum detectable integrated cross section for 235U is presented.« less

A new method to measure the U-235 content in fresh LWR fuel assemblies via fast-neutron passive self-interrogation

DOE PAGES

Menlove, Howard Olsen; Belian, Anthony P.; Geist, William H.; ...

2017-10-07

The purpose of this paper is to provide a solution to a decades old safeguards problem in the verification of the fissile concentration in fresh light water reactor (LWR) fuel assemblies. The problem is that the burnable poison (e.g. Gd 2O 3) addition to the fuel rods decreases the active neutron assay for the fuel assemblies. This paper presents a new innovative method for the verification of the 235U linear mass density in fresh LEU fuel assemblies that is insensitive to the burnable poison content. The technique makes use of the 238U atoms in the fuel rods to self-interrogate themore » 235U mass. The innovation for the new approach is that the 238U spontaneous fission (SF) neutrons from the rods induces fission reactions (IF) in the 235U that are time correlated with the SF source neutrons. Thus, the coincidence gate counting rate benefits from both the nu-bar of the 238U SF (2.07) and the 235U IF (2.44) for a fraction of the IF reactions. Whereas, the 238U SF background has no time-correlation boost. The higher the detection efficiency, the higher the correlated boost because background neutron counts from the SF are being converted to signal doubles. This time-correlation in the IF signal increases signal/background ratio that provides a good precision for the net signal from the 235U mass. The hard neutron energy spectrum makes the technique insensitive to the burnable poison loading where a Cd or Gd liner on the detector walls is used to prevent thermal-neutron reflection back into the fuel assembly from the detector. Here, we have named the system the fast-neutron passive collar (FNPC).« less

A new method to measure the U-235 content in fresh LWR fuel assemblies via fast-neutron passive self-interrogation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Menlove, Howard Olsen; Belian, Anthony P.; Geist, William H.

The purpose of this paper is to provide a solution to a decades old safeguards problem in the verification of the fissile concentration in fresh light water reactor (LWR) fuel assemblies. The problem is that the burnable poison (e.g. Gd 2O 3) addition to the fuel rods decreases the active neutron assay for the fuel assemblies. This paper presents a new innovative method for the verification of the 235U linear mass density in fresh LEU fuel assemblies that is insensitive to the burnable poison content. The technique makes use of the 238U atoms in the fuel rods to self-interrogate themore » 235U mass. The innovation for the new approach is that the 238U spontaneous fission (SF) neutrons from the rods induces fission reactions (IF) in the 235U that are time correlated with the SF source neutrons. Thus, the coincidence gate counting rate benefits from both the nu-bar of the 238U SF (2.07) and the 235U IF (2.44) for a fraction of the IF reactions. Whereas, the 238U SF background has no time-correlation boost. The higher the detection efficiency, the higher the correlated boost because background neutron counts from the SF are being converted to signal doubles. This time-correlation in the IF signal increases signal/background ratio that provides a good precision for the net signal from the 235U mass. The hard neutron energy spectrum makes the technique insensitive to the burnable poison loading where a Cd or Gd liner on the detector walls is used to prevent thermal-neutron reflection back into the fuel assembly from the detector. Here, we have named the system the fast-neutron passive collar (FNPC).« less

A new method to measure the U-235 content in fresh LWR fuel assemblies via fast-neutron passive self-interrogation

NASA Astrophysics Data System (ADS)

Menlove, Howard; Belian, Anthony; Geist, William; Rael, Carlos

2018-01-01

The purpose of this paper is to provide a solution to a decades old safeguards problem in the verification of the fissile concentration in fresh light water reactor (LWR) fuel assemblies. The problem is that the burnable poison (e.g. Gd2O3) addition to the fuel rods decreases the active neutron assay for the fuel assemblies. This paper presents a new innovative method for the verification of the 235U linear mass density in fresh LEU fuel assemblies that is insensitive to the burnable poison content. The technique makes use of the 238U atoms in the fuel rods to self-interrogate the 235U mass. The innovation for the new approach is that the 238U spontaneous fission (SF) neutrons from the rods induces fission reactions (IF) in the 235U that are time correlated with the SF source neutrons. Thus, the coincidence gate counting rate benefits from both the nu-bar of the 238U SF (2.07) and the 235U IF (2.44) for a fraction of the IF reactions. Whereas, the 238U SF background has no time-correlation boost. The higher the detection efficiency, the higher the correlated boost because background neutron counts from the SF are being converted to signal doubles. This time-correlation in the IF signal increases signal/background ratio that provides a good precision for the net signal from the 235U mass. The hard neutron energy spectrum makes the technique insensitive to the burnable poison loading where a Cd or Gd liner on the detector walls is used to prevent thermal-neutron reflection back into the fuel assembly from the detector. We have named the system the fast-neutron passive collar (FNPC).

238U-234U-230Th disequilibrium in hydrogenous oceanic Fe-Mn crusts: Palaeoceanographic record or diagenetic alteration?

USGS Publications Warehouse

Chabaux, F.; O'Nions, R. K.; Cohen, A.S.; Hein, J.R.

1997-01-01

A detailed TIMS study of (234Uexc/238U), (230Th/232Th), and Th/U ratios have been performed on the outermost margin of ten hydrogenous Fe-Mn crusts from the equatorial Pacific Ocean and west-central Indian Ocean. Th/U concentration ratios generally decrease from the crust's surface down to 0.5-1 mm depth and growth rates estimated by uranium and thorium isotope ratios are significantly different in Fe-Mn crusts from the Peru Basin and the west-central Indian Ocean. Fe-Mn crusts from the same geographical area define a single trend in plots of Ln (234Uexc/238U) vs. Ln(230Th/232Th) and Th/U ratios vs. age of the analysed fractions. Results suggest that (1) hydrogenous Fe-Mn crusts remain closed-systems after formation, and consequently (2) the discrepancy observed between the 230Th and 234U chronometers in Fe-Mn crusts, and the variations of the Th/U ratios through the margin of Fe-Mn crusts, are not due to redistribution of uranium and thorium isotopes after oxyhydroxide precipitation, but rather to temporal variations of both Th/U and initial thorium activity ratios recorded by the Fe-Mn layers. Implications of these observations for determination of Fe-Mn crust growth-rates are discussed. Variations of both Th/U and initial Th activity ratios in Fe-Mn crusts might be related to changes in particle input to seawater and/or changes in ocean circulation during the last 150 ka. Copyright ?? 1997 Elsevier Science Ltd.

Consequences of slow growth for 230Th/U dating of Quaternary opals, Yucca Mountain, NV, USA

USGS Publications Warehouse

Neymark, L.A.; Paces, J.B.

2000-01-01

Thermal ionization mass-spectrometry 234U/238U and 230Th/238U data are reported for uranium-rich opals coating fractures and cavities within the silicic tuffs forming Yucca Mountain, NV, the potential site of a high-level radioactive waste repository. High uranium concentrations (up to 207 ppm) and extremely high 230Th/232Th activity ratios (up to about 106) make microsamples of these opals suitable for precise 230Th/U dating. Conventional 230Th/U ages range from 40 to greater than 600 ka, and initial 234U/238U activity ratios between 1.03 and 8.2. Isotopic evidence indicates that the opals have not experienced uranium mobility; however, wide variations in apparent ages and initial 234U/238U ratios for separate subsamples of the same outermost mineral surfaces, positive correlation between ages and sample weights, and negative correlation between 230Th/U ages and calculated initial 234U/238U are inconsistent with the assumption that all minerals in a given subsample was deposited instantaneously. The data are more consistent with a conceptual model of continuous deposition where secondary mineral growth has occurred at a constant, slow rate up to the present. This model assumes that individual subsamples represent mixtures of older and younger material, and that calculations using the resulting isotope ratios reflect an average age. Ages calculated using the continuous-deposition model for opals imply average mineral growth rates of less than 5 mm/m.y. The model of continuous deposition also predicts discordance between ages obtained using different radiometric methods for the same subsample. Differences in half-lives will result in younger apparent ages for the shorter-lived isotope due to the greater influence of younger materials continuously added to mineral surfaces. Discordant 14C, 230Th/U and U-Pb ages obtained from outermost mineral surfaces at Yucca Mountain support this model. (C) 2000 Elsevier Science B.V. All rights reserved.

Uranium comminution age tested by the eolian deposits on the Chinese Loess Plateau

NASA Astrophysics Data System (ADS)

Li, Le; Liu, Xiangjun; Li, Tao; Li, Laifeng; Zhao, Liang; Ji, Junfeng; Chen, Jun; Li, Gaojun

2017-06-01

The 234U/238U ratio of fine particles can record the time since their separation from bed rock because of the disruption of uranium series equilibrium introduced by the recoil of daughter 234Th nuclei (precursor of 234U) out of particle surfaces during the decay of 238U. Application of the uranium comminution age method, which has great potential in tracing production and transportation of sediments is however complicated by the weathering dissolution of 234U depleted particle surfaces, the difficulty in determining the fraction of recoiled nuclei, and the precipitation of exogenetic 234U. Here we minimize these complications by using a newly developed precise size separation using electroformed sieve, and a chemical protocol that involves reductive and oxidative leaching. Eolian deposits collected from the Chinese Loess Plateau (CLP) were used to test the validity of our method. Possible effects of weathering dissolution were also evaluated by comparing samples with different weathering intensities. The results show decreasing 234U/238U ratios in fine eolian particles with increasing sedimentation age, agreeing well with the theoretical prediction of the comminution age model. This successful application of the uranium comminution age approach to the eolian deposits on the CLP is also aided by a stable dust source, the low weathering intensity, the lack of consolidation, and the well-defined age model of the deposits. A transportation time of 242 ± 18 ka was calculated for the eolian deposits, which indicates a long residence time, and thus extensive mixing, of the dust particles in source regions, partly explaining the stable and homogeneous composition of the eolian dust over glacial-interglacial cycles.

All possible tripartitions of {}(236) 236U isotope in collinear configuration

NASA Astrophysics Data System (ADS)

Santhosh, K. P.; Krishnan, Sreejith; Joseph, Jayesh George

2018-07-01

Using the recently proposed unified ternary fission model (UTFM), the tripartition of ^{236}U isotope was studied for all possible fragmentations, in which the interacting potential barrier is taken as the sum of the Coulomb and proximity potentials with fragments in collinear configuration. The highest yield is obtained for the fragmentation ^{48}Ca{+}^{58}Ti{+}^{130}Sn and next highest yield is found for ^{58}Cr{+}^{46}Ar{+}^{132}Sn, which stress the importance of doubly magic or near doubly magic nuclei in the tripartition of ^{236}U isotope. The formation of ^{68}Ni and ^{70}Ni as the edge fragments linking the doubly magic nucleus ^{132}Sn by the isotope of Si is in good agreement with experimental and theoretical studies, in the collinear cluster tripartition of ^{236}U isotope which reveals the reliability of our model (UTFM) in ternary fission.

CONTROL SYSTEM FOR ISOTOPE SEPARATING APPARATUS

DOEpatents

Barnes, S.W.

1960-01-26

A method is described for controlling the position of the ion beams in a calutron used for isotope separation. The U/sup 238/ beams is centered over the U/sup 235/ receiving pocket, the operator monitoring the beam until a maximum reading is achieved on the meter connected to that pocket. Then both beams are simultaneously shifted by a preselected amount to move the U/sup 235/ beam over the U/sup 235/ pocket. A slotted door is placed over the entrance to that pocket during the U/sup 238/ beam centering to reduce the contamination to the pocket, while allowing enough beam to pass for monitoring purposes.

238,234U contents on Lepomis Cyanellus from San Marcos dam located in a uraniferous area

NASA Astrophysics Data System (ADS)

Lares, Magaly Cabral; Luna-Porres, Mayra Y.; Montero-Cabrera, María E.; Renteria-Villalobos, Marusia

2014-07-01

Fish species are suitable biomonitors of radioisotopes in aquatic systems. In the present study, it was made the determination of uranium isotopic contents on fish fillet (Lepomis Cyanellus) from San Marcos dam which is located in uranium mineralized zone. Uranium activity concentrations (AC) in fish samples were obtained on wet weight (ww), using liquid scintillation. 238U and 234U AC in fish fillet ranged from 0.0004 to 0.0167 Bq kg-1, and from 0.0013 to 0.0394 Bq kg-1, respectively. The activity ratio (234U/overflow="scroll">238U) in fish fillet ranged from 2.2 to 8.8. Lepomis cyanellus from San Marcos dam shows bioaccumulation factor (FB) of 0.6 L kg-1. The results suggest that the Lepomis Cyanellus in environments with high U contents tends to have a greater bioaccumulation compared to others.

Weathering processes and dating of soil profiles from São Paulo State, Brazil, by U-isotopes disequilibria.

PubMed

Bonotto, Daniel Marcos; Jiménez-Rueda, Jairo Roberto; Fagundes, Isabella Cruz; Filho, Carlos Roberto Alves Fonseca

2017-01-01

This study reports the use of the U-series radionuclides 238 U and 234 U for dating two soil profiles. The soil horizons developed over sandstones from Tatuí and Pirambóia formations at the Paraná sedimentary basin, São Paulo State, Brazil. Chemical data in conjunction with the 234 U/ 238 U activity ratios (AR's) of the soil horizons allowed investigating the U-isotopes mobility in the shallow oxidizing environment. Kaolinization and laterization processes are taking place in the profiles sampled, as they are especially common in regions characterized by a wet and dry tropical climate and a water table that is close to the surface. These processes are implied by inverse significant correlations between silica and iron in both soil profiles. Iron oxides were also very important to retain uranium in the two sites investigated, helping on the understanding of the weathering processes acting there. 238 U and its progeny 234 U permitted evaluating the processes of physical and chemical alteration, allowing the suggestion of a possible timescale corresponding to the Middle Pleistocene for the development of the more superficial soil horizons. Copyright © 2016 Elsevier Ltd. All rights reserved.

Plutonium and uranium in human bones from areas surrounding the Semipalatinsk nuclear test site.

PubMed

Yamamoto, Masayoshi; Hoshi, Masaharu; Sakaguchi, Aya; Shinohara, Kunihiko; Kurihara, Osamu; Apsalikov, Kazbek N; Gusev, Boris I

2006-02-01

To evaluate the present levels of 239,240Pu and U in residents living near the Semipalatinsk nuclear test site, more than 70 bone samples were obtained at autopsy. The subjects ranged in age from 30 to 86 years (mean 59.3+/-12.9). Most of the samples consisted of victims who died of various diseases. Plutonium and U were radiochemically separated and determined by alpha-ray spectrometry. The mean concentrations of 239,240Pu and 238U observed were 0.050+/-0.041 mBq/g-ash (vertebrae 71, long-bones 18) and 0.28+/-0.13 mBq/g-ash (22.8+/-10.6 microg U/kg-ash) (vertebrae 58, long bones 16), respectively. The present 239,240Pu levels were within the range found for human bone samples from other countries due solely to global fallout in the early 1980s. The average U concentration was close to the estimate (mean 22.5 microg U/kg-ash) for the UK, and about 10 times higher than those estimated for residents in New York City and Japan. By assuming that the average concentration of 239,240Pu in bone samples is the value at 45 years after instantaneous inhalation in 1955, the initial total intake and the effective dose for 45 years were estimated as 10 Bq and 0.2 mSv, respectively. The annual intake of total U (234,235,238U) and its effective dose for 60 years were estimated as 30 Bq for adult and 0.1 mSv, respectively, for chronic ingestion.

Nuclear reactor for breeding U.sup.233

DOEpatents

Bohanan, Charles S.; Jones, David H.; Raab, Jr., Harry F.; Radkowsky, Alvin

1976-01-01

A light-water-cooled nuclear reactor capable of breeding U.sup.233 for use in a light-water breeder reactor includes physically separated regions containing U.sup.235 fissile material and U.sup.238 fertile material and Th.sup.232 fertile material and Pu.sup.239 fissile material, if available. Preferably the U.sup.235 fissile material and U.sup.238 fertile material are contained in longitudinally movable seed regions and the Pu.sup.239 fissile material and Th.sup.232 fertile material are contained in blanket regions surrounding the seed regions.

Nuclear Excitation by Electronic Transition of U-235

NASA Astrophysics Data System (ADS)

Chodash, Perry

2017-01-01

Nuclear excitation by electronic transition (NEET) is a rare nuclear excitation that is theorized to exist in numerous isotopes. NEET is the inverse of bound internal conversion and occurs when an electronic transition couples to a nuclear transition causing the nucleus to enter an excited state. This process can only occur for isotopes with low-lying nuclear levels due to the requirement that the electronic and nuclear transitions have similar energies. One of the candidate isotopes for NEET, 235U, has been studied several times over the past 40 years and NEET of 235U has never been conclusively observed. These past experiments generated conflicting results with some experiments claiming to observe NEET of 235U and others setting limits for the NEET rate. If NEET of 235U were to occur, the uranium would be excited to its first excited nuclear state. The first excited nuclear state in 235U is only 76 eV, the second lowest known nuclear state. Additionally, the 76 eV state is a nuclear isomer that decays by internal conversion with a half-life of 26 minutes. In order to measure whether NEET occurs in 235U and at what rate, a uranium plasma was required. The plasma was generated using a Q-switched Nd:YAG laser outputting 789 mJ pulses of 1064 nm light. The laser light was focused onto uranium targets generating an intensity on target of order 1012 W/cm2. The resulting plasma was captured on a catcher plate and electrons emitted from the catcher plate were accelerated and focused onto a microchannel plate detector. Measurements performed using a variety of uranium targets spanning depleted uranium up to 99.4% enriched uranium did not observe a 26 minute decay. An upper limit for the NEET rate of 235U was determined. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. The U.S. DHS, UC Berkeley, the NNIS fellowship and the NSSC further supported this work.

Rates of carbonate soil evolution from carbon, U- and Th-series isotope studies: Example of the Astian sands (SE France)

NASA Astrophysics Data System (ADS)

Barbecot, Florent; Ghaleb, Bassam; Hillaire-Marcel, Claude

2015-04-01

In carbonate rich soils, C-isotopes (14C, 13C) and carbonate mass budget may inform on centennial to millennial time scale dissolution/precipitation processes and weathering rates, whereas disequilibria between in the U- and Th-decay series provide tools to document high- (228Ra-228Th-210Pb) to low- (234U, 230Th, 231Pa, 226Ra) geochemical processes rate, covering annual to ~ 1Ma time scales, governing both carbonate and silicate soil fractions. Because lithology constitutes a boundary condition, we intend to illustrate the behavior of such isotopes in soils developed over Astian sands formation (up to ~ 30% carbonate) from the Béziers area (SE France). A >20 m thick unsaturated zone was sampled firstly along a naturally exposed section, then in a cored sequence. Geochemical and mineralogical analyses, including stable isotopes and 14C-measurements, were complemented with 228U, 234U, 230Th, 226Ra, 210Pb and 228Th, 232Th measurements. Whereas the upper 7 m depict geochemical and isotopic features forced by dissolution/precipitation processes leading to variable radioactive disequilibria, but overall deficits in more soluble elements of the decay series, the lower part of the sequence shows strong excesses in 234U and 230Th over parent isotopes (i.e., 238U and 234U, respectively). These features might have been interpreted as the result of successive phases of U-loss and gains. However, 226Ra and 230Th are in near-equilibrium, thus leading to conclude at a more likely slow enrichment process in both 234Th(234U) and 230Th, which we link to dissolved U-decay during groundwater recharge events. In addition, 210Pb deficits (vs parent 226Ra) are observed down to 12 m along the natural outcropping section and below the top-soil 210Pb-excess in the cored sequence, due to gaseous 222Rn-diffusion over the cliff outcrop. Based on C-isotope and chemical analysis, reaction rates at 14C-time scale are distinct from those estimates at the short- or long-lived U-series isotopes, but provide a specific insight into carbonate budgets when confronted with data on dissolved and gaseous phases as well as on solid matter, and possibly best integrate the overall soil behavior through time. It is concluded from this example that if first order estimates of long-term geochemical fluxes in soils can be obtained from disequilibria in the 238U-234U-230Th sequence or from C-isotope data. While insights into recent to "Anthropocene" processes require information on the shorter-lived isotopes of the U and Th series, adding specific information on physical and chemical erosion budgets from 232Th data. As also illustrated in the present example, a robust assessment of overall chemical and physical erosion rates must be based on measurements in cored sequences away from natural or recent man-made cuts.

Origin of uranium isotope variations in early solar nebula condensates.

PubMed

Tissot, François L H; Dauphas, Nicolas; Grossman, Lawrence

2016-03-01

High-temperature condensates found in meteorites display uranium isotopic variations ((235)U/(238)U), which complicate dating the solar system's formation and whose origin remains mysterious. It is possible that these variations are due to the decay of the short-lived radionuclide (247)Cm (t 1/2 = 15.6 My) into (235)U, but they could also be due to uranium kinetic isotopic fractionation during condensation. We report uranium isotope measurements of meteoritic refractory inclusions that reveal excesses of (235)U reaching ~+6% relative to average solar system composition, which can only be due to the decay of (247)Cm. This allows us to constrain the (247)Cm/(235)U ratio at solar system formation to (1.1 ± 0.3) × 10(-4). This value provides new clues on the universality of the nucleosynthetic r-process of rapid neutron capture.

Integral cross section measurement of the U 235 ( n , n ' ) U 235 m reaction in a pulsed reactor

DOE PAGES

Bélier, G.; Bond, E. M.; Vieira, D. J.; ...

2015-04-08

The integral measurement of the neutron inelastic cross section leading to the 26-minute half-life 235mU isomer in a fission-like neutron spectrum is presented. The experiment has been performed at a pulsed reactor, where the internal conversion decay of the isomer was measured using a dedicated electron detector after activation. The sample preparation, efficiency measurement, irradiation, radiochemistry purification, and isomer decay measurement will be presented. We determined the integral cross section for the ²³⁵U(n,n') 235mU reaction to be 1.00±0.13b. This result supports an evaluation performed with TALYS-1.4 code with respect to the isomer excitation as well as the total neutron inelasticmore » scattering cross section.« less

Uranium-series disequilibrium in tuffs from Yucca Mountain, Nevada, as evidence of pore-fluid flow over the last million years

USGS Publications Warehouse

Gascoyne, M.; Miller, N.H.; Neymark, L.A.

2002-01-01

Samples of tuff from boreholes drilled into fault zones in the Exploratory Studies Facility (ESF) and relatively unfractured rock of the Cross Drift tunnels, at Yucca Mountain, Nevada, have been analysed by U-series methods. This work is part of a project to verify the finding of fast flow-paths through the tuff to ESF level, indicated by the presence of 'bomb' 36Cl in pore fluids. Secular radioactive equilibrium in the U decay series, (i.e. when the radioactivity ratios 234U/238U, 230Th/234U and 226Ra/230Th all equal 1.00) might be expected if the tuff samples have not experienced radionuclide loss due to rock-water interaction occurring within the last million years. However, most fractured and unfractured samples were found to have a small deficiency of 234U (weighted mean 234U/238U=0.95??0.01) and a small excess of 230Th (weighted mean 230Th/234U 1.10??0.02). The 226Ra/230Th ratios are close to secular equilibrium (weighted mean = 0.94??0.07). These data indicate that 234U has been removed from the rock samples in the last ???350 ka, probably by pore fluids. Within the precision of the measurement, it would appear that 226Ra has not been mobilized and removed from the tuff, although there may be some localised 226Ra redistribution as suggested by a few ratio values that are significantly different from 1.0. Because both fractured and unfractured tuffs show approximately the same deficiency of 234U, this indicates that pore fluids are moving equally through fractured and unfractured rock, More importantly, fractured rock appears not to be a dominant pathway for groundwater flow (otherwise the ratio would be more strongly affected and the Th and Ra isotopic ratios would likely also show disequilibrium). Application of a simple mass-balance model suggests that surface infiltration rate is over an order of magnitude greater than the rate indicated by other infiltration models and that residence time of pore fluids at ESF level is about 400 a. Processes of U sorption, precipitation and re-solution are believed to be occurring and would account for these anomalous results but have not been included in the model. Despite the difficulties, the U-series data suggest that fractured rock, specifically the Sundance and Drill Hole Wash faults, are not preferred flow paths for groundwater flowing through the Topopah Spring tuff and, by implication, rapid-flow, within 50 a, from the surface to the level of the ESF is improbable. ?? 2002 Elsevier Science Ltd. All rights reserved.

Uranium Isotope Fractionation during Oxidation of Dissolved U(iv) and Synthetic Solid UO2

NASA Astrophysics Data System (ADS)

Wang, X.; Johnson, T. M.; Lundstrom, C. C.

2013-12-01

U isotopes (238U/235U) show promise as a tool for environmental monitoring of U contamination as well as a proxy for paleo-redox conditions. However, the isotopic fractionation mechanisms of U are still poorly understood. In groundwater systems, U(VI), a mobile contaminant, can be reduced to immobile U(IV) and thus remediated. Previous work shows that 238U/235U of the remaining U(VI) changes with the extent of reduction. Therefore, U(VI) isotope composition in groundwater can potentially be used to detect and perhaps quantify the extent of reduction. However, knowing if isotopic fractionation occurs during U(IV) oxidation is equally important. First, the reduced U(IV) (either solid or as dissolved organic complexes) potentially can be reoxidized to U(VI). If isotope fractionation occurs during oxidation, it would complicate the use of U isotope composition as a monitoring technique. Further, in natural weathering processes, U(IV) minerals are oxidized to form dissolved U(VI), which is carried to rivers and eventually to the ocean and deposited in marine sediments. The weathering cycle is thus sensitive to redox conditions, meaning the sedimentary U isotope record may serve as a paleoredox indicator, provided U isotope fractionation during oxidation and reduction are well known. We conducted experiments oxidizing 2 different U(IV) species by O2 and measuring isotopic fractionation factors. In one experiment, dissolved U(IV) in 0.1 N HCl (pH 1) was oxidized by entrained air. As oxidation proceeds at pH 1, the remaining dissolved U(IV) becomes progressively enriched in 238U in a linear trend, while the product U(VI) paralleled, but was offset to 1.0‰ lighter in 238U/235U. This linear progression of both remaining reactant and product suggests equilibrium fractionation during oxidation of dissolved U(IV) by O2. A second experiment oxidized synthetic, solid UO2 (in 20 mM NaHCO3, pH 7) with entrained air. The oxidative fractionation is very weak in this case with product U(VI) ~0.1‰ heavier than the remaining UO2. We attribute the lack of strong fractionation during oxidation of solid UO2 to a 'rind effect', where the surface layer must be completely oxidized before the next layer is exposed to oxidant. Hence, nearly complete, congruent conversion of each layer of U(IV) to U(VI) results in minimal isotope fractionation. A small amount of transient fractionation probably occurs initially, but this is quickly negated as the surface becomes isotopically fractionated. Interestingly, our measured ~0.1‰ U isotope fractionation during oxidation of solid U(IV) agrees with the natural observation that 238U/235U ratios in river water (mainly U(VI)) are ~0.1‰ greater than those in fresh continental rocks (primarily U(IV) minerals). Application of these results to natural settings should be done with caution, however. Oxidation of natural uraninite in continental rocks is a much slower process. If the U(VI) product and the U(IV) reactant remain in contact for long periods of time (e.g., months), they may evolve toward isotopic equilibrium. Measurements of 238U/235U in various natural weathering environments should be undertaken to examine this idea.

An alternative procedure for uranium analysis in drinking water using AQUALIX columns: application to varied French bottled waters.

PubMed

Bouvier-Capely, C; Bonthonneau, J P; Dadache, E; Rebière, F

2014-01-01

The general population is chronically exposed to uranium ((234)U, (235)U, and (238)U) and polonium ((210)Po) mainly through day-to-day food and beverage intake. The measurement of these naturally-occurring radionuclides in drinking water is important to assess their health impact. In this work the applicability of calix[6]arene-derivatives columns for uranium analysis in drinking water was investigated. A simple and effective method was proposed on a specific column called AQUALIX, for the separation and preconcentration of U from drinking water. This procedure is suitable for routine analysis and the analysis time is considerably shortened (around 4h) by combining the separation on AQUALIX with fast ICP-MS measurement. This new method was tested on different French bottled waters (still mineral water, sparkling mineral water, and spring water). Then, the case of simultaneous presence of uranium and polonium in water was considered due to interferences in alpha spectrometry measurement. A protocol was proposed using a first usual step of spontaneous deposition of polonium on silver disc in order to separate Po, followed by the uranium extraction on AQUALIX column before alpha spectrometry counting. © 2013 Published by Elsevier B.V.

The Effect of Early Diagenesis on the 238U/235U Ratio of Platform Carbonates.

NASA Astrophysics Data System (ADS)

Tissot, F.; Chen, C.; Go, B. M.; Naziemiec, M.; Healy, G.; Swart, P. K.; Dauphas, N.

2017-12-01

In the past 15 years, the so-called non-traditional stable isotopes systems (e.g., Mg, Fe, Mo, U) have emerged as powerful tracers of both high-T and low-T geochemical processes (e.g., [1]). Of particular interest for paleoredox studies is the ratio of "stable" isotopes of U (238U/235U), which has the potential to track the global extent of oceanic anoxia (e.g., [2, 3]). Indeed, in the modern ocean, U exists in two main oxidation states, soluble U6+ and insoluble U4+, and has a mean residence time of 400 kyr ([4]), much longer than the global ocean mixing time (1-2 kyr). As such the salinity-normalized ocean is homogeneous with regards to both U concentrations and isotopes (δ238USW = -0.392±0.005 ‰, [2]). The value of δ238USW at any given time is therefore the balance between U input to the ocean, mainly from rivers, and U removal, mostly into biogenic carbonates, anoxic/euxinic sediments and suboxic/hypoxic sediments (e.g., [2, 5]). Because the 238U/235U ratio of the past ocean cannot be measured directly, it has to be estimated from the measurement of the 238U/235U ratio of a sedimentary rock and assuming a constant fractionation factor. Carbonates appear as a promising record since they span most of Earth's history, and the δ238U values of modern primary carbonate precipitates and well-preserved fossil aragonitic coral up to 600 ka are indistinguishable from that of seawater (e.g., [2, 6, 7]). Yet, the effect of secondary processes on the δ238U values of non-coral carbonates, which represent the bulk of the rock record, has only been studied in a handful of shallow samples (down to 40cm, [6]) and remains poorly understood. To investigate the effect of early diagenesis on the 238U/235U ratio of carbonates on the 30kyr to 1Myr timescale, we measured δ13C, δ18O, and δ238U in samples from a 220m long drill core from the Bahamas carbonate platform. In order to separate lattice bound U from secondary U we developed a leaching protocol applicable to carbonate of all ages. We find that early diagenesis results in a 0 to +0.50 ‰ offset between the δ238U of carbonates and that of seawater. [1] Teng et al (2017) RiMG 82. [2] Tissot & Dauphas (2015) GCA 167. [3] Andersen et al. (2016) Chem. Geol. 420. [4] Ku et al (1977) Deep-Sea Research 24. [5] Dunk et al (2002) Chem. Geol. 190. [6] Romaniello et al (2013) Chem. Geol. 362. [7] Andersen et al. (2014) EPSL 400.

Round-robin 230Th– 234U age dating of bulk uranium for nuclear forensics

DOE PAGES

Gaffney, Amy M.; Hubert, Amélie; Kinman, William S.; ...

2015-07-30

We report that in an inter-laboratory measurement comparison study, four laboratories determined 230Th– 234U model ages of uranium certified reference material NBL U050 using isotope dilution mass spectrometry. The model dates determined by the participating laboratories range from 9 March 1956 to 19 October 1957, and are indistinguishable given the associated measurement uncertainties. These model ages are concordant with to slightly older than the known production age of NBL U050.

234U/238U as a ground-water tracer, SW Nevada-SE California

USGS Publications Warehouse

Ludwig, K. R.; Peterman, Z.E.; Simmons, K.R.; Gutentag, E.D.

1993-01-01

The 234U/238U ratio of uranium in oxidizing ground waters is potentially an excellent ground-water tracer because of its high solubility and insensitivity to chemical reactions. Moreover, recent advances in analytical capability have made possible very precise uranium-isotopic analyses on modest (approx.100 ml) amounts of normal ground water. Preliminary results on waters from SW Nevada/Se California indicate two main mixing trends, but in detail indicate significant complexity requiring three or more main components.

Round-robin 230Th– 234U age dating of bulk uranium for nuclear forensics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gaffney, Amy M.; Hubert, Amélie; Kinman, William S.

We report that in an inter-laboratory measurement comparison study, four laboratories determined 230Th– 234U model ages of uranium certified reference material NBL U050 using isotope dilution mass spectrometry. The model dates determined by the participating laboratories range from 9 March 1956 to 19 October 1957, and are indistinguishable given the associated measurement uncertainties. These model ages are concordant with to slightly older than the known production age of NBL U050.

Isotopic determination of uranium in soil by laser induced breakdown spectroscopy

DOE PAGES

Chan, George C. -Y.; Choi, Inhee; Mao, Xianglei; ...

2016-03-26

Laser-induced breakdown spectroscopy (LIBS) operated under ambient pressure has been evaluated for isotopic analysis of uranium in real-world samples such as soil, with U concentrations in the single digit percentage levels. The study addresses the requirements for spectral decomposition of 235U and 238U atomic emission peaks that are only partially resolved. Although non-linear least-square fitting algorithms are typically able to locate the optimal combination of fitting parameters that best describes the experimental spectrum even when all fitting parameters are treated as free independent variables, the analytical results of such an unconstrained free-parameter approach are ambiguous. In this work, five spectralmore » decomposition algorithms were examined, with different known physical properties (e.g., isotopic splitting, hyperfine structure) of the spectral lines sequentially incorporated into the candidate algorithms as constraints. It was found that incorporation of such spectral-line constraints into the decomposition algorithm is essential for the best isotopic analysis. The isotopic abundance of 235U was determined from a simple two-component Lorentzian fit on the U II 424.437 nm spectral profile. For six replicate measurements, each with only fifteen laser shots, on a soil sample with U concentration at 1.1% w/w, the determined 235U isotopic abundance was (64.6 ± 4.8)%, and agreed well with the certified value of 64.4%. Another studied U line - U I 682.691 nm possesses hyperfine structure that is comparatively broad and at a significant fraction as the isotopic shift. Thus, 235U isotopic analysis with this U I line was performed with spectral decomposition involving individual hyperfine components. For the soil sample with 1.1% w/w U, the determined 235U isotopic abundance was (60.9 ± 2.0)%, which exhibited a relative bias about 6% from the certified value. The bias was attributed to the spectral resolution of our measurement system - the measured line width for this U I line was larger than its isotopic splitting. In conclusion, although not the best emission line for isotopic analysis, this U I emission line is sensitive for element analysis with a detection limit of 500 ppm U in the soil matrix; the detection limit for the U II 424.437 nm line was 2000 ppm.« less

Environmental control of U concentration and 234U/238U in speleothems at subannual resolution

NASA Astrophysics Data System (ADS)

Hu, C.; Henderson, G. M.

2003-12-01

Trace element and isotope variability in speleothems encodes a range of information about the past environment, although its interpretation is often problematic. U concentration and isotopes have frequently been analysed in speleothems in order to provide chronology, but their use as environmental proxies in their own right has not been comprehensively investigated. In this study, we have investigated the environmental controls of U in a stalagmite from the Central Yangtze Valley in China. This stalagmite grew rapidly throughout the Holocone and contains visible annual layers about 300microns thick. Analysis of a portion of the stalagmite corresponding to the 1970s by electron probe, LA-ICP-MS, and by physical subsampling indicate clear annual cycles in Sr/Ca, Mg/Ca, and Ba/Ca. The reasonably open cave structure and the correlation of Sr/Ca with Mg/Ca suggest that temperature exerts considerable control over these trace element variations. U/Ca also varies seasonally by up to 42 % and shows a clear anti-correlation with Mg/Ca (correlation coefficient -0.64). Based on the inverse relationship between U/Ca and temperature exhibited in other carbonates (e.g. corals) the speleothem U/Ca is suggested to be controlled primarily by temperature and may provide a paleo cave thermometer with less rainfall influence than Mg/Ca. Ongoing monitoring of the cave temperature and humidity will assess the robustness of this conclusion and the sensitivity of speleothem U/Ca to temperature. (234U/238U) in this stalagmite range from 1.733 to 1.872 during the Holocene. The U concentration is high enough (typically 0.48 ppm) and growth rate fast enough, that (234U/238U) can also be measured at a subannual resolution. The expected alpha-recoil control of excess 234U supply suggests that these measurements may provide a measure of the transit time of recharge waters to the stalagmite during the seasonal cycle. Such a proxy would enable deconvolution of temperature and recharge-rate control in trace element records from speleothems.

Evaluation of Pleistocene groundwater flow through fractured tuffs using a U-series disequilibrium approach, Pahute Mesa, Nevada, USA

USGS Publications Warehouse

Paces, James B.; Nichols, Paul J.; Neymark, Leonid A.; Rajaram, Harihar

2013-01-01

Groundwater flow through fractured felsic tuffs and lavas at the Nevada National Security Site represents the most likely mechanism for transport of radionuclides away from underground nuclear tests at Pahute Mesa. To help evaluate fracture flow and matrix–water exchange, we have determined U-series isotopic compositions on more than 40 drill core samples from 5 boreholes that represent discrete fracture surfaces, breccia zones, and interiors of unfractured core. The U-series approach relies on the disruption of radioactive secular equilibrium between isotopes in the uranium-series decay chain due to preferential mobilization of 234U relative to 238U, and U relative to Th. Samples from discrete fractures were obtained by milling fracture surfaces containing thin secondary mineral coatings of clays, silica, Fe–Mn oxyhydroxides, and zeolite. Intact core interiors and breccia fragments were sampled in bulk. In addition, profiles of rock matrix extending 15 to 44 mm away from several fractures that show evidence of recent flow were analyzed to investigate the extent of fracture/matrix water exchange. Samples of rock matrix have 234U/238U and 230Th/238U activity ratios (AR) closest to radioactive secular equilibrium indicating only small amounts of groundwater penetrated unfractured matrix. Greater U mobility was observed in welded-tuff matrix with elevated porosity and in zeolitized bedded tuff. Samples of brecciated core were also in secular equilibrium implying a lack of long-range hydraulic connectivity in these cases. Samples of discrete fracture surfaces typically, but not always, were in radioactive disequilibrium. Many fractures had isotopic compositions plotting near the 230Th-234U 1:1 line indicating a steady-state balance between U input and removal along with radioactive decay. Numerical simulations of U-series isotope evolution indicate that 0.5 to 1 million years are required to reach steady-state compositions. Once attained, disequilibrium 234U/238U and 230Th/238U AR values can be maintained indefinitely as long as hydrological and geochemical processes remain stable. Therefore, many Pahute Mesa fractures represent stable hydrologic pathways over million-year timescales. A smaller number of samples have non-steady-state compositions indicating transient conditions in the last several hundred thousand years. In these cases, U mobility is dominated by overall gains rather than losses of U.

Temporal Variations in 234U/238U Activity Ratios in Four Mississippi River Tributaries

NASA Astrophysics Data System (ADS)

Grzymko, T. J.; Marcantonio, F.

2005-05-01

In 2004 we sampled the four tributaries that are the major contributors to the Mississippi River in terms of water discharge, i.e., the Arkansas, Missouri, Upper Mississippi, and Ohio rivers. Each river was sampled four times over the course of the year at variable levels of discharge in an attempt to constrain the causes of the temporal variations of 234U/238U activity ratios in the lower Mississippi River at New Orleans. The tributary uranium data support the idea that lower river uranium isotope and elemental systematics are controlled by a simple mass balance of the source tributary discharges. Furthermore, the uranium isotope ratios of the individual tributaries show coherent patterns of variability. Specifically, the data obtained from the four sampling trips yielded similar patterns of temporal variation in the 234U/238U activity ratios of all of the rivers, although the absolute values of these ratios were distinctly different from one river to the next. The pattern was such that the highest 234U/238U activity ratios were observed during the highest flow associated with the spring freshet while the lowest ratios occurred during the summer. For example, in the Missouri River, the 234U/238U activity ratios varied from 1.51 (February 12) to 1.37 (April 14) to 1.34 (July 16) to 1.37 (November 12), while in the Ohio River the same ratios varied from 1.36 (February 12) to 1.29 (April 14) to 1.21 (July 16) to 1.23 (November 12). The apparent seasonal pattern of these ratios in each tributary has led to several ideas as to the causes of the observed trends. The first, and most obvious, is that in each individual drainage basin there are various source tributaries that contribute to the uranium isotope systematics of the main stem of the tributary of interest. It follows that the variations in the uranium activity ratios may be caused by spatial variations in the source rock chemistry of the drainage basin. Other more complex scenarios can also be envisioned and will be discussed. For example, we explore the possibility that the highest ratios associated with the spring freshet are a consequence of snow melt and the flushing of 234U from fresh surfaces created via physical weathering associated with the winter freeze-thaw cycles.

Development and evaluation of a collection apparatus for recoil products for study of the deexcitation process of (235m)U.

PubMed

Shigekawa, Y; Kasamatsu, Y; Shinohara, A

2016-05-01

The nucleus (235m)U is an isomer with extremely low excitation energy (76.8 eV) and decays dominantly through the internal conversion (IC) process. Because outer-shell electrons are involved in the IC process, the decay constant of (235m)U depends on its chemical environment. We plan to study the deexcitation process of (235m)U by measuring the energy spectra of IC electrons in addition to the decay constants for various chemical forms. In this paper, the preparation method of (235m)U samples from (239)Pu by using alpha-recoil energy is reported. A Collection Apparatus for Recoil Products was fabricated, and then collection efficiencies under various conditions were determined by collecting (224)Ra recoiling out of (228)Th electrodeposited and precipitated sources. The pressure in the apparatus (vacuum or 1 atm of N2 gas) affected the variations of the collection efficiencies depending on the negative voltage applied to the collector. The maximum values of the collection efficiencies were mainly affected by the thickness of the (228)Th sources. From these results, the suitable conditions of the (239)Pu sources for preparation of (235m)U were determined. In addition, dissolution efficiencies were determined by washing collected (224)Ra with solutions. When (224)Ra was collected in 1 atm of N2 gas and dissolved with polar solutions such as water, the dissolution efficiencies were nearly 100%. The method of rapid dissolution of recoil products would be applicable to rapid preparation of short-lived (235m)U samples for various chemical forms.

Powerplant Selection for Conceptual Helicopter Design.

DTIC Science & Technology

1983-06-01

40𔃾 4 41 H IN I = oqINc"- m IN .0 A . L CCI - I =u votI --4d& 81 -4- ZwI o. o * *I= IM 1 "= * " C4P - 9E4n =E ............... t....... 0 0WW04 4l kW1...288 / 181 STO 34 231 SORT 281 STO 09 182.BL 10 232 RCL 98 282 RCL 29 183LBL -Vl- 233 - 283 FS? 02 184 FS? 92 234 SORT 284 RCL 28 185 GTO 11 235 FS

Archaeological and Historical Literature Search and Research Design, Lava Flow Control Study, Hilo, Hawaii

DTIC Science & Technology

1979-05-01

introduced species are heavily represented in these forests, as well as in dense shrub and herb formations typical of secondary forests (i.e., a...e.g., Stenogyne oalaminthoides, Phyllosiegia vestita, P. villosa), and herbs (e.g., Peperomia spp.) (Knapp 1975:100-101; Fosberg 1972:148-150...flows where ad- jacent populations still exist. In Handy and Handy*s (1972:183, 234, 235) discussion on wild foods used during times of famine, ’Ama’u

Uranium-series dating of pedogenic silica and carbonate, Crater Flat, Nevada

NASA Astrophysics Data System (ADS)

Ludwig, K. R.; Paces, J. B.

2002-02-01

A 230Th-234U-238U dating study on pedogenic silica-carbonate clast rinds and matrix laminae from alluvium in Crater Flat, Nevada was conducted using small-sample thermal-ionization mass spectrometry (TIMS) analyses on a large suite of samples. Though the 232Th content of these soils is not particularly low (mostly 0.1-9 ppm), the high U content of the silica component (mostly 4-26 ppm) makes them particularly suitable for 230Th/U dating on single, 10 to 200 mg totally-digested samples using TIMS. We observed that (1) both micro- (within-rind) and macro-stratigraphic (mappable deposit) order of the 230Th/U ages were preserved in all cases; (2) back-calculated initial 234U/238U fall in a restricted range (typically 1.67±0.19), so that 234U/238U ages with errors of about 100 kyr (2σ) could be reliably determined for the oldest, 400 to 1000 ka rinds; and (3) though 13 of the samples were >350 ka, only three showed evidence for an open-system history, even though the sensitivity of such old samples to isotopic disruption is very high. An attempt to use leach-residue techniques to separate pedogenic from detrital U and Th failed, yielding corrupt 230Th/U ages. We conclude that 230Th/U ages determined from totally dissolved, multiple sub-mm size subsamples provide more reliable estimates of soil chronology than methods employing larger samples, chemical enhancement of 238U/232Th, or isochrons.

Separation of uranium isotopes by chemical exchange

DOEpatents

Ogle, P.R. Jr.

1974-02-26

A chemical exchange method is provided for separating /sup 235/U from / sup 238/U comprising contacting a first phase containing UF/sub 6/ with a second phase containing a compound selected from the group consisting of NOUF/sub 6/, NOUF/sub 7/, and NO/sub 2/UF/sub 7/ until the U Fsub 6/ in the first phase becomes enriched in the /sup 235/U isotope. (Official Gazette)

Theoretical Estimate of Maximum Possible Nuclear Explosion

DOE R&D Accomplishments Database

Bethe, H. A.

1950-01-31

The maximum nuclear accident which could occur in a Na-cooled, Be moderated, Pu and power producing reactor is estimated theoretically. (T.R.H.) 2O82 Results of nuclear calculations for a variety of compositions of fast, heterogeneous, sodium-cooled, U-235-fueled, plutonium- and power-producing reactors are reported. Core compositions typical of plate-, pin-, or wire-type fuel elements and with uranium as metal, alloy, and oxide were considered. These compositions included atom ratios in the following range: U-23B to U-235 from 2 to 8; sodium to U-235 from 1.5 to 12; iron to U-235 from 5 to 18; and vanadium to U-235 from 11 to 33. Calculations were performed to determine the effect of lead and iron reflectors between the core and blanket. Both natural and depleted uranium were evaluated as the blanket fertile material. Reactors were compared on a basis of conversion ratio, specific power, and the product of both. The calculated results are in general agreement with the experimental results from fast reactor assemblies. An analysis of the effect of new cross-section values as they became available is included. (auth)

Uranium Isotope Systematic in Saanich Inlet

NASA Astrophysics Data System (ADS)

Amini, M.; Holmden, C.; Francois, R.

2008-12-01

As a redox-sensitive element Uranium has become the focus of stable isotope studies. Based on the nuclear field shift effect [1], U isotope fractionation was predicted as a function of U(IV)-U(VI) exchange reactions with the insoluble reduced U(IV) species being heavier than the soluble oxidized U(VI) species. Recently, variations in 238U/235U were reported in low temperature aqueous and sedimentary environments [2,3] indicating that U deposited in well-oxygenated environments is characterized by light isotopic composition, whereas suboxic and anoxic deposits tend towards a heavy isotopic signature. U isotope fractionation has been hence proposed as a promising new paleo-redox proxy. In order to test the efficacy of U isotope fractionation to record oxidation states in marine systems, we are investigating sediment samples deposited over a range of redox conditions in the seasonally anoxic Saanich Inlet, on the east coast of Vancouver Island. We have also made δ238U measurements for water samples from above and below the redoxcline. The measurements were carried out by MC-ICPMS using 233U/236U-double spike technique. The data are reported as δ238U relative to NBL 112a with a 238U/235U ratio of 137.88 (2sd). External precision is better than 0.10 permil (2sd). Eleven analyses of seawater performed over the course of this work yielded δ238U of -0.41±0.07 permil (2sd). No clear difference in δ238U values has been found, thus far, in water samples collected at 10m (O2~380μM) and 200m (O2~1μM) depths from a single location in the middle of the inlet. The mean of two measurements of the deepwater sample yielded -0.43±0.01 permil (2sd). Two measurements of the shallow water sample yielded a mean value of -0.38±0.03 permil (2sd). The δ238U values for HF-HNO3 digestions of the organic rich sediments, one taken in the middle of the basin (3.11% organic carbon) below seasonally anoxic bottom waters (-0.22±0.01 permil, n=2), and the other taken from the sill (1.29% organic carbon) below well-oxygenated bottom waters (-0.22 permil, n=1) are identical. The δ238U value matches previously reported values for suboxic sediments from the Peru margin [3], but is lighter than organic rich sediments from the Black Sea [3], where the bottom waters are strongly euxinic. The consistency in δ238U vaues between previously investigated suboxic sediment samples [3] and our two sediment samples indicates that the magnitude of the U isotopic fractionation is identical between seawater and sediments deposited under a range of bottom water oxygen conditions from oxygenated to anoxic. However, differences between the U isotope compositions in Saanich Inlet and those from the Black Sea remain to be explained, if U isotope fractionation is be used as a quantitative proxy for paleoredox in ancient oceans. [1] Schauble (2007) GCA 71, 2170- 2189. [2] Stirling et al. (2007) EPSL 264, 208-225. [3] Weyer et al. (2007) GCA 72, 345-399.

Predicting equilibrium uranium isotope fractionation in crystals and solution

NASA Astrophysics Data System (ADS)

Schauble, E. A.

2015-12-01

Despite the rapidly growing interest in using 238U/235U measurements as a proxy for changes in oxygen abundance in surface and near-surface environments, the present theoretical understanding of uranium isotope fractionation is limited to a few simple gas-phase molecules and analogues of dissolved species (e.g., 1,2,3). Understanding uranium isotope fractionation behavior in more complicated species, such as crystals and adsorption complexes, will help in the design and interpretation of experiments and field studies, and may suggest other uses for 38U/235U measurements. In this study, a recently developed first-principles method for estimating the nuclear volume component of field shift fractionation in crystals and complex molecular species (4) is combined with mass-dependent fractionation theory to predict equilibrium 38U/235U fractionations in aqueous and crystalline uranium compounds, including uraninite (UO2). The nuclear field shift effect, caused by the interaction of electrons with the finite volume of the positive charge distribution in uranium nuclei, is estimated using Density Functional Theory and the Projector Augmented Wave method (DFT-PAW). Tests against relativistic electronic structure calculations and Mössbauer isomer shift data indicate that the DFT-PAW method is reasonably accurate, while being much better suited to models of complex and crystalline species. Initial results confirm previous predictions that the nuclear volume effect overwhelms mass depdendent fractionation in U(VI)-U(IV) exchange reactions, leading to higher 238U/235U in U(IV) species (i.e., for UO2 xtal vs. UO22+aq, ln αNV ≈ +1.8‰ , ln αMD ≈ -0.8‰, ln αTotal ≈ +1.0‰ at 25ºC). UO2 and U(H2O)94+, are within ~0.4‰ of each other, while U(VI) species appear to be more variable. This suggests that speciation is likely to significantly affect natural uranium isotope fractionations, in addition to oxidation state. Tentatively, it appears that uranyl-type (UO22+-bearing) structures will tend to have higher 238U/235U than uranate-type structures that lack strong U=O bonds. References: 1. Bigeleisen (1996) JACS 118:3676; 2. Schauble (2006) Eos 87:V21B-0570; 3. Abe et al. (2008) J Chem Phys 128:144309, 129:164309, & Abe et al. (2010) J Chem Phys 133:044309; 4. Schauble (2013) PNAS 110:17714.

Biological availability of (238)U, (234)U and (226)Ra for wild berries and meadow grasses in natural ecosystems of Belarus.

PubMed

Sokolik, G A; Ovsiannikova, S V; Voinikava, K V; Ivanova, T G; Papenia, M V

2014-01-01

This work is devoted to investigation of behavior of (234)U, (238)U and (226)Ra by determining the soil to plant transfer under different natural conditions such as forest or swamped areas and meadow lands with different soil types. The paper summarizes the data on investigation of uranium and radium uptake by wild berries and natural meadow grasses in the typical conditions of Belarus. Parameters characterizing the biological availability of (234)U, (238)U and (226)Ra for bilberry (Vaccinium myrtillus), lingonberry (Vaccinium viti-idaea), blueberry (Vaccinium iliginosum) and cranberry (Vaccinium oxycoccus palustris) as well as for widely occurring mixed meadow vegetation, which belongs to the sedge-grass or grass-sedge associations and forbs, have been established. In the sites under investigation, the deposition levels of (238+239+240)Pu were less than 0.37 kBq m(-2) and (137)Cs deposition ranged between less than 0.37 and 37 kBq m(-2). It was found that activity concentrations of radionuclides in berries varied in the ranges of 0.037-0.11 for (234)U, 0.036-0.10 for (238)U and 0.11-0.43 Bq kg(-1) for (226)Ra, but in the mixed meadow grasses they were 0.32-4.4, 0.24-3.9 and 0.14-6.9 Bq kg(-1) accordingly. The (234)U/(238)U activity ratios were 1.02 ± 0.01 for wild berries, 1.20 ± 0.09 for underground meadow grasses and 1.02 ± 0.02 for proper soils. The concentration ratios (CRs, dry weight basis) of (234)U and (238)U for mixed meadow grasses were 0.036-0.42 and 0.041-0.46 respectively. The correspondent geometric means (GM) were 0.13 and 0.15 with geometric standard deviations (GSD) of 2.4. The CRs of (226)Ra for meadow grasses were 0.031-1.0 with GM 0.20 and GSD 2.6. The CRs of (234)U, (238)U and (226)Ra for wild berries ranged within 0.0018-0.008 (GM is 0.0034, GSD is 1.8), 0.0018-0.008 (GM is 0.0035, GSD is 1.8) and 0.005-0.033 (GM is 0.016, GSD is 2.1) accordingly. The highest CR values of uranium for mixed meadow grasses were found in the sites with high-moor peat and sandy soils. The lowest CRs for grasses were common to loamy and peat-gley soils. The CRs for the same berry species in the sites with sandy soils exceeded the appropriate CR values in the sites with loamy soils by factors of 3-4 for uranium and 4-6 for radium. The data obtained on radionuclide accumulation by plants were used to estimate the average annual effective doses to the population from radionuclide intake through the "soil - wild berries - man" and "soil - meadow vegetation - animal - cow milk-beef - man" trophic chains. The effective doses resulting from (234)U, (238)U and (226)Ra intake with the wild berries for adults were estimated as 0.02-0.09 μSv y(-1) (GM is 0.044, GSD is 1.6). It was established that only in the territory with (137)Cs deposition of ∼1.0-1.5 kBq m(-2) the doses resulting from (234)U, (238)U and (226)Ra intake with wild berries can be comparable with corresponding doses from (137)Cs. In the territories with higher levels of (137)Cs deposition the doses resulting from its intake with the wild berries are usually over the summarized doses of uranium and (226)Ra. The total doses for adults resulting from uranium and (226)Ra intake with cow milk and beef ranged between 0.2 and 7.2 μSv y(-1) (GM is 2.0; GSD is 2.9) and the doses from (226)Ra usually exceeded the appropriate doses of uranium with a factor of 3-37. In the sites with (137)Cs deposition less than 3.7 kBq m(-2), the doses from (234)U, (238)U and (226)Ra intake with cow milk and beef were assessing as 1.1-7.2 μSv y(-1) and they were usually higher than the doses from (137)Cs, which were assessing as 0.4-3.2 μSv y(-1) for its deposition 2 kBq m(-2). In the territory with (137)Cs deposition 10-20 kBq m(-2) and higher, the internal doses resulting from (137)Cs intake with cow milk and beef (10-50 μSv y(-1)) exceeded the proper doses from natural (234)U, (238)U and (226)Ra. Copyright © 2013 Elsevier Ltd. All rights reserved.

The estuarine chemistry and isotope systematics of 234,238U in the Amazon and Fly Rivers

USGS Publications Warehouse

Swarzenski, P.; Campbell, P.; Porcelli, D.; McKee, B.

2004-01-01

Natural concentrations of 238U and ??234U values were determined in estuarine surface waters and pore waters of the Amazon and Fly (Papua New Guinea) Rivers to investigate U transport phenomena across river-dominated land-sea margins. Discharge from large, tropical rivers is a major source of dissolved and solid materials transported to the oceans, and are important in defining not only oceanic mass budgets, but also terrestrial weathering rates. On the Amazon shelf, salinity-property plots of dissolved organic carbon, pH and total suspended matter revealed two vastly contrasting water masses that were energetically mixed. In this mixing zone, the distribution of uranium was highly non-conservative and exhibited extensive removal from the water column. Uranium removal was most pronounced within a salinity range of 0-16.6, and likely the result of scavenging and flocculation reactions with inorganic (i.e., Fe/Mn oxides) and organic colloids/particles. Removal of uranium may also be closely coupled to exchange and resuspension processes at the sediment/water interface. An inner-shelf pore water profile indicated the following diagenetic processes: extensive (???1 m) zones of Fe(III) - and, to a lesser degree, Mn(IV) - reduction in the absence of significant S(II) concentrations appeared to facilitate the formation of various authigenic minerals (e.g., siderite, rhodocrosite and uraninite). The pore water dissolved 238U profile co-varied closely with Mn(II). Isotopic variations as evidenced in ??234U pore waters values from this site revealed information on the origin and history of particulate uranium. Only after a depth of about 1 m did the ??234U value approach unity (secular equilibrium), denoting a residual lattice bound uranium complex that is likely an upper-drainage basin weathering product. This suggests that the enriched ??234U values represent a riverine surface complexation product that is actively involved in Mn-Fe diagenetic cycles and surface complexation reactions. In the Fly River estuary, 238U appears to exhibit a reasonably conservative distribution as a function of salinity. The absence of observed U removal does not necessarily imply non-reactivity, but instead may record an integration of concurrent U removal and release processes. There is not a linear correlation between ??234U vs. 1/ 238U that would imply simple two component mixing. It is likely that resuspension of bottom sediments, prolonged residence times in the lower reaches of the Fly River, and energetic particle-colloid interactions contribute to the observed estuarine U distribution. The supply of uranium discharged from humid, tropical river systems to the sea appears to be foremost influenced by particle/water interactions that are ultimately governed by the particular physiographic and hydrologic characteristics of an estuary. ?? 2004 Elsevier Ltd. All rights reserved.

Cross section for the subthreshold fission of 236U

NASA Astrophysics Data System (ADS)

Alekseev, A. A.; Bergman, A. A.; Berlev, A. I.; Koptelov, E. A.; Samylin, B. F.; Trufanov, A. M.; Fursov, B. I.; Shorin, V. S.

2008-08-01

The cross section for 236U fission in the neutron-energy range E n = 0.001 20 keV was measured by using the INR RAS (Institute of Nuclear Research, Russian Academy of Sciences, Moscow) LSDS-100 neutron spectrometer of the lead slowing-down spectrometer type. The resonance fission areas of the resonances at 5.45 eV and 1.28 keV were found, and the fission widths of these resonances were evaluated. The cross section for the 238U( n, f) fission process was measured, and the threshold sensitivity of the LSDS-100 to small values of fission cross sections was estimated. The well-known intermediate structure in the cross section for the neutron-induced subbarrier fission of 236U was confirmed.

Estimation of annual effective dose due to ingestion of natural radionuclides in foodstuffs and water at a proposed uranium mining site in India.

PubMed

Giri, Soma; Jha, V N; Singh, Gurdeep; Tripathi, R M

2013-12-01

To study the distribution of (210)Po, (226)Ra, (230)Th and U(nat) (naturally occurring radioisotopes of uranium [(234)U, (235)U and (238)U]) in food and water around the Bagjata uranium mining area in India. Radionuclides were analyzed in food samples of plant and animal origin after acid digestion. Intake and ingestion dose of the radionuclides were estimated. (210)Po, (226)Ra, (230)Th and U(nat) in all the dietary components ranged widely from < 0.2-36, < 0.02-1.58, < 0.01-2.8 and < 0.017-0.39 Bqkg(-1), respectively. The range of (226)Ra and U(nat) in water was < 3.5-206 and < 12.6-693 mBql(-1), respectively. The intake of radionuclides considering food and water was calculated to be 760 BqY(-1) while the ingestion dose was 601 μSvY(-1). The estimated doses reflect the natural background dose via route of ingestion, which is below the 1 mSvY(-1) limit set by the International Commission on Radiological Protection (ICRP). However, the doses are more than the dose constraint of 300 μSvY(-1) as suggested by the ICRP for members of the public for planned disposal of long-lived radioactive waste. The study confirms that current levels of radionuclides do not pose significant radiological risk to the local inhabitants, but they need close investigation in the near future.

U, Th, and Pb isotopes in hot springs on the Juan de Fuca Ridge

NASA Technical Reports Server (NTRS)

Chen, J. H.

1987-01-01

Concentrations and isotopic compositions of U, Th, and Pb in three hydrothermal fluids from the Juan de Fuca Ridge were determined from samples obtained by the Alvin submersible. The samples were enriched in Pb and Th relative to deep-sea water, and were deficient in U. No clear relationship with Mg was found, suggesting nonideal mixing between the hot hydrothermal fluids and the cold ambient seawater. Values for U-234/U-238 have a seawater signature, and show a U-234 enrichment relative to the equilibrium value. The Pb isotopic composition has a uniform midocean ridge basalt signature, and it is suggested that Pb in these fluids may represent the best average value of the local oceanic crust.

Monte Carlo analyses of TRX slightly enriched uranium-H/sub 2/O critical experiments with ENDF/B-IV and related data sets (AWBA Development Program)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hardy, J. Jr.

1977-12-01

Four H/sub 2/O-moderated, slightly-enriched-uranium critical experiments were analyzed by Monte Carlo methods with ENDF/B-IV data. These were simple metal-rod lattices comprising Cross Section Evaluation Working Group thermal reactor benchmarks TRX-1 through TRX-4. Generally good agreement with experiment was obtained for calculated integral parameters: the epi-thermal/thermal ratio of U238 capture (rho/sup 28/) and of U235 fission (delta/sup 25/), the ratio of U238 capture to U235 fission (CR*), and the ratio of U238 fission to U235 fission (delta/sup 28/). Full-core Monte Carlo calculations for two lattices showed good agreement with cell Monte Carlo-plus-multigroup P/sub l/ leakage corrections. Newly measured parameters for themore » low energy resonances of U238 significantly improved rho/sup 28/. In comparison with other CSEWG analyses, the strong correlation between K/sub eff/ and rho/sup 28/ suggests that U238 resonance capture is the major problem encountered in analyzing these lattices.« less

Studies of Neutron-Induced Fission of 235U, 238U, and 239Pu

NASA Astrophysics Data System (ADS)

Duke, Dana; TKE Team

2014-09-01

A Frisch-gridded ionization chamber and the double energy (2E) analysis method were used to study mass yield distributions and average total kinetic energy (TKE) release from neutron-induced fission of 235U, 238U, and 239Pu. Despite decades of fission research, little or no TKE data exist for high incident neutron energies. Additional average TKE information at incident neutron energies relevant to defense- and energy-related applications will provide a valuable observable for benchmarking simulations. The data can also be used as inputs in theoretical fission models. The Los Alamos Neutron Science Center-Weapons Neutron Research (LANSCE - WNR) provides a neutron beam from thermal to hundreds of MeV, well-suited for filling in the gaps in existing data and exploring fission behavior in the fast neutron region. The results of the studies on 238U, 235U, and 239Pu will be presented. LA-UR-14-24921.

Evaluation of new geological reference materials for uranium-series measurements: Chinese Geological Standard Glasses (CGSG) and macusanite obsidian.

PubMed

Denton, J S; Murrell, M T; Goldstein, S J; Nunn, A J; Amato, R S; Hinrichs, K A

2013-10-15

Recent advances in high-resolution, rapid, in situ microanalytical techniques present numerous opportunities for the analytical community, provided accurately characterized reference materials are available. Here, we present multicollector thermal ionization mass spectrometry (MC-TIMS) and multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) uranium and thorium concentration and isotopic data obtained by isotope dilution for a suite of newly available Chinese Geological Standard Glasses (CGSG) designed for microanalysis. These glasses exhibit a range of compositions including basalt, syenite, andesite, and a soil. Uranium concentrations for these glasses range from ∼2 to 14 μg g(-1), Th/U weight ratios range from ∼4 to 6, (234)U/(238)U activity ratios range from 0.93 to 1.02, and (230)Th/(238)U activity ratios range from 0.98 to 1.12. Uranium and thorium concentration and isotopic data are also presented for a rhyolitic obsidian from Macusani, SE Peru (macusanite). This glass can also be used as a rhyolitic reference material, has a very low Th/U weight ratio (around 0.077), and is approximately in (238)U-(234)U-(230)Th secular equilibrium. The U-Th concentration data agree with but are significantly more precise than those previously measured. U-Th concentration and isotopic data agree within estimated errors for the two measurement techniques, providing validation of the two methods. The large (238)U-(234)U-(230)Th disequilibria for some of the glasses, along with the wide range in their chemical compositions and Th/U ratios should provide useful reference points for the U-series analytical community.

Isotopic compositions of (236)U and Pu isotopes in "black substances" collected from roadsides in Fukushima prefecture: fallout from the Fukushima Dai-ichi nuclear power plant accident.

PubMed

Sakaguchi, Aya; Steier, Peter; Takahashi, Yoshio; Yamamoto, Masayoshi

2014-04-01

Black-colored road dusts were collected in high-radiation areas in Fukushima Prefecture. Measurement of (236)U and Pu isotopes and (134,137)Cs in samples was performed to confirm whether refractory elements, such as U and Pu, from the fuel core were discharged and to ascertain the extent of fractionation between volatile and refractory elements. The concentrations of (134,137)Cs in all samples were exceptionally high, ranging from 0.43 to 17.7 MBq/kg, respectively. (239+240)Pu was detected at low levels, ranging from 0.15 to 1.14 Bq/kg, and with high (238)Pu/(239+240)Pu activity ratios of 1.64-2.64. (236)U was successfully determined in the range of (0.28 to 6.74) × 10(-4) Bq/kg. The observed activity ratios for (236)U/(239+240)Pu were in reasonable agreement with those calculated for the fuel core inventories, indicating that trace amounts of U from the fuel cores were released together with Pu isotopes but without large fractionation. The quantities of U and (239+240)Pu emitted to the atmosphere were estimated as 3.9 × 10(6) Bq (150 g) and 2.3 × 10(9) Bq (580 mg), respectively. With regard to U, this is the first report to give a quantitative estimation of the amount discharged. Appreciable fractionation between volatile and refractory radionuclides associated with the dispersal/deposition processes with distance from the Fukushima Dai-ichi Nuclear Power Plant was found.

U-series ages of solitary corals from the California coast by mass spectrometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stein, M.; Wasserburg, G.J.; Chen, J.H.

1991-12-01

The purpose of this study is to evaluate the feasibility of dating fossil solitary corals from Pleistocene marine strandlines outside tropical latitudes using the recently developed high sensitivity, high-precision U-series technique based on thermal-ionization mass-spectrometry (TIMS). The TIMS technique is much more efficient than conventional {alpha} spectrometry and, as a result, multiple samples of an individual coral skeleton, or different specimens from the same bed can be analyzed. Detached and well-rounded fossil specimens of the solitary coral Balanophyllia elegans were collected from relict littoral deposits on emergent marine terraces along the California coast at Cayucos terrace, Shell Beach terrace, Nestormore » terrace, San Diego, Bird Rock terrace, San Diego. Attached living specimens were collected from the intertidal zone on the modern terrace at Moss Beach. The calculated initial {sup 234}U activities in the fossil specimens of Balanophyllia elegans are higher than the {sup 234}U activity in modern seawater or in the modern specimen. The higher initial activities could possibly reflect the influx of {sup 234}U-enriched continental water into Pleistocene coastal waters, or it could reflect the influx of {sup 234}U-enriched continental water into Pleistocene coastal waters, or it could reflect minor diagenetic alteration, a persistent and fundamental problem in dating all corals.« less

Analysis of benchmark critical experiments with ENDF/B-VI data sets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hardy, J. Jr.; Kahler, A.C.

1991-12-31

Several clean critical experiments were analyzed with ENDF/B-VI data to assess the adequacy of the data for U{sup 235}, U{sup 238} and oxygen. These experiments were (1) a set of homogeneous U{sup 235}-H{sub 2}O assemblies spanning a wide range of hydrogen/uranium ratio, and (2) TRX-1, a simple, H{sub 2}O-moderated Bettis lattice of slightly-enriched uranium metal rods. The analyses used the Monte Carlo program RCP01, with explicit three-dimensional geometry and detailed representation of cross sections. For the homogeneous criticals, calculated k{sub crit} values for large, thermal assemblies show good agreement with experiment. This supports the evaluated thermal criticality parameters for U{supmore » 235}. However, for assemblies with smaller H/U ratios, k{sub crit} values increase significantly with increasing leakage and flux-spectrum hardness. These trends suggest that leakage is underpredicted and that the resonance eta of the ENDF/B-VI U{sup 235} is too large. For TRX-1, reasonably good agreement is found with measured lattice parameters (reaction-rate ratios). Of primary interest is rho28, the ratio of above-thermal to thermal U{sup 238} capture. Calculated rho28 is 2.3 ({+-} 1.7) % above measurement, suggesting that U{sup 238} resonance capture remains slightly overpredicted with ENDF/B-VI. However, agreement is better than observed with earlier versions of ENDF/B.« less

Characterization of bauxite residue (red mud) for 235U, 238U, 232Th and 40K using neutron activation analysis and the radiation dose levels as modeled by MCNP.

PubMed

Landsberger, S; Sharp, A; Wang, S; Pontikes, Y; Tkaczyk, A H

2017-07-01

This study employs thermal and epithermal neutron activation analysis (NAA) to quantitatively and specifically determine absorption dose rates to various body parts from uranium, thorium and potassium. Specifically, a case study of bauxite residue (red mud) from an industrial facility was used to demonstrate the feasibility of the NAA approach for radiological safety assessment, using small sample sizes to ascertain the activities of 235 U, 238 U, 232 Th and 40 K. This proof-of-concept was shown to produce reliable results and a similar approach could be used for quantitative assessment of other samples with possible radiological significance. 238 U and 232 Th were determined by epithermal and thermal neutron activation analysis, respectively. 235 U was determined based on the known isotopic ratio of 238 U/ 235 U. 40 K was also determined using epithermal neutron activation analysis to measure total potassium content and then subtracting its isotopic contribution. Furthermore, the work demonstrates the application of Monte Carlo Neutral-Particle (MCNP) simulations to estimate the radiation dose from large quantities of red mud, to assure the safety of humans and the surrounding environment. Phantoms were employed to observe the dose distribution throughout the human body demonstrating radiation effects on each individual organ. Copyright © 2016 Elsevier Ltd. All rights reserved.

Relative intensities of 2. 5 and 14-MeV source neutrons from comparative responses of U-235 and U-238 detectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jassby, D.L.; Hendel, H.W.; Bosch, H.S.

1988-05-01

The response of polyethylene-moderated U-235 fission counters is only weakly dependent on incident neutron energy, while the response of unmoderated U-238 or Th-232 fission counters increases strongly with energy. A given concentration of D-T neutrons in a mixed DT-DD source results in a unique relative detector response that depends on the parameters R14 and R2.5, where R14 is the ratio of the unmoderated U-238 and moderated U-235 detector efficiencies for a pure 14-MeV neutron source, and R2.5 is the corresponding ratio for a pure 2.5 MeV source. We have determined R14 and R2.5 using D-D and D-T neutron generators insidemore » the TFTR vacuum vessel. The results indicate that, for our detector geometry, the ratio of U-238 to U-235 count rates should increase by a factor of about 3 when the fusion neutron source changes from pure D-D to pure D-T. This calibration is being applied to recent TFTR /open quotes/supershot/close quotes/ data, where the uncollided neutron flux in the post-beam phase contains a high proportion of D-T neutrons from the burnup of D-D tritons. 8 refs., 4 figs,. 2 tabs.« less

U-Th-Ra variations in Himalayan river sediments (Gandak river, India): Weathering fractionation and/or grain-size sorting?

NASA Astrophysics Data System (ADS)

Bosia, Clio; Chabaux, François; Pelt, Eric; France-Lanord, Christian; Morin, Guillaume; Lavé, Jérôme; Stille, Peter

2016-11-01

Understanding the origin of U-Th-Ra variations in the Ganga river sediments is a prerequisite for correctly using U-series nuclides to constrain the sediment transport times in Himalayan rivers. For this purpose, U, Th, and Ra concentrations, along with 238U-234U-230Th-226Ra radioactive disequilibria, were analyzed in bank, bedload and suspended sediments from the Gandak river, one of the main tributaries of the Ganga river. The data confirm that U and Th budgets of the Himalayan sediments are significantly influenced by minor resistant minerals, such as zircon, garnet and Ti-bearing minerals, the dissolution of which required the use of a high-pressure acid digestion process. Most importantly, the results indicate that the variations in (238U/232Th) and (230Th/232Th) activity ratios and 238U-234U-230Th-226Ra disequilibria in sediments along the river alluvial plain mainly reflect modifications in the mineralogical and grain-size compositions rather than the degree of weathering during transport. The (238U/232Th) and (230Th/232Th) activity ratios in the bank and bed sediments are related to variations in the minor primary minerals strongly enriched in U and Th (i.e., zircon, REE-bearing minerals and Ti-bearing minerals), whereas the activity ratios in the suspended load are related to variations in the proportions of clay, Fe-oxyhydroxides and the silt-sand fraction, which contains U- and Th-bearing minor minerals. The data also indicate that 238U-234U-230Th-226Ra disequilibria are strongly influenced by secondary mineral phases: the 230Th budget is likely mainly controlled by Fe-oxyhydroxides, and the 226Ra budget is likely mainly controlled by clay minerals. Therefore, the variations in the 238U-234U-230Th-232Th system in the sediments of the Gandak river cannot simply be interpreted as the result of fractionation due to chemical transformation of the bulk sediment during its transport within the alluvial plain and/or the result of radioactive decay. Consequently, they cannot be used to infer long sediment transport times within the Gandak plain (10-100 ka), as previously proposed. Such analytical and interpretative artifacts are certainly not specific to the present study on the Gandak basin. These issues will certainly be encountered anytime this technique is applied to alluvial systems in which the U and Th budgets of the sediments are influenced by ;heavy; minerals that can be sorted during the transport of sediments within the plain.

Investigating Pu and U isotopic compositions in sediments: a case study in Lake Obuchi, Rokkasho Village, Japan using sector-field ICP-MS and ICP-QMS.

PubMed

Zheng, Jian; Yamada, Masatoshi

2005-08-01

The objectives of the present work were to study isotope ratios and the inventory of plutonium and uranium isotope compositions in sediments from Lake Obuchi, which is in the vicinity of several nuclear fuel facilities in Rokkasho, Japan. Pu and its isotopes were determined using sector-field ICP-MS and U and its isotopes were determined with ICP-QMS after separation and purification with a combination of ion-exchange and extraction chromatography. The observed (240)Pu/(239)Pu atom ratio (0.186 +/- 0.016) was similar to that of global fallout, indicating that the possible early tropospheric fallout Pu did not deliver Pu from the Pacific Proving Ground to areas above 40 degrees N. The previously reported higher Pu inventory in the deep water area of Lake Obuchi could be attributed to the lateral transportation of Pu deposited in the shallow area which resulted from the migration of deposited global fallout Pu from the land into the lake by river runoff and from the Pacific Ocean by tide movement and sea water scavenging, as well as from direct soil input by winds. The (235)U/(238)U atom ratios ranged from 0.00723 to 0.00732, indicating the natural origin of U in the sediments. The average (234)U/(238)U activity ratio of 1.11 in a sediment core indicated a significant sea water U contribution. No evidence was found for the release of U containing wastes from the nearby nuclear facilities. These results will serve as a reference baseline on the levels of Pu and U in the studied site so that any further contamination from the spent nuclear fuel reprocessing plants, the radioactive waste disposal and storage facilities, and the uranium enrichment plant can be identified, and the impact of future release can be rapidly assessed.

A study on possible use of Urtica dioica (common nettle) plants as uranium (234U, 238U) contamination bioindicator near phosphogypsum stockpile.

PubMed

Olszewski, Grzegorz; Boryło, Alicja; Skwarzec, Bogdan

The aim of this study was to determine uranium concentrations in common nettle ( Urtica dioica ) plants and corresponding soils samples which were collected from the area of phosphogypsum stockpile in Wiślinka (northern Poland). The uranium concentrations in roots depended on its concentrations in soils. Calculated BCF and TF values showed that soils characteristics and air deposition affect uranium absorption and that different uranium species have different affinities to U . dioica plants. The values of 234 U/ 238 U activity ratio indicate natural origin of these radioisotopes in analyzed plants. Uranium concentration in plants roots is negatively weakly correlated with distance from phosphogypsum stockpile.

The ability of Helianthus annuus L. and Brassica juncea to uptake and translocate natural uranium and 226Ra under different milieu conditions.

PubMed

Vera Tomé, F; Blanco Rodríguez, P; Lozano, J C

2009-01-01

Seedlings of Helianthus annuus L. (HA) and Brassica juncea (BJ) were used to test the effect of the pH, the presence of phosphates, and the addition of ethylene-diamine-tetraacetic acid (EDTA) or citrate on the uptake and the translocation of uranium isotopes ((238)U, (235)U, and (234)U) and (226)Ra. The results indicated that the presence of phosphates generally reduces the uptake and transfer of uranium from the roots to the shoots of HA. In the case of BJ, while phosphate enhanced the retention of uranium by roots, the translocation was poorer. Likewise, for (226)Ra, the best translocation was in the absence of phosphates for both species. The addition of citrate increased the translocation of uranium for both species, but had no clear effect on the transfer of (226)Ra. The effect of EDTA was much more moderate both for uranium and for (226)Ra, and for both plant species. Only noticeable was a slightly better uptake of (226)Ra by BJ at neutral pH, although the translocation was lower.

Evaluation of the use of reverse osmosis to eliminate natural radionuclides from water samples.

PubMed

Nieto, Antonio; Palomo, Marta; Ruana, Josep; Peñalver, Alejandra; Aguilar, Carme; Borrull, Francesc

2013-12-01

The objective of drinking water treatment plants (DWTP) is to supply the population with tap water that is in optimal condition and in compliance with water quality regulations. In the DWTP of L'Ampolla (Tarragona, Spain), slightly high values of gross alpha activity and the amount of salts in the raw water have been observed. Conventional treatment has reduced these levels only minimally. This study tested a tertiary treatment based on reverse osmosis is tested in an industrial pilot plant (240 m3/day) The efficiency of this pilot plant to reduce the gross alpha and beta activities and the activity of some individual radioisotopes (U(238), U(234), U(235) and Ra(226)) was tested. Results showed that the elimination of alpha emitters was greater than 90%, whereas the elimination of beta emitters was about 35%. Overall, the data provided evidence that the pilot plant is effective for removing different radionuclides that can be present in the incoming water treated. Therefore, tertiary treatment based on reverse osmosis has a positive effect in water quality.

Isotope Analysis of Uranium by Optical Spectroscopy; ANALYSE ISOTOPIQUE DE L'URANIUM PAR SPECTROSCOPIE OPTIQUE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gerstenkorn, S.

1958-06-01

Isotopic analysis of urarium is made by means of hollow cathode lamp and a Fabry-Perot photoelectric spectrometer. The line U/sup 235/, 5027 A is used. This method allows a deterraination of the isotopic concentrations in U /sup 235/ down to 0.1%. The relative precision is about 2% for amounts of U/sup 235/ over 1%. For weaker amounts this line allows relative measurements of better precision when using standard mixtures. (auth)

Crustal subsidence rate off Hawaii determined from sup 234 U/ sup 238 U ages of drowned coral reefs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ludwig, K.R.; Szabo, B.J.; Simmons, K.R.

1991-02-01

A series of submerged coral reefs off northwestern Hawaii was formed during (largely glacial) intervals when the rate of local sea-level rise was less than the maximum upward growth rate of the reefs. Mass-spectrometric {sup 234}U/{sup 238}U ages for samples from six such reefs range from 17 to 475 ka and indicate that this part of the Hawaiian Ridge has been subsiding at a roughly uniform rate of 2.6 mm/yr for the past 475 ka. The {sup 234}U/{sup 238}U ages are in general agreement with model ages of reef drowning (based on estimates of paleo-sea-level stands derived from oxygen-isotope ratiosmore » of deep-sea sediments), but there are disagreements in detail. The high attainable precision ({plus minus}10 ka or better on samples younger than {approximately}800 ka), large applicable age range, relative robustness against open-system behavior, and ease of analysis for this technique hold great promise for future applications of dating of 50-1,000 ka coral.« less

S/sub n/ analysis of the TRX metal lattices with ENDF/B version III data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wheeler, F.J.; Pearlstein, S.

1975-03-01

Two critical assemblies, designated as thermal-reactor benchmarks TRX-1 and TRX-2 for ENDF/B data testing, were analyzed using the one-dimensional S/sub n/-theory code SCAMP. The two assemblies were simple lattices of aluminum-clad, uranium-metal fuel rods in triangular arrays with D$sub 2$O as moderator and reflector. The fuel was low-enriched (1.3 percent $sup 235$U), 0.387-inch in diameter and had an active height of 48 inches. The volume ratio of water to uranium was 2.35 for the TRX-1 lattice and 4.02 for TRX-2. Full-core S/sub n/ calculations based on Version III data were performed for these assemblies and the results obtained were comparedmore » with the measured values of the multiplication factors, the ratio of epithermal-to-thermal neutron capture in $sup 238$U, the ratio of epithermal-to-thermal fission in $sup 235$U, the ratio of $sup 238$U fission to $sup 235$U fission, and the ratio of capture in $sup 238$U to fission in $sup 235$U. Reaction rates were obtained from a central region of the full- core problems. Multigroup cross sections for the reactor calculation were obtained from S/sub n/ cell calculations with resonance self-shielding calculated using the RABBLE treatment. The results of the analyses are generally consistent with results obtained by other investigators. (auth)« less

Photofission cross-section ratio measurement of 235U/238U using monoenergetic photons in the energy range of 9.0-16.6 MeV

NASA Astrophysics Data System (ADS)

Krishichayan; Bhike, Megha; Finch, S. W.; Howell, C. R.; Tonchev, A. P.; Tornow, W.

2017-05-01

Photofission cross-section ratios of 235U and 238U have been measured using monoenergetic photon beams at the HIγS facility of TUNL. These measurements have been performed in small energy steps between 9.0 and 16.6 MeV using a dual-fission ionization chamber. Measured cross-section ratios are compared with the previous experimental data as well as with the recent evaluated nuclear data library ENDF.

Investigating Uranium Mobility Using Stable Isotope Partitioning of 238U/235U and a Reactive Transport Model

NASA Astrophysics Data System (ADS)

Bizjack, M.; Johnson, T. M.; Druhan, J. L.; Shiel, A. E.

2015-12-01

We report a numerical reactive transport model which explicitly incorporates the effectively stable isotopes of uranium (U) and the factors that influence their partitioning in bioactive systems. The model reproduces trends observed in U isotope ratios and concentration measurements from a field experiment, thereby improving interpretations of U isotope ratios as a tracer for U reactive transport. A major factor contributing to U storage and transport is its redox state, which is commonly influenced by the availability of organic carbon to support metal-reducing microbial communities. Both laboratory and field experiments have demonstrated that biogenic reduction of U(VI) fractionates the stable isotope ratio 238U/235U, producing an isotopically heavy solid U(IV) product. It has also been shown that other common reactive transport processes involving U do not fractionate isotopes to a consistently measurable level, which suggests the capacity to quantify the extent of bioreduction occurring in groundwater containing U using 238U/235U ratios. A recent study of a U bioremediation experiment at the Rifle IFRC site (Colorado, USA) applied Rayleigh distillation models to quantify U stable isotope fractionation observed during acetate amendment. The application of these simplified models were fit to the observations only by invoking a "memory-effect," or a constant source of low-concentration, unfractionated U(VI). In order to more accurately interpret the measured U isotope ratios, we present a multi-component reactive transport model using the CrunchTope software. This approach is capable of quantifying the cycling and partitioning of individual U isotopes through a realistic network of transport and reaction pathways including reduction, oxidation, and microbial growth. The model incorporates physical heterogeneity of the aquifer sediments through zones of decreased permeability, which replicate the observed bromide tracer, major ion chemistry, U concentration, and U isotope ratios. These results suggest that the rate-limited transport properties of U in the Rifle aquifer are governed by the presence of low-permeability regions in the modeling domain and that these zones are responsible for the suggested "memory" effect observed in previous U isotope studies at this site.

Measurement of the normalized 238U(n ,f )/235U(n ,f ) cross section ratio from threshold to 30 MeV with the NIFFTE fission Time Projection Chamber

NASA Astrophysics Data System (ADS)

Casperson, R. J.; Asner, D. M.; Baker, J.; Baker, R. G.; Barrett, J. S.; Bowden, N. S.; Brune, C.; Bundgaard, J.; Burgett, E.; Cebra, D. A.; Classen, T.; Cunningham, M.; Deaven, J.; Duke, D. L.; Ferguson, I.; Gearhart, J.; Geppert-Kleinrath, V.; Greife, U.; Grimes, S.; Guardincerri, E.; Hager, U.; Hagmann, C.; Heffner, M.; Hensle, D.; Hertel, N.; Higgins, D.; Hill, T.; Isenhower, L. D.; King, J.; Klay, J. L.; Kornilov, N.; Kudo, R.; Laptev, A. B.; Loveland, W.; Lynch, M.; Lynn, W. S.; Magee, J. A.; Manning, B.; Massey, T. N.; McGrath, C.; Meharchand, R.; Mendenhall, M. P.; Montoya, L.; Pickle, N. T.; Qu, H.; Ruz, J.; Sangiorgio, S.; Schmitt, K. T.; Seilhan, B.; Sharma, S.; Snyder, L.; Stave, S.; Tate, A. C.; Tatishvili, G.; Thornton, R. T.; Tovesson, F.; Towell, D. E.; Towell, R. S.; Walsh, N.; Watson, S.; Wendt, B.; Wood, L.; Yao, L.; Younes, W.; Niffte Collaboration

2018-03-01

The normalized 238U(n ,f )/235U(n ,f ) cross section ratio has been measured using the NIFFTE fission Time Projection Chamber (fissionTPC) from the reaction threshold to 30 MeV . The fissionTPC is a two-volume MICROMEGAS time projection chamber that allows for full three-dimensional reconstruction of fission-fragment ionization profiles from neutron-induced fission. The measurement was performed at the Los Alamos Neutron Science Center, where the neutron energy is determined from neutron time of-flight. The 238U(n ,f )/235U(n ,f ) ratio reported here is the first cross section measurement made with the fissionTPC, and will provide new experimental data for evaluation of the 238U(n ,f ) cross section, an important standard used in neutron-flux measurements. Use of a development target in this work prevented the determination of an absolute normalization, to be addressed in future measurements. Instead, the measured cross section ratio has been normalized to ENDF/B-VIII.β 5 at 14.5 MeV.

Transmission electron microscopy investigation of neutron irradiated Si and ZrN coated UMo particles prepared using FIB

NASA Astrophysics Data System (ADS)

Van Renterghem, W.; Miller, B. D.; Leenaers, A.; Van den Berghe, S.; Gan, J.; Madden, J. W.; Keiser, D. D.

2018-01-01

Two fuel plates, containing Si and ZrN coated U-Mo fuel particles dispersed in an Al matrix, were irradiated in the BR2 reactor of SCK•CEN to a burn-up of ∼70% 235U. Five samples were prepared by INL using focused ion beam milling and transported to SCK•CEN for transmission electron microscopy (TEM) investigation. Two samples were taken from the Si coated U-Mo fuel particles at a burn-up of ∼42% and ∼66% 235U and three samples from the ZrN coated U-Mo at a burn-up of ∼42%, ∼52% and ∼66% 235U. The evolution of the coating, fuel structure, fission products and the formation of interaction layers are discussed. Both coatings appear to be an effective barrier against fuel matrix interaction and only on the samples having received the highest burn-up and power, the formation of an interaction between Al and U(Mo) can be observed on those locations where breaches in the coatings were formed during plate fabrication.

Evidence of isotopic fractionation of natural uranium in cultured human cells

NASA Astrophysics Data System (ADS)

Paredes, Eduardo; Avazeri, Emilie; Malard, Véronique; Vidaud, Claude; Reiller, Pascal E.; Ortega, Richard; Nonell, Anthony; Isnard, Hélène; Chartier, Frédéric; Bresson, Carole

2016-12-01

The study of the isotopic fractionation of endogen elements and toxic heavy metals in living organisms for biomedical applications, and for metabolic and toxicological studies, is a cutting-edge research topic. This paper shows that human neuroblastoma cells incorporated small amounts of uranium (U) after exposure to 10 µM natural U, with preferential uptake of the 235U isotope with regard to 238U. Efforts were made to develop and then validate a procedure for highly accurate n(238U)/n(235U) determinations in microsamples of cells. We found that intracellular U is enriched in 235U by 0.38 ± 0.13‰ (2σ, n = 7) relative to the exposure solutions. These in vitro experiments provide clues for the identification of biological processes responsible for uranium isotopic fractionation and link them to potential U incorporation pathways into neuronal cells. Suggested incorporation processes are a kinetically controlled process, such as facilitated transmembrane diffusion, and the uptake through a high-affinity uranium transport protein involving the modification of the uranyl (UO22+) coordination sphere. These findings open perspectives on the use of isotopic fractionation of metals in cellular models, offering a probe to track uptake/transport pathways and to help decipher associated cellular metabolic processes.

Evidence of isotopic fractionation of natural uranium in cultured human cells

PubMed Central

Paredes, Eduardo; Avazeri, Emilie; Malard, Véronique; Vidaud, Claude; Reiller, Pascal E.; Ortega, Richard; Nonell, Anthony; Isnard, Hélène; Chartier, Frédéric; Bresson, Carole

2016-01-01

The study of the isotopic fractionation of endogen elements and toxic heavy metals in living organisms for biomedical applications, and for metabolic and toxicological studies, is a cutting-edge research topic. This paper shows that human neuroblastoma cells incorporated small amounts of uranium (U) after exposure to 10 µM natural U, with preferential uptake of the 235U isotope with regard to 238U. Efforts were made to develop and then validate a procedure for highly accurate n(238U)/n(235U) determinations in microsamples of cells. We found that intracellular U is enriched in 235U by 0.38 ± 0.13‰ (2σ, n = 7) relative to the exposure solutions. These in vitro experiments provide clues for the identification of biological processes responsible for uranium isotopic fractionation and link them to potential U incorporation pathways into neuronal cells. Suggested incorporation processes are a kinetically controlled process, such as facilitated transmembrane diffusion, and the uptake through a high-affinity uranium transport protein involving the modification of the uranyl (UO22+) coordination sphere. These findings open perspectives on the use of isotopic fractionation of metals in cellular models, offering a probe to track uptake/transport pathways and to help decipher associated cellular metabolic processes. PMID:27872304

Evidence of isotopic fractionation of natural uranium in cultured human cells.

PubMed

Paredes, Eduardo; Avazeri, Emilie; Malard, Véronique; Vidaud, Claude; Reiller, Pascal E; Ortega, Richard; Nonell, Anthony; Isnard, Hélène; Chartier, Frédéric; Bresson, Carole

2016-12-06

The study of the isotopic fractionation of endogen elements and toxic heavy metals in living organisms for biomedical applications, and for metabolic and toxicological studies, is a cutting-edge research topic. This paper shows that human neuroblastoma cells incorporated small amounts of uranium (U) after exposure to 10 µM natural U, with preferential uptake of the 235 U isotope with regard to 238 U. Efforts were made to develop and then validate a procedure for highly accurate n( 238 U)/n( 235 U) determinations in microsamples of cells. We found that intracellular U is enriched in 235 U by 0.38 ± 0.13‰ (2σ, n = 7) relative to the exposure solutions. These in vitro experiments provide clues for the identification of biological processes responsible for uranium isotopic fractionation and link them to potential U incorporation pathways into neuronal cells. Suggested incorporation processes are a kinetically controlled process, such as facilitated transmembrane diffusion, and the uptake through a high-affinity uranium transport protein involving the modification of the uranyl (UO 2 2+ ) coordination sphere. These findings open perspectives on the use of isotopic fractionation of metals in cellular models, offering a probe to track uptake/transport pathways and to help decipher associated cellular metabolic processes.

Uranium and plutonium in anoxic marine sediments of the Santiago River mouth (Eastern Pacific, Mexico).

PubMed

Almazán-Torres, María Guadalupe; Ordóñez-Regil, Eduardo; Ruiz-Fernández, Ana Carolina

2016-11-01

The uranium (U) and plutonium (Pu) content with depth in a sediment core collected in the continental shelf off the mouth of the Santiago River in the Mexican Pacific was studied to evaluate the contamination effects of the effluent of the Santiago-Lerma River as it moves into the sea. The large mass of terrestrial detritus delivered by the river influences the physicochemical and geochemical processes in the seafloor. Abnormal concentrations of U and Pu in sediments were examined as indicative of the effects of anoxic conditions. One of the indicators of pollution of seawater is the bacterial activity of the shallow seabed layer; and among the prevailing bacteria, the magnetotactic ones induce the formation of euhedral and framboidal shapes (pyrite). These pyrite entities are by-products of anoxic environments loaded with decomposing detrital material and are very abundant in the surface layers of the sediment core analyzed. The pyrite formation is the result of a biochemical reaction between iron and organic sulphur reduced by bacteria, and the pyrite entities precipitate to the seafloor. In the same upper zone of the profile, 238 U is readily immobilized, while 234 U is oxidized and dissolved in seawater by the effect of hot atom chemistry. This may cause the activity ratio (AR) 234 U/ 238 U disequilibrium (near 0.41). Furthermore, in the shallow layer of the sediment core, an abnormally high concentration of 239+240 Pu was detected. In this upper layer, the activity concentrations found were 3.19 Bq kg -1 for 238 U, 1.32 kg -1 for 234 U and 2.78 Bq kg -1 for 239+240 Pu. In the lower fractions of the sediment core, normal values of AR 234 U/ 238 U (≈1) were found, with traces of 239+240 Pu. Copyright © 2016 Elsevier Ltd. All rights reserved.

Trace metal cycling and 238U/235U in New Zealand's fjords: Implications for reconstructing global paleoredox conditions in organic-rich sediments

NASA Astrophysics Data System (ADS)

Hinojosa, Jessica L.; Stirling, Claudine H.; Reid, Malcolm R.; Moy, Christopher M.; Wilson, Gary S.

2016-04-01

Reconstructing the history of ocean oxygenation provides insight into links between ocean anoxia, biogeochemical cycles, and climate. Certain redox-sensitive elements respond to changes in marine oxygen content through phase shifts and concomitant isotopic fractionation, providing new diagnostic proxies of past ocean hypoxia. Here we explore the behavior and inter-dependence of a suite of commonly utilized redox-sensitive trace metals (U, Mo, Fe, and Mn) and the emerging ;stable; isotope system of U (238U/235U, or δ238U) in New Zealand fjords. These semi-restricted basins have chemical conditions spanning the complete redox spectrum from fully oxygenated to suboxic to intermittently anoxic/euxinic. In the anoxic water column, U and Mo concentrations decrease, while Fe and Mn concentrations increase. Similarly, signals of past euxinic conditions can be found by U, Mo, Fe, and Mn enrichment in the underlying sediments. The expected U isotopic shift toward a lower δ238U in the anoxic water column due to U(VI)-U(IV) reduction is not observed; instead, water column δ238U profiles are consistent in fjords of all oxygen content, falling within previously reported ranges for open ocean seawater (δ238U = -0.42 ± 0.07‰). Additionally, surface sediment δ238U results show evidence for competing U isotope fractionation processes. One site indicates increased export of 238U from seawater to the underlying sediments (fractionation between aqueous seawater U and particulate sediment U, or ΔU(aq)-U(solid) = -0.25‰), consistent with redox-driven fractionation. Another site suggests potential U(VI) adsorption-driven fractionation, reflecting increased export of 235U from seawater to sediments (ΔU(aq)-U(solid) = 0.25‰). We discuss several potential factors that could alter δ238U in waters and sediments beyond redox-driven shifts, including adsorption to organic matter in waters of high primary productivity, reaction rates for competing processes of U adsorption and release, and isotopic constraints of U coming into the system from terrestrial environments. These potential complications should be understood and constrained through observations, experiments, and models before future application of δ238U as a global paleoredox tracer can achieve its full potential.

Determination of depleted uranium in urine via isotope ratio measurements using large-bore direct injection high efficiency nebulizer-inductively coupled plasma mass spectrometry.

PubMed

Westphal, Craig S; McLean, John A; Hakspiel, Shelly J; Jackson, William E; McClain, David E; Montaser, Akbar

2004-09-01

Inductively coupled plasma mass spectrometry (ICP-MS), coupled with a large-bore direct injection high efficiency nebulizer (LB-DIHEN), was utilized to determine the concentration and isotopic ratio of uranium in 11 samples of synthetic urine spiked with varying concentrations and ratios of uranium isotopes. Total U concentrations and (235)U/(238)U isotopic ratios ranged from 0.1 to 10 microg/L and 0.0011 and 0.00725, respectively. The results are compared with data from other laboratories that used either alpha-spectrometry or quadrupole-based ICP-MS with a conventional nebulizer-spray chamber arrangement. Severe matrix effects due to the high total dissolved solid content of the samples resulted in a 60 to 80% loss of signal intensity, but were compensated for by using (233)U as an internal standard. Accurate results were obtained with LB-DIHEN-ICP-MS, allowing for the positive identification of depleted uranium based on the (235)U/(238)U ratio. Precision for the (235)U/(238)U ratio is typically better than 5% and 15% for ICP-MS and alpha-spectrometry, respectively, determined over the concentrations and ratios investigated in this study, with the LB-DIHEN-ICP-MS system providing the most accurate results. Short-term precision (6 min) for the individual (235)U and (238)U isotopes in synthetic urine is better than 2% (N = 7), compared to approximately 5% for conventional nebulizer-spray chamber arrangements and >10% for alpha-spectrometry. The significance of these measurements is discussed for uranium exposure assessment of Persian Gulf War veterans affected by depleted uranium ammunitions.

Evaluation strategies for isotope ratio measurements of single particles by LA-MC-ICPMS.

PubMed

Kappel, S; Boulyga, S F; Dorta, L; Günther, D; Hattendorf, B; Koffler, D; Laaha, G; Leisch, F; Prohaska, T

2013-03-01

Data evaluation is a crucial step when it comes to the determination of accurate and precise isotope ratios computed from transient signals measured by multi-collector-inductively coupled plasma mass spectrometry (MC-ICPMS) coupled to, for example, laser ablation (LA). In the present study, the applicability of different data evaluation strategies (i.e. 'point-by-point', 'integration' and 'linear regression slope' method) for the computation of (235)U/(238)U isotope ratios measured in single particles by LA-MC-ICPMS was investigated. The analyzed uranium oxide particles (i.e. 9073-01-B, CRM U010 and NUSIMEP-7 test samples), having sizes down to the sub-micrometre range, are certified with respect to their (235)U/(238)U isotopic signature, which enabled evaluation of the applied strategies with respect to precision and accuracy. The different strategies were also compared with respect to their expanded uncertainties. Even though the 'point-by-point' method proved to be superior, the other methods are advantageous, as they take weighted signal intensities into account. For the first time, the use of a 'finite mixture model' is presented for the determination of an unknown number of different U isotopic compositions of single particles present on the same planchet. The model uses an algorithm that determines the number of isotopic signatures by attributing individual data points to computed clusters. The (235)U/(238)U isotope ratios are then determined by means of the slopes of linear regressions estimated for each cluster. The model was successfully applied for the accurate determination of different (235)U/(238)U isotope ratios of particles deposited on the NUSIMEP-7 test samples.

EXAFS Reveals the Mechanism of U Isotope Fractionation During Adsorption to Mn Oxyhydroxide

NASA Astrophysics Data System (ADS)

Wasylenki, L. E.; Brennecka, G.; Bargar, J.; Weyer, S.; Anbar, A. D.

2010-12-01

Natural variations in the ratio of 238U/235U due to “stable” isotope fractionation have now been reported for a range of geological samples [1-3]. Among the observed variations are a small difference in 238U/235U between seawater and ferromanganese sediments (seawater slightly heavier) and a larger difference, with opposite sense, between seawater and black shales (seawater lighter). These variations suggest that long-term changes in the proportions of oxic and anoxic/sulfidic sinks for U in the ocean over Earth’s history may be recorded as shifts in the isotopic compositions of marine sediments. Thus U isotopes are a potential paleoredox proxy for the oceans, as suggested by [4]. In order to investigate the mechanism behind fractionation of U isotopes in oxidizing marine environments, we previously conducted simple adsorption experiments in which an isotopically known pool of dissolved U partly adsorbed onto synthetic birnessite, a common Mn oxyhydroxide in hydrogenetic ferromanganese crusts. Our experimental result agreed very well with that observed between seawater and natural ferromanganese sediments: δ238U/235U of adsorbed U was 0.2‰ lighter than δ238U/235U of dissolved U [5]. The magnitude of fractionation is constant as a function of experimental duration and fraction of U adsorbed, suggesting an equilibrium isotope effect. Many metal isotope effects are driven by changes in oxidation state for the metal of interest. Because both dissolved and adsorbed U are hexavalent in this system, a redox reaction cannot be causing isotope fractionation. We therefore hypothesized that a difference in uranium’s coordination environment between dissolved and adsorbed U is likely responsible for the isotope effect. We analyzed a sample from our experimental study with extended X-ray absorption fine structure (EXAFS) spectroscopy. Comparison of the EXAFS spectrum of U adsorbed on birnessite with the spectra of aqueous U species (UO22+ and UO2(CO3)34-) reveals subtle, but important differences in the U-O coordination shell between dissolved and adsorbed U. In particular, there is an increase in disorder in the bond distances to equatorial oxygens in the adsorbed complex. Our EXAFS data support our hypothesis that a difference in coordination chemistry drives the isotope effect observed in our experiments. The same mechanism may well explain the U isotope fractionation observed between seawater and hydrogenetic ferromanganese nodules, although a similar investigation of U isotope behavior during adsorption to Fe oxyhydroxides should be undertaken. [1] Weyer et al. (2008) GCA 72, 345. [2] Stirling et al. (2007) EPSL 264, 208. [3] Bopp et al. (2009) Geology, 37, 611. [4] Montoya-Pino et al. (2010) Geology 38, 315. [5] Brennecka et al. (2008) GCA 72(12) Suppl., A114.

The age of universe

NASA Astrophysics Data System (ADS)

Ali, Zeeshan

The presence of short-lived isotope Curium-247 in the early Solar System complicates the job of dating the earliest events in the solar nebula. Primitive components in meteorites contain a detailed record of the conditions and processes in the solarnebula, the cloud of dust and gas surrounding the infant Sun. Determining accurately when the first materialsformed re-quires the lead-lead (Pb-Pb) dating method, a method based on the decay of uranium (U) isotopes toPb isotopes. The initial ratio of U-238 to U-235 is critical to determining theages correctly, and many studies have concluded that the ratio is constant for any given age. How-ever, my colleagues at Arizona State University(Frankfurt, Germany), and the Senckenberg Forschungsinstitut und Naturmuseum (also in Frankfurt) and I have found that some calcium-aluminum-rich inclusions (CAIs) in chondritic meteorites deviate from the conventional value for the U-238/U-235 ratio. This could lead to inaccuracies of up to 5 million years in the age of these objects, if no correction is made.Variations in the concentrations of thorium and neodymium with the U-238/U-235 ratio suggest that the ratio may have been lowered by the decay of curium-247, which decays to U-235 with a half-life of 15.6 million years. Curium-247 is created in certain types of energetic supernovae, so its presence suggests that a supernova added material to the pre-solar interstellar cloud between 110 and 140 million years before theSolar System began to form.

A Complication in Determining the Precise Age of the Solar System

NASA Astrophysics Data System (ADS)

Brennecka, G. A.

2010-01-01

Primitive components in meteorites contain a detailed record of the conditions and processes in the solar nebula, the cloud of dust and gas surrounding the infant Sun. Determining accurately when the first materials formed requires the lead-lead (Pb-Pb) dating method, a method based on the decay of uranium (U) isotopes to Pb isotopes. The initial ratio of U-238 to U-235 is critical to determining the ages correctly, and many studies have concluded that the ratio is constant for any given age. However, my colleagues at Arizona State University, Institut fur Geowissenschaften, Goethe-Universitat (Frankfurt, Germany), and the Senckenberg Forschungsinstitut und Naturmuseum (also in Frankfurt) and I have found that some calcium-aluminum-rich inclusions (CAIs) in chondritic meteorites deviate from the conventional value for the U-238/U-235 ratio. This could lead to inaccuracies of up to 5 million years in the age of these objects, if no correction is made. Variations in the concentrations of thorium and neodymium with the U-238/U-235 ratio suggest that the ratio may have been lowered by the decay of curium-247, which decays to U-235 with a half-life of 15.6 million years. Curium-247 is created in certain types of energetic supernovae, so its presence suggests that a supernova added material to the pre-solar interstellar cloud between 110 and 140 million years before the Solar System began to form.

Uranium isotopes and dissolved organic carbon in loess permafrost: Modeling the age of ancient ice

USGS Publications Warehouse

Ewing, Stephanie A.; Paces, James B.; O'Donnell, J.A.; Jorgenson, M.T.; Kanevskiy, M.Z.; Aiken, George R.; Shur, Y.; Harden, Jennifer W.; Striegl, Robert G.

2015-01-01

The residence time of ice in permafrost is an indicator of past climate history, and of the resilience and vulnerability of high-latitude ecosystems to global change. Development of geochemical indicators of ground-ice residence times in permafrost will advance understanding of the circumstances and evidence of permafrost formation, preservation, and thaw in response to climate warming and other disturbance. We used uranium isotopes to evaluate the residence time of segregated ground ice from ice-rich loess permafrost cores in central Alaska. Activity ratios of 234U vs. 238U (234U/238U) in water from thawed core sections ranged between 1.163 and 1.904 due to contact of ice and associated liquid water with mineral surfaces over time. Measured (234U/238U) values in ground ice showed an overall increase with depth in a series of five neighboring cores up to 21 m deep. This is consistent with increasing residence time of ice with depth as a result of accumulation of loess over time, as well as characteristic ice morphologies, high segregated ice content, and wedge ice, all of which support an interpretation of syngenetic permafrost formation associated with loess deposition. At the same time, stratigraphic evidence indicates some past sediment redistribution and possibly shallow thaw among cores, with local mixing of aged thaw waters. Using measures of surface area and a leaching experiment to determine U distribution, a geometric model of (234U/238U) evolution suggests mean ages of up to ∼200 ky BP in the deepest core, with estimated uncertainties of up to an order of magnitude. Evidence of secondary coatings on loess grains with elevated (234U/238U) values and U concentrations suggests that refinement of the geometric model to account for weathering processes is needed to reduce uncertainty. We suggest that in this area of deep ice-rich loess permafrost, ice bodies have been preserved from the last glacial period (10–100 ky BP), despite subsequent fluctuations in climate, fire disturbance and vegetation. Radiocarbon (14C) analysis of dissolved organic carbon (DOC) in thaw waters supports ages greater than ∼40 ky BP below 10 m. DOC concentrations in thaw waters increased with depth to maxima of >1000 ppm, despite little change in ice content or cryostructures. These relations suggest time-dependent production of old DOC that will be released upon permafrost thaw at a rate that is mediated by sediment transport, among other factors.

Nuclear Resonance Fluorescence of U-235 above 3 MeV

DOE Office of Scientific and Technical Information (OSTI.GOV)

Warren, Glen A.; Caggiano, Joseph A.; Miller, Erin A.

Pacific Northwest National Laboratory and Passport Systems have collaborated to conduct measurements to search for a nuclear resonance fluorescence response of U-235 from 3 to 5 MeV using an 8 g sample of highly enriched uranium. These new measurements complement previously reported measurements below 3 MeV. Preliminary analysis indicates that no strong resonances exist for U-235 in this energy range. A second set of measurements focused on a signature search in the 5 to 10 MeV range is still under analysis.

Environmental site description for a Uranium Atomic Vapor Laser Isotope Separation (U-AVLIS) production plant at the Paducah Gaseous Diffusion Plant site

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marmer, G.J.; Dunn, C.P.; Moeller, K.L.

Uranium enrichment in the United States has utilized a diffusion process to preferentially enrich the U-235 isotope in the uranium product. The U-AVLIS process is based on electrostatic extraction of photoionized U-235 atoms from an atomic vapor stream created by electron-beam vaporization of uranium metal alloy. The U-235 atoms are ionized when precisely tuned laser light -- of appropriate power, spectral, and temporal characteristics -- illuminates the uranium vapor and selectively photoionizes the U-235 isotope. A programmatic document for use in screening DOE site to locate a U-AVLIS production plant was developed and implemented in two parts. The first partmore » consisted of a series of screening analyses, based on exclusionary and other criteria, that identified a reasonable number of candidate sites. These sites were subjected to a more rigorous and detailed comparative analysis for the purpose of developing a short list of reasonable alternative sites for later environmental examination. This environmental site description (ESD) provides a detailed description of the PGDP site and vicinity suitable for use in an environmental impact statement (EIS). The report is based on existing literature, data collected at the site, and information collected by Argonne National Laboratory (ANL) staff during a site visit. 65 refs., 15 tabs.« less

Photofission cross-section ratio measurement of 235 U/ 238 U using monoenergetic photons in the energy range of 9.0–16.6 MeV

DOE PAGES

Krishichayan,; Bhike, Megha; Finch, S. W.; ...

2017-05-01

Photofission cross-section ratios of 235U and 238U have been measured using monoenergetic photon beams from the High Intensity Gamma-ray Source facility at the Triangle Universities Nuclear Laboratory. These measurements have been performed in small energy steps between 9.0 and 16.6 MeV using a dual-fission ionization chamber. The measured cross-section ratios are compared with the previous experimental data as well as with the recent evaluated nuclear data library ENDF.

Neutron-induced fission cross section measurement of 233U, 241Am and 243Am in the energy range 0.5 MeV En 20 MeV at n TOF at CERN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Belloni, F.; Milazzo, P. M.; Calviani, M.

2012-01-01

Neutron-induced fission cross section measurements of 233U, 243Am and 241Am relative to 235U have been carried out at the neutron time-of-flight facility n TOF at CERN. A fast ionization chamber has been employed. All samples were located in the same detector; therefore the studied elements and the reference 235U target are subject to the same neutron beam.

On the Relative Signs of "ROT-Effects" in Ternary and Binary Fission of 233U and 235U Nuclei Induced by Polarized Cold Neutrons

NASA Astrophysics Data System (ADS)

Danilyan, G. V.

2018-02-01

Signs of the ROT-effects in ternary fission of 233U and 235U experimentally defined by PNPI group are the same, whereas in binary fission defined by ITEP group are opposite. This contradiction cannot be explained by the errors in the experiments of both groups, since such instrumental effects would be too large not to be noticed. Therefore, it is necessary to find the answer to this problem in the differences of the ternary and binary fission mechanisms.

Nuclear Resonance Fluorescence of U-235

DOE Office of Scientific and Technical Information (OSTI.GOV)

Warren, Glen A.; Caggiano, Joseph A.; Hensley, Walter K.

Nuclear resonance fluorescence is a physical process that provides an isotopic-specific signature that could be used for the identification and characterization of materials. The technique involves the detection of prompt discrete-energy photons emitted from a sample which is exposed to photons in the MeV energy range. Potential applications of the technique range from detection of high explosives to characterization of special nuclear materials. One isotope of significant interest is 235U. Pacific Northwest National Laboratory and Passport Systems have collaborated to conduct measurements to search for a nuclear resonance fluorescence response of 235U below 3 MeV using a 200 g samplemore » of highly enriched uranium. Nine 235U resonances between 1650 and 2010 keV were identified in the preliminary analysis. Analysis of the measurement data to determine the integrated cross sections of the resonances is in progress.« less

Drastic shifts in the Levant hydroclimate during the last interglacial indicate changes in the tropical climate and winter storm tracks

NASA Astrophysics Data System (ADS)

Kiro, Y.; Goldstein, S. L.; Kushnir, Y.; Lazar, B.; Stein, M.

2017-12-01

Marine Isotope Stage (MIS) 5e was a warm interglacial with where with significantly varying insolation and hence varied significantly throughout this time suggesting highly variable climate. The ICDP Dead Sea Deep Drilling Project recovered a 460m record of the past 220ka, reflecting the variable climate along MIS 5e. This time interval is reflected by alternating halite and detritus sequences, including 20m of halite-free detritus during the peak insolation at 125 ka. The Dead Sea salt budget indicates that the Levant climate was extremely arid when halite formed, reaching 20% of the present runoff. The halite-free detritus layer reflects increased precipitation to levels similar to present day, assuming similar spatial and temporal rainfall patterns. However, the 234U/238U activity ratio in the lake, reflected by authigenic minerals (aragonite, gypsum and halite), shifts from values of 1.5 (reflecting the Jordan River, the present main water source) down to 1.3 at 125-122ka during the MIS5e insolation peak and 1.0 at 118-116ka. The low 234U/238U reflects increased flash floods and eastern water sources (234U/238U 1.05-1.2) from the drier part of the watershed in the desert belt. The intermediate 234U/238U of 1.3 suggests that the Jordan River, fed from Mediterranean-sourced storm tracks, continued to flow along with an increase in southern and eastern water sources. NCAR CCSM3 climate model runs for 125ka indicate increases in both Summer and Winter precipitation. The drastic decrease to 234U/238U 1.0 occurs during the driest period, indicating a near shutdown of Jordan River flow, and water input only through flash floods and southern and eastern sources. The 120ka climate model runs shows a decrease in Winter and increase in Fall precipitation as a result of an increased precipitation in the tropics. The extreme aridity, associated with increased flooding is similar to patterns expected due to future warming. The increase in aridity is the result of expansion of the desert-belt and increases in southern precipitation and indicates an important link between the tropical and mid-latitude climate.

Uranium isotopes in rivers, estuaries and adjacent coastal sediments of western India: their weathering, transport and oceanic budget

NASA Astrophysics Data System (ADS)

Borole, D. V.; Krishnaswami, S.; Somayajulu, B. L. K.

1982-02-01

The two major river systems on the west coast of India, Narbada and Tapti, their estuaries and the coastal Arabian sea sediments have been extensively studied for their uranium concentrations and 238U /238U activity ratios. The 238U concentrations in the aqueous phase of these river systems exhibit a strong positive correlation with the sum of the major cations, σ Na + K + Mg + Ca, and with the HCO 3- ion contents. The abundance ratio of dissolved U to the sum of the major cations in these waters is similar to their ratio in typical crustal rocks. These findings lead us to conclude that 238U is brought into the aqueous phase along with major cations and bicarbonate. The strong positive correlation between 238U and total dissolved salts for selected rivers of the world yield an annual dissolved 238U flux of 0.88 × 10 10g/ yr to the oceans, a value very similar to its removal rate from the oceans, 1.05 × 10 10g/ yr, estimated based on its correlation with HCO 3- contents of rivers. In the estuaries, both 238U and its great-grand daughter 234U behave conservatively beyond chlorosities 0.14 g/l. These data confirm our earlier findings in other Indian estuaries. The behavior of uranium isotopes in the chlorosity zone 0.02-0.14 g/l, was studied in the Narbada estuary in some detail. The results, though not conclusive, seem to indicate a minor removal of these isotopes in this region. Reexamination of the results for the Gironde and Zaire estuaries (Martin et al., 1978a and b) also appear to confirm the conservative behavior of U isotopes in unpolluted estuaries. It is borne out from all the available data that estuaries beyond 0.14 g/l chlorosities act neither as a sink nor as a source for uranium isotopes, the behavior in the low chlorosity zones warrants further detailed investigation. A review of the uranium isotope measurements in river waters yield a discharge weighted-average 238U concentration of 0.22 μg/l with a 234U /238U activity ratio of 1.20 ± 0.06 ismissing. The residence time of uranium isotopes in the oceans estimated from the 238U concentration and the 234U /238U A. R. of the rivers yield conflicting results; the material balance of uranium isotopes in the marine environment still remains a paradox. If the disparity between the results is real, then an additional 234U flux of about 0.25 dpm/cm 2·10 3 yr into the oceans (about 20% of its river supply) is necessitated.

Measurement of the normalized U 238 ( n , f ) / U 235 ( n , f ) cross section ratio from threshold to 30 MeV with the NIFFTE fission Time Projection Chamber

DOE PAGES

Casperson, R. J.; Asner, D. M.; Baker, J.; ...

2018-03-23

We present that the normalized 238U(n,f)/ 235U(n,f) cross section ratio has been measured using the NIFFTE fission Time Projection Chamber (fissionTPC) from the reaction threshold to 30 MeV . The fissionTPC is a two-volume MICROMEGAS time projection chamber that allows for full three-dimensional reconstruction of fission-fragment ionization profiles from neutron-induced fission. The measurement was performed at the Los Alamos Neutron Science Center, where the neutron energy is determined from neutron time of-flight. The 238U(n,f)/ 235U(n,f) ratio reported here is the first cross section measurement made with the fissionTPC, and will provide new experimental data for evaluation of the 238U(n,f) crossmore » section, an important standard used in neutron-flux measurements. Use of a development target in this work prevented the determination of an absolute normalization, to be addressed in future measurements. Instead, the measured cross section ratio has been normalized to ENDF/B-VIII.β5 at 14.5 MeV.« less

Measurement of the normalized U 238 ( n , f ) / U 235 ( n , f ) cross section ratio from threshold to 30 MeV with the NIFFTE fission Time Projection Chamber

DOE Office of Scientific and Technical Information (OSTI.GOV)

Casperson, R. J.; Asner, D. M.; Baker, J.

We present that the normalized 238U(n,f)/ 235U(n,f) cross section ratio has been measured using the NIFFTE fission Time Projection Chamber (fissionTPC) from the reaction threshold to 30 MeV . The fissionTPC is a two-volume MICROMEGAS time projection chamber that allows for full three-dimensional reconstruction of fission-fragment ionization profiles from neutron-induced fission. The measurement was performed at the Los Alamos Neutron Science Center, where the neutron energy is determined from neutron time of-flight. The 238U(n,f)/ 235U(n,f) ratio reported here is the first cross section measurement made with the fissionTPC, and will provide new experimental data for evaluation of the 238U(n,f) crossmore » section, an important standard used in neutron-flux measurements. Use of a development target in this work prevented the determination of an absolute normalization, to be addressed in future measurements. Instead, the measured cross section ratio has been normalized to ENDF/B-VIII.β5 at 14.5 MeV.« less

Reactive transport of uranium in a groundwater bioreduction study: Insights from high-temporal resolution 238U/235U data

NASA Astrophysics Data System (ADS)

Shiel, A. E.; Johnson, T. M.; Lundstrom, C. C.; Laubach, P. G.; Long, P. E.; Williams, K. H.

2016-08-01

We conducted a detailed investigation of U isotopes in conjunction with a broad geochemical investigation during field-scale biostimulation and desorption experiments. This investigation was carried out in the uranium-contaminated alluvial aquifer of the Rifle field research site. In this well-characterized setting, a more comprehensive understanding of U isotope geochemistry is possible. Our results indicate that U isotope fractionation is consistently observed across multiple experiments at the Rifle site. Microbially-mediated reduction is suggested to account for most or all of the observed fractionation as abiotic reduction has been demonstrated to impart much smaller, often near-zero, isotopic fractionation or isotopic fractionation in the opposite direction. Data from some time intervals are consistent with a simple model for transport and U(VI) reduction, where the fractionation factor (ε = +0.65‰ to +0.85‰) is consistent with experimental studies. However, during other time intervals the observed patterns in our data indicate the importance of other processes in governing U concentrations and 238U/235U ratios. For instance, we demonstrate that departures from Rayleigh behavior in groundwater systems arise from the presence of adsorbed species. We also show that isotope data are sensitive to the onset of oxidation after biostimulation ends, even in the case where reduction continues to remove contaminant uranium downstream. Our study and the described conceptual model support the use of 238U/235U ratios as a tool for evaluating the efficacy of biostimulation and potentially other remedial strategies employed at Rifle and other uranium-contaminated sites.

Uncertainty analysis on reactivity and discharged inventory for a pressurized water reactor fuel assembly due to {sup 235,238}U nuclear data uncertainties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Da Cruz, D. F.; Rochman, D.; Koning, A. J.

2012-07-01

This paper discusses the uncertainty analysis on reactivity and inventory for a typical PWR fuel element as a result of uncertainties in {sup 235,238}U nuclear data. A typical Westinghouse 3-loop fuel assembly fuelled with UO{sub 2} fuel with 4.8% enrichment has been selected. The Total Monte-Carlo method has been applied using the deterministic transport code DRAGON. This code allows the generation of the few-groups nuclear data libraries by directly using data contained in the nuclear data evaluation files. The nuclear data used in this study is from the JEFF3.1 evaluation, and the nuclear data files for {sup 238}U and {supmore » 235}U (randomized for the generation of the various DRAGON libraries) are taken from the nuclear data library TENDL. The total uncertainty (obtained by randomizing all {sup 238}U and {sup 235}U nuclear data in the ENDF files) on the reactor parameters has been split into different components (different nuclear reaction channels). Results show that the TMC method in combination with a deterministic transport code constitutes a powerful tool for performing uncertainty and sensitivity analysis of reactor physics parameters. (authors)« less

A Signature Distinguishing Fissile From Non-Fissile Materials Using Linearly Polarized Gamma Rays

NASA Astrophysics Data System (ADS)

Mueller, J. M.; Ahmed, M. W.; Karwowski, H. J.; Myers, L. S.; Sikora, M. H.; Stave, S.; Tompkins, J. R.; Zimmerman, W. R.; Weller, H. R.

2013-04-01

Photofission of ^233,235,238U, ^239,240Pu, and ^232Th was induced by nearly 100% linearly polarized, high intensity (˜10^7 γs per second), and nearly-monoenergetic γ-ray beams of energies between 5.6 and 7.3 MeV at the High Intensity γ-ray Source (HIγS). An array of 18 liquid scintillating detectors was used to measure prompt fission neutron angular distributions. The ratio of prompt fission neutron yields parallel to the plane of beam polarization to the yields perpendicular to this plane was measured as a function of beam and neutron energy, as described in a recent publication showing results from ^235,238U, ^239Pu, and ^232Th [1]. A ratio near unity was found for ^233,235U and ^239Pu while a significant ratio (˜1.5-3) was found for ^238U, ^240Pu, and ^232Th. This large difference could be used to distinguish fissile isotopes (such as ^233,235U and ^239Pu) from non-fissile isotopes (such as ^238U, ^240Pu, and ^232Th). Polarization ratios as a function of the relative abundance of fissile to non-fissile isotopes will be presented. [4pt] [1] J. M. Mueller et al., Phys. Rev. C 85, 014605 (2012).

Modeling non-steady state radioisotope transport in the vadose zone--A case study using uranium isotopes at Pena Blanca, Mexico

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ku, T. L.; Luo, S.; Goldstein, S. J.

2009-06-01

Current models using U- and Th-series disequilibria to study radioisotope transport in groundwater systems mostly consider a steady-state situation. These models have limited applicability to the vadose zone (UZ) where the concentration and migratory behavior of radioisotopes in fluid are often transitory. We present here, as a first attempt of its kind, a model simulating the non-steady state, intermittent fluid transport in vadose layers. It provides quantitative constraints on in-situ migration of dissolved and colloidal radioisotopes in terms of retardation factor and rock-water interaction (or water transit) time. For uranium, the simulation predicts that intermittent flushing in the UZ leadsmore » to a linear relationship between reciprocal U concentration and {sup 234}U/{sup 238}U ratio in percolating waters, with the intercept and slope bearing information on the rates of dissolution and {alpha}-recoil of U isotopes, respectively. The general validity of the model appears to be borne out by the measurement of uranium isotopes in UZ waters collected at various times over a period during 1995-2006 from a site in the Pena Blanca mining district, Mexico, where the Nopal I uranium deposit is located. Enhanced {sup 234}U/{sup 238}U ratios in vadose-zone waters resulting from lengthened non-flushing time as prescribed by the model provide an interpretative basis for using {sup 234}U/{sup 238}U in cave calcites to reconstruct the regional changes in hydrology and climate. We also provide a theoretical account of the model's potential applications using radium isotopes.« less

Modeling non-steady state radioisotope transport in the vadose zone - A case study using uranium isotopes at Peña Blanca, Mexico

NASA Astrophysics Data System (ADS)

Ku, T. L.; Luo, S.; Goldstein, S. J.; Murrell, M. T.; Chu, W. L.; Dobson, P. F.

2009-10-01

Current models using U- and Th-series disequilibria to study radioisotope transport in groundwater systems mostly consider a steady-state situation. These models have limited applicability to the vadose zone (UZ) where the concentration and migratory behavior of radioisotopes in fluid are often transitory. We present here, as a first attempt of its kind, a model simulating the non-steady state, intermittent fluid transport in vadose layers. It provides quantitative constraints on in-situ migration of dissolved and colloidal radioisotopes in terms of retardation factor and rock-water interaction (or water transit) time. For uranium, the simulation predicts that intermittent flushing in the UZ leads to a linear relationship between reciprocal U concentration and 234U/ 238U ratio in percolating waters, with the intercept and slope bearing information on the rates of dissolution and α-recoil of U isotopes, respectively. The general validity of the model appears to be borne out by the measurement of uranium isotopes in UZ waters collected at various times over a period during 1995-2006 from a site in the Peña Blanca mining district, Mexico, where the Nopal I uranium deposit is located. Enhanced 234U/ 238U ratios in vadose-zone waters resulting from lengthened non-flushing time as prescribed by the model provide an interpretative basis for using 234U/ 238U in cave calcites to reconstruct the regional changes in hydrology and climate. We also provide a theoretical account of the model's potential applications using radium isotopes.

Chemical and U-Sr isotopic variations of stream and source waters at a small catchment scale (the Strengbach case; Vosges mountains; France)

NASA Astrophysics Data System (ADS)

Pierret, M. C.; Stille, P.; Prunier, J.; Viville, D.; Chabaux, F.

2014-03-01

This is the first comprehensive study dealing with major and trace element data as well as 87Sr/86Sr isotope and (234U/238U) activity ratios (AR) determined on the totality of springs and brooks of the Strengbach catchment. It shows that the small and more or less monolithic catchment drains different sources and streamlets with very different isotopic and geochemical signatures. Different parameters control the diversity of the source characteristics. Of importance is especially the hydrothermal overprint of the granitic bedrock, which was stronger for the granite from the northern than from the southern slope; also significant are the different meteoric alteration processes of the bedrock causing the formation of 0.5 to 9 m thick saprolite and above the formation of an up to 1 m thick soil system. These processes mainly account for springs and brooks from the northern slope having higher Ca/Na, Mg/Na, Sr/Na ratios but lower 87Sr/86Sr isotopic ratios than those from the southern slope. The chemical compositions of the source waters in the Strengbach catchment are only to a small extent the result of alteration of primary bedrock minerals and rather reflect dissolution/precipitation processes of secondary mineral phases like clay minerals. The (234U/238U) AR, however, are decoupled from the 87Sr/86Sr isotope system and reflect to some extent the level of altitude of the source and, thus, the degree of alteration of the bedrock. The sources emerging at high altitudes have circulated through already weathered materials (saprolite and fractured rock depleted in 234U) implying (234U/238U) AR < 1, which is uncommon for surface waters. Preferential flow paths along constant fractures in the bedrocks might explain the over time homogeneous U AR of the different spring waters. However, the geochemical and isotopic variations of stream waters at the outlet of the catchment are controlled by variable contributions of different springs depending on the hydrological conditions. It appears that the (234U/238U) AR is an appropriate very important tracer for studying and deciphering the contribution of the different source fluxes at the catchment scale because this unique geochemical parameter is different for each individual spring and at the same time remains unchanged for each of the springs with changing discharge and fluctuating hydrological conditions. This study further highlights the important impact of different and independent water pathways in fractured granite controlling the different geochemical and isotopic signatures of the waters.

Uranium and Calcium Isotope Ratio Measurements using the Modified Total Evaporation Method in TIMS

NASA Astrophysics Data System (ADS)

Richter, S.; Kuehn, H.; Berglund, M.; Hennessy, C.

2010-12-01

A new version of the "modified total evaporation" (MTE) method for isotopic analysis by multi-collector thermal ionization mass spectrometry (TIMS), with high analytical performance and designed in a more user-friendly and routinely applicable way, is described in detail. It is mainly being used for nuclear safeguards measurements of U and Pu and nuclear metrology, but can readily be applied to other scientific tasks in geochemistry, e.g. for Sr, Nd and Ca, as well. The development of the MTE method was organized in collaboration of several "key nuclear mass spectrometry laboratories", namely the New Brunswick Laboratory (NBL), the Institute for Transuranium Elements (ITU), the Safeguards Analytical Laboratory (now Safeguards Analytical Services, SGAS) of the International Atomic Energy Agency (IAEA) and the Institute for Reference Materials and Measurements (IRMM), with IRMM taking the leading role. The manufacturer of the TRITON TIMS instrument, Thermo Fisher Scientific, integrated this method into the software of the instrument. The development has now reached its goal to become a user-friendly and routinely useable method for uranium isotope ratio measurements with high precision and accuracy. Due to the use of the “total evaporation” (TE) method the measurement of the "major" uranium isotope ratio 235U/238U is routinely being performed with a precision of 0.01% to 0.02%. The use of a (certified) reference material measured under comparable conditions is emphasized to achieve an accuracy at a level of 0.02% - depending on the stated uncertainty of the certified value of the reference material. In contrast to the total evaporation method (TE), in the MTE method the total evaporation sequence is interrupted on a regular basis to allow for correction for background from peak tailing, internal calibration of a secondary electron multiplier (SEM) detector versus the Faraday cups, and ion source re-focusing. Therefore, the most significant improvement using the MTE method is in the analytical performance achieved for the "minor" ratios 234U/238U and 236U/238U. The MTE method is now routinely used at all collaborating laboratories and possibly more in the future. Additional applications for the MTE method, e.g. to take advantage of the good external precision in combination with the possibilities of internal background and detector calibrations or mass jumps between different cup configurations, are presented as well. One interesting application concerns new absolute isotope ratio measurements for Ca with an unprecedented level of accuracy. This is important because up to now most reported Ca isotope data are only calculated as relative deviations from a standard like NIST-SRM 915. Using the MTE method measurements on new gravimetrically prepared Ca isotope mixtures were performed. A significantly improved level of accuracy at the level of about 0.02% for both the 42Ca/40Ca and 44Ca/40Ca ratios was obtained.

Traditional and Model Based Assay of Irregular Geometry Items

DOE Office of Scientific and Technical Information (OSTI.GOV)

MOORE, FRANK S.; SALAYMEH, SALEEM

The Analytical Development Section (ADS) of SRNL was requested to perform a waste disposal assay of two heater boxes which had been used in the HB Line dissolvers. They had been sent to SRNL for study to make recommendations on how to prevent future failure of the units when they were replaced. The study having been completed, the units needed to be characterized prior to sending to Solid Waste for disposal. An assay station consisting of a turntable, HPGe detector, CANBERRA Inspector, transmission source and a portable computer was set up to do the required assays. The assays indicate themore » presence of U-235, Pu-239 and Cs-137. No measurable amounts of U-235 or Pu-239 were found. Therefore the Minimum Detectable Activities for U-235 and Pu-239 were calculated. For Heater Box 1, 0.23 grams of U-235 and 0.24 grams of Pu-239. For Heater Box 2, the results were 0.21 grams of U-235 and 0.21 grams of Pu-239. This paper describes and documents the assays employed to determine the amount of U, Pu and Cs contents of the heater boxes. The paper provides results of SNM assays using traditional calibration of the system and on one based on modeling. It also provides the scientific community with data that will assist the user in determining the method of choice for assaying items with irregular geometries.« less

Benchmark experiments at ASTRA facility on definition of space distribution of {sup 235}U fission reaction rate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bobrov, A. A.; Boyarinov, V. F.; Glushkov, A. E.

2012-07-01

Results of critical experiments performed at five ASTRA facility configurations modeling the high-temperature helium-cooled graphite-moderated reactors are presented. Results of experiments on definition of space distribution of {sup 235}U fission reaction rate performed at four from these five configurations are presented more detail. Analysis of available information showed that all experiments on criticality at these five configurations are acceptable for use them as critical benchmark experiments. All experiments on definition of space distribution of {sup 235}U fission reaction rate are acceptable for use them as physical benchmark experiments. (authors)

Nuclear weapons produced 236U, 239Pu and 240Pu archived in a Porites Lutea coral from Enewetak Atoll.

PubMed

Froehlich, M B; Tims, S G; Fallon, S J; Wallner, A; Fifield, L K

2017-11-01

A slice from a Porites Lutea coral core collected inside the Enewetak Atoll lagoon, within 15 km of all major nuclear tests conducted at the atoll, was analysed for 236 U, 239 Pu and 240 Pu over the time interval 1952-1964 using a higher time resolution than previously reported for a parallel slice from the same core. In addition two sediment samples from the Koa and Oak craters were analysed. The strong peaks in the concentrations of 236 U and 239 Pu in the testing years are confirmed to be considerably wider than the flushing time of the lagoon. This is likely due to the growth mechanism of the coral. Following the last test in 1958 atom concentrations of both 236 U and 239 Pu decreased from their peak values by more than 95% and showed a seasonal signal thereafter. Between 1959 and 1964 the weighted average of the 240 Pu/ 239 Pu atom ratio is 0.124 ± 0.008 which is similar to that in the lagoon sediments (0.129 ± 0.006) but quite distinct from the global fallout value of ∼0.18. This, and the high 239,240 Pu and 236 U concentrations in the sediments, provides clear evidence that the post-testing signal in the coral is dominated by remobilisation of the isotopes from the lagoon sediments rather than from global fallout. Copyright © 2017 Elsevier Ltd. All rights reserved.

The importance of colloids and mires for the transport of uranium isotopes through the Kalix River watershed and Baltic Sea

DOE Office of Scientific and Technical Information (OSTI.GOV)

Porcelli, D.; Wasserburg, G.J.; Andersson, P.S.

The importance of colloids and organic deposits for the transport of uranium isotopes from continental source regions and through the estuarine environment was investigated in the mire-rich Kalix River drainage basin in northern Sweden and the Baltic Sea. Ultrafiltration techniques were used to separate uranium and other elements associated with colloids > 10 kD and >3 kD from {open_quotes}solute{close_quotes} uranium and provided consistent results and high recovery rates for uranium as well as for other elements from large volume samples. Uranium concentrations in 0.45 {mu}m-filtered Kalix River water samples increased by a factor of 3 from near the headwaters inmore » the Caledonides to the river mouth while major cation concentrations were relatively constant. {sup 234}U {sup 238}U ratios were high ({delta}{sup 234}U = 770-1500) throughout the basin, without showing any simple pattern, and required a supply of {sup 234}U-rich water. Throughout the Kalix River, a large fraction (30-90%) of the uranium is carried by >10 kD colloids, which is compatible with uranium complexation with humic acids. No isotopic differences were found between colloid-associated and solute uranium. Within the Baltic Sea, about half of the uranium is removed at low salinities. The proportion that is lost is equivalent to that of river-derived colloid-bound uranium, suggesting that while solute uranium behaves conservatively during estuarine mixing, colloid-bound uranium is lost due to rapid flocculation of colloidal material. The association of uranium with colloids therefore may be an important parameter in determining uranium estuarine behavior. Mire peats in the Kalix River highly concentrate uranium and are potentially a significant source of recoil {sup 234}U to the mirewaters and river waters. However, mirewater data clearly demonstrate that only small {sup 234}U/{sup 238}U shifts are generated relative to inflowing groundwater. 63 refs., 8 figs., 3 tabs.« less

CHEMICAL DIFFERENCES BETWEEN SLUDGE SOLIDS AT THE F AND H AREA TANK FARMS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reboul, S.

2012-08-29

The primary source of waste solids received into the F Area Tank Farm (FTF) was from PUREX processing performed to recover uranium and plutonium from irradiated depleted uranium targets. In contrast, two primary sources of waste solids were received into the H Area Tank Farm (HTF): a) waste from PUREX processing; and b) waste from H-modified (HM) processing performed to recover uranium and neptunium from burned enriched uranium fuel. Due to the differences between the irradiated depleted uranium targets and the burned enriched uranium fuel, the average compositions of the F and H Area wastes are markedly different from onemore » another. Both F and H Area wastes contain significant amounts of iron and aluminum compounds. However, because the iron content of PUREX waste is higher than that of HM waste, and the aluminum content of PUREX waste is lower than that of HM waste, the iron to aluminum ratios of typical FTF waste solids are appreciably higher than those of typical HTF waste solids. Other constituents present at significantly higher concentrations in the typical FTF waste solids include uranium, nickel, ruthenium, zinc, silver, cobalt and copper. In contrast, constituents present at significantly higher concentrations in the typical HTF waste solids include mercury, thorium, oxalate, and radionuclides U-233, U-234, U-235, U-236, Pu-238, Pu-242, Cm-244, and Cm-245. Because of the higher concentrations of Pu-238 in HTF, the long-term concentrations of Th-230 and Ra-226 (from Pu-238 decay) will also be higher in HTF. The uranium and plutonium distributions of the average FTF waste were found to be consistent with depleted uranium and weapons grade plutonium, respectively (U-235 comprised 0.3 wt% of the FTF uranium, and Pu-240 comprised 6 wt% of the FTF plutonium). In contrast, at HTF, U-235 comprised 5 wt% of the uranium, and Pu-240 comprised 17 wt% of the plutonium, consistent with enriched uranium and high burn-up plutonium. X-ray diffraction analyses of various FTF and HTF samples indicated that the primary crystalline compounds of iron in sludge solids are Fe{sub 2}O{sub 3}, Fe{sub 3}O{sub 4}, and FeO(OH), and the primary crystalline compounds of aluminum are Al(OH){sub 3} and AlO(OH). Also identified were carbonate compounds of calcium, magnesium, and sodium; a nitrated sodium aluminosilicate; and various uranium compounds. Consistent with expectations, oxalate compounds were identified in solids associated with oxalic acid cleaning operations. The most likely oxidation states and chemical forms of technetium are assessed in the context of solubility, since technetium-99 is a key risk driver from an environmental fate and transport perspective. The primary oxidation state of technetium in SRS sludge solids is expected to be Tc(IV). In salt waste, the primary oxidation state is expected to be Tc(VII). The primary form of technetium in sludge is expected to be a hydrated technetium dioxide, TcO{sub 2} {center_dot} xH{sub 2}O, which is relatively insoluble and likely co-precipitated with iron. In salt waste solutions, the primary form of technetium is expected to be the very soluble pertechnetate anion, TcO{sub 4}{sup -}. The relative differences between the F and H Tank Farm waste provide a basis for anticipating differences that will occur as constituents of FTF and HTF waste residue enter the environment over the long-term future. If a constituent is significantly more dominant in one of the Tank Farms, its long-term environmental contribution will likely be commensurately higher, assuming the environmental transport conditions of the two Tank Farms share some commonality. It is in this vein that the information cited in this document is provided - for use during the generation, assessment, and validation of Performance Assessment modeling results.« less

Distribution of radioactive isotopes in rock and ore of Arkhangelskaya pipe from the Arkhangelsk diamond province

NASA Astrophysics Data System (ADS)

Kiselev, G. P.; Yakovlev, E. Yu.; Druzhinin, S. V.; Galkin, A. S.

2017-09-01

The contents of radioactive elements and the uranium isotopic composition of kimberlite in the Arkhangelskaya pipe at the M.V. Lomonosov deposit and of nearby country rocks have been studied. A surplus of 234U isotope has been established in rocks from the near-pipe space. The high γ = 234U/238U ratio is controlled by the geological structure of the near-pipe space. A nonequilibrium uranium halo reaches two pipe diameters in size and can be regarded as a local ore guide for kimberlite discovery. The rocks in the nearpipe space are also characterized by elevated or anomalous U, Th, and K contents with respect to the background.

Evaluation of the 235 U resonance parameters to fit the standard recommended values

DOE PAGES

Leal, Luiz; Noguere, Gilles; Paradela, Carlos; ...

2017-09-13

A great deal of effort has been dedicated to the revision of the standard values in connection with the neutron interaction for some actinides. While standard data compilation are available for decades nuclear data evaluations included in existing nuclear data libraries (ENDF, JEFF, JENDL, etc.) do not follow the standard recommended values. Indeed, the majority of evaluations for major actinides do not conform to the standards whatsoever. In particular, for the n + 235U interaction the only value in agreement with the standard is the thermal fission cross section. We performed a resonance re-evaluation of the n + 235U interactionmore » in order to address the issues regarding standard values in the energy range from 10-5 eV to 2250 eV. Recently, 235U fission cross-section measurements have been performed at the CERN Neutron Time-o-Flight facility (TOF), known as n_TOF, in the energy range from 0.7 eV to 10 keV. The data were normalized according to the recommended standard of the fission integral in the energy range 7.8 eV to 11 eV. As a result, the n_TOF averaged fission cross sections above 100 eV are in good agreement with the standard recommended values. The n_TOF data were included in the 235U resonance analysis that was performed with the code SAMMY. In addition to the average standard values related to the fission cross section, standard thermal values for fission, capture, and elastic cross sections were also included in the evaluation. Our paper presents the procedure used for re-evaluating the 235U resonance parameters including the recommended standard values as well as new cross section measurements.« less

Evaluation of the 235 U resonance parameters to fit the standard recommended values

DOE Office of Scientific and Technical Information (OSTI.GOV)

Leal, Luiz; Noguere, Gilles; Paradela, Carlos

A great deal of effort has been dedicated to the revision of the standard values in connection with the neutron interaction for some actinides. While standard data compilation are available for decades nuclear data evaluations included in existing nuclear data libraries (ENDF, JEFF, JENDL, etc.) do not follow the standard recommended values. Indeed, the majority of evaluations for major actinides do not conform to the standards whatsoever. In particular, for the n + 235U interaction the only value in agreement with the standard is the thermal fission cross section. We performed a resonance re-evaluation of the n + 235U interactionmore » in order to address the issues regarding standard values in the energy range from 10-5 eV to 2250 eV. Recently, 235U fission cross-section measurements have been performed at the CERN Neutron Time-o-Flight facility (TOF), known as n_TOF, in the energy range from 0.7 eV to 10 keV. The data were normalized according to the recommended standard of the fission integral in the energy range 7.8 eV to 11 eV. As a result, the n_TOF averaged fission cross sections above 100 eV are in good agreement with the standard recommended values. The n_TOF data were included in the 235U resonance analysis that was performed with the code SAMMY. In addition to the average standard values related to the fission cross section, standard thermal values for fission, capture, and elastic cross sections were also included in the evaluation. Our paper presents the procedure used for re-evaluating the 235U resonance parameters including the recommended standard values as well as new cross section measurements.« less

Evaluation of the 235U resonance parameters to fit the standard recommended values

NASA Astrophysics Data System (ADS)

Leal, Luiz; Noguere, Gilles; Paradela, Carlos; Durán, Ignacio; Tassan-Got, Laurent; Danon, Yaron; Jandel, Marian

2017-09-01

A great deal of effort has been dedicated to the revision of the standard values in connection with the neutron interaction for some actinides. While standard data compilation are available for decades nuclear data evaluations included in existing nuclear data libraries (ENDF, JEFF, JENDL, etc.) do not follow the standard recommended values. Indeed, the majority of evaluations for major actinides do not conform to the standards whatsoever. In particular, for the n + 235U interaction the only value in agreement with the standard is the thermal fission cross section. A resonance re-evaluation of the n + 235U interaction has been performed to address the issues regarding standard values in the energy range from 10-5 eV to 2250 eV. Recently, 235U fission cross-section measurements have been performed at the CERN Neutron Time-of-Flight facility (TOF), known as n_TOF, in the energy range from 0.7 eV to 10 keV. The data were normalized according to the recommended standard of the fission integral in the energy range 7.8 eV to 11 eV. As a result, the n_TOF averaged fission cross sections above 100 eV are in good agreement with the standard recommended values. The n_TOF data were included in the 235U resonance analysis that was performed with the code SAMMY. In addition to the average standard values related to the fission cross section, standard thermal values for fission, capture, and elastic cross sections were also included in the evaluation. This paper presents the procedure used for re-evaluating the 235U resonance parameters including the recommended standard values as well as new cross section measurements.

Metal poisons for criticality in waste streams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Williamson, T.G.; Goslen, A.Q.

1996-12-31

Many of the wastes from processing fissile materials contain metals that may serve as neutron poisons. It would be advantageous to the criticality evaluation of these wastes to demonstrate that the poisons remain with the fissile materials and to demonstrate an always safe poison-to-fissile ratio. The first task, demonstrating that the materials stay together, is the job of the chemist; the second, calculating an always safe ratio, is an object of this paper. In an earlier study, the authors demonstrated safe ratios for iron, manganese, and chromium oxides to {sup 235}U. In these studies, the Hansen-Roach 16-group cross sections weremore » used with the Savannah River site code HRXN. Multiplication factors were computed, and safe ratios were defined such that the adjusted neutron multiplication factors (k values) were <0.95. These safe weight ratios were Fe:{sup 235}U - 77:1; Mn:{sup 235}U - 30:1; and Cr:{sup 235}U - 52:1. Palmer has shown that for certain mixtures of aluminum, iron, and zirconium with {sup 235}U, the computed infinite multiplication factors may differ by as much as 20% with different cross sections and processing systems. Parks et al. have further studied these mixtures and state, {open_quotes}...these metal/uranium mixtures are very sensitive to the metal cross-section data in the intermediate-energy range and the processing methods that are used.{close_quotes} They conclude with a call for more experimental data. The purpose of this study is to reexamine earlier work with cross sections and processing codes used at Westinghouse Savannah River Company today. This study will focus on {sup 235}U mixtures with iron, manganese and chromium. Sodium will be included in the list of poisons because it is abundant in many of the waste materials.« less

Radionuclide inventories for the F- and H-area seepage basin groundwater plumes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hiergesell, Robert A; Kubilius, Walter P.

2016-05-01

Within the General Separations Areas (GSA) at the Savannah River Site (SRS), significant inventories of radionuclides exist within two major groundwater contamination plumes that are emanating from the F- and H-Area seepage basins. These radionuclides are moving slowly with groundwater migration, albeit more slowly due to interaction with the soil and aquifer matrix material. The purpose of this investigation is to quantify the activity of radionuclides associated with the pore water component of the groundwater plumes. The scope of this effort included evaluation of all groundwater sample analyses obtained from the wells that have been established by the Environmental Compliancemore » & Area Completion Projects (EC&ACP) Department at SRS to monitor groundwater contamination emanating from the F- and H-Area Seepage Basins. Using this data, generalized groundwater plume maps for the radionuclides that occur in elevated concentrations (Am-241, Cm-243/244, Cs-137, I-129, Ni-63, Ra-226/228, Sr-90, Tc-99, U-233/234, U-235 and U-238) were generated and utilized to calculate both the volume of contaminated groundwater and the representative concentration of each radionuclide associated with different plume concentration zones.« less

Loading blended, low-enriched uranium fuel in browns ferry units 2 and 3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brown, C.; Eichenberg, T.; Haun, J.

2006-07-01

This paper summarizes fuel and cycle design results for the Tennessee Valley Authority (TVA) / Dept. of Energy (DOE) program to burn blended, low-enriched uranium (BLEU) material in the Browns Ferry Nuclear Units 2 and 3. The BLEU material typically has about 60 times the allowed limit of U-236 in what would be defined as commercial, i.e., virgin, uranium. U-236 in particular is a strong neutron absorber. Also included is a comparison of cycles using commercial uranium versus BLEU to determine the impact on key core design parameters of the high U-236 content in the BLEU. Finally, there is amore » short discussion of the economic advantages of BLEU fuel. (authors)« less

Reactor Neutronics: Impact of Fissile Material

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heidet, F.; Hill, R. N.

Here, given a wide variety of reactor designs and fuel types, it can be difficult to identify the underlying cause of basic performance differences such as flux level and enrichment requirement. In this paper, using solely the definitions of the core multiplication factor and core power, simple relations have been derived allowing estimates of the flux ratio and fissile material concentration ratio for any reactor concept when 235U is replaced with 239Pu or vice-versa. These relations are functions of the neutron non-leakage probability, and one only needs to know number of neutrons emitted per fission, and the fission cross-section ratiomore » between the 235U system and the 239Pu system. It is found that for a reactor concept having significant leakage, the achievable flux level when using 239Pu as fissile material can be up to 45% larger than when using 235U as fissile material, and the required fissile concentration of 239Pu is up to 48% lower than that of 235U to achieve criticality.« less

Reactor Neutronics: Impact of Fissile Material

DOE PAGES

Heidet, F.; Hill, R. N.

2017-06-09

Here, given a wide variety of reactor designs and fuel types, it can be difficult to identify the underlying cause of basic performance differences such as flux level and enrichment requirement. In this paper, using solely the definitions of the core multiplication factor and core power, simple relations have been derived allowing estimates of the flux ratio and fissile material concentration ratio for any reactor concept when 235U is replaced with 239Pu or vice-versa. These relations are functions of the neutron non-leakage probability, and one only needs to know number of neutrons emitted per fission, and the fission cross-section ratiomore » between the 235U system and the 239Pu system. It is found that for a reactor concept having significant leakage, the achievable flux level when using 239Pu as fissile material can be up to 45% larger than when using 235U as fissile material, and the required fissile concentration of 239Pu is up to 48% lower than that of 235U to achieve criticality.« less

RAPID DETERMINATION OF ACTINIDES IN URINE BY INDUCTIVELY-COUPLED PLASMA MASS SPECTROMETRY AND ALPHA SPECTROMETRY: A HYBRID APPROACH

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maxwell, S.; Jones, V.

2009-05-27

A new rapid separation method that allows separation and preconcentration of actinides in urine samples was developed for the measurement of longer lived actinides by inductively coupled plasma mass spectrometry (ICP-MS) and short-lived actinides by alpha spectrometry; a hybrid approach. This method uses stacked extraction chromatography cartridges and vacuum box technology to facilitate rapid separations. Preconcentration, if required, is performed using a streamlined calcium phosphate precipitation. Similar technology has been applied to separate actinides prior to measurement by alpha spectrometry, but this new method has been developed with elution reagents now compatible with ICP-MS as well. Purified solutions are splitmore » between ICP-MS and alpha spectrometry so that long- and short-lived actinide isotopes can be measured successfully. The method allows for simultaneous extraction of 24 samples (including QC samples) in less than 3 h. Simultaneous sample preparation can offer significant time savings over sequential sample preparation. For example, sequential sample preparation of 24 samples taking just 15 min each requires 6 h to complete. The simplicity and speed of this new method makes it attractive for radiological emergency response. If preconcentration is applied, the method is applicable to larger sample aliquots for occupational exposures as well. The chemical recoveries are typically greater than 90%, in contrast to other reported methods using flow injection separation techniques for urine samples where plutonium yields were 70-80%. This method allows measurement of both long-lived and short-lived actinide isotopes. 239Pu, 242Pu, 237Np, 243Am, 234U, 235U and 238U were measured by ICP-MS, while 236Pu, 238Pu, 239Pu, 241Am, 243Am and 244Cm were measured by alpha spectrometry. The method can also be adapted so that the separation of uranium isotopes for assay is not required, if uranium assay by direct dilution of the urine sample is preferred instead. Multiple vacuum box locations may be set-up to supply several ICP-MS units with purified sample fractions such that a high sample throughput may be achieved, while still allowing for rapid measurement of short-lived actinides by alpha spectrometry.« less

Quantifying weathering advance rates in basaltic andesite rinds with uranium-series isotopes: a case study from Guadeloupe

NASA Astrophysics Data System (ADS)

Ma, L.; Chabaux, F. J.; Pelt, E.; Granet, M.; Sak, P. B.; Gaillardet, J.; Brantley, S. L.

2010-12-01

Weathering of basaltic rocks plays an important role in many Earth surface processes. It is thus of great interest to quantify their weathering rates. Because of their well-documented behaviors during water-rock interaction, U-series isotopes have been shown to have utility as a potential chronometer to constrain the formation rates of weathering rinds developed on fresh basaltic rocks. In this study, U-series isotopes and trace element concentrations were analyzed in a basaltic andesite weathering rind collected from the Bras David watershed, Guadeloupe. From the clast, core and rind samples were obtained by drilling along a 63.8 mm linear profile across a low curvature segment of the core-rind boundary. Trace element concentrations reveal: significant loss of REE, Y, Rb, Sr, and Ba in the weathering rind; conservative behaviors of Ti and Th; and external addition of U into the rind during clast weathering. Measured (234U/238U) activity ratios of the rind samples are much higher than the core samples and show excess 234U. Measured (238U/232Th) and (230Th/232Th) activity ratios of the core and rind samples increase gradually from the core into the weathering rind. The observed depletion profiles for the trace elements in the clast suggest that the earliest chemical reaction that creates significant porosity is dissolution of plagioclase, consistent with the previous study [Sak et al., 2010, CG, in press]. The porosity growth within the rind allows for an influx of soil solution that carries dissolved U with (234U/238U) activity ratios >1 into the clast. The deposition of U in the rind is most likely associated with precipication of secondary minerals during clast weathering. Such a continuous U addition is responsible for the observed gradual increase of (238U/232Th) activity ratios in the rind. Subsequent production of 230Th in the rind over time from the decay of excess 234U accounts for the observed continuous increase of (230Th/232Th) activity ratios. The U-series activity ratios in the clast were modeled with a weathering advance rate of ~0.3 mm kyr-1. This represents the rind advance rate at the low curvature segment of the core-rind boundary under tropical climate. This rate is consistent with the previously estimated formation rates of basaltic rinds under similar tropic conditions in Costa Rica [Sak et al., 2004, GCA 68, 1453; Pelt et al., 2008, EPSL 276, 98]. This rate is about one order of magnitude greater than those in temperate regions, documenting the important control of temperature on basalt weathering. This work illustrates that the weathering advance rates of rinds can be successfully estimated by U-series isotopes, demonstrating their great potential as dating tools for Earth surface processes. Furthermore, U-series chronometry provides a suitable method for independently testing the hypothesis that rind advance rates around an individual clast increase with increasing interfacial curvature.

Upwelling Rates Beneath Hotspots : Evidence From U-Series in Basalts From the Mid-Atlantic Ridge and the Azores Islands

NASA Astrophysics Data System (ADS)

Bourdon, B. P.; Turner, S. P.

2001-12-01

In this study, we have analyzed U-series in lavas from the Azores islands and the nearby Mid-Atlantic Ridge (FAZAR cruise) in an attempt to assess the relative importance of melting processes versus source variations in the context of ridge-hotpsot interaction. The lavas were analyzed for 238U-230Th (Turner et al. 1997, Bourdon et al. 1996) 226Ra-230Th and 235U-231Pa disequilibria by thermal ionisation mass spectrometry. Our results for the historic lavas from the Azores islands show that the 231Pa excess are at the low end of the trend found for other OIB (Pickett et al. 1997 and Bourdon et al. 1998) and fall on a positive correlation in a 231Pa/235U versus 230Th/238U diagram. In contrast, lavas from the nearby Mid-Atlantic ridge are characterized by larger (231Pa/235U) activity ratios for similar and greater (230Th/238U) ratios. There is also a weak correlation between 226Ra/230Th and 231Pa/235U. These data do not indicate a simple mixing trend between an N-MORB and an enriched component in the 231Pa/235U versus 230Th/238U diagram since the MORBs which do not have the most radiogenic isotope signatures compared with the Azores island basalts have some of the largest (230Th/238U) and 231Pa/235U. Clearly, the dynamics of melting must have played a role in generating larger 230Th and 231Pa excesses beneath the Mid-Atlantic ridge. We infer that this must be due to the absence of a lithospheric lid as larger excesses of 230Th and 231Pa can be generated for longer melting columns. Thus, ridge-hotspot interaction cannot imply a simple transfer of melt from the hotspot to the ridge. The 230Th/238U and 226Ra/230Th data across the Azores plateau shows a maximum for the island of Terceira and mimics the depth anomaly which is thought to result from the hotspot. This trend is also consistent with observations of rare gases (M. Moreira pers. comm.) and suggests that it must be related to the presence of deep material. The U-series trend is the reverse of the trend found in Hawaii by Sims et al. (2000) which was attributed to variations in upwelling rates across the rising plume. This observation can be rationalized in the context of an equilibrium melt transport model (Spiegelman and Elliott, 1993) where U-series disequilibria are sensitive to upwelling rates. For slow upwelling rates such as below the Azores, larger 230Th excesses are predicted in the center of the plume. This suggests that the upwelling rate beneath the center of the plume must be of the order of a few cm per year which is an order of magnitude lower than values estimated for Hawaii. Turner et al. 1997, Chem. Geol. 139, 145-164. Bourdon et al. 1996, Earth Planet. Sci. Lett. 142, 175-189. Pickett et al. 1997, Earth Planet. Sci. Lett. 148, 259-271. Sims et al. 1999, Geochim. Cosmochim. Acta. 63, 4119-4138. Spiegelman and Elliot, 1993, Earth Planet. Sci. Lett., 118, 1-20.

Improvement of Modeling HTGR Neutron Physics by Uncertainty Analysis with the Use of Cross-Section Covariance Information

NASA Astrophysics Data System (ADS)

Boyarinov, V. F.; Grol, A. V.; Fomichenko, P. A.; Ternovykh, M. Yu

2017-01-01

This work is aimed at improvement of HTGR neutron physics design calculations by application of uncertainty analysis with the use of cross-section covariance information. Methodology and codes for preparation of multigroup libraries of covariance information for individual isotopes from the basic 44-group library of SCALE-6 code system were developed. A 69-group library of covariance information in a special format for main isotopes and elements typical for high temperature gas cooled reactors (HTGR) was generated. This library can be used for estimation of uncertainties, associated with nuclear data, in analysis of HTGR neutron physics with design codes. As an example, calculations of one-group cross-section uncertainties for fission and capture reactions for main isotopes of the MHTGR-350 benchmark, as well as uncertainties of the multiplication factor (k∞) for the MHTGR-350 fuel compact cell model and fuel block model were performed. These uncertainties were estimated by the developed technology with the use of WIMS-D code and modules of SCALE-6 code system, namely, by TSUNAMI, KENO-VI and SAMS. Eight most important reactions on isotopes for MHTGR-350 benchmark were identified, namely: 10B(capt), 238U(n,γ), ν5, 235U(n,γ), 238U(el), natC(el), 235U(fiss)-235U(n,γ), 235U(fiss).

Nuclear excitation by electronic transition of 235U

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chodash, P. A.; Norman, E. B.; Burke, J. T.

Here, nuclear excitation by electronic transition (NEET) is a rare nuclear excitation that can occur in isotopes containing a low-lying nuclear excited state. Over the past 40 yr, several experiments have attempted to measure NEET of 235U and those experiments have yielded conflicting results.

Nuclear excitation by electronic transition of 235U

DOE PAGES

Chodash, P. A.; Norman, E. B.; Burke, J. T.; ...

2016-03-11

Here, nuclear excitation by electronic transition (NEET) is a rare nuclear excitation that can occur in isotopes containing a low-lying nuclear excited state. Over the past 40 yr, several experiments have attempted to measure NEET of 235U and those experiments have yielded conflicting results.

Munitions Classification Library Update and Expansion Data Collection Report: Camp Lejeune and Eglin

DTIC Science & Technology

2015-10-09

Motor 4.5-in T160ES HE R N N N N W without Motor Rocket Motor R N N N N W 66mm M72A1 R Y Y N N U with Coupler and Motor ...66mm M74 R N Y N N W with Motor 3.5-in M30A1 R Y Y N N W WP Smoke with M405 Dummy Fuze and Motor Rocket Motor R Y N N N W 3.5-in M30A1 R N Y N N...N U/P with Motor without Fins 2.36-in M6 R Y Y N N U/P with Motor with Fins Rocket Motor R Y Y N N U/P 2.36-in M6 R N N N N U/P Rifle

Time-resolved record of 236U and 239,240Pu isotopes from a coral growing during the nuclear testing program at Enewetak Atoll (Marshall Islands).

PubMed

Froehlich, M B; Chan, W Y; Tims, S G; Fallon, S J; Fifield, L K

2016-12-01

A comprehensive series of nuclear tests were carried out by the United States at Enewetak Atoll in the Marshall Islands, especially between 1952 and 1958. A Porites Lutea coral that was growing in the Enewetak lagoon within a few km of all of the high-yield tests contains a continuous record of isotopes, which are of interest (e.g. 14 C, 236 U, 239,240 Pu) through the testing period. Prior to the present work, 14 C measurements at ∼2-month resolution had shown pronounced peaks in the Δ 14 C data that coincided with the times at which tests were conducted. Here we report measurements of 236 U and 239,240 Pu on the same coral using accelerator mass spectrometry, and again find prominent peaks in the concentrations of these isotopes that closely follow those in 14 C. Consistent with the 14 C data, the magnitudes of these peaks do not, however, correlate well with the explosive yields of the corresponding tests, indicating that smaller tests probably contributed disproportionately to the debris that fell in the lagoon. Additional information about the different tests can also be obtained from the 236 U/ 239 Pu and 240 Pu/ 239 Pu ratios, which are found to vary dramatically over the testing period. In particular, the first thermonuclear test, Ivy-Mike, has characteristic 236 U/ 239 Pu and 240 Pu/ 239 Pu signatures which are diagnostic of the first arrival of nuclear test material in various archives. Copyright © 2016 Elsevier Ltd. All rights reserved.

U-TH-PA-RA study of the Kamchatka arc: new constraints on the genesis of arc lavas

NASA Astrophysics Data System (ADS)

Dosseto, Anthony; Bourdon, Bernard; Joron, Jean-Louis; Dupré, Bernard

2003-08-01

The 238U- 230Th- 226Ra and 235U- 231Pa disequilibria have been measured by mass spectrometry in historic lavas from the Kamchatka arc. The samples come from three closely located volcanoes in the Central Kamchatka Depression (CKD), the most active region of subducted-related volcanism in the world. The large excesses of 226Ra over 230Th found in the CKD lavas are believed to be linked to slab dehydration. Moreover, the samples show the uncommon feature of ( 230Th/ 238U) activity ratios both lower and higher than 1. The U-series disequilibria are characterized by binary trends between activity ratios, with ( 231Pa/ 235U) ratios all >1. It is shown that these correlations cannot be explained by a simple process involving a combination of slab dehydration and melting. We suggest that they are more likely to reflect mixing between two end-members: a high-magnesia basalt (HMB) end-member with a clear slab fluid signature and a high-alumina andesite (HAA) end-member reflecting the contribution of a slab-derived melt. The U-Th-Ra characteristics of the HMB end-member can be explained either by a two-step fluid addition with a time lag of 150 ka between each event or by continuous dehydration. The inferred composition for the dehydrating slab is a phengite-bearing eclogite. Equilibrium transport or dynamic melting can both account for 231Pa excess over 235U in HMB end-member. Nevertheless, dynamic melting is preferred as equilibrium transport melting requires unrealistically high upwelling velocities to preserve fluid-derived 226Ra/ 230Th. A continuous flux melting model is also tested. In this model, 231Pa- 235U is quickly dominated by fluid addition and, for realistic extents of melting, this process cannot account for ( 231Pa/ 235U) ratios as high as 1.6, as observed in the HMB end-member. The involvement of a melt derived from the subducted oceanic crust is more likely for explaining the HAA end-member compositions than crustal assimilation. Melting of the oceanic crust is believed to occur in presence of residual phengite and rutile, resulting in no 226Ra- 230Th disequilibrium and low 231Pa excess over 235U in the high-alumina andesites. Consequently, it appears that high-alumina andesites and high-magnesia basalts have distinct origins: the former being derived from melting of the subducted oceanic crust and the latter from hydrated mantle. It seems that there is no genetic link between these two magma types, in contrast with what was previously believed.

Photon-induced Fission Product Yield Measurements on 235U, 238U, and 239Pu

NASA Astrophysics Data System (ADS)

Krishichayan, Fnu; Bhike, M.; Tonchev, A. P.; Tornow, W.

2015-10-01

During the past three years, a TUNL-LANL-LLNL collaboration has provided data on the fission product yields (FPYs) from quasi-monoenergetic neutron-induced fission of 235U, 238U, and 239Pu at TUNL in the 0.5 to 15 MeV energy range. Recently, we have extended these experiments to photo-fission. We measured the yields of fission fragments ranging from 85Kr to 147Nd from the photo-fission of 235U, 238U, and 239Pu using 13-MeV mono-energetic photon beams at the HIGS facility at TUNL. First of its kind, this measurement will provide a unique platform to explore the effect of the incoming probe on the FPYs, i.e., photons vs. neutrons. A dual-fission ionization chamber was used to determine the number of fissions in the targets and these samples (along with Au monitor foils) were gamma-ray counted in the low-background counting facility at TUNL. Details of the experimental set-up and results will be presented and compared to the FPYs obtained from neutron-induced fission at the same excitation energy of the compound nucleus. Work supported in part by the NNSA-SSAA Grant No. DE-NA0001838.

[Determination of 235U/238U isotope ratios in camphor tree bark samples by MC-ICP-MS after separation of uranium from matrix elements].

PubMed

Wang, Xiao-Ping; Zhang, Ji-Long

2007-07-01

Twelve camphor (cinnamomum camphora) tree bark samples were collected from Hiroshima and Kyoto, and the matrix element composition and morphology of the outer surface of these camphor tree bark samples were studied by EDXS and SEM respectively. After a dry decomposition, DOWEX 1-X8 anion exchange resin was used to separate uranium from matrix elements in these camphor tree bark samples. Finally, 235U/238 U isotope ratios in purified uranium solutions were determined by MC-ICP-MS. It was demonstrated that the outer surface of these camphor tree bark samples is porous and rough, with Al, Ca, Fe, K, Mg, Si, C, O and S as its matrix element composition. Uranium in these camphor tree bark samples can be efficiently separated and quantitatively recovered from the matrix element composition. Compared with those collected from Kyoto, the camphor tree bark samples collected from Hiroshima have significantly higher uranium contents, which may be due to the increased aerosol mass concentration during the city reconstruction. Moreover, the 235 U/23.U isotope ratios in a few camphor tree bark samples collected from Hiroshima are slightly higher than 0.007 25.

Uranium series dating of Allan Hills ice

NASA Technical Reports Server (NTRS)

Fireman, E. L.

1986-01-01

Uranium-238 decay series nuclides dissolved in Antarctic ice samples were measured in areas of both high and low concentrations of volcanic glass shards. Ice from the Allan Hills site (high shard content) had high Ra-226, Th-230 and U-234 activities but similarly low U-238 activities in comparison with Antarctic ice samples without shards. The Ra-226, Th-230 and U-234 excesses were found to be proportional to the shard content, while the U-238 decay series results were consistent with the assumption that alpha decay products recoiled into the ice from the shards. Through this method of uranium series dating, it was learned that the Allen Hills Cul de Sac ice is approximately 325,000 years old.

Fertilizer-derived uranium and sulfur in rangeland soil and runoff: A case study in central Florida

USGS Publications Warehouse

Zielinski, R.A.; Orem, W.H.; Simmons, K.R.; Bohlen, P.J.

2006-01-01

Fertilizer applications to rangeland and pastures in central Florida have potential impact on the nutrient-sensitive ecosystems of Lake Okeechobee and the Northern Everglades. To investigate the effects of fertilizer applications, three soil profiles from variably managed and improved rangeland, and four samples of surface runoff from both fertilized and unfertilized pasture were collected. In addition to determining nutrient concentrations, isotopic analyses of uranium (U) and sulfur (S) were performed to provide isotopic evidence for U derived from historically applied phosphate (P)-bearing fertilizer ( 234 U 238U activity ratio =1.0 ?? 0.05), and Sderived from recently applied ammonium sulfate fertilizer(??34 S=3.5permil).The distribution and mobility of fertilizer-derived U in these samples is considered to be analogous to that of fertilizer-derived phosphate.Variations of U concentrations and 234 U/238 U activity ratios in soils indicate contribution of fertilizer-derived U in the upper portions of the fertilized soil (15-}34 percent of total U). The U isotope data for runoff from the fertilized field also are consistent with some contribution from fertilizer-derived U. Parallel investigations of S showed no consistent chemical or isotopic evidence for significant fertilizer-derived sulfate in rangeland soil or runoff. Relatively abundant and isotopically variable S present in the local environment hinders detection of fertilizer-derived sulfate. The results indicate a continuing slow-release of fertilizer-derived U and, by inference, P, to the P-sensitive ecosystem, and a relatively rapid release of sulfate of possible natural origin. ?? Springer 2006.

In-situ measurements of U-series nuclides by electron microprobe on zircons and monazites from Gandak river sediments

NASA Astrophysics Data System (ADS)

Bosia, C.; Deloule, E.; France-Lanord, C.; Chabaux, F.

2015-12-01

Determination of sediment transfer time during transport in the alluvial plains is a critical issue to correctly understand the relationship between climate, tectonics and Earth surface evolution. The residence time of river sediments may be constrained by analyzing the U series nuclides fractionations (e.g. [1] and [2]), which are created during water rock interactions by the ejection of the daughter nuclides of the grain (α-recoil) and the preferential mobilization of nuclides in decay damaged crystal structure. However, recent studies on sediments from the Gandak river, one of the main Ganga tributary, highlighted the difficulties to obtain reproducible data on bulk sediments, due to the nuggets distribution of U-Th enriched minor minerals in the samples (Bosia et al., unpublished data). We therefore decided to analyze the U and Th isotopic systematic at a grain-scale for Himalayan sediments from the Gandak river. This has been tested by performing in situ depth profiles of 238U-234U-230Th and 232Th on zircons and monazites (50-250 μm) by Secondary Ion Mass Spectrometry (SIMS) at the CRPG, Nancy, France. The first results point the occurrence of 238U-234U-230Th disequilibria in the outermost parts of both monazite and zircon minerals with a return to the equilibrium state in the core of the grains. The relative U and Th enrichment is however slightly different depending on considered minerals, suggesting possible adsorption processes of 230-Th. Coupled to a simple model of U and Th mobility during water-mineral interactions, these data should help to constrain the origin of 238U-234U-230Th disequilibria in these minerals. Moreover, the results of the study should be relevant to discuss the potential of this approach to constrain the residence time of zircons and monazites in the Gandak alluvial plain. [1] Chabaux et al., 2012, C. R. Geoscience, 344 (11-12): 688-703; [2] Granet et al., 2007, Earth and Planet. Sci. Lett., 261 (3-4): 389-406.

Validation of uranium determination in urine by ICP-MS.

PubMed

Bouvier-Capely, C; Baglan, N; Montègue, A; Ritt, J; Cossonnet, C

2003-08-01

A rapid procedure--dilution of urine+ICP-MS measurement--for the determination of uranium in urine was validated. Large ranges of concentration and isotopic composition were studied on urine samples excreted by occupationally exposed workers. The results were consistent with those obtained by fluorimetry and by alpha spectrometry after a purification procedure, two currently used techniques. However, the proposed procedure is limited for determination of the minor isotope 234U. Thus for worker monitoring, the conversion of 234U mass concentration into activity concentration can lead to an erroneous value of the effective dose, in particular for a contamination at very low level with highly enriched uranium. A solution to avoid this hazard is to perform a chemical purification prior to ICP-MS measurement to lower uncertainty and detection limit for 234U.

Capture and fission with DANCE and NEUANCE

DOE PAGES

Jandel, M.; Baramsai, B.; Bond, E.; ...

2015-12-23

A summary of the current and future experimental program at DANCE is presented. Measurements of neutron capture cross sections are planned for many actinide isotopes with the goal to reduce the present uncertainties in nuclear data libraries. Detailed studies of capture gamma rays in the neutron resonance region will be performed in order to derive correlated data on the de-excitation of the compound nucleus. New approaches on how to remove the DANCE detector response from experimental data and retain the correlations between the cascade gamma rays are presented. Studies on 235U are focused on quantifying the population of short-lived isomericmore » states in 236U after neutron capture. For this purpose, a new neutron detector array NEUANCE is under construction. It will be installed in the central cavity of the DANCE array and enable the highly efficient tagging of fission and capture events. In addition, developments of fission fragment detectors are also underway to expand DANCE capabilities to measurements of fully correlated data on fission observables.« less

Capture and fission with DANCE and NEUANCE

NASA Astrophysics Data System (ADS)

Jandel, M.; Baramsai, B.; Bond, E.; Rusev, G.; Walker, C.; Bredeweg, T. A.; Chadwick, M. B.; Couture, A.; Fowler, M. M.; Hayes, A.; Kawano, T.; Mosby, S.; Stetcu, I.; Taddeucci, T. N.; Talou, P.; Ullmann, J. L.; Vieira, D. J.; Wilhelmy, J. B.

2015-12-01

A summary of the current and future experimental program at DANCE is presented. Measurements of neutron capture cross sections are planned for many actinide isotopes with the goal to reduce the present uncertainties in nuclear data libraries. Detailed studies of capture gamma rays in the neutron resonance region will be performed in order to derive correlated data on the de-excitation of the compound nucleus. New approaches on how to remove the DANCE detector response from experimental data and retain the correlations between the cascade gamma rays are presented. Studies on 235U are focused on quantifying the population of short-lived isomeric states in 236U after neutron capture. For this purpose, a new neutron detector array NEUANCE is under construction. It will be installed in the central cavity of the DANCE array and enable the highly efficient tagging of fission and capture events. In addition, developments of fission fragment detectors are also underway to expand DANCE capabilities to measurements of fully correlated data on fission observables.

Evaluation of naturally occurring radioactivity across the State of Kuwait using high-resolution gamma-ray spectrometry

NASA Astrophysics Data System (ADS)

Bajoga, A. D.; Alazemi, N.; Shams, H.; Regan, P. H.; Bradley, D. A.

2017-08-01

A study of natural radioactivity from 90 different soil samples from the state of Kuwait has been carried out to ascertain the NORM concentration values across the country. The calculated activity concentrations were determined from: (i) the decays of the 226Ra, 214Pb and 214Bi members of the 4n+2 decay chain headed by 238U and; (ii) the 228Ac, 212Pb and 208Tl members of the 4n chain headed by 232Th. The study also included evaluations for the 235U decay chain with the 186 keV doublet transition used together with the measured 4n+2 activity concentration values to determine the 235U/238U isotopic ratios for each sample. The values for the arithmetic mean activity concentrations for 90 separate locations across Kuwait as determined in the current work were 17.2, 14.1, and 368 Bq/kg, with standard deviations of 5.2, 3.7 and 90 Bq/kg for the 238U, 232Th and 40K activity concentrations respectively. Measured isotope ratios for 235U/238U give an arithmetic mean value for all of the samples of 0.045±0.003, consistent with that expected for natural uranium. These results indicate no evidence for a radiologically significant dispersion of additional depleted uranium across the entire State of Kuwait from the 1991 Gulf War.

Uranium isotope fractionation in biogenic carbonates: biological effects

NASA Astrophysics Data System (ADS)

Chen, X.; Romaniello, S. J.; Herrmann, A. D.; Anbar, A. D.

2017-12-01

Recent laboratory experiments have demonstrated small but potentially significant isotope fractionation ( 0.10 ‰ for 238U/235U) during uranium (U) incorporation into abiotic calcite and aragonite, with heavier U isotopes preferentially enriched in the precipitates [1]. In contrast, measurements of natural biogenic carbonates to date have not been able to resolve significant U isotopic fractionation from seawater although this might be expected given a typical measurement precision of ± 0.10 ‰. Determining whether or not biogenic carbonates display U isotope fractionation similar to abiotic carbonates could have important implications for understanding the mechanisms of U incorporation into various biogenic carbonates. Furthermore, because most marine carbonates are biogenic, the extent of isotopic fractionation, if any, could have important implications for the interpretation of sedimentary carbonates record similar to effects observed for Cr and B isotopes [2, 3]. To resolve this discrepancy, we utilized a higher precision 238U/235U method which uses larger sample sizes to improve measurement precision of natural samples to ± 0.02 ‰ (2 se, N = 6) [4]. Using this method, we have surveyed 238U/235U in primary biogenic skeletal carbonates including scleractinian corals, green and red algae, and mollusks, as well as non-skeletal carbonates such as stromatolites, ooids, and carbonate sands from the Bahamas, Gulf of California, and French Polynesia. New high-precision U isotopes measurements reveal that biogenic skeletal carbonates are typically 0.02 - 0.08 ‰ heavier than modern seawater. Scleractinian corals display values closest to seawater (- 0.37 ‰), while green algae, red algae, mollusks, and echinoderms display variable but larger extents of fractionation up to 0.08 ‰. The direction and magnitude of U isotope fractionation in these biogenic precipitates are generally consistent with results from abiotic coprecipitation experiments, but may be subject to variations in U speciation and carbonate chemistry at calcification sites. [1] Chen et a., (2016), GCA, 188, 189-207. [2] Wang et a., (2016), Geobiology, 5, 51-64. [3] Pagani et al., (2005) GCA, 69, 953-961. [4] Andersen et al., (2016) CG, 420, 11-22.

Experimental investigations of a uranium plasma pertinent to a self-sustaining plasma source

NASA Technical Reports Server (NTRS)

Schneider, R. T.

1971-01-01

The research is pertinent to the realization of a self-sustained fissioning plasma for applications such as nuclear propulsion, closed cycle MHD power generation using a plasma core reactor, and heat engines such as the nuclear piston engine, as well as the direct conversion of fission energy into optical radiation (nuclear pumped lasers). Diagnostic measurement methods and experimental devices simulating plasma core reactor conditions are discussed. Studies on the following topics are considered: (1) ballistic piston compressor (U-235); (2) high pressure uranium plasma (natural uranium); (3) sliding spark discharge (natural uranium); (4) fission fragment interaction (He-3 and U-235); and (5) nuclear pumped lasers (He-3 and U-235).

Saprolite Formation Rates using U-series Isotopes in a Granodiorite Weathering Profile from Boulder Creek CZO (Colorado, USA)

NASA Astrophysics Data System (ADS)

Pelt, Eric; Chabaux, Francois; Mills, T. Joseph; Anderson, Suzanne P.; Foster, Melissa A.

2015-04-01

Timescales of weathering profile formation and evolution are important kinetic parameters linked to erosion, climatic, and biological processes within the critical zone. In order to understand the complex kinetics of landscape evolution, water and soil resources, along with climate change, these parameters have to be estimated for many different contexts. The Betasso catchment, within the Boulder Creek Critical Zone Observatory (BC-CZO) in Colorado, is a mountain catchment in Proterozoic granodiorite uplifted in the Laramide Orogeny ca. 50 Ma. In an exposure near the catchment divide, an approximately 1.5 m deep profile through soil and saprolite was sampled and analysed for bulk U-series disequilibria (238U-234U-230Th-226Ra) to estimate the profile weathering rate. The (234U/238U), (230Th/234U) and (226Ra/230Th) disequilibria through the entire profile are small but vary systematically with depth. In the deepest samples, values are close to equilibrium. Above this, values are progressively further from equilibrium with height in the profile, suggesting a continuous leaching of U and Ra compared to Th. The (234U/238U) disequilibria remain < 1 along the profile, suggesting no significant U addition from pore waters. Only the shallowest sample (~20 cm depth) highlights a 226Ra excess, likely resulting from vegetation cycling. In contrast, variations of Th content and (230Th/232Th) - (238U/232Th) activity ratios in the isochron diagram are huge, dividing the profile into distinct zones above and below 80 cm depth. Below 80 cm, the Th content gradually increases upward from 1.5 to 3.5 ppm suggesting a relative accumulation linked to chemical weathering. Above 80 cm, the Th content jumps to ~15 ppm with a similar increase of Th/Ti or Th/Zr ratios that clearly excludes the same process of relative accumulation. This strong shift is also observed in LREE concentrations, such as La, Ce and Nd, and in Sr isotopic composition, which suggests an external input of radiogenic material such as dust from the western Colorado deserts or eroding landscapes. For the deeper part of the profile, the strong upward decrease of the (230Th/232Th) and (238U/232Th) activity ratio without generation of strong disequilibria could suggest a long history (~0.5-1 Ma) of U leaching with a very slow saprolite development (~1 m/Ma). Such a result is in agreement with slow weathering rates deduced from modern solute chemistry of rivers, but would be much lower than 10Be denudation rates on the same profile of ~10-20 m/Ma. As the 10Be rates integrate denudation over a timescale of 40-80 ka, the apparent inconsistency between rates deduced by U-series data and Be data might suggest that erosion rates have increased during the 10Be integrating time.

Natural uranium and thorium isotopes in sediment cores off Malaysian ports

NASA Astrophysics Data System (ADS)

Yusoff, Abdul Hafidz; Sabuti, Asnor Azrin; Mohamed, Che Abd Rahim

2015-06-01

Sediment cores collected from three Malaysian marine ports, namely, Kota Kinabalu, Labuan and Klang were analyzed to determine the radioactivities of 234U, 238U, 230Th, 232Th and total organic carbon (TOC) content. The objectives of this study were to determine the factors that control the activity of uranium isotopes and identify the possible origin of uranium and thorium in these areas. The activities of 234U and 238U show high positive correlation with TOC at the middle of sediment core from Kota Kinabalu port. This result suggests that activity of uranium at Kota Kinabalu port was influenced by organic carbon. The 234U/238U value at the upper layer of Kota Kinabalu port was ≥1.14 while the ratio value at Labuan and Klang port was ≤ 1.14. These results suggest a reduction process occurred at Kota Kinabalu port where mobile U(VI) was converted to immobile U(IV) by organic carbon. Therefore, it can be concluded that the major input of uranium at Kota Kinabalu port is by sorptive uptake of authigenic uranium from the water column whereas the major inputs of uranium to Labuan and Klang port are of detrital origin. The ratio of 230Th/232Th was used to estimate the origin of thorium. Low ratio value (lt; 1.5) at Labuan and Klang ports support the suggestion that thorium from both areas were come from detrital input while the high ratio (> 1.5) of 230Th/232Th at Kota Kinabalu port suggest the anthropogenic input of 230Th to this area. The source of 230Th is probably from phosphate fertilizers used in the oil-palm cultivation in Kota Kinabalu that is adjacent to the Kota Kinabalu port.

76 FR 65206 - Agency Information Collection Activities: Small Vessel Reporting System

Federal Register 2010, 2011, 2012, 2013, 2014

2011-10-20

... States. SVRS is authorized by 8 U.S.C. 1103, 8 U.S.C. 1225, 8 CFR 235.1, 19 U.S.C. 1433, 19 U.S.C. 1498... Review: Approval of a new collection. Affected Public: Individuals. Estimated Number of Respondents: 10... Filed 10-19-11; 8:45 am] BILLING CODE 9111-14-P ...

Exploratory study of fission product yields of neutron-induced fission of 235U , 238U , and 239Pu at 8.9 MeV

NASA Astrophysics Data System (ADS)

Bhatia, C.; Fallin, B. F.; Gooden, M. E.; Howell, C. R.; Kelley, J. H.; Tornow, W.; Arnold, C. W.; Bond, E.; Bredeweg, T. A.; Fowler, M. M.; Moody, W.; Rundberg, R. S.; Rusev, G. Y.; Vieira, D. J.; Wilhelmy, J. B.; Becker, J. A.; Macri, R.; Ryan, C.; Sheets, S. A.; Stoyer, M. A.; Tonchev, A. P.

2015-06-01

Using dual-fission chambers each loaded with a thick (200 -400 -mg /c m2) actinide target of 235 ,238U or 239Pu and two thin (˜10 -100 -μ g /c m2) reference foils of the same actinide, the cumulative yields of fission products ranging from 92Sr to 147Nd have been measured at En= 8.9 MeV . The 2H(d ,n ) 3He reaction provided the quasimonoenergetic neutron beam. The experimental setup and methods used to determine the fission product yield (FPY) are described, and results for typically eight high-yield fission products are presented. Our FPYs for 235U(n ,f ) , 238U(n ,f ) , and 239Pu(n ,f ) at 8.9 MeV are compared with the existing data below 8 MeV from Glendenin et al. [Phys. Rev. C 24, 2600 (1981), 10.1103/PhysRevC.24.2600], Nagy et al. [Phys. Rev. C 17, 163 (1978), 10.1103/PhysRevC.17.163], Gindler et al. [Phys. Rev. C 27, 2058 (1983), 10.1103/PhysRevC.27.2058], and those of Mac Innes et al. [Nucl. Data Sheets 112, 3135 (2011), 10.1016/j.nds.2011.11.009] and Laurec et al. [Nucl. Data Sheets 111, 2965 (2010), 10.1016/j.nds.2010.11.004] at 14.5 and 14.7 MeV, respectively. This comparison indicates a negative slope for the energy dependence of most fission product yields obtained from 235U and 239Pu , whereas for 238U the slope issue remains unsettled.

Prospects for improved understanding of isotopic reactor antineutrino fluxes

NASA Astrophysics Data System (ADS)

Gebre, Y.; Littlejohn, B. R.; Surukuchi, P. T.

2018-01-01

Predictions of antineutrino fluxes produced by fission isotopes in a nuclear reactor have recently received increased scrutiny due to observed differences in predicted and measured inverse beta decay (IBD) yields, referred to as the "reactor antineutrino flux anomaly." In this paper, global fits are applied to existing IBD yield measurements to produce constraints on antineutrino production by individual plutonium and uranium fission isotopes. We find that fits including measurements from highly U 235 -enriched cores and fits including Daya Bay's new fuel evolution result produce discrepant best-fit IBD yields for U 235 and Pu 239 . This discrepancy can be alleviated in a global analysis of all data sets through simultaneous fitting of Pu 239 , U 235 , and U 238 yields. The measured IBD yield of U 238 in this analysis is (7.02 ±1.65 )×10-43 cm2/fission , nearly two standard deviations below existing predictions. Future hypothetical IBD yield measurements by short-baseline reactor experiments are examined to determine their possible impact on the global understanding of isotopic IBD yields. It is found that future improved short-baseline IBD yield measurements at both high-enriched and low-enriched cores can significantly improve constraints for U 235 , U 238 , and Pu 239 , providing comparable or superior precision to existing conversion- and summation-based antineutrino flux predictions. Systematic and experimental requirements for these future measurements are also investigated.

Uranium isotopes in groundwater occurring at Amazonas State, Brazil.

PubMed

da Silva, Márcio Luiz; Bonotto, Daniel Marcos

2015-03-01

This paper reports the behavior of the dissolved U-isotopes (238)U and (234)U in groundwater providing from 15 cities in Amazonas State, Brazil. The isotope dilution technique accompanied by alpha spectrometry were utilized for acquiring the U content and (234)U/(238)U activity ratio (AR) data, 0.01-1.4µgL(-1) and 1.0-3.5, respectively. These results suggest that the water is circulating in a reducing environment and leaching strata containing minerals with low uranium concentration. A tendency to increasing ARs values following the groundwater flow direction is identified in Manaus city. The AR also increases according to the SW-NE directions: Uarini→Tefé; Manacapuru→Manaus; Presidente Figueiredo→São Sebastião do Uatumã; and Boa Vista do Ramos→Parintins. Such trends are possibly related to several factors, among them the increasing acid character of the waters. The waters analyzed are used for human consumption and the highest dissolved U content is much lower than the maximum established by the World Health Organization. Therefore, in view of this radiological parameter they can be used for drinking purposes. Copyright © 2014 Elsevier Ltd. All rights reserved.

Diagenesis of fossil coral skeletons: Correlation between trace elements, textures, and [sup 234]U/[sup 238]U

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bar-Matthews, M.; Wasserburg, G.J.; Chen, J.H.

1993-01-01

A comparative study of Pleistocene fossil coral skeletons and of modern coral skeletons was carried out using petrographic and trace element analyses on a suite of Pleistocene samples that had previously been studied from [sup 234]U, [sup 230]Th, and U-[sup 230]Th ages (Chen et al. 1991). Evidence of a range of diagenetic changes can be recognized by optical (OM) and scanning electron microscopy (SEM). Using an electron microprobe and SEM, concentrations of Na, S, Sr, and Mg were measured. No other trace elements were detected. Na, S, and Mg contents of the matrix, the fibrous micropores, and radiating needles aremore » highly variable and well correlated. High concentrations of Na, S, and Mg were found in modern living corals with lower concentrations in fossil corals and fibrous micropores, and the lowest value in the radiating needles. The reason for the correlations of Na, S, and Mg and crystal chemistry and the response to diagenesis of these trace elements is not understood. The average concentrations of Na, S, and Mg for each sample, when plotted against the whole coral initial [delta][sup 234]U, are generally correlated (Chen et al., 1991). As all these diagenetic changes involve the recystallization and deposition of aragonite, the authors infer that the geologic site of diagenesis both for forming the secondary aragonitic phases and for the enhancement of the [sup 234]U content in the fossil corals was the marine environment. It is possible that the textural and Na, S, and Mg trace element contents of fossil corals be used to ascertain the reliability of fossil coral skeletons for U-[sup 230]Th dating. The basic problem of identifying a priori unaltered coral skeletons for [sup 230]Th dating is not yet resolved. 64 refs., 16 figs., 5 tabs.« less

Determination of natural radioactivity in irrigation water of drilled wells in northwestern Saudi Arabia.

PubMed

Alkhomashi, N; Al-Hamarneh, Ibrahim F; Almasoud, Fahad I

2016-02-01

The levels of natural radiation in bedrock groundwater extracted from drilled wells in selected farms in the northwestern part of Saudi Arabia were addressed. The investigated waters form a source of irrigation for vegetables, agricultural crops, wheat, and alfalfa to feed livestock consumed by the general public. Information about water radioactivity in this area is not available yet. Therefore, this study strives to contribute to the quality assessment of the groundwater of these wells that are drilled into the non-renewable Saq sandstone aquifer. Hence, gross alpha and beta activities as well as the concentrations of (224)Ra, (226)Ra, (228)Ra, (234)U, (238)U, and U(total) were measured, compared to national and international limits and contrasted with data quoted from the literature. Correlations between the activities of the analyzed radionuclides were discussed. The concentrations of gross alpha and beta activities as well as (228)Ra were identified by liquid scintillation counting whereas alpha spectrometry was used to determine (224)Ra, (226)Ra, (234)U and (238)U after separation from the matrix by extraction chromatography. The mean activity concentrations of gross α and β were 3.15 ± 0.26 Bq L(-1) and 5.39 ± 0.44 Bq L(-1), respectively. Radium isotopes ((228)Ra and (226)Ra) showed mean concentrations of 3.16 ± 0.17 Bq L(-1) and 1.12 ± 0.07 Bq L(-1), respectively, whereas lower levels of uranium isotopes ((234)U and (238)U) were obtained. Copyright © 2015 Elsevier Ltd. All rights reserved.

Transformation of Upland Water and Carbon Dynamics by Thawing Permafrost in the Alaskan Interior

NASA Astrophysics Data System (ADS)

Ewing, S. A.; Paces, J. B.; O'Donnell, J. A.; Kanevskiy, M. Z.; Shur, Y.; Jorgenson, M. T.; Harden, J.; Aiken, G. R.; Striegl, R.

2009-05-01

Large arctic rivers can provide an integrated signal of regional permafrost thaw and associated carbon dynamics. A long-term (30-y) decrease in dissolved organic carbon (DOC) and increase in dissolved inorganic carbon in the Yukon River Basin (YRB) suggest increased flow through mineral soils as a result of permafrost thaw. We used U series isotopes to test for the influence of thaw on soil and surface waters in small upland catchments at two sites within the YRB. In natural waters, 234U/238U activity ratios exceed 1.00 (secular equilibrium) as a function of water-rock contact time. Previous work has shown that in major YRB rivers, seasonally and spatially variable 234U/238U ratios could indicate both groundwater inputs and permafrost thaw, with ratios ranging from 1.1 to 2.6. We show that 234U/238U ratios in soil and surface water from these small catchments span the range of values observed in the major rivers, and indicate greater influence of older water where the mineral soil and underlying sediment facilitate drainage and permafrost degradation. Analysis of deep, ice-rich loess permafrost cores (2-10 m) reveals that thaw of Pleistocene ice can release high concentrations of DOC (>1000 ppm) and ammonium in thaw waters. The age and chemical composition of these waters allows for improved prediction of downstream carbon dynamics upon thaw. Field observation of hillslope soil sequences indicates that both topography and mineral substrate influence the effects of thaw on water and carbon dynamics in small catchments.

Mass Yields and Average Total Kinetic Energy Release in Fission for 235U, 238U, and 239Pu

NASA Astrophysics Data System (ADS)

Duke, Dana

2015-10-01

Mass yield distributions and average total kinetic energy (TKE) in neutron induced fission of 235U, 238U, and 239Pu targets were measured with a gridded ionization chamber. Despite decades of fission research, our understanding of how fragment mass yields and TKE depend on incident neutron energy is limited, especially at higher energies (above 5-10 MeV). Improved accuracy in these quantities is important for nuclear technology as it enhances our simulation capabilities and increases the confidence in diagnostic tools. The data can also guide and validate theoretical fission models where the correlation between the fragment mass and TKE is of particular value for constraining models. The Los Alamos Neutron Science Center - Weapons Neutron Research (LANSCE - WNR) provides a neutron beam with energies from thermal to hundreds of MeV, well-suited for filling in the gaps in existing data and exploring fission behavior in the fast neutron region. The results of the studies on target nuclei 235U, 238U, and 239Pu will be presented with a focus on exploring data trends as a function of neutron energy from thermal through 30 MeV. Results indicate clear evidence of structure due to multi-chance fission in the TKE . LA-UR-15-24761.

Depleted uranium analysis in blood by inductively coupled plasma mass spectrometry

USGS Publications Warehouse

Todorov, T.I.; Xu, H.; Ejnik, J.W.; Mullick, F.G.; Squibb, K.; McDiarmid, M.A.; Centeno, J.A.

2009-01-01

In this study we report depleted uranium (DU) analysis in whole blood samples. Internal exposure to DU causes increased uranium levels as well as change in the uranium isotopic composition in blood specimen. For identification of DU exposure we used the 235U/238U ratio in blood samples, which ranges from 0.00725 for natural uranium to 0.002 for depleted uranium. Uranium quantification and isotopic composition analysis were performed by inductively coupled plasma mass spectrometry. For method validation we used eight spiked blood samples with known uranium concentrations and isotopic composition. The detection limit for quantification was determined to be 4 ng L-1 uranium in whole blood. The data reproduced within 1-5% RSD and an accuracy of 1-4%. In order to achieve a 235U/238U ratio range of 0.00698-0.00752% with 99.7% confidence limit a minimum whole blood uranium concentration of 60 ng L??1 was required. An additional 10 samples from a cohort of veterans exposed to DU in Gulf War I were analyzed with no knowledge of their medical history. The measured 235U/ 238U ratios in the blood samples were used to identify the presence or absence of DU exposure within this patient group. ?? 2009 The Royal Society of Chemistry.

Plant uptake of 238U, 235U, 232Th, 226Ra, 210Pb and 40K from a coal ash and slag disposal site and control soil under field conditions: A preliminary study.

PubMed

Skoko, Božena; Marović, Gordana; Babić, Dinko; Šoštarić, Marko; Jukić, Mirela

2017-06-01

The aim of this study was to investigate the uptake of 238 U, 235 U, 232 Th, 226 Ra, 210 Pb and 40 K by plants that grow on a coal ash and slag disposal site known for its higher content of naturally occurring radionuclides. Plant species that were sampled are common for the Mediterranean flora and can be divided as follows: grasses & herbs, shrubs and trees. To compare the activity concentrations and the resultant concentration ratios of the disposal site with those in natural conditions, we used control data specific for the research area, obtained for plants growing on untreated natural soil. Radionuclide activity concentrations were determined by high resolution gamma-ray spectrometry. Media parameters (pH, electrical conductivity and organic matter content) were also analysed. We confirmed significantly higher activity concentrations of 238 U, 235 U, 226 Ra and 210 Pb in ash and slag compared to control soil. However, a significant increase in the radionuclide activity concentration in the disposal site's vegetation was observed only for 226 Ra. On the contrary, a significantly smaller activity concentration of 40 K in ash and slag had no impact on its activity concentration in plant samples. The calculated plant uptake of 238 U, 235 U, 226 Ra and 210 Pb is significantly smaller in comparison with the uptake at the control site, while it is vice versa for 40 K. No significant difference was observed between the disposal site and the control site's plant uptake of 232 Th. These results can be the foundation for further radioecological assessment of this disposal site but also, globally, they can contribute to a better understanding of nature and long-term management of such disposal sites. Copyright © 2017 Elsevier Ltd. All rights reserved.

48 CFR 1552.235-71 - Treatment of confidential business information.

Code of Federal Regulations, 2013 CFR

2013-10-01

... Control Act (33 U.S.C. 1251, et seq.), the Safe Drinking Water Act (42 U.S.C. 300f et seq.), the Federal Insecticide, Fungicide, and Rodenticide Act (7 U.S.C. 136 et seq.), the Federal Food, Drug, and Cosmetic Act... Toxic Substances Control Act (15 U.S.C. 2601 et seq.). EPA regulations on confidentiality of business...

48 CFR 1552.235-71 - Treatment of confidential business information.

Code of Federal Regulations, 2011 CFR

2011-10-01

... Control Act (33 U.S.C. 1251, et seq.), the Safe Drinking Water Act (42 U.S.C. 300f et seq.), the Federal Insecticide, Fungicide, and Rodenticide Act (7 U.S.C. 136 et seq.), the Federal Food, Drug, and Cosmetic Act... Toxic Substances Control Act (15 U.S.C. 2601 et seq.). EPA regulations on confidentiality of business...

48 CFR 1552.235-71 - Treatment of confidential business information.

Code of Federal Regulations, 2014 CFR

2014-10-01

... Control Act (33 U.S.C. 1251, et seq.), the Safe Drinking Water Act (42 U.S.C. 300f et seq.), the Federal Insecticide, Fungicide, and Rodenticide Act (7 U.S.C. 136 et seq.), the Federal Food, Drug, and Cosmetic Act... Toxic Substances Control Act (15 U.S.C. 2601 et seq.). EPA regulations on confidentiality of business...

48 CFR 1552.235-71 - Treatment of confidential business information.

Code of Federal Regulations, 2012 CFR

2012-10-01

... Control Act (33 U.S.C. 1251, et seq.), the Safe Drinking Water Act (42 U.S.C. 300f et seq.), the Federal Insecticide, Fungicide, and Rodenticide Act (7 U.S.C. 136 et seq.), the Federal Food, Drug, and Cosmetic Act... Toxic Substances Control Act (15 U.S.C. 2601 et seq.). EPA regulations on confidentiality of business...

Breeding of 233U in the thorium-uranium fuel cycle in VVER reactors using heavy water

NASA Astrophysics Data System (ADS)

Marshalkin, V. E.; Povyshev, V. M.

2015-12-01

A method is proposed for achieving optimal neutron kinetics and efficient isotope transmutation in the 233U-232Th oxide fuel of water-moderated reactors with variable water composition (D2O, H2O) that ensures breeding of the 233U and 235U isotopes. The method is comparatively simple to implement.

Neutron-induced fission cross-section measurement of 234U with quasi-monoenergetic beams in the keV and MeV range using micromegas detectors

NASA Astrophysics Data System (ADS)

Tsinganis, A.; Kokkoris, M.; Vlastou, R.; Kalamara, A.; Stamatopoulos, A.; Kanellakopoulos, A.; Lagoyannis, A.; Axiotis, M.

2017-09-01

Accurate data on neutron-induced fission cross-sections of actinides are essential for the design of advanced nuclear reactors based either on fast neutron spectra or alternative fuel cycles, as well as for the reduction of safety margins of existing and future conventional facilities. The fission cross-section of 234U was measured at incident neutron energies of 560 and 660 keV and 7.5 MeV with a setup based on `microbulk' Micromegas detectors and the same samples previously used for the measurement performed at the CERN n_TOF facility (Karadimos et al., 2014). The 235U fission cross-section was used as reference. The (quasi-)monoenergetic neutron beams were produced via the 7Li(p,n) and the 2H(d,n) reactions at the neutron beam facility of the Institute of Nuclear and Particle Physics at the `Demokritos' National Centre for Scientific Research. A detailed study of the neutron spectra produced in the targets and intercepted by the samples was performed coupling the NeuSDesc and MCNPX codes, taking into account the energy spread, energy loss and angular straggling of the beam ions in the target assemblies, as well as contributions from competing reactions and neutron scattering in the experimental setup. Auxiliary Monte-Carlo simulations were performed with the FLUKA code to study the behaviour of the detectors, focusing particularly on the reproduction of the pulse height spectra of α-particles and fission fragments (using distributions produced with the GEF code) for the evaluation of the detector efficiency. An overview of the developed methodology and preliminary results are presented.

Chemical and U-Sr isotopic variations in stream and source waters of the Strengbach watershed (Vosges mountains, France)

NASA Astrophysics Data System (ADS)

Pierret, M. C.; Stille, P.; Prunier, J.; Viville, D.; Chabaux, F.

2014-10-01

This is the first comprehensive study dealing with major and trace element data as well as 87Sr/86Sr isotope and (234U/238U) activity ratios (AR) determined on the totality of springs and brooks of the Strengbach catchment. It shows that the small and more or less monolithic catchment drains different sources and streamlets with very different isotopic and geochemical signatures. Different parameters control the diversity of the source characteristics. Of importance is especially the hydrothermal overprint of the granitic bedrock, which was stronger for the granite from the northern slope; also significant are the different meteoric alteration processes of the bedrock causing the formation of 0.5 to 9 m thick saprolite and above the formation of an up to 1m thick soil system. These processes mainly account for springs and brooks from the northern slope having higher Ca / Na, Mg / Na, and Sr / Na ratios, but lower 87Sr/86Sr isotopic ratios than those from the southern slope. The chemical compositions of the source waters in the Strengbach catchment are only to a small extent the result of alteration of primary bedrock minerals, and rather reflect dissolution/precipitation processes of secondary mineral phases like clay minerals. The (234U/238U) AR, however, are decoupled from the 87Sr/86Sr isotope system, and reflect to some extent the level of altitude of the source and, thus, the degree of alteration of the bedrock. The sources emerging at high altitudes have circulated through already weathered materials (saprolite and fractured bedrock depleted in 234U), implying (234U/238U) AR below 1, which is uncommon for surface waters. Preferential flow paths along constant fractures in the bedrocks might explain the - over time - homogeneous U AR of the different spring waters. However, the geochemical and isotopic variations of stream waters at the outlet of the catchment are controlled by variable contributions of different springs, depending on the hydrological conditions. It appears that the (234U/238U) AR are a very appropriate, important tracer for studying and deciphering the contribution of the different source fluxes at the catchment scale, because this unique geochemical parameter is different for each individual spring and at the same time remains unchanged for each of the springs with changing discharge and fluctuating hydrological conditions. This study further highlights the important impact of different and independent water pathways on fractured granite controlling the different geochemical and isotopic signatures of the waters. Despite the fact that soils and vegetation cover have a great influence on the water cycle balance (evapotranspiration, drainage, runoff), the chemical compositions of waters are strongly modified by processes occurring in deep saprolite and bedrock rather than in soils along the specific water pathways.

The geochemistry of water near a surficial organic-rich uranium deposit, northeastern Washington State, U.S.A.

USGS Publications Warehouse

Zielinski, R.A.; Otton, J.K.; Wanty, R.B.; Pierson, C.T.

1987-01-01

The chemistry of three stream, three spring and six near-surface waters in the vicinity of a Holocene organic-rich uranium deposit is described, with particular emphasis on the chemistry of U. Results characterize the solution behavior of uranium as U-bearing water interacts with relatively undecomposed, surficial organic matter. Of the measured major and trace chemical species, only U is consistently highly enriched (17-318 ppb) relative to reported values for regional waters, or to literature values for waters in largely granitic terrains. R-mode factor analysis of the chemical data suggests that most U is present in a soluble form, but that some U is also associated with fine suspended particulates of clay, organic matter, or hydrous oxides. Calculations that apply thermodynamic data to predict U speciation in solution indicate the relative importance of uranyl carbonate and uranyl phosphate complexes. Analysis of more finely filtered samples (0.05 ??m vs. 0.45 ??m), and direct radiographic observations using fission-track detectors suspended in the waters indicate the presence of some uraniferous particulate matter. Application of existing thermodynamic data for uranous- and uranyl-bearing minerals indicates that all waters are undersaturated with U minerals as long as ambient Eh ??? +0.1 v. If coexisting surface and near-surface waters are sufficiently oxidizing, initial fixation of U in the deposit should be by a mechanism of adsorption. Alternatively, more reducing conditions may prevail in deeper pore waters of the organic-rich host sediments, perhaps leading to direct precipitation or diagenetic formation of U4+ minerals. A 234U 238U alpha activity ratio of 1.08 ?? 0.02 in a spring issuing from a hillslope above the deposit suggests a relatively soluble source of U. In contrast, higher activity ratios of 234U 238U (??? 1.3) in waters in contact with the uraniferous valley-fill sediments suggest differences in the nature of interaction between groundwater and the local, U-rich source rocks. ?? 1987.

Isotopic Clues on Factors Controlling Geochemical Fluxes From Large Watersheds in Eastern Canada

NASA Astrophysics Data System (ADS)

Rosa, E.; Helie, J.; Ghaleb, B.; Hillaire-Marcel, C.; Gaillardet, J.

2008-12-01

A monitoring and monthly sampling program of the Nelson, Ottawa, St. Lawrence, La Grande and Great Whale rivers was started in September 2007. It provides information on the seasonality and sources of geochemical fluxes into the Hudson Bay and the North Atlantic from watersheds covering more than 2.6 106 km2 of the eastern Canadian boreal domain. Measurements of pH and alkalinity, analyses of major ions, strontium and dissolved silica, 2H and 18O of water, concentrations and isotopic properties of dissolved organic and inorganic carbon (13C) and uranium (234U/238U) were performed. Lithology more than latitudinal climatic gradients controls the river geochemistry. Rivers draining silicate terrains show lower dissolved U concentrations but greater 234U/238U disequilibria than rivers draining carbonates (average of 1.38 vs. 1.23). Groundwater supplies might exert some control on these U- isotope signatures. No clear seasonality is observed in 234U/238U ratios, but U concentrations are correlated to dissolved organic carbon (DOC) concentrations in most rivers. Rivers draining carbonates present higher total dissolved carbon concentrations and higher 13C-contents in dissolved inorganic carbon (DIC), in response to the dissolution of soil carbonates. DOC/DIC ratios above 2.4 are observed in rivers draining silicates; their lower 13C-DIC content directly reflects the organic matter oxidation in soils. Total dissolved solids are one order of magnitude or more greater in rivers draining carbonates, showing the strong difference in chemical weathering rates according to the geological setting. The stability in chemical fluxes and water isotopic compositions in the La Grande River, which hosts hydroelectric reservoirs covering more than 12 000 km2, indicates that it is the most buffered hydrological system among the investigated watersheds. Seasonal fluctuations are observed elsewhere, with maximum geochemical fluxes during the spring snowmelt. 2H-18O content of river water appears to be the only parameter presenting a strong latitudinal and climatic gradient (independent of lithology).

Regolith production rates calculated with uranium-series isotopes at Susquehanna/Shale Hills Critical Zone Observatory

NASA Astrophysics Data System (ADS)

Ma, Lin; Chabaux, Francois; Pelt, Eric; Blaes, Estelle; Jin, Lixin; Brantley, Susan

2010-08-01

In the Critical Zone where rocks and life interact, bedrock equilibrates to Earth surface conditions, transforming to regolith. The factors that control the rates and mechanisms of formation of regolith, defined here as material that can be augered, are still not fully understood. To quantify regolith formation rates on shale lithology, we measured uranium-series (U-series) isotopes ( 238U, 234U, and 230Th) in three weathering profiles along a planar hillslope at the Susquehanna/Shale Hills Observatory (SSHO) in central Pennsylvania. All regolith samples show significant U-series disequilibrium: ( 234U/ 238U) and ( 230Th/ 238U) activity ratios range from 0.934 to 1.072 and from 0.903 to 1.096, respectively. These values display depth trends that are consistent with fractionation of U-series isotopes during chemical weathering and element transport, i.e., the relative mobility decreases in the order 234U > 238U > 230Th. The activity ratios observed in the regolith samples are explained by i) loss of U-series isotopes during water-rock interactions and ii) re-deposition of U-series isotopes downslope. Loss of U and Th initiates in the meter-thick zone of "bedrock" that cannot be augered but that nonetheless consists of up to 40% clay/silt/sand inferred to have lost K, Mg, Al, and Fe. Apparent equivalent regolith production rates calculated with these isotopes for these profiles decrease exponentially from 45 m/Myr to 17 m/Myr, with increasing regolith thickness from the ridge top to the valley floor. With increasing distance from the ridge top toward the valley, apparent equivalent regolith residence times increase from 7 kyr to 40 kyr. Given that the SSHO experienced peri-glacial climate ˜ 15 kyr ago and has a catchment-wide averaged erosion rate of ˜ 15 m/Myr as inferred from cosmogenic 10Be, we conclude that the hillslope retains regolith formed before the peri-glacial period and is not at geomorphologic steady state. Both chemical weathering reactions of clay minerals and translocation of fine particles/colloids are shown to contribute to mass loss of U and Th from the regolith, consistent with major element data at SSHO. This research documents a case study where U-series isotopes are used to constrain the time scales of chemical weathering and regolith production rates. Regolith production rates at the SSHO should be useful as a reference value for future work at other weathering localities.

Uranium: A Dentist's perspective

PubMed Central

Toor, R. S. S.; Brar, G. S.

2012-01-01

Uranium is a naturally occurring radionuclide found in granite and other mineral deposits. In its natural state, it consists of three isotopes (U-234, U-235 and U-238). On an average, 1% – 2% of ingested uranium is absorbed in the gastrointestinal tract in adults. The absorbed uranium rapidly enters the bloodstream and forms a diffusible ionic uranyl hydrogen carbonate complex (UO2HCO3+) which is in equilibrium with a nondiffusible uranyl albumin complex. In the skeleton, the uranyl ion replaces calcium in the hydroxyapatite complex of the bone crystal. Although in North India, there is a risk of radiological toxicity from orally ingested natural uranium, the principal health effects are chemical toxicity. The skeleton and kidney are the primary sites of uranium accumulation. Acute high dose of uranyl nitrate delays tooth eruption, and mandibular growth and development, probably due to its effect on target cells. Based on all previous research and recommendations, the role of a dentist is to educate the masses about the adverse effects of uranium on the overall as well as the dental health. The authors recommended that apart from the discontinuation of the addition of uranium to porcelain, the Public community water supplies must also comply with the Environmental Protection Agency (EPA) standards of uranium levels being not more than 30 ppb (parts per billion). PMID:24478959

Investigation of the /sup 234/U//sup 238/U disequilibrium in the natural waters of the Santa Fe River basin north-central Florida

DOE Office of Scientific and Technical Information (OSTI.GOV)

Briel, L.I.

1976-01-01

Typical surface water masses in the Santa Fe basin are characterized by a /sup 238/U concentration of 0.224 +- .014 ppB and a /sup 234/U//sup 238/U activity ratio of 1.081 +- .038. The Floridan aquifer in this area is represented by at least two distinct regimes of ground water. The effluent from the Poe Springs group has a nominal uranium concentration of 0.938 +- .014 ppB and an activity ratio of 0.900 +- .012, while the effluent from the Ichetucknee Springs group has a nominal uranium concentration of 0.558 +- .018 ppB and an activity ratio of 0.707 +- .022.more » The effluent from ten additional springs in the Santa Fe system can be represented by hypothetical mixtures of these two ground water regimes and a hypothetical surface water component, which may reflect the extent of local recharge to the aquifer in different parts of the basin.« less

Undiagnosed illnesses and radioactive warfare.

PubMed

Duraković, Asaf

2003-10-01

The internal contamination with depleted uranium (DU) isotopes was detected in British, Canadian, and United States Gulf War veterans as late as nine years after inhalational exposure to radioactive dust in the Persian Gulf War I. DU isotopes were also identified in a Canadian veteran's autopsy samples of lung, liver, kidney, and bone. In soil samples from Kosovo, hundreds of particles, mostly less than 5 microm in size, were found in milligram quantities. Gulf War I in 1991 resulted in 350 metric tons of DU deposited in the environment and 3-6 million grams of DU aerosol released into the atmosphere. Its legacy, Gulf War disease, is a complex, progressive, incapacitating multiorgan system disorder. The symptoms include incapacitating fatigue, musculoskeletel and joint pains, headaches, neuropsychiatric disorders, affect changes, confusion, visual problems, changes of gait, loss of memory, lymphadenopathies, respiratory impairment, impotence, and urinary tract morphological and functional alterations. Current understanding of its etiology seems far from being adequate. After the Afghanistan Operation Anaconda (2002), our team studied the population of Jalalabad, Spin Gar, Tora Bora, and Kabul areas, and identified civilians with the symptoms similar to those of Gulf War syndrome. Twenty-four-hour urine samples from 8 symptomatic subjects were collected by the following criteria: 1) the onset of symptoms relative to the bombing raids; 2) physical presence in the area of the bombing; and 3) clinical manifestations. Control subjects were selected among the sympotom-free residents in non-targeted areas. All samples were analyzed for the concentration and ratio of four uranium isotopes, (234)U, (235)U, (236)U and (238)U, by using a multicollector, inductively coupled plasma ionization mass spectrometry. The first results from the Jalalabad province revealed urinary excretion of total uranium in all subjects significantly exceeding the values in the nonexposed population. The analysis of the isotopic ratios identified non-depleted uranium. Studies of specimens collected in 2002 revealed uranium concentrations up to 200 times higher in the districts of Tora Bora, Yaka Toot, Lal Mal, Makam Khan Farm, Arda Farm, Bibi Mahro, Poli Cherki, and the Kabul airport than in the control population. Uranium levels in the soil samples from the bombsites show values two to three times higher than worldwide concentration levels of 2 to 3 mg/kg and significantly higher concentrations in water than the World Health Organization maximum permissible levels. This growing body of evidence undoubtedly puts the problem of prevention and solution of the DU contamination high on the priority list.

Fission-fragment total kinetic energy and mass yields for neutron-induced fission of 235U and 238U with En =200 keV - 30 MeV

NASA Astrophysics Data System (ADS)

Duke, D. L.; Tovesson, F.; Brys, T.; Geppert-Kleinrath, V.; Hambsch, F.-J.; Laptev, A.; Meharchand, R.; Manning, B.; Mayorov, D.; Meierbachtol, K.; Mosby, S.; Perdue, B.; Richman, D.; Shields, D.; Vidali, M.

2017-09-01

The average Total Kinetic Energy (TKE) release and fission-fragment yields in neutron-induced fission of 235U and 238U was measured using a Frisch-gridded ionization chamber. These observables are important nuclear data quantites that are relevant to applications and for informing the next generation of fission models. The measurements were performed a the Los Alamos Neutron Science Center and cover En = 200 keV - 30 MeV. The double-energy (2E) method was used to determine the fission-fragment yields and two methods of correcting for prompt-neutron emission were explored. The results of this study are correlated mass and TKE data.

Nuclear energy release from fragmentation

NASA Astrophysics Data System (ADS)

Li, Cheng; Souza, S. R.; Tsang, M. B.; Zhang, Feng-Shou

2016-08-01

It is well known that binary fission occurs with positive energy gain. In this article we examine the energetics of splitting uranium and thorium isotopes into various numbers of fragments (from two to eight) with nearly equal size. We find that the energy released by splitting 230,232Th and 235,238U into three equal size fragments is largest. The statistical multifragmentation model (SMM) is applied to calculate the probability of different breakup channels for excited nuclei. By weighing the probability distributions of fragment multiplicity at different excitation energies, we find the peaks of energy release for 230,232Th and 235,238U are around 0.7-0.75 MeV/u at excitation energy between 1.2 and 2 MeV/u in the primary breakup process. Taking into account the secondary de-excitation processes of primary fragments with the GEMINI code, these energy peaks fall to about 0.45 MeV/u.

Natural radionuclides in lichens, mosses and ferns in a thermal power plant and in an adjacent coal mine area in southern Brazil.

PubMed

Galhardi, Juliana Aparecida; García-Tenorio, Rafael; Díaz Francés, Inmaculada; Bonotto, Daniel Marcos; Marcelli, Marcelo Pinto

2017-02-01

The radio-elements 234 U, 235 U, 238 U, 230 Th, 232 Th and 210 Po were characterized in lichens, mosses and ferns species sampled in an adjacent coal mine area at Figueira City, Paraná State, Brazil, due to their importance for the assessment of human exposure related to the natural radioactivity. The coal is geologically associated with a uranium deposit and has been used as a fossil fuel in a thermal power plant in the city. Samples were initially prepared at LABIDRO (Isotopes and Hydrochemistry Laboratory), UNESP, Rio Claro (SP), Brazil. Then, alpha-spectrometry after several radiochemical steps was used at the Applied Nuclear Physics Laboratories, University of Seville, Seville, Spain, for measuring the activity concentration of the radionuclides. It was 210 Po the radionuclide that most bio-accumulates in the organisms, reaching the highest levels in mosses. The ferns species were less sensitive as bio-monitor than the mosses and lichens, considering polonium in relation to other radionuclides. Fruticose lichens exhibited lower polonium content than the foliose lichens sampled in the same site. Besides biological features, environmental characteristics also modify the radio-elements absorption by lichens and mosses like the type of vegetation covering these organisms, their substrate, the prevailing wind direction, elevation and climatic conditions. Only 210 Po and 238 U correlated in ferns and in soil and rock materials, being particulate emissions from the coal-fired power plant the most probable U-source in the region. Thus, the biomonitors used were able to detect atmospheric contamination by the radionuclides monitored. Copyright © 2016 Elsevier Ltd. All rights reserved.

Uranium isotope fractionation induced by aqueous speciation: Implications for U isotopes in marine CaCO3 as a paleoredox proxy

NASA Astrophysics Data System (ADS)

Chen, Xinming; Romaniello, Stephen J.; Anbar, Ariel D.

2017-10-01

Natural variations of 238U/235U in marine CaCO3 rocks are being explored as a novel paleoredox proxy to investigate oceanic anoxia events. Although it is generally assumed that U isotopes in CaCO3 directly record 238U/235U of seawater, recently published laboratory experiments demonstrate slight U isotope fractionation during U(VI) incorporation into abiotic calcium carbonates. This fractionation is hypothesized to depend on aqueous U(VI) speciation, which is controlled by pH, ionic strength, pCO2 and Mg2+ and Ca2+ concentrations. Secular variation in seawater chemistry could lead to changes in aqueous U(VI) speciation, and thus, may affect the extent of U isotope fractionation during U(VI) incorporation into CaCO3. In this study, we combine estimates of seawater composition over the Phanerozoic with a model of aqueous U speciation and isotope fractionation to explore variations in the expected offset between the U isotope composition of seawater and primary marine CaCO3 through time. We find that U isotope fractionation between U in primary marine CaCO3 and seawater could have varied between 0.11 and 0.23‰ over the Phanerozoic due to secular variations in seawater chemistry. Such variations would significantly impact estimates of the extent of marine anoxia derived from the U isotope record. For example, at the Permo-Triassic boundary, this effect might imply that the estimated extent of anoxia is ∼32% more extreme than previously inferred. One significant limitation of our model is that the existing experimental database covers only abiotic carbonate precipitation, and does not include a possible range of biological effects which might enhance or suppress the range of isotopic fractionation calculated here. As biotic carbonates dominate the marine carbonate record, more work is need to assess controls on U isotopic fractionation into biotic marine carbonates.

7 CFR 235.7 - Records and reports.

Code of Federal Regulations, 2012 CFR

2012-01-01

... surveys. (Sec. 14, Pub. L. 95-166, 91 Stat. 1338 (42 U.S.C. 1776); sec. 7, Pub. L. 95-627, 92 Stat. 3621 (42 U.S.C. 1776); 93 Stat. 837, Pub. L. 96-108 (42 U.S.C. 1776); secs. 804, 816, 817 and 819, Pub. L...

7 CFR 235.11 - Other provisions.

Code of Federal Regulations, 2014 CFR

2014-01-01

.... 14, Pub. L. 95-166, 91 Stat. 1338 (42 U.S.C. 1776); sec. 7, Pub. L. 95-627, 92 Stat. 3621 (42 U.S.C. 1776); secs. 805 and 819, Pub. L. 97-35, 95 Stat. 521-535 (42 U.S.C. 1773); sec. 7(a), Pub. L. 95-627...

7 CFR 235.7 - Records and reports.

Code of Federal Regulations, 2014 CFR

2014-01-01

... surveys. (Sec. 14, Pub. L. 95-166, 91 Stat. 1338 (42 U.S.C. 1776); sec. 7, Pub. L. 95-627, 92 Stat. 3621 (42 U.S.C. 1776); 93 Stat. 837, Pub. L. 96-108 (42 U.S.C. 1776); secs. 804, 816, 817 and 819, Pub. L...

7 CFR 235.11 - Other provisions.

Code of Federal Regulations, 2010 CFR

2010-01-01

.... 14, Pub. L. 95-166, 91 Stat. 1338 (42 U.S.C. 1776); sec. 7, Pub. L. 95-627, 92 Stat. 3621 (42 U.S.C. 1776); secs. 805 and 819, Pub. L. 97-35, 95 Stat. 521-535 (42 U.S.C. 1773); sec. 7(a), Pub. L. 95-627...

7 CFR 235.7 - Records and reports.

Code of Federal Regulations, 2010 CFR

2010-01-01

... surveys. (Sec. 14, Pub. L. 95-166, 91 Stat. 1338 (42 U.S.C. 1776); sec. 7, Pub. L. 95-627, 92 Stat. 3621 (42 U.S.C. 1776); 93 Stat. 837, Pub. L. 96-108 (42 U.S.C. 1776); secs. 804, 816, 817 and 819, Pub. L...

7 CFR 235.7 - Records and reports.

Code of Federal Regulations, 2013 CFR

2013-01-01

... surveys. (Sec. 14, Pub. L. 95-166, 91 Stat. 1338 (42 U.S.C. 1776); sec. 7, Pub. L. 95-627, 92 Stat. 3621 (42 U.S.C. 1776); 93 Stat. 837, Pub. L. 96-108 (42 U.S.C. 1776); secs. 804, 816, 817 and 819, Pub. L...

7 CFR 235.11 - Other provisions.

Code of Federal Regulations, 2012 CFR

2012-01-01

.... 14, Pub. L. 95-166, 91 Stat. 1338 (42 U.S.C. 1776); sec. 7, Pub. L. 95-627, 92 Stat. 3621 (42 U.S.C. 1776); secs. 805 and 819, Pub. L. 97-35, 95 Stat. 521-535 (42 U.S.C. 1773); sec. 7(a), Pub. L. 95-627...

7 CFR 235.11 - Other provisions.

Code of Federal Regulations, 2013 CFR

2013-01-01

.... 14, Pub. L. 95-166, 91 Stat. 1338 (42 U.S.C. 1776); sec. 7, Pub. L. 95-627, 92 Stat. 3621 (42 U.S.C. 1776); secs. 805 and 819, Pub. L. 97-35, 95 Stat. 521-535 (42 U.S.C. 1773); sec. 7(a), Pub. L. 95-627...

7 CFR 235.7 - Records and reports.

Code of Federal Regulations, 2011 CFR

2011-01-01

... surveys. (Sec. 14, Pub. L. 95-166, 91 Stat. 1338 (42 U.S.C. 1776); sec. 7, Pub. L. 95-627, 92 Stat. 3621 (42 U.S.C. 1776); 93 Stat. 837, Pub. L. 96-108 (42 U.S.C. 1776); secs. 804, 816, 817 and 819, Pub. L...

7 CFR 235.11 - Other provisions.

Code of Federal Regulations, 2011 CFR

2011-01-01

.... 14, Pub. L. 95-166, 91 Stat. 1338 (42 U.S.C. 1776); sec. 7, Pub. L. 95-627, 92 Stat. 3621 (42 U.S.C. 1776); secs. 805 and 819, Pub. L. 97-35, 95 Stat. 521-535 (42 U.S.C. 1773); sec. 7(a), Pub. L. 95-627...

76 FR 30228 - Culturally Significant Object Imported for Exhibition; Determinations: “Portrait of a Man”

Federal Register 2010, 2011, 2012, 2013, 2014

2011-05-24

...Notice is hereby given of the following determinations: Pursuant to the authority vested in me by the Act of October 19, 1965 (79 Stat. 985; 22 U.S.C. 2459), Executive Order 12047 of March 27, 1978, the Foreign Affairs Reform and Restructuring Act of 1998 (112 Stat. 2681, et seq.; 22 U.S.C. 6501 note, et seq.), Delegation of Authority No. 234 of October 1, 1999, and Delegation of Authority No. 236-3 of August 28, 2000, I hereby determine that the object to be included in the exhibition ``Portrait of a Man'', imported from abroad for temporary exhibition within the United States, is of cultural significance. The object is imported pursuant to a loan agreement with the foreign owner or custodian. I also determine that the exhibition or display of the exhibit object at The Metropolitan Museum of Art, New York, New York, from on or about June 1, 2011, until on or about December 31, 2016, is in the national interest. Public Notice of these Determinations is ordered to be published in the Federal Register.

Benchmark Gamma Spectroscopy Measurements of Uranium Hexafluoride in Aluminmum Pipe with a Sodium Iodide Detector

DOE Office of Scientific and Technical Information (OSTI.GOV)

March-Leuba, Jose A; Uckan, Taner; Gunning, John E

2010-01-01

The expected increased demand in fuel for nuclear power plants, combined with the fact that a significant portion of the current supply from the blend down of weapons-source material will soon be coming to an end, has led to the need for new sources of enriched uranium for nuclear fuel. As a result, a number of countries have announced plans, or are currently building, gaseous centrifuge enrichment plants (GCEPs) to supply this material. GCEPs have the potential to produce uranium at enrichments above the level necessary for nuclear fuel purposes-enrichments that make the uranium potentially usable for nuclear weapons. Asmore » a result, there is a critical need to monitor these facilities to ensure that nuclear material is not inappropriately enriched or diverted for unintended use. Significant advances have been made in instrument capability since the current International Atomic Energy Agency (IAEA) monitoring methods were developed. In numerous cases, advances have been made in other fields that have the potential, with modest development, to be applied in safeguards applications at enrichment facilities. A particular example of one of these advances is the flow and enrichment monitor (FEMO). (See Gunning, J. E. et al., 'FEMO: A Flow and Enrichment Monitor for Verifying Compliance with International Safeguards Requirements at a Gas Centrifuge Enrichment Facility,' Proceedings of the 8th International Conference on Facility Operations - Safeguards Interface. Portland, Oregon, March 30-April 4th, 2008.) The FEMO is a conceptual instrument capable of continuously measuring, unattended, the enrichment and mass flow of {sup 235}U in pipes at a GCEP, and consequently increase the probability that the potential production of HEU and/or diversion of fissile material will be detected. The FEMO requires no piping penetrations and can be installed on pipes containing the flow of uranium hexafluoride (UF{sub 6}) at a GCEP. This FEMO consists of separate parts, a flow monitor (FM) and an enrichment monitor (EM). Development of the FM is primarily the responsibility of Oak Ridge National Laboratory, and development of the EM is primarily the responsibility of Los Alamos National Laboratory. The FM will measure {sup 235}U mass flow rate by combining information from measuring the UF{sub 6} volumetric flow rate and the {sup 235}U density. The UF{sub 6} flow rate will be measured using characteristics of the process pumps used in product and tail UF{sub 6} header process lines of many GCEPs, and the {sup 235}U density will be measured using commercially available sodium iodide (NaI) gamma ray scintillation detectors. This report describes the calibration of the portion of the FM that measures the {sup 235}U density. Research has been performed to define a methodology and collect data necessary to perform this calibration without the need for plant declarations. The {sup 235}U density detector is a commercially available system (GammaRad made by Amptek, www.amptek.com) that contains the NaI crystal, photomultiplier tube, signal conditioning electronics, and a multichannel analyzer (MCA). Measurements were made with the detector system installed near four {sup 235}U sources. Two of the sources were made of solid uranium, and the other two were in the form of UF{sub 6} gas in aluminum piping. One of the UF{sub 6} gas sources was located at ORNL and the other at LANL. The ORNL source consisted of two pipe sections (schedule 40 aluminum pipe of 4-inch and 8-inch outside diameter) with 5.36% {sup 235}U enrichment, and the LANL source was a 4-inch schedule 40 aluminum pipe with 3.3% {sup 235}U enrichment. The configurations of the detector on these test sources, as well as on long straight pipe configurations expected to exist at GCEPs, were modeled using the computer code MCNP. The results of the MCNP calculations were used to define geometric correction factors between the test source and the GCEP application. Using these geometric correction factors, the experimental 186 keV counts in the test geometry were extrapolated to the expected GCEP geometry, and calibration curves were developed. A unique method to analyze the measurement was also developed that separated the detector spectrum into the five detectable decay gamma rays emitted by {sup 235}U in the 120 to 200 keV energy range. This analysis facilitated the assignment of a consistent value for the detector counts originating from {sup 235}U decays at 186 keV. This value is also more accurate because it includes the counts from gamma energies other than 186 keV, which results in increased counting statistics for the same measurement time. The 186 keV counts expected as a function of pressure and enrichment are presented in the body of this report. The main result of this research is a calibration factor for 4-inch and 8-inch schedule 40 aluminum pipes. For 4-inch pipes, the {sup 235}U density is 0.62 {sup 235}U g/m{sup 3} per each measured 186 keV count.« less

Heterogeneous UO2 fuel irradiated up to a high burn-up: Investigation of the HBS and of fission product releases

NASA Astrophysics Data System (ADS)

Noirot, J.; Lamontagne, J.; Nakae, N.; Kitagawa, T.; Kosaka, Y.; Tverberg, T.

2013-11-01

A UO2 fuel with a heterogeneous distribution of 235U was irradiated up to a high burn-up in the Halden Boiling Water Reactor (HBWR). The last 100 days of irradiation were performed with an increased level of linear power. The effect of the heterogeneous fissile isotope distribution on the formation of the HBS was studied free of the possible influence of Pu which exists in heterogeneous MOX fuels. The HBS formed in 235U-rich agglomerates and its main characteristics were very similar to those of the HBS formed in Pu-rich agglomerates of heterogeneous MOX fuels. The maximum local contents of Nd and Xe before HBS formation were studied in this fuel. In addition to a Pu effect that promotes the HBS phenomenon, comparison with previous results for heterogeneous MOX fuels showed that the local fission product concentration was not the only parameter that has to be taken into consideration. It appears that the local actinide depletion by fission and/or the energy locally deposited through electronic interactions in the fission fragment recoils also have an effect on the HBS formation threshold. Moreover, a major release of fission gases from the peripheral 235U-rich agglomerates of HBS bubbles and a Cs radial movement are also evidenced in this heterogeneous UO2. Cs deposits on the peripheral grain boundaries, including the HBS grain boundaries, are considered to reveal the release paths. SUP>235U-rich agglomerates, SUP>235U-poor areas, an intermediate phase with intermediate 235U concentrations. Short fuel rods were fabricated with these pellets. The main characteristics of these fuel rods are shown in Table 1.These rods were irradiated to high burn-ups in the IFA-609/626 of the HBWR and then one was irradiated in the IFA-702 for 100 days. Fig. 2 shows the irradiation history of this fuel. The final average burn-up of the rod was 69 GWd/tU. Due to the flux differences along the rod, however, the average burn-up of the cross section examined was 63 GWd/tU. This fuel experienced high linear powers during the first year of irradiation, but at the end of the IFA-609/626 period, the average linear power of the rod was around 12 kW/m. In the IFA-702, the power was gradually increased over 7 days from 12 kW/m to 22.5 kW/m before it was decreased again to reach ˜19 kW/m at the end of the 100 days forming this part of the irradiation. A LEICA (DM RXA2) optical microscope. A shielded electronic microprobe (EPMA) SX-100R by CAMECA. A shielded scanning electron microscope (SEM): the Philips XL30. Image acquisitions were performed using the ADDA "SIS" system with the AnalySIS software for image analysis. A shielded secondary ion mass spectrometer (SIMS): the CAMECA IMS 6f was capable of analysing the same samples as the SEM and EPMA [16-22]. In the central part of the pellet for all three phases, Xe precipitated into bubbles with very little Xe remaining outside the bubbles. Some Xe-filled bubbles were detected under the surface in this area. They appear as bright spots. Around mid-radius on the periphery of the 235U-poor areas and in the intermediate phase, Xe was depleted on the periphery of the grains. This depletion was not associated with Xe-filled bubbles that would be detected under the polished surface. Moreover, no large intergranular open bubbles were visible. Therefore, this missing gas must have been released. In the 235U-rich agglomerates all over the section, Xe precipitated into bubbles with very little Xe remaining outside the bubbles. The Xe quantitative analyses through 235U-rich agglomerates on the pellet periphery (Fig. 9) confirmed the low quantity of Xe remaining outside the bubbles. This Xe content was around 0.1 wt%. Fig. 10 shows the Xe and Nd EPMA quantitative measurements along a radius of the cross section. In this figure and in Fig. 9, the weight percentage scales were set so that the two profiles would be almost identical without Xe release or precipitation. Along the Xe axis, the Nd profile can be considered as the local Xe production. Fig. 10 shows that the Xe measurement all through the central part is low except for a few points corresponding to unopened but close to the polished surface and detected by EPMA. These points correspond to the bright spots detected in the central part in Fig. 8. High concentrations were detected locally all over the radius on the Nd profile. They correspond to the 235U-rich agglomerates or their surroundings. Outside the central part, these high Nd concentrations correspond to low Xe concentrations, consistent with the maps in Fig. 8 and the detailed analyses across large 235U-rich agglomerates (Fig. 9).Fig. 11 shows a set of Xe (wt%) and (145Nd + 146Nd)/heavy metal radial profiles both acquired by SIMS. Three profiles are show for each set: one in the 235U-rich agglomerates, one in the 235U-poor areas and one in the intermediate phase. The three phases are not homogeneous themselves. This induces differences between (145Nd + 146Nd)/HM SIMS measurement points of a given phase. The (145Nd + 146Nd)/HM results are a reference for the Xe measurements, giving an estimation of the relative Xe local production. The (145Nd + 146Nd)/HM was high in the 235U-rich agglomerates, lower in the intermediate phase and even lower in the 235U-poor areas. Differences similar to those obtained herein between the phases would have been found in the Xe measurements if no release had occurred in any of those phases. The Xe (wt%) results show that this is not the case. The Xe measurements were quite similar in the intermediate phase and in the 235U-poor areas; they would have been higher in the intermediate phase if no release had occurred. The Xe measurements in the 235U-rich agglomerates were very low and lower than in the two other phases. For the 235U-rich agglomerates, there was a very big difference, across the entire radius, between the Xe measured and the Xe local production.In the SIMS Xe measurements, local depth profiles show peaks on a base line [19]. The base line corresponds to the solid solution Xe and to the nano-bubbles. The peaks correspond to Xe in larger bubbles opened by ion beam fuel sputtering. The SIMS total values correspond to the Xe outside these bubbles plus the Xe trapped in these bubbles.Fig. 12 shows the total Xe SIMS results (already shown in Fig. 11) together with the base line measurements for each measurement point and in separate graphs for each phase. The Xe EPMA quantitative measurements used as a background for these three graphs are the same as those in Fig. 10 and are the same for the three graphs, without any phase distinction. The SIMS Xe relative measurements were calibrated through a correspondence between the SIMS base line results and the EPMA measurements [20]. As expected, the SIMS base line profile was consistent with the EPMA all along the profile for each corresponding phase. For example, the SIMS base line in the 235U-rich agglomerates corresponds to the low EPMA measurement points of the Xe in this zone, i.e. the points of the EPMA profile in the 235U-rich agglomerates. By way of comparison between the Xe and the Nd measurements (the latter being rescaled to be representative of the creation level of Xe), Fig. 11 made it possible to identify two main parts on the Xe SIMS radius: The central part 0R to ˜0.5R: In the intermediate phase and the 235U-poor areas, the SIMS total was used to identify this part as a release area. The average fraction of gas measured in the bubbles (the ratio between the gas in the bubbles and the total measurement) was between 60% and 90%. The Xe content outside the bubbles was very low. In the 235U-rich agglomerates, the SIMS total represents only a small fraction of the produced Xe, which means that a large fraction of the Xe is released or not detected by SIMS due to the large size of some agglomerate bubbles compared with the volume of the crater analysed. sim;0.5R to ˜1R: The 235U-poor areas are not release areas. The fraction of gas in bubbles measured in these areas remained low, ˜5%. The intermediate phase is a release area with moderate release. The average fraction of gas measured in the bubbles was around 20%. In the 235U-rich agglomerates, the Xe SIMS total was very low. This part is a release area. Sharp transitions between initial microstructure and the HBS, often inside one grain. Increase in the resulting grain size with increasing distance from the pellet periphery. The grain sizes are in fact consistent with the MOX measurements [2]. Increase in the bubble size with the increasing distance from the pellet periphery, consistent with the MOX measurements. Smaller bubbles tend to be found in the peripheral part of the 235U-rich agglomerates rather than in their central part. Sharp transition, around 0.5R, between the peripheral area where the conventional form of HBS forms in the 235U-rich agglomerates and the central part where much larger bubbles form and where the grain size is also clearly larger. Xe concentration of 0.1 wt% outside the bubbles in the HBS areas is consistent with the [2] MOX measurements at equivalent local burn-ups. The heterogeneous MOX fuels examinations have firmly established that the HBS can extend outside the Pu-rich agglomerates due to the implantation of fission products around these agglomerates. Similarly, it has been shown that the small Pu-rich agglomerates can remain with the initial microstructure even if there is a similar actual local burn-up, a large rate of fission products being implanted outside the agglomerates themselves so that the local fission product concentration remains low.In this 235U heterogeneous UO2, the Xe and Nd concentration levels reached at the HBS formation limit ranged between 0.8 wt% and 1.1 wt% for Xe and between 0.63 wt% and 0.83 wt% for Nd. These ranges are similar to what was reported in [23] for the UO2 rim. These limits are, however, slightly higher than those found for Pu-rich agglomerates in heterogeneous MOX fuels in [2] or in [24]. Nonetheless, they are clearly lower than the concentrations reached without HBS in the special Pu-poor spots in [2]. In these spots, UO2 particles in heterogeneous MOX were really close or even surrounded by Pu-rich areas. As a result, their fission product content, due to recoil, was almost the same as that in the surrounding Pu-rich agglomerates themselves despite a very low actual local burn-up. In these special UO2 spots in MOX fuel, 1.4 wt% was reached for Xe and no HBS formed.If these high Xe concentrations without HBS in the special spots in [2] were made possible by the very low Pu local concentration only, very high Xe concentrations should have been common around the heterogeneous UO2 fuel 235U-rich agglomerates, since the Pu level was low everywhere in this fuel. This is not what was observed.Even if this effect due to a high fission product level reached without the formation of a HBS (as reported in [2] for heterogeneous MOX fuels in the special spots) is partially due to the very low local Pu level, it does not seem to be the only reason. It also seems to be partly due to the very low level of actual fissions occurring there. Between a rich agglomerate and such a highly implanted area there is: The same local fission product build-up and associated damage (due to cascades from the nuclei interactions during the last part of the fission fragment recoil). A large difference in the actinide isotope depletion to the extent that a difference in chemical composition exists between the two. A difference in the electronic excitation level at the beginning of the fission fragment recoil, higher in Pu agglomerates and in 235U-rich agglomerates than in the low fissile content areas, even surrounded by rich areas. The last two points may have an effect on the formation of a HBS though this paper cannot say which one is the most significant.The highest levels reached for Xe and Nd without HBS in the 235U heterogeneous fuel are very likely to correspond to places where the initial 235U content was particularly low but where fission recoil led to these high levels. The maximum concentrations of fission products reached before the formation of a HBS in the 235U heterogeneous fuel are lower than for the heterogeneous MOX special Pu-poor spots. This is most certainly due to the local 235U initial concentration in the 235U-poor areas which is nonetheless high when compared with the initial Pu concentrations in the Pu-poor areas in the MOX fuel. Consequently, there are more fission reactions there in the heterogeneous UO2 fuel than in the MOX fuel.This fission and/or fission spike effect has in fact little impact on the overall fuel behaviour, be it homogeneous or heterogeneous, but it has to be taken into account in the separate-effect experiments where unirradiated UO2 is submitted to ion irradiation to simulate the irradiation effects [9,25-30]. The depletion of the actinide isotopes cannot be simulated in these experiments. The IFA-702 re-irradiation, with the high power during the last period of the irradiation most certainly having played a role. The other major difference between this fuel was irradiated under BWR conditions, whereas those used in [2] were all PWR fuels. The images of the IFA-702 heterogeneous UO2 fuel on the periphery show that an internal zirconia layer was formed during the irradiation, which is a sign of gap closure under hot conditions, though a thin gap was still measured at room temperature. Therefore, the stress field in the pellet of this fuel must have been significantly different from that of the fuel used in [2]. The resulting release is all the more interesting since the release path is more or less revealed by the Cs deposits. This Cs is released from the hot central part of the pellet and is not only in the fuel-cladding gap and along the obvious radial cracks, but also in: All the grain boundaries around those radial cracks. The HBS 235U-rich agglomerates around those radial cracks. Like for Xe, the general trend for Cs was a release from the 235U peripheral agglomerates. The higher Cs measurement in the 235U-rich agglomerates close to the radial cracks results from both this release and the deposition of the Cs released from the hot central part.This singular release of Xe from the HBS bubbles of the 235U-rich agglomerates on the fuel periphery is all the more surprising that the Pu-rich agglomerates of the MIMAS MOX fuel irradiated under the same conditions [15] retained their fission gases in these areas. We found no definitive reason for that difference. the fission product implantation level has an effect. the local Pu content has also an effect. the actual local burn-up has an effect. This effect may be linked to fission through the local depletion of the fissile isotopes which changes the local chemical composition, as well as to the higher energy deposited there by electronic interactions at the beginning of the fission fragment recoils when compared with implanted areas with a low actual burn-up. Moreover, the major release of fission gases from the peripheral 235U-rich agglomerate HBS bubbles was evidenced in this heterogeneous UO2 fuel.The radial movement of Cs from the central part of the pellet towards its periphery was shown. This involved a deposition at the grain boundaries, including the HBS ones, around the radial cracks in the periphery. This showed the intergranular paths existing for the release of fission gases and Cs all through the fuel periphery. Grain Equivalent Circular Diameter (ECD) for which half of the surface is made of smaller grains and half of larger grains

Measurement of 235U(n,n'γ) and 235U(n,2nγ) reaction cross sections

NASA Astrophysics Data System (ADS)

Kerveno, M.; Thiry, J. C.; Bacquias, A.; Borcea, C.; Dessagne, P.; Drohé, J. C.; Goriely, S.; Hilaire, S.; Jericha, E.; Karam, H.; Negret, A.; Pavlik, A.; Plompen, A. J. M.; Romain, P.; Rouki, C.; Rudolf, G.; Stanoiu, M.

2013-02-01

The design of generation IV nuclear reactors and the studies of new fuel cycles require knowledge of the cross sections of various nuclear reactions. Our research is focused on (n,xnγ) reactions occurring in these new reactors. The aim is to measure unknown cross sections and to reduce the uncertainty on present data for reactions and isotopes of interest for transmutation or advanced reactors. The present work studies the 235U(n,n'γ) and 235U(n,2nγ) reactions in the fast neutron energy domain (up to 20 MeV). The experiments were performed with the Geel electron linear accelerator GELINA, which delivers a pulsed white neutron beam. The time characteristics enable measuring neutron energies with the time-of-flight (TOF) technique. The neutron induced reactions [in this case inelastic scattering and (n,2n) reactions] are identified by on-line prompt γ spectroscopy with an experimental setup including four high-purity germanium (HPGe) detectors. A fission ionization chamber is used to monitor the incident neutron flux. The experimental setup and analysis methods are presented and the model calculations performed with the TALYS-1.2 code are discussed.

Fission fragment yields and total kinetic energy release in neutron-induced fission of235,238U,and239Pu

NASA Astrophysics Data System (ADS)

Tovesson, F.; Duke, D.; Geppert-Kleinrath, V.; Manning, B.; Mayorov, D.; Mosby, S.; Schmitt, K.

2018-03-01

Different aspects of the nuclear fission process have been studied at Los Alamos Neutron Science Center (LANSCE) using various instruments and experimental techniques. Properties of the fragments emitted in fission have been investigated using Frisch-grid ionization chambers, a Time Projection Chamber (TPC), and the SPIDER instrument which employs the 2v-2E method. These instruments and experimental techniques have been used to determine fission product mass yields, the energy dependent total kinetic energy (TKE) release, and anisotropy in neutron-induced fission of U-235, U-238 and Pu-239.

25 CFR 152.5 - Issuance of patent in fee.

Code of Federal Regulations, 2011 CFR

2011-04-01

... BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR LAND AND WATER ISSUANCE OF PATENTS IN FEE... shall be given to the patentee. (Acts of Feb. 8, 1887 (24 Stat. 388), as amended (25 U.S.C. 349); June 25, 1910 (36 Stat. 855), as amended (25 U.S.C. 372); and May 14, 1948 (62 Stat. 236; 25 U.S.C. 483...

25 CFR 152.5 - Issuance of patent in fee.

Code of Federal Regulations, 2013 CFR

2013-04-01

... BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR LAND AND WATER ISSUANCE OF PATENTS IN FEE... shall be given to the patentee. (Acts of Feb. 8, 1887 (24 Stat. 388), as amended (25 U.S.C. 349); June 25, 1910 (36 Stat. 855), as amended (25 U.S.C. 372); and May 14, 1948 (62 Stat. 236; 25 U.S.C. 483...

25 CFR 152.5 - Issuance of patent in fee.

Code of Federal Regulations, 2014 CFR

2014-04-01

... BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR LAND AND WATER ISSUANCE OF PATENTS IN FEE... shall be given to the patentee. (Acts of Feb. 8, 1887 (24 Stat. 388), as amended (25 U.S.C. 349); June 25, 1910 (36 Stat. 855), as amended (25 U.S.C. 372); and May 14, 1948 (62 Stat. 236; 25 U.S.C. 483...

25 CFR 152.5 - Issuance of patent in fee.

Code of Federal Regulations, 2012 CFR

2012-04-01

... BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR LAND AND WATER ISSUANCE OF PATENTS IN FEE... shall be given to the patentee. (Acts of Feb. 8, 1887 (24 Stat. 388), as amended (25 U.S.C. 349); June 25, 1910 (36 Stat. 855), as amended (25 U.S.C. 372); and May 14, 1948 (62 Stat. 236; 25 U.S.C. 483...

Beta decay heat following U-235, U-238 and Pu-239 neutron fission

NASA Astrophysics Data System (ADS)

Li, Shengjie

1997-09-01

This is an experimental study of beta-particle decay heat from 235U, 239Pu and 238U aggregate fission products over delay times 0.4-40,000 seconds. The experimental results below 2s for 235U and 239Pu, and below 20s for 238U, are the first such results reported. The experiments were conducted at the UMASS Lowell 5.5-MV Van de Graaff accelerator and 1-MW swimming-pool research reactor. Thermalized neutrons from the 7Li(p,n)7Be reaction induced fission in 238U and 239Pu, and fast neutrons produced in the reactor initiated fission in 238U. A helium-jet/tape-transport system rapidly transferred fission fragments from a fission chamber to a low background counting area. Delay times after fission were selected by varying the tape speed or the position of the spray point relative to the beta spectrometer that employed a thin-scintillator-disk gating technique to separate beta-particles from accompanying gamma-rays. Beta and gamma sources were both used in energy calibration. Based on low-energy(<1 MeV) internal-conversion electron studies, a set of trial responses for the spectrometer was established and spanned electron energies 0-10 MeV. Measured beta spectra were unfolded for their energy distributions by the program FERD, and then compared to other measurements and summation calculations based on ENDF/B-VI fission-product data performed on the LANL Cray computer. Measurements of the beta activity as a function of decay time furnished a relative normalization. Results for the beta decay heat are presented and compared with other experimental data and the summation calculations.

Preliminary study on weapon grade uranium utilization in molten salt reactor miniFUJI

NASA Astrophysics Data System (ADS)

Aji, Indarta Kuncoro; Waris, A.

2014-09-01

Preliminary study on weapon grade uranium utilization in 25MWth and 50MWth of miniFUJI MSR (molten salt reactor) has been carried out. In this study, a very high enriched uranium that we called weapon grade uranium has been employed in UF4 composition. The 235U enrichment is 90 - 95 %. The results show that the 25MWth miniFUJI MSR can get its criticality condition for 1.56 %, 1.76%, and 1.96% of UF4 with 235U enrichment of at least 93%, 90%, and 90%, respectively. In contrast, the 50 MWth miniFUJI reactor can be critical for 1.96% of UF4 with 235U enrichment of at smallest amount 95%. The neutron spectra are almost similar for each power output.

46 CFR 282.22 - Maintenance (upkeep) and repairs.

Code of Federal Regulations, 2010 CFR

2010-10-01

...) (Percent) Japan Japan 85 36.21 30.78 U.S 15 0 0 100 30.78 23.4 7.20 Norway Norway 15 44.72 6.71 Netherlands 20 43.23 8.65 Japan 45 36.21 16.29 U.S 20 0 0 100 31.65 31.1 9.84 United Kingdom U.K 80 19.00 15.20...

Recent results in nucleocosmochronology

NASA Astrophysics Data System (ADS)

Cowan, John J.; Thielemann, F.-K.; Truran, J. W.

Rates for beta-delayed neutron emission and fission have recently been calculated for the mass range 70-100. Using these new rates and the calculated rates for neutron capture, photodisintegration and beta decay, dynamical r-process calculations have been performed. For certain assumed conditions, these r-process calculations give a good fit to the solar system r-process abundance curve. These calculations have been used to obtain new production ratios for the nuclear chronometer pairs used to determine the age of the Galaxy - (Th-232)/(U-238) = 1.60, (U-235)/(U-238) = 1.16, and (Pu-244)/(U-238) = 0.40. Using the new production ratio for (Th-232)/(U-238) and (U-235)/(U238), with the observed meteoritic values for these nuclei and assuming a model of chemical evolution of the Galaxy, the age of the Galaxy has been determined. The results depend upon the initial nucleosynthesis enrichment in the Galactic disk, S0. While there are uncertainties in the calculations for a range of S0 from 0.1 to 0.3 (i.e., from 10 to 30 percent), the age of the Galaxy is found to be 12.4-14.7 Gyr.

A Delayed Neutron Counting System for the Analysis of Special Nuclear Materials

NASA Astrophysics Data System (ADS)

Sellers, Madison Theresa

Nuclear forensic analysis is a modem science that uses numerous analytical techniques to identify and attribute nuclear materials in the event of a nuclear explosion, radiological terrorist attack or the interception of illicit nuclear material smuggling. The Canadian Department of National Defence has participated in recent international exercises that have highlighted the Nation's requirement to develop nuclear forensics expertise, protocol and capabilities, specifically pertaining to the analysis of special nuclear materials (SNM). A delayed neutron counting (DNC) system has been designed and established at the Royal Military College of Canada (RMC) to enhance the Government's SNM analysis capabilities. This analytical technique complements those already at RMC by providing a rapid and non-destructive method for the analysis of the fissile isotopes of both uranium (U) and plutonium (Pu). The SLOWPOKE-2 reactor at RMC produces a predominately thermal neutron flux. These neutrons induce fission in the SNM isotopes 233U, 235U and 239Pu releasing prompt fast neutrons, energy and radioactive fission fragments. Some of these fission fragments undergo beta - decay and subsequently emit neutrons, which can be recorded by an array of sensitive 3He detectors. The significant time period between the fission process and the release of these neutrons results in their identification as 'delayed neutrons'. The recorded neutron spectrum varies with time and the count rate curve is unique to each fissile isotope. In-house software, developed by this project, can analyze this delayed neutron curve and provides the fissile mass in the sample. Extensive characterization of the DNC system has been performed with natural U samples with 235 U content ranging from 2--7 microg. The system efficiency and dead time behaviour determined by the natural uranium sample analyses were validated by depleted uranium samples with similar quantities of 235 U resulting in a typical relative error of 3.6%. The system has accurately determined 235U content over three orders of magnitude with 235U amounts as low as 10 ng. The results have also been proven to be independent of small variations in total analyte volume and geometry, indicating that it is an ideal technique for the analysis of samples containing SNM in a variety of different matrices. The Analytical Sciences Group at RMC plans to continue DNC system development to include 233U and 239pu analysis and mixtures of SNM isotopes. Keywords: delayed neutron counting, special nuclear materials, nuclear forensics.

Rotating Fluidized Bed Reactor for Space Nuclear Propulsion. Annual Report; Design Studies and Experimental Results

NASA Technical Reports Server (NTRS)

1971-01-01

The rotating fluidized bed reactor concept is being investigated for possible application in nuclear propulsion systems. Physics calculations show U-233 to be superior to U-235 as a fuel for a cavity reactor of this type. Preliminary estimates of the effect of hydrogen in the reactor, reflector material, and power peaking are given. A preliminary engineering analysis was made for U-235 and U-233 fueled systems. An evaluation of the parameters affecting the design of the system is given, along with the thrust-to-weight ratios. The experimental equipment is described, as are the special photographic techniques and procedures. Characteristics of the fluidized bed and experimental results are given, including photographic evidence of bed fluidization at high rotational velocities.

Preliminary results of calculations for heavy-water nuclear-power-plant reactors employing 235U, 233U, and 232Th as a fuel and meeting requirements of a nonproliferation of nuclear weapons

NASA Astrophysics Data System (ADS)

Ioffe, B. L.; Kochurov, B. P.

2012-02-01

A physical design is developed for a gas-cooled heavy-water nuclear reactor intended for a project of a nuclear power plant. As a fuel, the reactor would employ thorium with a small admixture of enriched uranium that contains not more than 20% of 235U. It operates in the open-cycle mode involving 233U production from thorium and its subsequent burnup. The reactor meets the conditions of a nonproliferation of nuclear weapons: the content of fissionable isotopes in uranium at all stages of the process, including the final one, is below the threshold for constructing an atomic bomb, the amount of product plutonium being extremely small.

The isotopic composition of uranium and lead in Allende inclusions and meteoritic phosphates

NASA Technical Reports Server (NTRS)

Chen, J. H.; Wasserburg, G. J.

1981-01-01

The isotopic compositions of uranium and lead in Ca-Al-rich inclusions from the Allende chondrite and in whitlockite from the St. Severin chondrite and the Angra dos Reis achondrite are reported. Isoptopic analysis of acid soluble fractions of the Allende inclusions and the meteoritic whitlockite, which show isotopic anomalies in other elements, reveals U-235/U-238 ratios from 1/137.6 to 1/138.3, within 20 per mil of normal terrestrial U abundances. The Pb isotopic compositions of five coarse-grained Allende inclusions give a mean Pb-207/Pb-206 model age of 4.559 + or - 0.015 AE, in agreement with the U results. Pb isotope ratios of two fine-grained inclusions and a coarse-grained inclusion with strong mass fractionation and some nonlinear isotopic anomalies indicate that the U-Pb systems of these inclusions have evolved differently from the rest of Allende. Th/U abundance ratios in the Allende inclusions and meteoritic phosphate are found to range from 3.8 to 96, presumably indicating an optimal case for Cm/U fractionation, although the normal U concentrations do not support claims of abundant live Cm-247 or Cm-247/U-238 fractionation at the time of meteorite formation, in contrast to previous results. A limiting Cm-247/U-235 ratio of 0.004 at the time of meteorite formation is calculated which implies that the last major r process contribution at the protosolar nebula was approximately 100 million years prior to Al-26 formation and injection.

Analysis of actinides in an ombrotrophic peat core - evidence of post-depositional migration of fallout radionuclides

NASA Astrophysics Data System (ADS)

Quinto, Francesca; Hrnecek, Erich; Krachler, Michael; Shotyk, William; Steier, Peter; Winkler, Stephan R.

2013-04-01

Plutonium (239Pu, 240Pu, 241Pu, 242Pu) and uranium (236U, 238U) isotopes were analyzed in an ombrotrophic peat core from the Black Forest, Germany, representing the last 80 years of atmospheric deposition. The reliable determination of these isotopes at ultra-trace levels was possible using ultra-clean laboratory procedures and accelerator mass spectrometry. The 240Pu/239Pu isotopic ratios are constant along the core with a mean value of 0.19 ±0.02 (N = 32). This result is consistent with the acknowledged average 240Pu/239Pu isotopic ratio from global fallout in the Northern Hemisphere. The global fallout origin of Pu is confirmed by the corresponding 241Pu/239Pu (0.0012 ±0.0005) and 242Pu/239Pu (0.004 ± 0.001) isotopic ratios. The identification of the Pu isotopic composition characteristic for global fallout in peat layers pre-dating the period of atmospheric atom bomb testing (AD 1956 - AD 1980) is a clear evidence of the migration of Pu downwards the peat profile. The maximum of global fallout derived 236U is detected in correspondence to the age/depth layer of maximum stratospheric fallout (AD 1963). This finding demonstrates that the 236U bomb peak can be successfully used as an independent chronological marker complementing the 210Pb dating of peat cores. The profiles of the global fallout derived 236U and 239Pu are compared with those of 137Cs and 241Am. As typical of ombrothrophic peat, the temporal fallout pattern of 137Cs is poorly retained. Similarly like for Pu, post-depositional migration of 241Am in peat layers preceding the era of atmospheric nuclear tests is observed.

Distribution of uranium and radium isotopes in an aquifer of a semi-arid region (Manouba-Essijoumi, Northern Tunisia).

PubMed

Added, A; Ben Mammou, A; Fernex, F; Rezzoug, S; Bernat, M

2005-01-01

Groundwaters from the Sebkhet Essijoumi drainage basin, situated in northern Tunisia, West of the city of Tunis, were sampled and analyzed for uranium and radium isotopes. Low (234)U/(238)U activity ratios coupled with relatively high (228)Ra and (238)U concentrations were found in the Manouba plain phreatic aquifer, at the northern part of the basin, where remote sensing has indicated that this plain corresponds to the main humid zone of the area. Low (234)U/(238)U ratios probably reflected short residence time for waters in the Manouba plain, and high ratios longer residence time in the south, where water reaching the phreatic aquifer seems to have previously circulated in rocks constituting the southern hills. Assuming that, in the Manouba plain aquifer, the groundwater flows downstream from the Oued Lill pass area to the South-West of the Sebkha, the difference in the (228)Ra/(226)Ra activity ratio suggests that the residence time of water has been 2.8 years longer near the Sebkha than upstream.

Thallium, uranium, and {sup 235}U/{sup 238}U ratios in the digestive gland of American lobster (Homarus americanus) from an industrialized harbor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chou, C.L.; Uthe, J.F.

1995-01-01

Only a few studies have concentrated on elements such as thallium (TI). Uranium (U) has been studied as a radionuclide of concern in food and the environment. Foodstuffs contain 10-100 ng U{center_dot}{sup -1} with vegetables and cereals contributing most heavily to the daily intake of ca 1.5 ug U. Between 10-30% of ingested U is absorbed, with most being stored in bone. Rainbow trout (onchorynchus mykiss) and longnose sucker (Catostomus catostomus) from a lake with naturally high radioactivity contained < 5 ng U{center_dot}g{sup -1} in the flesh. Trout bone contained 40 ng U{center_dot}g{sup -1}. Higher tissue U concentrations occurred inmore » fish from areas receiving U mining wastes. Bioconcentration factors for bone and flesh were estimated to be low, 118 and 14.7, respectively. This paper describes the Inductively coupled plasma-mass spectrometry (ICP-MS) determination of Tl and U in digestive gland tissue from lobsters captured in the vicinity of Belledune Harbor, New Brunswick, Canada. The harbor is the site of a lead smelter, a fertilizer plant, and a coal-fired power station (the latter due to enter production in late 1993) and thus has the potential of adding significant amounts of Tl to the local marine environment. The accumulation of Tl from water by marine shellfish is low, at least for bivalves, and the accumulated Tl is eliminated in a number of days when the animals are transferred to clean water. Bioconcentration factors for U in finfish ranged from 0.4-17 for larger species. However, because of the high concentrations of various trace elements in lobster digestive gland, its desirability as a foodstuff, and its relatively large size (approximately 20% of the edible tissue yield), we have investigated Tl and U concentrations and {sup 235U}/{sup 238U} ratios in it. 15 refs., 1 fig., 3 tabs.« less

Search for Nuclear Excitation by Electronic Transition in U-235

NASA Astrophysics Data System (ADS)

Chodash, P. A.; Norman, E. B.; Burke, J. T.; Wilks, S. C.; Casperson, R. J.; Swanberg, E. L.; Wakeling, M. A.; Cordeiro, T. J.

2013-10-01

Nuclear excitation by electronic transition (NEET) is a rare nuclear excitation that is predicted to occur in numerous isotopes, including U-235. When a nuclear transition matches the energy and the multipolarity of an electronic transition, there is a possibility that NEET will occur. If NEET were to occur in U-235, the nucleus would be excited to its 1/2 + isomeric state that subsequently decays by internal conversion with a decay energy of 77 eV and a half-life of 26 minutes. Theory predicts that NEET can occur in partially ionized uranium plasma with a charge state of 23 +. A pulsed Nd:YAG laser operating at 1064 nm with a pulse energy of 780 mJ and a pulse width of 9 ns was used to generate the uranium plasma. The plasma was collected on a plate and the internal conversion electrons were focused onto a microchannel plate detector by a series of electrostatic lenses. Depleted uranium and highly enriched uranium samples were used for the experiment. Preliminary results will be presented. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. This work was further supported by the U.S. DHS, UC Berkeley, and the NNIS Fellowship.

Neutron Fission of 235,237,239U and 241,243Pu: Cross Sections, Integral Cross Sections and Cross Sections on Excited States

DOE Office of Scientific and Technical Information (OSTI.GOV)

Younes, W; Britt, H C

In a recent paper submitted to Phys. Rev. C they have presented estimates for (n,f) cross sections on a series of Thorium, Uranium and Plutonium isotopes over the range E{sub n} = 0.1-2.5 MeV. The (n,f) cross sections for many of these isotopes are difficult or impossible to measure in the laboratory. The cross sections were obtained from previous (t,pf) reaction data invoking a model which takes into account the differences between (t,pf) and (n,f) reaction processes, and which includes improved estimates for the neutron compound formation process. The purpose of this note is: (1) to compare the estimated crossmore » sections to current data files in both ENDF and ENDL databases; (2) to estimate ratios of cross sections relatively to {sup 235}U integrated over the ''tamped flattop'' critical assembly spectrum that was used in the earlier {sup 237}U report; and (3) to show the effect on the integral cross sections when the neutron capturing state is an excited rotational state or an isomer. The isomer and excited state results are shown for {sup 235}U and {sup 237}U.« less

A Study of the Gaseous Diffusion Plant for U$sup 235$ Enrichment; STUDI SU GLI IMPIANTI A DISSUFIONE GASOSA PER L'ARRICCHIMENTO DELL' U$sup 23$$sup 5$

DOE Office of Scientific and Technical Information (OSTI.GOV)

Perona, G.

1959-04-01

The gaseous diffusion process for the enrichment of U/sup 235/ is discussed. The physical principles of the process, the cascades and selection of the pressures, temperatures, and barriers are described. The gaseous diffusion plant is discussed with a consideration of the preliminary calculation of the plant yields the diffusor, operating temperature, layout of the plants control, and cost analysis. The chemical properties of UF/sub 6/, its preparation and purification, and the transformation of UF/sub 6/ to UF/sub 4/ are reviewed. (J.S.R)

Fractionation of uranium isotopes in minerals screened by gamma spectrometry.

NASA Astrophysics Data System (ADS)

Geiger, Jeffrey L.; Baldwin, Austin M.; Blatchley, Charles C.

2008-03-01

At least two groups have reported finding shifts in the ratio of U-235/U-238 for sandstone, black shale, and other sedimentary samples using precision ICP-MS. These shifts were tentatively attributed to a recently predicted isotope effect based on nuclear volume that causes fractionation for U^IV-U^VI transitions. However, fractionation of high Z elements may be less likely an explanation than U-235 depletion induced by galactic cosmic ray neutrons. Isotope depletion in marine sediments could therefore be an indicator of changes in cosmic ray flux due to nearby supernovae, gamma-ray bursts, or longer term changes during the 62 million year cycle of the Sun above and below the galactic plane. We report using a less precise approach than ICP-MS, but one which can quickly screen samples to look for anomalies in isotope ratios, namely HPGe gamma ray spectrometry. Various levels of depletion were measured for uranium rich minerals, including brannerite, carnotite, and pitchblende, as well as coal and limestone samples.

Isotopic tracing of the dissolved U fluxes of Himalayan rivers: implications for present and past U budgets of the Ganges-Brahmaputra system

NASA Astrophysics Data System (ADS)

Chabaux, François; Riotte, Jean; Clauer, Norbert; France-Lanord, Christian

2001-10-01

U activity ratios have been measured in the dissolved loads of selected rivers from the Himalayan range, in Central Nepal, and from the Bangladesh, as well as in some rain waters. A few European and Asian rivers have also been analyzed for their U activity ratios. The data confirm the negligible effect of rainwater on the budget of dissolved U in river waters. The results also indicate that rivers on each Himalayan structural unit have homogeneous and specific U isotope compositions: i) (234U/238U) activity ratios slightly lower than unity in the dissolved load of the streams draining the Tethyan Sedimentary Series (TSS); ii) values slightly higher than unity for waters from the High Himalaya Crystalline (HHC) and the Lesser Himalaya (LH); iii) systematically higher (234U/238U) activity ratios for waters from the Siwaliks. Thus, U activity ratios, in association with Sr isotopic ratios, can be used to trace the sources of dissolved fluxes carried by these rivers. Coupling of U with Sr isotope data shows (1) that the U carried by the dissolved load of the Himalayan rivers mainly originates from U-rich lithologies of the TSS in the northern formations of the Tibetan plateau; and (2) that the elemental U and Sr fluxes carried by the Himalayan rivers at the outflow of the highlands are fairly homogeneous at the scale of the Himalayan chain. Rivers flowing on the Indian plain define a different trend from that of the Himalayan rivers in the U-Sr isotopic diagram, indicating the contribution of a specific floodplain component to the U and Sr budgets of the Ganges and the Brahmaputra. The influence of this component remains limited to 10 to 15 percent for the U flux, but can contribute 35 to 55% of the Sr flux. The variations of the Sr and U fluxes of the Ganges-Brahmaputra river system in response to climatic variations have been estimated by assuming a temporary cut off of the chemical fluxes from high-altitude terrains during glacial episodes. This scenario would significantly decrease the dissolved U flux of the Ganges-Brahmaputra river system and increase its U activity ratio. Such a climatic dependence of the Himalayan U flux could induce a periodic variation of the mean U activity ratio of the world rivers on glacial-interglacial timescales

The 235U Prompt Fission Neutron Spectrum in the BR1 Reactor at SCK•CEN

NASA Astrophysics Data System (ADS)

Wagemans, Jan; Malambu, Edouard; Borms, Luc; Fiorito, Luca

2016-02-01

The BR1 research reactor at SCK•CEN has a spherical cavity in the graphite above the reactor core. In this cavity an accurately characterised Maxwellian thermal neutron field is present. Different converters can be loaded in the cavity in order to obtain other types of neutron (and gamma) irradiation fields. Inside the so-called MARK III converter a fast 235U(n,f) prompt fission neutron field can be obtained. With the support of MCNP calculations, irradiations in MARK III can be directly related to the pure 235U(n,f) prompt fission neutron spectrum. For this purpose MARK III spectrum averaged cross sections for the most relevant fluence dosimetry reactions have been determined. A calibration factor for absolute measurements has been determined applying activation dosimetry following ISO/IEC 17025 standards.

Experimental investigation of neutronic characteristics of the IR-8 reactor to confirm the results of calculations by MCU-PTR code

DOE Office of Scientific and Technical Information (OSTI.GOV)

Surkov, A. V., E-mail: surkov.andrew@gmail.com; Kochkin, V. N.; Pesnya, Yu. E.

2015-12-15

A comparison of measured and calculated neutronic characteristics (fast neutron flux and fission rate of {sup 235}U) in the core and reflector of the IR-8 reactor is presented. The irradiation devices equipped with neutron activation detectors were prepared. The determination of fast neutron flux was performed using the {sup 54}Fe (n, p) and {sup 58}Ni (n, p) reactions. The {sup 235}U fission rate was measured using uranium dioxide with 10% enrichment in {sup 235}U. The determination of specific activities of detectors was carried out by measuring the intensity of characteristic gamma peaks using the ORTEC gamma spectrometer. Neutron fields inmore » the core and reflector of the IR-8 reactor were calculated using the MCU-PTR code.« less

Preliminary study on weapon grade uranium utilization in molten salt reactor miniFUJI

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aji, Indarta Kuncoro; Waris, A., E-mail: awaris@fi.itb.ac.id

Preliminary study on weapon grade uranium utilization in 25MWth and 50MWth of miniFUJI MSR (molten salt reactor) has been carried out. In this study, a very high enriched uranium that we called weapon grade uranium has been employed in UF{sub 4} composition. The {sup 235}U enrichment is 90 - 95 %. The results show that the 25MWth miniFUJI MSR can get its criticality condition for 1.56 %, 1.76%, and 1.96% of UF{sub 4} with {sup 235}U enrichment of at least 93%, 90%, and 90%, respectively. In contrast, the 50 MWth miniFUJI reactor can be critical for 1.96% of UF{sub 4}more » with {sup 235}U enrichment of at smallest amount 95%. The neutron spectra are almost similar for each power output.« less

Measurement of the ^235mU Production Cross Section Using a Critical Assembly*

NASA Astrophysics Data System (ADS)

Macri, Robert; Authier, Nicolas; Becker, John; Belier, Gilbert; Bond, Evelyn; Bredeweg, Todd; Glover, S.; Meot, Vincent; Rundberg, Robert; Vieira, David; Wilhelmy, Jerry

2006-10-01

Measurements of the creation and destruction cross sections for actinide nuclei constitute an important experimental effort in support of Stockpile Stewardship. In this talk I will give a progress report on the effort to measure the production cross section of the ^235mU isomer integrated over a fission neutron spectrum. This ongoing experiment is fielded at CEA in Valduc, France, taking advantage of the CALIBAN critical assembly. This effort is performed in collaboration with LANL, LLNL, Bruyeres le Chatel, and Valduc staff. This experiment utilizes a technique to measure internal conversion electrons from the ^235mU isomer with the French BIII detector (Bruyeres le Chatel), and involves a substantial chemistry effort (LANL) to prepare targets for irradiation and counting, as well as to remove fission fragments after irradiation. Experimental techniques will be discussed and preliminary data presented. *Work performed under the auspices of the U.S. Department of Energy by Los Alamos National Laboratory (W-7405-ENG-36) and Lawrence Livermore National Laboratory (W-7405-ENG-48), and CEA-DAM under CEA-DAM NNSA-DOE agreement.

Measurement of the ROT effect in the neutron induced fission of 235U in the 0.3 eV resonance at a hot source of polarized neutrons

NASA Astrophysics Data System (ADS)

Kopatch, Yuri; Novitsky, Vadim; Ahmadov, Gadir; Gagarsky, Alexei; Berikov, Daniyar; Danilyan, Gevorg; Hutanu, Vladimir; Klenke, Jens; Masalovich, Sergey

2018-03-01

The TRI and ROT asymmetries in fission of heavy nuclei have been extensively studied during more than a decade. The effects were first discovered in the ternary fission in a series of experiments performed at the ILL reactor (Grenoble) by a collaboration of Russian and European institutes, and were carefully measured for a number of fissioning nuclei. Later on, the ROT effect has been observed in the emission of prompt gamma rays and neutrons in fission of 235U and 233U, although its value was an order of magnitude smaller than in the α-particle emission from ternary fission. All experiments performed so far are done with cold polarized neutrons, what assumes a mixture of several spin states, the weights of these states being not well known. The present paper describes the first attempt to get "clean" data by performing the measurement of gamma and neutron asymmetries in an isolated resonance of 235U at the POLI instrument of the FRM2 reactor in Garching.

Managing the Nuclear Fuel Cycle: Policy Implications of Expanding Global Access to Nuclear Power

DTIC Science & Technology

2008-01-20

critical aspect of the nuclear fuel cycle for the United States, where longstanding nonproliferation policy discouraged commercial nuclear fuel...have U.S. government officials. However, the case of Iran raises perhaps the most critical question in this decade for strengthening the nuclear...slight difference in atomic mass between 235U and 238U. The typical enrichment process requires about 10 lbs of uranium U3O8 to produce 1 lb of low

Surface engineering of low enriched uranium-molybdenum

NASA Astrophysics Data System (ADS)

Leenaers, A.; Van den Berghe, S.; Detavernier, C.

2013-09-01

Recent attempts to qualify the LEU(Mo) dispersion plate fuel with Si addition to the Al matrix up to high power and burn-up have not yet been successful due to unacceptable fuel plate swelling at a local burn-up above 60% 235U. The root cause of the failures is clearly related directly to the formation of the U(Mo)-Al(Si) interaction layer. Excessive formation of these layers around the fuel kernels severely weakens the local mechanical integrity and eventually leads to pillowing of the plate. In 2008, SCK·CEN has launched the SELENIUM U(Mo) dispersion fuel development project in an attempt to find an alternative way to reduce the interaction between U(Mo) fuel kernels and the Al matrix to a significantly low level: by applying a coating on the U(Mo) kernels. Two fuel plates containing 8gU/cc U(Mo) coated with respectively 600 nm Si and 1000 nm ZrN in a pure Al matrix were manufactured. These plates were irradiated in the BR2 reactor up to a maximum heat flux of 470 W/cm2 until a maximum local burn-up of approximately 70% 235U (˜50% plate average) was reached. Awaiting the PIE results, the advantages of applying a coating are discussed in this paper through annealing experiments and TRIM (the Transport of Ions in Matter) calculations.

Prospects for dating monazite via single-collector HR-ICP-MS

NASA Astrophysics Data System (ADS)

Kohn, M. J.; Vervoort, J. D.

2006-12-01

ICP-MS analysis permits rapid and precise dating of minerals with high U and Th contents. Here we describe a new method for in situ determination of 206Pb/238U, 207Pb/^{235}U, ^{208}Pb/232Th, and 207Pb/206Pb ages in monazite via laser ablation (New Wave Research UP-213 laser system), single-collector, magnetic sector ICP-MS (ThermoFinnigan Element2), using spot sizes of 8-30 μm, a repetition rate of 5 Hz, and a fluence of 10 J/cm2. Based on analysis of 9 monazite samples of known ages ranging from 280 to 1800 Ma, analytical precision (single sample) is ±2-3% (2σ), and reproducibility (single sample) is ±2-4% (2σ), yielding age precisions of ±3- 5% (2σ) for single points, or ±1-2% (2 s.e.) for pooled multiple analyses (n > 4). Issues of accuracy are paramount. 207Pb/206Pb ages are consistently the most accurate and agree to ±2% with accepted TIMS ages. In contrast, 206Pb/238U, 207Pb/^{235}U, and ^{208}Pb/232Th ages can differ by as much as ±5% (2σ), a problem that has also been observed for SIMS Th-Pb dating. The sources of the interelement standardization disparities among monazites remain enigmatic, but do not result from molecular interferences on Pb, U, or Th peaks. Unresolvable mass interference between 204Pb and trace contaminant 204Hg in commercial Ar gas precludes precise common Pb corrections. Instead common Pb corrections are made assuming concordancy between 207Pb/^{235}U and either 206Pb/238U or ^{208}Pb/232Th ages. The new method offers rapid analysis (~1 minute), minimal sample preparation (polished thin section), and high sensitivity. Comparatively large errors on the 206Pb/238U, 207Pb/^{235}U, and ^{208}Pb/232Th ages will likely restrict analysis of younger monazite grains (<250 Ma) to applications where 5% accuracy is sufficient. Older grains (c. 500 Ma and older) can be dated more precisely and accurately using 207Pb/206Pb. One application to young materials involves dating a large vein monazite from the Llallagua tin district of Bolivia, which resolves a ~2 Myr history of mineralization at 20-22 Ma. These data support mineralization age estimates of 21 Ma (K-Ar on wallrock minerals) rather than 44 Ma (Sm-Nd on apatite).

Depleted and natural uranium: chemistry and toxicological effects.

PubMed

Craft, Elena; Abu-Qare, Aquel; Flaherty, Meghan; Garofolo, Melissa; Rincavage, Heather; Abou-Donia, Mohamed

2004-01-01

Depleted uranium (DU) is a by-product from the chemical enrichment of naturally occurring uranium. Natural uranium is comprised of three radioactive isotopes: (238)U, (235)U, and (234)U. This enrichment process reduces the radioactivity of DU to roughly 30% of that of natural uranium. Nonmilitary uses of DU include counterweights in airplanes, shields against radiation in medical radiotherapy units and transport of radioactive isotopes. DU has also been used during wartime in heavy tank armor, armor-piercing bullets, and missiles, due to its desirable chemical properties coupled with its decreased radioactivity. DU weapons are used unreservedly by the armed forces. Chemically and toxicologically, DU behaves similarly to natural uranium metal. Although the effects of DU on human health are not easily discerned, they may be produced by both its chemical and radiological properties. DU can be toxic to many bodily systems, as presented in this review. Most importantly, normal functioning of the kidney, brain, liver, and heart can be affected by DU exposure. Numerous other systems can also be affected by DU exposure, and these are also reviewed. Despite the prevalence of DU usage in many applications, limited data exist regarding the toxicological consequences on human health. This review focuses on the chemistry, pharmacokinetics, and toxicological effects of depleted and natural uranium on several systems in the mammalian body. A section on risk assessment concludes the review.

U, Th and Pa insights into sedimentological and paleoceanographic changes off Hudson Strait (Labrador Sea) during the last ∼37 ka with special attention to methodological issues

NASA Astrophysics Data System (ADS)

Nuttin, Laurence; Maccali, Jenny; Hillaire-Marcel, Claude

2015-05-01

A ∼9 m-long sediment core spanning the last ∼37 ka has been raised from the lower Labrador continental slope, off the Hudson Strait shelf edge. It has been analyzed for its U, Th and Pa isotope contents, along with current sedimentological parameters, as a means to retrieve information about sedimentological changes in response to northeastern Laurentide Ice Sheet (LIS) margin instabilities. The sequence yielded a high-resolution record of subglacial detrital carbonate pulses from Hudson Strait assigned to "Heinrich events" H2 and H1, whereas H0 was missing. Large variations in bulk sediment U- and Th-contents as well as in 234U/238U activity ratio are observed throughout the sequence, leading to large uncertainties when calculating excesses in 231Pa and 230Th (231Paxs and 230Thxs) over their supported and in-growth fractions (i.e., inherited from detrital minerals and produced from authigenic and diagenetic U-uptake). In particular, 234U excesses or deficits vs 238U (-115‰ < δ234U < +126‰) are observed throughout the sequence, suggesting occasional U-uptake from the water column and/or some late diagenetic mobility along discrete redox gradients, despite the overall low and little variable organic carbon content (0.3 ± 0.1%) observed. The above uncertainties in 231Paxs and 230Thxs estimates and the large variability in geochemical and sedimentary fluxes off the northeastern LIS margin, lead us to downgrade the potential paleoceanographic information yielded by these isotopes in such a setting. Nonetheless, the H2 and H1 layers are highlighted by very low initial excesses in both 230Thxs and 231Paxs, indicating their extremely fast deposition. Throughout most of the sedimentary sequence, the calculated initial 230Thxs fluxes are nearly in balance with 230Th production in the overlying water column. Exceptions are the H2 layer, an interval succeeding H1, and the post-glacial sediment. The estimated initial (231Paxs/230Thxs) ratios are generally lower than their production rate in the water column (i.e., 0.092), indicating nearly continuous preferential export of 231Paxs over the last ∼37 cal ka BP, thus the persistence of some deep currents throughout the interval.

Regolith formation rate from U-series nuclides: Implications from the study of a spheroidal weathering profile in the Rio Icacos watershed (Puerto Rico)

NASA Astrophysics Data System (ADS)

Chabaux, F.; Blaes, E.; Stille, P.; di Chiara Roupert, R.; Pelt, E.; Dosseto, A.; Ma, L.; Buss, H. L.; Brantley, S. L.

2013-01-01

A 2 m-thick spheroidal weathering profile, developed on a quartz diorite in the Rio Icacos watershed (Luquillo Mountains, eastern Puerto Rico), was analyzed for major and trace element concentrations, Sr and Nd isotopic ratios and U-series nuclides (238U-234U-230Th-226Ra). In this profile a 40 cm thick soil horizon is overlying a 150 cm thick saprolite which is separated from the basal corestone by a ˜40 cm thick rindlet zone. The Sr and Nd isotopic variations along the whole profile imply that, in addition to geochemical fractionations associated to water-rock interactions, the geochemical budget of the profile is influenced by a significant accretion of atmospheric dusts. The mineralogical and geochemical variations along the profile also confirm that the weathering front does not progress continuously from the top to the base of the profile. The upper part of the profile is probably associated with a different weathering system (lateral weathering of upper corestones) than the lower part, which consists of the basal corestone, the associated rindlet system and the saprolite in contact with these rindlets. Consequently, the determination of weathering rates from 238U-234U-230Th-226Ra disequilibrium in a series of samples collected along a vertical depth profile can only be attempted for samples collected in the lower part of the profile, i.e. the rindlet zone and the lower saprolite. Similar propagation rates were derived for the rindlet system and the saprolite by using classical models involving loss and gain processes for all nuclides to interpret the variation of U-series nuclides in the rindlet-saprolite subsystem. The consistency of these weathering rates with average weathering and erosion rates derived via other methods for the whole watershed provides a new and independent argument that, in the Rio Icacos watershed, the weathering system has reached a geomorphologic steady-state. Our study also indicates that even in environments with differential weathering, such as observed for the Puerto Rico site, the radioactive disequilibrium between the nuclides of a single radioactive series (here 238U-234U-230Th-226Ra) can still be interpreted in terms of a simplified scenario of congruent weathering. Incidentally, the U-Th-Ra disequilibrium in the corestone samples confirms that the outermost part of the corestone is already weathered.

Cooperation on Improved Isotopic Identification and Analysis Software for Portable, Electrically Cooled High-Resolution Gamma Spectrometry Systems Final Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dreyer, Jonathan G.; Wang, Tzu-Fang; Vo, Duc T.

Under a 2006 agreement between the Department of Energy (DOE) of the United States of America and the Institut de Radioprotection et de Sûreté Nucléaire (IRSN) of France, the National Nuclear Security Administration (NNSA) within DOE and IRSN initiated a collaboration to improve isotopic identification and analysis of nuclear material [i.e., plutonium (Pu) and uranium (U)]. The specific aim of the collaborative project was to develop new versions of two types of isotopic identification and analysis software: (1) the fixed-energy response-function analysis for multiple energies (FRAM) codes and (2) multi-group analysis (MGA) codes. The project is entitled Action Sheet 4more » – Cooperation on Improved Isotopic Identification and Analysis Software for Portable, Electrically Cooled, High-Resolution Gamma Spectrometry Systems (Action Sheet 4). FRAM and MGA/U235HI are software codes used to analyze isotopic ratios of U and Pu. FRAM is an application that uses parameter sets for the analysis of U or Pu. MGA and U235HI are two separate applications that analyze Pu or U, respectively. They have traditionally been used by safeguards practitioners to analyze gamma spectra acquired with high-resolution gamma spectrometry (HRGS) systems that are cooled by liquid nitrogen. However, it was discovered that these analysis programs were not as accurate when used on spectra acquired with a newer generation of more portable, electrically cooled HRGS (ECHRGS) systems. In response to this need, DOE/NNSA and IRSN collaborated to update the FRAM and U235HI codes to improve their performance with newer ECHRGS systems. Lawrence Livermore National Laboratory (LLNL) and Los Alamos National Laboratory (LANL) performed this work for DOE/NNSA.« less

A Metal Stable Isotope Approach to Understanding Uranium Mobility Across Roll Front Redox Boundaries

NASA Astrophysics Data System (ADS)

Brown, S. T.; Basu, A.; Christensen, J. N.; DePaolo, D. J.; Heikoop, J. M.; Reimus, P. W.; Maher, K.; Weaver, K. L.

2015-12-01

Sedimentary roll-front uranium (U) ore deposits are the principal source of U for nuclear fuel in the USA and an important part of the current all-of-the-above energy strategy. Mining of roll-front U ore in the USA is primarily by in situ alkaline oxidative dissolution of U minerals. There are significant environmental benefits to in situ mining including no mine tailings or radioactive dust, however, the long-term immobilization of U in the aquifer after the completion of mining remains uncertain. We have utilized the metal stable isotopes U, Se and Mo in groundwater from roll-front mines in Texas and Wyoming to quantify the aquifer redox conditions and predict the onset of U reduction after post mining aquifer restoration. Supporting information from the geochemistry of groundwater and aquifer sediments are used to understand the transport of U prior to and after in situ mining. Groundwater was collected across 4 mining units at the Rosita mine in the Texas coastal plain and 2 mining units at the Smith Ranch mine in the Powder River Basin, Wyoming. In general, the sampled waters are moderately reducing and ore zone wells contain the highest aqueous U concentrations. The lowest U concentrations occur in monitoring wells downgradient of the ore zone. 238U/235U is lowest in downgradient wells and is correlated with aqueous U concentrations. Rayleigh distillation models of the 238U/235U are consistent with U isotope fractionation factors of 1.0004-1.001, similar to lab-based studies. Based on these results we conclude that redox reactions continue to affect U distribution in the ore zone and downgradient regions. We also measured aqueous selenium isotope (δ82Se) and molybdenum isotope (δ98Mo) compositions in the Rosita groundwater. Se(VI) primarily occurs in the upgradient wells and is absent in most ore zone and downgradient wells. Rayleigh distillation models suggest reduction of Se(VI) along the groundwater flow path and when superimposed on the U isotope data Se reduction is favored over U reduction. The δ98Mo of Rosita groundwater is significantly elevated compared to the U ore and is negatively correlated with the groundwater Eh, which suggests localized strong reducing conditions capable of Mo reduction. Ongoing work will determine the Mo isotope systematics of U ores and groundwater from roll-front deposits.

Polonium (²¹⁰Po), uranium (²³⁴U, ²³⁸U) isotopes and trace metals in mosses from Sobieszewo Island, northern Poland.

PubMed

Boryło, Alicja; Nowicki, Waldemar; Olszewski, Grzegorz; Skwarzec, Bogdan

2012-01-01

The activity of polonium (210)Po and uranium (234)U, (238)U radionuclides, as well as trace metals in mosses, collected from Sobieszewo Island area (northern Poland), were determined using the alpha spectrometry, AAS (atomic absorption spectrometry) and OES-ICP (atomic emission spectrometry with inductively coupled plasma). The concentrations of mercury (directly from the solid sample) were determined by the cold vapor technique of CV AAS. The obtained results revealed that the concentrations of (210)Po, (234)U, and (238)U in the two analyzed kinds of mosses: schrebers big red stem moss (Pleurozium schreberi) and broom moss (Dicranum scoparium) were similar. The higher polonium concentrations were found in broom moss (Dicranum scoparium), but uranium concentrations were relatively low for both species of analyzed mosses. Among the analyzed trace metals the highest concentration in mosses was recorded for iron, while the lowest for nickel, cadmium and mercury. The obtained studies showed that the sources of polonium and uranium isotopes, as well as trace metals in analyzed mosses are air city contaminations transported from Gdańsk and from existing in the vicinity the phosphogypsum waste heap in Wiślinka (near Gdańsk).

Under-ascertainment from healthcare settings of child abuse events among children of soldiers by the U.S. Army Family Advocacy Program.

PubMed

Wood, Joanne N; Griffis, Heather M; Taylor, Christine M; Strane, Douglas; Harb, Gerlinde C; Mi, Lanyu; Song, Lihai; Lynch, Kevin G; Rubin, David M

2017-01-01

In cases of maltreatment involving children of U.S. Army service members, the U.S. Army Family Advocacy Program (FAP) is responsible for providing services to families and ensuring child safety. The percentage of cases of maltreatment that are known to FAP, however, is uncertain. Thus, the objective of this retrospective study was to estimate the percentage of U.S. Army dependent children with child maltreatment as diagnosed by a military or civilian medical provider who had a substantiated report with FAP from 2004 to 2007. Medical claims data were used to identify 0-17year old child dependents of soldiers who received a medical diagnosis of child maltreatment. Linkage rates of maltreatment medical diagnoses with corresponding substantiated FAP reports were calculated. Bivariate and multivariable analyses examined the association of child, maltreatment episode, and soldier characteristics with linkage to substantiated FAP reports. Across 5945 medically diagnosed maltreatment episodes, 20.3% had a substantiated FAP report. Adjusting for covariates, the predicted probability of linkage to a substantiated FAP report was higher for physical abuse than for sexual abuse, 25.8%, 95% CI (23.4, 28.3) versus 14.5%, 95% CI (11.2, 17.9). Episodes in which early care was provided at civilian treatment facilities were less likely to have a FAP report than those treated at military facilities, 9.8%, 95% CI (7.3, 12.2) versus 23.6%, 95% CI (20.8, 26.4). The observed low rates of linkage of medically diagnosed child maltreatment to substantiated FAP reports may signal the need for further regulation of FAP reporting requirements, particularly for children treated at civilian facilities. Copyright © 2016 Elsevier Ltd. All rights reserved.

230Th-234U Model-Ages of Some Uranium Standard Reference Materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Williams, R W; Gaffney, A M; Kristo, M J

The 'age' of a sample of uranium is an important aspect of a nuclear forensic investigation and of the attribution of the material to its source. To the extent that the sample obeys the standard rules of radiochronometry, then the production ages of even very recent material can be determined using the {sup 230}Th-{sup 234}U chronometer. These standard rules may be summarized as (a) the daughter/parent ratio at time=zero must be known, and (b) there has been no daughter/parent fractionation since production. For most samples of uranium, the 'ages' determined using this chronometer are semantically 'model-ages' because (a) some assumptionmore » of the initial {sup 230}Th content in the sample is required and (b) closed-system behavior is assumed. The uranium standard reference materials originally prepared and distributed by the former US National Bureau of Standards and now distributed by New Brunswick Laboratory as certified reference materials (NBS SRM = NBL CRM) are good candidates for samples where both rules are met. The U isotopic standards have known purification and production dates, and closed-system behavior in the solid form (U{sub 3}O{sub 8}) may be assumed with confidence. We present here {sup 230}Th-{sup 234}U model-ages for several of these standards, determined by isotope dilution mass spectrometry using a multicollector ICP-MS, and compare these ages with their known production history.« less

Future research program on prompt γ-ray emission in nuclear fission

NASA Astrophysics Data System (ADS)

Oberstedt, S.; Billnert, R.; Hambsch, F.-J.; Lebois, M.; Oberstedt, A.; Wilson, J. N.

2015-12-01

In recent years the measurement of prompt fission γ-ray spectra (PFGS) has gained renewed interest, after about forty years since the first comprehensive studies of the reactions 235U(n th , f), 239Pu(n th ,f) and 252Cf(sf). The renaissance was initiated by requests for new values especially for γ-ray multiplicity and average total energy release per fission in neutron-induced fission of 235U and 239Pu. Both isotopes are considered the most important ones with respect to the modeling of innovative cores required for the Generation-IV reactors, the majority working with fast neutrons. During the last 5 years we have conducted a systematic study of spectral data for thermal-neutron-induced fission on 235U and 241Pu as well as for the spontaneous fission of 252Cf with unprecedented accuracy. From the new data we conclude that those reactions do not considerably contribute to the observed heat excess and suspect other reactions playing a significant role. Possible contributions may originate from fast-neutron-induced reactions on 238U, which is largely present in the fuel, or from γ-induced fission from neutron capture in the construction material. A first experiment campaign on prompt γ-ray emission from fast-neutron-induced fission on 235,238U was successfully performed in order to test our assumptions. In the following we attempt to summarize, what has been done in the field to date, and to motivate future measurement campaigns exploiting dedicated neutron and photon beams as well as upcoming highly efficient detector assemblies.

ORNL Resolved Resonance Covariance Generation for ENDF/B-VII.1

DOE Office of Scientific and Technical Information (OSTI.GOV)

Leal, Luiz C.; Guber, Klaus H.; Wiarda, Dorothea

2012-12-01

Resonance-parameter covariance matrix (RPCM) evaluations in the resolved resonance regionwere done at the Oak Ridge National Laboratory (ORNL) for the chromium isotopes, titanium isotopes, 19F, 58Ni, 60Ni, 35Cl, 37Cl, 39K, 41K, 55Mn, 233U, 235U, 238U, and 239Pu using the computer code SAMMY. The retroactive approach of the code SAMMY was used to generate the RPCMs for 233U. For 235U, the approach used for covariance generation was similar to the retroactive approach with the distinction that real experimental data were used as opposed to data generated from the resonance parameters. RPCMs for 238U and 239Pu were generated together with the resonancemore » parameter evaluations. The RPCMs were then converted in the ENDF format using the FILE32 representation. Alternatively, for computer storage reasons, the FILE32 was converted in the FILE33 cross section covariance matrix (CSCM). Both representations were processed using the computer code PUFF-IV. This paper describes the procedures used to generate the RPCM and CSCM in the resonance region for ENDF/B-VII.1. The impact of data uncertainty in nuclear reactor benchmark calculations is also presented.« less

Validation of the fission yield and decay data libraries with the 10 s-delayed 235 U fission γ-ray energy spectrum

NASA Astrophysics Data System (ADS)

Mendoza, E.; Álvarez-Velarde, F.; Bécares, V.; Cano-Ott, D.; González-Romero, E.; Martínez, T.; Villamarín, D.

2017-10-01

We have measured with a LaCl3 detector the γ-ray spectrum emitted by a 235 U enriched UO2 fuel rod 10 s after being irradiated with thermal neutrons. The experimental results are compared with simulations performed with the fission product yield and radioactive decay data libraries present in the most recent releases of ENDF/B, JEFF and JENDL.

Using the Time-Correlated Induced Fission Method to Simultaneously Measure the 235U Content and the Burnable Poison Content in LWR Fuel Assemblies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Root, M. A.; Menlove, H. O.; Lanza, R. C.

The uranium neutron coincidence collar uses thermal neutron interrogation to verify the 235U mass in low-enriched uranium (LEU) fuel assemblies in fuel fabrication facilities. Burnable poisons are commonly added to nuclear fuel to increase the lifetime of the fuel. The high thermal neutron absorption by these poisons reduces the active neutron signal produced by the fuel. Burnable poison correction factors or fast-mode runs with Cd liners can help compensate for this effect, but the correction factors rely on operator declarations of burnable poison content, and fast-mode runs are time-consuming. Finally, this paper describes a new analysis method to measure themore » 235U mass and burnable poison content in LEU nuclear fuel simultaneously in a timely manner, without requiring additional hardware.« less

Using the Time-Correlated Induced Fission Method to Simultaneously Measure the 235U Content and the Burnable Poison Content in LWR Fuel Assemblies

DOE PAGES

Root, M. A.; Menlove, H. O.; Lanza, R. C.; ...

2018-03-21

The uranium neutron coincidence collar uses thermal neutron interrogation to verify the 235U mass in low-enriched uranium (LEU) fuel assemblies in fuel fabrication facilities. Burnable poisons are commonly added to nuclear fuel to increase the lifetime of the fuel. The high thermal neutron absorption by these poisons reduces the active neutron signal produced by the fuel. Burnable poison correction factors or fast-mode runs with Cd liners can help compensate for this effect, but the correction factors rely on operator declarations of burnable poison content, and fast-mode runs are time-consuming. Finally, this paper describes a new analysis method to measure themore » 235U mass and burnable poison content in LEU nuclear fuel simultaneously in a timely manner, without requiring additional hardware.« less

Managing the Nuclear Fuel Cycle: Policy Implications of Expanding Global Access to Nuclear Power

DTIC Science & Technology

2009-07-01

inalienable right and, by and large, neither have U.S. government officials. However, the case of Iran raises perhaps the most critical question in this...slight difference in atomic mass between 235U and 238U. The typical enrichment process requires about 10 lbs of uranium U3O8 to produce 1 lb of low...thermal neutrons but can induce fission in all actinides , including all plutonium isotopes. Therefore, nuclear fuel for a fast reactor must have a

Image fusion of Secondary Ion Mass Spectrometry and Energy-dispersive X-Ray Spectroscopy data for the characterization of uranium-molybdenum fuel foils

NASA Astrophysics Data System (ADS)

Willingham, David; Naes, Benjamin E.; Tarolli, Jay G.; Schemer-Kohrn, Alan; Rhodes, Mark; Dahl, Michael; Guzman, Anthony; Burkes, Douglas E.

2018-01-01

Uranium-molybdenum (U-Mo) monolithic fuels represent one option for converting civilian research and test reactors operating with high enriched uranium (HEU) to low enriched uranium (LEU), effectively reducing the threat of nuclear proliferation world-wide. However, processes associated with fabrication of U-Mo monolithic fuels result in regions of elemental heterogeneity, observed as bands traversing the cross-section of representative samples. Isotopic variations (e.g., 235U and 238U) could also be introduced because of associated processing steps, particularly since HEU feedstock is melted with natural or depleted uranium diluent to produce LEU. This study demonstrates the utility of correlative analysis of Energy-Dispersive X-ray Spectroscopy (EDS) and Secondary Ion Mass Spectrometry (SIMS) with their image data streams using image fusion, resulting in a comprehensive microanalytical characterization toolbox. Elemental and isotopic measurements were made on a sample from the Advanced Test Reactor (ATR) Full-sized plate In-center flux trap Position (AFIP)-7 experiment and compared to previous optical and electron microscopy results. The image fusion results are characteristic of SIMS isotopic maps, but with the spatial resolution of EDS images and, therefore, can be used to increase the effective spatial resolution of the SIMS imaging results to better understand homogeneity or heterogeneity that persists because of processing selections. Visual inspection using the image fusion methodology indicated slight variations in the 235U/238U ratio and quantitative analysis using the image intensities across several FoVs revealed an average 235U atom percent value of 17.9 ± 2.4%, which was indicative of a non-uniform U isotopic distribution in the area sampled. Further development of this capability is useful for understanding the connections between the properties of LEU fuel alternatives and the ability to predict performance under irradiation.

Natural radionuclides in plants, soils and sediments affected by U-rich coal mining activities in Brazil.

PubMed

Galhardi, Juliana Aparecida; García-Tenorio, Rafael; Bonotto, Daniel Marcos; Díaz Francés, Inmaculada; Motta, João Gabriel

2017-10-01

Mining activities can increase the mobility of metals by accelerating the dissolution and leaching of minerals from the rocks and tailing piles to the environment and, consequently, their availability for plants and subsequent transfer to the food chain. The weathering of minerals and the disposal of coal waste in tailing piles can accelerate the generation of acid mine drainage (AMD), which is responsible for the higher dissolution of metals in mining areas. In this context, the behavior of U, Th and K in soils and sediment, and the transfer factor (TF) of 238 U, 234 U and 210 Po for soybean, wheat, pine and eucalyptus cultivated around a coal mine in southern Brazil was evaluated. Alpha and gamma spectrometry were used for the measurements of the activity concentration of the radioelements. 210 Po was the radionuclide that is most accumulated in the plants, especially in the leaves. When comparing the plant species, pine showed the highest TF values for 234 U (0.311 ± 0.420) for leaves, while eucalyptus showed the highest TF for 238 U (0.344 ± 0.414) for leaves. In general, TF were higher for the leaves of soybean and wheat when compared to the grains, and grains of wheat showed higher TF for 210 Po and 238 U than grains of soybean. Deviations from the natural U isotopic ratio were recorded at all investigated areas, indicating possible industrial and mining sources of U for the vegetables. A safety assessment of transport routes and accumulation of radionuclides in soils with a potential for cultivation is important, mainly in tropical areas contaminated with solid waste and effluents from mines and industry. Copyright © 2017 Elsevier Ltd. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bushuev, A. V.; Kozhin, A. F., E-mail: alexfkozhin@yandex.ru; Aleeva, T. B.

An active neutron method for measuring the residual mass of {sup 235}U in spent fuel assemblies (FAs) of the IRT MEPhI research reactor is presented. The special measuring stand design and uniform irradiation of the fuel with neutrons along the entire length of the active part of the FA provide high accuracy of determination of the residual {sup 235}U content. AmLi neutron sources yield a higher effect/background ratio than other types of sources and do not induce the fission of {sup 238}U. The proposed method of transfer of the isotope source in accordance with a given algorithm may be usedmore » in experiments where the studied object needs to be irradiated with a uniform fluence.« less

TEMPERATURE COEFFICIENTS OF HETEROGENEOUS U-238-U-235 FUELED REACTORS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Astley, E.R.; Mansius, C.A.

1958-05-14

An analytical method of determining the effective reactivity coefficient from fundamental cross sections using the four factor formula is presented. Values of the coefficient obtained by this method compare well with experiment. (A.C.)

78 FR 79057 - Culturally Significant Objects Imported for Exhibition Determinations: “Gauguin: Metamorphoses”

Federal Register 2010, 2011, 2012, 2013, 2014

2013-12-27

.... 2681, et seq.; 22 U.S.C. 6501 note, et seq.), Delegation of Authority No. 234 of October 1, 1999, and... of State (telephone: 202-632- 6469). The mailing address is U.S. Department of State, SA-5, L/PD...

Jordanian National Security and the Future of Middle East Stability

DTIC Science & Technology

2008-01-01

East. This analysis should be especially useful to U.S. strategic leaders as they seek to address the complicated interplay of factors related to...explosion.185 The internationally known film director, Moustapha Akkad, along with his daughter, was also killed at the Radisson SAS hotel.186...236 The U.S. Marine Corps works with the Jordanian military in Exercise Infinite Moonlight and U.S. Special Forces conduct Exercise Early Victor

DEVELOPMENT OF A GEOCHEMICAL MODEL FOR URANIUM TRANSPORT IN THE UNSATURATED AND SATURATED SEDIMENTS AT THE 200 WEST AREA OF THE US DEPARTMENT OF ENERGY HANFORD SITE WASHINGTON (SEPTEMBER 2004)

DOE Office of Scientific and Technical Information (OSTI.GOV)

ADAMS SC; PETERSEN SW

2010-03-24

Final Deliverable under GWP-HQ-LMT-02 contract for Hanford Sci. & Tech. Gp. to BHI. The scope of work covered laboratory analyses and gephysical logging for 299-W19-43 near the 200 West U Plant. Other isotopic analyses were conducted for holes around 216-U-1&2, including U-236.

Limits on uranium and thorium bulk content in GERDA Phase I detectors

NASA Astrophysics Data System (ADS)

Collaboration, Gerda; Agostini, M.; Allardt, M.; Bakalyarov, A. M.; Balata, M.; Barabanov, I.; Baudis, L.; Bauer, C.; Becerici-Schmidt, N.; Bellotti, E.; Belogurov, S.; Belyaev, S. T.; Benato, G.; Bettini, A.; Bezrukov, L.; Bode, T.; Borowicz, D.; Brudanin, V.; Brugnera, R.; Caldwell, A.; Cattadori, C.; Chernogorov, A.; D'Andrea, V.; Demidova, E. V.; di Vacri, A.; Domula, A.; Doroshkevich, E.; Egorov, V.; Falkenstein, R.; Fedorova, O.; Freund, K.; Frodyma, N.; Gangapshev, A.; Garfagnini, A.; Grabmayr, P.; Gurentsov, V.; Gusev, K.; Hakemüller, J.; Hegai, A.; Heisel, M.; Hemmer, S.; Hofmann, W.; Hult, M.; Inzhechik, L. V.; Janicskó Csáthy, J.; Jochum, J.; Junker, M.; Kazalov, V.; Kihm, T.; Kirpichnikov, I. V.; Kirsch, A.; Kish, A.; Klimenko, A.; Kneißl, R.; Knöpfle, K. T.; Kochetov, O.; Kornoukhov, V. N.; Kuzminov, V. V.; Laubenstein, M.; Lazzaro, A.; Lebedev, V. I.; Lehnert, B.; Liao, H. Y.; Lindner, M.; Lippi, I.; Lubashevskiy, A.; Lubsandorzhiev, B.; Lutter, G.; Macolino, C.; Majorovits, B.; Maneschg, W.; Medinaceli, E.; Mingazheva, R.; Misiaszek, M.; Moseev, P.; Nemchenok, I.; Palioselitis, D.; Panas, K.; Pandola, L.; Pelczar, K.; Pullia, A.; Riboldi, S.; Rumyantseva, N.; Sada, C.; Salamida, F.; Salathe, M.; Schmitt, C.; Schneider, B.; Schönert, S.; Schreiner, J.; Schütz, A.-K.; Schulz, O.; Schwingenheuer, B.; Selivanenko, O.; Shevchik, E.; Shirchenko, M.; Simgen, H.; Smolnikov, A.; Stanco, L.; Stepaniuk, M.; Vanhoefer, L.; Vasenko, A. A.; Veresnikova, A.; von Sturm, K.; Wagner, V.; Walter, M.; Wegmann, A.; Wester, T.; Wiesinger, C.; Wojcik, M.; Yanovich, E.; Zhitnikov, I.; Zhukov, S. V.; Zinatulina, D.; Zuber, K.; Zuzel, G.

2017-05-01

Internal contaminations of 238U, 235U and 232Th in the bulk of high purity germanium detectors are potential backgrounds for experiments searching for neutrinoless double beta decay of 76Ge. The data from GERDA Phase I have been analyzed for alpha events from the decay chain of these contaminations by looking for full decay chains and for time correlations between successive decays in the same detector. No candidate events for a full chain have been found. Upper limits on the activities in the range of a few nBq/kg for 226Ra, 227Ac and 228Th, the long-lived daughter nuclides of 238U, 235U and 232Th, respectively, have been derived. With these upper limits a background index in the energy region of interest from 226Ra and 228Th contamination is estimated which satisfies the prerequisites of a future ton scale germanium double beta decay experiment.

An aerosol particle containing enriched uranium encountered in the remote upper troposphere.

PubMed

Murphy, D M; Froyd, K D; Apel, E; Blake, D; Blake, N; Evangeliou, N; Hornbrook, R S; Peischl, J; Ray, E; Ryerson, T B; Thompson, C; Stohl, A

2018-04-01

We describe a submicron aerosol particle sampled at an altitude of 7 km near the Aleutian Islands that contained a small percentage of enriched uranium oxide. 235 U was 3.1 ± 0.5% of 238 U. During twenty years of aircraft sampling of millions of particles in the global atmosphere, we have rarely encountered a particle with a similarly high content of 238 U and never a particle with enriched 235 U. The bulk of the particle consisted of material consistent with combustion of heavy fuel oil. Analysis of wind trajectories and particle dispersion model results show that the particle could have originated from a variety of areas across Asia. The source of such a particle is unclear, and the particle is described here in case it indicates a novel source where enriched uranium was dispersed. Published by Elsevier Ltd.

Laser ablation inductively coupled plasma mass spectrometry measurement of isotope ratios in depleted uranium contaminated soils.

PubMed

Seltzer, Michael D

2003-09-01

Laser ablation of pressed soil pellets was examined as a means of direct sample introduction to enable inductively coupled plasma mass spectrometry (ICP-MS) screening of soils for residual depleted uranium (DU) contamination. Differentiation between depleted uranium, an anthropogenic contaminant, and naturally occurring uranium was accomplished on the basis of measured 235U/238U isotope ratios. The amount of sample preparation required for laser ablation is considerably less than that typically required for aqueous sample introduction. The amount of hazardous laboratory waste generated is diminished accordingly. During the present investigation, 235U/238U isotope ratios measured for field samples were in good agreement with those derived from gamma spectrometry measurements. However, substantial compensation was required to mitigate the effects of impaired pulse counting attributed to sample inhomogeneity and sporadic introduction of uranium analyte into the plasma.

238U, and its decay products, in grasses from an abandoned uranium mine

NASA Astrophysics Data System (ADS)

Childs, Edgar; Maskall, John; Millward, Geoffrey

2016-04-01

Bioaccumulation of radioactive contaminants by plants is of concern particularly where the sward is an essential part of the diet of ruminants. The abandoned South Terras uranium mine, south west England, had primary deposits of uraninite (UO2) and pitchblende (U3O8), which contained up to 30% uranium. When the mine was active uranium and radium were extracted but following closure it was abandoned without remediation. Waste rock and gangue, consisting of inefficiently processed minerals, were spread around the site, including a field where ruminants are grazed. Here we report the activity concentrations of 238U, 235U 214,210Pb, and the concentrations of selected metals in the soils, roots and leaves of grasses taken from the contaminated field. Soil samples were collected at the surface, and at 30 cm depth, using an auger along a 10-point transect in the field from the foot of a waste heap. Whole, individual grass plants were removed with a spade, ensuring that their roots were intact. The soils and roots and grass leaves were freeze-dried. Activity concentrations of the radionuclides were determined by gamma spectroscopy, following 30 days incubation for development of secular equilibrium. Dried soils, roots and grasses were also digested in aqua regia and the concentrations of elements determined by ICP techniques. Maximum activity concentrations of 238U, 235U, 214Pb and 210Pb surface soils were 63,300, 4,510, 23,300 and 49,400 Bq kg-1, respectively. The mean 238U:235U ratio was 11.8 ± 1.8, an order of magnitude lower than the natural value of 138, indicating disequilibrium within the decay chain due to mineral processing. Radionuclides in the roots had 5 times lower concentration and only grass leaves in the vicinity of the waste heap had measureable values. The mean soil to root transfer factor for 238U was 36%, the mean root to leaf was 3% and overall only 0.7% of 238U was transferred from the soil to the leaves. The roots contained 0.8% iron, possibly as iron plaque acting to mediate 238U transfer within the plants. The results are discussed in the context of remediation of grazing land contaminated with radionuclides.

Uranium series isotopes concentration in sediments at San Marcos and Luis L. Leon reservoirs, Chihuahua, Mexico

NASA Astrophysics Data System (ADS)

Méndez-García, C.; Renteria-Villalobos, M.; García-Tenorio, R.; Montero-Cabrera, M. E.

2014-07-01

Spatial and temporal distribution of the radioisotopes concentrations were determined in sediments near the surface and core samples extracted from two reservoirs located in an arid region close to Chihuahua City, Mexico. At San Marcos reservoir one core was studied, while from Luis L. Leon reservoir one core from the entrance and another one close to the wall were investigated. 232Th-series, 238U-series, 40K and 137Cs activity concentrations (AC, Bq kg-1) were determined by gamma spectrometry with a high purity Ge detector. 238U and 234U ACs were obtained by liquid scintillation and alpha spectrometry with a surface barrier detector. Dating of core sediments was performed applying CRS method to 210Pb activities. Results were verified by 137Cs AC. Resulting activity concentrations were compared among corresponding surface and core sediments. High 238U-series AC values were found in sediments from San Marcos reservoir, because this site is located close to the Victorino uranium deposit. Low AC values found in Luis L. Leon reservoir suggest that the uranium present in the source of the Sacramento - Chuviscar Rivers is not transported up to the Conchos River. Activity ratios (AR) 234U/overflow="scroll">238U and 238U/overflow="scroll">226Ra in sediments have values between 0.9-1.2, showing a behavior close to radioactive equilibrium in the entire basin. 232Th/overflow="scroll">238U, 228Ra/overflow="scroll">226Ra ARs are witnesses of the different geological origin of sediments from San Marcos and Luis L. Leon reservoirs.

Partially-reflected water-moderated square-piteched U(6.90)O 2 fuel rod lattices with 0.67 fuel to water volume ratio (0.800 CM Pitch)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harms, Gary A.

The US Department of Energy (DOE) Nuclear Energy Research Initiative funded the design and construction of the Seven Percent Critical Experiment (7uPCX) at Sandia National Laboratories. The start-up of the experiment facility and the execution of the experiments described here were funded by the DOE Nuclear Criticality Safety Program. The 7uPCX is designed to investigate critical systems with fuel for light water reactors in the enrichment range above 5% 235U. The 7uPCX assembly is a water-moderated and -reflected array of aluminum-clad square-pitched U(6.90%)O 2 fuel rods.

Distinguishing Fissile From Non-Fissile Materials Using Linearly Polarized Gamma Rays

NASA Astrophysics Data System (ADS)

Mueller, J. M.; Ahmed, M. W.; Karwowski, H. J.; Myers, L. S.; Sikora, M. H.; Weller, H. R.; Zimmerman, W. R.; Randrup, J.; Vogt, R.

2014-03-01

Photofission of 232Th, 233 , 235 , 238U, 237Np, and 239,240Pu was induced by nearly 100% linearly polarized, high intensity (~107 γs per second), and nearly-monoenergetic γ-ray beams of energies between 5.3 and 7.6 MeV at the High Intensity γ-ray Source (HI γS). An array of 12-18 liquid scintillating detectors was used to measure prompt fission neutron yields. The ratio of prompt fission neutron yields parallel to the plane of beam polarization to the yields perpendicular to this plane was measured as a function of beam and neutron energy. A ratio near unity was found for 233,235U, 237Np, and 239Pu while a significant ratio (~1.5-3) was found for 232Th, 238U, and 240Pu. This large difference could be used to distinguish fissile isotopes (such as 233,235U and 239Pu) from non-fissile isotopes (such as 232Th, 238U, and 240Pu). The measured ratios agree with the results of a fission calculation (FREYA) which used with previously measured photofission fragment angular distributions as input. Partially supported by DHS (2010-DN-077-ARI046-02), DOE (DE-AC52-07NA27344 and DE-AC02-05CH11231), and the DOE Office of Science Graduate Fellowship Program (DOE SCGF).

Environmental Survey of the B-3 and Ford’s Farm Ranges,

DTIC Science & Technology

1983-08-01

reported have an estimated analytical error of *35% unless noted otherwise. 14 Isotopic Analysis The isotopic uranium analysis procedure used by UST...sulfate buffer and elec- trodeposited on a stainless steel disc, and isotopes of uranium (234U, 23 5U, and 2 38U) were determined by pulse height analysis ...measurements and some environmental sampling. Several special studies were also conducted, including analyses of the isotopic composition of uranium in

Irradiated microstructure of U-10Mo monolithic fuel plate at very high fission density

NASA Astrophysics Data System (ADS)

Gan, J.; Miller, B. D.; Keiser, D. D.; Jue, J. F.; Madden, J. W.; Robinson, A. B.; Ozaltun, H.; Moore, G.; Meyer, M. K.

2017-08-01

Monolithic U-10Mo alloy fuel plates with Al-6061 cladding are being developed for use in research and test reactors as low enrichment fuel (<20% U-235 enrichment) as a result of its high uranium loading capacity compared to that of U-7Mo dispersion fuel. These fuel plates contain a Zr diffusion barrier between the U-10Mo fuel and Al-6061 cladding that suppresses the interaction between the U-Mo fuel foil and Al alloy cladding that is known to be problematic under irradiation. Different methods have been employed to fabricate monolithic fuel plates, including hot-rolling with no cold-rolling. L1P09T is a hot-rolled fuel plate irradiated to high fission density in the RERTR-9B experiment. This paper discusses the TEM characterization results for this U-10Mo/Zr/Al6061 monolithic fuel plate (∼59% U-235 enrichment) irradiated in Advanced Test Reactor at Idaho National Laboratory with an unprecedented high local fission density of 9.8E+21 fissions/cm3. The calculated fuel foil centerline temperature at the beginning of life and the end of life is 141 and 194 °C, respectively. TEM lamellas were prepared using focus ion beam lift-out technique. The estimated U-Mo fuel swelling, based on the fuel foil thickness change from SEM, is approximately 76%. Large bubbles (>1 μm) are distributed evenly in U-Mo and interlink of these bubbles is evident. The average size of subdivided grains at this fission density appears similar to that at 5.2E+21 fissions/cm3. The measured average Mo and Zr content in the fuel matrix is ∼30 at% and ∼7 at%, respectively, in general agreement with the calculated Mo and Zr from fission density.

Irradiated microstructure of U-10Mo monolithic fuel plate at very high fission density

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gan, J.; Miller, B. D.; Keiser, D. D.

Monolithic U-10Mo alloy fuel plates with Al-6061 cladding are being developed for use in research and test reactors as low enrichment fuel (< 20% U-235 enrichment) as a result of its high uranium loading capacity compared to that of U-7Mo dispersion fuel. These fuel plates contain a Zr diffusion barrier between the U-10Mo fuel and Al-6061 cladding that suppresses the interaction between the U-Mo fuel foil and Al alloy cladding that is known to be problematic under irradiation. This paper discusses the TEM results of the U-10Mo/Zr/Al6061 monolithic fuel plate (Plate ID: L1P09T, ~ 59% U-235 enrichment) irradiated in Advancedmore » Test Reactor at Idaho National Laboratory as part of RERTR-9B irradiation campaign with an unprecedented high local fission density of 9.8E+21 fissions/cm3. The calculated fuel foil centerline temperature at the beginning of life and the end of life is 141 and 194 C, respectively. A total of 5 TEM lamellas were prepared using focus ion beam lift-out technique. The estimated U-Mo fuel swelling, based on the fuel foil thickness change from SEM, is approximately 76%. Large bubbles (> 1 µm) are distributed evenly in U-Mo and interlink of these bubbles is evident. The average size of subdivided grains at this fission density appears similar to that at 5.2E+21 fissions/cm3. The measured average Mo and Zr content in the fuel matrix is ~ 30 at% and ~ 7 at%, respectively, in general agreement with the calculated Mo and Zr from fission density.« less

78 FR 22362 - Culturally Significant Objects Imported for Exhibition Determinations: “40 Part Motet”

Federal Register 2010, 2011, 2012, 2013, 2014

2013-04-15

..., et seq.; 22 U.S.C. 6501 note, et seq.), Delegation of Authority No. 234 of October 1, 1999... address is U.S. Department of State, SA-5, L/PD, Fifth Floor (Suite 5H03), Washington, DC 20522-0505...

75 FR 43225 - Culturally Significant Objects Imported for Exhibition Determinations: “Man, Myth, and Sensual...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-07-23

...Notice is hereby given of the following determinations: Pursuant to the authority vested in me by the Act of October 19, 1965 (79 Stat. 985; 22 U.S.C. 2459), Executive Order 12047 of March 27, 1978, the Foreign Affairs Reform and Restructuring Act of 1998 (112 Stat. 2681, et seq.; 22 U.S.C. 6501 note, et seq.), Delegation of Authority No. 234 of October 1, 1999, and Delegation of Authority No. 236-3 of August 28, 2000, I hereby determine that the objects to be included in the exhibition ``Man, Myth, and Sensual Pleasures: Jan Gossart's Renaissance,'' imported from abroad for temporary exhibition within the United States, are of cultural significance. The objects are imported pursuant to loan agreements with the foreign owners or custodians. I also determine that the exhibition or display of the exhibit objects at the Metropolitan Museum of Art, New York, NY, from on or about October 5, 2010, until on or about January 17, 2011, and at possible additional exhibitions or venues yet to be determined, is in the national interest. Public Notice of these Determinations is ordered to be published in the Federal Register.

78 FR 77772 - Culturally Significant Objects Imported for Exhibition Determinations: “A Royal Passion: Queen...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-12-24

...Notice is hereby given of the following determinations: Pursuant to the authority vested in me by the Act of October 19, 1965 (79 Stat. 985; 22 U.S.C. 2459), Executive Order 12047 of March 27, 1978, the Foreign Affairs Reform and Restructuring Act of 1998 (112 Stat. 2681, et seq.; 22 U.S.C. 6501 note, et seq.), Delegation of Authority No. 234 of October 1, 1999, and Delegation of Authority No. 236-3 of August 28, 2000, I hereby determine that the objects to be included in the exhibition ``A Royal Passion: Queen Victoria and Photography,'' imported from abroad for temporary exhibition within the United States, are of cultural significance. The objects are imported pursuant to loan agreements with the foreign owners or custodians. I also determine that the exhibition or display of the exhibit objects at the J. Paul Getty Museum, Los Angeles, California, from on or about February 4, 2014, until on or about June 8, 2014, and at possible additional exhibitions or venues yet to be determined, is in the national interest. I have ordered that Public Notice of these Determinations be published in the Federal Register.

75 FR 53013 - Culturally Significant Objects Imported for Exhibition Determinations: “The Pre-Raphaelite Lens...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-08-30

...Notice is hereby given of the following determinations: Pursuant to the authority vested in me by the Act of October 19, 1965 (79 Stat. 985; 22 U.S.C. 2459), Executive Order 12047 of March 27, 1978, the Foreign Affairs Reform and Restructuring Act of 1998 (112 Stat. 2681, et seq.; 22 U.S.C. 6501 note, et seq.), Delegation of Authority No. 234 of October 1, 1999, and Delegation of Authority No. 236-3 of August 28, 2000, I hereby determine that the objects to be included in the exhibition ``The Pre-Raphaelite Lens: British Photography and Painting, 1848-1875,'' imported from abroad for temporary exhibition within the United States, are of cultural significance. The objects are imported pursuant to loan agreements with the foreign owners or custodians. I also determine that the exhibition or display of the exhibit objects at the National Gallery of Art, Washington, DC, from on or about October 31, 2010, until on or about January 30, 2011, and at possible additional exhibitions or venues yet to be determined, is in the national interest. I have ordered that Public Notice of these Determinations be published in the Federal Register.

76 FR 68256 - Culturally Significant Objects Imported for Exhibition Determinations: “Shapeshifting...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-11-03

...Notice is hereby given of the following determinations: Pursuant to the authority vested in me by the Act of October 19, 1965 (79 Stat. 985; 22 U.S.C. 2459), Executive Order 12047 of March 27, 1978, the Foreign Affairs Reform and Restructuring Act of 1998 (112 Stat. 2681, et seq.; 22 U.S.C. 6501 note, et seq.), Delegation of Authority No. 234 of October 1, 1999, Delegation of Authority No. 236-3 of August 28, 2000 (and, as appropriate, Delegation of Authority No. 257 of April 15, 2003), I hereby determine that the objects to be included in the exhibition ``Shapeshifting: Transformations in Native American Art,'' imported from abroad for temporary exhibition within the United States, are of cultural significance. The objects are imported pursuant to loan agreements with the foreign owners or custodians. I also determine that the exhibition or display of the exhibit objects at the Peabody Essex Museum, Salem, MA, from on or about January 14, 2012, until on or about April 29, 2012, and at possible additional exhibitions or venues yet to be determined, is in the national interest. I have ordered that Public Notice of these Determinations be published in the Federal Register.

78 FR 51802 - Culturally Significant Objects Imported for Exhibition Determinations: “Silla: Korea's Golden...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-08-21

...Notice is hereby given of the following determinations: Pursuant to the authority vested in me by the Act of October 19, 1965 (79 Stat. 985; 22 U.S.C. 2459), Executive Order 12047 of March 27, 1978, the Foreign Affairs Reform and Restructuring Act of 1998 (112 Stat. 2681, et seq.; 22 U.S.C. 6501 note, et seq.), Delegation of Authority No. 234 of October 1, 1999, Delegation of Authority No. 236-3 of August 28, 2000 (and, as appropriate, Delegation of Authority No. 257 of April 15, 2003), I hereby determine that the objects to be included in the exhibition ``Silla: Korea's Golden Kingdom,'' imported from abroad for temporary exhibition within the United States, are of cultural significance. The objects are imported pursuant to a loan agreement with foreign owners or custodians. I also determine that the exhibition or display of the exhibit objects at The Metropolitan Museum of Art, New York, NY, from on or about November 4, 2013, until on or about February 23, 2014, and at possible additional exhibitions or venues yet to be determined, is in the national interest. I have ordered that Public Notice of these Determinations be published in the Federal Register.

76 FR 6650 - Culturally Significant Objects Imported for Exhibition Determinations: “Heinrich Kühn”

Federal Register 2010, 2011, 2012, 2013, 2014

2011-02-07

...Notice is hereby given of the following determinations: Pursuant to the authority vested in me by the Act of October 19, 1965 (79 Stat. 985; 22 U.S.C. 2459), Executive Order 12047 of March 27, 1978, the Foreign Affairs Reform and Restructuring Act of 1998 (112 Stat. 2681, et seq.; 22 U.S.C. 6501 note, et seq.), Delegation of Authority No. 234 of October 1, 1999, and Delegation of Authority No. 236-3 of August 28, 2000, I hereby determine that the objects to be included in the exhibition ``Heinrich K[uuml]hn,'' imported from abroad for temporary exhibition within the United States, are of cultural significance. The objects are imported pursuant to loan agreements with the foreign owners or custodians. I also determine that the exhibition or display of the exhibit objects at The Museum of Fine Arts, Houston, Houston, TX, from on or about March 6, 2011, until on or about May 30, 2011, and at possible additional exhibitions or venues yet to be determined, is in the national interest. I have ordered that Public Notice of these Determinations be published in the Federal Register.

49 CFR 234.6 - Penalties.

Code of Federal Regulations, 2012 CFR

2012-10-01

... death or injury to persons, or has caused death or injury, a penalty not to exceed $105,000 per... 49 Transportation 4 2012-10-01 2012-10-01 false Penalties. 234.6 Section 234.6 Transportation... SYSTEMS General § 234.6 Penalties. (a) Civil penalty. Any person (an entity of any type covered under 1 U...

49 CFR 234.6 - Penalties.

Code of Federal Regulations, 2014 CFR

2014-10-01

... death or injury to persons, or has caused death or injury, a penalty not to exceed $105,000 per... 49 Transportation 4 2014-10-01 2014-10-01 false Penalties. 234.6 Section 234.6 Transportation... SYSTEMS General § 234.6 Penalties. (a) Civil penalty. Any person (an entity of any type covered under 1 U...

49 CFR 234.6 - Penalties.

Code of Federal Regulations, 2013 CFR

2013-10-01

... death or injury to persons, or has caused death or injury, a penalty not to exceed $105,000 per... 49 Transportation 4 2013-10-01 2013-10-01 false Penalties. 234.6 Section 234.6 Transportation... SYSTEMS General § 234.6 Penalties. (a) Civil penalty. Any person (an entity of any type covered under 1 U...

49 CFR 234.6 - Penalties.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 49 Transportation 4 2011-10-01 2011-10-01 false Penalties. 234.6 Section 234.6 Transportation... TRANSPORTATION GRADE CROSSING SIGNAL SYSTEM SAFETY AND STATE ACTION PLANS General § 234.6 Penalties. (a) Civil penalty. Any person (an entity of any type covered under 1 U.S.C. 1, including but not limited to the...

49 CFR 234.6 - Penalties.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 49 Transportation 4 2010-10-01 2010-10-01 false Penalties. 234.6 Section 234.6 Transportation... TRANSPORTATION GRADE CROSSING SIGNAL SYSTEM SAFETY AND STATE ACTION PLANS General § 234.6 Penalties. (a) Civil penalty. Any person (an entity of any type covered under 1 U.S.C. 1, including but not limited to the...

The Prompt Fission Neutron Spectrum of 235U for Einc 0.7-5.0 MeV

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gomez, Jaime A.; Devlin, Matthew James; Haight, Robert Cameron

2017-03-23

The Chi-Nu experiment aims to accurately measure the prompt fission neutron spectrum (PFNS) for the major actinides. At the Los Alamos Neutron Science Center (LANSCE), fission can be induced using the white neutron source. Using a two arm time of flight (T.O.F) technique; Chi-Nu presents a preliminary result of the low energy component of the 235U PFNS measured using an array of 22-Lithium glass scintillators.

n+235U resonance parameters and neutron multiplicities in the energy region below 100 eV

NASA Astrophysics Data System (ADS)

Pigni, Marco T.; Capote, Roberto; Trkov, Andrej; Pronyaev, Vladimir G.

2017-09-01

In August 2016, following the recent effort within the Collaborative International Evaluated Library Organization (CIELO) pilot project to improve the neutron cross sections of 235U, Oak Ridge National Laboratory (ORNL) collaborated with the International Atomic Energy Agency (IAEA) to release a resonance parameter evaluation. This evaluation restores the performance of the evaluated cross sections for the thermal- and above-thermal-solution benchmarks on the basis of newly evaluated thermal neutron constants (TNCs) and thermal prompt fission neutron spectra (PFNS). Performed with support from the US Nuclear Criticality Safety Program (NCSP) in an effort to provide the highest fidelity general purpose nuclear database for nuclear criticality applications, the resonance parameter evaluation was submitted as an ENDF-compatible file to be part of the next release of the ENDF/B-VIII.0 nuclear data library. The resonance parameter evaluation methodology used the Reich-Moore approximation of the R-matrix formalism implemented in the code SAMMY to fit the available time-of-flight (TOF) measured data for the thermal induced cross section of n+235U up to 100 eV. While maintaining reasonably good agreement with the experimental data, the validation analysis focused on restoring the benchmark performance for 235U solutions by combining changes to the resonance parameters and to the prompt resonance v̅

Micrometer FX/DLX: A Pedagogic Compiler

DTIC Science & Technology

1992-03-01

delimited by double-quotes L E Literal = Integer-Numeral U Boolean-literal U String-literal E::= L ’I (lambda (1*) EB) (Eo E*) (let ((I E)*) EB) (letrec...except VAL, ATEMP, and RETADR) are saved in this activation frame. Arguments to the procedure are evaluated and placed in registers ARGO, ARGi , etc. By...ENV) "ENV") ((ru FP) "FP11) ((u ru SP) ’Isp") Us u ARGO) "ARGO") ru ARGI ) *"ARG1**) ((ru ARG2) "LRG2") ((ru ARG3) "ARG3") Us~ ru ARG4) "ARG4’) ((x ru

40 CFR 261.33 - Discarded commercial chemical products, off-specification species, container residues, and spill...

Code of Federal Regulations, 2012 CFR

2012-07-01

... L-Phenylalanine, 4-[bis(2-chloroethyl)amino]- U145 7446-27-7 Phosphoric acid, lead(2+) salt (2:3...-Naphthacenedione, 8-acetyl-10-[(3-amino-2,3,6-trideoxy)-alpha-L-lyxo-hexopyranosyl)oxy]-7,8,9,10-tetrahydro-6,8,11... sulfide SeS2 (R,T) U015 115-02-6 L-Serine, diazoacetate (ester) See F027 93-72-1 Silvex (2,4,5-TP) U206...

40 CFR 261.33 - Discarded commercial chemical products, off-specification species, container residues, and spill...

Code of Federal Regulations, 2014 CFR

2014-07-01

... L-Phenylalanine, 4-[bis(2-chloroethyl)amino]- U145 7446-27-7 Phosphoric acid, lead(2+) salt (2:3...-Naphthacenedione, 8-acetyl-10-[(3-amino-2,3,6-trideoxy)-alpha-L-lyxo-hexopyranosyl)oxy]-7,8,9,10-tetrahydro-6,8,11... sulfide SeS2 (R,T) U015 115-02-6 L-Serine, diazoacetate (ester) See F027 93-72-1 Silvex (2,4,5-TP) U206...

40 CFR 261.33 - Discarded commercial chemical products, off-specification species, container residues, and spill...

Code of Federal Regulations, 2013 CFR

2013-07-01

... L-Phenylalanine, 4-[bis(2-chloroethyl)amino]- U145 7446-27-7 Phosphoric acid, lead(2+) salt (2:3...-Naphthacenedione, 8-acetyl-10-[(3-amino-2,3,6-trideoxy)-alpha-L-lyxo-hexopyranosyl)oxy]-7,8,9,10-tetrahydro-6,8,11... sulfide SeS2 (R,T) U015 115-02-6 L-Serine, diazoacetate (ester) See F027 93-72-1 Silvex (2,4,5-TP) U206...

Calibrating multiple isotopic proxies in a modern aragonite speleothem from northeast India

NASA Astrophysics Data System (ADS)

Ronay, E.; Oster, J. L.; Sharp, W. D.; Marks, N.; Erhardt, A.; Breitenbach, S. F. M.

2017-12-01

Uranium, strontium, and calcium isotope ratios in calcite speleothems are used as proxies for water-soil-rock interactions and prior calcite precipitation, and thus provide information about effective rainfall amount variations, primarily in semi-arid or highly seasonal regions. However, less is known about how these proxies function in humid regions and in aragonite speleothems. In this study, we use meteorological data to calibrate (234U/238U)i and 87Sr/86Sr in a modern aragonite speleothem from northeast India, the rainiest place on Earth, to determine how these proxies reflect effective monsoon rainfall amount. MAW-0201 is an annually laminated aragonite stalagmite that grew from 1960-2013 in Mawmluh Cave, Meghalaya, India. Rainfall here is extremely seasonal due to the Indian Summer Monsoon (ISM), which brings several meters of rain to the region each summer, but with inter-annual variability in total rainfall. The δ18O in Mawmluh dripwater and speleothems reflects moisture source and transport, rather than rainfall amount. Variations in Mg, U, and Ba concentrations in MAW-0201 show seasonal and multi-annual variability. U and Mg are closely correlated, but multi-year periods show significant anti-correlation. The Mg and U distribution coefficients in calcite and aragonite indicate correlated periods are times of prior calcite precipitation (PCP) and anti-correlated periods are times of prior aragonite precipitation (PAP) in the epikarst. We use δ44/40Ca to test this hypothesis, as Ca isotopes fractionate differently during calcite and aragonite precipitation and speleothem δ44/40Ca will record unique PAP and PCP fingerprints. We propose such shifts from PCP to PAP reflect hydrologic variability and/or flow path changes, which provide a useful tool for understanding epikarst hydrology but may also be a complicating factor in speleothem-based paleoclimate interpretations. Preliminary (234U/238U)i (always <1) and 87Sr/86Sr spanning 1991-2009 each show significant variability outside of analytical error. (234U/238U)i displays a decadal trend, gradually increasing until 2000 and decreasing to the end of the record. Several years in the 87Sr/86Sr record have anomalously high values, which may reflect increased sea spray input and provide unique information on the wind component of the ISM.

U–Pb, Rb–Sr, and U-series isotope geochemistry of rocks and fracture minerals from the Chalk River Laboratories site, Grenville Province, Ontario, Canada

USGS Publications Warehouse

Neymark, Leonid; Peterman, Zell E.; Moscati, Richard J.; Thivierge, R. H.

2013-01-01

As part of the Geologic Waste Management Facility feasibility study, Atomic Energy of Canada Ltd. (AECL) is evaluating the suitability of the Chalk River Laboratories (CRL) site in Ontario, situated in crystalline rock of the southwestern Grenville Province, for the possible development of an underground repository for low- and intermediate-level nuclear waste. This paper presents petrographic and trace element analyses, U–Pb zircon dating results, and Rb–Sr, U–Pb and U-series isotopic analyses of gneissic drill core samples from the deep CRG-series characterization boreholes at the CRL site. The main rock types intersected in the boreholes include hornblende–biotite (±pyroxene) gneisses of granitic to granodioritic composition, leucocratic granitic gneisses with sparse mafic minerals, and garnet-bearing gneisses with variable amounts of biotite and/or hornblende. The trace element data for whole-rock samples plot in the fields of within-plate, syn-collision, and volcanic arc-type granites in discrimination diagrams used for the tectonic interpretation of granitic rocks.Zircons separated from biotite gneiss and metagranite samples yielded SHRIMP-RG U–Pb ages of 1472 ± 14 (2σ) and 1045 ± 6 Ma, respectively, in very good agreement with widespread Early Mesoproterozoic plutonic ages and Ottawan orogeny ages in the Central Gneiss Belt. The Rb–Sr, U–Pb, and Pb–Pb whole-rock errorchron apparent ages of most of the CRL gneiss samples are consistent with zircon U–Pb age and do not indicate substantial large-scale preferential element mobility during superimposed metamorphic and water/rock interaction processes. This may confirm the integrity of the rock mass, which is a positive attribute for a potential nuclear waste repository. Most 234U/238U activity ratios (AR) in whole rock samples are within errors of the secular equilibrium value of one, indicating that the rocks have not experienced any appreciable U loss or gain within the past 1 Ma. However, 234U/238U AR in fracture mineral samples collected down to borehole lengths of about 740 m deviate from the secular equilibrium value and 234U/238U model ages calculated for fracture mineral samples showing excess 234U range from 593 to 1415 ka, thus providing evidence of fracture flow in the associated bedrock during the past 1.5 Ma. Rare earth element patterns are variable in fracture-filling calcites and Fe oxides/hydroxides but are similar to those observed in associated whole-rock samples. The observed Ce anomalies are very small (CeN/CeN∗≈1">CeN/CeN∗≈1), do not vary with depth, and, therefore, do not contain evidence that the studied fracture minerals precipitated from oxidizing waters at the conceptual depth of a repository.

Determination of elemental impurities and U and O isotopic compositions with a view to identify the geographical and industrial origins of uranium ore concentrates

NASA Astrophysics Data System (ADS)

Salaun, A.; Hubert, A.; Pointurier, F.; Aupiais, J.; Pili, E.; Richon, P.; Fauré, A.; Diallo, S.

2012-12-01

First events of illicit trafficking of nuclear and radiological materials occurred 50 years ago. Nuclear forensics expertise are aiming at determining the use of seized material, its industrial history and provenance (geographical area, place of production or processing), at assisting in the identification and dismantling of illicit trafficking networks. This information is also valuable in the context of inspections of declared facilities to verify the consistency of operator's declaration. Several characteristics can be used to determine the origin of uranium ore concentrates such as trace elemental impurity patterns (Keegan et al., 2008 ; Varga et al., 2010a, 2010b) or uranium, oxygen and lead isotopic compositions (Tamborini et al., 2002a, 2002b ; Wallenius et al., 2006; Varga et al., 2009). We developed analytical procedures for measuring the isotopic compositions of uranium (234U/238U and 235U/238U) and oxygen (18O/16O) and levels of elemental impurities (e.g. REE, Th) from very small amounts of uranium ore concentrates (or yellow cakes). Micrometer particles and few milligrams of material are used for oxygen isotope measurements and REE determination, respectively. Reference materials were analyzed by mass spectrometry (TIMS, SF-ICP-MS and SIMS) to validate testing protocols. Finally, materials of unknown origin were analyzed to highlight significant differences and determine whether these differences allow identifying the origin of these ore concentrates. References: Keegan, E., et al. (2008). Applied Geochemistry 23, 765-777. Tamborini, G., et al. (2002a). Analytical Chemistry 74, 6098-6101. Tamborini, G., et al. (2002b). Microchimica Acta 139, 185-188. Varga, Z., et al. (2009). Analytical Chemistry 81, 8327-8334. Varga, Z., et al. (2010a). Talanta 80, 1744-1749. Varga, Z., et al. (2010b). Radiochimica Acta 98, 771-778 Wallenius, M., et al. (2006). Forensic Science International 156, 55-62.

Natural radionuclides in fish species from surface water of Bagjata and Banduhurang uranium mining areas, East Singhbhum, Jharkhand, India.

PubMed

Giri, Soma; Singh, Gurdeep; Jha, V N; Tripathi, R M

2010-11-01

To study the natural radionuclides in the freshwater fish samples around the uranium mining areas of Bagjata and Banduhurang, East Singhbhum, Jharkhand, India. The naturally occurring radioisotopes of uranium, U(nat), consisting of (234)U, (235)U and (238)U; (226)Ra, (230)Th and (210)Po were analysed in the fish samples from the surface water of Bagjata and Banduhurang mining areas after acid digestion. The ingestion dose, concentration factor and excess lifetime cancer risk of the radionuclides were estimated. The geometric mean activity of U(nat), (226)Ra, (230)Th and (210)Po in the fish samples was found to be 0.05, 0.19, 0.29 and 0.95 Bq kg(-1)(fresh) (Becquerel per kilogram fresh fish), respectively, in the Bagjata mining area, while for Banduhurang mining area it was estimated to be 0.08, 0.41, 0.22 and 2.48 Bq kg(-1)(fresh), respectively. The ingestion dose was computed to be 1.88 and 4.16 μSvY(-1), respectively, for both the areas which is much below the 1 mSv limit set in the new International Commission on Radiological Protection (ICRP) recommendations. The estimation of the Concentration Factors (CF) reveal that the CF from water is greater than 1 l/kg(-1)in most of the cases while from sediment CF is less than 1. The excess individual lifetime cancer risk due to the consumption of fish was calculated to be 2.53 × 10(-5) and 6.48 × 10(-5), respectively, for Bagjata and Banduhurang areas, which is within the acceptable excess individual lifetime cancer risk value of 1 × 10(-4). The study confirms that current levels of radioactivity do not pose a significant radiological risk to freshwater fish consumers.

77 FR 75489 - Culturally Significant Objects Imported for Exhibition Determinations: “Projects 99: Meiro Koizumi”

Federal Register 2010, 2011, 2012, 2013, 2014

2012-12-20

.... 2681, et seq.; 22 U.S.C. 6501 note, et seq.), Delegation of Authority No. 234 of October 1, 1999, and... mailing address is U.S. Department of State, SA-5, L/PD, Fifth Floor (Suite 5H03), Washington, DC 20522...

78 FR 77772 - Culturally Significant Objects Imported for Exhibition Determinations: “Georges Braque: 1882-1963”

Federal Register 2010, 2011, 2012, 2013, 2014

2013-12-24

.... 2681, et seq.; 22 U.S.C. 6501 note, et seq.), Delegation of Authority No. 234 of October 1, 1999, and... of State (telephone: 202- 632-6469). The mailing address is U.S. Department of State, SA-5, L/PD...

Comprehensive Monitoring Program, Final Air Quality Data Assessment Report for 1989, Version 2.1. Volume 4

DTIC Science & Technology

1990-06-01

8.3U 11.94 23.4 214.71 6 6 36.9 17.54 4 I U SFM6 DATA LSTM i SIGA SA AX "DAR OR 03 CO S02 NO N02 NOX U S D THUA TEN PRE$ PRECIP RAD RH WS STAB S115...Hodgson, 1974: Predicted dry deposition velocities. Atmospheric-Surface Exchange of Particulate and Gaseous Pollutants. Available as CONF-740921

Measurements of rare isotopes of U and Th by MC-ICP-MS using a 1013 ohm resistor

NASA Astrophysics Data System (ADS)

Pythoud, M.; Edwards, R. L.; Cheng, H.; Lu, Y.; Zhang, P.; Nissen, J.; Berry, A. E.

2016-12-01

We have tested a 1013 ohm resistor on a Thermo-Scientific Neptune Plus, a multi-collector inductively-coupled plasma mass spectrometer (MC-ICP-MS), for the measurement of rare isotopes of uranium (U) and thorium (Th). In nature, the isotopic disequilibrium among U-series nuclides provides the potential to date materials and time processes over the last 700,000 years. Using gravimetric standards and a Minnesota stalagmite, we demonstrate the reproducibility of δ234U and 230Th dates with uncertainties at the 1-‰ to sub-‰ level (2σ), with relatively small samples. Compared to traditional secondary electron multiplier (SEM) techniques, measurement times decrease from > 1 hour to < 5 min for U and from tens of min to < 2 min for Th, with comparable or better precision. The characteristics of the new amplifier design and typical instrumental conditions allow for 234U and 230Th sample loads as small as 1-2 pg, a reduction in sample size close to an order of magnitude over cup measurements with 1011 ohm resistors. The main sources of error include the amplifier noise, uncertainty in the characterization of the tailing effect, and in some cases, counting statistics. Importantly, our overall characterization suggests that this new method forms the basis for future and further improvements on instrumental precision.

Assessment of the vertical distribution of natural radionuclides in a mineralized uranium area in south-west Spain.

PubMed

Blanco Rodríguez, P; Vera Tomé, F; Lozano, J C

2014-01-01

Low-level alpha spectrometry techniques using semiconductor detectors (PIPS) and liquid scintillation (LKB Quantulus 1220™) were used to determine the activity concentration of (238)U, (234)U, (230)Th, (226)Ra, (232)Th, and (210)Pb in soil samples. The soils were collected from an old disused uranium mine located in southwest Spain. The soils were sampled from areas with different levels of influence from the installation and hence had different levels of contamination. The vertical profiles of the soils (down to 40 cm depth) were studied in order to evaluate the vertical distribution of the natural radionuclides. To determine the origin of these natural radionuclides the Enrichment Factor was used. Also, study of the activity ratios between radionuclides belonging to the same radioactive series allowed us to assess the different types of behaviors of the radionuclides involved. The vertical profiles for the radionuclide members of the (238)U series were different at each sampling point, depending on the level of influence of the installation. However, the profiles of each point were similar for the long-lived radionuclides of the (238)U series ((238)U, (234)U, (230)Th, and (226)Ra). Moreover, a major imbalance was observed between (210)Pb and (226)Ra in the surface layer, due to (222)Rn exhalation and the subsequent surface deposition of (210)Pb. Copyright © 2013 Elsevier Ltd. All rights reserved.

(236)U and (239,)(240)Pu ratios from soils around an Australian nuclear weapons test site.

PubMed

Tims, S G; Froehlich, M B; Fifield, L K; Wallner, A; De Cesare, M

2016-01-01

The isotopes (236)U, (239)Pu and (240)Pu are present in surface soils as a result of global fallout from nuclear weapons tests carried out in the 1950's and 1960's. These isotopes potentially constitute artificial tracers of recent soil erosion and sediment movement. Only Accelerator Mass Spectrometry has the requisite sensitivity to measure all three isotopes at these environmental levels. Coupled with its relatively high throughput capabilities, this makes it feasible to conduct studies of erosion across the geographical extent of the Australian continent. In the Australian context, however, global fallout is not the only source of these isotopes. As part of its weapons development program the United Kingdom carried out a series of atmospheric and surface nuclear weapons tests at Maralinga, South Australia in 1956 and 1957. The tests have made a significant contribution to the Pu isotopic abundances present in the region around Maralinga and out to distances ∼1000 km, and impact on the assessment techniques used in the soil and sediment tracer studies. Quantification of the relative fallout contribution derived from detonations at Maralinga is complicated owing to significant contamination around the test site from numerous nuclear weapons safety trials that were also carried out around the site. We show that (236)U can provide new information on the component of the fallout that is derived from the local nuclear weapons tests, and highlight the potential of (236)U as a new fallout tracer. Crown Copyright © 2015. Published by Elsevier Ltd. All rights reserved.

34 CFR 75.236 - Effect of the grant.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 34 Education 1 2014-07-01 2014-07-01 false Effect of the grant. 75.236 Section 75.236 Education... Make A Grant § 75.236 Effect of the grant. The grant obligates both the Federal Government and the grantee to the requirements that apply to the grant. (Authority: 20 U.S.C. 1221e-3 and 3474) Cross...

Exploratory study of fission product yields of neutron-induced fission of U 235 ,   U 238 , and Pu 239 at 8.9 MeV

DOE PAGES

Bhatia, C.; Fallin, B. F.; Gooden, M. E.; ...

2015-06-05

Using dual-fission chambers each loaded with a thick (200–400–mg/cm 2) actinide target of 235,238U or 239Pu and two thin (~10–100–μg/cm 2) reference foils of the same actinide, the cumulative yields of fission products ranging from 92Sr to 147Nd have been measured at E n = 8.9MeV. The 2H(d,n) 3He reaction provided the quasimonoenergetic neutron beam. Here, the experimental setup and methods used to determine the fission product yield (FPY) are described, and results for typically eight high-yield fission products are presented.

A setup for active neutron analysis of the fissile material content in fuel assemblies of nuclear reactors

NASA Astrophysics Data System (ADS)

Bushuev, A. V.; Kozhin, A. F.; Aleeva, T. B.; Zubarev, V. N.; Petrova, E. V.; Smirnov, V. E.

2016-12-01

An active neutron method for measuring the residual mass of 235U in spent fuel assemblies (FAs) of the IRT MEPhI research reactor is presented. The special measuring stand design and uniform irradiation of the fuel with neutrons along the entire length of the active part of the FA provide high accuracy of determination of the residual 235U content. AmLi neutron sources yield a higher effect/background ratio than other types of sources and do not induce the fission of 238U. The proposed method of transfer of the isotope source in accordance with a given algorithm may be used in experiments where the studied object needs to be irradiated with a uniform fluence.

Breeding of {sup 233}U in the thorium–uranium fuel cycle in VVER reactors using heavy water

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marshalkin, V. E., E-mail: marshalkin@vniief.ru; Povyshev, V. M.

A method is proposed for achieving optimal neutron kinetics and efficient isotope transmutation in the {sup 233}U–{sup 232}Th oxide fuel of water-moderated reactors with variable water composition (D{sub 2}O, H{sub 2}O) that ensures breeding of the {sup 233}U and {sup 235}U isotopes. The method is comparatively simple to implement.

7 CFR 235.4 - Allocation of funds to States.

Code of Federal Regulations, 2010 CFR

2010-01-01

.... (Sec. 14, Pub. L. 95-166, 91 Stat. 1338 (42 U.S.C. 1776); sec. 7, Pub. L. 95-627, 92 Stat. 3621 (42 U.S.C. 1776); sec. 7(a), Pub. L. 95-627, 92 Stat. 3622 (42 U.S.C. 1751); Pub. L. 96-499, secs. 201 and..., 1759a, 1774 and 1776); E.O. 12372 (July 14, 1982, 47 FR 30959); sec. 401(b) Intergovernmental...

7 CFR 235.4 - Allocation of funds to States.

Code of Federal Regulations, 2012 CFR

2012-01-01

.... (Sec. 14, Pub. L. 95-166, 91 Stat. 1338 (42 U.S.C. 1776); sec. 7, Pub. L. 95-627, 92 Stat. 3621 (42 U.S.C. 1776); sec. 7(a), Pub. L. 95-627, 92 Stat. 3622 (42 U.S.C. 1751); Pub. L. 96-499, secs. 201 and..., 1759a, 1774 and 1776); E.O. 12372 (July 14, 1982, 47 FR 30959); sec. 401(b) Intergovernmental...

7 CFR 235.4 - Allocation of funds to States.

Code of Federal Regulations, 2013 CFR

2013-01-01

.... (Sec. 14, Pub. L. 95-166, 91 Stat. 1338 (42 U.S.C. 1776); sec. 7, Pub. L. 95-627, 92 Stat. 3621 (42 U.S.C. 1776); sec. 7(a), Pub. L. 95-627, 92 Stat. 3622 (42 U.S.C. 1751); Pub. L. 96-499, secs. 201 and..., 1759a, 1774 and 1776); E.O. 12372 (July 14, 1982, 47 FR 30959); sec. 401(b) Intergovernmental...

7 CFR 235.4 - Allocation of funds to States.

Code of Federal Regulations, 2014 CFR

2014-01-01

.... (Sec. 14, Pub. L. 95-166, 91 Stat. 1338 (42 U.S.C. 1776); sec. 7, Pub. L. 95-627, 92 Stat. 3621 (42 U.S.C. 1776); sec. 7(a), Pub. L. 95-627, 92 Stat. 3622 (42 U.S.C. 1751); Pub. L. 96-499, secs. 201 and..., 1759a, 1774 and 1776); E.O. 12372 (July 14, 1982, 47 FR 30959); sec. 401(b) Intergovernmental...

7 CFR 235.4 - Allocation of funds to States.

Code of Federal Regulations, 2011 CFR

2011-01-01

.... (Sec. 14, Pub. L. 95-166, 91 Stat. 1338 (42 U.S.C. 1776); sec. 7, Pub. L. 95-627, 92 Stat. 3621 (42 U.S.C. 1776); sec. 7(a), Pub. L. 95-627, 92 Stat. 3622 (42 U.S.C. 1751); Pub. L. 96-499, secs. 201 and..., 1759a, 1774 and 1776); E.O. 12372 (July 14, 1982, 47 FR 30959); sec. 401(b) Intergovernmental...

A new experimental proposal for {sup 235}U PFNS to answer a fifty years old question

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kornilov, N.; Massey, T.; Grimes, S.

2011-07-01

The Prompt Fission Neutron Spectrum (PFNS) from {sup 235}U(n,f) is very important for various nuclear applications. It has been investigated in different experiments. In spite of {approx}50 years of experimental efforts, a continuing conflict exists at thermal neutron energy. Microscopic experimental PFNS cannot describe macroscopic data. In this report we discuss the current status of this problem and suggest a new experiment, which could possibly resolve this problem. (authors)

Control of the U and Th behaviour in forest soils

NASA Astrophysics Data System (ADS)

Rihs, Sophie; Gontier, Adrien; Chabaux, François; Pelt, Eric; Turpault, Marie-Pierre

2015-04-01

U- and Th-series disequilibria and U, Th, Fe and Al speciation, were measured in several soil profiles from the experimental forest site of Breuil (Morvan, France) in order to address the impact of the vegetation on U and Th nuclides behaviour in soils. Thirty-five years after an experimental clear-felling of the native forest, the soil developed under two replacing mono-specific plantations (Oak and Douglas fir) were therefore compared to the undisturbed native forest soil. The analogous physical and chemical properties of these soils before the replacement were formerly demonstrated. Our results suggest that a shift in the Iron distribution seems to occur under the stand replaced by Oaks, with a significant replacement of Fe-bearing silicates by well crystallized Fe oxides. In contrast, such evolution was not demonstrated in the soils under Douglas fir. The concurrent loss of U and Th from the soils under Oak was tentatively related to the dissolution of Fe-bearing minerals. A mass balance calculation demonstrates that the observed increase in U oxalate-extracted fractions can quantitatively be explained through the entire profiles by a mere dissolution of up to 20% of U-Fe-bearing silicated minerals, without significant re-adsorption onto the amorphous Fe-Al oxides for U. Beside this primary release from Fe-bearing silicate minerals, the mobility of U and Th seems more likely controlled by Al phases rather than Fe oxides in surface layers during further pedogenic processes. Indeed, some of the U- and Th series disequilibria seem to be strongly related to Al dynamic in these layers. This relationship can be seen in the native forest profiles as well as in the replaced profiles, suggesting that this feature is not linked to the cover change. The redistribution of U and Th isotopes through these pedogenic processes therefore rule out the use of U-series for weathering rate determination in shallowest soils layers. In contrast, below 25 cm, the release of U and Th as well as the change of their distribution among the soil phases does not affect U- and Th series disequilibria. The activity ratios measured in oxalate leachates and the residues allow to demonstrate that the dissolution of a U-bearing silicate mineral and the consequent release of up to 20% of U would shift the (234U/238U) and (230Th/234U) ratios by less than 2%. These results therefore reveal that, after 35 years, no significant impact of the cover change on U-series disequilibria was recorded in the main part of the soil profiles, which, at this stage, justify the use of these nuclides as chronometers for weathering determination.

Experimental criticality specifications. An annotated bibliography through 1977

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paxton, H.C.

1978-05-01

The compilation of approximately 300 references gives sources of experimental criticality parameters of systems containing /sup 235/U, /sup 233/U, and /sup 239/Pu. The intent is to cover basic data for criticality safety applications. The references are arranged by subject.

China Naval Modernization: Implications for U.S. Navy Capabilities - Background and Issues for Congress

DTIC Science & Technology

2007-07-20

coordinate all these forces in two major simultaneous operations: (1) to bring Taiwan to its knees and (2) cause the U.S. to be tardy , indecisive, or...years), the Philippines (where the U.S. Navy ships used as a major repair port until the early 1990s), and Australia. On-Station and Early-Arriving...affect the mainland, Japan, the Philippines , and commercial shipping and air routes in the region.236 Whether China would agree with the above view that

Isolation of 236U and 239,240Pu from seawater samples and its determination by Accelerator Mass Spectrometry.

PubMed

López-Lora, Mercedes; Chamizo, Elena; Villa-Alfageme, María; Hurtado-Bermúdez, Santiago; Casacuberta, Núria; García-León, Manuel

2018-02-01

In this work we present and evaluate a radiochemical procedure optimised for the analysis of 236 U and 239,240 Pu in seawater samples by Accelerator Mass Spectrometry (AMS). The method is based on Fe(OH) 3 co-precipitation of actinides and uses TEVA® and UTEVA® extraction chromatography resins in a simplified way for the final U and Pu purification. In order to improve the performance of the method, the radiochemical yields are analysed in 1 to 10L seawater volumes using alpha spectrometry (AS) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Robust 80% plutonium recoveries are obtained; however, it is found that Fe(III) concentration in the precipitation solution and sample volume are the two critical and correlated parameters influencing the initial uranium extraction through Fe(OH) 3 co-precipitation. Therefore, we propose an expression that optimises the sample volume and Fe(III) amounts according to both the 236 U and 239,240 Pu concentrations in the samples and the performance parameters of the AMS facility. The method is validated for the current setup of the 1MV AMS system (CNA, Sevilla, Spain), where He gas is used as a stripper, by analysing a set of intercomparison seawater samples, together with the Laboratory of Ion Beam Physics (ETH, Zürich, Switzerland). Copyright © 2017 Elsevier B.V. All rights reserved.

Fission Product Yield Study of 235U, 238U and 239Pu Using Dual-Fission Ionization Chambers

NASA Astrophysics Data System (ADS)

Bhatia, C.; Fallin, B.; Howell, C.; Tornow, W.; Gooden, M.; Kelley, J.; Arnold, C.; Bond, E.; Bredeweg, T.; Fowler, M.; Moody, W.; Rundberg, R.; Rusev, G.; Vieira, D.; Wilhelmy, J.; Becker, J.; Macri, R.; Ryan, C.; Sheets, S.; Stoyer, M.; Tonchev, A.

2014-05-01

To resolve long-standing differences between LANL and LLNL regarding the correct fission basis for analysis of nuclear test data [M.B. Chadwick et al., Nucl. Data Sheets 111, 2891 (2010); H. Selby et al., Nucl. Data Sheets 111, 2891 (2010)], a collaboration between TUNL/LANL/LLNL has been established to perform high-precision measurements of neutron induced fission product yields. The main goal is to make a definitive statement about the energy dependence of the fission yields to an accuracy better than 2-3% between 1 and 15 MeV, where experimental data are very scarce. At TUNL, we have completed the design, fabrication and testing of three dual-fission chambers dedicated to 235U, 238U, and 239Pu. The dual-fission chambers were used to make measurements of the fission product activity relative to the total fission rate, as well as for high-precision absolute fission yield measurements. The activation method was employed, utilizing the mono-energetic neutron beams available at TUNL. Neutrons of 4.6, 9.0, and 14.5 MeV were produced via the 2H(d,n)3He reaction, and for neutrons at 14.8 MeV, the 3H(d,n)4He reaction was used. After activation, the induced γ-ray activity of the fission products was measured for two months using high-resolution HPGe detectors in a low-background environment. Results for the yield of seven fission fragments of 235U, 238U, and 239Pu and a comparison to available data at other energies are reported. For the first time results are available for neutron energies between 2 and 14 MeV.

Development of a Scalable Process Control System for Chemical Soil Washing to Remove Uranyl Oxide

DTIC Science & Technology

2015-05-01

ICET also has a fully equipped counting laboratory for the evaluation of radioactive samples . Photographs of the 1-meter and 3-meter motorized...the leachate will be monitored using a gamma detector. There are numerous naturally occurring radioactive materials in soil . ICET has developed a...48.6% from 238U and 49.2% from 234U. The 238U in NU also contains daughters that are radioactive . This increases the activity of samples over long

Evaluation of potential hazard exposure resulting from DOE waste treatment and disposal at Rollins Environmental Services, Baton Rouge, LA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1992-04-01

The equivalent dose rate to populations potentially exposed to wastes shipped to Rollins Environmental Services, Baton Rouge, LA from Oak Ridge and Savannah River Operations of the Department of Energy was estimated. Where definitive information necessary to the estimation of a dose rate was unavailable, bounding assumptions were employed to ensure an overestimate of the actual dose rate experienced by the potentially exposed population. On this basis, it was estimated that a total of about 3.85 million pounds of waste was shipped from these DOE operations to Rollins with a maximum combined total activity of about 0.048 Curies. Populations nearmore » the Rollins site could potentially be exposed to the radionuclides in the DOE wastes via the air pathway after incineration of the DOE wastes or by migration from the soil after landfill disposal. AIRDOS was used to estimate the dose rate after incineration. RESRAD was used to estimate the dose rate after landfill disposal. Calculations were conducted with the estimated radioactive specie distribution in the wastes and, as a test of the sensitivity of the results to the estimated distribution, with the entire activity associated with individual radioactive species such as Cs-137, Ba-137, Sr-90, Co-60, U-234, U-235 and U-238. With a given total activity, the dose rates to nearby individuals were dominated by the uranium species.« less

Radius anomaly in the diffraction model for heavy-ion elastic scattering

NASA Astrophysics Data System (ADS)

Pandey, L. N.; Mukherjee, S. N.

1984-04-01

The elastic scattering of heavy ions, 20Ne on 208Pb, 20Ne on 235U, 84Kr on 208Pb, and 84Kr on 232Th, is examined within the framework of Frahn's diffraction model. An analysis of the experiment using the "quarter point recipe" of the expected Fresnel cross sections yields a larger radius for 208Pb than the radii for 235U and 232Th. It is shown that inclusion of the nuclear deformation in the model removes the above anomaly in the radii, and the assumption of smooth cutoff of the angular momentum simultaneously leads to a better fit to elastic scattering data, compared to those obtained by the earlier workers on the assumption of sharp cutoff. [NUCLEAR REACTIONS Elastic scattering, 20Ne+208Pb (161.2 MeV), 20Ne+235U (175 MeV), 84Kr+208Pb (500 MeV), 84Kr+232Th (500 MeV), diffraction model, nuclear deformation.

Effects of surface-water irrigation on sources, fluxes, and residence times of water, nitrate, and uranium in an alluvial aquifer

USGS Publications Warehouse

Böhlke, J.K.; Verstraeten, Ingrid M.; Kraemer, T.F.

2007-01-01

Effects of surface-water irrigation on an alluvial aquifer were evaluated using chemical and isotopic data including ??2H, ??18O, 3H, ??3He, Ar, Ne, N2, ??15N, and 234U/238U activity ratios in a transect of nested wells in the North Platte River valley in western Nebraska, USA. The data were used to evaluate sources and fluxes of H2O, NO3- and U, all of which were strongly affected by irrigated agriculture. Combined results indicate that the alluvial aquifer was dominated by irrigation water that had distinctive chemical and isotopic features that were inherited from the North Platte River or acquired from agricultural soils or recharge processes. Values of ??2H, ??18O, Ar and Ne indicate that most of the ground water in the alluvial aquifer was irrigation water that was derived from the North Platte River and distributed during the growing season. The irrigation water was identified by an evaporated isotopic signature that was acquired by the river in major upstream reservoirs in Wyoming, and by relatively warm gas-equilibration temperatures related to warm-season recharge. Apparent 3H-3He ages indicate that the ground water in the alluvium was stratified and mostly 3.0 m/a. Age gradients and NO3- concentrations indicate that recharge occurred by a combination of focused leakage from irrigation canals (rapid local recharge, low NO3-) and distributed infiltration beneath the irrigated agricultural fields (lower recharge, high NO3-). Large amounts of U with relatively low 234U/238U activity ratios were present in the alluvial aquifer as a result of irrigation with U-bearing river water, and minor amounts of U with higher 234U/238U activity ratios were added locally from basal and underlying volcanic-rich sediments. Distributions of NO3-, ?? 15 N [NO3-], dissolved gases, and ground-water ages indicate that NO3- concentrations increased and ?? 15 N [NO3-] values decreased in distributed recharge in the last few decades, possibly in relation to a documented increase in the agricultural use of artificial fertilizers. Canal leakage caused substantial dilution of NO3- within the alluvial aquifer, whereas denitrification occurred mainly near the bottom of the alluvium. The average residence time of the irrigation water within the aquifer was relatively short (about 9 a) and reactions such as respiration, denitrification and U exchange in the saturated zone had relatively little effect on the overall composition of the alluvial ground water in comparison to what they might have had in the absence of irrigation recharge.

EC comparison on the determination of 226Ra, 228Ra, 234U and 238U in water among European monitoring laboratories.

PubMed

Wätjen, U; Benedik, L; Spasova, Y; Vasile, M; Altzitzoglou, T; Beyermann, M

2010-01-01

In anticipation of new European requirements for monitoring radioactivity concentration in drinking water, IRMM organized an interlaboratory comparison on the determination of low levels of activity concentrations (about 10-100 mBq L(-1)) of the naturally occurring radionuclides (226)Ra, (228)Ra, (234)U and (238)U in three commercially available mineral waters. Using two or three different methods with traceability to the International System of Reference (SIR), the reference values of the water samples were determined prior to the proficiency test within combined standard uncertainties of the order of 3%-10%. An overview of radiochemical separation and measurement methods used by the 45 participating laboratories are given. The results of the participants are evaluated versus the reference values. Several of the participants' results deviate by more than a factor of two from the reference values, in particular for the radium isotopes. Such erroneous analysis results may lead to a crucial omission of remedial actions on drinking water supplies or to economic loss by an unjustified action. Copyright 2009 Elsevier Ltd. All rights reserved.

Radionuclide Concentrations in Soils and Vegetation at Low-Level Radioactive Waste Disposal Area G during the 1997 Growing Season

DOE Office of Scientific and Technical Information (OSTI.GOV)

L. Naranjo, Jr.; P. R. Fresquez; R. J. Wechsler

1998-08-01

Soil and overstory and understory vegetation (washed and unwashed) collected at eight locations within and around Area G-a low-level radioactive solid-waste disposal facility at Los Alamos National Laboratory-were analyzed for 3H, 238Pu, 239Pu, 137CS, 234U, 235U, 228AC, Be, 214Bi, 60Co, 40& 54Mn, 22Na, 214Pb and 208Tl. In general, most radionuclide concentrations, with the exception of 3Ef and ~9Pu, in soils and overstory and understory vegetation collected from within and around Area G were within upper (95'%) level background concentrations. Although 3H concentrations in vegetation from most sites were significantly higher than background (>2 pCi mL-l), concentrations decreased markedly in comparisonmore » to last year's results. The highest `H concentration in vegetation was detected from a juniper tree that was growing over tritium shaft /+150; it contained 530,000 pCi 3H mL-l. Also, as in the pas~ the transuranic waste pad area contained the highest levels of 239Pu in soils and in understory vegetation as compared to other areas at Area G.« less

Effect of Silicon in U-10Mo Alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kautz, Elizabeth J.; Devaraj, Arun; Kovarik, Libor

2017-08-31

This document details a method for evaluating the effect of silicon impurity content on U-10Mo alloys. Silicon concentration in U-10Mo alloys has been shown to impact the following: volume fraction of precipitate phases, effective density of the final alloy, and 235-U enrichment in the gamma-UMo matrix. This report presents a model for calculating these quantities as a function of Silicon concentration, which along with fuel foil characterization data, will serve as a reference for quality control of the U-10Mo final alloy Si content. Additionally, detailed characterization using scanning electron microscope imaging, transmission electron microscope diffraction, and atom probe tomography showedmore » that Silicon impurities present in U-10Mo alloys form a Si-rich precipitate phase.« less

Uranium isotope composition of a laterite profile during extreme weathering of basalt in Guangdong, South China

NASA Astrophysics Data System (ADS)

Huang, J.; Zhou, Z.; Gong, Y.; Lundstrom, C.; Huang, F.

2015-12-01

Rock weathering and soil formation in the critical zone are important for material cycle from the solid Earth to superficial system. Laterite is a major type of soil in South China forming at hot-humid climate, which has strong effect on the global uranium cycle. Uranium is closely related to the environmental redox condition because U is stable at U(Ⅳ) in anoxic condition and U(Ⅵ) as soluble uranyl ion (UO22+) under oxic circumstance. In order to understand the behavior of U isotopes during crust weathering, here we report uranium isotopic compositions of soil and base rock samples from a laterite profile originated from extreme weathering of basalt in Guangdong, South China. The uranium isotopic data were measured on a Nu Plasma MC-ICP-MS at the University of Illinois at Urbana-Champaign using the double spike method. The δ238U of BCR-1 is -0.29±0.03‰ (relative to the international standard CRM-112A), corresponding to a 238U/235U ratio of 137.911±0.004. Our result of BCR-1 agrees with previous analyses (e.g., -0.28‰ in Weyer et al. 2008) [1]. U contents of the laterite profile decrease from 1.9 ppm to 0.9 ppm with depth, and peak at 160 - 170 cm (2.3 ppm), much higher than the U content of base rocks (~0.5 ppm). In contrary, U/Th of laterites is lower than that of base rock (0.27) except the peak at the depth of 160-170 cm (0.38), indicating significant U loss during weathering. Notably, U isotope compositions of soils show a small variation from -0.38 to -0.28‰, consistent with the base rock within analytical error (0.05‰ to 0.08‰, 2sd). Such small variation can be explained by a "rind effect" (Wang et al., 2015) [2], by which U(Ⅳ) can be completely oxidized to U(VI) layer by layer during basalt weathering by dissolved oxygen. Therefore, our study indicates that U loss during basalt weathering at the hot-humid climate does not change U isotope composition of superficial water system. [1] Weyer S. et al. (2008) Natural fractionation of 238U/235U. GCA 72,345-359 [2] Wang X. et al. (2015) Isotope fractionation during oxidation of tetravalent uranium by dissolved oxygen. GCA 150, 160-170

Actinide Foil Production for MPACT Research

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beller, Denis

Sensitive fast-neutron detectors are required for use in lead slowing down spectrometry (LSDS), an active interrogation technique for used nuclear fuel assay for Materials Protection, Accounting, and Controls Technologies (MPACT). During the past several years UNLV sponsored a research project at RPI to investigate LSDS; began development of fission chamber detectors for use in LSDS experiments in collaboration with INL, LANL, and Oregon State U.; and participated in a LSDS experiment at LANL. In the LSDS technique, research has demonstrated that these fission chamber detectors must be sensitive to fission energy neutrons but insensitive to thermal-energy neutrons. Because most systemsmore » are highly sensitive to large thermal neutron populations due to the well-known large thermal cross section of 235U, even a miniscule amount of this isotope in a fission chamber will overwhelm the small population of higher-energy neutrons. Thus, fast-fission chamber detectors must be fabricated with highly depleted uranium (DU) or ultra-pure thorium (Th), which is about half as efficient as DU. Previous research conducted at RPI demonstrated that the required purity of DU for assay of used nuclear fuel using LSDS is less than 4 ppm 235U, material that until recently was not available in the U.S. In 2009 the PI purchased 3 grams of ultra-depleted uranium (uDU, 99.99998% 238U with just 0.2 ± 0.1 ppm 235U) from VNIIEF in Sarov, Russia. We received the material in the form of U3O8 powder in August of 2009, and verified its purity and depletion in a FY10 MPACT collaboration project. In addition, chemical processing for use in FC R&D was initiated, fission chamber detectors and a scanning alpha-particle spectrometer were developed, and foils were used in a preliminary LSDS experiment at a LANL/LANSCE in Sept. of 2010. The as-received U3O8 powder must be chemically processed to convert it to another chemical form while maintaining its purity, which then must be used to electro-deposit U or UO2 in extremely thin layers (1 to 2 mg/cm2) on various media such as films, foils, or discs. After many months of investigation and trials in FY10 and 11, UNLV researchers developed a new method to produce pure UO2 deposits on foils using a unique approach, which has never been demonstrated, that involves dissolution of U3O8 directly into room temperature ionic liquid (RTIL) followed by electrodeposition from the RTIL-uDU solution (Th deposition from RTIL had been previously demonstrated). The high-purity dissolution of the U3O8 permits the use of RTIL solutions for deposition of U on metal foils in layers without introducing contamination. In FY10 and early FY11 a natural U surrogate for the uDU was used to investigate this and other techniques. In this research project UNLV will deposit directly from RTIL to produce uDU and Th foils devoid of possible contaminants. After these layers have been deposited, they will be examined for purity and uniformity. UNLV will complete the development and demonstration of the RTIL technology/ methodology to prepare uDU and Th samples for use in constructing fast-neutron detectors. Although this material was purchased for use in research using fast-fission chamber detectors for active inspection techniques for MPACT, it could also contribute to R&D for other applications, such as cross section measurements or neutron spectroscopy for national security« less

Photo-fission Product Yield Measurements at Eγ=13 MeV on 235U, 238U, and 239Pu

NASA Astrophysics Data System (ADS)

Tornow, W.; Bhike, M.; Finch, S. W.; Krishichayan, Fnu; Tonchev, A. P.

2016-09-01

We have measured Fission Product Yields (FPYs) in photo-fission of 235U, 238U, and 239Pu at TUNL's High-Intensity Gamma-ray Source (HI γS) using mono-energetic photons of Eγ = 13 MeV. Details of the experimental setup and analysis procedures will be discussed. Yields for approximately 20 fission products were determined. They are compared to neutron-induced FPYs of the same actinides at the equivalent excitation energies of the compound nuclear systems. In the future photo-fission data will be taken at Eγ = 8 . 0 and 10.5 MeV to find out whether photo-fission exhibits the same so far unexplained dependence of certain FPYs on the energy of the incident probe, as recently observed in neutron-induced fission, for example, for the important fission product 147Nd. Work supported by the U. S. Dept. of Energy, under Grant No. DE-FG02-97ER41033, and by the NNSA, Stewardship Science Academic Alliances Program, Grant No. DE-NA0001838 and the Lawrence Livermore, National Security, LLC under Contract No. DE-AC52-07NA27344.

Performance of the MTR core with MOX fuel using the MCNP4C2 code.

PubMed

Shaaban, Ismail; Albarhoum, Mohamad

2016-08-01

The MCNP4C2 code was used to simulate the MTR-22 MW research reactor and perform the neutronic analysis for a new fuel namely: a MOX (U3O8&PuO2) fuel dispersed in an Al matrix for One Neutronic Trap (ONT) and Three Neutronic Traps (TNTs) in its core. Its new characteristics were compared to its original characteristics based on the U3O8-Al fuel. Experimental data for the neutronic parameters including criticality relative to the MTR-22 MW reactor for the original U3O8-Al fuel at nominal power were used to validate the calculated values and were found acceptable. The achieved results seem to confirm that the use of MOX fuel in the MTR-22 MW will not degrade the safe operational conditions of the reactor. In addition, the use of MOX fuel in the MTR-22 MW core leads to reduce the uranium fuel enrichment with (235)U and the amount of loaded (235)U in the core by about 34.84% and 15.21% for the ONT and TNTs cases, respectively. Copyright © 2016 Elsevier Ltd. All rights reserved.

Early-Mid Holocene climatic variations in Tasmania, Australia: multi-proxy records in a stalagmite from Lynds Cave

NASA Astrophysics Data System (ADS)

Xia, Qikai; Zhao, Jian-xin; Collerson, K. D.

2001-12-01

Mass spectrometric uranium-series dating and C-O isotopic analysis of a stalagmite from Lynds Cave, northern Tasmania, Australia provide a high-resolution record of regional climate change between 5100 and 9200 yr before present (BP). Combined δ18O, δ13C, growth rate, initial 234U/238U and physical property (color, transparency and porosity) records allow recognition of seven climatic stages: Stage I (>9080 yr BP) - a relatively dry period at the beginning of stalagmite growth evidenced by elevated 234U/238U; Stage II (9080-8600 yr BP) - a period of unstable climate characterized by high-frequency variability in temperature and bio-productivity; Stage III (8600-8000 yr BP) - a period of stable and moderate precipitation and stable and high bio-productivity, with a continuously rising temperature; Stage IV (8000-7400 yr BP) - the warmest period with high evaporation and low effective precipitation (rainfall less evaporation); Stage V (7400-7000 yr BP) - the wettest period with highest stalagmite growth and enhanced but unstable bio-productivity; Stage VI (7000-6600 yr BP) - a period with a significantly reduced precipitation and bio-productivity without noticeable change in temperature; Stage VII (6600-5100 yr BP) - a period of lowest temperature and precipitation marking a significant climatic deterioration. Overall, the records suggest that the warmest climate occurred between 8000 and 7400 yr BP, followed by a wettest period between 7400 and 7000 yr BP. These are broadly correlated with the so-called 'Mid Holocene optimum' previously proposed using pollen and lake level records. However, the timing and resolution of the speleothem record from Lynds Cave are significantly higher than in both the pollen and lake level records. This allows us to correlate the abrupt change in physical property, δ18O, δ13C, growth rate, and initial 234U/238U of the stalagmite at ˜8000 yr BP with a global climatic event at Early-Mid Holocene transition.

Optical detection of special nuclear materials: an alternative approach for standoff and remote sensing

NASA Astrophysics Data System (ADS)

Johnson, J. Bruce; Reeve, S. W.; Burns, W. A.; Allen, Susan D.

2010-04-01

Termed Special Nuclear Material (SNM) by the Atomic Energy Act of 1954, fissile materials, such as 235U and 239Pu, are the primary components used to construct modern nuclear weapons. Detecting the clandestine presence of SNM represents an important capability for Homeland Security. An ideal SNM sensor must be able to detect fissile materials present at ppb levels, be able to distinguish between the source of the detected fissile material, i.e., 235U, 239Pu, 233U or other fission source, and be able to perform the discrimination in near real time. A sensor with such capabilities would provide not only rapid identification of a threat but, ultimately, information on the potential source of the threat. For example, current detection schemes for monitoring clandestine nuclear testing and nuclear fuel reprocessing to provide weapons grade fissile material rely largely on passive air sampling combined with a subsequent instrumental analysis or some type of wet chemical analysis of the collected material. It would be highly useful to have a noncontact method of measuring isotopes capable of providing forensic information rapidly at ppb levels of detection. Here we compare the use of Kr, Xe and I as "canary" species for distinguishing between 235U and 239Pu fission sources by spectroscopic methods.

Relatively Recent Volcanism on Oahu, Hawaii: New U-series and Paleomagnetic Age Constraints on the Hanauma Bay Eruption

NASA Astrophysics Data System (ADS)

Rubin, K. H.; Jurado-Chichay, Z.; Urrutia-Fucugauchi, J.

2002-12-01

The Koko Rift Zone (KRZ), eastern Oahu, is generally regarded as among the youngest volcanic features on the island. Previous workers have suggested that the 9 or 10 vents of this rift erupted near-simultaneously. However, K-Ar data in the literature (32-39 ka vs 320 ka) provide only general guidance on the youthfulness of these eruptions. We present new age constraints on KRZ volcanism using deposits of the phreatomagmatic eruption that produced Hanauma Bay (a popular snorkeling spot) and spatially associated lava flows. Numerous continuous basaltic ash units within the walls of Hanauma crater contain lithic fragments of well-preserved coral reef, beach rock, and marine mollusks, indicating that the eruption occurred in a near shore environment. 238U-234U-230Th dating of coral clasts in the deposit demonstrates that the eruption breached reef of MIS stage 7 age (200 +/- 30 ka), thereby ruling out the K-Ar age of 320 ka. U-series nuclides in "normal" MIS 7 coral lithics are indistinguishable from those in the island encircling Waianae Reef of the same age. However, U-series components in some originally aragonitic coral clasts were offset during the eruption when the rims recrystallized to calcite. 87Sr/86Sr, 234U/238U and Sr and U concentration indicate chemical mixing with host basaltic ash during this event, from which potential ages of the eruption can be constructed using isochron methods. More modeling of the data remains to be done but our preliminary estimate places the eruption at less than 100 ka. This result is consistent with new data on paleointensity and paleomagnetic secular variation within the lava flows exposed in or around the crater. This U-series dating approach should prove useful for eruptions in other locales where carbonate bioclast lithics are present in the deposits.

The Feasibility of Ending HEU Fuel Use in the U.S. Navy

DOE PAGES

Philippe, Sebastian; von Hippel, Frank

2016-11-01

We report that since September 11, 2001, the U.S. government has sought to remove weapons-useable highly enriched uranium (HEU) containing 20 percent or more uranium-235 from as many locations as possible because of concerns about the possibility of nuclear terrorism.

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Federal Register 2010, 2011, 2012, 2013, 2014

2011-05-13

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Code of Federal Regulations, 2010 CFR

2010-01-01

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Temporal Variations in 234U/238U Activity Ratios in the Lower Mississippi River due to Changes in Source Tributary Discharges

NASA Astrophysics Data System (ADS)

Grzymko, T. J.; Marcantonio, F.; McKee, B. A.; Stewart, C. M.

2004-12-01

The world's 25 largest river systems contribute nearly 50% of all freshwater to the global ocean and carry large quantities of dissolved trace metals annually. Trace metal concentrations in these systems show large variances on seasonal time scales. In order to constrain the causes of these variations, consistent sampling on sub-seasonal time intervals is essential. Here, we focus on the Mississippi River, the seventh largest river in the world in terms of freshwater discharge and the third largest in terms of drainage basin area. Biweekly sampling of the lower Mississippi River at New Orleans was performed from January 2003 to August 2004. Uranium concentrations and 234U/238U activity ratios were measured for the dissolved component (<0.2 μ m-fraction) of river water. Over the course of this study, dissolved U activity ratios spanned a range of about 25%, from 1.23 to 1.60. Dissolved U concentrations ranged from 0.28 to 1.06 ppb. The relationship between concentrations, activity ratios, and lower river discharge is complicated, and no clear pattern is observed on both biweekly and seasonal timescales. However, there does seem to be a relationship between the larger seasonal trends in the lower Mississippi River and variations in the discharge of its upstream tributaries. To constrain this relationship, we have sampled water from the Missouri River, the upper Mississippi River above the confluence with the Missouri, the Ohio River, and the Arkansas River in February, April, and August of 2004. For the upstream samples measured thus far, the highest dissolved uranium concentrations are observed for the Missouri River at 2.02 ppb, while the lowest are found in the Ohio River at 0.38 ppb. Dissolved 234U/238U activity ratios are as unique for each tributary and vary from 1.36 in the Ohio River to 1.51 in the Missouri River. A preliminary mass balance analysis reveals that the lower river uranium activity ratios are controlled simply by the quantity and isotope signature of the waters discharged from the upstream tributaries. A discussion of the implications of this work for global ocean budgets of uranium will be presented.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cherdyntsev, V.V.; Kazachevskii, I.V.; Kuzmina, E.A.

The ratio of Th isotopes (Io,/sup -/UX/sub 1/, Th/sup 232/, RdTh) and U isotopes (U/sup 234/ and U/sup 238/) in natural waters, fossil bones, and soils, as well as in shells of fresh-water mollusks of the Paleolithic site Molodovo and other areas of the Dniester foreland was investigated. In the waters of Molodovo are distinguished waters of neogenic limestones with a low value of gamma =U/sup 234//U/sup 238/ = 10.3 x 10.5 and waters of the Paleozoic: gamma = 1.34, apparently feeding the quarternary stratum. The mineralization of fossil bones was realized in the Upper Paleolith by waters with lowmore » values and in the Middle Paleolith by waters with high gamma -values. Uranium migration was confirmed by the investigation of the radioelement ratios in fossil bones of the sites Molodovo I and Molodovo V. This process apparently did not affect the Mousterian layers of the site Molodovo V, so that the age of the layers, according to Io/UX/sub 1/ and gamma , equaling 130 thousand years, is near to the truth. The age of the fossil soil of the lower horizon of Molodovo I (end of Riss -RissWurm) is more than 260 thousand years. In the shells of fresh-water mollusks an intensive migration of U and Ra isotopes occurs For example, an exceptional high value RdTh/Th = 12.3 450 deg C in a 0.9 (activity units) was obtained. (auth)« less