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Sample records for 234u 232th 230th

  1. sup 234 U/ sup 238 U and sup 230 Th/ sup 234 U activity ratios in the collidal phases of aquifers in lateritic weathered zones

    SciTech Connect

    Short, S.A.; Lowson, R.T. ); Ellis, J. )

    1988-11-01

    A procedure was developed for comparing solute and colloid phases of groundwaters in contact with uranium ore bodies at Nabarlek and Koongarra in the Alligator Rivers region, Northern Territory, Australia. Single-pass ultrafiltration of large volumes with cut-offs of 18 nm and 1 {mu}m was used. Colloids were composed of Fe and Si species with sorbed U and U daughters. Uranium isotopes were mostly present as soluble species. Thorium was significantly associated with the colloids. The {sup 234}U/{sup 238}U activity ratios (ARs) were similar in solute and colloid phases close to the ore bodies but further down-gradient colloids were generally more depleted of {sup 234}U than the solute. The {sup 230}Th/{sup 234}U ARs rose from very low values for both solute and colloid phases close to the ore bodies through several orders of magnitude to much higher values further down-gradient. Colloid {sup 230}Th/{sup 234}U ARs were always significantly greater than solute ARs. Results were consistent with a systematic leaching of U from colloids going down-gradient and very little mobilization of ore body. {sup 230}Th relative to U. Ubiquitous complexes {sup 232}Th appeared to suppress the solubility of {sup 230}Th.

  2. 234U /238U and 230Th /234U activity ratios in the colloidal phases of aquifers in lateritic weathered zones

    NASA Astrophysics Data System (ADS)

    Short, Stephen A.; Lowson, Richard T.; Ellis, John

    1988-11-01

    A procedure was developed for comparing solute and colloid phases of groundwaters in contact with uranium ore bodies at Nabarlek and Koongarra in the Alligator Rivers region, Northern Territory, Australia. Single-pass ultrafiltration of large volumes with cut-offs of 18 nm and 1 μm was used. Colloids were composed of Fe and Si species with sorbed U and U daughters. Uranium isotopes were mostly present as soluble species. Thorium was significantly associated with the colloids. The 234U /238U activity ratios (ARs) were similar in solute and colloid phases close to the ore bodies but further down-gradient colloids were generally more depleted of 234U than the solute. The 230Th /234U ARs rose from very low values for both solute and colloid phases close to the ore bodies through several orders of magnitude to much higher values further down-gradient. Colloid 230Th /234U ARs were always significantly greater than solute ARs. Results were consistent with a systematic leaching of U from colloids going down-gradient and very little mobilization of ore-body 230Th relative to U. Ubiquitous complexed 232Th appeared to suppress the solubility of 230Th.

  3. Dating open systems by the 238U- 234U- 230Th method: application to Quaternary reef terraces

    NASA Astrophysics Data System (ADS)

    Villemant, B.; Feuillet, N.

    2003-05-01

    The sedimentation conditions and diagenetic processes of biogenic and inorganic carbonates are such that the assumptions of a closed system evolution and the absence of initial Th invoked in classical 238U- 234U- 230Th dating methods are very often not fulfilled for such material. This problem is of interest for all studies requiring accurate dating of corals or aragonite-rich sediments as in palaeoclimatology or neotectonics. Extending the approach of Henderson and Slowey [Nature 404 (2000) 61-66], we propose a consistent model that takes into account possible initial 230Th excess and where continuous selective redistribution (gain or loss) of 234U, 234Th and 230Th is controlled by recoil processes. This model applied to Quaternary marine terraces in Barbados, Marie Galante (Lesser Antilles arc) and Pacific islands, is able to explain the large scatter in isotopic compositions observed in the series of cogenetic corals or sediments. We show that recoil processes generally tend to increase the ( 234U/ 238U) and ( 230Th/ 234U) ratios with time, leading to an overestimation of the apparent ages calculated using classical methods. On the basis of simple assumptions (identical 'marine' initial ( 234U/ 238U) 0 and ( 230Th/ 232Th) 0 ratios), we propose a method for calculating a best estimate of the age of cogenetic series. Our model offers an alternative way to date old reef terraces where corals are almost systematically altered and where classical dating methods do not apply. It may also explain the apparent variations of the ( 234U/ 238U) seawater initial ratio estimated from corals formed in the last 300 ka and the apparent uncoupling between sea-level highstands and high-latitude Northern Hemisphere summer insolation. Our set of equations can be applied to all weathering processes where the mobility of U-series isotopes is controlled by recoil.

  4. 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.

  5. 234U /238U and 230Th /234U activity ratios in mineral phases of a lateritic weathered zone

    NASA Astrophysics Data System (ADS)

    Lowson, Richard T.; Short, Stephen A.; Davey, Brian G.; Gray, David J.

    1986-08-01

    A selective phase extraction procedure was developed for the identification of the significant phases of a typical deep soil profile sampled in the vicinity of the Ranger No. 1 uranium ore body, Alligator Rivers region, N.T., Australia. The significant phases were identified as amorphous iron oxide, crystalline iron oxide and a clay/quartz resistate. The distribution of 238U, 234U, 230Th and 226Ra between the phases was measured. The results indicated that the amorphous iron oxide phase is in adsorption/desorption equilibrium with the ground water. The crystalline iron oxide phase contains a chemical control, the kinetics of which are commensurate with or less than the half-life of 230Th (7.52 × 10 4 y). The clay/quartz resistate is enriched in 238U descendants in such a way that they are not readily accessible to the ground water.

  6. High precision {sup 230}Th and {sup 232}Th in the Norwegian Sea and Denmark by thermal ionization mass spectrometry

    SciTech Connect

    Moran, S.B.; Hoff, J.A.; Edwards, R.L.

    1995-10-01

    Seawater samples (1-2 liters) were collected from the Norwegian Sea and Denmark Strait and analyzed for {sup 230}Th and {sup 232}Th using highly sensitive thermal ionization mass spectrometry (TIMS). Depth profiles of dissolved {sup 230}Th and {sup 232}Th are characterized by surface water minima (<1 fg/kg, <5 pg/kg), subsurface maxima (12 fg/kg, 134 pg/kg), and intermediate concentrations that progressively decrease toward the bottom ({approximately}5 fg/kg, {approximately}17 pg/kg), respectively. The lack of an increase in {sup 230}Th with depth is suggested to result from the short ventilation age of Norwegian Sea Deep Water combined with enhanced scavenging near the basin margins. The {sup 230}Th maximum is attributed to advection of high {sup 230}Th in the Arctic Intermediate Water, whereas the {sup 232}Th maximum may he related to a particulate source. The low dissolved {sup 230}Th and {sup 232}Th concentrations observed in the NADW formation regions implies a minor advective export of these long-lived Th tracers to the North Atlantic. 24 refs., 1 fig., 1 tab.

  7. 230Th-234U Model-Ages of Some Uranium Standard Reference Materials

    SciTech Connect

    Williams, R W; Gaffney, A M; Kristo, M J; Hutcheon, I D

    2009-05-28

    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 assumption 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.

  8. 230Th-234U Age-Dating Uranium by Mass Spectrometry

    SciTech Connect

    Williams, R W; Gaffney, A M

    2012-04-18

    This is the standard operating procedure used by the Isotope Ratio Mass Spectrometry Group of the Chemical Sciences Division at LLNL for the preparation of a sample of uranium oxide or uranium metal for {sup 230}Th-{sup 234}U age-dating. The method described here includes the dissolution of a sample of uranium oxide or uranium metal, preparation of a secondary dilution, spiking of separate aliquots for uranium and thorium isotope dilution measurements, and purification of uranium and thorium aliquots for mass spectrometry. This SOP may be applied to uranium samples of unknown purity as in a nuclear forensic investigation, and also to well-characterized samples such as, for example, U{sub 3}O{sub 8} and U-metal certified reference materials. The sample of uranium is transferred to a quartz or PFA vial, concentrated nitric acid is added and the sample is heated on a hotplate at approximately 100 C for several hours until it dissolves. The sample solution is diluted with water to make the solution approximately 4 M HNO{sub 3} and hydrofluoric acid is added to make it 0.05 M HF. A secondary dilution of the primary uranium solution is prepared. Separate aliquots for uranium and thorium isotope dilution measurements are taken and spiked with {sup 233}U and {sup 229}Th, respectively. The spiked aliquot for uranium isotope dilution analysis is purified using EiChrom UTEVA resin. The spiked aliquot for thorium isotope dilution analysis is purified by, first, a 1.8 mL AG1x8 resin bed in 9 M HCl on which U adsorbs and Th passes through; second, adsorbing Th on a 1 mL AG1x8 resin bed in 8 M HNO{sub 3} and then eluting it with 9 M HCl followed by 0.1 M HCl + 0.005 M HF; and third, by passing the Th through a final 1.0 mL AG1x8 resin bed in 9 M HCl. The mass spectrometry is performed using the procedure 'Th and U Mass Spectrometry for {sup 230}Th-{sup 234}U Age Dating'.

  9. 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

  10. Measurements of /sup 234/U, /sup 238/U and /sup 230/Th in excreta of uranium-mill crushermen

    SciTech Connect

    Fisher, D.R.; Jackson, P.O.; Brodacynski, G.G.; Scherpelz, R.I.

    1982-07-01

    Uranium and thorium levels in excreta of uranium mill crushermen who are routinely exposed to airborne uranium ore dust were measured. The purpose was to determine whether /sup 230/Th was preferentially retained over either /sup 234/U or /sup 238/U in the body. Urine and fecal samples were obtained from fourteen active crushermen with long histories of exposure to uranium ore dust, plus four retired crushermen and three control individuals for comparison. Radiochemical procedures were used to separate out the uranium and thorium fractions, which were then electroplated on stainless steel discs and assayed by alpha spectrometry. Significantly greater activity levels of /sup 234/U and /sup 238/U were measured in both urine and fecal samples obtained from uranium mill crushermen, indicating that uranium in the inhaled ore dust was cleared from the body with a shorter biological half-time than the daughter product /sup 230/Th. The measurements also indicated that uranium and thorium separate in vivo and have distinctly different metabolic pathways and transfer rates in the body. The appropriateness of current ICRP retention and clearance parameters for /sup 230/Th in ore dust is questioned.

  11. Absolute L X-ray intensities in the decays of 230Th, 234U, 238Pu and 244Cm

    NASA Astrophysics Data System (ADS)

    Johnston, Peter N.; Burns, Peter A.

    1995-02-01

    The absolute L X-ray emission rates of 230Th, 234U, 238Pu and 244Cm have been measured. The rates were obtained by an alpha-particle gated photon spectrometry technique involving the use of a highly calibrated Ge(HP) detector in coincidence with a SiSB detector. The directional correlation between L X-rays and alpha-particles has been accounted for. The present results are compared with previous experimental values and theoretical estimates. Agreement with theoretical estimates is good, however few of the previous experimental values agree with the present work. Differences with previous work partly seem to lie with the detector calibration.

  12. 234U and 230Th determination by FIA-ICP-MS and application to uranium-series disequilibrium in marine samples.

    PubMed

    Godoy, Maria Luiza D P; Godoy, José Marcus; Kowsmann, Renato; Dos Santos, Guaciara M; Petinatti da Cruz, Rosana

    2006-01-01

    A 234U and 230Th determination method based on an extraction chromatographic separation on a flow injection system coupled to a quadruple ICP-MS was developed. Two-milliliter UTEVA (Eichrom Co.) cartridges were applied as separation tool and 236U and 229Th as spikes. Loading and washing steps were carried out in 3 M HNO3 solution and 0.05 M ammonium oxalate applied to elute both uranium and thorium. The method was applied initially to the IAEA-327 soil reference sample and NIST SRM 4357 ocean sediment reference material, with the obtained 234U and 230Th concentrations in agreement with the reference levels. Samples from a deep-sea sediment core (2450 m water depth) were analyzed and based on 230Th/234U dating, a mean sedimentation rate of 3.3 cm ky(-1) was calculated. Samples from two sediment layers were also dated by 14C-AMS and the observed ages agree with the 230Th/234U results.

  13. ESR dating of tooth enamel: comparison with {230Th }/{234U } speleothem dates at La Chaise-de-Vouthon (Charente), France

    NASA Astrophysics Data System (ADS)

    Blackwell, Bonnie; Porat, N.; Schwarcz, H. P.; Debénath, A.

    One way to assess a new dating method's reliability is by comparing its results with those from well established, independent techniques. A controlled test of the electron spin resonance (ESR) dating method as it is currently being applied to teeth was attempted for the time range 100-250 ka, beyond that of 14C, at the archaeological site of La Chaise-de-Vouthon (Charente, France). Although absent in modern enamel, a single ESR signal with g = 2.0018 in fossil tooth enamel hydroxyapatite increases in amplitude with increasing irradiation doses. ESR ages are derived from the ratio of the AD, the radiation dose needed to produce the observed ESR signal, relative to the natural, environmental dose rate (ED) experienced by the tooth after deposition. Since the age depends on the uranium (U) uptake history assumed, three ages are calculated assuming: (1) early U uptake (EU); (2) continuous (linear) uptake (LU); (3) recent uptake (RU). Generally, the LU age agrees best with known ages determined by other methods, although the RU model is better for some teeth. ESR dating assumes that the fossil has not suffered recrystallization or significant diagenetic alteration. In the preliminary test, three teeth were dated. In Bourgeois-Delaunay, a bovid molar associated with Palaeolithic artefacts was collected from layers dated at 101 ± 12 to 114 ± 7 ka by {230Th }/{234U } dating of the over- and underlying stalagmitic floors. From Suard, two Equus teeth were collected from beneath a stalagmitic floor dating 112 ± 12 ka. ESR dating teeth significantly underestimated the true age for the teeth: the mean ESR ages range from 37 to 94 ka with standard errors of 2-6 ka, and good replicability. Although more teeth at La Chaise need to be tested to ascertain that the underestimation does not result from random variation commonly seen among teeth within one unit, the consistent underestimation suggests a fault in one of the assumptions underlying the dating method. The most obvious

  14. sup 238 U- and sup 232 Th-series chronology of phonolite fractionation at Mount Erebus, Antarctica

    SciTech Connect

    Reagan, M.K. ); Volpe, A.M. ); Cashman, K.V. )

    1992-03-01

    Uranium, thorium, radium, and barium abundances and {sup 234}U/{sup 238}U and {sup 230}Th/{sup 232}Th isotopic ratios determined by thermal ionization mass spectrometry and ({sup 228}Th)/({sup 232}Th) activity ratios determined by alpha spectrometry are used to date anorthoclase growth and infer magma chamber residence times of phonolites erupted in 1984 and 1988 from Mount Erebus, Antarctica. The 1984 and 1988 glasses have slightly different ({sup 230}Th)/({sup 232}Th) ratios but both have a 10% excess of ({sup 230}Th) over ({sup 238}U) and equilibrium ({sup 228}Th) values. By comparing these data and Pb-isotopic data reported in SUN and HANSON (1975) to similar data for oceanic basalts, the duration of differentiation from basanite to phonolite is limited to less than 150,000 years. The anorthoclase separates have ({sup 230}Th)/({sup 238}U) ratios exceeding those of the associated glasses but have ({sup 230}Th)/({sup 232}Th) ratios like those of the glasses. Both glasses are depleted in {sup 226}Ra with respect to {sup 230}Th by about 25%, whereas associated anorthoclase separates have extreme excesses of {sup 226}Ra over {sup 230}Th and ({sup 228}Th)/({sup 232}Th) = 2.2. On a plot of ({sup 226}Ra)/Ba vs. ({sup 230}Th)/BA, the glass-anorthoclase pairs produce isochrons averaging 2,380 y, which represents the average age of anorthoclase growth in the shallow magma system at Erebus. The implied residence time of phonolite magmas in the shallow magma chamber system of Erebus is about 3,000 y. Final crystal growth occurred after intrusion into the convecting lava lake less than decades before eruption.

  15. Geochronology and petrogenesis of MORB from the Juan de Fuca and Gorda ridges by 238U230Th disequilibrium

    USGS Publications Warehouse

    Goldstein, S.J.; Murrell, M.T.; Janecky, D.R.; Delaney, J.R.; Clague, D.A.

    1991-01-01

    A highly precise mass spectrometric method of analysis was used to determine 238U234U230Th232Th in axial and off-axis basalt glasses from Juan de Fuca (JDF) and Gorda ridges. Initial 230Th activity excesses in the axial samples range from 3 to 38%, but generally lie within a narrow range of 12 to 15%. Secondary alteration effects were evaluated using ??234U and appear to be negligible; hence the 230Th excesses are magmatic in origin. Direct dating of MORB was accomplished by measuring the decrease in excess 230Th in off-axis samples. 238U230Th ages progressively increase with distance from axis. Uncertainties in age range from 10 to 25 ka for UTh ages of 50 to 200 ka. The full spreading rate based on UTh ages for Endeavour segment of JDF is 5.9 ?? 1/2 cm/yr, with asymmetry in spreading between the Pacific (4.0 ?? 0.6 cm/yr) and JDF (1.9 ?? 0.6 cm/yr) plates. For northern Gorda ridge, the half spreading rate for the JDF plate is found to be 3.0 ?? 0.4 cm/yr. These rates are in agreement with paleomagnetic spreading rates and topographic constraints. This suggests that assumptions used to determine ages, including constancy of initial 230Th 232Th ratio over time, are generally valid for the areas studied. Samples located near the axis of spreading are typically younger than predicted by these spreading rates, which most likely reflects recent volcanism within a 1-3 km wide zone of crustal accretion. Initial 230Th/232Th ratios and 230Th activity were also used to examine the recent Th/U evolution and extent of melting of mantle sources beneath these ridges. A negative anomaly in 230Th 232Th for Axial seamount lavas provides the first geochemical evidence of a mantle plume source for Axial seamount and the Cobb-Eickelberg seamount chain and indicates recent depletion of other JDF segment sources. Large 230Th activity excesses for lavas from northern Gorda ridge and Endeavour segment indicate formation from a lower degree of partial melting than other segments. An

  16. Remeasurement of (234)U Half-Life.

    PubMed

    Varga, Zsolt; Nicholl, Adrian; Wallenius, Maria; Mayer, Klaus

    2016-03-01

    The half-life of (234)U has been measured using a novel approach. In this method, a uranium material was chemically purified from its thorium decay product at a well-known time. The ingrowth of the (230)Th daughter product in the material was followed by measuring the accumulated (230)Th daughter product relative to its parent (234)U nuclide using inductively coupled plasma mass spectrometry. Then, the (234)U decay constant and the respective half-life could be calculated using the radioactive decay equations based on the n((230)Th)/n((234)U) amount ratio. The obtained (234)U half-life is 244 900 ± 670 years (k = 1), which is in good agreement with the previously reported results in the literature with comparable uncertainty. The main advantages of the proposed method are that it does not require the assumption of secular equilibrium between (234)U and (238)U. Moreover, the calculation is independent from the (238)U half-life value and its uncertainty. The suggested methodology can also be applied for the remeasurement of the half-lives of several other long-lived radionuclides.

  17. 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.

  18. 238U series isotopes and 232Th in carbonates and black shales from the Lesser Himalaya: implications to dissolved uranium abundances in Ganga-Indus source waters.

    PubMed

    Singh, S K; Dalai, Tarun K; Krishnaswami, S

    2003-01-01

    238U and (232)Th concentrations and the extent of (238)U-(234)U-(230)Th radioactive equilibrium have been measured in a suite of Precambrian carbonates and black shales from the Lesser Himalaya. These measurements were made to determine their abundances in these deposits, their contributions to dissolved uranium budget of the headwaters of the Ganga and the Indus in the Himalaya and to assess the impact of weathering on (238)U-(234)U-(230)Th radioactive equilibrium in them. (238)U concentrations in Precambrian carbonates range from 0.06 to 2.07 microg g(-1). The 'mean' U/Ca in these carbonates is 2.9 ng U mg(-1) Ca. This ratio, coupled with the assumption that all Ca in the Ganga-Indus headwaters is of carbonate origin and that U and Ca behave conservatively in rivers after their release from carbonates, provides an upper limit on the U contribution from these carbonates, to be a few percent of dissolved uranium in rivers. There are, however, a few streams with low uranium concentrations, for which the carbonate contribution could be much higher. These results suggest that Precambrian carbonates make only minor contributions to the uranium budget of the Ganga-Indus headwaters in the Himalaya on a basin wide scale, however, they could be important for particular streams. Similar estimates of silicate contribution to uranium budget of these rivers using U/Na in silicates and Na* (Na corrected for cyclic and halite contributions) in river waters show that silicates can contribute significantly (approximately 40% on average) to their U balance. If, however, much of the uranium in these silicates is associated with weathering resistant minerals, then the estimated silicate uranium component would be upper limits. Uranium concentration in black shales averages about 37 microg g(-1). Based on this concentration, supply of U from at least approximately 50 mg of black shales per liter of river water is needed to balance the average river water U concentration, 1.7 microg L

  19. Activity measurements of a suite of radionuclides (241Am, 239,240Pu, 238Pu, 238U, 234U, 235U, 232Th, 230Th, 228Th, 228Ra, 137Cs, 210Pb, 90Sr and 40K) in biota reference material (Ocean Shellfish): CCRI(II)-S3

    NASA Astrophysics Data System (ADS)

    Nour, S.; Karam, L. R.; Inn, K. G. W.

    2012-01-01

    In 2005, the CCRI decided that a comparison undertaken from 2002 to 2008 by the NIST (under the auspices of the Inter-America Metrology System [SIM]) in the development of a new biota (Ocean Shellfish) standard reference material (SRM) was sufficiently well constructed that it could be converted into a supplementary comparison under CCRI(II), with comparison identifier CCRI(II)-S3. This would enable the comparison to be used to support calibration and measurement capability (CMC) claims for radionuclide measurements in reference materials (specifically, animal-based organic materials). Previous comparisons of radionuclides have been of single or multiple nuclides in non-complex matrices and results of such could not be extended to support capabilities to measure the same nuclides in reference materials. The results of this comparison have been used to determine the certified reference value of the SRM. The key comparison working group (KCWG) of the CCRI(II) has approved this approach as a mechanism to link all the results to certified 'reference values' in lieu of the key comparison reference value (KCRV) of these specified radionuclides in this type of matrix (shellfish) so as to support CMCs of similar materials submitted by the present participants. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

  20. Why are so many arc magmas close to 238U- 230Th radioactive equilibrium?

    NASA Astrophysics Data System (ADS)

    Condomines, Michel; Sigmarsson, Olgeir

    1993-09-01

    New analyses of 238U- 230Th disequilibria are reported for four active volcanoes: Merapi and Krakatoa in the Sunda arc (Indonesia), Masaya in Central America (Nicaragua), and Ambrym in the New Hebrides island arc. Despite a large range in ( 230Th /232Th ) ratios (from 0.65 in Merapi andesites to 2.5 in Masaya basalts), 238U and 230Th are close to radioactive equilibrium, as in many other arc magmas. In several mantle sources, Th/U ratios have clearly been modified by metasomatic processes associated with subduction. This is demonstrated in Central America by the correlation between ( 230Th /232Th ) and 10Be /9Be ratios for several active volcanoes along the arc. It is proposed that the 238U- 230Th radioactive equilibrium found in many arc magmas is the result of disequilibrium melting involving an easily melted, slab-derived, metasomatic component which dominates the uranium and thorium budget of the mantle sources. The departure from equilibrium may be either due to mixing with 230Th enriched melts derived from unmetasomatized mantle sources or to a late stage uranium addition by fluids. This latter process, producing uranium enriched magmas, has a greater influence in uranium and thorium poor magmas.

  1. /sup 230/Th - /sup 238/U disequilibrium systematics in young volcanic rocks

    SciTech Connect

    Newman, S.

    1983-01-01

    Radioactive disequilibrium between /sup 230/Th (t/sub .5/ = 75,200 years) and its parent, /sup 238/U, has two major applications to the study of young volcanic rocks: 1) geochronology and 2) geochemical tracer studies. Geochronological investigations include both the dating of young (< approx.250,000 year-old) lavas by the internal isochron method and the study of the temporal evolution of magma systems feeding volcanoes. Older, K-Ar-dated lavas from Mauna Kea, Hawaii and Marion Island (Prince Edward hot spot) exhibit constant initial (/sup 230/Th//sup 232/Th) (activity) ratios for the past 100,000-275,000 years. At Mt. Shasta, California, a general decrease in (/sup 230/Th//sup 232/Th)/sub 0/ through time, with evidence of possible mixing corroborated by other geochemical data, is observed. Geochemical tracer studies depend on the observations that Th/U and (/sup 230/Th//sup 238/U) can be changed by such processes as partial melting, mixing, or fluid transport, whereas (/sup 230/Th//sup 232/Th) can only be modified by mixing or the passage of time. The (/sup 230/Th//sup 238/U) ratio can be used to identify possible petrogenetic processes. All lavas exhibit (/sup 230/Th//sup 238/U) greater than or equal to 1 except for some from the Aleutians and Marianas. These observations suggest that subduction-related volcanism is the only type in which U may behave as a more incompatible element than Th, although it need not (Cascades). Recent vapor transport of U or retention of Th may explain the U-enrichment in island arc lavas.

  2. Interpretation of the 231Pa/ 230Th paleocirculation proxy: New water-column measurements from the southwest Indian Ocean

    NASA Astrophysics Data System (ADS)

    Thomas, Alex L.; Henderson, Gideon M.; Robinson, Laura F.

    2006-01-01

    Measurements of 231Pa, 230Th and 232Th concentrations have been made on five water-column profiles along the western margin of the Madagascar and Mascarene Basins in the southern Indian Ocean. These measurements help to fill a significant gap in the global coverage of water-column 232Th, 230Th and 231Pa data. 232Th concentrations vary, but generally increase with depth, suggesting higher particle loading in deeper waters, and the presence of a significant dissolved fraction of 232Th. 230Th concentrations increase with depth, and profiles are similar to the average of existing data from other regions. 231Pa concentrations, on the other hand, show significant depth structure, apparently reflecting the various water masses sampled at this location. The modified remnants of North Atlantic Deep Water are found at a depth of ≈ 2000 m and exhibit elevated 231Pa concentrations exported from the South Atlantic. Antarctic Intermediate and Bottom Waters have lower 231Pa, probably due to scavenging onto opal particles during transit from the Southern Ocean. The differences between water masses raises a question: which water mass is important in controlling the 231Pa/ 230Th ratio in underlying sediments? A simple one-dimensional model is used to demonstrate that the 230Th and 231Pa exported to sea-floor sediments last equilibrates with waters close to the seafloor (within ≈ 1000 m), rather than averaging the whole water column. These findings suggest that 231Pa xs/ 230Th xs in sediments provides information primarily about deep-water masses. In this region, sedimentary records will therefore provide information about the past flow of Antarctic Bottom Water into the Indian Ocean. Interpretation of data from other regions, such as the North Atlantic where this proxy has most successfully been applied, requires careful consideration of regional oceanography and knowledge of the composition of the water masses being investigated.

  3. 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.

  4. 230Th/U dating of Last Interglacial brain corals from Bonaire (southern Caribbean) using bulk and theca wall material

    NASA Astrophysics Data System (ADS)

    Obert, J. Christina; Scholz, Denis; Felis, Thomas; Brocas, William M.; Jochum, Klaus P.; Andreae, Meinrat O.

    2016-04-01

    We compared the suitability of two skeletal materials of the Atlantic brain coral Diploria strigosa for 230Th/U-dating: the commonly used bulk material comprising all skeletal elements and the denser theca wall material. Eight fossil corals of presumably Last Interglacial age from Bonaire, southern Caribbean Sea, were investigated, and several sub-samples were dated from each coral. For four corals, both the ages and the activity ratios of the bulk material and theca wall agree within uncertainty. Three corals show significantly older ages for their bulk material than for their theca wall material as well as substantially elevated 232Th content and (230Th/238U) ratios. The bulk material samples of another coral show younger ages and lower (230Th/238U) ratios than the corresponding theca wall samples. This coral also contains a considerable amount of 232Th. The application of the available open-system models developed to account for post-depositional diagenetic effects in corals shows that none of the models can successfully be applied to the Bonaire corals. The most likely explanation for this observation is that the assumptions of the models are not fulfilled by our data set. Comparison of the theca wall and bulk material data enables us to obtain information about the open-system processes that affected the corals. The corals showing apparently older ages for their bulk material were probably affected by contamination with a secondary (detrital) phase. The most likely source of the detrital material is carbonate sand. The higher (230Th/232Th) ratio of this material implies that detrital contamination would have a much stronger impact on the ages than a contaminant with a bulk Earth (230Th/232Th) ratio and that the threshold for the commonly applied 232Th reliability criterion would be much lower than the generally used value of 1 ng g-1. The coral showing apparently younger ages for its bulk material was probably influenced by more than one diagenetic process. A

  5. Measurement of cross sections for the {sup 232}Th(P,4n){sup 229}Pa reaction at low proton energies

    SciTech Connect

    Jost, C. U.; Griswold, J. R.; Bruffey, S. H.; Mirzadeh, S.; Stracener, D. W.; Williams, C. L.

    2013-04-19

    The alpha-emitters {sup 225}Ac and {sup 213}Bi are of great interest for alpha-radioimmunotherapy which uses radioisotopes attached to cancer-seeking antibodies to efficiently treat various types of cancers. Both radioisotopes are daughters of the long-lived {sup 229}Th(t{sub 1/2} = 7880y). {sup 229}Th can be produced by proton irradiation of {sup 232}Th and {sup 230}Th, either directly or through production of isobars that beta-decay into {sup 229}Th. To obtain excitation functions, {sup 232}Th and {sup 230}Th have been irradiated at the On-Line Test Facility at the Holifield Radioactive Ion Beam Facility at ORNL. Benchmark tests conducted with Cu and Ni foils show very good agreement with literature results. The experiments with thorium targets were focused on the production of {sup 229}Pa and its daughter {sup 225}Ac from both {sup 232}Th and {sup 230}Th. Differential cross-sections for production of {sup 229}Pa and other Pa isotopes have been obtained.

  6. Vertical distributions of 230Th in mid-latitude of the Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Okubo, A.; Obata, H.; Gamo, T.; Zheng, J.

    2007-12-01

    Thorium is one of the least soluble elements in seawater: its dissolved species is considered as Th(OH)n(4-n)+ [Turner et al., 1981]. Th-232 (t1/2 = 1.4 × 10^10 years) in the oceans is almost entirely contributed by continental weathering, whereas 230Th (t1/2 = 75,200 years) is produced in situ within the water column through the decay of a parent nuclide 234U in the seawater. Vertical distributions of 230Th have been well described by reversible scavenging model in the Pacific Ocean [Nozaki et al., 1981; Bacon and Anderson, 1982; Nozaki, 1983; Nozaki and Nakanishi, 1985; Nozaki et al., 1987]. Scavenging-mixing models have been adopted in regions where horizontal advection is the dominant factor controlling 230Th distribution, such as in the Weddell Sea [Rutgers van der Loeff and Berger, 1993], the Atlantic Ocean [Vogler et al., 1998; Moran et al., 1997; 2001; 2002] and the Andaman Sea [Okubo et al., 2004]. Previous studies on thorium isotopes in seawater have elucidated scavenging processes in water columns in various oceans. Nevertheless, thorium isotope studies have not been performed sufficiently in mid-latitude of the Pacific Ocean. This study clarifies vertical distributions of thorium isotopes, especially 230Th, to study scavenging processes of thorium and trace metals in this region. We investigated the vertical distribution of thorium isotopes in mid-latitudes of the Pacific Ocean especially 230Th as a test case of scavenging of metals, and discuss the control factor of the distribution of 230Th. In comparison with previous studies in the Pacific Ocean [Nozaki et al., 1981; Nozaki and Nakanishi, 1985; Nozaki et al., 1987], the higher latitude stations show lower 230Th concentrations. This tendency corresponds to the primary productivity in surface oceans. The prominent feature is the depletion of 230Th concentrations compared with that estimated by reversible scavenging model calculations in deep water in BO-3 (30o 01'N, 160o 00'W, Depth: 5778 m) and BO-5

  7. Diagenesis of fossil coral skeletons: Correlation between trace elements, textures, and [sup 234]U/[sup 238]U

    SciTech Connect

    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 are 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.

  8. Sources of alluvium in a coastal plain stream based on radionuclide signatures from the 238U and 232Th decay series

    NASA Astrophysics Data System (ADS)

    Yeager, Kevin M.; Santschi, Peter H.; Phillips, Jonathan D.; Herbert, Bruce E.

    2002-11-01

    Discerning alluvial sources and their change over time or distance is a fundamental question in hydrology and geology, often critical in identifying impacts of human and natural perturbations on fluvial systems. Surfaces of upland interfluves and subsoils, sources of alluvium in the lower Loco Bayou basin, Texas, were distinguished using the isotope ratios 226Ra/232Th, 226Ra/230Th, and 230Th/232Th. Channel alluvium indicates a transition from interfluve surface to subsoil sources during flood (subsoil ˜34% to ˜91%, over about 8 km) and bank-full stages (subsoil ˜9% to ˜74%, over about 12 km), with distance downstream. These results indicate strong coupling between hillslope and channel processes, reflecting land use change from forested to agricultural, concentrated in lower Loco Bayou. This methodology shows that sediment sources can be differentiated based upon landscape placement where lithologic contrast is absent. The geochemistry, long half-lives, and fractionation of 238U and 232Th decay series radionuclides during pedogenic and fluvial processes in humid climates suggest that these methods are applicable in a wide variety of fluvial systems.

  9. Coulomb excitation of states in 232Th

    NASA Astrophysics Data System (ADS)

    McGowan, F. K.; Milner, W. T.

    1993-09-01

    Twenty-five states in 232Th have been observed with 18 MeV 4He ions on a thick target. Eleven 2 + states between 774 and 1554 keV and three 3 - states are populated by direct E2 and E3, respectively. The remaining states are either weakly excited by multiple Coulomb excitation and/or populated by the decay of the directly excited states. Spin assignments are based on γ-ray angular distributions. Reduced transition probabilities have been deduced from the γ-ray yields. The B(E2) values for excitation of the 2 + states range from 0.024 to 3.5 W.u. (222 W.u. for the first 2 + state). For the 3 - states, the B(E3,0 → 3 -) values are 1.7, 11, and 24 W.u. A possible two-phonon state at 1554 keV, which is nearly harmonic, decays to four members of the one-phonon states, to the ground-state band, and to the K = 0 - octupole band. The B(E2) value for excitation of this state is 0.66 ± 0.05 W.u. and the B(E1) values for decay of this state are (2 and 6)×10 -4 W.u. The B(E2) values between two- and one-phonon vibrational states range between 16 and 53 W.u. which are an order of magnitude larger than the B(E2) values between the one- and zero-phonon states. This disagrees with our present understanding of collectivity in nuclei if this 2 + state is considered to be a collective two-phonon excitation. The 2 + states at 1477 and 1387 keV, which are also nearly harmonic, are possible candidates with two-phonon structure. The agreement between the experimental results and the microscopic calculations by Neergård and Vogel of the B(E3,0 → 3) for the 3 - members of the one-phonon octupole quadruplet is satisfactory when the Coriolis coupling between the states with K and K ± 1 is included. The B(E1) branching ratios for transitions from the 3 - and 1 - states to the ground-state band have large deviations from the Alaga-rule predictions. These deviations can be understood by the strong Coriolis coupling between the states of the octupole quadruplet in deformed nuclei.

  10. 238U-230Th-226Ra disequilibria in dacite and plagioclase from the 2004-2005 eruption of Mount St. Helens: Chapter 36 in A volcano rekindled: the renewed eruption of Mount St. Helens, 2004-2006

    USGS Publications Warehouse

    Cooper, Kari M.; Donnelly, Carrie T.; Sherrod, David R.; Scott, William E.; Stauffer, Peter H.

    2008-01-01

    230Th)/(232Th) measured for the 1980s reference suite. However, (230Th)/(232Th) for plagioclase separates for dome samples erupted during October and November 2004 are significantly different from corresponding whole-rock values, which suggests that a large fraction (>30 percent) of crystals in each sample are foreign to the host liquid. Furthermore, plagioclase in the two 2004 samples have U-series characteristics distinct from each other and from plagioclase in dacite erupted in 1982, indicating that (1) the current eruption must include a component of crystals (and potentially associated magma) that were not sampled by the 1980-86 eruption, and (2) dacite magmas erupted only a month apart in 2004 contain different populations of crystals, indicating that this foreign component is highly heterogeneous within the 2004-5 magma reservoir.

  11. Investigation of Small-Scale Age Inversions in Stalagmites Using in Situ 230Th/U-Dating By Laser Ablation-MC-ICP-MS

    NASA Astrophysics Data System (ADS)

    Jochum, K. P.; Lin, Y.; Scholz, D.; Weis, U.; Stoll, B.; Andreae, M. O.

    2014-12-01

    Post-depositional U loss or addition in stalagmites lead to increasing/decreasing (230Th/238U) activity ratios and thus to older/younger 230Th/U-ages, respectively. In order to determine potential small-scale age inversions, we determined 230Th, 234U, and 238U isotope abundances in a stalagmite from the Hüttenbläserschachthöhle, western Germany, applying a high-spatial-resolution in-situ LA-MC-ICP-MS technique. This sample has the advantage that - because of its aragonitic composition - the U content is high (several µg g-1) and that large-scale age inversions have been previously detected by solution MC-ICP-MS. Due to the low intensity of 230Th (20 - 80 cps), we carefully optimized the operating parameters of the 213 nm Nd:YAG laser, such as scan speed (4 µm s-1), ablation time (1000 s), spot size (110 µm), and pulse repetition rate (20 Hz). We obtained a repeatability (RSE) of about 0.6 % - 0.9 % for 230Th/238U. The isotope ratios were corrected for instrumental biases using an external carbonate reference material (i.e., a flowstone in secular equilibrium). Including all sources of analytical uncertainty, we obtain a total age error (2 SE) of ca. 8 ka for a 215 ka old sample. Repeated dating of the same layers of the stalagmite yields a reproducibility of ca. 4 %. The LA-MC-ICPMS ages agree with the solution MC-ICP-MS ages within the analytical uncertainty. The high spatial resolution enables to detect small, but significant age inversions, which could not be detected by solution MC-ICP-MS. These inversions can be explained by diagenesis of speleothem CaCO3, which may play an important role for the alteration of speleothem ages.

  12. Discriminating assimilants and decoupling deep- vs. shallow-level crystal records at Mount Adams using 238U-230Th disequilibria and Os isotopes

    USGS Publications Warehouse

    Jicha, B.R.; Johnson, C.M.; Hildreth, W.; Beard, B.L.; Hart, G.L.; Shirey, S.B.; Singer, B.S.

    2009-01-01

    A suite of 23 basaltic to dacitic lavas erupted over the last 350??kyr from the Mount Adams volcanic field has been analyzed for U-Th isotope compositions to evaluate the roles of mantle versus crustal components during magma genesis. All of the lavas have (230Th/238U) > 1 and span a large range in (230Th/232Th) ratios, and most basalts have higher (230Th/232Th) ratios than andesites and dacites. Several of the lavas contain antecrysts (crystals of pre-existing material), yet internal U-Th mineral isochrons from six of seven lavas are indistinguishable from their eruption ages. This indicates a relatively brief period of time between crystal growth and eruption for most of the phenocrysts (olivine, clinopyroxene, plagioclase, magnetite) prior to eruption. One isochron gave a crystallization age that is ~ 20-25??ka older than its corresponding eruptive age, and is interpreted to reflect mixing of older and juvenile crystals or a protracted period of magma storage in the crust. Much of the eruptive volume since 350??ka consists of lavas that have small to moderate 230Th excesses (2-16%), which are likely inherited from melting of a garnet-bearing intraplate ("OIB-like") mantle source. Following melt generation and subsequent migration through the upper mantle, most Mt. Adams magmas interacted with young, mafic lower crust, as indicated by 187Os/188Os ratios that are substantially more radiogenic than the mantle or those expected via mixing of subducted material and the mantle wedge. Moreover, Os-Th isotope variations suggest that unusually large 230Th excesses (25-48%) and high 187Os/188Os ratios in some peripheral lavas reflect assimilation of small degree partial melts of pre-Quaternary basement that had residual garnet or Al-rich clinopyroxene. Despite the isotopic evidence for lower crustal assimilation, these processes are not generally recorded in the erupted phenocrysts, indicating that the crystal record of the deep-level 'cryptic' processes has been

  13. 230Th, 226Ra and 222Rn in abyssal sediments

    NASA Astrophysics Data System (ADS)

    Kadko, David

    1980-09-01

    A model that predicts the flux of 222Rn out of deep-sea sediment is presented. The radon is ultimately generated by 230Th which is stripped from the overlying water into the sediment. Data from many authors are compared with the model predictions. It is shown that the continental contribution of ionium is not significant, and that at low sedimentation rates, biological mixing and erosional processes strongly affect the surface concentration of the ionium. Two cores from areas of slow sediment accumulation, one from a manganese nodule region of the central Pacific and one from the Rio Grande Rise in the Atlantic were analyzed at closely spaced intervals for 230Th, 226Ra, and 210Pb. The Pacific core displayed evidence of biological mixing down to 12 cm and had a sedimentation rate of only 0.04 cm/kyr. The Atlantic core seemed to be mixed to 8 cm and had a sedimentation rate of 0.07 cm/kyr. Both cores had less total excess 230Th than predicted. Radium sediment profiles are generated from the 230Th model. Adsorbed, dissolved, and solid-phase radium is considered. According to the model, diffusional losses of radium are especially important at low sedimentation rates. Any particulate, or excess radium input is ignored in this model. The model fits the two analyzed cores if the fraction of total radium available for adsorption-desorption is about 0.5-0.7, and if K, the distribution coefficient, is about 1000. Finally, the flux of radon out of the sediments is derived from the model-generated radium profiles. It is shown that the resulting standing crop of 222Rn in the overlying water may be considered as an added constraint in budgeting 230Th and 226Ra in deep-sea sediments.

  14. Neutron Capture Cross Sections of 236U and 234U

    SciTech Connect

    Rundberg, R. S.; Bredeweg, T. A.; Bond, E. M.; Haight, R. C.; Hunt, L. F.; O'Donnell, J. M.; Schwantes, J. M.; Ullmann, J. L.; Vieira, D. J.; Wilhelmy, J. B.; Wouters, J. M.; Kronenberg, A.

    2006-03-13

    Accurate neutron capture cross sections of the actinide elements at neutron energies up to 1 MeV are needed to better interpret archived nuclear test data, for post-detonation nuclear attribution, and the Advanced Fuel Cycle Initiative. The Detector for Advance Neutron Capture Experiments, DANCE, has unique capabilities that allow the differentiation of capture gamma rays from fission gamma rays and background gamma rays from scattered neutrons captured by barium isotopes in the barium fluoride scintillators. The DANCE array has a high granularity, 160 scintillators, high efficiency, and nearly 4-{pi} solid angle. Through the use of cuts in cluster multiplicity and calorimetric energy the capture gamma-rays are differentiated from other sources of gamma rays. The preliminary results for the capture cross sections of 236U are in agreement with the ENDF/B-VI evaluation. The preliminary results for 234U lower are than ENDF/B-VI evaluation and are closer to older evaluations.

  15. Activity ratios of (234)U/(238)U and (226)Ra/(228)Ra for transport mechanisms of elevated uranium in alluvial aquifers of groundwater in south-western (SW) Punjab, India.

    PubMed

    Kumar, A; Karpe, R K; Rout, S; Gautam, Y P; Mishra, M K; Ravi, P M; Tripathi, R M

    2016-01-01

    The concentrations of total dissolved uranium (U), its isotopic composition ((234)U, (235)U, (238)U) and two long lived Ra isotopes ((226)Ra and (228)Ra) in alluvial aquifers of groundwater were determined to investigate the groundwater flow pattern in the south-western (SW) Punjab, India. Particular attention was given to the spatial variability of activity ratios (ARs) of (234)U/(238)U and (226)Ra/(228)Ra to predict the possible sources and supply process of U into the water from the solid phase. The measured groundwater (234)U/(238)U ARs were ∼1 or >1 in the shallow zone (depth < 30 m) with high U concentration and <1 in the deeper zone (depth > 30 m) with relatively low U concentration. The simultaneous elevated U concentration and (234)U/(238)U ARs in waters were possibly due to differences in imprints of rock-water interactions under hydrologic conditions. However, (234)U/(238)U ARs < 1 clearly indicate the lack of recharge from surface water to groundwater leading to (234)U deficit in groundwater. This deficit might be also attributed to alpha recoil processes under strong dissolution. Overall, the decreasing pattern of (234)U/(238)U ARs observed from SE to SW or NW ward clearly indicates a groundwater flow paths from SE to SW/NW. Similarly, (226)Ra/(238)U ARs < 1 for all water samples reflect that the precursor (238)U is fairly mobile relative to (226)Ra. This might be due to unusually high amount of (238)U in groundwaters and subsequently the different geochemistry of the two isotopes. On the other hand, (226)Ra/(228)Ra ARs in groundwaters varied widely and observed about 50-300 times higher than (238)U/(232)Th ARs in granitic rocks or soils. Such elevation in ARs might be attributed to different dissolution properties of their parents during water-rock interactions or lattice damage during decay or local enrichments of uranium in the aquifers.

  16. 230Th-U dating of surficial deposits using the ion microprobe (SHRIMP-RG): A microstratigraphic perspective

    USGS Publications Warehouse

    Maher, K.; Wooden, J.L.; Paces, J.B.; Miller, D.M.

    2007-01-01

    We used the sensitive high-resolution ion microprobe reverse-geometry (SHRIMP-RG) to date pedogenic opal using the 230Th-U system. Due to the high-spatial resolution of an ion microprobe (typically 30 ??m), regions of pure opal within a sample can be targeted and detrital material can be avoided. In addition, because the technique is non-destructive, the sample can be preserved for other types of analyses including electron microprobe or other stable isotope or trace element ion microprobe measurements. The technique is limited to material with U concentrations greater than ???50 ppm. However, the high spatial resolution, small sample requirements, and the ability to avoid detrital material make this technique a suitable technique for dating many Pleistocene deposits formed in semi-arid environments. To determine the versatility of the method, samples from several different deposits were analyzed, including silica-rich pebble coatings from pedogenic carbonate horizons, a siliceous sinter deposit, and opaline silica deposited as a spring mound. U concentrations for 30-??m-diameter spots ranged from 50 to 1000 ppm in these types of materials. The 230Th/232Th activity ratios also ranged from ???100 to 106, eliminating the need for detrital Th corrections that reduce the precision of traditional U-Th ages for many milligram- and larger-sized samples. In pedogenic material, layers of high-U opal (ca. 500 ppm) are commonly juxtaposed next to layers of calcite with much lower U concentrations (1-2 ppm). If these types of samples are not analyzed using a technique with the appropriate spatial resolution, the ages may be strongly biased towards the age of the opal. Comparison with standard TIMS (Thermal Ionization Mass Spectrometry) measurements from separate microdrilled samples suggests that although the analytical precision of the ion microprobe (SHRIMP-RG) measurements is less than TIMS, the high spatial resolution results in better accuracy in the age determination for

  17. Concentrations of (226)Ra, (232)Th and (4)(0)K in industrial kaolinized granite.

    PubMed

    Todorović, Nataša; Hansman, Jan; Mrđa, Dušan; Nikolov, Jovana; Kardos, Richárd; Krmar, Miodrag

    2017-03-01

    Activity concentrations of (226)Ra, (232)Th and (4)(0)K in 120 kaolinized granite samples imported in Serbia from the Motajica mine, Bosnia and Herzegovina, were measured. The (226)Ra concentration ranged from 61 to 319 Bq kg(-1), the (232)Th from 44 to 272 Bq kg(-1), and the (4)(0)K from 590 to 1470 Bq kg(-1). The frequency distribution of (4)(0)K concentrations was near-Gaussian, where those of (226)Ra and (232)Th were right-skewed. In 6 samples, the gamma index, I, was higher than 2, which exceeds the exemption dose criterion (0.3 mSv y(-1)). The absorbed dose rate and annual effective doses for workers in the ceramic industries in Serbia who worked with kaolinized granite were below levels of concern.

  18. (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.

  19. Dating ivory by determination of 14C, 90Sr and 228/232Th.

    PubMed

    Schmied, Stefanie A K; Brunnermeier, Matthias J; Schupfner, Robert; Wolfbeis, Otto S

    2012-09-10

    A method is described to determine the time of death of elephants. This is accomplished by analysis of the radionuclides 14C, 90Sr and 228/232Th in known samples of ivory, and in samples of unknown age. The reliability of this method is considerably increased by multi nuclide analysis.

  20. Efficacy of 230Th normalization in sediments from the Juan de Fuca Ridge, northeast Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Costa, Kassandra; McManus, Jerry

    2017-01-01

    230Th normalization is an indispensable method for reconstructing sedimentation rates and mass fluxes over time, but the validity of this approach has generated considerable debate in the paleoceanographic community. 230Th systematics have been challenged with regards to grain size bias, sediment composition (CaCO3), water column advection, and other processes. In this study, we investigate the consequences of these effects on 230Th normalization from a suite of six cores on the Juan de Fuca Ridge. The proximity of these cores (<30 km) suggests that they should receive the same particle rain rate of sediment, but the steep bathymetry of the ridge leads to substantial sediment redistribution and variable carbonate preservation, both of which may limit the usage of 230Th in this region. Despite anticipated complications, 230Th normalization effectively reconstructs nearly identical particle rain rates from all six cores, which are summarily unrelated to the total sedimentation rates as calculated from the age models. Instead the total sedimentation rates are controlled almost entirely by sediment focusing and winnowing, which are highly variable even over the short spatial scales investigated in this study. Furthermore, no feedbacks on 230Th systematics were detected as a consequence of sediment focusing, coarse fraction variability, or calcium carbonate content, supporting the robustness of the 230Th normalization technique.

  1. 230Th/U dating of a late pleistocene alluvial fan along the southern san andreas fault

    USGS Publications Warehouse

    Fletcher, K.E.K.; Sharp, W.D.; Kendrick, K.J.; Behr, W.M.; Hudnut, K.W.; Hanks, T.C.

    2010-01-01

    U-series dating of pedogenic carbonate-clast coatings provides a reliable, precise minimum age of 45.1 ?? 0.6 ka (2??) for the T2 geomorphic surface of the Biskra Palms alluvial fan, Coachella Valley, California. Concordant ages for multiple subsamples from individual carbonate coatings provide evidence that the 238U-234U-230Th system has remained closed since carbonate formation. The U-series minimum age is used to assess previously published 10Be exposure ages of cobbles and boulders. All but one cobble age and some boulder 10Be ages are younger than the U-series minimum age, indicating that surface cobbles and some boulders were partially shielded after deposition of the fan and have been subsequently exhumed by erosion of fine-grained matrix to expose them on the present fan surface. A comparison of U-series and 10Be ages indicates that the interval between final alluvial deposition on the T2 fan surface and accumulation of dateable carbonate is not well resolved at Biskra Palms; however, the "time lag" inherent to dating via U-series on pedogenic carbonate can be no larger than ~10 k.y., the uncertainty of the 10Be-derived age of the T2 fan surface. Dating of the T2 fan surface via U-series on pedogenic carbonate (minimum age, 45.1 ?? 0.6 ka) and 10Be on boulder-top samples using forward modeling (preferred age, 50 ?? 5 ka) provides broadly consistent constraints on the age of the fan surface and helps to elucidate its postdepositional development. ?? 2010 Geological Society of America.

  2. 230Th/U dating of a late Pleistocene alluvial fan along the southern San Andreas fault

    USGS Publications Warehouse

    Fletcher, Kathryn E.K.; Sharp, Warren D.; Kendrick, Katherine J.; Behr, Whitney M.; Hudnut, Kenneth W.; Hanks, Thomas C.

    2010-01-01

    U-series dating of pedogenic carbonate-clast coatings provides a reliable, precise minimum age of 45.1 ± 0.6 ka (2σ) for the T2 geomorphic surface of the Biskra Palms alluvial fan, Coachella Valley, California. Concordant ages for multiple subsamples from individual carbonate coatings provide evidence that the 238U-234U-230Th system has remained closed since carbonate formation. The U-series minimum age is used to assess previously published 10Be exposure ages of cobbles and boulders. All but one cobble age and some boulder 10Be ages are younger than the U-series minimum age, indicating that surface cobbles and some boulders were partially shielded after deposition of the fan and have been subsequently exhumed by erosion of fine-grained matrix to expose them on the present fan surface. A comparison of U-series and 10Be ages indicates that the interval between final alluvial deposition on the T2 fan surface and accumulation of dateable carbonate is not well resolved at Biskra Palms; however, the “time lag” inherent to dating via U-series on pedogenic carbonate can be no larger than ∼10 k.y., the uncertainty of the 10Be-derived age of the T2 fan surface. Dating of the T2 fan surface via U-series on pedogenic carbonate (minimum age, 45.1 ± 0.6 ka) and 10Be on boulder-top samples using forward modeling (preferred age, 50 ± 5 ka) provides broadly consistent constraints on the age of the fan surface and helps to elucidate its postdepositional development.

  3. (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.

  4. (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.

  5. Ocean mixing and ice-sheet control of seawater 234U/238U during the last deglaciation

    NASA Astrophysics Data System (ADS)

    Chen, Tianyu; Robinson, Laura F.; Beasley, Matthew P.; Claxton, Louis M.; Andersen, Morten B.; Gregoire, Lauren J.; Wadham, Jemma; Fornari, Daniel J.; Harpp, Karen S.

    2016-11-01

    Seawater 234U/238U provides global-scale information about continental weathering and is vital for marine uranium-series geochronology. Existing evidence supports an increase in 234U/238U since the last glacial period, but the timing and amplitude of its variability has been poorly constrained. Here we report two seawater 234U/238U records based on well-preserved deep-sea corals from the low-latitude Atlantic and Pacific Oceans. The Atlantic 234U/238U started to increase before major sea-level rise and overshot the modern value by 3 per mil during the early deglaciation. Deglacial 234U/238U in the Pacific converged with that in the Atlantic after the abrupt resumption of Atlantic meridional overturning. We suggest that ocean mixing and early deglacial release of excess 234U from enhanced subglacial melting of the Northern Hemisphere ice sheets have driven the observed 234U/238U evolution.

  6. [Cytogenetic effects of separate and combined action of 232Th and Cd nitrates on Allum cepa root meristem cells].

    PubMed

    Evseeva, T I; Geras'kin, S A; Khramova, E S

    2001-01-01

    Effects of separate and combined action of 232Th and Cd on Allium cepa root tip cells were investigated. It has been shown that cytogenetic effects of 232Th results mainly from its ability to induce genome damages. Cadmium in the examined concentration does not induce chromosomal vagrants, and this effect is not intensified by the combined action of 232Th and Cd (with 232Th). Cd induced increased aberrations of chromosome type frequency (1.5 times more than in control group), and fragment frequence, while mitotic index was significantly decreased. While taking into consideration the frequency of anaphase--telophase damages, and the number of aberrations per cell, the combined effects of 232Th and Cd may be considered as synergic. The aberration type ratio, frequencies of bridges and fragments, and also the level of proliferative activity of 232Th and Cd in the presence of both ions were similar with the corresponding parameters obtained when Cd acted alone. Possible mechanisms of formation of 232Th and Cd synergic effects are discussed.

  7. Study of contents of 226Ra, 232Th and 40K in fertilisers.

    PubMed

    Tahir, S N A; Alaamer, A S; Omer, R M

    2009-02-01

    In this study concentrations of naturally occurring radionuclides (226)Ra, (232)Th and (40)K were measured in the fertiliser samples in Pakistan using a high-resolution and high-purity germanium detector. Samples were collected from main fertiliser depots located in 10 big cities in the Punjab province. Gamma spectrometric analysis revealed that concentrations of (226)Ra, (232)Th and (40)K existed in the ranges from 232 to 511 Bq kg(-1), 21 to 58 Bq kg(-1) and 556 to 1302 Bq kg(-1) with average values of 386 +/- 92, 38 +/- 14 and 885 +/- 220 Bq kg(-1), respectively. Average values of the three natural radionuclides measured in this study were within the range of reported values from some of the other countries of the world. Correlations drawn between measured concentrations were not significant.

  8. Feasibility of 99Mo production by proton-induced fission of 232Th

    NASA Astrophysics Data System (ADS)

    Abbas, Kamel; Holzwarth, Uwe; Simonelli, Federica; Kozempel, Jan; Cydzik, Izabela; Bulgheroni, Antonio; Cotogno, Giulio; Apostolidis, Christos; Bruchertseifer, Frank; Morgenstern, Alfred

    2012-05-01

    The current global crisis in supply of the medical isotope generator 99Mo/99mTc has triggered much research into alternative non-reactor based production methods for 99Mo including innovative radionuclide production techniques using ion accelerators. A novel method is presented here that has thus far not been considered: 232Th is used as target material to produce carrier-free 99Mo for 99Mo/99mTc generators by proton-induced fission (232Th (p, f) 99Mo). The thick target yields of 99Mo are estimated as 3.6 MBq/μA·h and 21 MBq/μA·h for proton energies of 22 MeV and 40 MeV, respectively, energies that are available from many cyclotrons. With respect to 99Mo reactor based methods using uranium targets, the presented concept using 232Th does not pose proliferation concerns, transport of highly radioactive target materials can be reduced and unused cyclotron capacities could be exploited. Radiochemical target processing could be based on existing technologies of extraction of 99Mo from reactor irradiated 235U. The presented method could be used for co-production of other radioisotopes of medical interest such as 131I.

  9. Ultra Sensitive Neutron Activation Measurements of {sup 232}Th in Copper

    SciTech Connect

    Clemenza, M.; Previtali, E.; Borio di Tigliole, A.; Salvini, A.

    2011-04-27

    Copper, thanks to its low content in radioactive contaminations, is a material widely used for shielding, holders and other objects close to the sensitive parts of the detectors in many experiments in rare event physics. This implies that tools able to reach sensitivity of the order of <10{sup -12} gram of contaminants per gram of copper are of crucial importance. A methodology based in Neutron Activation Analysis (NAA) has been developed to obtain an extremely high sensitivity in the analysis of {sup 232}Th in copper samples. A detection limit of 5x10{sup -13} g {sup 232}Th/g Cu has been achieved through the irradiation of 200 g of copper sample which subsequently was radio-chemically concentrated using nitric acid and then actinide resin from Eichrom Inc. Several elutions were performed with various inorganic acids to concentrate the {sup 232}Th activation product ({sup 233}Pa) from the copper matrix and to also eliminate the radioactive background induced by the neutron bombardment to reach higher sensitivity.

  10. Measurement of (233)U/(234)U ratios in contaminated groundwater using alpha spectrometry.

    PubMed

    Harrison, Jennifer J; Payne, Timothy E; Wilsher, Kerry L; Thiruvoth, Sangeeth; Child, David P; Johansen, Mathew P; Hotchkis, Michael A C

    2016-01-01

    The uranium isotope (233)U is not usually observed in alpha spectra from environmental samples due to its low natural and fallout abundance. It may be present in samples from sites in the vicinity of nuclear operations such as reactors or fuel reprocessing facilities, radioactive waste disposal sites or sites affected by clandestine nuclear operations. On an alpha spectrum, the two most abundant alpha emissions of (233)U (4.784 MeV, 13.2%; and 4.824 MeV, 84.3%) will overlap with the (234)U doublet peak (4.722 MeV, 28.4%; and 4.775 MeV, 71.4%), if present, resulting in a combined (233+234)U multiplet. A technique for quantifying both (233)U and (234)U from alpha spectra was investigated. A series of groundwater samples were measured both by accelerator mass spectrometry (AMS) to determine (233)U/(234)U atom and activity ratios and by alpha spectrometry in order to establish a reliable (233)U estimation technique using alpha spectra. The Genie™ 2000 Alpha Analysis and Interactive Peak Fitting (IPF) software packages were used and it was found that IPF with identification of three peaks ((234)U minor, combined (234)U major and (233)U minor, and (233)U major) followed by interference correction on the combined peak and a weighted average activity calculation gave satisfactory agreement with the AMS data across the (233)U/(234)U activity ratio range (0.1-20) and (233)U activity range (2-300 mBq) investigated. Correlation between the AMS (233)U and alpha spectrometry (233)U was r(2) = 0.996 (n = 10).

  11. 231Pa/ 230Th as a Paleocirculation Proxy in the Southern Hemisphere

    NASA Astrophysics Data System (ADS)

    Henderson, G. M.; Hickey, B. J.; Rae, J. W.; Thomas, A. L.

    2008-12-01

    Since its first application as a proxy for the rate of past ocean circulation more than a decade ago (Yu et al. 1996), 231Pa/ 230Th has been applied predominantly to cores in the North Atlantic. At present, in this setting, the advection of surface waters to depth resets the 231Pa/ 230Th "clock" allowing the proxy to work, and the uniform southward movement of water masses make interpretation of sediment values relatively straightforward. The applicability of 231Pa/ 230Th in other settings, where water-masses may not be clearly reset, or where several water masses with different flow paths overlie one another remains unclear, but its use to reconstruct past flow rates in such settings would provide a powerful tool to understand past climate. We will present an overview of the potential for 231Pa/ 230Th use in the Southern Hemisphere, including new data from the Argentine basin. Data from the southern Indian Ocean (e.g. Thomas et al. 2007) demonstrate that advection of water to depth, and scavenging of 231Pa at the opal belt, effectively reset the 231Pa/ 230Th clock providing potential for application of the proxy to northward flowing water masses in the Southern Hemisphere. Modelling also indicates the sensitivity of Southern Hemisphere sediment 231Pa/ 230Th to changes in ocean circulation, particularly in the Argentine Basin (Siddall et al. 2007). We have investigated the use of the 231Pa/ 230Th proxy in four cores spanning all deep-water masses in that basin. The modern-day conditions in that basin are similar to those expected in the North Atlantic during the last glacial maximum with a southward and northward flowing water mass overlying one another. Results demonstrate that sediment 231Pa/ 230Th values vary significantly with water-mass throughout the last 20 kyr - offering the potential to reconstruct multiple water masses through time. Down-core results show variations that reflect changes in ocean circulation, but these are compounded with other effects

  12. Thorium-230 dating of natural waters at the Nevada Test Site

    SciTech Connect

    Bakhtiar, S.N.

    1990-01-01

    Radiocarbon determinations have been used in the past to estimate the ages of groundwater from the Paleozoic aquifer underlying the Nevada Test Site and adjacent areas. We measured the concentrations of {sup 230}Th, {sup 232}Th, {sup 234}U and {sup 238}U in several water samples taken from the wells and spring at the Nevada Test Site and calculated the {sup 230}Th ages. 2 refs.

  13. Studies of positron electron pair production in {sup 238}U + {sup 232}Th

    SciTech Connect

    Ahmad, I.; Back, B.B.; Betts, R.R.

    1995-08-01

    Following the non-observation of sharp sum-energy lines in our earlier {sup 238}U + {sup 181}Ta measurements, it was decided to pursue measurements of the {sup 238}U + {sup 232}Th system which, in the previously published work, showed the most striking evidence for near-equal-energy back-to-back pairs leading to sharp sum-energy lines. Following the refurbishing of the APEX silicon arrays and extensive tests of the rotating target wheel assembly, a major positron run took place in November 1994. Rolled 1-mg/cm{sub 2} {sup 232}Th targets were bombarded with 5.95-MeV/u {sup 238}U. The target rotation allowed up to 2 pnA of beam to be used without serious deterioration of the targets. Over 300,000 pairs were accumulated, representing an order-of-magnitude improvement in statistics over the previously published results. Preliminary analysis shows no evidence for the sharp lines at a cross section level orders of magnitude below those previously reported. The analysis of these data is currently being completed in preparation for publication.

  14. The low-energy dipole structure of 232Th , 236U and 238U actinide nuclei

    NASA Astrophysics Data System (ADS)

    Kuliev, A. A.; Guliyev, E.; Ertugral, F.; Özkan, S.

    2010-03-01

    In this study, ensuremath I^{π} = 1+ and ensuremath I^{π} = 1- dipole mode excitations are systematically investigated within the rotational and translational + Galilean invariant quasiparticle random-phase approximation for 232Th , 236U , and 238U actinide nuclei. It is shown that the investigated nuclei reach a B( M1) strength structure, which corresponds to the scissors mode. The calculated mean excitation energies as well as the summed B( M1) value of the scissors mode excitations are consistent with the available experimental data. The results of calculations indicate large differences to the rare-earth nuclei as is the case for the experiment: a doubling of the observed dipole strengths and a shift of the energy centroid to the lower energies by about 800keV. The calculations indicate the presence of a few prominent negative-parity ensuremath K^{π} = 1- states in the 2.0-4.0MeV energy interval. The occurrence of the negative-parity dipole states with the rather high B( E1) value less than 4MeV shows the necessity of explicit parity measurements for the correct determination of the scissors mode strength in 232Th , 236U , and 238U isotopes.

  15. 232Th(n,{gamma})233Th Thermal Reaction Cross-Section Measurement

    SciTech Connect

    Maidana, Nora L.; Vanin, Vito R.; Pascholati, Paulo R.; Helene, Otaviano; Castro, Ruy M.; Dias, Mauro S.; Koskinas, Marina F.

    2005-05-24

    The 232Th(n,{gamma})233Th thermal neutron-capture reaction cross section was measured using targets of {approx} 1.5 mg of high-purity metallic thorium irradiated in the IPEN IEA-R1m 5 MW pool research reactor. The 197Au(n,{gamma})198Au reaction was used to monitor the thermal and epithermal neutron fluxes in the irradiation position, which was found using the Westcott formalism. The residual gamma-ray activity was followed with an HPGe detector. The detector efficiency curve was fitted by the least-squares method applying covariance analysis to all uncertainties involved. The experimental result is {sigma}0 =7.20{+-}0.20 b, in agreement with previous published values.

  16. Systematics of the mean energy and the mean multiplicity of prompt neutrons originating from {sup 232}Th fission

    SciTech Connect

    Svirin, M. I.

    2012-12-15

    The cross section for the neutron-induced fission of {sup 232}Th target nuclei, {sigma}{sub f} (E{sub n}), was described within statistical theory. The spectra of the mean multiplicity, v-bar (E{sub n}), and the mean energy, E-bar(E{sub n}), of secondary neutrons accompanying {sup 232}Th fission induced by neutrons of energy extending up to E{sub n} = 20 MeV were analyzed on the basis of the chance structure of the cross section.

  17. 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

    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. As a result, these model ages are concordant with to slightly older than the known production age of NBL U050.

  18. 231Pa/230Th records of Arctic/Atlantic interchange in Fram Strait

    NASA Astrophysics Data System (ADS)

    Hoffmann, S. S.; McDermott, K. J.; McManus, J. F.; Mukasa, S. B.

    2014-12-01

    Fram Strait, the Arctic Ocean's only deep passage for exchange with lower latitude oceans, today serves as a conduit for waters flowing north into the Arctic Ocean and south into the Atlantic. Reconstruction of circulation patterns and strength at depth in the strait can help to clarify the history of Arctic/Atlantic deep water exchange and Arctic contributions to global meridional overturning circulation. We will present new sedimentary measurements of radioisotopes 231Pa and 230Th to provide information on this exchange in the past and its relationship to sedimentation and climatic events. Coretop and downcore 231Pa/230Th ratios from Arctic sediments indicate that 231Pa has been exported from the central Arctic basin throughout the Holocene and deglaciation. Fram Strait represents a possible sink for this "missing" 231Pa. Preliminary results from ODP Holes 908A and 909A, at 1274 m and 2519 m water depths respectively in the central strait, suggest that ratios in this region during the Holocene have varied between ~0.106 (above the 231Pa/230Th production ratio of 0.093 in seawater, indicating net import of 231Pa)and ~0.055 (well below the production ratio, indicating net export of 231Pa). Further measurements in cores from the Greenland and Svalbard continental slopes will give a fuller regional picture of 231Pa deposition and transport across the strait.

  19. New evaluation of the{sup 232}Th resonance parameters in the energy range

    SciTech Connect

    Derrien, H.; Leal, L. C.; Larson, N. M.

    2006-07-01

    Neutron resonance parameters of {sup 232}Th were obtained from a Reich-Moore SAMMY analysis of high-resolution neutron transmission measurements performed at the Oak Ridge Linear Accelerator (ORELA) by Olsen et al. in 1981 and of high-resolution neutron capture measurements performed recently at the Geel Linear Accelerator (GELINA (Belgium)) by Schillebeeckx et al. and at n-TOF (CERN (Switzerland)) by Aerts et al. The ORELA data were analyzed previously by Olsen using the Breit-Wigner multilevel code SIOB, and their results were used for the ENDF/B-VI evaluation. In our new analysis of the Olsen neutron transmissions using the modern computer code SAMMY, better accuracy is obtained for the resonance parameters by including recent experimental neutron capture data in the experimental data base. The experimental data base and the method of analysis are described in the report. Neutron transmissions and capture cross sections calculated with the resonance parameters are compared to the experimental values. A description is given of the statistical properties of the resonance parameters. The new evaluation produces a decrease in the capture resonance integral, and improves the prediction of integral thermal benchmarks. (authors)

  20. Retardation of 238U and 232Th decay chain radionuclides in Long Island and Connecticut aquifers

    NASA Astrophysics Data System (ADS)

    Copenhaver, Sally A.; Krishnaswami, S.; Turekian, Karl K.; Epler, Nathan; Cochran, J. K.

    1993-02-01

    Knowledge of the ability of an aquifer to retard the groundwater transport of toxic or radioactive ions can be inferred from the analysis of groundwater for the radionuclides of the 238U- and 232Th-decay chains. Groundwaters of varying chemical composition were analyzed from wells in Long Island, New York, and Connecticut. Aquifer lithologies are arkose, quartz sandstone, granite, and glacial drift. Adsorption ( k1) and desorption ( k2) coefficients for Ra and Pb were calculated using 222Rn activity as a measure of the supply of other α-recoil nuclides. Laboratory tests of the validity of this assumption were made by measuring the flux of 224Ra and 222Rn from aquifer solids. The ratio k 1/k 2 is the distribution coefficient, K, which is effectively equal to R ƒ, the retardation factor. The average value of K for Ra is 6 × 10 2 in Long Island aquifers and 5 × 10 4 in Connecticut. The distribution coefficient for Pb is 10 4 in Long Island and 10 5 in Connecticut. Results from this and other studies reveal a strong dependence of retardation on pH, ƒ O 2, and ionic strength that tends to overwhelm any dependence of retardation on lithology.

  1. Mass distribution and mass resolved angular distribution of fission products in 28Si+232Th

    NASA Astrophysics Data System (ADS)

    Sodaye, Suparna; Tripathi, R.; John, B. V.; Ramachandran, K.; Pujari, P. K.

    2017-01-01

    Background: Fission process with heavier projectiles and actinide targets has contributions from processes, such as compound nucleus fission, transfer-induced fission, and noncompound nucleus fission. Mass distribution and mass-dependent anisotropy can be used to identify and delineate the contributions due to these different processes. Purpose: Mass distribution in 28Si+232Th has been studied at beam energies of 180 and 158 MeV to investigate the nature of mass distribution arising from complete and incomplete momentum-transfer fission events. Mass-dependent angular anisotropy has been measured at 166 MeV to investigate the dominant noncompound nucleus process contributing to the fission. Method: Mass distribution and mass resolved angular distribution of fission products were measured by the recoil catcher method followed by off-line γ -ray spectrometry. Results: Mass distributions for full momentum-transfer fission processes were found to be symmetric, and those for transfer-induced fission were found to be asymmetric at both beam energies. The relative contribution from transfer-induced fission was found to be higher at lower beam energy. The anisotropy of the fission product angular distribution was found to increase with decreasing mass asymmetry. Conclusions: The mass distribution indicates that, apart from the full momentum-transfer fission process, there is a significant contribution due to transfer-induced fission. The mass dependence of angular anisotropy indicated that preequilibrium fission is the dominant noncompound nucleus process in the present reaction system at near barrier energy (Ec .m ./VC=1.06 ) .

  2. Study of 234U(n,f) Resonances Measured at the CERN n_TOF Facility

    NASA Astrophysics Data System (ADS)

    Leal-Cidoncha, E.; Durán, I.; Paradela, C.; Tarrío, D.; Leong, L. S.; Audouin, L.; Tassan-Got, L.; Praena, J.; Berthier, B.; Ferrant, L.; Isaev, S.; Le Naour, C.; Stephan, C.; Trubert, D.; Abbondanno, U.; Aerts, G.; Álvarez, H.; Álvarez-Velarde, F.; Andriamonje, S.; Andrzejewski, J.; Badurek, G.; Baumann, P.; Bečvář, F.; Berthoumieux, E.; Calviño, F.; Calviani, M.; Cano-Ott, D.; Capote, R.; Carrapiço, C.; Cennini, P.; Chepel, V.; Chiaveri, E.; Colonna, N.; Cortes, G.; Couture, A.; Cox, J.; Dahlfors, M.; David, S.; Dillmann, I.; Domingo-Pardo, C.; Dridi, W.; Eleftheriadis, C.; Embid-Segura, M.; Ferrari, A.; Ferreira-Marques, R.; Fujii, K.; Furman, W.; Gonçalves, I.; González-Romero, E.; Gramegna, F.; Guerrero, C.; Gunsing, F.; Haas, B.; Haight, R.; Heil, M.; Herrera-Martinez, A.; Igashira, M.; Jericha, E.; Kadi, Y.; Käppeler, F.; Karadimos, D.; Kerveno, M.; Koehler, P.; Kossionides, E.; Krtička, M.; Lampoudis, C.; Leeb, H.; Lindote, A.; Lopes, I.; Lozano, M.; Lukic, S.; Marganiec, J.; Marrone, S.; Martínez, T.; Massimi, C.; Mastinu, P.; Mengoni, A.; Milazzo, P. M.; Moreau, C.; Mosconi, M.; Neves, F.; Oberhummer, H.; O'Brien, S.; Oshima, M.; Pancin, J.; Papadopoulos, C.; Pavlik, A.; Pavlopoulos, P.; Perrot, L.; Pigni, M. T.; Plag, R.; Plompen, A.; Plukis, A.; Poch, A.; Pretel, C.; Quesada, J.; Rauscher, T.; Reifarth, R.; Rubbia, C.; Rudolf, G.; Rullhusen, P.; Salgado, J.; Santos, C.; Sarchiapone, L.; Savvidis, I.; Tagliente, G.; Tain, J. L.; Tavora, L.; Terlizzi, R.; Vannini, G.; Vaz, P.; Ventura, A.; Villamarin, D.; Vincente, M. C.; Vlachoudis, V.; Vlastou, R.; Voss, F.; Walter, S.; Wiescher, M.; Wisshak, K.

    2014-05-01

    We present the analysis of the resolved resonance region for the 234U(n,f) cross section data measured at the CERN n_TOF facility. The resonance parameters in the energy range from 1 eV to 1500 eV have been obtained with the SAMMY code by using as initial parameters for the fit the resonance parameters of the JENDL-3.3 evaluation. In addition, the statistical analysis has been accomplished, partly with the SAMDIST code, in order to study the level spacing and the Mehta-Dyson correlation.

  3. Study of 232Th(n, γ) and 232Th(n,f) reaction rates in a graphite moderated spallation neutron field produced by 1.6 GeV deuterons on lead target

    NASA Astrophysics Data System (ADS)

    Asquith, N. L.; Hashemi-Nezhad, S. R.; Westmeier, W.; Zhuk, I.; Tyutyunnikov, S.; Adam, J.

    2015-02-01

    The Gamma-3 assembly of the Joint Institute for Nuclear Research (JINR), Dubna, Russia is designed to emulate the neutron spectrum of a thermal Accelerator Driven System (ADS). It consists of a lead spallation target surrounded by reactor grade graphite. The target was irradiated with 1.6 GeV deuterons from the Nuclotron accelerator and the neutron capture and fission rate of 232Th in several locations within the assembly were experimentally measured. 232Th is a proposed fuel for envisaged Accelerator Driven Systems and these two reactions are fundamental to the performance and feasibility of 232Th in an ADS. The irradiation of the Gamma-3 assembly was also simulated using MCNPX 2.7 with the INCL4 intra-nuclear cascade and ABLA fission/evaporation models. Good agreement between the experimentally measured and calculated reaction rates was found. This serves as a good validation for the computational models and cross section data used to simulate neutron production and transport of spallation neutrons within a thermal ADS.

  4. Covariance data for{sup 232}Th in the resolved resonance region from 0 to 4 keV

    SciTech Connect

    Leal, L. C.; Derrien, H.; Arbanas, G.; Larson, N. M.; Wiarda, D.

    2006-07-01

    This paper reports on the generation and testing of the covariance matrix associated with the resonance parameter evaluation for {sup 232}Th up to 4 keV. [1] Covariance data are required to correctly assess uncertainties in design parameters in nuclear applications. The error estimation of calculated quantities relies on the nuclear data uncertainty information available in the basic nuclear data libraries, such as the US Evaluated Nuclear Data Library, ENDF/B. Uncertainty files in the ENDF/B library are obtained from analysis of experimental data and are stored as variance and covariance data. In this paper, we address the generation of covariance data in the resonance region via the computer code SAMMY, which is used in the evaluation of experimental data in the resolved and unresolved resonance energy regions. The resolved resonance parameter covariance matrix for {sup 232}Th, obtained using the retroactive approach, is also presented here. (authors)

  5. The Concentrations of {sup 40}K, {sup 226}Ra and {sup 232}Th in Soil Sample in Osmaniye (Turkey)

    SciTech Connect

    Akkurt, I.; Guenoglu, K.; Kara, A.; Mavi, B.; Karaboerklue, S.

    2011-12-26

    The {sup 40}K, {sup 226}Ra and {sup 232}Th concentration is due to the magmatic structure of the earth and it can be varied from place to place. Osmaniye is located in the Eastern side of Mediteranean Region. It holds the climatic characteristics of the same region and arises with Middle Taurus Mountains from west to North and with Amonos Mounations in East and West-east parts and is situated between 35 deg. .52'-36 deg. .42' east longitudes and 36 deg. .57'-37 deg. .45' north latitudes. In this study, the natural radioactivity concentrations {sup 40}K, {sup 226}Ra and {sup 232}Th in some soil samples collected in Osmaniye have been investigated. The measurements have been performed using 3x3{sup ''} NaI(Tl) detector system.

  6. Radionuclide ((226)Ra, (232)Th, (40)K) accumulation among plant species in mangrove ecosystems of Pattani Bay, Thailand.

    PubMed

    Kaewtubtim, Pungtip; Meeinkuirt, Weeradej; Seepom, Sumalee; Pichtel, John

    2017-02-15

    Little is known regarding phytoremediation of radionuclides from soil; even less is known about radionuclide contamination and removal in tropical ecosystems such as mangrove forests. In mangrove forests in Pattani Bay, Thailand, 18 plant species from 17 genera were evaluated for radionuclide concentrations within selected plant parts. Two shrub species, Avicennia marina and Pluchea indica, accumulated the highest (232)Th (24.6Bqkg(-1)) and (40)K (220.7Bqkg(-1)) activity concentrations in roots, respectively. Furthermore, the aquatic species Typha angustifolia accumulated highest (232)Th, (40)K and (226)Ra activity concentrations (85.2, 363.5, 16.6Bqkg(-1), respectively) with the highest transfer factors (TFs) (3.0, 2.0, 5.9, respectively) in leaves. Leaves of T. angustifolia had an absorbed dose rate in air (D) over the recommended value (74.8nGyh(-1)) that was considered sufficiently high to be of concern for human consumption.

  7. Quasi-elastic scattering and transfer angular distribution for B,1110+232Th systems at near-barrier energies

    NASA Astrophysics Data System (ADS)

    Dubey, Shradha; Biswas, D. C.; Mukherjee, S.; Patel, D.; Gupta, Y. K.; Prajapati, G. K.; Joshi, B. N.; Danu, L. S.; Mukhopadhyay, S.; John, B. V.; Suryanarayana, S. V.; Vind, R. P.

    2016-12-01

    Quasi-elastic scattering and transfer angular distributions for B,1110+232Th reactions have been measured simultaneously in a wide range of bombarding energies around the Coulomb barrier. The quasi-elastic angular distribution data are analyzed using the optical model code ecis with phenomenological Woods-Saxon potentials. The obtained potential parameters suggest the presence of usual threshold anomaly, confirming tightly bound characteristics for both the projectiles. The reaction cross sections are obtained from the fitting of quasi-elastic angular distribution data. The reduced cross sections at sub-barrier energies compared with Li,76+232Th systems show a systematic dependence on projectile breakup energy. The angular distribution of the transfer products show similar behavior for both the systems.

  8. Interpreting 231Pa/230Th observations and changes in ocean circulation

    NASA Astrophysics Data System (ADS)

    Tretkoff, Ernie

    2011-05-01

    Understanding past changes in ocean circulation is important, because the ocean transports heat and changes in ocean circulation can affect climate. To better understand past ocean circulation changes, some researchers have used the ratio of two isotopes, protactinium-231 (231Pa) and thorium-230 (230Th), in sediments as a proxy to infer changes in the Atlantic meridional overturning circulation (AMOC). Some studies have suggested that AMOC during the climate fluctuations of the Last Glacial Maximum (LGM; ˜21,000-18,000 years ago) and Heinrich Event 1 (H1; ˜17,000-15,000 years ago) was different from modern AMOC.

  9. Development of a method for activity measurements of 232Th daughters with a multidetector gamma-ray coincidence spectrometer.

    PubMed

    Antovic, N; Svrkota, N

    2009-06-01

    The method for activity measurements of the (232)Th daughters, developed at the six-crystal gamma-ray coincidence spectrometer PRIPYAT-2M and based on coincidence counting of the 583 and 2615 keV photons from cascade transitions which follow beta(-)-decay of (208)Tl, as well as on counting the 911 keV photons which follow beta(-)-decay of (228)Ac in the integral and non-coincidence mode of counting, is presented.

  10. Solubility assessment of 232Th from various types of soil in Malaysia using USP and DIN In Vitro digestion method

    NASA Astrophysics Data System (ADS)

    Rashid, Nur Shahidah Abdul; Perama, Yasmin Mohd Idris; Salih, Fitri Hakeem Mohd; Sarmani, Sukiman; Majid, Amran Ab.; Siong, Khoo Kok

    2016-11-01

    The overall results of the study showed that the concentrations of 232Th radionuclide using DIN digestion method during gastric phase are 0.0015 mg/kg - 0.0554 mg/kg and 0.0015 mg/kg - 0.0139 mg/kg during intestinal phase, respectively. As for USP digestion method during gastric phase are between 0.0877 mg/kg - 0.4964 mg/kg and 0.0207 mg/kg - 0.2291 mg/kg. The results from the measurements in various types of soils indicates some elevation of 232Th concentration in some types of soil compared to UNSCEAR reference values, in which may be a result from the impact of previous mining activity in the surrounding area and considered to be safe. In general, the results of 232Th concentrations from in vitro extraction technique is considered to be safe. By natural processes, thorium ingestion is getting transferred to living beings through different pathways and need to be monitored in order to assess possible hazards. Environmental studies are generally carried out to trace the pathway of radionuclides/radiotoxic elements to reach living organism. Environmental monitoring and meaningful interpretation of data from man-made pollution are more complicated without adequate knowledge about the natural abundance of radioactive elements in the environment.

  11. [About the contents of 40K, 226Ra and 232Th in forest soils of the Republic of Belarus].

    PubMed

    Perevolotskiĭ, A N; Perevolotskaia, T V

    2014-01-01

    The specific activity of 40K, 232Th and 226Ra in forest soil ecotopes (A2-B2-C2-D2) has been investigated. When the fertility of the soil increases from A2 to D2, then the specific activity of 40K increases in the rooting zone of the soil from 275 ± 6.9 up to 499 ± 11 Bq/kg, 232Th--from 11.8 ± 0.5 to 17.1 ± 1.1 Bq/kg, 226Ra- from 19.2 γ 0.8 to 27.9 ± 1.5 Bq/kg. The calculated capacity of the absorbed dose of γ-radiation conditioned by 40K, 232Th and 226Ra increases from A2 to D2 from 27.5 ± 0.5 to 44.1 ± 1.1 nGy / h at the height of 1 m.

  12. Minimum speed limit for ocean ridge magmatism from 210Pb-226Ra-230Th disequilibria.

    PubMed

    Rubin, K H; van der Zander, I; Smith, M C; Bergmanis, E C

    2005-09-22

    Although 70 per cent of global crustal magmatism occurs at mid-ocean ridges-where the heat budget controls crustal structure, hydrothermal activity and a vibrant biosphere-the tempo of magmatic inputs in these regions remains poorly understood. Such timescales can be assessed, however, with natural radioactive-decay-chain nuclides, because chemical disruption to secular equilibrium systems initiates parent-daughter disequilibria, which re-equilibrate by the shorter half-life in a pair. Here we use 210Pb-226Ra-230Th radioactive disequilibria and other geochemical attributes in oceanic basalts less than 20 years old to infer that melts of the Earth's mantle can be transported, accumulated and erupted in a few decades. This implies that magmatic conditions can fluctuate rapidly at ridge volcanoes. 210Pb deficits of up to 15 per cent relative to 226Ra occur in normal mid-ocean ridge basalts, with the largest deficits in the most magnesium-rich lavas. The 22-year half-life of 210Pb requires very recent fractionation of these two uranium-series nuclides. Relationships between 210Pb-deficits, (226Ra/230Th) activity ratios and compatible trace-element ratios preclude crustal-magma differentiation or daughter-isotope degassing as the main causes for the signal. A mantle-melting model can simulate observed disequilibria but preservation requires a subsequent mechanism to transport melt rapidly. The likelihood of magmatic disequilibria occurring before melt enters shallow crustal magma bodies also limits differentiation and heat replenishment timescales to decades at the localities studied.

  13. 230Th/U ages Supporting Hanford Site-Wide Probabilistic Seismic Hazard Analysis

    SciTech Connect

    Paces, James B.

    2014-08-31

    This product represents a USGS Administrative Report that discusses samples and methods used to conduct uranium-series isotope analyses and resulting ages and initial 234U/238U activity ratios of pedogenic cements developed in several different surfaces in the Hanford area middle to late Pleistocene. Samples were collected and dated to provide calibration of soil development in surface deposits that are being used in the Hanford Site-Wide probabilistic seismic hazard analysis conducted by AMEC. The report includes description of sample locations and physical characteristics, sample preparation, chemical processing and mass spectrometry, analytical results, and calculated ages for individual sites. Ages of innermost rinds on a number of samples from five sites in eastern Washington are consistent with a range of minimum depositional ages from 17 ka for cataclysmic flood deposits to greater than 500 ka for alluvium at several sites.

  14. 230Th/U ages Supporting Hanford Site‐Wide Probabilistic Seismic Hazard Analysis

    USGS Publications Warehouse

    Paces, James B.

    2014-01-01

    This product represents a USGS Administrative Report that discusses samples and methods used to conduct uranium-series isotope analyses and resulting ages and initial 234U/238U activity ratios of pedogenic cements developed in several different surfaces in the Hanford area middle to late Pleistocene. Samples were collected and dated to provide calibration of soil development in surface deposits that are being used in the Hanford Site-Wide probabilistic seismic hazard analysis conducted by AMEC. The report includes description of sample locations and physical characteristics, sample preparation, chemical processing and mass spectrometry, analytical results, and calculated ages for individual sites. Ages of innermost rinds on a number of samples from five sites in eastern Washington are consistent with a range of minimum depositional ages from 17 ka for cataclysmic flood deposits to greater than 500 ka for alluvium at several sites.

  15. Measurement and modeling of the cross sections for the reaction 230Th(3He,3n)230U

    NASA Astrophysics Data System (ADS)

    Morgenstern, A.; Abbas, K.; Simonelli, F.; Capote, R.; Sin, M.; Zielinska, B.; Bruchertseifer, F.; Apostolidis, C.

    2013-06-01

    230U and its daughter nuclide 226Th are promising therapeutic nuclides for application in targeted α therapy of cancer. We investigated the feasibility of producing 230U/226Th via irradiation of 230Th with 3He particles according to the reaction 230Th(3He,3n)230U. The experimental excitation function for this reaction is reported here. Cross sections were measured by using thin targets of 230Th prepared by electrodeposition, and 230U yields were analyzed by using α spectrometry. Beam intensities were obtained via monitor reactions on aluminum foils by using high-resolution γ spectrometry and International Atomic Energy Agency recommended cross sections. Incident particle energies were calculated by using the srim-2003 code. The experimental cross sections for the reaction 230Th(3He,3n)230U are in good agreement with model calculations by the empire-3 code once breakup and transfer reactions are properly considered in the incident channel. The obtained cross sections are too low to allow for the production of 230U/226Th in clinically relevant levels.

  16. Covariances of Evaluated Nuclear Cross Section Data for (232)Th, (180,182,183,184,186)W and (55)Mn

    SciTech Connect

    Trkov, A.; Capote, R.; Soukhovitskii, E; Leal, Luiz C; Sin, M; Kodeli, I.; Muir, D W

    2011-01-01

    The EMPIRE code system is a versatile package for nuclear model calculations that is often used for nuclear data evaluation. Its capabilities include random sampling of model parameters, which can be utilized to generate a full covariance matrix of all scattering cross sections, including cross-reaction correlations. The EMPIRE system was used to prepare the prior covariance matrices of reaction cross sections of (232)Th, (180,182,183,184,186)W and (55)Mn nuclei for incident neutron energies up to 60 MeV. The obtained modeling prior was fed to the GANDR system, which is a package for a global assessment of nuclear data, based on the Generalized Least-Squares method. By introducing experimental data from the EXFOR database into GANDR, the constrained covariance matrices and cross section adjustment functions were obtained. Applying the correction functions on the cross sections and formatting the covariance matrices, the final evaluations in ENDF-6 format including covariances were derived. In the resonance energy range, separate analyses were performed to determine the resonance parameters with their respective covariances. The data files thus obtained were then subjected to detailed testing and validation. Described evaluations with covariances of (232)Th, (180,182,183,184,186)W and (55)Mn nuclei are included into the ENDF/B-VII.1 library release.

  17. Primordial radioactivity ((238)U, (232)Th and (40)K) measurements for soils of Ludhiana district of Punjab, India.

    PubMed

    Badhan, K; Mehra, R

    2012-11-01

    The aim of the present work was to study the activity concentration and absorbed gamma dose rates due to primordial radionuclides ((238)U, (232)Th and (40)K) for the soil of different villages of Ludhiana district of Punjab, India using a high-purity germanium detector based on high resolution gamma-ray spectrometry. The average activity concentrations of (238)U, (232)Th and (40)K in the soil samples have been found to be 28.58, 50.95 and 569.59 Bq kg(-1), respectively, which gives the total gamma dose rate contribution of 68.50 nGy h(-1). To evaluate the radiological hazard of the natural radioactivity, the radium equivalent activity, the external hazard index, the absorbed dose rate and the effective dose rate have been calculated. The calculated radium equivalent activity values are on the lower side of the recommended safe limit value of 370 Bq kg(-1) by Organization of Economic and Control Department. The calculated value of external health hazard index is lower than unity.

  18. A dispersive optical model potential for nucleon induced reactions on 238U and 232Th nuclei with full coupling

    NASA Astrophysics Data System (ADS)

    Quesada, José Manuel; Soukhovitskiĩ, EfremS.; Capote, Roberto; Chiba, Satoshi

    2013-03-01

    A dispersive coupled-channel optical model potential (DCCOMP) that couples the ground-state rotational and low-lying vibrational bands of 238U and 232Th nuclei is studied. The derived DCCOMP couples almost all excited levels below 1 MeV of excitation energy of the corresponding even-even actinides. The ground state, octupole, beta, gamma, and non-axial bands are coupled. The first two isobar analogue states (IAS) populated in the quasi-elastic (p,n) reaction are also coupled in the proton induced calculation, making the potential approximately Lane consistent. The coupled-channel potential is based on a soft-rotor description of the target nucleus structure, where dynamic vibrations are considered as perturbations of the rigid rotor underlying structure. Matrix elements required to use the proposed structure model in Tamura coupled-channel scheme are derived. Calculated ratio R(U238/Th232) of the total cross-section difference to the averaged σT for 238U and 232Th nuclei is shown to be in excellent agreement with measured data.

  19. Covariances of Evaluated Nuclear Cross Section Data for 232Th, 180,182,183,184,186W and 55Mn

    NASA Astrophysics Data System (ADS)

    Trkov, A.; Capote, R.; Soukhovitskii, E. Sh.; Leal, L. C.; Sin, M.; Kodeli, I.; Muir, D. W.

    2011-12-01

    The EMPIRE code system is a versatile package for nuclear model calculations that is often used for nuclear data evaluation. Its capabilities include random sampling of model parameters, which can be utilised to generate a full covariance matrix of all scattering cross sections, including cross-reaction correlations. The EMPIRE system was used to prepare the prior covariance matrices of reaction cross sections of 232Th, 180,182,183,184,186W and 55Mn nuclei for incident neutron energies up to 60 MeV. The obtained modelling prior was fed to the GANDR system, which is a package for a global assessment of nuclear data, based on the Generalised Least-Squares method. By introducing experimental data from the EXFOR database into GANDR, the constrained covariance matrices and cross section adjustment functions were obtained. Applying the correction functions on the cross sections and formatting the covariance matrices, the final evaluations in ENDF-6 format including covariances were derived. In the resonance energy range, separate analyses were performed to determine the resonance parameters with their respective covariances. The data files thus obtained were then subjected to detailed testing and validation. Described evaluations with covariances of 232Th, 180,182,183,184,186W and 55Mn nuclei are included into the ENDF/B-VII.1 library release.

  20. U-Th-Ra disequilibria in sediments of the Dora Baltea river (Italia)

    NASA Astrophysics Data System (ADS)

    Chabaux, F.; Deloche, A.; Pelt, E.; Granet, M.; Perrone, Th.; Boutin, R.; Viville, D.; Rihs, S.; Stille, P.

    2012-04-01

    In order to constrain the transfer time of sediments in Alpine rivers, we propose to use the U-series nuclides approach recently developed for Himalayan rivers (e.g., Chabaux et al., 2008; Granet et al., 2010). Therefore, a series of bank sediments has beeen collected along the Dora Baltea river (Italia), one of the Po's tributaries draining the southern slope of the Mont Blanc Massif. In addition to U series nuclides, major and trace element concentrations and Sr and Nd isotope ratios have been analyzed for each sample. The study indicates that the (234U/238U)-, (230Th/234U)- and the (226Ra/230Th)- activity ratios are very similar for all the samples, whereas the 230Th/232Th ratios can differ from one sample to another. Such a variation, consistent with the Sr and Nd isotope data, is certainly the consequence of mineralogical heterogeneities in the samples. This suggests that the use of 238U-230Th-232Th systematics alone is probably insufficient for constraining the transfer time of sediments in the Po rivers alluvial plain, whereas the combination of 238U-230Th disequilibrium with the 230Th-226Ra disequilibrium can help to constrain such time information.

  1. 238U-230Th crystallization ages for the oldest domes of the Mono Craters, eastern California

    NASA Astrophysics Data System (ADS)

    Marcaida, M.; Vazquez, J. A.

    2014-12-01

    The Mono Craters volcanic chain is one of the youngest areas of rhyolitic volcanism in the Mono Lake-Long Valley region of eastern California. Located just south of Mono Lake, the Mono Craters comprise at least 28 individual domes and flows (numbered 3-30, north to south); however, the timing and frequency of eruptions remain poorly resolved. The earliest signs of volcanic activity are preserved as numerous tephra layers (Ashes 1-19, top to bottom) in the late Pleistocene Wilson Creek formation of ancestral Mono Lake, which indicate that rhyolitic volcanism from Mono Craters began by at least ca. 62 ka [1]. Although the current chronology indicates that most of the Mono Craters are younger than ca. 20 ka [2-4], similar compositions of titanomagnetite from both pumice and lava potentially correlate several Wilson Creek tephras to porphyritic biotite-bearing domes 11, 24, and 19 of the Mono Craters [5], suggesting that multiple domes in the Mono Craters chain reflect volcanism older than ca. 20 ka. Ash 3 is correlated to dome 11 based on similar ca. 20 ka ages and titanomagnetite compositions [6]. More recently, we performed ion microprobe 238U-230Th dating of unpolished rims of allanite and zircon from domes 24 and 19, yielding isochron ages of ca. 38 ka and ca. 42 ka, respectively. The age of dome 24 is consistent with the ca. 38 ka age of its potential correlative tephra layers [1, 5], indicating that dome 24 is likely the extrusive equivalent of Ashes 9-10. Dome 19 has titanomagnetite crystals with similar bimodal chemistry to titanomagnetites from Ash 15 [5]. The age of dome 19 is indistinguishable from the 238U-230Th age of Ash 15 [1], which erupted during a prominent geomagnetic excursion, originally designated as the "Mono Lake" excursion. Combining geochronological and titanomagnetite compositional data confirms that Ash 15 and its extrusive equivalent, dome 19, erupted during the Laschamp excursion. [1] Vazquez, J.A. and Lidzbarski, M.I. (2012) EPSL 357

  2. Thorium-uranium disequilibrium in a geothermal discharge zone at Yellowstone

    SciTech Connect

    Sturchio, N.C.; Binz, C.M.; Lewis C.H. III

    1987-07-01

    Whole rock samples of hydrothermally-altered Biscuit Basin rhyolite from Yellowstone drill cores Y-7 and Y-8 were analyzed for /sup 230/Th, /sup 234/U, /sup 238/U, and /sup 232/Th. Extreme disequilibrium was found, with (/sup 230/Th//sup 234/U) ranging from 0.30 to 1.27. Values of (/sup 230/Th//sup 232/Th) and (/sup 234/U//sup 232/Th) define a linear correlation with a slope of 0.16 +/- 0.01, which corresponds to a (/sup 230/Th//sup 234/) age of approximately 19 ka. The (/sup 230/Th//sup 234/U) disequilibrium was apparently caused by U redistribution which occurred mostly at about 19 ka, and is not related simply to the relative degree of hydrothermal alteration and self-sealing of the rhyolite. Mass balance of U requires a large flux of U-bearing ground water through the rhyolite at the time of U redistribution; rough estimates of minimum water/rock ratio range from 10/sup 2/ to 10/sup 4/, for a range of possible ground water U concentrations. Conservative hydraulic calculations indicate that the required ground water flux could have occurred within a period of hundreds of years prior to self-sealing. The disequilibrium data are consistent with a model involving U redistribution during the initial stages of development of a geothermal discharge zone that formed in response to the hydrogeologic effects of glacial melting and unloading during the decline of the Pinedale Glaciation.

  3. 230Th/238U dating of hydrothermal sulfides from Duanqiao hydrothermal field, Southwest Indian Ridge

    NASA Astrophysics Data System (ADS)

    Yang, Weifang; Tao, Chunhui; Li, Huaiming; Liang, Jin; Liao, Shili; Long, Jiangping; Ma, Zhibang; Wang, Lisheng

    2016-11-01

    Duanqiao hydrothermal field is located between the Indomed and Gallieni fracture zones at the central volcano, at 50°28'E in the ultraslow-spreading Southwest Indian Ridge (SWIR). Twenty-eight subsamples from a relict chimney and massive sulfides were dated using the 230Th/238U method. Four main episodes of hydrothermal activity were determined according to the restricted results: 68.9-84.3, 43.9-48.4, 25.3-34.8, and 0.7-17.3 kyrs. Hydrothermal activity of Duanqiao probably started about 84.3 (±0.5) kyrs ago and ceased about 0.737 (±0.023) kyrs ago. The periodic character of hydrothermal activity may be related to the heat source provided by the interaction of local magmatism and tectonism. The estimated mean growth rate of the sulfide chimney is <0.02 mm/yr. This study is the first to estimate the growth rate of chimneys in the SWIR. The maximum age of the relict chimney in Duanqiao hydrothermal filed is close to that of the chimneys from Mt. Jourdanne (70 kyrs). The hydrothermal activity in Dragon Flag field is much more recent than that of Duanqiao or Mt. Jourdanne fields. The massive sulfides are younger than the sulfides from other hydrothermal fields such as Rainbow, Sonne and Ashadze-2. The preliminarily estimated reserves of sulfide ores of Duanqiao are approximately 0.5-2.9 million tons.

  4. Atlantic Meridional Overturning Circulation during Heinrich-Stadial 1 & 2 as seen by 231Pa/230Th

    NASA Astrophysics Data System (ADS)

    Antz, B.; Lippold, J. A.; Schulz, H.; Frank, N.; Mangini, A.

    2014-12-01

    Assessing the sensitivity of the Atlantic Meridional Overturning Circulation (AMOC) is a major challenge for paleoclimatology, because its strength and structure is a crucial element of the global heat- and carbon distribution towards the deep ocean. Here the focus is set on how excessive freshwater input through abrupt melting of continental ice sheets can affect its overturning vigour. Such forcing can be tested by investigating its behaviour during extreme iceberg discharge events into the open North Atlantic during the last glacial period, so called Heinrich-Events [Heinrich 1988; Hemming 2004]. The sedimentary activity ratio 231Pa/230Th has been increasingly used as a kinematic circulation proxy in the Atlantic Ocean over the past decade [Gherardi et al. 2009; McManus et al. 2004; Lippold et al. 2012]. Here we present 231Pa/230Th ratios from several Atlantic sediment cores across Heinrich Events 1 (~17 ka BP) and 2 (~24 ka BP). The comparison of the profiles demonstrates the potential pitfalls when interpreating a single 231Pa/230Th profile. E. g. core IODP 1313 (Mid Atlantic Ridge, 3412 m water depth) shows 231Pa/230Th between 0.04 and 0.06, which would indicate a vigorous circulation over the entire time period. On the other hand core GeoB 16202-2 (Brasilan coastal area, 2248 m water depth) has a profile similar to the well known data set of [McManus et al. 2004] (i.e. during Heinrich Stadials values close to the production ratio of ~0.093, lower values at Holocene and LGM). Such divergency can be explained by 231Pa/230Th dependence on water depth, latitude, water mass and water mass age [Luo et al. 2010; Lippold et al. 2011], but also on changes in bioproductivity especially the flux of biogenic opal [Anderson et al. 1983A; Bradtmiller et al. 2007; Chase et al. 2002]. To avoid misleading interpretations, the here shown data set is accompanied by measurements of biogenic opal contents to appraise possible influences on the proxies. We observe large

  5. Meridional circulation across the Antarctic Circumpolar Current serves as a double 231Pa and 230Th trap

    NASA Astrophysics Data System (ADS)

    Rutgers van der Loeff, Michiel; Venchiarutti, Celia; Stimac, Ingrid; van Ooijen, Jan; Huhn, Oliver; Rohardt, Gerd; Strass, Volker

    2016-12-01

    Upwelling of Circumpolar Deep Water in the Weddell Gyre and low scavenging rates south of the Antarctic Circumpolar Current (ACC) cause an accumulation of particle reactive nuclides in the Weddell Gyre. A ventilation/reversible scavenging model that successfully described the accumulation of 230Th in this area was tested with other particle reactive nuclides and failed to adequately describe the depth-distributions of 231Pa and 210Pb. We present here a modified model that includes a nutrient-like accumulation south of the Antarctic Polar Front in an upper meridional circulation cell, as well as transport to a deep circulation cell in the Weddell Gyre by scavenging and subsequent release at depth. The model also explains depletion of 231Pa and 230Th in Weddell Sea Bottom Water (WSBW) by ventilation of newly formed deep water on a timescale of 10 years, but this water mass is too dense to leave the Weddell Gyre. In order to quantify the processes responsible for the 231Pa- and 230Th-composition of newly formed Antarctic Bottom Water (AABW) we present a mass balance of 231Pa and 230Th in the Atlantic sector of the Southern Ocean based on new data from the GEOTRACES program. The ACC receives 6.0 ± 1.5 ×106 dpms-1 of 230Th from the Weddell Sea, similar in magnitude to the net input of 4.2 ± 3.0 ×106 dpms-1 from the north. For 231Pa, the relative contribution from the Weddell Sea is much smaller, only 0.3 ± 0.1 ×106, compared to 2.7 ± 1.4 ×106 dpms-1 from the north. Weddell Sea Deep Water (WSDW) leaving the Weddell Gyre northward to form AABW is exposed in the ACC to resuspended opal-rich sediments that act as efficient scavengers with a Th/Pa fractionation factor F ≤ 1. Hydrothermal inputs may provide additional removal with low F. Scavenging in the full meridional circulation across the opal-rich ACC thus acts as a double 231Pa and 230Th trap that preconditions newly formed AABW.

  6. 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

  7. 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.

  8. Evaluation of the 232Th Neutron Cross Sections between 4 keV and 140 keV

    SciTech Connect

    Volev, K.; Koyumdjieva, N.; Brusegan, A.; Borella, A.; Siegler, P.; Schillebeeckx, P.; Janeva, N.; Lukyanov, A.; Leal, L.

    2005-05-24

    An evaluation of the 232Th neutron total and capture cross sections has been performed in the energy region between 4 keV and 140 keV. The evaluation results from a simultaneous analysis of capture, transmission, and self-indication measurement data, including the most recent capture cross-section data obtained at the GELINA facility of the Institute for Reference Materials and Measurements at Geel (B) and at the n-TOF facility at CERN (CH). The experimental data have been analysed in terms of average resonance parameters exploiting two independent theoretical approaches -- the Characteristic Function model and the Hauser-Feshbach-Moldauer theory. The resulting parameters are consistent with the resolved resonance parameters deduced from the transmission measurements of Olsen et al. at the ORELA facility.

  9. Measurement of resolved resonances of 232Th(n,γ) at the n_TOF facility at CERN

    NASA Astrophysics Data System (ADS)

    Gunsing, F.; Berthoumieux, E.; Aerts, G.; Abbondanno, U.; Álvarez, H.; Alvarez-Velarde, F.; Andriamonje, S.; Andrzejewski, J.; Assimakopoulos, P.; Audouin, L.; Badurek, G.; Baumann, P.; Bečvář, F.; Calviño, F.; Cano-Ott, D.; Capote, R.; Carrillo de Albornoz, A.; Cennini, P.; Chepel, V.; Chiaveri, E.; Colonna, N.; Cortes, G.; Couture, A.; Cox, J.; Dahlfors, M.; David, S.; Dillman, I.; Dolfini, R.; Domingo-Pardo, C.; Dridi, W.; Duran, I.; Eleftheriadis, C.; Embid-Segura, M.; Ferrant, L.; Ferrari, A.; Ferreira-Marques, R.; Fitzpatrick, L.; Frais-Koelbl, H.; Fujii, K.; Furman, W.; Goncalves, I.; Gonzalez-Romero, E.; Goverdovski, A.; Gramegna, F.; Griesmayer, E.; Guerrero, C.; Haas, B.; Haight, R.; Heil, M.; Herrera-Martinez, A.; Igashira, M.; Isaev, S.; Jericha, E.; Käppeler, F.; Kadi, Y.; Karadimos, D.; Karamanis, D.; Kerveno, M.; Ketlerov, V.; Koehler, P.; Konovalov, V.; Kossionides, E.; Krtička, M.; Lampoudis, C.; Leeb, H.; Lindote, A.; Lopes, I.; Lozano, M.; Lukic, S.; Marganiec, J.; Marques, L.; Marrone, S.; Mastinu, P.; Mengoni, A.; Milazzo, P. M.; Moreau, C.; Mosconi, M.; Neves, F.; Oberhummer, H.; O'Brien, S.; Oshima, M.; Pancin, J.; Papachristodoulou, C.; Papadopoulos, C.; Paradela, C.; Patronis, N.; Pavlik, A.; Pavlopoulos, P.; Perrot, L.; Pigni, M. T.; Plag, R.; Plompen, A.; Plukis, A.; Poch, A.; Pretel, C.; Quesada, J.; Rauscher, T.; Reifarth, R.; Rosetti, M.; Rubbia, C.; Rudolf, G.; Rullhusen, P.; Salgado, J.; Sarchiapone, L.; Savvidis, I.; Stephan, C.; Tagliente, G.; Tain, J. L.; Tassan-Got, L.; Tavora, L.; Terlizzi, R.; Vannini, G.; Vaz, P.; Ventura, A.; Villamarin, D.; Vincente, M. C.; Vlachoudis, V.; Vlastou, R.; Voss, F.; Walter, S.; Wendler, H.; Wiescher, M.; Wisshak, K.

    2012-06-01

    The yield of the neutron capture reaction 232Th(n,γ) has been measured at the neutron time-of-flight facility n_TOF at CERN in the energy range from 1 eV to 1 MeV. The reduction of the acquired data to the capture yield for resolved resonances from 1 eV to 4 keV is described and compared to a recent evaluated data set. The resonance parameters were used to assign an orbital momentum to each resonance. A missing level estimator was used to extract the s-wave level spacing of D0=17.2±0.9 eV.

  10. IUPAC-IUGS status report on the half-lives of 238U, 235U and 234U

    NASA Astrophysics Data System (ADS)

    Villa, I. M.; Bonardi, M. L.; De Bièvre, P.; Holden, N. E.; Renne, P. R.

    2016-01-01

    The current state of knowledge on the half-lives of the long-lived U radionuclides has been reviewed by the IUPAC-IUGS joint Task Group "Isotopes in Geosciences". 238U is assigned a half-life of (4.4683 ± 0.0096) Ga, i.e. a decay constant λ238 = (0.155125 ± 0.000333) Ga-1. The coverage factor is k = 2 for this and all other estimates presented here. The 238U half-life can be used as a reference for the half-lives/decay constants of all other isotopic geochronometers. A revision of the half-life of 235U based on intercomparison of natural geological samples is premature. The improved repeatability of mass spectrometric measurements has revealed Type B uncertainties that had been dismissed as subordinate in the past. The combined uncertainty of these as yet incompletely charted and quantified sources of Type B uncertainty may be no smaller than the currently accepted uncertainty of the α counting experiments. A provisional value for the 234U half-life can be calculated with the assumption of secular equilibrium in the analyzed natural samples. This assumption has not yet been verified independently and its metrological traceability appears sub-optimum. A Type B evaluation suggests that the ca. 0.17% offset between the N(234U)/N(238U) number-ratios of the natural samples used to estimate the 235U half-life and those of the four samples used to estimate the 234U half-life should be compounded into the standard measurement uncertainty of the latter. The resulting provisional uncertainty interval (k = 2) for the 234U half-life is (244.55-247.77) ka, corresponding to λ234 = (2.8203-2.8344) Ma-1.

  11. The first case study of 230Th/U and 14C dating of mid-valdai organic deposits

    NASA Astrophysics Data System (ADS)

    Maksimov, F. E.; Kuznetsov, V. Yu.; Zaretskaya, N. E.; Subetto, D. A.; Shebotinov, V. V.; Zherebtsov, I. E.; Levchenko, S. B.; Kuznetsov, D. D.; Larsen, E.; Lysö, A.; Jensen, M.

    2011-05-01

    From the viewpoint of precision and reliability of radioisotopic dating, deposits whose quantitative age can be determined through several methods of geochronometry are of special interest. The mutually conforming finite 14C and 230Th/U dates of buried Neopleistocene organic deposits, taken from the Tolokonka section by the North Dvina River (100 km downstream from the city of Kotlas), have been obtained for the first time in Russia. The stratigraphical reference of these results to those obtained via the optically induced luminescence for upper and lower bedding layers has been established. The presented geochronometric data have allowed us to consider the age of oxbow lake organic deposits completely reliable and refer the time of their formation to the Tyrbei warming within the MIS-3. The applicability of the new version of the 230Th/U method for dating of interglacial and interstadial deposits, for the purpose of solving the Middle and Late Neopleistocene chronostratigraphy issues, is confirmed.

  12. 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

  13. 238U-230Th dating of chevkinite in high-silica rhyolites from La Primavera and Yellowstone calderas

    USGS Publications Warehouse

    Vazquez, Jorge A.; Velasco, Noel O.; Schmitt, Axel K.; Bleick, Heather A.; Stelten, Mark E.

    2014-01-01

    Application of 238U-230Th disequilibrium dating of accessory minerals with contrasting stabilities and compositions can provide a unique perspective on magmatic evolution by placing the thermochemical evolution of magma within the framework of absolute time. Chevkinite, a Th-rich accessory mineral that occurs in peralkaline and metaluminous rhyolites, may be particularly useful as a chronometer of crystallization and differentiation because its composition may reflect the chemical changes of its host melt. Ion microprobe 128U-230Th dating of single chevkinite microphenocrysts from pre- and post-caldera La Primavera, Mexico, rhyolites yields model crystallization ages that are within 10's of k.y. of their corresponding K-Ar ages of ca. 125 ka to 85 ka, while chevkinite microphenocrysts from a post-caldera Yellowstone, USA, rhyolite yield a range of ages from ca. 110 ka to 250 ka, which is indistinguishable from the age distribution of coexisting zircon. Internal chevkinite-zircon isochrons from La Primavera yield Pleistocene ages with ~5% precision due to the nearly two order difference in Th/U between both minerals. Coupling chevkinite 238U-230Th ages and compositional analyses reveals a secular trend of Th/U and rare earth elements recorded in Yellowstone rhyolite, likely reflecting progressive compositional evolution of host magma. The relatively short timescale between chevkinite-zircon crystallization and eruption suggests that crystal-poor rhyolites at La Primavera were erupted shortly after differentiation and/or reheating. These results indicate that 238U-230Th dating of chevkinite via ion microprobe analysis may be used to date crystallization and chemical evolution of silicic magmas.

  14. Testing the 234U/238U weathering tracer in a tropical granitoid watershed, Luquillo, Puerto Rico

    NASA Astrophysics Data System (ADS)

    Pett-Ridge, J. C.; Derry, L. A.

    2006-12-01

    Recent studies have employed U-series disequilibria as a tracer of both weathering profile development and of timescale of erosion for whole watersheds. We have undertaken a detailed analysis of the behavior of the U- series isotopes in a previously well-characterized watershed in order to test this approach. In the Rio Icacos watershed in the Luquillo Mountains of Puerto Rico, previous studies have determined both the rate of propagation of the chemical weathering front by regolith mass balance analysis, and the surface denudation rate using the cosmogenic 10Be tracer. Our study aims to determine whether the U-series approach provides regolith development and erosion rates in agreement with those previously determined. In order to better constrain interpretations based on U-series data, we have coupled the U-series analysis with analyses of trace element concentrations, δ^{30}Si, Ge/Si, and 87Sr/86Sr ratios. Used together, these geochemical tracers provide a powerful tool for understanding weathering reactions, chemical transfers within and out of the weathering profile, and the timing of these chemical transfers. Analyses of soil, saprolite and pore water samples reveal a complex history of U and Th transformations including mobilization of both U and Th in the soil followed by re-adsorption deeper in the profile. 234U/238U activity ratios in soil and saprolite show significant variability both with depth, and also among individual mineral phases at any particular depth. This variation among mineral phases, combined with the likely physical sorting of these phases during erosional transport, results in an additional isotopic fractionation unrelated to that imparted by the weathering process. This implies that suspended sediment samples taken from streamwater are unlikely to accurately reflect the average disequilibria carried by the secondary minerals phases in the soil and saprolite. Our analyses also reveal a significant contribution of atmospheric mineral

  15. Cross-sections of the reaction 232Th(p,3n)230Pa for production of 230U for targeted alpha therapy.

    PubMed

    Morgenstern, Alfred; Apostolidis, Christos; Bruchertseifer, Frank; Capote, Roberto; Gouder, Thomas; Simonelli, Federica; Sin, Mihaela; Abbas, Kamel

    2008-10-01

    (230)U/(226)Th is a promising novel alpha-emitter system for application in targeted alpha therapy of cancer. The therapeutic nuclides can be produced by proton irradiation of natural (232)Th according to the reaction (232)Th(p,3n)(230)Pa, followed by subsequent beta decay of (230)Pa to (230)U. In this study, the experimental excitation function for the (232)Th(p,3n)(230)Pa reaction up to 34 MeV proton energy has been measured using the stacked-foil technique. The proton energies in the various foils were calculated with the SRIM 2003 code and gamma-ray spectrometry was used to measure the activities of the various radioisotopes produced. The measured cross-sections are in good agreement with selected literature values and with model calculations using the EMPIRE II code. The reaction (232)Th(p,3n)(230)Pa allows the production of carrier-free (230)U in clinically relevant levels.

  16. Controls on 231Pa/230Th in the Indian Ocean: Circulation or Productivity?

    NASA Astrophysics Data System (ADS)

    Thomas, A. L.; Henderson, G. M.; McCave, N.

    2004-12-01

    (231Paxs/230Thxs)0 ratios in marine sediments are a potential proxy of palaeoproductivity and/or past ocean circulation. Studies in the Atlantic have demonstrated the particular potential of this proxy to assess the rate of past circulation AƒAøAøâ_sA¬Aøâ,¬Å" an important environmental variable which is otherwise difficult to reconstruct {[1, 2]}. In this study, we present new water-column and sediment data from the western Indian Ocean to improve understanding of the controls on (231Paxs/230Thxs)0 and test the use of this proxy. The Indian Ocean differs from the Atlantic because deep waters forming in the Southern Ocean and transported into the basin have high rather than low Pa and Th concentrations [3]. The ability to reconstruct past rates of flow into the Indian Ocean would be a powerful new use of Pa/Th, but no data presently exist to test this application. Water samples (10 litre), surface sediments, and a 5.5m Kasten core were collected on the Charles Darwin cruise CD154 from the area East of Madagascar. The down-core record, from10°S extends to 150 ka, and is coupled with a stable isotope stratigraphy and a sortable silt record. Water and sediment samples were analysed for isotopes of Pa, Th and U on a Nu Instruments MC-ICP-MS. The water-column dataset (26 samples) indicate that Pa concentrations are high in NADW transported into the Indian Ocean from the Atlantic, while opal scavenging has lowered Pa concentrations in deeper water masses. Sedimentary 230Th data indicate that there has been significant sediment focusing and that sediment mass fluxes are low. Preliminary sedimentary Pa/Th data show little relation to the sortable silt record. Ongoing Pa/Th and Ba data will complete this downcore record and allow comparison of a Pa/Th record with independent proxies of current speed and productivity in the same core. [1] E.F. Yu, et al, Nature 379, 689-694, 1996. [2] J.F. McManus, et al, Nature 428, 834-837, 2004. [3] M. M. Rutgers van der Loeff

  17. Fission fragments mass distributions of nuclei populated by the multinucleon transfer channels of the 18O + 232Th reaction

    NASA Astrophysics Data System (ADS)

    Léguillon, R.; Nishio, K.; Hirose, K.; Makii, H.; Nishinaka, I.; Orlandi, R.; Tsukada, K.; Smallcombe, J.; Chiba, S.; Aritomo, Y.; Ohtsuki, T.; Tatsuzawa, R.; Takaki, N.; Tamura, N.; Goto, S.; Tsekhanovich, I.; Petrache, C. M.; Andreyev, A. N.

    2016-10-01

    It is shown that the multinucleon transfer reactions is a powerful tool to study fission of exotic neutron-rich actinide nuclei, which cannot be accessed by particle-capture or heavy-ion fusion reactions. In this work, multinucleon transfer channels of the 18O + 232Th reaction are used to study fission of fourteen nuclei 231,232,233,234Th, 232,233,234,235,236Pa, and 234,235,236,237,238U. Identification of fissioning nuclei and of their excitation energy is performed on an event-by-event basis, through the measurement of outgoing ejectile particle in coincidence with fission fragments. Fission fragment mass distributions are measured for each transfer channel, in selected bins of excitation energy. In particular, the mass distributions of 231,234Th and 234,235,236Pa are measured for the first time. Predominantly asymmetric fission is observed at low excitation energies for all studied cases, with a gradual increase of the symmetric mode towards higher excitation energy. The experimental distributions are found to be in general agreement with predictions of the fluctuation-dissipation model.

  18. Retardation of [sup 238]U and [sup 232]Th decay chain radionuclides in Long Island and Connecticut aquifers

    SciTech Connect

    Copenhaver, S.A.; Krishnaswami, S.; Turekian, K.K. ); Epler, N.; Cochran, J.K. )

    1993-02-01

    Knowledge of the ability of an aquifer to retard the groundwater transport of toxic or radioactive ions can be inferred from the analysis of groundwater for the radionuclides of the [sup 238]U- and [sup 232]Th-decay chains. Groundwaters of varying chemical composition were analyzed from wells in Long Island, New York, and Connecticut. Aquifer lithologies are arkose, quartz sandstone, granite, and glacial drift. Adsorption (k[sub 1]) and desorption (k[sub 2]) coefficients for Ra and Pb were calculated using [sup 222]Rn activity as a measure of the supply of other [alpha]-recoil nuclides. Laboratory tests of the validity of this assumption were made by measuring the flux of [sup 224]Ra and [sup 222]Rn from aquifer solids. The ratio k[sub 1]/k[sub 2] is the distribution coefficient, K, which is effective equal to R[sub f], the retardation factor. The average value of K for Ra is 6 [times] 10[sup 2] in Long Island aquifers and 5 [times] 10[sup 4] in Connecticut. The distribution coefficient for Pb is 10[sup 4] in Long Island and 10[sup 5] in Connecticut. Results from this and other studies reveal a strong dependence of retardation on pH, f[sub o[sub 2

  19. Correction methodology for the spectral interfering γ-rays overlapping to the analytical peaks used in the analysis of 232Th.

    PubMed

    Yücel, H; Köse, E; Esen, A N; Bor, D

    2011-06-01

    In the γ-ray spectrometric analysis of the radionuclides, a correction factor is generally required for the spectral interfering γ-rays in determining the net areas of the analytical peaks because some interfering γ-rays often might contribute to the analytical peaks of interest. In present study, a correction methodology for the spectral interfering γ-rays (CSI) is described. In particular, in the analysis of (232)Th contained in samples, the interfering γ-rays due to (226)Ra, (235)U, (238)U and their decay products often overlap to the peaks of interest from (232)Th decay products, and vise versa. For the validation of the proposed CSI method, several certified reference materials (CRM) containing U and Th were measured by using a 76.5% efficient n-type Ge detector. The required correction factors were quantified for spectral interference, self-absorption and true coincidence summing (TCS) effects for the relevant γ-rays. The measured results indicate that if one ignores the contributions of the interfering γ-rays to the analytical peaks at 583.2 keV of (208)Tl and 727.3 keV of (212)Bi, this leads to a significantly systematic influence on the resulted activities of (232)Th. The correction factors required for spectral interference and TCS effects are estimated to be ∼13.6% and ∼15.4% for 583.2 keV peak. For the 727.3 keV peak, the correction factor is estimated to be ∼15% for spectral interference, and ∼5% for the TCS effects at the presently used detection geometry. On the other hand, the measured results also indicate that ignoring the contribution of the interfering γ-rays to the areas of the analytical peaks at 860.6 keV of (208)Tl, 338.3 and 911.2 keV of (228)Ac does not lead to any significant systematic influence on the (232)Th analysis. Because these factors are remained generally less than ∼5%, i.e., within overall uncertainty limits. The present study also showed that in view of both the spectral interference and TCS effects, the

  20. Uranium concentrations and 234U/238U activity ratios in fault-associated groundwater as possible earthquake precursors

    NASA Astrophysics Data System (ADS)

    Finkel, R. C.

    In order to assess the utility of uranium isotopes as fluid phase earthquake precursors, uranium concentrations and 234U/238U activity ratios have been monitored on a monthly or bimonthly basis in water from 24 wells and springs associated with Southern California fault zones. Uranium concentrations vary from 0.002 ppb at Indian Canyon Springs on the San Jacinto fault to 8.3 ppb at Lake Hughes well on the San Andreas fault in the Palmdale area. 234U/238U activity ratios vary from 0.88 at Agua Caliente Springs on the Elsinore fault to 5.4 at Niland Slab well on the San Andreas fault in the Imperial Valley. There was one large earthquake in the study area during 1979, the 15 October 1979 M=6.6 Imperial Valley earthquake. Correlated with this event, uranium concentrations varied by a factor of more than 60 and activity ratios by a factor of 3 at the Niland Slab site, about 70 km from the epicenter. At the other sites monitored, uranium concentrations varied in time, but with no apparent pattern, while uranium activity ratios remained essentially constant throughout the monitoring period.

  1. 234U and 238U concentration in brine from geopressured aquifers of the northern Gulf of Mexico basin

    USGS Publications Warehouse

    Kraemer, T.F.

    1981-01-01

    The 234U and 238U concentration in brine from six Gulf Coast geopressured aquifers has been determined. The results reveal very low uranium concentrations (from 0.003 to 0.03 ??g/l) and uranium activity ratios slightly greater than unity (from 1.06 to 1.62). Reducing conditions within the aquifers are responsible for the low uranium concentrations. The uranium activity ratios observed are well below those calculated using theoretical considerations of alpha-particle recoil effects. This can be explained by interference with alpha-recoil nuclides entering the liquid phase as a result of quartz overgrowths on sand grains and high-temperature re-equilibration that tends to minimize the effects of the alpha-recoil process. The fact that the uranium activity ratios of the brines are slightly greater than unity instead of the equilibrium value of 1.000 indicates that either the alpha particle recoil blocking and re-equlibration effects are not complete or that another process is operative that enriches the fluid in excess 234U by selectively removing uranium from radiation induced damage sites in the mineral (sand grain) matrix. ?? 1981.

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

    SciTech Connect

    Ludwig, K.R.; Szabo, B.J.; Simmons, K.R. ); Moore, J.G. )

    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 ratios 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.

  3. Resonance Region Covariance Analysis Method and New Covariance Data for {sup 232}Th, {sup 233}U, {sup 235}U, {sup 238}U, and {sup 239}Pu

    SciTech Connect

    Leal, L.C. Arbanas, G.; Wiarda, D.; Derrien, H.

    2008-12-15

    Resonance-parameter covariance matrix (RPCM) evaluations in the resolved resonance region were done for {sup 232}Th, {sup 233}U, {sup 235}U, {sup 238}U, and {sup 239}Pu using the computer code SAMMY. The retroactive approach of the code SAMMY was used to generate the RPCMs for {sup 233}U and {sup 235}U. RPCMs for {sup 232}Th, {sup 238}U and {sup 239}Pu were generated together with the resonance 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 with SAMMY.

  4. A beta-alpha coincidence counting system for measurement of trace quantities of 238U and 232Th in aqueous samples at the Sudbury Neutrino Observatory.

    NASA Astrophysics Data System (ADS)

    Dawson, M.; Doucas, G.; Fergani, H.; Jelley, N. A.; Majerus, S.; O'Keeffe, H. M.; Peeters, S. J. M.; Perry, C.

    2016-08-01

    The Sudbury Neutrino Observatory experiment was built to measure the total flux of 8B solar neutrinos via the neutral current disintegration deuterium nuclei. This process can be mimiced by daughter isotopes of 232Th and 238U which can photodisintegrate the deuterium nucleus. Measurement of the concentration of such radioisotopes in the heavy water was critical to the success of the experiment. A radium assay technique using Hydrous Titanium Oxide coated filters was developed for this purpose and it was used in conjunction with a delayed beta-alpha coincidence counting system. The design, calibration and operation of this counting system are described in this paper. The counting efficiency for 232Th (224Ra) and 238U (226Ra) were measured to be 50 ± 5% and 62 ± 7%

  5. 226Ra, 232Th and 40K contents in water samples in part of central deserts in Iran and their potential radiological risk to human population

    PubMed Central

    2014-01-01

    Background The radiological quality of 226Ra, 232Th and 40K in some samples of water resources collected in Anarak-Khour a desertic area, Iran has been measured by direct gamma ray spectroscopy using high purity germanium detector in this paper. Result The concentration ranged from ≤0.5 to 9701 mBq/L for 226Ra; ≤0.2 to 28215 mBq/L for 232Th and < MDA to 10332 mBq/L for 40K. The radium equivalent activity was well below the defined limit of 370Bq/L. The calculated external hazard indices were found to be less than 1 which shows a low dose. Conclusion These results can be contributed to the database of this area because it may be used as disposal sites of nuclear waste in future. PMID:24883192

  6. Measurement of 226Ra, 232Th, 137Cs and 40K activities of Wheat and Corn Products in Ilam Province – Iran and Resultant Annual Ingestion Radiation Dose

    PubMed Central

    CHANGIZI, Vahid; SHAFIEI, Elham; ZAREH, Mohammad Reza

    2013-01-01

    Background: Background: Natural background radiation is the main source of human exposure to radioactive material. Soils naturally have radioactive mineral contents. The aim of this study is to determine natural (238 U, 232 Th, 40 K) and artificial (137 Cs) radioactivity levels in wheat and corn fields of Eilam province. Methods: HPGe detector was used to measure the concentration activity of 238 U and 232 Th series, 40 K and 137 Cs in wheat and corn samples taken from different regions of Eilam province, in Iran. Results: In wheat and corn samples, the average activity concentrations of 226 Ra, 232 Th, 40 K and 137 Cs were found to be 1, 67, 0.5, 91.73, 0.01 and 0.81, 0.85, 101.52, 0.07 Bq/kg (dry weight), respectively. H ex and H in in the present work are lower than 1. The average value of H ex was found to be 0.02 and 0.025 and average value of H in to be found 0.025 and 0.027 in wheat fields samples and corn samples in Eilam provinces, respectively. The obtained values of AGDE are 30.49 mSv/yr for wheat filed samples and 37.89 mSv/yr for corn samples; the AEDE rate values are 5.28 mSv/yr in wheat filed samples and this average value was found to be 6.13 mSv/yr in corn samples in Eilam. Transfer factors (TFs) of long lived radionuclide such as 137 Cs, 226 Ra, 232 Th and 40 K from soils to corn and wheat plants have been studied by radiotracer experiments. Conclusion: The natural radioactivity levels in Eilam province are not at the range of high risk of morbidity and are under international standards. PMID:26056646

  7. Comparison of activity concentration of 238U, 232Th and 40K in different Layers of subsurface Structures in Dei-Dei and Kubwa, Abuja, northcentral Nigeria

    NASA Astrophysics Data System (ADS)

    Maxwell, Omeje; Wagiran, Husin; Ibrahim, Noorddin; Lee, Siak Kuan; Sabri, Soheil

    2013-10-01

    The study of activity concentration of 232Th, 238U and 40K of rock samples from site one (S1L1-S1L11, 70 m) and site two (S2L1-S2L9, 60 m) boreholes in Dei-Dei and Kubwa was presented and the first time in the region to be compared. Activity concentrations were analysed using a high resolution co-axial HPGe gamma ray spectrometer system. The activity concentration ranges in site one borehole were from 45±1 to 98±6 Bq kg-1 for 232Th, from 18±2 to 37±4 Bq kg-1 for 238U and from 254 ±32 Bq kg-1 to 1195 ±151 Bq kg-1 for 40K. The activity concentration ranges in site two borehole were from 32±3 to 84±7 Bq kg-1 for 232Th, from 15±2 to 52±5 Bq kg-1 for 238U and from 119±15 to 705±94 for 40K Bq kg-1. Significantly higher concentration of 232Th and 238U occurs in samples collected from S1L7, S1L11 and S2L1 layers. These zones experienced granitic intrusions produced by denudation and tectonism. 40K in rock samples of S1L4 and S2L4 activity concentrations is close; it could be that biotite granitic intrusion that is inferred as the formation in that layer reflects the same activity of potassium in rock's radioactivity measurement. The area requires further investigation of soil geochemistry and activity concentration of radionuclides in groundwater.

  8. STUDY OF NATURAL RADIOACTIVITY (226Ra, 232Th AND 40K) IN SOIL SAMPLES FOR THE ASSESSMENT OF AVERAGE EFFECTIVE DOSE AND RADIATION HAZARDS.

    PubMed

    Bangotra, Pargin; Mehra, Rohit; Kaur, Kirandeep; Jakhu, Rajan

    2016-10-01

    The activity concentration of (226)Ra (radium), (232)Th (thorium) and (40)K (potassium) has been measured in the soil samples collected from Mansa and Muktsar districts of Punjab (India) using NaI (Tikl) gamma detector. The concentration of three radionuclides ((226)Ra, (232)Th and (40)K) in the studied area has been varied from 18±4 to 46±5, 53±7 to 98±8 and 248±54 to 756±110 Bq kg(-1), respectively. Radium equivalent activities (Raeq) have been calculated in soil samples for the assessment of the radiation hazards arising due to the use of these soil samples. The absorbed dose rate of (226)Ra, (232)Th and (40)K in studied area has been varied from 8 to 21, 33 to 61 and 9 to 25 nGy h(-1), respectively. The corresponding indoor and outdoor annual effective dose in studied area was 0.38 and 0.09 mSv, respectively. The external and internal hazard has been also calculated for the assessment of radiation hazards in the studied area.

  9. Assay Methods for 238U, 232Th, and 210Pb in Lead and Calibration of 210Bi Bremsstrahlung Emission from Lead

    SciTech Connect

    Orrell, John L.; Aalseth, Craig E.; Arnquist, Isaac J.; Eggemeyer, Tere A.; Glasgow, Brian D.; Hoppe, Eric W.; Keillor, Martin E.; Morley, Shannon M.; Myers, Allan W.; Overman, Cory T.; Shaff, Sarah M.; Thommasson, Kimbrelle S.

    2016-02-13

    Assay methods for measuring 238U, 232Th, and 210Pb concentrations in refined lead are presented. The 238U and 232Th concentrations are assayed via inductively coupled plasma mass spectrometry (ICP-MS) after anion exchange column separation on dissolved lead samples. The 210Pb concentration is inferred through α-spectroscopy of a daughter isotope, 210Po, after chemical precipitation separation on dissolved lead samples. Subsequent to the 210Po α-spectroscopy assay, a method for evaluating 210Pb concentrations in solid lead samples was developed via measurement of bremsstrahlung radiation from β-decay of a daughter isotope, 210Bi, by employing a 14-crystal array of high purity germanium (HPGe) detectors. Ten sources of refined lead were assayed. The 238U concentrations were <34 microBq/kg and the 232Th concentrations ranged <0.6 – 15 microBq/kg, as determined by the ICP-MS assay method. The 210Pb concentrations ranged from ~0.1 – 75 Bq/kg, as inferred by the 210Po α-spectroscopy assay method.

  10. Activity concentration, transfer factors and resultant radiological risk of 226Ra, 232Th, and 40K in soil and some vegetables consumed in Selangor, Malaysia

    NASA Astrophysics Data System (ADS)

    Solehah, A. R.; Yasir, M. S.; Samat, S. B.

    2016-11-01

    The activity concentrations of the natural radionuclides 226Ra, 232Th, and 40K were determined in vegetable crops consumed by Malaysian people in Sungai Besar, Selangor. Sample of vegetables and the soil where the crops were cultivated and collected at five different location. The activity concentrations in Bq/kg of 226Ra, 232Th, and 40K were measured by the gamma-ray spectroscopy using the high purity germanium detector. The range activity concentration in soil is between 51.81 and 71.84 Bq/kg, 64.18 and 78.00 Bq/kg, and 210.49 and 244.29 Bq/kg for 226Ra, 232Th, and 40K, respectively. The activity concentration of 226Ra, 232Th, and 40K in vegetables were found to be in the range of 2.06 to 5.44 Bq/kg, Not Detectable to 0.61 Bq/kg, and 101.00 to 1223.09 Bq/kg, respectively. The activity concentration in both soil and vegetables were all less than lower limit stated by UNSCEAR. The Transfer Factors range value for 226Ra, 232Th, and 40K varied from 0.02 to 0.06, 0.003 to 0.008, and 1.79 to 5.19 respectively. Radium equivalent for soil range from 165.57 to 194.84 Bq/kg. It was within the international accepted value (370 Bq/kg). Absorb dose rate for soil range between 73.5 to 86.40 nGyh-1, in safe range from limit of international accepted value (55nGyh-1). Effective dose rate is found to be in range of 0.09 to 0.11 mSvy-1 for soil which is less than 2.4 mSv/y. External and Internal Hazard indices of soil was all below 1, within agreement of other researcher and UNSCEAR. The estimation of the consequent radiological risk due to the presence of those radionuclides is significantly low.

  11. Coupling groundwater residence time and 234U/238U isotopic ratios in a granitic catchment (Vosges, Eastern France)

    NASA Astrophysics Data System (ADS)

    Viville, Daniel; Aquilina, Luc; Ackerer, Julien; Chatton, Eliot; Labasque, Thierry; Pierret, Marie-Claire; Granet, Mathieu; Perrone, Thierry; Chabaux, François

    2016-04-01

    Weathering processes are active in surface waters but groundwater also represents no neglectable chemical fluxes. As residence-time in groundwater are high, silicate weathering might take place and control Si, Ca and C fluxes. Weathering processes can be deduced from U isotopic ratios but the kinetics of these processes remain relatively poorly constrained. In order to better characterize these processes, we have coupled residence-times deduced from anthropogenic gases (CFC and SF6) analysis and 234U/238U isotopic ratios determination. Samples were collected in the Strengbach catchment (Hydro-geochemical Observatory OHGE, Vosges, eastern France). Two campaigns were carried out in May and August 2015 during two highly contrasted hydro-climatic periods. Both springs and boreholes down to 80 m depth have been sampled. A very clear geochemical distinction is observed between groundwater from surface springs and deeper groundwater from boreholes. Springs show much lower residence-time (few years) and specific chemical composition. Deeper groundwater have residence-time of several decades and different geochemical composition. A clear SF6 production is observed with increasing SF6 concentrations with residence-time. The campaign of May is characterized by highly groundwater levels and spring fluxes. All groundwater show very low residence time, except in the boreholes at depth greater than 40 m. Conversely, during low groundwater-level period in August, the residence times are much higher and CFC concentrations indicate a large mixing process between surface groundwater and deeper levels. The 234U/238U isotopic ratios confirm this vertical zonation in the boreholes, with much higher activity ratios in the deep ground-waters from borehole than in the surface and spring waters; Such high U activity ratios are indicative of long water-rock interactions, which is consistent with the long residence times deducted from the CFC and SF6 data.

  12. Magma differentiation rates from ( 226Ra / 230Th) and the size and power output of magma chambers

    NASA Astrophysics Data System (ADS)

    Blake, Stephen; Rogers, Nick

    2005-08-01

    We present a mathematical model for the evolution of the ( 226Ra / 230Th) activity ratio during simultaneous fractional crystallization and ageing of magma. The model is applied to published data for four volcanic suites that are independently known to have evolved by fractional crystallization. These are tholeiitic basalt from Ardoukoba, Djibouti, MORB from the East Pacific Rise, alkali basalt to mugearite from Vestmannaeyjar, Iceland, and basaltic andesites from Miyakejima, Izu-Bonin arc. In all cases ( 226Ra / 230Th) correlates with indices of fractional crystallization, such as Th, and the data fall close to model curves of constant fractional crystallization rate. The best fit rates vary from 2 to 6 × 10 - 4 yr - 1 . Consequently, the time required to generate moderately evolved magmas ( F ≤ 0.7) is of the order of 500 to 1500 yrs and closed magma chambers will have lifetimes of 1700 to 5000 yrs. These rates and timescales are argued to depend principally on the specific power output (i.e., power output per unit volume) of the magma chambers that are the sites of fractional crystallization. Equating the heat flux at the EPR to the heat flux from the sub-axial magma chamber that evolves at a rate of ca. 3 × 10 - 4 yr - 1 implies that the magma body is a sill of ca. 100 m thickness, a value which coincides with independent estimates from seismology. The similarity of the four inferred differentiation rates suggests that the specific power output of shallow magma chambers in a range of tectonic settings covers a similarly narrow range of ca. 10 to 50 MW km - 3 . Their differentiation rates are some two orders of magnitude slower than that of the basaltic Makaopuhi lava lake, Hawaii, that cooled to the atmosphere. This is consistent with the two orders of magnitude difference in heat flux between Makaopuhi and the East Pacific Rise. ( 226Ra / 230Th) data for magma suites related by fractional crystallization allow the magma differentiation rate to be estimated

  13. Rapid evolution of ritual architecture in central Polynesia indicated by precise 230Th/U coral dating

    PubMed Central

    Sharp, Warren D.; Kahn, Jennifer G.; Polito, Christina M.; Kirch, Patrick V.

    2010-01-01

    In Polynesia, the complex Society Islands chiefdoms constructed elaborate temples (marae), some of which reached monumental proportions and were associated with human sacrifice in the ‘Oro cult. We investigated the development of temples on Mo‘orea Island by 230Th/U dating of corals used as architectural elements (facing veneers, cut-and-dressed blocks, and offerings). The three largest coastal marae (associated with the highest-ranked chiefly lineages) and 19 marae in the inland ‘Opunohu Valley containing coral architectural elements were dated. Fifteen corals from the coastal temples meet geochemical criteria for accurate 230Th/U dating, yield reproducible ages for each marae, and have a mean uncertainty of 9 y (2σ). Of 41 corals from wetter inland sites, 12 show some diagenesis and may yield unreliable ages; however, the majority (32) of inland dates are considered accurate. We also obtained six 14C dates on charcoal from four marae. The dates indicate that temple architecture on Mo‘orea Island developed rapidly over a period of approximately 140 y (ca. AD 1620–1760), with the largest coastal temples constructed immediately before initial European contact (AD 1767). The result of a seriation of architectural features corresponds closely with this chronology. Acropora coral veneers were superceded by cut-and-dressed Porites coral blocks on altar platforms, followed by development of multitier stepped altar platforms and use of pecked basalt stones associated with the late ‘Oro cult. This example demonstrates that elaboration of ritual architecture in complex societies may be surprisingly rapid. PMID:20616079

  14. Rapid evolution of ritual architecture in central Polynesia indicated by precise 230Th/U coral dating.

    PubMed

    Sharp, Warren D; Kahn, Jennifer G; Polito, Christina M; Kirch, Patrick V

    2010-07-27

    In Polynesia, the complex Society Islands chiefdoms constructed elaborate temples (marae), some of which reached monumental proportions and were associated with human sacrifice in the 'Oro cult. We investigated the development of temples on Mo'orea Island by 230Th/U dating of corals used as architectural elements (facing veneers, cut-and-dressed blocks, and offerings). The three largest coastal marae (associated with the highest-ranked chiefly lineages) and 19 marae in the inland 'Opunohu Valley containing coral architectural elements were dated. Fifteen corals from the coastal temples meet geochemical criteria for accurate 230Th/U dating, yield reproducible ages for each marae, and have a mean uncertainty of 9 y (2sigma). Of 41 corals from wetter inland sites, 12 show some diagenesis and may yield unreliable ages; however, the majority (32) of inland dates are considered accurate. We also obtained six 14C dates on charcoal from four marae. The dates indicate that temple architecture on Mo'orea Island developed rapidly over a period of approximately 140 y (ca. AD 1620-1760), with the largest coastal temples constructed immediately before initial European contact (AD 1767). The result of a seriation of architectural features corresponds closely with this chronology. Acropora coral veneers were superceded by cut-and-dressed Porites coral blocks on altar platforms, followed by development of multitier stepped altar platforms and use of pecked basalt stones associated with the late 'Oro cult. This example demonstrates that elaboration of ritual architecture in complex societies may be surprisingly rapid.

  15. (226Ra)/(230Th) Excess Generated in the Lower Crust: Implications for Magma Transport Rates in Arc Settings

    NASA Astrophysics Data System (ADS)

    Dufek, J. D.; Cooper, K. M.

    2004-12-01

    226Ra-excesses in arc magmas have been interpreted to result from flux melting of the mantle above subducting slabs and subsequent fast ascent rates of magma from slab to surface, up 1000 m/yr and higher. Implied by this hypothesis is that the magma has not stalled at any depth for long periods of time, limiting the amount of time for assimilation of crustal material and homogenization of magmas. However, mixing of mantle melts with mid to lower crustal melts has been inferred in numerous localities, especially in continental arc settings. In addition, very short residence times may be in conflict with crystal residence of thousands to tens of thousands of years in arc lavas. We present calculations that demonstrate that incongruent melting of the lower crust could either maintain or augment mantle-derived Ra-excesses and so reduce vertical transport rates to 10 m/yr or less. In particular, we found that dehydration melting of amphibolite can produce modeled 226Ra-excesses greater than 300 percent with corresponding 230Th-excesses of approx. 14 percent. Both the modal percentage of garnet and melt fraction contribute to the degree of Ra-excess, and a wide range of garnet compositions can produce significant disequilibria. Mixtures of such an amphibolite dehydration melt with mantle melts will likely retain a 238U-excess (subducted slab) signature, although lower crustal melting without such mixing could help explain some of the enigmatic silicic magmas observed that have 230Th-excesses. This amphibolite dehydration melting process will also produce elevated Sr/Y and La/Yb ratios, similar to those observed in several arc settings, that may distinguish these magmas from those with 226Ra-excesses produced by slab-dewatering alone.

  16. SUPPLEMENTARY COMPARISON: Activity measurements of a suite of radionuclides (40K, 137Cs, 210Pb, 210Po, 228Ra, 232Th, 234U, 235U, 238U, 238Pu, 239Pu, 239+240Pu, 241Am) in vegetal reference material (seaweed)

    NASA Astrophysics Data System (ADS)

    Outola, I.; Inn, K. G. W.; Karam, L. R.

    2008-01-01

    In 2005, the CCRI decided that a comparison undertaken from 2002 to 2005 by the NIST (SIM) in the development of a new seaweed standard reference material (SRM) was sufficiently well constructed that it could be converted into a supplementary comparison under CCRI(II), with comparison identifier CCRI(II)-S1, so as to support calibration and measurement capability (CMC) claims for radionuclide measurements in reference material (specifically, plant material). Previous comparisons of radionuclides have been of single or multiple nuclides in non-complex matrices and results of such could not be extended to support capabilities to measure the same nuclides in reference materials. The results of this comparison have been reported to the participants, and were also used to determine the certified reference values of the SRM. The key comparison working group (KCWG) of the CCRI(II) has approved this approach as a mechanism to link all the results to the certified 'reference values' in lieu of the key comparison reference value (KCRV) of these specified radionuclides in this type of matrix (vegetative) so as to support CMCs of similar materials. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCRI Section II, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

  17. 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.

  18. Measurement of the Total Kinetic Energy Release (TKE) in 232 Th(n,f) with En = 2.59 - 87.31 MeV

    NASA Astrophysics Data System (ADS)

    King, Jonathan; Yanez, Ricardo; Barrett, Jonathan; Loveland, Walter; Tovesson, Fredrik; Fotiades, Nick; Lee, Hye Young

    2015-04-01

    Experimental results for the Total Kinetic Energy Release (TKE) of 232 Th(n,f) with En = 2.59 - 87.31 MeV will be presented. The experiment was performed at the 15R beamline at the Weapons Neutron Research(WNR) facility at LANL-LANSCE. WNR provides a white spectrum of neutrons peaking at 2 MeV and reaching up to 800 MeV, with neutron energies being deduced from measurements of the neutron time of flight (TOF). A thin-backed 232 ThF4 target of 2 cm diameter with a thorium areal density of 178.9 μg/cm2 was placed between two arrays of Hammamatsu PIN diodes (active area 4 cm2 each). The beam was collimated to 1 cm diameter. The target was placed 45 degrees off of the beam axis, with the detectors at 60 degrees and 120 degrees from the beam axis. Over 25,000 fission fragment coincidence events were recorded, allowing for sixteen energy bins between 2.59 and 87.31 MeV. We believe that this will be the most comprehensive published measurement of the TKE for 232 Th(n,f) with En = 2.59 - 87.31 MeV. This work was supported in part by the Director, Office of Energy Research, Division of Nuclear Physics of the Office of High Energy and Nuclear Physics of the USDoE under Grant DE-FG06-97ER41026. This work has benefited from the use of the Los Alamos Neutron Science Center at the Los Alamos National Laboratory. This facility is funded by the USDoE under DOE Contract No. DE-AC52-06NA25396.

  19. Quantification of transfer of (238)U, (226)Ra, (232)Th, (40)K and (137)Cs in mosses of a semi-natural ecosystem.

    PubMed

    Dragović, S; Mihailović, N; Gajić, B

    2010-02-01

    There is a lack of appropriate data on transfer of some radionuclides on many terrestrial biota groups. To expand the available data concentration ratios of (238)U, (226)Ra, (232)Th, (40)K and (137)Cs in mosses are presented in this paper. The relationship between concentration ratios of radionuclides and physicochemical characteristics of the underlying soil was also investigated. The data on concentration ratios obtained here will provide a useful addition to the currently used database of transfer parameters, particularly for natural radionuclides.

  20. Comparison of the (p,xn) cross sections from /sup 238/U, /sup 235/U, and /sup 232/Th targets irradiated with 200-MeV protons

    SciTech Connect

    Chu, Y.Y.; Zhou, M.L.

    1982-01-01

    We have measured absolute cross sections for (p,xn) reactions (x ranges from 0 to 8) from /sup 238/U, /sup 235/U, and /sup 232/Th targets irradiated with 200-MeV protons at the Brookhaven AGS Linac injector. Chemical yields were determined by using /sup 239/Np and /sup 233/Pa as tracers. Yield patterns obtained in this work can be compared to the experimental results and theoretical calculations from earlier work, and they are consistent within the framework of intranuclear cascade followed by neutron evaporation and fission competition.

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

    USGS Publications Warehouse

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

    2002-01-01

    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 (mappabe 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 (2??) 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. Copyright ?? 2002 Elsevier Science Ltd.

  2. Determination of (238)U, (232)Th and (40)K activity concentrations in riverbank soil along the Chao Phraya river basin in Thailand.

    PubMed

    Santawamaitre, T; Malain, D; Al-Sulaiti, H A; Bradley, D A; Matthews, M C; Regan, P H

    2014-12-01

    The activity concentrations of (238)U, (232)Th and (40)K in riverbank soil along the Chao Phraya river basin was determined through gamma-ray spectrometry measurements made using a hyper-pure germanium detector in a low background configuration. The ranges of activity concentrations of (238)U, (232)Th and (40)K were found to be 13.9 ↔ 76.8, 12.9 ↔ 142.9 and 178.4 ↔ 810.7 Bq kg(-1), respectively. The anthropogenic radionuclide, (137)Cs, was not observed in statistically significant amounts above the background level in the current study. The absorbed gamma dose rate in air at 1 m above the ground surface, the outdoor annual effective dose equivalent, the values of the radium equivalent activity and the external hazard index associated with all the soil samples in the present work were evaluated. The results indicate that the radiation hazard from primordial radionuclides in all soil samples from the area studied in this current work is not significant.

  3. Assessment of (226)Ra, (238)U, (232)Th, (137)Cs and (40)K activities from the northern coastline of Oman Sea (water and sediments).

    PubMed

    Darabi-Golestan, F; Hezarkhani, A; Zare, M R

    2017-02-27

    Water and sediment samples were collected from northern coast of Oman Sea covering from Goatr to Hormoz canyon seaport. Water and sediment quality assessment for naturally or anthropogenic radionuclides at Oman Sea as a main strategic golf for trade and transit, is an important issue. Correspondence analysis (CA) by R-mode analysis represents that sigma(T)-temperature-conductivity-O2 parameters are well-correlated with (226)Ra, (232)Th and (40)K. Accordingly Q-mode analysis revealed an indicator samples of ST13W for different radionuclides, ST03W for O2, and simultaneously ST34W-ST21W-ST08W-ST04W for sigma(T) parameters. The CA results overlapped with factor and cluster analysis results that explained 85.8% of total variance of water samples. Descriptive analysis of sediments indicates more significant variation than water samples. The (232)Th and (226)Ra generally showing that ST13D to ST25D sediments that restricted to Pi Bashk coastline are concentrated from (137)Cs and (40)K. By comparison with reference-values from Iran and other parts of the world, they are acceptable with respect to environmental and radioisotope hazards.

  4. Assessment of environmental (226)Ra, (232)Th and (40)K concentrations in the region of elevated radiation background in Segamat District, Johor, Malaysia.

    PubMed

    Saleh, Muneer Aziz; Ramli, Ahmad Termizi; Alajerami, Yasser; Aliyu, Abubakar Sadiq

    2013-10-01

    Extensive environmental survey and measurements of gamma radioactivity in the soil samples collected from Segamat District were conducted. Two gamma detectors were used for the measurements of background radiation in the area and the results were used in the computation of the mean external radiation dose rate and mean weighted dose rate, which are 276 nGy h(-1) and 1.169 mSv y(-1), respectively. A high purity germanium (HPGe) detector was used in the assessment of activity concentrations of (232)Th, (226)Ra and (40)K. The results of the gamma spectrometry range from 11 ± 1 to 1210 ± 41 Bq kg(-1) for (232)Th, 12 ± 1 to 968 ± 27 Bq kg(-1) for (226)Ra, and 12 ± 2 to 2450 ± 86 Bq kg(-1) for (40)K. Gross alpha and gross beta activity concentrations range from 170 ± 50 to 4360 ± 170 Bq kg(-1) and 70 ± 20 to 4690 ± 90 Bq kg(-1), respectively. These results were used in the plotting of digital maps (using ARCGIS 9.3) for isodose. The results are compared with values giving in UNSCEAR 2000.

  5. Protactinium and isotopes of thorium in metalliferous sediments from the Bauer depression

    SciTech Connect

    Arslanov, K.A.; Kuznetsov, V.Yu.; Lokshin, N.V.; Pospelov, Yu.N.

    1989-01-01

    Results are presented of a study of the vertical distribution of /sup 238/U, /sup 234/U, /sup 232/Th, /sup 230/Th, and /sup 231/Pa isotopes in a column of metalliferous sediments from the Bauer depression (southeastern part of the Pacific Ocean). On the basis of the obtained data a hypothesis is formulated concerning the authigenic production of /sup 230/Th and /sup 231/Pa in these deposits, i.e, the similarity of the physicochemical behavior of /sup 230/Th and /sup 231/Pa found in pelagic sediments is found in these specific sediments also. We present arguments in favor of the identical behavior of these radionuclides in the marine environment. With the help of the ionium method of dating marine sediments, the average rate of sedimentation of the investigated column of metalliferous sediments from the Bauer depression was calculated.

  6. Measurement of activity concentrations of 40K, 226Ra and 232Th for assessment of radiation hazards from soils of the southwestern region of Nigeria.

    PubMed

    Ajayi, Oladele Samuel

    2009-08-01

    Activity concentrations of the selected radionuclides (40)K, (226)Ra and (232)Th were measured in surface soil samples collected from 38 cities in the southwest region of Nigeria by means of gamma spectroscopy with a high-purity germanium detector. Measured activity concentration values of (40)K varied from 34.9 +/- 4.4 to 1,358.6 +/- 28.5 Bq kg(-1) (given on a dry mass (DM) basis) with a mean value of 286.5 +/- 308.5 Bq kg(-1); that of (226)Ra varied from 9.3 +/- 3.7 to 198.1 +/- 13.8 Bq kg(-1) with a mean value of 54.5 Bq kg(-1) and a standard deviation of 38.7 Bq kg(-1), while that of (232)Th varied from 5.4 +/- 1.1 to 502.0 +/- 16.5 Bq kg(-1) with a mean value of 91.1 Bq kg(-1) and standard deviation of 100.9 Bq kg(-1). The mean activity concentration values obtained for (226)Ra and (232)Th are greater than the world average values reported by the United Nations Scientific Committee on Effects of Atomic Radiation for areas of normal background radiation. Radiological indices were estimated for the radiation/health hazards of the natural radioactivity of all soil samples. Estimated absorbed dose rates in air varied from 12.42 +/- 2.25 to 451.33 +/- 19.06 nGy h(-1), annual outdoor effective dose rates from 0.015 +/- 0.003 to 0.554 +/- 0.023 mSv year(-1), internal hazard index from 0.10 +/- 0.03 to 3.02 +/- 0.16, external hazard index from 0.07 +/- 0.01 to 2.60 +/- 0.11, representative level index from 0.19 +/- 0.03 to 6.84 +/- 0.29, activity index from 0.09 +/- 0.02 to 3.42 +/- 0.15, and radium equivalent activity from 26.95 +/- 5.04 to 963.15 +/- 41.87 Bq kg(-1). Only the mean value of the representative level index exceeds the limit for areas of normal background radiation. All other indices show mean values that are lower than the recommended limits.

  7. Comment on "Radiocarbon Calibration Curve Spanning 0 to 50,000 Years B.P. Based on Paired 230Th/234U/238U and 14C Dates on Pristine Corals" by R.G. Fairbanks, R. A. Mortlock, T.-C. Chiu, L. Cao, A. Kaplan, T. P. Guilderson, T. W. Fairbanks, A. L. Bloom, P

    SciTech Connect

    Reimer, P J; Baillie, M L; Bard, E; Beck, J W; Blackwell, P G; Buck, C E; Burr, G S; Edwards, R L; Friedrich, M; Guilderson, T P; Hogg, A G; Hughen, K A; Kromer, B; McCormac, G; Manning, S; Reimer, R W; Southon, J R; Stuiver, M; der Plicht, J v; Weyhenmeyer, C E

    2005-10-02

    Radiocarbon calibration curves are essential for converting radiocarbon dated chronologies to the calendar timescale. Prior to the 1980's numerous differently derived calibration curves based on radiocarbon ages of known age material were in use, resulting in ''apples and oranges'' comparisons between various records (Klein et al., 1982), further complicated by until then unappreciated inter-laboratory variations (International Study Group, 1982). The solution was to produce an internationally-agreed calibration curve based on carefully screened data with updates at 4-6 year intervals (Klein et al., 1982; Stuiver and Reimer, 1986; Stuiver and Reimer, 1993; Stuiver et al., 1998). The IntCal working group has continued this tradition with the active participation of researchers who produced the records that were considered for incorporation into the current, internationally-ratified calibration curves, IntCal04, SHCal04, and Marine04, for Northern Hemisphere terrestrial, Southern Hemisphere terrestrial, and marine samples, respectively (Reimer et al., 2004; Hughen et al., 2004; McCormac et al., 2004). Fairbanks et al. (2005), accompanied by a more technical paper, Chiu et al. (2005), and an introductory comment, Adkins (2005), recently published a ''calibration curve spanning 0-50,000 years''. Fairbanks et al. (2005) and Chiu et al. (2005) have made a significant contribution to the database on which the IntCal04 and Marine04 calibration curves are based. These authors have now taken the further step to derive their own radiocarbon calibration extending to 50,000 cal BP, which they claim is superior to that generated by the IntCal working group. In their papers, these authors are strongly critical of the IntCal calibration efforts for what they claim to be inadequate screening and sample pretreatment methods. While these criticisms may ultimately be helpful in identifying a better set of protocols, we feel that there are also several erroneous and misleading statements made by these authors which require a response by the IntCal working group. Furthermore, we would like to comment on the sample selection criteria, pretreatment methods, and statistical methods utilized by Fairbanks et al. in derivation of their own radiocarbon calibration.

  8. Uranium ((234)U, (235)U and (238)U) contamination of the environment surrounding phosphogypsum waste heap in Wiślinka (northern Poland).

    PubMed

    Olszewski, Grzegorz; Boryło, Alicja; Skwarzec, Bogdan

    2015-08-01

    The aim of this work was to determine the uranium concentration ((234)U, (235)U and (238)U) and values of the activity ratio (234)U/(238)U in soil samples collected near phosphogypsum waste heap in Wiślinka (northern Poland). On the basis of the studies it was found that the values of the (234)U/(238)U activity ratio in the analyzed soils collected in the vicinity of phosphogypsum dump in Wiślinka are in most cases close to one and indicate the phosphogypsum origin of the analyzed nuclides. The obtained results of uranium concentrations are however much lower than in previous years before closing of the phosphogypsum stockpile. After this process and covering the phosphogypsum stockpile in Wiślinka with sewage sludge, phosphogypsum particles are successfully immobilized. In the light of the results the use of phosphate fertilizers seems to be a major problem. Prolonged and heavy rains can cause leaching accumulated uranium isotopes in the phosphogypsum stockpile, which will be washed into the Martwa Wisła and on the fields in the immediate vicinity of this storage.

  9. 230Th and 231Pa on GEOTRACES GA03, the U.S. GEOTRACES North Atlantic transect, and implications for modern and paleoceanographic chemical fluxes

    NASA Astrophysics Data System (ADS)

    Hayes, Christopher T.; Anderson, Robert F.; Fleisher, Martin Q.; Huang, Kuo-Fang; Robinson, Laura F.; Lu, Yanbin; Cheng, Hai; Edwards, R. Lawrence; Moran, S. Bradley

    2015-06-01

    The long-lived uranium decay products 230Th and 231Pa are widely used as quantitative tracers of adsorption to sinking particles (scavenging) in the ocean by exploiting the principles of radioactive disequilibria. Because of their preservation in the Pleistocene sediment record and through largely untested assumptions about their chemical behavior in the water column, the two radionuclides have also been used as proxies for a variety of chemical fluxes in the past ocean. This includes the vertical flux of particulate matter to the seafloor, the lateral flux of insoluble elements to continental margins (boundary scavenging), and the southward flux of water out of the deep North Atlantic. In a section of unprecedented vertical and zonal resolution, the distributions of 230Th and 231Pa across the North Atlantic shed light on the marine cycling of these radionuclides and further inform their use as tracers of chemical flux. Enhanced scavenging intensities are observed in benthic layers of resuspended sediments on the eastern and western margins and in a hydrothermal plume emanating from the Mid-Atlantic Ridge. Boundary scavenging is clearly expressed in the water column along a transect between Mauritania and Cape Verde which is used to quantify a bias in sediment fluxes calculated using 230Th-normalization and to demonstrate enhanced 231Pa removal from the deep North Atlantic by this mechanism. The influence of deep ocean ventilation that leads to the southward export of 231Pa is apparent. The 231Pa/230Th ratio, however, predominantly reflects spatial variability in scavenging intensity, complicating its applicability as a proxy for the Atlantic meridional overturning circulation.

  10. Dramatic changes in the dissolved 230Th concentration of seawater in Canada Basin between 1995 and 2009: a transient Arctic circulation signal?

    NASA Astrophysics Data System (ADS)

    Francois, Roger; Soon, Maureen

    2010-05-01

    A dissolved 230Th profile measured in the Arctic Ocean in 1983 under permanent ice cover (Alpha Ridge; 85°50'N, 108°50'W) documented concentrations substantially higher than in any other ocean basins, reflecting very low particle flux and scavenging intensity (Bacon et al., 1989). In contrast, similar measurements closer to the ice edge conducted in Canada Basin in 1995 (72°32'N, 143°50'W, 3500 m) found much lower concentrations, reflecting higher rates of particle flux and particle scavenging (Edmonds et al, 1998). In November 2007, we measured dissolved 230Th at two Canada Basin stations (KC2000; 71°44'N, 135°30'W, 1925m; KC2700; 72°28'N, 136°56'W, 2490m) and compared these profiles to that obtained in 1995. While the earlier 230Th profile displayed a linear increase in concentration with depth, as predicted by a simple reversible absorption model which neglects water mass transport, the 2007 profile obtained at KC2700 documented very large deviations from linearity, with a prominent maximum centered within the Atlantic Water. The profile taken closer to the shelf (KC2000) did not show this feature. These observations suggested that the prominent maximum in 230Th concentration at KC2700 could have been produced by entrainment of water from the permanently ice-covered Arctic interior into the warm Atlantic Water which is slowly penetrating into the eastern sector of Canada Basin and as such could provide information on the path of Atlantic Water intrusion. New data obtained from the same area in September 2009 during the Canadian IPY-GEOTRACES program documents the evolution of this signal. Reference: Bacon et al. (1989), Earth and Planet. Sci. Letters, 95, 15-22. Edmonds et al. (1998), Science, 280, 405-407.

  11. Measurement of 232Th(n,5n γ) cross sections from 29 MeV to 42 MeV

    NASA Astrophysics Data System (ADS)

    Kerveno, M.; Nolte, R.; Baumann, P.; Dessagne, Ph.; Jericha, E.; Jokic, S.; Koning, A. J.; Lukic, S.; Meulders, J. P.; Nachab, A.; Pavlik, A.; Reginatto, M.; Rudolf, G.

    2014-10-01

    The excitation function of the reaction 232 Th( n, 5 nγ)228 Th from 29 to 42 MeV has been measured for the first time at the quasi-monoenergetic neutron beam of the UCL cyclotron CYCLONE employing the 7Li(p,n) source reaction. Taking advantage of the good energy resolution of the planar High-Purity Germanium (HPGe) detectors, prompt γ-ray spectroscopy was used to detect the γ-rays resulting from the decay of excited states of nuclei created by the (n, xn) reactions. The neutron beam was characterized by a combination of time of flight measurements carried out using a liquid scintillation detector and a 238U fission ionization chamber. Fluence measurements were performed using a proton recoil telescope. The results are compared with TALYS-1.4 code calculations.

  12. Thorium distributions in high- and low-dust regions and the significance for iron supply

    NASA Astrophysics Data System (ADS)

    Hayes, Christopher T.; Rosen, Jeffrey; McGee, David; Boyle, Edward A.

    2017-02-01

    Thorium and uranium isotopes (232Th, 230Th, 238U, and 234U) were investigated to refine their use for estimating mineral dust deposition and Fe delivery to the ocean. U concentrations and isotope ratios were consistent with conservative behavior and can safely be described using published U-salinity relationships and global average seawater isotopic composition. Near Barbados, waters affected by the Amazon outflow contained elevated 232Th. This signals one region where the thorium-dust method is inaccurate because of a confounding continental input. Dissolved 232Th fluxes in this region suggest that Amazonian Fe supply to the adjacent open ocean is much larger than local atmospheric deposition. The colloidal content of dissolved Th south of Bermuda was found to be quite small (2-6%), similar to that found north of Hawaii, despite the order of magnitude higher dust deposition in the Atlantic. This finding supports the assumption that dissolved 232Th and 230Th are scavenged at the same rate despite their different sources and also sheds light on the increase of dissolved 232Th fluxes with integrated depth. Outside the region influenced by Amazon River waters, dissolved 232Th fluxes are compared with Bermudan aerosol Fe deposition to estimate that fractional Th solubility is around 20% in this region. Finally, new dissolved and soluble Fe, Mn, and Cr data from the subtropical North Pacific support the idea that Fe concentrations in the remote ocean are highly buffered, whereas 232Th has a larger dynamic range between high- and low-dust regions.

  13. Radioactivity of cigarettes and the importance of (210)Po and thorium isotopes for radiation dose assessment due to smoking.

    PubMed

    Kubalek, Davor; Serša, Gregor; Štrok, Marko; Benedik, Ljudmila; Jeran, Zvonka

    2016-05-01

    Tobacco and tobacco smoke are very complex mixtures. In addition to various chemical and organic compounds they also contain natural radioactive elements (radionuclides). In this work, the natural radionuclide activity concentrations ((234)U, (238)U, (228)Th, (230)Th, (232)Th, (226)Ra, (210)Pb and (210)Po) of nine different cigarette samples available on the Slovenian market are reported. In addition to (210)Po, the transfer of thorium isotopes from a cigarette to a smoker's body and lungs have been determined for the first time. Cigarette smoke and exhaled air from smokers' lungs were collected from volunteer smokers (C-4 brand) to determinate what quantity of (210)Po and thorium isotopes is transferred from the tobacco to the smoker's lungs. Cigarette ash and smoked filters were also collected and analysed. Among the determined isotopes, (210)Pb and (210)Po showed the highest activity concentrations. During the smoking of one cigarette approximately 22% of (210)Po (and presumably its predecessor (210)Pb), 0.6% of (228)Th, 24% of (230)Th, and 31% of (232)Th are transferred from the cigarette and retained in the smoker's body. The estimated annual effective dose for smokers is 61 μSv/year from (210)Po; 9 μSv/year from (210)Pb; 6 μSv/year from (228)Th; 47 μSv/year from (230)Th, and 37 μSv/year from (232)Th. These results show the importance of thorium isotopes in contributing to the annual effective dose for smoking.

  14. 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

  15. Transfer Rates of 238U and 232Th for E. globulus, A. mearnsii, H. filipendula and Hazardous Effects of the Usage of Medicinal Plants From Around Gold Mine Dump Environs

    PubMed Central

    Tshivhase, Victor M.; Njinga, Raymond L.; Mathuthu, Manny; Dlamini, Thulani C.

    2015-01-01

    Medicinal plant consumption can be a source of human exposure to radioactive elements such as 238U and 232Th, which can lead to internal radiation doses. The uptake of 238U and 232Th from soils to the leaf samples of three different medicinal plant species (Eucalyptus globulus, Acacia mearnsii and Hyparrhenia filipendula) from the purlieu of the Princess gold mine dump, an abandoned contaminated tailings storage site (TSS), located at longitude 27°55′00″E and latitude 26°09′30″S in Davidsonville (Roodepoort, west of Johannesburg, South Africa) was measured. This was done using ICP-MS spectrometry and substantial differences were observed in the soil-plant transfer factor (TF) values between these radionuclides. The plant species E. globulus exhibited the highest uptake of 238U, with an average TF of 3.97, while that of H. filipendula was 0.01 and the lowest TF of 0.15 × 10−2 was measured for A. mearnsii. However, in the case of 232Th, the highest average TF was observed for A. mearnsii (0.29), followed by E. globulus (0.10) and lowest was measured for H. filipendula (0.27 × 10−2). The ratio of TF average value i.e., 238U to 232Th in the soil-plant leaves was 38.05 for E. globulus, 0.01 for A. mearnsii and 4.38 for H. filipendula. PMID:26690462

  16. 230Th and 234Th as coupled tracers of particle cycling in the ocean: A maximum likelihood approach

    NASA Astrophysics Data System (ADS)

    Wang, Wei-Lei; Armstrong, Robert A.; Cochran, J. Kirk; Heilbrun, Christina

    2016-05-01

    We applied maximum likelihood estimation to measurements of Th isotopes (234,230Th) in Mediterranean Sea sediment traps that separated particles according to settling velocity. This study contains two unique aspects. First, it relies on settling velocities that were measured using sediment traps, rather than on measured particle sizes and an assumed relationship between particle size and sinking velocity. Second, because of the labor and expense involved in obtaining these data, they were obtained at only a few depths, and their analysis required constructing a new type of box-like model, which we refer to as a "two-layer" model, that we then analyzed using likelihood techniques. Likelihood techniques were developed in the 1930s by statisticians, and form the computational core of both Bayesian and non-Bayesian statistics. Their use has recently become very popular in ecology, but they are relatively unknown in geochemistry. Our model was formulated by assuming steady state and first-order reaction kinetics for thorium adsorption and desorption, and for particle aggregation, disaggregation, and remineralization. We adopted a cutoff settling velocity (49 m/d) from Armstrong et al. (2009) to separate particles into fast- and slow-sinking classes. A unique set of parameters with no dependence on prior values was obtained. Adsorption rate constants for both slow- and fast-sinking particles are slightly higher in the upper layer than in the lower layer. Slow-sinking particles have higher adsorption rate constants than fast-sinking particles. Desorption rate constants are higher in the lower layer (slow-sinking particles: 13.17 ± 1.61, fast-sinking particles: 13.96 ± 0.48) than in the upper layer (slow-sinking particles: 7.87 ± 0.60 y-1, fast-sinking particles: 1.81 ± 0.44 y-1). Aggregation rate constants were higher, 1.88 ± 0.04, in the upper layer and just 0.07 ± 0.01 y-1 in the lower layer. Disaggregation rate constants were just 0.30 ± 0.10 y-1 in the upper

  17. U-series Disequilibria in Continental Arcs: NE Japan Case

    NASA Astrophysics Data System (ADS)

    Tepley, F. J.; Gill, J. B.; Williams, R. W.

    2005-12-01

    Basalts and andesites from continental arcs typically are close to equilibrium between (238U) and (230Th), and have subdued excesses of 226Ra compared to oceanic arcs (Turner et al., 2003). There is ambiguity whether these and other geochemical features derive from subducted sediment, subcontinental lithosphere, or the crust. We report new 238U-234U-230Th-226Ra data for 20 historical to Holocene samples from Asama in the south of NE Japan to Tarumai in the north. Most straddle the equiline with <5% excess U or Th, yet have 10-60% excess 226Ra. The only significant excess U occurs at Usu and Iwaki in the north where it correlates with higher (230Th)/(232Th) as in other arcs (e.g., Mariana). Otherwise (230Th)/(232Th) ratios are 0.75-1.05 which is less than in the surrounding Izu and Kurile oceanic arcs. Most ratios <0.95 are associated with trace element evidence of crustal contamination that drags samples down the equiline. The exception is Iwate where Th/U ratios are ~4.0 even in depleted basalts. Excess 226Ra is greater in basalts than andesites. The excess 226Ra, plus elevated 10Be and Th, is attributed to ubiquitous slab inputs that are overprinted by even higher Th contents from a crustal source with Th/U >4.

  18. Study on the radioactivity and soil-to-plant transfer factor of (226)Ra, (234)U and (238)U radionuclides in irrigated farms from the northwestern Saudi Arabia.

    PubMed

    Al-Hamarneh, Ibrahim F; Alkhomashi, N; Almasoud, Fahad I

    2016-08-01

    The present study addresses the soil-to-plant transfer factors (TFs) of (226)Ra, (234)U and (238)U for 13 types of vegetables and agricultural crops planted under semi-arid environment in the northwestern part of Saudi Arabia. Crop plants along with plant-growing soils were collected from selected farms, which are irrigated from the non-renewable Saq aquifer, and investigated for their radioactivity content by means of alpha spectrometry after applying a radiochemical separation procedure. Hence, TF data for plant roots, green parts (stem and leaves) and fruits were calculated and contrasted to those reported in the literature. Substantial differences were observed in the TFs of Ra and U radioisotopes among plant species. In crop fruits, eggplant exhibited the highest uptake of (226)Ra (TF value of 0.11), while beans (0.16) have the highest TF for (234)U and (238)U. The geometric mean TF values indicated that the crop roots tend to accumulate Ra and U about four to six-folds higher than fruits. The relation between TF values and soil concentrations showed a weak correlation. Activity ratios between radionuclides in crop plants indicated the preferential translocation of U in fruits than Ra even though Ra is more available for root uptake. The fruit/root (F/R) ratios obtained for the investigated plants shown that pepper had the smallest F/R ratios (0.07 ± 0.01, 0.12 ± 0.02 and 0.11 ± 0.02 for (226)Ra, (234)U and (238)U, respectively), while the highest F/R ratios were observed in potatoes (0.71 ± 0.15, 0.44 ± 0.10 and 0.40 ± 0.08 for (226)Ra, (234)U and (238)U, respectively). The TF and F/R ratios data of natural radionuclides in the study region can hopefully improve the scientific knowledge for future studies.

  19. A study on possible use of Urtica dioica (common nettle) plants as uranium ((234)U, (238)U) 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.

  20. Determination of specific activity of (226)Ra, (232)Th and (40)K for assessment of radiation hazards from Turkish pumice samples.

    PubMed

    Turhan, Seref; Gündüz, Lüfullah

    2008-02-01

    The specific activity of (226)Ra, (232)Th and (40)K in 52 Turkish pumice samples collected from 11 geographical areas located in Central Anatolia, Eastern Anatolia, Mediterranean and Aegean regions was determined by gamma-ray spectrometry with a high-purity germanium (HPGe) detector. The specific activity of (226)Ra, (232)Th and (40)K ranged from 12.7+/-0.5 to 256.2+/-9.1Bqkg(-1) with a mean of 89.1+/-65.2Bqkg(-1), 12.3+/-1.0 to 237.9+/-12.2Bqkg(-1) with a mean of 87.0+/-61.4Bqkg(-1) and 300.1+/-5.5 to 1899.0+/-30.8Bqkg(-1) with a mean of 1211.9+/-419.8Bqkg(-1), respectively. Elemental concentrations were determined for U (from 1.0 to 20.7ppm with a mean of 7.2+/-5.3ppm), Th (from 3.0 to 58.6ppm with a mean of 21.4+/-15.1ppm) and K (from 1.0 to 6.1% with a mean of 3.9+/-1.3%). The radium equivalent activity (Ra(eq)), the activity index, the emanation coefficient, the (222)Rn mass exhalation rate, the indoor absorbed dose rate and the effective dose rate were estimated for the radiation hazard of the natural radioactivity in all samples. The calculated mean Ra(eq) value was 306.6+/-177.7Bqkg(-1) (54.6+/-5.5 to 737.6+/-49.0Bqkg(-1)) for all pumice samples. This value is lower than the recommended limit value of 370Bqkg(-1) for building raws and products. The emanation coefficient and the (222)Rn mass exhalation rate of all samples ranged from 29.4 to 42.9% with a mean of 36.2% and from 11.0 to 196.4microBqkg(-1)s(-1) with a mean of 73.5microBqkg(-1)s(-1), respectively. The mean indoor absorbed dose rate and the corresponding mean effective dose rate were 274.6+/-153.6nGyh(-1) (50.4-644.6nGyh(-1)) and 1.35+/-0.75mSvy(-1) (0.24-3.16mSvy(-1)), respectively. For all pumice samples the mean indoor absorbed dose rate is about three times higher than the population-weighted average of 84nGyh(-1), while the mean effective dose rate values except for PUM 05, PUM 06, PUM 10 and PUM 15 exceed the dose criterion of 1mSvy(-1).

  1. In situ Th and U isotope determinations of low-U geological samples using laser ablation single-collector sector-field ICPMS

    NASA Astrophysics Data System (ADS)

    Mertz-Kraus, R.; Jochum, K. P.; Sharp, W. D.; Stoll, B.; Weis, U.; Andreae, M. O.

    2009-12-01

    In situ spatially resolved U-series dating of geological and biological silicates, phosphates and carbonates (e.g., bone, speleothem, coral, and pedogenic silica and carbonate), facilitates measurement of the rates of natural processes (e.g., precipitation, crystallization) during the past 500,000 years. We present a LA-ICPMS technique for precise and accurate determination of Th and U isotopic ratios applicable to samples with U concentrations as low as 0.4 µg/g. Previously, in situ U-series determinations have been done using multi-collector ICPMS. We use a single-collector sector-field ICPMS connected to a 213 Nd:YAG laser ablation system. Precision and accuracy were determined for different matrices, such as synthetic NIST SRM 612, diverse silicate MPI-DING and USGS reference glasses, 91500 zircon, and a travertine previously analyzed by TIMS.230Th and 234U (~0.00001 to 0.0001 µg/g), required laser tracks up to 1800 µm long, rastering over a 400 x 400 µm square and measurement times of 5 to 25 minutes. We applied corrections for background (< 0.2 cps), the tails of 232Th, 235U and 238U peaks on 230Th and 234U (0.1 to 6 cps corresponding to a proportion of 0.3 to 30 % of the measured peak for 232Th and 238U concentrations of 0.003 to 10 µg/g), instrumental mass fractionation (~1 % per atomic mass unit), and differences in element sensitivity of Th and U using the certified values of the reference glasses.230Th/238U and 234U/238U determinations varies between 1.6 and 5 % depending on the extent of peak tailing corrections. We obtained 230Th/238U = 1.65 x 10-5 and 234U/238U = 5.29 x 10-5 for BCR-2G (1.7 µg/g U, 5.9 µg/g Th) which agree within 2 % and 4 %, respectively, with TIMS values (Matthews et al., 2008). For the travertine (2.5 µg/g U, 0.003 µg/g Th) the mean values for four scans (~0.14 mg sample each) are 230Th/238U = 2.47 x 10-5 and 234U/238U = 7.49 x 10-5, within 2 % of TIMS values. Matthews K. et al. (2008), Evaluation of Solid Geologic

  2. R-MATRIX ANALYSIS of 232Th NEUTRON TRANSMISSIONS and CAPTURE CROSS SECTIONS in the ENERGY RANGE THERMAL to 4 keV

    SciTech Connect

    Derrien, Herve; Leal, Luiz C; Larson, Nancy M

    2008-01-01

    Neutron resonance parameters of 232Th were obtained from the Reich-Moore SAMMY analysis of high-resolution neutron transmission measurements performed at the Oak Ridge Electron Linear Accelerator (ORELA) by Olsen in 1981, along with the high-resolution neutron capture measurements performed in 2005 at the Geel Linear Accelerator (GELINA, Belgium) by Schillebeeckx and at the n-TOF facility (CERN, Switzerland) by Aerts. The ORELA data were analyzed previously by Olsen with the Breit-Wigner multilevel code SIOB, and the results were used in the ENDF/B-VI evaluation. In the new analysis of the Olsen neutron transmissions by the modern computer code SAMMY, better accuracy is obtained for the resonance parameters by including in the experimental data base the recent experimental neutron capture data. The experimental data base and the method of analysis are described in the report. The neutron transmissions and the capture cross sections calculated with the resonance parameters are compared to the experimental values. A description is given of the statistical properties of the resonance parameters. The new evaluation results in a decrease in the capture resonance integral and improves the prediction of integral thermal benchmarks.

  3. Activity concentrations of 226Ra, 232Th, 40K and 137Cs radionuclides in Turkish medicinal herbs, their ingestion doses and cancer risks

    NASA Astrophysics Data System (ADS)

    Parmaksız, Aydın; Ağuş, Yusuf

    2014-11-01

    Twenty-two medicinal herb samples, each representing a distinct species, were collected from Turkish markets and measured by the gamma spectrometric method. The activity concentration of 226Ra in medicinal herbs was found in the range of minimum detectable activity (MDA) and 15.1 ± 2.2 Bqkg-1. The activity concentration of 232Th ranged from MDA values to 3.5 ± 0.8 Bqkg-1. The activity concentration of 40K varied between 50.0 ± 16.8 and 1311.5 ± 57.3 Bqkg-1. All 137Cs activity concentrations of medicinal herbs were found to have lower than MDA values. The bone surface dose, lower large intestine and colon doses were found to be 182.9, 18.8 and 18.7 µSvy-1, respectively. The highest committed effective dose originated from the annual ingestion of 1 kg medicinal herb was calculated notably low as 9.0 µSv. The cancer risk of ingestion of medicinal herbs was found to be small enough to be neglected. The selected Turkish medicinal herbs are considered safe for human consumption.

  4. Calibration factors for determination of relativistic particle induced fission rates in natU, 235U, 232Th, natPb and 197Au foils

    NASA Astrophysics Data System (ADS)

    Hashemi-Nezhad, S. R.; Zhuk, Igor; Potapenko, A.; Kievets, M.; Krivopustov, M. I.

    2012-02-01

    Calibration factors w, for determination of fission rate in metallic foils of natU, 235U, 232Th, natPb and 197Au were determined for foils in contact with synthetic mica track detectors. Proton-induced fission at proton energies of 0.7 GeV and 1.5 GeV were used. Using our experimental results as well as those of the other authors, w for different foil-mica systems were determined. Two methods were used to calculate w, relative to the calibration factor for uranium-mica system, which has been obtained in a standard neutron field of energy 14.7 MeV. One of these methods requires the knowledge of the mean range of the fission fragments in the foils of interest and other method needs information on the values of the fission cross-sections at the required energies as well as the density of the tracks recorded in the track detectors in contact with the foil surfaces. The obtained w-values were compared with Monte Carlo calculations and good agreements were found. It is shown that a calibration factor obtained at low energy neutron induced fissions in uranium isotopes deviates only by less than 10% from those obtained at relativistic proton induced fissions.

  5. Large scale accelerator production of (225)Ac: Effective cross sections for 78-192MeV protons incident on (232)Th targets.

    PubMed

    Griswold, J R; Medvedev, D G; Engle, J W; Copping, R; Fitzsimmons, J M; Radchenko, V; Cooley, J C; Fassbender, M E; Denton, D L; Murphy, K E; Owens, A C; Birnbaum, E R; John, K D; Nortier, F M; Stracener, D W; Heilbronn, L H; Mausner, L F; Mirzadeh, S

    2016-12-01

    Actinium-225 and (213)Bi have been used successfully in targeted alpha therapy (TAT) in preclinical and clinical research. This paper is a continuation of research activities aiming to expand the availability of (225)Ac. The high-energy proton spallation reaction on natural thorium metal targets has been utilized to produce millicurie quantities of (225)Ac. The results of sixteen irradiation experiments of thorium metal at beam energies between 78 and 192MeV are summarized in this work. Irradiations have been conducted at Brookhaven National Laboratory (BNL) and Los Alamos National Laboratory (LANL), while target dissolution and processing was carried out at Oak Ridge National Laboratory (ORNL). Excitation functions for actinium and thorium isotopes, as well as for some of the fission products, are presented. The cross sections for production of (225)Ac range from 3.6 to 16.7mb in the incident proton energy range of 78-192MeV. Based on these data, production of curie quantities of (225)Ac is possible by irradiating a 5.0gcm(-2 232)Th target for 10 days in either BNL or LANL proton irradiation facilities.

  6. Vertical and horizontal distribution of radionuclides (232Th, 238U and 40K) in sediment from Manjung coastal water area Perak, Malaysia

    NASA Astrophysics Data System (ADS)

    Abdullah, Anisa; Hamzah, Zaini; Saat, Ahmad; Wood, Ab. Khalik

    2016-01-01

    Distribution of radionuclides from anthropogenic activities has been widely studied in marine coastal area. Due to rapid population growth and socio-economic development in Manjung area such as coal fired power plant, iron foundries, port development, waste discharged from factories and agriculture runoff may contribute to increase in pollution rate. The radioactive materials from anthropogenic activities could deteriorate the quality of the marine ecosystem and thus lead to possible radiological health risk to the population. Radionuclides (232Th, 238U and 40K) content in surface and profile sediment from Manjung coastal area was determined in this study. Radionuclides in sediment from seven locations were collected using sediment core sampling and measurements were carried out using Energy Dispersive X-ray Fluorescence (EDXRF) spectroscopy. The results show that the concentration of radionuclides in surface sediment and distribution trend of depth vertical profile sediment generally varies depending on locations. Enrichment factors (EF), geo-accumulation index (Igeo) and pollution index (PI) were applied to determine level of pollution of this study area. The radiological risks related to human exposure were evaluated based on external hazard index (Hex).

  7. Vertical and horizontal distribution of radionuclides ({sup 232}Th, {sup 238}U and {sup 40}K) in sediment from Manjung coastal water area Perak, Malaysia

    SciTech Connect

    Abdullah, Anisa Hamzah, Zaini; Wood, Ab. Khalik; Saat, Ahmad

    2016-01-22

    Distribution of radionuclides from anthropogenic activities has been widely studied in marine coastal area. Due to rapid population growth and socio-economic development in Manjung area such as coal fired power plant, iron foundries, port development, waste discharged from factories and agriculture runoff may contribute to increase in pollution rate. The radioactive materials from anthropogenic activities could deteriorate the quality of the marine ecosystem and thus lead to possible radiological health risk to the population. Radionuclides ({sup 232}Th, {sup 238}U and {sup 40}K) content in surface and profile sediment from Manjung coastal area was determined in this study. Radionuclides in sediment from seven locations were collected using sediment core sampling and measurements were carried out using Energy Dispersive X-ray Fluorescence (EDXRF) spectroscopy. The results show that the concentration of radionuclides in surface sediment and distribution trend of depth vertical profile sediment generally varies depending on locations. Enrichment factors (EF), geo-accumulation index (I{sub geo}) and pollution index (PI) were applied to determine level of pollution of this study area. The radiological risks related to human exposure were evaluated based on external hazard index (H{sub ex})

  8. Variation of uranium isotopic composition in soil within the JCO grounds from the 30 September 1999 criticality accident at JCO, Tokai-mura, Japan.

    PubMed

    Yamamoto, Masayoshi; Kawabata, Yoshiko; Murata, Yoshimasa; Komura, Kazuhisa

    2002-08-01

    Following the 30 September 1999 criticality accident at JCO, 29 surface and 3 core soil samples were collected inside and outside the JCO grounds to evaluate possible contamination by 235U-enriched uranium (18.8%) being handled at the time of the accident. Uranium (234U, 235U, and 238U) and thorium (228Th, 230Th, and 232Th) isotopes were determined by alpha-spectrometry and ICP-MS after radiochemical separation. Concentrations of 238U and 234U ranged from 11.3 to 63.5 and 11.6 to 360 mBq g(-1), respectively. Higher amounts of 238U and/or 234U were found in the vicinity of the uranium conversion building. The calculated 234U/235U activity ratios ranged from a 1.0 radioactive equilibrium value to an unusually high 5.7 value. Several of the soil samples showed considerably higher 235U/238U atomic ratios (1.06-4.37%) than 0.725% for natural uranium. Based on the assumption that measured U-series nuclides in soil samples taken from the JCO grounds were almost at radioactive equilibrium up to 230Th, excess uranium could be calculated for each sample. The results suggest that the excess uranium in the soils have lower 235U/238U atomic ratios (a few %) than the 18.8% enrichment of the precipitation tank uranium.

  9. Resolving the early chronology of Mono Craters volcanism with combined 238U-230Th and 40Ar/39Ar dating

    NASA Astrophysics Data System (ADS)

    Vazquez, J. A.; Calvert, A. T.; Marcaida, M.; Mangan, M.; Lidzbarski, M. I.; Stelten, M. E.

    2013-12-01

    California's largest locus of Pleistocene-Holocene rhyolitic volcanism is the Mono Lake-Long Valley region of eastern California. The Mono Craters chain marks the northern portion of this locus, and is composed of at least 28 individual domes of high-silica rhyolite. The record of Holocene volcanism at Mono Craters is relatively well constrained by tephrostratigraphy and radiocarbon dating. However, the timing and frequency of late Pleistocene dome emplacement is poorly resolved, with most of the chronology based on hydration-rind dating of obsidian. A well-exposed archive of late Pleistocene volcanism from Mono Craters is recorded by tephra beds (ashes numbered 1-19, youngest to oldest) of the informal Wilson Creek formation that accumulated in ancestral Mono Lake. To resolve a precise chronology for late Pleistocene volcanism at Mono Craters and tune the time-series of explosive volcanism preserved by Wilson Creek tephras, we performed ion microprobe 238U-230Th dating of allanite and zircon together with laser-fusion 40Ar/39Ar dating of sanidine from rhyolite domes that yield the oldest hydration rind ages and have relatively subdued morphology. Sanidine from multiple domes, including both hornblende-biotite and fayalite-bearing rhyolite types, yield 40Ar/39Ar ages up to ca. 25 ka. Ion microprobe analyses of unpolished rims on indium-mounted allanite and zircon crystals yield U-Th isochron ages that are indistinguishable from their associated sanidine 40Ar/39Ar ages. However, the interiors of sectioned allanite crystals yield model U-Th ages that may be up to 30 kyr older than their rims. Rims on allanite and zircon from ashes 7-19 in the lower portion of the Wilson Creek stratigraphy yield isochron ages of ca. 27-62 ka [1], which are supported by ages from magnetostratigraphy [2]. Ash 3 contains titanomagnetites that are compositionally distinct from other Wilson Creek tephras, but match those in the hornblende-biotite rhyolite of dome 11. Rims on allanite and

  10. Reliability of using 238U/235U and 234U/238U ratios from alpha spectrometry as qualitative indicators of enriched uranium contamination.

    PubMed

    Minteer, Mark; Winkler, Paul; Wyatt, Bill; Moreland, Scott; Johnson, Jamie; Winters, Tim

    2007-05-01

    Alpha spectrometry is a commonly used technique for the measurement of uranium isotopes in environmental samples because it is widely available at a relatively low cost. For natural uranium the (234)U to (238)U activity ratio should be 1 and the (238)U to (235)U activity ratio should be 21.7. However, a lower (238)U to (235)U ratio is usually observed in alpha spectrometric analysis of environmental soil samples. This observation has led to the conclusion that soils from nuclear weapons facilities were contaminated with highly enriched uranium. This study was undertaken to test the reliability of using activity ratios from alpha spectrometry to infer the presence of highly enriched uranium in soil samples. The results of these experiments indicate that the (238)U to (235)U activity ratio is not a reliable indicator, but that the (234)U to (238)U activity ratio can be used to qualitatively indicate the presence of highly enriched uranium at concentrations near 10 ng g(-1) and above.

  11. Uranium concentrations and /sup 234/U//sup 238/U activity ratios in fault-associated groundwater as possible earthquake precursors

    SciTech Connect

    Finkel, R.C.

    1981-05-01

    In order to assess the utility of uranium isotopes as fluid phase earthquake precursors, uranium concentrations and /sup 234/U//sup 238/U activity ratios have been monitored on a monthly or bimonthly basis in water from 24 wells and springs associated with Southern California fault zones. Uranium concentrations vary from 0.002 ppb at Indian Canyon Springs on the San Jacinto fault to 8.3 ppb at Lake Hughes well on the San Andreas fault in the Palmdale area. /sup 234/U//sup 238/U activity ratios vary from 0.88 at Agua Caliente Springs on the Elsinore fault to 5.4 at Niland Slab well on the San Andreas fault in the Imperial Valley. There was one large earthquake in the study area during 1979, the 15 October 1979 M = 6.6 Imperial Valley earthquake. Correlated with this event, uranium concentrations varied by a factor of more than 60 and activity ratios by a factor of 3 at the Niland Slab site, about 70 km from the epicenter. At the other sites monitored, uranium concentrations varied in time, but with no apparent pattern, while uranium activity ratios remained essentially constant throughout the monitoring period.

  12. A large drop in atmospheric [sup 14]C/[sup 12]C and reduced melting in the younger dryas, documented with [sup 230]Th ages of corals

    SciTech Connect

    Edwards, R.L.; Beck, J.W. ); Burr, G.S.; Donahue, D.J. ); Chappell, J.M.A. ); Bloom, A.L. ); Druffel, E.R.M. ); Taylor, F.W. )

    1993-05-14

    Paired carbon-14 ([sup 14]C) and thorium-230 ([sup 230]Th) ages were determined on fossil corals from the Huon Peninsula, Papua New Guinea. The ages were used to calibrate part of the [sup 14]C time scale and to estimate rates of sea-level rise during the last deglaciation. An abrupt offset between the [sup 14]C and [sup 230]Th ages suggests that the atmospheric [sup 14]C/[sup 12]C ratio dropped by 15 percent during the latter part of and after the Younger Dryas (YD). This prominent drop coincides with greatly reduced rates of sea-level rise. Reduction of melting because of cooler conditions during the YD may have caused an increase in the rate of ocean ventilation, which caused the atmospheric [sup 14]C/[sup 12]C ratio to fall. The record of sea-level rise also shows that globally averaged rates of melting were relatively high at the beginning of the YD. Thus, these measurements satisfy one of the conditions required by the hypothesis that the diversion of meltwater from the Mississippi to the St. Lawrence River triggered the YD event. 41 refs., 5 figs., 1 tab.

  13. 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

  14. 234U/238U Disequilibrium along stylolitic discontinuities in deep Mesozoic limestone formations of the Eastern Paris basin: evidence for discrete uranium mobility over the last 1-2 million years

    NASA Astrophysics Data System (ADS)

    Deschamps, P.; Hillaire-Marcel, C. E.; Michelot, J.-L.; Doucelance, R.; Ghaleb, B.; Buschaert, S.

    The (234U/238) equilibrium state of borehole core samples from the deep, low-permeability limestone formations surrounding the target argilite layer of the Meuse/Haute-Marne experimental site of the French agency for nuclear waste management -ANDRA- (Agence nationale pour la gestion des déchets radioactifs) was examined to improve understanding of naturally occurring radionuclide behaviour in such geological settings. Highly precise, accurate MC-ICP-MS measurements of the (234U/238U) activity ratio show that limestone samples characterised by pressure dissolution structures (stylolites or dissolution seams) display systematic (234U/238U) disequilibria, while the pristine carbonate samples remain in the secular equilibrium state. The systematic feature is observed throughout the zones marked by pressure dissolution structures: (i) the material within the seams shows a deficit of 234U over 238U ((234U/238U) down to 0.80) and (ii) the surrounding carbonate matrix is characterised by an activity ratio greater than unity (up to 1.05). These results highlight a centimetric-scale uranium remobilisation in the limestone formations along these sub-horizontal seams. Although their nature and modalities are not fully understood, the driving processes responsible for these disequilibria were active during the last 1-2 Ma.

  15. Measurement of 238U and 232Th in Petrol, Gas-oil and Lubricant Samples by Using Nuclear Track Detectors and Resulting Radiation Doses to the Skin of Mechanic Workers.

    PubMed

    Misdaq, M A; Chaouqi, A; Ouguidi, J; Touti, R; Mortassim, A

    2015-10-01

    Workers in repair shops of vehicles (cars, buses, truck, etc.) clean carburetors, check fuel distribution, and perform oil changes and greasing. To explore the exposure pathway of (238)U and (232)Th and its decay products to the skin of mechanic workers, these radionuclides were measured inside petrol, gas-oil, and lubricant material samples by means of CR-39 and LR-115 type II solid state nuclear track detectors (SSNTDs), and corresponding annual committed equivalent doses to skin were determined. The maximum total equivalent effective dose to skin due to the (238)U and (232)Th series from the application of different petrol, gas-oil, and lubricant samples by mechanic workers was found equal to 1.2 mSv y(-1) cm(-2).

  16. Study of secondary neutron interactions with 232Th, 129I, and 127I nuclei with the uranium assembly “QUINTA” at 2, 4, and 8GeV deuteron beams of the JINR Nuclotron accelerator

    DOE PAGES

    Adam, J.; Chilap, V. V.; Furman, V. I.; ...

    2015-11-04

    The natural uranium assembly, “QUINTA”, was irradiated with 2, 4, and 8 GeV deuterons. The 232Th, 127I, and 129I samples have been exposed to secondary neutrons produced in the assembly at a 20-cm radial distance from the deuteron beam axis. The spectra of gamma rays emitted by the activated 232Th, 127I, and 129I samples have been analyzed and several tens of product nuclei have been identified. For each of those products, neutron-induced reaction rates have been determined. The transmutation power for the 129I samples is estimated. Furthermore, experimental results were compared to those calculated with well-known stochastic and deterministic codes.

  17. Allanite from the El Muerto Pegmatite, Oaxaca, Mexico: A Potential New Standard for 232Th-208Pb Dating by LA-ICP-MS

    NASA Astrophysics Data System (ADS)

    Price, J.; Crowley, J. L.; Solari, L.; Prol-Ledesma, R.

    2012-12-01

    Allanite dating may be important to studies addressing tectonomagmatic evolution, provenance of monocyclic sediment, and mineral weathering. Obtaining accurate allanite ages by SIMS has been challenging and time-consuming due to the mineral's extreme chemical variability which often prevents finding adequately matrix-matched standards. Isotopic measurements by LA-ICP-MS minimize the need for standards of nearly identical composition to the unknown allanite being analyzed, and it is done relatively rapidly. Dating by LA-ICP-MS requires high quality standards for isotopic fractionation corrections. However, readily accessible and well characterized allanite standards are scarce. We investigated gemstone allanite from the El Muerto pegmatite, Oaxaca, Mexico, as a potential new geochronology standard for 232Th-208Pb allanite dating by LA-ICP-MS. Compositional homogeneity was thoroughly investigated by scanning and backscatter electron microscopy, cathodoluminescence, quantitative and qualitative energy dispersive x-ray spectroscopy, electron microprobe, and LA-ICP-MS. The possibility of metamictization was investigated by extensive X-ray diffraction analyses. The El Muerto allanite was U-Pb dated by ID-TIMS, with common Pb ratios determined from cogenetic K-feldspar by ID-TIMS and LA-MC-ICP-MS. Future work includes Th-Pb dating by ID-TIMS. The samples investigated are homogeneous with respect to major and trace elements. Major element compositional results are generally in agreement with published values, and no metamictization was identified despite the allanite being nearly 1 Ga. The only limitation of the El Muerto allanite is that it contains small, generally <100 μm, scarce inclusions of quartz, calciothorite, albite, calcite, and biotite. However, these grains are easily recognized and avoided during LA-ICP-MS analyses. Based on these results, the El Muerto allanite has the potential to serve as a standard for LA-ICP-MS dating.

  18. The applicability of MGA method for depleted and natural uranium isotopic analysis in the presence of actinides (232Th, 237Np, 233Pa and 241Am).

    PubMed

    Yücel, Haluk

    2007-11-01

    The multi-group analysis (MGA) method for the determination of uranium isotopic abundances in depleted uranium (DU) and natural uranium (NU) samples is applied in this study. A set of non-destructive gamma-ray measurements of DU and NU samples were performed using a planar Ge detector. The relative abundances of 235U and 238U isotopes were compared with the declared values of the standards. The relative abundance for 235U obtained by MGA for a "clean" DU or NU sample with a content of uranium>1wt% is determined with an accuracy of about +/-5%. However, when several actinides such as 232Th, 237Np, 233Pa and 241Am are present along with uranium isotopes simulating "dirty" DU or NU, it has been observed that MGA method gives erroneous results. The 235U abundance results for the samples were 6-25 times higher than the declared values in the presence of above-mentioned actinides, since MGA is utilized the X-ray and gamma-ray peaks in the 80-130 keV energy region, covering XKalpha and XKbeta regions. After the least-squares fitting of the spectra, it is found that the increases in the intensities of the X-ray and gamma-ray peaks of uranium are remarkably larger in the complex 80-130 keV region. On the other hand, it is observed that the interferences of the actinide peaks are relatively less dominant in the higher gamma-ray region of 130-300 keV. The results imply the need for dirty DU and NU samples that the MGA method should utilize the higher energy gamma-rays (up to 1001 keV of (234m)Pa) combined with lower energies of the spectra, which may be collected in a two detector mode (a planar Ge and a high efficient coaxial Ge).

  19. A precise 232Th-208Pb chronology of fine-grained monazite: Age of the Bayan Obo REE-Fe-Nb ore deposit, China

    USGS Publications Warehouse

    Wang, Jingyuan; Tatsumoto, M.; Li, X.; Premo, W.R.; Chao, E.C.T.

    1994-01-01

    We have obtained precise Th-Pb internal isochron ages on monazite and bastnaesite for the world's largest known rare earth elements (REE)-Fe-Nb ore deposit, the Bayan Obo of Inner Mongolia, China. The monazite samples, collected from the carbonate-hosted ore zone, contain extremely small amounts of uranium (less than 10 ppm) but up to 0.7% ThO2. Previous estimates of the age of mineralization ranged from 1.8 to 0.255 Ga. Magnetic fractions of monazite and bastnaesite samples (<60-??m size) showed large ranges in 232Th 204Pb values (900-400,000) and provided precise Th-Pb internal isochron ages for paragenetic monazite mineralization ranging from 555 to 398 Ma within a few percent error (0.8% for two samples). These results are the first indication that REE mineralization within the giant Bayan Obo ore deposit occurred over a long period of time. The initial lead isotopic compositions (low 206Pb 204Pb and high 208Pb 204Pb) and large negative ??{lunate}Nd values for Bayan Obo ore minerals indicate that the main source(s) for the ores was the lower crust which was depleted in uranium, but enriched in thorium and light rare earth elements for a long period of time. Zircon from a quartz monzonite, located 50 km south of the ore complex and thought to be related to Caledonian subduction, gave an age of 451 Ma, within the range of monazite ages. Textural relations together with the mineral ages favor an epigenetic rather than a syngenetic origin for the orebodies. REE mineralization started around 555 Ma (disseminated monazite in the West, the Main, and south of the East Orebody), but the main mineralization (banded ores) was related to the Caledonian subduction event ca. 474-400 Ma. ?? 1994.

  20. 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

  1. Marked disequilibrium between 234Th and 230Th of the 238U natural radioactive decay chain in IAEA reference materials n. 312, 313 and 314.

    PubMed

    Colaianni, A; D'Erasmo, G; Pantaleo, A; Schiavulli, L

    2011-02-01

    A new laboratory for the spectroscopy of natural radioactivity with a good energy resolution is presented. It consists of two distinct parts equipped, respectively, the first one with a HpGe γ-ray detector, whose setup has been already completed, and the second one with large area Silicon α-ray detectors and a radiochemical section for thin α-samples preparation, whose setup is yet in progress and will be the argument of a separate work. The γ-ray spectrometer was calibrated by means of IAEA Reference Materials n. 312, 313, 314 and 375. A large difference from the predictions of secular equilibrium emerged between the activities of (234)Th and (230)Th in Materials n. 312, 313 and 314.

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

    SciTech Connect

    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 oases 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.

  3. Trajectoires de moindre action et temps de vie pour trois modes de désintégration du noyau ^{234}U

    NASA Astrophysics Data System (ADS)

    Benfoughal, T.; Mirea, M.

    1996-10-01

    A numerical method is used to obtain the optimum cold fission paths for three decay modes of ^{234}U. The WKB-integral is minimized with respect the necking and the elongation. A term which takes into account the effect of the diffuse surface is added to the deformation energy in the framework of the macroscopic model of binary system with different charge densities. The effective masses are computed with more correct coordinates of deformation in order to include the variations of the asymmetry during the processes. Calculations are performed to obtain the fission trajectories in a large range of mass-asymmetry including cold fission, cluster emission and alpha-decay. Estimations of T_{1/2} are reported. Les trajectoires optimales de fission pour trois modes de désintégration du noyau ^{234}U sont obtenus à l'aide d'une méthode numérique. L'intégrale WKB est minimisée en fonction des coordonnées généralisées qui caractérisent le col et l'élongation. Un terme d'énergie qui prend en considération les effets dus à une surface diffuse du noyau est ajouté à l'énergie de déformation calculée dans le cadre du modèle macroscopique des systèmes binaires avec différentes densités de charge. Les masses effectives sont calculées avec des coordonnées généralisées choisis pour inclure les variations de l'asymétrie durant le processus nucléaire. Des calculs ont été effectués por obtenir les trajectoires de fission dans un grand domaine d'asymétrie de masse rendant compte de la fission froide, de l'émission spontanée de noyaux lourds et de la désintégration alpha. Des estimations de temps de vie sont reproduites.

  4. U-series disequilibrium of basaltic rocks from Kick'em-Jenny submarine volcano, Lesser Antilles island arc

    NASA Astrophysics Data System (ADS)

    Huang, F.; Lundstrom, C. C.

    2005-12-01

    Kick'em Jenny (KEJ) submarine volcano located 9 km to the north of Grenada in the Lesser Antilles volcanic arc produces lavas ranging in composition from high MgO basalts to moderately evolved andesites. We have determined U-series disequilibria in 12 porphyritic lavas erupted from KEJ volcano by TIMS and MC-ICP-MS methods to constrain the timing and identify the processes creating the magma diversity observed. The SiO2 contents of samples studied here vary from 47 to 55 wt.% SiO2 while REE patterns evolve from slightly LREE enriched, MREE/HREE = 1 patterns to strongly LREE enriched, MREE depleted concave-up patterns. Separate dissolutions of sample KEJ100 indicate an external reproducibility (1s) of 0.7% for (230Th/238U) (n=4), 0.8% for (230Th/232Th) (n=4) and 0.6% for (226Ra/230Th) (n=3), respectively. For all sample, (234U/238U) lies within 0.7% of unity, suggesting that secondary alteration by seawater has not disturbed the U-series data significantly. Sample ages for these submarine erupted samples are unknown, resulting in uncertain values for initial (226Ra/230Th); however, 10 out of 12 of the measured (226Ra/230Th) range between 3.16 and 1.13 and are thus unequivocally young with respect to decay of 230Th and 231Pa since eruption. The U (0.535 - 4.876 ppm) and Th (1.25 - 10.78 ppm) concentrations increase with SiO2 contents. (230Th/232Th) has a restricted range, varying from 0.994 to 1.093 with the exception of one sample. (230Th/238U) ranges from 0.684 to 0.875 while (231Pa/235U) ranges from 1.76 up to 2.84, among the highest 231Pa excess in island arcs yet reported. These data confirm previous observations of the unusual behavior of KEJ lavas relative to global observations in having both large 238U and 231Pa excesses. Combined with (226Ra/230Th), these disequilibria observations require that 238U excesses reflect more than solely fluid addition to the mantle wedge from the subducted oceanic slab.

  5. High-resolution tephrochronology of the Wilson Creek Formation (Mono Lake, California) and Laschamp event using 238U-230Th SIMS dating of accessory mineral rims

    NASA Astrophysics Data System (ADS)

    Vazquez, Jorge A.; Lidzbarski, Marsha I.

    2012-12-01

    Sediments of the Wilson Creek Formation surrounding Mono Lake preserve a high-resolution archive of glacial and pluvial responses along the eastern Sierra Nevada due to late Pleistocene climate change. An absolute chronology for the Wilson Creek stratigraphy is critical for correlating the paleoclimate record to other archives in the western U.S. and the North Atlantic region. However, multiple attempts to date the Wilson Creek stratigraphy using carbonates and tephras yield discordant results due to open-system effects and radiocarbon reservoir uncertainties as well as abundant xenocrysts. New ion microprobe 238U-230Th dating of the final increments of crystallization recorded by allanite and zircon autocrysts from juvenile pyroclasts yield ages that effectively date eruption of key tephra beds and delimit the timing of basal Wilson Creek sedimentation to the interval between 26.8±2.1 and 61.7±1.9 ka. Tephra (Ash 15) erupted during the geomagnetic excursion originally designated the Mono Lake excursion yields an age of 40.8±1.9 ka, indicating that the event is instead the Laschamp excursion. The new ages support a depositional chronology from magnetostratigraphy that indicates quasi-synchronous glacial and hydrologic responses in the Sierra Nevada and Mono Basin to regional climate change, with intervals of lake filling and glacial-snowpack melting that are in phase with peaks in spring insolation.

  6. High-resolution tephrochronology of the Wilson Creek Formation (Mono Lake, California) and Laschamp event using 238U-230Th SIMS dating of accessory mineral rims

    USGS Publications Warehouse

    Vazquez, Jorge A.; Lidzbarski, Marsha I.

    2012-01-01

    Sediments of the Wilson Creek Formation surrounding Mono Lake preserve a high-resolution archive of glacial and pluvial responses along the eastern Sierra Nevada due to late Pleistocene climate change. An absolute chronology for the Wilson Creek stratigraphy is critical for correlating the paleoclimate record to other archives in the western U.S. and the North Atlantic region. However, multiple attempts to date the Wilson Creek stratigraphy using carbonates and tephras yield discordant results due to open-system effects and radiocarbon reservoir uncertainties as well as abundant xenocrysts. New ion microprobe 238U-230Th dating of the final increments of crystallization recorded by allanite and zircon autocrysts from juvenile pyroclasts yield ages that effectively date eruption of key tephra beds and delimit the timing of basal Wilson Creek sedimentation to the interval between 26.8±2.1 and 61.7±1.9 ka. Tephra (Ash 15) erupted during the geomagnetic excursion originally designated the Mono Lake excursion yields an age of 40.8±1.9 ka, indicating that the event is instead the Laschamp excursion. The new ages support a depositional chronology from magnetostratigraphy that indicates quasi-synchronous glacial and hydrologic responses in the Sierra Nevada and Mono Basin to regional climate change, with intervals of lake filling and glacial-snowpack melting that are in phase with peaks in spring insolation.

  7. Flank eruptions of Mt Etna during the Greek-Roman and Early Medieval periods: New data from 226Ra-230Th dating and archaeomagnetism

    NASA Astrophysics Data System (ADS)

    Branca, Stefano; Condomines, Michel; Tanguy, Jean-Claude

    2015-10-01

    In this paper, we present new data from 226Ra-230Th dating and archaeomagnetism with the aim of improving the knowledge of the flank eruptions that occurred at Mt Etna during the Greek-Roman and Early Medieval periods, as defined in the new geological map of the volcano. The combination of the two dating techniques demonstrates that three major flank eruptions occurred on the lower north and west flanks during Greek-Roman epochs, producing large scoria cones and extensive lava flows. In particular, the Mt Ruvolo and Mt Minardo events highly impacted the territory of the west flank, notably by damming the Simeto River. The new data of the Millicucco and Due Monti lava flows, on the lower north-east flank, indicate a younger age than their stratigraphic ages quoted in the 2011 geological map, since they occurred around 700 and 500 AD, respectively. None of the large flank eruptions occurring on the lower slopes of Etna during the Early Medieval age are reported in the historical sources. Overall, our paper shows that a comprehensive assessment of eruptions at Mount Etna in the last three millennia can only be achieved through a multidisciplinary approach.

  8. Investigation of (235)U, (226)Ra, (232)Th, (40)K, (137)Cs, and heavy metal concentrations in Anzali international wetland using high-resolution gamma-ray spectrometry and atomic absorption spectroscopy.

    PubMed

    Zare, Mohammad Reza; Kamali, Mahdi; Fallahi Kapourchali, Maryam; Bagheri, Hashem; Khoram Bagheri, Mahdi; Abedini, Ali; Pakzad, Hamid Reza

    2016-02-01

    Measurements of natural radioactivity levels and heavy metals in sediment and soil samples of the Anzali international wetland were carried out by two HPGe-gamma ray spectrometry and atomic absorption spectroscopy techniques. The concentrations of (235)U, (226)Ra, (232)Th, (40)K, and (137)Cs in sediment samples ranged between 1.05 ± 0.51-5.81 ± 0.61, 18.06 ± 0.63-33.36 ± .0.34, 17.57 ± 0.38-45.84 ± 6.23, 371.88 ± 6.36-652.28 ± 11.60, and 0.43 ± 0.06-63.35 ± 0.94 Bq/kg, while in the soil samples they vary between 2.36-5.97, 22.71-38.37, 29.27-42.89, 472.66-533, and 1.05-9.60 Bq/kg for (235)U, (226)Ra, (232)Th, (40)K, and (137)Cs, respectively. Present results are compared with the available literature data and also with the world average values. The radium equivalent activity was well below the defined limit of 370 Bq/kg. The external hazard indices were found to be less than 1, indicating a low dose. Heavy metal concentrations were found to decrease in order as Fe > Mn > Sr > Zn > Cu > Cr > Ni > Pb > Co > Cd. These measurements will serve as background reference levels for the Anzali wetland.

  9. 234U/238U and δ87Sr in peat as tracers of paleosalinity in the Sacramento-San Joaquin Delta of California, USA

    USGS Publications Warehouse

    Drexler, Judith Z.; Paces, James B.; Alpers, Charles N.; Windham-Myers, Lisamarie; Neymark, Leonid; Bullen, Thomas D.; Taylor, Howard E.

    2013-01-01

    The purpose of this study was to determine the history of paleosalinity over the past 6000+ years in the Sacramento-San Joaquin Delta (the Delta), which is the innermost part of the San Francisco Estuary. We used a combination of Sr and U concentrations, d87Sr values, and 234U/238U activity ratios (AR) in peat as proxies for tracking paleosalinity. Peat cores were collected in marshes on Browns Island, Franks Wetland, and Bacon Channel Island in the Delta. Cores were dated using 137Cs, the onset of Pb and Hg contamination from hydraulic gold mining, and 14C. A proof of concept study showed that the dominant emergent macrophyte and major component of peat in the Delta, Schoenoplectus spp., incorporates Sr and U and that the isotopic composition of these elements tracks the ambient water salinity across the Estuary. Concentrations and isotopic compositions of Sr and U in the three main water sources contributing to the Delta (seawater, Sacramento River water, and San Joaquin River water) were used to construct a three-end-member mixing model. Delta paleosalinity was determined by examining variations in the distribution of peat samples through time within the area delineated by the mixing model. The Delta has long been considered a tidal freshwater marsh region, but only peat samples from Franks Wetland and Bacon Channel Island have shown a consistently fresh signal (<0.5 ppt) through time. Therefore, the eastern Delta, which occurs upstream from Bacon Channel Island along the San Joaquin River and its tributaries, has also been fresh for this time period. Over the past 6000+ years, the salinity regime at the western boundary of the Delta (Browns Island) has alternated between fresh and oligohaline (0.5-5 ppt).

  10. Mount Etna eruptions of the last 2,750 years: revised chronology and location through archeomagnetic and 226Ra-230Th dating

    NASA Astrophysics Data System (ADS)

    Tanguy, Jean-Claude; Condomines, Michel; Le Goff, Maxime; Chillemi, Vito; La Delfa, Santo; Patanè, Giuseppe

    2007-09-01

    A careful re-examination of the well-known written documents pertaining to the 2,750-year-long historical period of Mount Etna was carried out and their interpretation checked through the high-accuracy archeomagnetic method (>1,200 large samples), combined with the 226Ra-230Th radiochronology. The magnetic dating is based upon secular variation of the direction of the geomagnetic field (DGF) and estimated to reach a precision of ±40 years for the last 1,200 years, and ±100 to 200 years up to circa 150 B.C. Although less precise, the 226Ra-230Th method provides a unique tool for distinguishing between historic and prehistoric lavas, which in some cases might have similar DGFs. We show that despite the abundance of details on ancient historical eruptions, the primary sources of information are often too imprecise to identify their lava flows and eruptive systems. Most of the ages of these lavas, which are today accepted on the geological maps and catalogues, were attributed in the 1800s on the basis of their morphology and without any stratigraphical control. In fact, we found that 80% of the “historically dated” flows and cones prior to the 1700s are usually several hundreds of years older than recorded, the discrepancies sometimes exceeding a millennium. This is proper the case for volcanics presumed of the “1651 east” (actually ˜1020), “1595” (actually two distinct flows, respectively, ˜1200 and ˜1060), “1566” (˜1180), “1536” (two branches dated ˜1250 and ˜950), “1444” (a branch dated ˜1270), “1408” (lower branches dated ˜450 and ˜350), “1381” (˜1160), “1329” (˜1030), “1284” (˜1450 and ˜700), “1169 or 812” (˜1000) eruptions. Conversely, well-preserved cones and flows that are undated on the maps were produced by recent eruptions that went unnoticed in historical accounts, especially during the Middle Ages. For the few eruptions that are recorded between A.D. 252 and 750 B.C., none of their presumed lava

  11. Compositional variation and 226Ra-230Th model ages of axial lavas from the southern Mid-Atlantic Ridge, 8°48'S

    NASA Astrophysics Data System (ADS)

    Haase, K. M.; Brandl, P. A.; Devey, C. W.; Hauff, F.; Melchert, B.; Garbe-Schönberg, D.; Kokfelt, T. F.; Paulick, H.

    2016-01-01

    We present geological observations and geochemical data for the youngest volcanic features on the slow spreading Mid-Atlantic Ridge at 8°48'S that shows seismic evidence for a thickened crust and excess magma formation. Young lava flows with high sonar reflectivity cover about 14 km2 in the axial rift and were probably erupted from two axial volcanic ridges each of about 3 km in length. Three different lava units occur along an about 11 km long portion of the ridge, and lavas from the northern axial volcanic ridge differ from those of the southern axial volcanic ridge and surrounding lava flows. Basalts from the axial rift flanks and from a pillow mound within the young flows are more incompatible element depleted than those from the young volcanic field. Lavas from this volcanic area have 226Ra-230Th disequilibria model ages of 1000 and 4000 years whereas the older lavas from the rift flank and the pillow mound, but also some of the lava field, are older than 8000 years. Glasses from the northern and southern ends of the southern lava unit indicate up to 100°C cooler magma temperatures than in the center and increased assimilation of hydrothermally altered material. The compositional heterogeneity on a scale of 3 km suggests small magma batches rising vertically from the mantle to the surface without significant lateral flow and mixing. The observations on the 8°48'S lava field support the model of low-frequency eruptions from single ascending magma batches that has been developed for slow spreading ridges.

  12. Decay of {sup 246}Bk* formed in similar entrance channel reactions of {sup 11}B+{sup 235}U and {sup 14}N+{sup 232}Th at low energies using the dynamical cluster-decay model

    SciTech Connect

    Singh, BirBikram; Sharma, Manoj K.; Gupta, Raj K.

    2008-05-15

    The decay of the {sup 246}Bk* nucleus, formed in entrance channel reactions {sup 11}B+{sup 235}U and {sup 14}N+{sup 232}Th at different incident energies, is studied by using the dynamical cluster-decay model (DCM) extended to include the deformations and orientations of nuclei. The main decay mode here is fission. The other (weaker) decay channels are the light particles evaporation (A{<=}4) and intermediate mass fragments (5{<=}A{<=}20). All decay products are calculated as emissions of preformed clusters through the interaction barriers. The calculated fission cross sections {sigma}{sub fiss}, taken as a sum of the energetically favored symmetric and near symmetric fragments (A{sub CN}/2{+-}7 and A=106-110 plus complementary fragments) show an excellent agreement with experimental data at all experimental incident c.m. energies for both reactions, except for the top three energies in the case of the {sup 11}B+{sup 235}U reaction. The disagreement between the DCM calculations and data at higher incident c.m. energies for the {sup 11}B+{sup 235}U entrance channel is associated with the presence of additional effects of noncompound, quasifission (qf) components, in contradiction with the measured anisotropy effects which indicate the other entrance channel {sup 14}N+{sup 232}Th to contain the noncompound nucleus contribution. The prediction of two fission windows, the symmetric fission (SF) and near symmetric or heavy mass fragments (HMFs), suggests the presence of a fine structure of fission fragments, which also need an experimental verification. The only parameter of the model is the neck length parameter {delta}R whose value is shown to depend strongly on limiting angular momentum, which in turn depends on the use of sticking or nonsticking moment of inertia for angular momentum effects.

  13. 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

  14. Crystallisation ages in coeval silicic magma bodies: 238U-230Th disequilibrium evidence from the Rotoiti and earthquake flat eruption deposits, Taupo volcanic zone, New Zealand

    USGS Publications Warehouse

    Charlier, B.L.A.; Peate, D.W.; Wilson, C.J.N.; Lowenstern, J. B.; Storey, M.; Brown, S.J.A.

    2003-01-01

    The timescales over which moderate to large bodies of silicic magma are generated and stored are addressed here by studies of two geographically adjacent, successive eruption deposits in the Taupo Volcanic Zone, New Zealand. The earlier, caldera-forming Rotoiti eruption (>100 km3 magma) at Okataina volcano was followed, within months at most, by the Earthquake Flat eruption (??? 10 km3 magma) from nearby Kapenga volcano; both generated nonwelded ignimbrite and coeval widespread fall deposits. The Rotoiti and Earthquake Flat deposits are both crystal-rich high-silica rhyolites, with sparse glass-bearing granitoid fragments also occurring in Rotoiti lag breccias generated during caldera collapse. Here we report 238U-230Th disequilibrium data on whole rocks and mineral separates from representative Rotoiti and Earthquake Flat pumices and the co-eruptive Rotoiti granitoid fragments using TIMS and in situ zircon analyses by SIMS. Multiple-grain zircon-controlled crystallisation ages measured by TIMS from the Rotoiti pumice range from 69??3 ka ( 350 ka, with a pronounced peak at 70-90 ka. The weighted mean of isochrons is 83??14 ka, in accord with the TIMS data. One glass-bearing Rotoiti granitoid clast yielded an age of 57??8 ka by TIMS (controlled by Th-rich phases that, however, are not apparently present in the juvenile pumices). Another glass-bearing Rotoiti granitoid yielded SIMS zircon model ages peaking at 60-90 ka, having a similar age distribution to the pumice. Age data from pumices are consistent with a published 64??4 ka eruptive age (now modified to 62??2 ka), but chemical and/or mineralogical data imply that the granitoid lithics are not largely crystalline Rotoiti rhyolite, but instead represent contemporaneous partly molten intrusions reflecting different sources in their chemistries and mineralogies. Similarly, although the Earthquake Flat eruption immediately followed (and probably was triggered by) the Rotoiti event, age data from juvenile material

  15. Eruption and magma crystallization ages of Las Tres Vírgenes (Baja California) constrained by combined 230Th/ 238U and (U-Th)/He dating of zircon

    NASA Astrophysics Data System (ADS)

    Schmitt, Axel K.; Stockli, Daniel F.; Hausback, Brian P.

    2006-11-01

    Las Tres Vírgenes volcano is a calc-alkaline composite cone located near the main Gulf of California escarpment on the E coast of the Baja California peninsula. High-sensitivity ion microprobe U-series ( 230Th/ 238U) ages for zircon from La Vírgen tephra average 121 - 10 + 12 ka (1σ; MSWD = 2.7), with discrete age peaks at ˜ 100 and 160 ka. The noble gas mass spectrometric (U-Th)/He zircon age, corrected for disequilibrium and pre-eruptive storage, is 36 ± 3 ka. This result for the eruption age of La Vírgen tephra is significantly older than previously postulated historic or Holocene ages that were based on an 18th century map reference and 14C dating of accidental charcoal, respectively. The new (U-Th)/He zircon age is consistent with a > 26 ± 4 ka age derived from cosmogenic He exposure dating of an overlying basaltic lava flow [Hausback, B.P. and Abrams, M.J., 1996. Plinian eruption of La Virgen Tephra, Volcán Las Tres Virgenes, Baja California Sur, Mexico. Eos, Transactions, American Geophysical Union, 77(46, Suppl.): 813-814.]. U-Pb zircon analysis of ignimbrites erupted from the adjacent Early Pleistocene La Reforma and El Aguajito calderas yielded ages of 1.38 ± 0.03 Ma ( n = 12; MSWD = 1.0) and 1.17 ± 0.07 Ma ( n = 23; MSWD = 1.3), respectively. No evidence for these ages is found among La Vírgen zircons, whereas pre-Quaternary zircon xenocrysts are common. The La Vírgen magma, therefore, evolved unrelated to Early Pleistocene magmatism in adjacent calderas, but assimilated local basement rocks. A gap between average Th-U and (U-Th)/He zircon ages suggests that zircon crystallization was discontinuous in the La Vírgen magma chamber. In addition, partial resorption of zircon suggests episodic thermal rejuvenation, most likely by basaltic recharge. Based on the zircon record, the > 100 ka lifetime of the thermal anomaly that sustained repeated intrusive pulses significantly exceeds the age of the last eruption. This strengthens the view that Tres

  16. Rapid time scales of basalt to andesite differentiation at Anatahan volcano, Mariana Islands

    NASA Astrophysics Data System (ADS)

    Reagan, Mark; Tepley, Frank J.; Gill, James B.; Wortel, Matthew; Hartman, Brian

    2005-08-01

    We present comprehensive U-series data ( 238U- 234U- 230Th- 226Ra- 210Pb- 210Po and ( 230Th)/( 232Th)) for an andesite from an oceanic arc. The juvenile Anatahan andesite has U-Th systematics colinear with other historical Mariana volcanic rocks, and is most similar to those of the other volcano in the Mariana arc with a significant proportion of silicic andesite: Uracas. Like Uracas, the parental basalt for the Anatahan andesite was generated by relatively low degrees of flux melting from a source previously enriched in a sediment component from the subducting slab. However, the Anatahan andesite is much more strongly enriched in 226Ra over 230Th than Uracas lavas, and has one of the highest ( 226Ra)/( 232Th) ratios of siliceous andesites globally. The long-lived disequilibria between 238U- 230Th- 226Ra in the Anatahan andesite are inherited from basalt genesis, not created during differentiation or eruption. Thus, the time between genesis of the parental basalt and eruption of andesite at Anatahan is shorter than for Uracas. Moreover, the near-equilibrium ( 210Pb)/( 226Ra) value indicates that the magma body did not persistently lose or gain 222Rn for more than 2 years before eruption. This permits differentiation of the parental basalt to form andesite within this 2-year time period, although a differentiation time period between 100 and a few thousand years also is possible. The relative activities between 210Po and 210Pb suggest erupted scoria degassed Po less than most lavas despite eruption plume heights of ˜10 km, which further suggests an unusually rapid ascent before eruption. These data also show that juvenile material was ejected from the first day of the eruption. Phreatomagmatic ejecta overlying the main Anatahan scoria is strongly enriched in 210Po over 210Pb, indicating that a significant proportion of the Po degassed from rising magmas sublimes in its shallow fumarolic conduit system.

  17. Reply to Comment on “Steady-state 226Ra/230Th disequilibrium in mantle minerals: implications for melt transport rates in island arcs” by R. George, M. Reagan, S. Turner, J. Gill, B. Bourdon

    NASA Astrophysics Data System (ADS)

    Feineman, M. D.; DePaolo, D. J.

    2004-12-01

    We agree with George et al. that high 226Ra/ 230Th and correlated Ba/Th, 238U/ 230Th, and other elemental and isotopic ratios are the result of fluid addition to the wedge. The Feineman and DePaolo [Earth Planet. Sci. Lett. 215 (2003) 339-355] manuscript addresses more specifically the pathway followed by the fluid en route to the surface. In particular, we address whether the 226Ra/ 230Th data directly yield the total time available for the fluid to migrate from the point of origin in the slab to the melting region in the wedge, and ultimately to the surface with the melt. All of the processes involved in generating arc volcanism would of necessity have to take place very rapidly within the constraints proposed by George et al. The alternative is that the upward fluid movement is hindered by the fluid flow regime and solid mantle flow, allowing more time for reaction with the mantle wedge. There is evidence in the U-series data for more than one time scale, and our model helps to explain how this could come about. The extent to which grainscale 226Ra/ 230Th disequilibrium affects the inferred melt transport time is yet another issue, and this could be achieved either with the small-degree melt mechanism we discussed or by additional effects associated with melt and fluid migration at later stages in the melt generation process. We agree that the final melt transport event is likely to happen quickly. One of the most puzzling features of volcanic arcs is that the volcanic front emerges considerably behind the presumed location of primary water release from the subducting slab (depth to slab is ˜120 km beneath the volcanic front, as opposed to the predicted ˜80 km). This offset between the expected site of fluid release and the location of the volcanic front can be attributed to coupled transport of the fluid—in the form of hydrous minerals, such as amphibole and/or phlogopite in the wedge [J. Geophys. Res. 97 (1992) 2037-2070] or redirection of the melt due to

  18. Porosity of the melting zone and variations in the solid mantle upwelling rate beneath Hawaii: Inferences from {sup 238}U-{sup 230}Th-{sup 226}Ra and {sup 235}U-{sup 231}Pa disequilibria

    SciTech Connect

    Sims, K.W.W.; DePaolo, D.J.; Murrell, M.T.; Baldridge, W.S.; Goldstein, S.; Clague, D.; Jull, M.

    1999-12-01

    Measurements of {sup 238}U-{sup 230}Th-{sup 226}Ra and {sup 235}U-{sup 231}Pa disequilibria in a suite of tholeiitic-to-basanitic lavas provide estimates of porosity, solid mantle upwelling rate and melt transport times beneath Hawaii. The observation that ({sup 230}Th/{sup 238}U) {gt} 1 indicates that garnet is required as a residual phase in the magma sources for all of the lavas. Both chromatographic porous flow and dynamic melting of a garnet peridotite source can adequately explain the combined U-Th-Ra and U-Pa data for these Hawaiian basalts. For chromatographic porous flow, the calculated maximum porosity in the melting zone ranges from 0.3--3% for tholeiites and 0.1--1% for alkali basalts and basanites, and solid mantle upwelling rates range from 40 to 100 cm/yr for tholeiites and from 1 to 3 cm/yr for basanites. For dynamic melting, the escape or threshold porosity is 0.5--2% for tholeiites and 0.1--0.8% for alkali basalts and basanites, and solid mantle upwelling rates range from 10 to 30 cm/yr for tholeiites and from 0.1 to 1 cm/yr for basanites. Assuming a constant melt productivity, calculated total melt fractions range from 15% for the tholeiitic basalts to 3% for alkali basalts and basanites.

  19. Ingestion dose from 238U, 232Th, 226Ra, 40K and 137Cs in cereals, pulses and drinking water to adult population in a high background radiation area, Odisha, India.

    PubMed

    Lenka, Pradyumna; Sahoo, S K; Mohapatra, S; Patra, A C; Dubey, J S; Vidyasagar, D; Tripathi, R M; Puranik, V D

    2013-03-01

    A natural high background radiation area is located in Chhatrapur, Odisha in the eastern part of India. The inhabitants of this area are exposed to external radiation levels higher than the global average background values, due to the presence of uranium, thorium and its decay products in the monazite sands bearing placer deposits in its beaches. The concentrations of (232)Th, (238)U, (226)Ra, (40)K and (137)Cs were determined in cereals (rice and wheat), pulses and drinking water consumed by the population residing around this region and the corresponding annual ingestion dose was calculated. The annual ingestion doses from cereals, pulses and drinking water varied in the range of 109.4-936.8, 10.2-307.5 and 0.5-2.8 µSv y(-1), respectively. The estimated total annual average effective dose due to the ingestion of these radionuclides in cereals, pulses and drinking water was 530 µSv y(-1). The ingestion dose from cereals was the highest mainly due to a high consumption rate. The highest contribution of dose was found to be from (226)Ra for cereals and drinking water and (40)K was the major dose contributor from the intake of pulses. The contribution of man-made radionuclide (137)Cs to the total dose was found to be minimum. (226)Ra was found to be the largest contributor to ingestion dose from all sources.

  20. Neutron scattering cross sections for /sup 232/Th and /sup 238/U inferred from proton scattering and charge exchange measurements. [7 MeV, 26 and 27 MeV

    SciTech Connect

    Hansen, L.F.; Grimes, S.M.; Pohl, B.A.; Poppe, C.H.; Wong, C.

    1980-01-01

    Differential cross sections for the (p,n) reactions to the isobaric analog states (IAS) of /sup 232/Th and /sup 238/U targets were measured at 26 and 27 MeV. The analysis of the data was done in conjunction with the proton elastic and inelastic (2/sup +/, 4/sup +/, 6/sup +/) differential cross sections measured at 26 MeV. Because collective effects are important in this mass region, deformed coupled-channels calculations were carried out for the simultaneous analysis of the proton and neutron outgoing channels. The sensitivity of the calculations was studied with respect to the optical model parameters used in the calculations, the shape of the nuclear charge distribution, the type of coupling scheme assumed among the levels, the magnitude of the deformation parameters, and the magnitude of the isovector potentials, V/sub 1/ and W/sub 1/. A Lane model-consistent analysis of the data was used to infer optical potential parameters for 6- to 7-MeV neutrons. The neutron elastic differential cross sections obtained from these calculations are compared with measurements available in the literature, and with results obtained using neutron parameters from global sets reported at these energies. 7 figures, 3 tables.

  1. Certified Reference Material IAEA-446 for radionuclides in Baltic Sea seaweed.

    PubMed

    Pham, M K; Benmansour, M; Carvalho, F P; Chamizo, E; Degering, D; Engeler, C; Gascó, C; Gwynn, J P; Harms, A V; Hrnecek, E; Ibanez, F L; Ilchmann, C; Ikaheimonen, T; Kanisch, G; Kloster, M; Llaurado, M; Mauring, A; Møller, B; Morimoto, T; Nielsen, S P; Nies, H; Norrlid, L D R; Pettersson, H B L; Povinec, P P; Rieth, U; Samuelsson, C; Schikowski, J; Silobritiene, B V; Smedley, P A; Suplinska, M; Vartti, V-P; Vasileva, E; Wong, J; Zalewska, T; Zhou, W

    2014-05-01

    A Certified Reference Material (CRM) for radionuclides in seaweed (Fucus vesiculosus) from the Baltic Sea (IAEA-446) is described and the results of the certification process are presented. The (40)K, (137)Cs, (234)U and (239+240)Pu radionuclides were certified for this material, and information values for 12 other radionuclides ((90)Sr, (99)Tc, (210)Pb ((210)Po), (226)Ra, (228)Ra, (228)Th, (230)Th, (232)Th, (235)U, (238)U, (239)Pu and (240)Pu) are presented. The CRM can be used for Quality Assurance/Quality Control of analysis of radionuclides in seaweed and other biota samples, as well as for development and validation of analytical methods, and for training purposes.

  2. A database of radionuclide activity and metal concentrations for the Alligator Rivers Region uranium province.

    PubMed

    Doering, Che; Bollhöfer, Andreas

    2016-10-01

    This paper presents a database of radionuclide activity and metal concentrations for the Alligator Rivers Region (ARR) uranium province in the Australian wet-dry tropics. The database contains 5060 sample records and 57,473 concentration values. The data are for animal, plant, soil, sediment and water samples collected by the Environmental Research Institute of the Supervising Scientist (ERISS) as part of its statutory role to undertake research and monitoring into the impacts of uranium mining on the environment of the ARR. Concentration values are provided in the database for 11 radionuclides ((227)Ac, (40)K, (210)Pb, (210)Po, (226)Ra, (228)Ra, (228)Th, (230)Th, (232)Th, (234)U, (238)U) and 26 metals (Al, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, Hg, K, Mg, Mn, Na, Ni, P, Pb, Rb, S, Sb, Se, Sr, Th, U, V, Zn). Potential uses of the database are discussed.

  3. Open system U-series ages of corals from a subsiding reef in New Caledonia: Implications for sea level changes, and subsidence rate

    NASA Astrophysics Data System (ADS)

    Frank, N.; Turpin, L.; Cabioch, G.; Blamart, D.; Tressens-Fedou, M.; Colin, C.; Jean-Baptiste, P.

    2006-09-01

    On the Amédée islet, 4 drill cores were recovered from the barrier reef of Western New Caledonia. The coral reef is slowly subsiding and is thus percolated by sea water during sea level highstands. The cores sample a ˜ 10 m thick Holocene reef overlying a 24 m thick reef of marine isotope stage (MIS) 5.5, which in turn overlies older reef material from MIS 7.5 and beyond. ( 234U/ 238U) and ( 230Th/ 238U) ratios and 232Th were determined by thermal ionization mass spectrometry on aragonitic coral samples that were carefully investigated using X-ray diffraction and scanning electron microscopy. The petrographic study shows an increasing coral weathering with growing coral age that causes different degree of U-series open system behavior and 232Th accumulation. Holocene corals exhibit a small degree of early diagenesis and yield 230Th/ 238U ages according to the Holocene sea level rise from ˜ 8200 years to 5000 years BP. Corals from the last Interglacial section have experienced more frequent replacement of aragonite fibers and minor dissolution, and U-series open system behavior is evident. To estimate the impact of recoil processes and alteration on the U-series system two models by Villemant and Feuillet [B. Villemant, N. Feuillet, Dating open systems by the 238U- 234U- 230Th method: application to Quaternary reef terraces, Earth and Planetary Science Letters 210(2003) 105-118.] and Thompson et al. [W. G. Thompson, M. W. Spiegelman, S. L. Goldstein, R. C. Speed, An open-system model for U-series age determinations of fossil corals, Earth and Planetary Science Letters 210(2003) 365-381.] have been tested. These models yield identical ages within uncertainty, which are in agreement to the sea level history of the past 250,000 years, as long as physico-chemical alteration and re-crystallization is small. Consequently, we were able to estimate the subsidence rate from the subsidence observed between the end of MIS 5.5 and the early Holocene, which is ˜ 0.16 ± 0

  4. High-precision measurements of uranium and thorium isotopic ratios by multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS)

    NASA Astrophysics Data System (ADS)

    Wang, Lisheng; Ma, Zhibang; Duan, Wuhui

    2015-04-01

    Isotopic compositions of U-Th and 230Th dating have been widely used in earth sciences, such as chronology, geochemistry, oceanography and hydrology. In this study, five ages of different carbonate samples were measured using 230Th dating technique with U-Th high-precision isotopic measurements by multi-collector inductively coupled plasma mass spectrometry, in Uranium-series Chronology Laboratory, Institute of Geology and Geophysics, Chinese Academy of Sciences.In this study, the precision and accuracy of uranium isotopic composition were estimated by measuring the uranium ratios of NBS-CRM 112A, NBS-CRM U500 and HU-1. The mean measured ratios, 234U/238U = 52.86 (±0.04) × 10-6 and δ234U = -38.36 (±0.77) × 10-3 for NBS-CRM 112A, 234U/238U = 10.4184 (±0.0001) × 10-3, 236U/238U = 15.43 (±0.01) × 10-4 and 238U/235U = 1.00021 (±0.00002) for NBS-CRM U500, 234U/238U = 54.911 (±0.007) and δ234U = -1.04 (±0.13) × 10-3 for HU-1 (95% confidence levels). The U isotope data for standard reference materials are in excellent agreement with previous studies, further highlighting the reliability and analytical capabilities of our technique. We measured the thorium isotopic ratios of three different thorium standards by MC-ICPMS. The three standards (Th-1, Th-2 and Th-3) were mixed by HU-1 and NBS 232Th standard, with the 230Th/232Th ratios from 10-4 to 10-6. The mean measured atomic ratios, 230Th/232Th = 2.1227 (±0.0024) × 10-6, 2.7246 (±0.0026) × 10-5, and 2.8358 (±0.0007) × 10-4 for Th-1, Th-2 and Th-3 (95% confidence levels), respectively. Using this technique, the following standard samples were dated by MC-ICPMS. Sample RKM-4, collected from Babardos Kendal Hill terrace, was used during the first stage of the Uranium-Series Intercomparison Project (USIP-I). Samples 76001, RKM-5 and RKM-6 were studied during the second stage of the USIP program (USIP-II). Sample 76001 is a laminated flowstone, collected from Sumidero Terejapa, Chiapas, Mexico, and samples

  5. Uranium-thorium isotope geochemistry of saline ground waters from central Missouri

    SciTech Connect

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

    1989-03-01

    The isotopic and elemental distributions of uranium and thorium were examined in a suite of saline ground waters from central Missouri using mass spectrometric techniques. The waters were sampled from natural springs and artesian wells in Mississippian and Ordovician aquifers and have a wide range in salinity (5 to 26 /per thousand/), deltaD (/minus/108 to /minus/45 /per thousand/), and delta/sup 18/O (/minus/14.7 to /minus/6.5 /per thousand/) values. The suite of samples has a large range in /sup 238/U (50 to 200 x 10/sup /minus/12/g/g) and /sup 232/Th (0.3 to 9.1 x 10/sup /minus/12/g/g) concentrations and extremely high /sup 234/U//sup 238/U activity ratios ranging from 2.15 to 16.0. These isotopic compositions represent pronounced uranium-series disequilibrium compared with the value of modern seawater (1.15) or the equilibrium value (1.00). For such /sup 234/U-enriched waters, /sup 234/U//sup 238/U isotope ratios can be determined with a precision of /+-/ 10 /per thousand/ (2sigma) on 10 mL of sample and less than /+-/5 /per thousand/ on 100 mL. In contrast to the large /sup 234/U enrichments, /sup 230/Th//sup 238/U activity ratios in the ground waters are significantly lower than the equilibrium value. The more saline samples have markedly higher /sup 234/U//sup 238/U activity ratios and lower deltaD and delta/sup 18/O values. Unfiltered and filtered (< 0.1 ..mu..m) aliquots of a saline sample have the same isotopic composition and concentration of uranium, indicating uranium essentially occurs entirely as a dissolved species. The filtered/unfiltered concentration ratio for thorium in this sample is 0.29, demonstrating the predominant association of thorium with particulates.

  6. Early diagenesis impact on precise U-series dating of deep-sea corals: Example of a 100 200-year old Lophelia pertusa sample from the northeast Atlantic

    NASA Astrophysics Data System (ADS)

    Pons-Branchu, Edwige; Hillaire-Marcel, Claude; Deschamps, Pierre; Ghaleb, Bassam; Sinclair, Daniel J.

    2005-10-01

    Deep-sea coral has proved useful for paleoceanographic reconstructions and for documenting 14C-ages of water masses using 230Th-ages. However, for precise and accurate U-series dating, further information on coral-age structure, growth rate and diagenetic evolution is still needed. To document such processes, we used U-Th- 226Ra systematics in a 40 cm diameter, Lophelia pertusa specimen collected in 1912 from the Eastern Atlantic (Sea of the Hebrides). External parts of the specimen are thought to have been alive when collected whereas more internal parts were likely dead. The "live-collected" and "dead" parts of the skeleton were sampled and analyzed for their 230Th, 232Th, 234U, 238U, 226Ra and Ba contents by thermal ionization and multicollector inductively coupled plasma mass spectrometry. 230Th/ 234U ratios in the most recent parts yielded ages of 86 ± 6 a and 92 ± 9 a, in agreement with the date of recovery. The older parts yielded 230Th ages ranging from 169 ± 15 to 211 ± 10 a (n = 5), but had a 31% higher U content than more recent parts of the skeleton. This raises concerns about the possibility of secondary diagenetic U uptake, although an environmentally controlled U/Ca shift between coral growth stages cannot be ruled out. 226Ra/Ba measurements were made, and model- 226Ra/Ba ages averaging 250 ± 12 yr were calculated for the older part, assuming a constant initial 226Ra/Ba ratio in bottom waters. These ages are slightly older than 230Th-ages, suggesting either that 226Ra/Ba ratios of ambient-seawater changed over time or that a diagenetic phenomenon have affected the U-series system, or both. Scanning electron microscope observations revealed bioerosion and secondary biomineralization in the older part of the coral skeleton, supporting the hypothesis that diagenetic processes may have influenced the ages obtained by the U-series toolbox. Modeled U-series ages for such an open system are discussed. However, a comparison between 14C- and 230Th

  7. Mixing and cycling of uranium, thorium and 210Pb in Puget Sound sediments

    NASA Astrophysics Data System (ADS)

    Carpenter, R.; Peterson, M. L.; Bennett, J. T.; Somayajulu, B. L. K.

    1984-10-01

    Activity profiles of excess 234Th, excess 210Pb, 232Th, 230Th, 234U and 238U, and 228/232Th ratios determined in eight box cores of sediment from six sites in central Puget Sound provide new insights into the dynamic nature of solid phase mixing in surface sediments, the exchange of 228Ra and other soluble species across the sediment-water interface, and the cycling of U, Th and 210Pb in this coastal zone. Comparison of excess 234Th inventories in sediments with its production rate in the overlying water column indicates a mean residence time of at most 14 days for particles in the central Puget Sound water column. Surface sediment horizons with excess 234Th have no excess 228Th which might be used to ascertain sediment accumulation rates over the past decade. Instead, deficiencies of 228Th due to loss of soluble 228Ra from pore water to the overlying water persist to 20-30 cm, revealing that exchange of soluble chemicals between pore and overlying waters reaches these depths in the extensively bioturbated sediments of Puget Sound. Solid phase U isotope concentrations tend to increase by up to a factor of two with depth in sediments, as a result of dissolved U being biologically pumped down into sediments where it is partially removed when conditions become mildly reducing. 232Th and 230Th activities and 230/232Th ratios are constant with depth in sediments, indicating constant detrital phase compositions and essentially no authigenic 230Th. Steady state 210Pb depositional activities in and fluxes to Puget Sound sediments average only about onehalf those for sediments of the open Washington coast north of the Columbia River mouth, primarily because of a much lower supply of dissolved 210Pb in sea waters adverting into Puget Sound. Excess 234Th profiles in sediments reveal much more detail about the depth dependency, dynamic nature and recent history of solid phase mixing processes than excess 210Pb profiles. At least six of eight 234Th profiles show that mixing

  8. The mechanisms and timescales of rhyolite generation at Yellowstone caldera: New insights from 238U-230Th crystallization ages, trace-elements, and isotope compositions of zircon and sanidine

    NASA Astrophysics Data System (ADS)

    Stelten, M. E.; Cooper, K. M.; Vazquez, J. A.; Calvert, A. T.

    2013-12-01

    The Yellowstone Plateau hosts one of the largest Quaternary magmatic systems on Earth, with caldera forming eruptions at ~2.1 Ma, ~1.3 Ma, and ~0.64 Ma, as well as numerous intracaldera rhyolitic eruptions between caldera-forming events. The most recent post-caldera eruptive episode at Yellowstone produced the Central Plateau Member (CPM) of the Plateau Rhyolite, which erupted intermittently between ca. 170-70 ka with a cumulative volume ≥600 km3. Thus, the CPM rhyolites provide snapshots of a large silicic magmatic system though time. We examine five CPM rhyolites that erupted from ~125 ka to ~70 ka, and constrain the mechanisms and timescales of generating eruptible rhyolites at Yellowstone caldera by comparing (1) 238U-230Th crystallization ages and trace-element compositions of the interiors and surfaces (i.e., unpolished rims) of individual zircons with (2) bulk 238U-230Th crystallization ages and in situ major-element, Ba, and Pb isotope data for sanidines hosted in each rhyolite. The zircon age and trace-element data show that zircons in CPM rhyolites record crystallization from their respective eruption age to >150 ka before eruption, with most zircon surfaces crystallizing close to eruption and many interiors crystallizing 10 kyr to 150 kyr before eruption. At any given age, zircon surfaces have homogeneous trace-element compositions relative to zircon interiors for most elements and element ratios. For example, when considering data from all five CPM rhyolites, the zircon surfaces and interiors show similar broad trends in Eu/Eu* and U/Th over time, but the surfaces display less scatter. These observations suggest that the zircon surfaces grew from a more homogeneous region of the magma reservoir relative to where the zircon interiors grew. Although the zircon surfaces and interiors are similar in some elements and element ratios (e.g., Eu/Eu*, U/Th) at a given age, zircon surfaces and interiors display distinct (Y, MREE, HREE)/(P, U) ratios at a given

  9. Temporal variation and provenance of thorium deposition observed at Tsukuba, Japan.

    PubMed

    Hirose, Katsumi; Kikawada, Yoshikazu; Igarashi, Yasuhito

    2012-06-01

    Temporal variations of monthly thorium (Th) deposition observed at Tsukuba, Japan during the period 1990-2007, comparing with plutonium deposition, was studied. The monthly (232)Th deposition as did (239,240)Pu, varied according to season and inter-annually. In particular, (232)Th deposition increased significantly in spring coinciding with Asian dust (Kosa) events. The (230)Th/(232)Th activity ratios vary according to sources and can therefore be used to differentiate between locally derived and remotely derived (232)Th. The (230)Th/(232)Th activity ratios in deposition samples showed large variability with high ratios occurring in early spring. These high (230)Th/(232)Th ratios in deposition can be attributed to local dust storms, especially in early spring, that cause resuspension of soils from cultivated fields which are characterized by high (230)Th/(232)Th activity ratios. The results reveal that both locally and remotely derived (232)Th deposition showed seasonal variations with maxima in spring, although the remotely derived fraction is dominant rather than the locally derived one. The (232)Th deposition maxima later in spring is attributable to the remotely derived fraction, corresponding to the Kosa events. Annual (232)Th deposition exhibited an increasing trend, suggesting the presence of sources other than soil dust such as fly ash from increasing coal burning.

  10. Uranium isotopes (U-234/U-238) in rivers of the Yukon Basin (Alaska and Canada) as an aid in identifying water sources, with implications for monitoring hydrologic change in arctic regions

    USGS Publications Warehouse

    Kraemer, Thomas F.; Brabets, Timothy P.

    2012-01-01

    The ability to detect hydrologic variation in large arctic river systems is of major importance in understanding and predicting effects of climate change in high-latitude environments. Monitoring uranium isotopes (234U and 238U) in river water of the Yukon River Basin of Alaska and northwestern Canada (2001–2005) has enhanced the ability to identify water sources to rivers, as well as detect flow changes that have occurred over the 5-year study. Uranium isotopic data for the Yukon River and major tributaries (the Porcupine and Tanana rivers) identify several sources that contribute to river flow, including: deep groundwater, seasonally frozen river-valley alluvium groundwater, and high-elevation glacial melt water. The main-stem Yukon River exhibits patterns of uranium isotopic variation at several locations that reflect input from ice melt and shallow groundwater in the spring, as well as a multi-year pattern of increased variability in timing and relative amount of water supplied from higher elevations within the basin. Results of this study demonstrate both the utility of uranium isotopes in revealing sources of water in large river systems and of incorporating uranium isotope analysis in long-term monitoring of arctic river systems that attempt to assess the effects of climate change.

  11. U-series Dating of Stalagmites from Borneo

    NASA Astrophysics Data System (ADS)

    Adkins, J. F.; Partin, J.; Cobb, K.; Clark, B.

    2006-12-01

    In a series of field campaigns dating back to the fall of 2003 we have collected over 60 stalagmites from the Gunung Buda cave system in Sarawak, Malaysia (4°N, 115°E). At least twenty of these samples have excellent calcite preservation and span an age range from modern to over 500,000 years old. The bulk of the collection is of early glacial to Holocene age and can provide multiple overlapping records of climate variability from the Western Pacific Warm Pool. However, generating absolute U-series ages from this collection is challenging. The host rock is a Miocene aged limestone that is covered by rainforest with virtually no topsoil development. This setting leaves the typical stalagmite sample with a low uranium concentration (100s of ppb), a low initial δ234U (-650‰ to -100‰), and a relatively high detrital Th concentration (10s to 100s of pmol/g). We have generated age models in these difficult circumstances by making over 150 MC-ICP-MS measurements of the 238U-234U-230Th-232Th disequilibrium system. Ages are limited by our correction for initial 230Th. This is a common problem in U-series dating of stalagmites that we have addressed by generating a "histogram" of initial 230/232 values. With 14 isochrons from four separate stalagmites spanning the glacial maximum through the Holocene we can conservatively constrain the initial 230/232 atom ratio to be 60±10x10-6. There are small differences in the weighted mean of this value between stalagmites, but no systematic differences with time within a stalagmite. The very low δ234U values are intriguing and must represent the effects of recent weathering of the host limestone. These low and variable δ234U ratios also make it imperative to calculate the initial 230/232 ratios with full three-dimensional isochrons, extrapolating to zero U-238 on a "Rosholt Diagram" does not produce a consistent answer between the samples. Overall we can produce 2 sigma age errors that are better than 1% for the combined

  12. Cold water corals of the Northeast Atlantic margin: Archives of intermediate water circulation during the Holocene

    NASA Astrophysics Data System (ADS)

    Frank, N.; Paterne, M.; Ayliffe, L.; Lutringer, A.; Blamart, D.; van Weering, T.

    2003-04-01

    We present combined 230Th/U and 14C dating and stable isotope analyses on benthic corals from the northeastern North Atlantic in order to investigate past changes of the thermohaline circulation. The reef forming cold water corals Lophelia pertusa and Madrepora oculata were raised from intermediate depth (˜750m bsl) from carbonate mounds along Rockall and Porcupine Bank and Porcupine Seabight.The 230Th/U ages range from today to 247,400yr. The δ234U, 230Th/232Th, and X-ray images indicate negligible alteration of the investigated corals, i.e. open system behavior. Very young deep-sea corals were accurately dated by means of 230Th/U dating. One in-situ living Lophelia coral yielded a mean age of 1995AD, matching the date of collection in 1999AD. From this coral, the measured and calculated seawater Δ14C values are indistinguishable, and the reservoir age Rinterm of the upper intermediate waters is 710±80 years. Several modern corals, being dated between 1950AD and 1986AD, recorded the atmospheric 14C/12C increase due to the nuclear tests in the early 60s. The modern pre-bomb Δ14C value of the North Atlantic intermediate waters was determined at an average of -65±7o/oo, and the mean reservoir age at 500±50 years. Finally, several investigated benthic coral grew during the second step of the deglaciation and during the Holocene climate optimum (from 10,900 to about 8,000 CAL yr BP). The reservoir age of average 530±65 years is equivalent to that of today indicating that, during the studied coral growth episodes, a modern type oceanic circulation, as well as the air-sea and surface to deeper adjacent water 14CO2 exchanges prevailed in the Northeast Atlantic Ocean.

  13. Geochemical and isotopic properties of Heinrich layers H2 to H0 off Hudson Strait

    NASA Astrophysics Data System (ADS)

    Nuttin, L.; Ghaleb, B.; Hillaire-Marcel, C.

    2011-12-01

    Information about the precise timing and transport/depositional mechanism of fine detrital-carbonate sedimentary pulses, which occurred off Hudson Strait during Heinrich-events and linked to ice-margin instability in this area, is still much fragmentary (see Hesse et al., Geology 32: 449-452, 2004). Here, we intend to document the properties and duration of the most recent of these sedimentary pulses (H2, H1, H0) based on mineralogical, geochemical and isotopic data in a 895-cm long core (HU08-029-004; 2674 m water-depth; 61°27'N, 58°2'W) raised from the lower slope, about 100 nm off Hudson Strait shelf edge. Measurements of 238U, 234U, 230Th and 232Th, supplemented by semi-quantitative mineralogical analysis and light isotope data (C, Corg, Cinorg, C/N, 14C, δ13C and δ18O) are used to document sedimentary features in this core. First investigations provide an estimated average sedimentation rate of ~33 cm/ka on the whole studied sequence. 230Th-excesses over supported fraction are estimated following Veiga-Pires & Hillaire-Marcel (Paleoceanography 14: 187-199, 1999). H-layer thicknesses are about 60 cm, 100 cm and 28 cm respectively (H2, H1, H0). They depict up to 60% of fine detrital carbonates (mostly calcite) and are also highlighted by relatively low 230Th-excesses (nearly 0 dpm/g) compared with excesses of about 3 dpm/g in the overlying Holocene sediments. The low 230Th-excesses in H-layers do indicate a very fast depositional process but prevent any meaningful estimation of sedimentation rates due to uncertainties in their estimates.

  14. Uranium-series disequilibrium, sedimentation, diatom frustules, and paleoclimate change in Lake Baikal

    USGS Publications Warehouse

    Edgington, D.N.; Robbins, J.A.; Colman, Steven M.; Orlandini, K.A.; Gustin, M.-P.

    1996-01-01

    The large volume of water, approximately one-fifth of the total surface fresh water on the planet, contained in Lake Baikal in southeastern Siberia is distinguished by having a relatively high concentration of uranium (ca. 2 nM), and, together with the surface sediments, an unusually high 234U/238U alpha activity ratio of 1.95. About 80% of the input of uranium to the lake, with a 234U/238U ratio of 2.0, comes from the Selenga River. Profiles of uranium, as well as the extent of isotopic disequilibrium in a 9 m sediment core collected on Academic Ridge, generally show high values during interglacial periods corresponding to high diatom frustule numbers (DiFr) and biogenic silica (BSi) data that have been reported elsewhere. During glacial periods (low DiFr and BSi), uranium progeny (234U and 230Th) were in secular equilibrium with low concentrations of their parent 238U. Radionuclide distributions were interpreted in terms of a quantitative model allowing for adsorption of riverine inputs of uranium onto two classes of sedimenting particles with differing 238U/232Th ratios and uranium progeny in secular equilibrium. If the 234U/238U activity ratio of adsorbed uranium has remained constant, mean sedimentation rates can be independently estimated as 3.6 ?? 0.6 and 3.7 ?? 0.9 cm ?? kyr-1 for the decay of 234U and in-growth of 230Th, respectively. These rates are consistent with a mean rate of 3.76 cm ?? kyr-1, calculated by optimization of the correspondence between adsorbed 238U and ??18O in dated oceanic sediments. The adsorbed uranium apparently tracks variable river flow during interglacials and is drastically reduced during periods of glaciation. Evidently, uranium has not been significantly redistributed within Baikal sediments over at least the past 250 kyr and is a unique, biologically non-essential, tracer for climate-sensitive processes, which provide their own internal geochronometers, potentially useful for ages up to 1 Myr BP.

  15. Radioactivity In Marine Organisms From Northeast Atlantic Ocean

    SciTech Connect

    Carvalho, Fernando P.; Oliveira, Joao M.

    2008-08-07

    Naturally-occurring radionuclides such as {sup 238}U, {sup 234}U, {sup 230}Th, {sup 226}Ra, {sup 210}Po, {sup 210}Pb and {sup 232}Th, and artificial radionuclides such as {sup 137}Cs, {sup 239+240}Pu and {sup 241}Am, were measured in a large number of marine species. In common fish species, typical concentrations of {sup 210}Po ranged from 10{sup 2} to 10{sup 4} mBq kg{sup -1} (wet weight), {sup 226}Ra concentrations ranged from 1x10{sup 2} to 5xl0{sup 2} mBq kg{sup -1}, {sup 238}U was at about 10 mBq kg{sup -1} and {sup 232}Th at about 0.5 mBq kg{sup -1}. Radiation doses to marine organisms originated by naturally-occurring and artificial radionuclides accumulated in tissues and by external radiation sources were computed and compared. Internal sources generally give higher contribution to the absorbed radiation dose than external sources. Amongst radionuclides accumulated in fish muscle and acting as internal radiation sources, natural {sup 210}Po and {sup 40}K give the largest contribution to the absorbed radiation dose, while artificial radionuclides such as {sup 137}Cs and {sup 239+240}Pu contribute with less than 0.5% to the absorbed radiation dose from all internal sources.

  16. Vegetation-derived insights on the mobilization and potential transport of radionuclides from the Nopal I natural analog site, Mexico

    SciTech Connect

    Leslie, B.W.; Pickett, D.A.; Pearcy, E.C.

    1999-07-01

    The Nopal I uranium (U) deposit, Pena Blanca, Mexico is a source term and contaminant transport natural analog to the proposed high-level nuclear waste repository at Yucca Mountain, Nevada. In an attempt to characterize the mobilization and potential transport of radionuclides in the unsaturated zone at the Nopal I deposit, vegetation growing on ore piles was analyzed for {sup 238}U, {sup 235}U, and {sup 232}Th decay-series isotopes. Specimens of Phacelia robusta growing on high-grade piles of U ore were collected and analyzed by alpha autoradiography, and by alpha and gamma spectrometry. Activities for U, thorium (Th), and radium (Ra) isotopes (Bq/kg dried plant) were 300, 1,000, and 7,000 for {sup 238}U, {sup 230}Th, and {sup 226}Ra, respectively. The {sup 226}Ra activities in these specimens are among the highest ever measured for plants; furthermore, the plant-to-soil {sup 226}Ra concentration ratio is higher than expected. These results demonstrate the large mobility and bio-availability of Ra in the Nopal I environment, and support previous indications of recent loss of {sup 226}Ra from the ore body. Comparison between the activities of {sup 238}U and {sup 232}Th decay-chain Th isotopes in the plants and in the ore substrate indicate that relative mobilization into pore solutions of {sup 228}Th > {sup 230}Th > {sup 232}Th, in a ratio of about 50--25:4:1, respectively. The similarity of the plant's {sup 234}U/{sup 238}U activity ratio ({approximately}1.2) to that of a caliche deposit that formed adjacent to the Nopal ore body around 54 ka suggests the {sup 234}U/{sup 238}U activity ratio of U released from the ore is approximately 1.2. The U and {sup 226}Ra isotope activities of the plants and ore substrate, and solubility considerations, are used to assess a source term model of the potential Yucca Mountain repository. These results suggest the use of a natural analog source term model in performance assessments may be non-conservative.

  17. Magma mixing and the generation of isotopically juvenile silicic magma at Yellowstone caldera inferred from coupling 238U–230Th ages with trace elements and Hf and O isotopes in zircon and Pb isotopes in sanidine

    USGS Publications Warehouse

    Stelten, Mark E.; Cooper, Kari M.; Vazquez, Jorge A.; Reid, Mary R.; Barfod, Gry H.; Wimpenny, Josh; Yin, Qing-Zhu

    2013-01-01

    The nature of compositional heterogeneity within large silicic magma bodies has important implications for how silicic reservoirs are assembled and evolve through time. We examine compositional heterogeneity in the youngest (~170 to 70 ka) post-caldera volcanism at Yellowstone caldera, the Central Plateau Member (CPM) rhyolites, as a case study. We compare 238U–230Th age, trace-element, and Hf isotopic data from zircons, and major-element, Ba, and Pb isotopic data from sanidines hosted in two CPM rhyolites (Hayden Valley and Solfatara Plateau flows) and one extracaldera rhyolite (Gibbon River flow), all of which erupted near the caldera margin ca. 100 ka. The Hayden Valley flow hosts two zircon populations and one sanidine population that are consistent with residence in the CPM reservoir. The Gibbon River flow hosts one zircon population that is compositionally distinct from Hayden Valley flow zircons. The Solfatara Plateau flow contains multiple sanidine populations and all three zircon populations found in the Hayden Valley and Gibbon River flows, demonstrating that the Solfatara Plateau flow formed by mixing extracaldera magma with the margin of the CPM reservoir. This process highlights the dynamic nature of magmatic interactions at the margins of large silicic reservoirs. More generally, Hf isotopic data from the CPM zircons provide the first direct evidence for isotopically juvenile magmas contributing mass to the youngest post-caldera magmatic system and demonstrate that the sources contributing magma to the CPM reservoir were heterogeneous in 176Hf/177Hf at ca. 100 ka. Thus, the limited compositional variability of CPM glasses reflects homogenization occurring within the CPM reservoir, not a homogeneous source.

  18. Cogenetic late Pleistocene rhyolite and cumulate diorites from Augustine Volcano revealed by SIMS 238U-230Th dating of zircon, and implications for silicic magma generation by extraction from mush

    NASA Astrophysics Data System (ADS)

    Coombs, Michelle L.; Vazquez, Jorge A.

    2014-12-01

    Volcano, a frequently active andesitic island stratocone, erupted a late Pleistocene rhyolite pumice fall that is temporally linked through zircon geochronology to cumulate dioritic blocks brought to the surface in Augustine's 2006 eruption. Zircon from the rhyolite yield a 238U-230Th age of ˜25 ka for their unpolished rims, and their interiors yield a bimodal age populations at ˜26 ka and a minority at ˜41 ka. Zircon from dioritic blocks, ripped from Augustine's shallow magmatic plumbing system and ejected during the 2006 eruption, have interiors defining a ˜26 ka age population that is indistinguishable from that for the rhyolite; unpolished rims on the dioritic zircon are dominantly younger (≤12 ka) indicating subsequent crystallization. Zircon from rhyolite and diorite overlap in U, Hf, Ti, and REE concentrations although diorites also contain a second population of high-U, high temperature grains. Andesites that brought dioritic blocks to the surface in 2006 contain zircon with young (≤9 ka) rims and a scattering of older ages, but few zircon that crystallized during the 26 ka interval. Both the Pleistocene-age rhyolite and the 2006 dioritic inclusions plot along a whole-rock compositional trend distinct from mid-Holocene-present andesites and dacites, and the diorites, rhyolite, and two early Holocene dacites define linear unmixing trends often oblique to the main andesite array and consistent with melt (rhyolite) extraction from a mush (dacites), leaving behind a cumulate amphibole-bearing residue (diorites). Rare zircon antecrysts up to ˜300 ka from all rock types indicate that a Quaternary center has been present longer than preserved surficial deposits.

  19. Magma mixing and the generation of isotopically juvenile silicic magma at Yellowstone caldera inferred from coupling 238U-230Th ages with trace elements and Hf and O isotopes in zircon and Pb isotopes in sanidine

    NASA Astrophysics Data System (ADS)

    Stelten, Mark E.; Cooper, Kari M.; Vazquez, Jorge A.; Reid, Mary R.; Barfod, Gry H.; Wimpenny, Josh; Yin, Qing-zhu

    2013-08-01

    The nature of compositional heterogeneity within large silicic magma bodies has important implications for how silicic reservoirs are assembled and evolve through time. We examine compositional heterogeneity in the youngest (~170 to 70 ka) post-caldera volcanism at Yellowstone caldera, the Central Plateau Member (CPM) rhyolites, as a case study. We compare 238U-230Th age, trace-element, and Hf isotopic data from zircons, and major-element, Ba, and Pb isotopic data from sanidines hosted in two CPM rhyolites (Hayden Valley and Solfatara Plateau flows) and one extracaldera rhyolite (Gibbon River flow), all of which erupted near the caldera margin ca. 100 ka. The Hayden Valley flow hosts two zircon populations and one sanidine population that are consistent with residence in the CPM reservoir. The Gibbon River flow hosts one zircon population that is compositionally distinct from Hayden Valley flow zircons. The Solfatara Plateau flow contains multiple sanidine populations and all three zircon populations found in the Hayden Valley and Gibbon River flows, demonstrating that the Solfatara Plateau flow formed by mixing extracaldera magma with the margin of the CPM reservoir. This process highlights the dynamic nature of magmatic interactions at the margins of large silicic reservoirs. More generally, Hf isotopic data from the CPM zircons provide the first direct evidence for isotopically juvenile magmas contributing mass to the youngest post-caldera magmatic system and demonstrate that the sources contributing magma to the CPM reservoir were heterogeneous in 176Hf/177Hf at ca. 100 ka. Thus, the limited compositional variability of CPM glasses reflects homogenization occurring within the CPM reservoir, not a homogeneous source.

  20. Fluxes of metals to a manganese nodule: Radiochemical, chemical, structural, and mineralogical studies

    USGS Publications Warehouse

    Moore, W.S.; Ku, T.-L.; Macdougall, J.D.; Burns, V.M.; Burns, R.; Dymond, J.; Lyle, M.W.; Piper, D.Z.

    1981-01-01

    Fluxes of metals to the top and bottom surfaces of a manganese nodule were determined by combining radiochemical (230Th, 231Pa, 232Th, 238U, 234U) and detailed chemical data. The top of the nodule had been growing in its collected orientation at 4.7 mm Myr-1 for at least 0.5 Myr and accreting Mn at 200 ??g cm-2 kyr-1. The bottom of the nodule had been growing in its collected orientation at about 12 mm Myr-1 for at least 0.3 Myr and accreting Mn at about 700 ??g cm-2 yr-1. Although the top of the nodule was enriched in iron relative to the bottom, the nodule had been accreting Fe 50% faster on the bottom. 232Th was also accumulating more rapidly in the bottom despite a 20-fold enrichment of 230Th on the top. The distribution of alpha-emitting nuclides calculated from detailed radiochemical measurements matched closely the pattern revealed by 109-day exposures of alpha-sensitive film to the nodule. However, the shape and slope of the total alpha profile with depth into the nodule was affected strongly by 226Ra and 222Rn migrations making the alpha-track technique alone an inadequate method of measuring nodule growth rates. Diffusion of radium in the nodule may have been affected by diagenetic reactions which produce barite, phillipsite and todorokite within 1 mm of the nodule surface; however, our sampling interval was too broad to document the effect. We have not been able to resolve the importance of nodule diagenesis on the gross chemistry of the nodule. ?? 1981.

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

    USGS Publications Warehouse

    Stein, Martin; Wasserburg, G.J.; Lajoie, K.R.; Chen, J.-H.

    1991-01-01

    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 a 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 (elevation 8 m, previously dated at 124 and 117 Ky by ?? counting), Shell Beach terrace (elevation about 25 m, previously undated), Nestor terrace, San Diego (elevation 23 m, previously dated at 131 to 109 Ky ), Bird Rock terrace, San Diego ( elevation 8 m, previously dated at 81 Ky ). Attached living specimens were collected from the intertidal zone on the modern terrace at Moss Beach. Concentrations of 232Th in both living and fossil specimens are much higher than in reef-building corals (12 to 624 pmol/g vs. 0.1 to 1.6 pmol/g, respectively). However, because 230Th/232Th in Balanophyllia elegans are very low (2.22 ?? 10-3 to 4.33 ?? 10-4), the high 232Th concentrations have negligible effect on the 230Th-234U dates. The high 232Th concentration in the living specimen (33.1 pmol/g) indicates that a significant amount of 232Th is incorporated in the aragonitic skeleton during growth, or attached to clay-sized silicates trapped in the skeletal material. The calculated initial 234U activities in the fossil specimens of Balanophyllia elegans are higher than the 234U activity in modern seawater or in the modern specimen. The higher initial activities could possibly reflect the influx of 234U-enriched continental water into Pleistocene coastal waters, or it could reflect minor diagenetic

  2. Accumulation rates of Th-230, Pa-231, and some transition metals on the Bermuda Rise

    USGS Publications Warehouse

    Bacon, M.P.; Rosholt, J.N.

    1982-01-01

    Measurements of 238U, 234U, 230Th, 232Th, 231Pa, Mn, Fe, Co, Ni, Cu, and Zn were made on 23 samples from core GPC-5, a 29-m giant piston core from a water depth of 4583 m on the northeastern Bermuda Rise (33??41.2???N, 57??36.9???W). This area is characterized by rapid deposition of sediment transported by abyssal currents. Unsupported 230Th and 231Pa are present throughout the core but, because of large variations in the sedimentation rate, show marked departures from exponential decay with depth. The trend with depth of the 231Paex 230Thex ratio is consistent with the average accumulation rate of 36 cm/1000 y reported earlier on the basis of radiocarbon dating and CaCO3 stratigraphy. When expressed on a carbonate-free basis, concentrations of Mn, Co, Ni, Cu, Zn, 230Thex, and 231Paex all show cyclic variations positively correlated with those of CaCO3. The correlations can be explained by a model in which all of these constituents, including CaCO3, are supplied to the sediments from the water column at a constant rate. Concentration variations are controlled mainly by varying inputs of terrigenous detritus, with low inputs occurring during interglacials and high inputs during glacials. Relationships between the metal and 230Thex concentrations permit estimates of the rates at which the metals are removed to the sediment by scavenging from the water column. The results, in ??g/cm2-1000 y, are: 4300 ?? 1100 for Mn, 46 ?? 16 for Ni and 76 ?? 26 for Cu. These rates are somewhat larger than ocean-wide averages estimated by other methods, and the absolute rate of 230Th accumulation in GPC-5 averages about nine times higher than production in the overlying water column. This part of the Bermuda Rise and similar bottom-current deposits may act as important accumulators of elements scavenged from seawater. ?? 1982.

  3. High-Precision Isotope Analysis of Uranium and Thorium by TIMS

    NASA Astrophysics Data System (ADS)

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

    2006-12-01

    =134).The mean fractionation factor in these analyses is 0.09±0.06 percent per mass unit. The ^{236}U/238U value of about 1.1×10-9 measured in this standard defines an upper limit for the ^{236}U background in the analyses. The mean atomic 234U/238U and activity 230Th/238U for 29 runs of an internal secular equilibrium uranium ore standard is (54.82±0.02) ×10-6 and 1.002±0.002, respectively. The Th isotopic composition in the IRMM-036 standard was obtained after addition of high-purity ^{229}Th tracer and measuring 232Th/^{229}Th and 230Th/^{229}Th ratios in separate lower- and higher-temperature runs, respectively. The resulting 230Th/232Th for 30 runs is 31.09±0.04 ×10-7, in excellent agreement with the certified value of 31.13±0.78 ×10-7. The USGS laboratory measured four samples of depleted to low-enriched uranium in the recent Regular European Inter-laboratory Measurement Evaluation Program (REIMEP-18). The results of these analyses are close to the certified values.

  4. Eastern North Atlantic deep-sea corals: tracing upper intermediate water Δ 14C during the Holocene

    NASA Astrophysics Data System (ADS)

    Frank, Norbert; Paterne, Martine; Ayliffe, Linda; van Weering, Tjeerd; Henriet, Jean-Pierre; Blamart, Dominique

    2004-03-01

    Paired 230Th/U and 14C dating were performed on deep-sea corals (Lophelia pertusa and Madrepora oculata) from the northeastern North Atlantic at ∼730 m bsl to investigate past changes of the thermohaline circulation. These were estimated using the Δ14C value of the upper intermediate waters, based on the 14C ages of the top and base of each coral, where possible, and the 230Th/U dating. The reliability of these estimates was checked by dating two very young corals of the species L. pertusa. One of these corals, collected alive in 1999 AD, gave a 230Th/U age of 1995±4 AD after correction for non-radiogenic 230Th. Another coral, the top of which dated to 1969±6 AD, recorded the atmospheric 14C/12C increase due to the nuclear tests in the early 1960s. The calculated Δ14C values from these two corals agree with those measured at GEOSECS Station 23 in 1972-1973 [Östlund et al., Earth Planet. Sci. Lett. 23 (1974) 69-86] and 1991-1992 [Nydal and Gisfelos, Radiocarbon 38 (1996) 389-406]. This, together with the 100% aragonite content and the δ234U and 230Th/232Th values of all the dated corals, indicates that none of the corals behaved as open systems with respect to their U-series nuclides and that they closely represent the water mass properties in which they lived. The pre-anthropogenic Δ14C value of the North Atlantic intermediate waters was estimated at -69±4‰. The reservoir age varies from ∼400 years to ∼600 years, and this variation is due to atmospheric 14C/12C changes. A reservoir age of 610±80 years, close to the pre-anthropogenic value, was determined from one coral dated at 10 430±120 cal yr BP, when the global sea level was approximately at -35 m [Bard et al., Nature 382 (1996) 241-244]. This suggests a modern-like pattern of the oceanic circulation prevailed in the Northeast Atlantic Ocean at this time although the deglaciation was not completely achieved.

  5. The Ins and Outs of U and Th Isotopic Measurements Using a Nu Plasma 1700 MC-ICP- MS

    NASA Astrophysics Data System (ADS)

    Pietruszka, A. J.; Rooney, T. O.

    2007-12-01

    The Nu Plasma 1700 is a relatively new type of large-geometry MC-ICP-MS that offers the potential to improve the accuracy and precision of U and Th isotopic measurements compared to previous instruments (e.g., the Plasma 54-30, or P54-30). The higher resolution of the Nu Plasma 1700 translates to more than a factor of 6 improvement in the abundance sensitivity at high mass (compared to the P54-30), and virtually eliminates the necessity of a tail correction on 230Th during the measurement of 232Th/230Th ratios (the major source of uncertainty using the P54-30). However, the Nu Plasma 1700 uses a discrete dynode secondary electron multiplier for ion-counting, which has a smaller dynamic range than the Daly detector used by the P54- 30. This prevents the placement of a relatively large 235U signal on the ion-counter, and thus, requires alternative methods to correct for the effects of instrumental mass bias. Initial efforts in our laboratory have focused on the development of standard-sample bracketing (SSB) techniques to correct for mass bias, with a careful evaluation of possible instrumental artifacts such as matrix effects, drift in the bias between the Faraday collectors and the ion-counting detector (Faraday/IC bias), and non-linearity of both the ion-counting detector and the retardation lens. Experiments with solution standards suggest that the major source of uncertainty on U and Th isotopic measurements using the Nu Plasma 1700 in SSB mode is drift in the Faraday/IC bias. Nevertheless, SSB analyses for U and Th solution standards are reproducible to 0.3% for 238U/234U and 0.4% for 232Th/230Th (±2σ), which is similar to the results obtained on the Plasma 54-30 (Luo et al., 1997; Pietruszka et al., 2002). So far, accuracy has been evaluated by repeatedly analyzing the UCSC Th isotopic standard against a previously characterized in-house Th isotopic standard in SSB mode. The result agrees within error of previous determinations for UCSC Th using the Plasma

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

    SciTech Connect

    Watson, David J.; Strom, Daniel J.

    2011-02-25

    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 were 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.

  7. Using U-series Isotopes To Determine Sources Of Pedogenic Carbonates: Comparison Of Natural And Agricultural Soils In The Semi-arid Southern New Mexico And Western Texas

    NASA Astrophysics Data System (ADS)

    Nyachoti, S. K.; Ma, L.; Borrok, D. M.; Jin, L.; Tweedie, C. E.

    2012-12-01

    Pedogenic carbonates commonly precipitate from infiltrating soil water in arid and semi-arid lands and are observed in soils of southern New Mexico and western Texas. These carbonates could form an impermeable layer in the soil horizons impairing water infiltration, thus affecting crop growth and yield. It is important to determine the source of C and Ca in these carbonates and to understand conditions favoring their formation, kinetics and precipitation rates. In this study, major elements and U-series isotopes in bulk calcic soils, and weak acid leachates and residues were measured from one irrigated alfalfa site in the Hueco basin near El Paso, TX and one natural shrubland site on the USDA Jornada experimental range in southern NM. The combined geochemical and isotopic results allow us to determine the formation ages of the carbonates; investigate the mobility of U, Th, and major elements in these soils; and infer for the effects of irrigation on carbonate formation in agricultural soils. Our results show distinctive U and Th isotope systems in the two soil profiles analyzed. For example, (234U/238U) ratios in the Jornada bulk soils decrease from ~1.01 to 0.96 towards the surface, consistent with a preferential loss of 234U over 238U during chemical weathering. At the Jornada site, (238U/232Th) ratios decrease while (230Th/238U) increase towards the surface, consistent with a general depletion of U and the immobility of Th in the natural soils. By contrast at the Alfalfa site, (234U/238U) ratios of bulk soils increase from ~ 0.97 to 1.02 towards the surface, suggesting an additional source of external uranium, most likely the irrigation water from Rio Grande which has a (234U/238U) ratio of ~ 1.5 near El Paso. The (238U/232Th) and (230Th/238U) ratios also imply leaching of U from shallower soils but precipitation in greater depths at Alfalfa site; suggests that partial dissolution and re-precipitation of younger carbonates occur. Calculated carbonate ages from U

  8. Evaluation of the diffuse contamination of soils caused by residues coming from the large scale production of phosphate fertilisers

    NASA Astrophysics Data System (ADS)

    Martinez, M. J.; Perez-Sirvent, C.; Martinez-Lopez, S.; Bolivar, J. P.; Mosqueda, F.; Vaca, F.; Garcia-Tenorio, R.

    2012-04-01

    The obtaining of phosphate fertilizers results in large amounts of residues that are frequently accumulated in deposits or pools occupying a wide area. These residues are acidic, and contain variable amounts of trace elements and radionuclides. The potentially polluting agents can be leached by rainwater, and so transferred to the surface waters and then to the groundwater after soil infiltration. Since the distribution and thickness of the residue deposits are variable, the contaminants cannot be easily traced back to a single, well defined source, and so a diffuse contamination (nonpoint source pollution) of the surrounding soils and waters occurs. This communication reports the results obtained in the study of soils close to the phosphogypsum deposits placed near Rio Tinto (Huelva, Spain). The zone is affected not only by the mentioned residues but also by the tides due to the vicinity of the sea. The samples studied had a low organic content and a low acidity with average values of 30 mS/cm for the EC. The mineralogical study allowed illite, goethite, quartz, gypsum and kaolinite to be identified as the main mineralogical components. Although the arsenic level was relatively high (about 600 mg/Kg) the data proved that this element is not mobilized into water. Analytical data for 238U , 234U, 235U, 228Th, 230Th, 232Th, 226Ra, 228Ra, 210Po, 40K , 137Cs were also obtained.

  9. An accurate method to measure alpha-emitting natural radionuclides in atmospheric filters: Application in two NORM industries

    NASA Astrophysics Data System (ADS)

    Lozano, R. L.; Bolívar, J. P.; San Miguel, E. G.; García-Tenorio, R.; Gázquez, M. J.

    2011-12-01

    In this work, an accurate method for the measurement of natural alpha-emitting radionuclides from aerosols collected in air filters is presented and discussed in detail. The knowledge of the levels of several natural alpha-emitting radionuclides (238U, 234U, 232Th, 230Th, 228Th, 226Ra and 210Po) in atmospheric aerosols is essential not only for a better understanding of the several atmospheric processes and changes, but also for a proper evaluation of the potential doses, which can inadvertently be received by the population via inhalation. The proposed method takes into account the presence of intrinsic amounts of these radionuclides in the matrices of the quartz filters used, as well as the possible variation in the humidity of the filters throughout the collection process. In both cases, the corrections necessary in order to redress these levels have been evaluated and parameterized. Furthermore, a detailed study has been performed into the optimisation of the volume of air to be sampled in order to increase the accuracy in the determination of the radionuclides. The method as a whole has been applied for the determination of the activity concentrations of U- and Th-isotopes in aerosols collected at two NORM (Naturally Occurring Radioactive Material) industries located in the southwest of Spain. Based on the levels found, a conservative estimation has been performed to yield the additional committed effective doses to which the workers are potentially susceptible due to inhalation of anthropogenic material present in the environment of these two NORM industries.

  10. Bioaccumulation of natural radionuclides in molluscs from the Ebro Delta area.

    PubMed

    Fonollosa, E; Peñalver, A; Aguilar, C; Borrull, F

    2017-01-01

    (210)Po, (210)Pb, (234)U, (238)U, (232)Th and (230)Th were analysed in the edible part of four different species of bivalves typically produced and consumed in the Ebro Delta area. The results show that the main contributor to the radioactive content in these species was (210)Po, with values ranging between 263.1 ± 26.6 and 813.0 ± 72.9 Bq/kg (d.w.), which are higher than the usual reported activity levels in other geographical areas. This can probably be attributed to the activities of a phosphate industrial plant located upstream on the Ebro River, which may lead to enhanced levels of naturally occurring radioactive isotopes in the aquatic ecosystem. To determine the possible impact on health, the committed effective doses through the consumption of the different species were evaluated and the cumulative total annual effective dose for their consumption was estimated to 187.6 μSv/year, which is in the range of 200-1000 μSv/year given by UNSCEAR.

  11. Preparation of actinide specimens for the US/UK joint experiment in the Dounreay Prototype Fast Reactor

    SciTech Connect

    Quinby, T C; Adair, H L; Kobisk, E H

    1982-05-01

    A joint research program involving the United States and the United Kingdom was initiated about four years ago for the purpose of studying the fuel behavior of higher actinides using in-core irradiation in the fast reactor at Dounreay, Scotland. Simultaneously, determination of integral cross sections of a wide variety of higher actinide isotopes (physics specimens) was proposed. Coincidental neutron flux and energy spectral measurements were to be made using vanadium encapsulated dosimetry materials in the immediate region of the fuel pellets and physics samples. The higher actinide samples chosen for the fuel study were /sup 241/Am and /sup 244/Cm in the forms of Am/sub 2/O/sub 3/, Cm/sub 2/O/sub 3/, and Am/sub 6/Cm(RE)/sub 7/O/sub 21/, where (RE) represents a mixture of lanthanides. Milligram quantities of actinide oxides of /sup 248/Cm, /sup 246/Cm, /sup 244/Cm, /sup 243/Cm, /sup 243/Am, /sup 241/Am, /sup 244/Pu, /sup 242/Pu, /sup 241/Pu, /sup 240/Pu, /sup 239/Pu, /sup 238/Pu, /sup 237/Np, /sup 238/U, /sup 236/U, /sup 235/U, /sup 234/U, /sup 233/U, /sup 232/Th, /sup 230/Th, and /sup 231/Pa were encapsulated to obtain nuclear cross section and reaction rate data for these materials.

  12. Determination of trace element concentrations and stable lead, uranium and thorium isotope ratios by quadrupole-ICP-MS in NORM and NORM-polluted sample leachates.

    PubMed

    Mas, J L; Villa, M; Hurtado, S; García-Tenorio, R

    2012-02-29

    This work focuses on the monitoring of the potential pollution in scenarios that involve NORM-related industrial activities (environmental or in-door scenarios). The objective was to develop a method to determine extent and origin of the contamination, suitable for monitoring (i.e. simple, fast and economical) and avoiding the use of too many different instruments. It is presented a radiochemical method that allows the determination of trace element concentrations and 206Pb/207Pb/208Pb, 238U/234U and 232Th/230Th isotope ratios using a single sample aliquot and a single instrument (ICP-QMS). Eichrom UTEVA® extraction chromatography minicolumns were used to separate uranium and thorium in sample leachates. Independent ICP-MS determinations of uranium and thorium isotope ratios were carried out afterwards. Previously a small aliquot of the leachate was used for the determination of trace element concentrations and lead isotope ratios. Several radiochemical arrangements were tested to get maximum performances and simplicity of the method. The performances of the method were studied in terms of chemical yields of uranium and thorium and removal of the potentially interfering elements. The established method was applied to samples from a chemical industry and sediments collected in a NORM-polluted scenario. The results obtained from our method allowed us to infer not only the extent, but also the sources of the contamination in the area.

  13. U-series Chronology of volcanoes in the Central Kenya Peralkaline Province, East African Rift

    NASA Astrophysics Data System (ADS)

    Negron, L. M.; Ma, L.; Deino, A.; Anthony, E. Y.

    2012-12-01

    We are studying the East African Rift System (EARS) in the Central Kenya Peralkaline Province (CKPP), and specifically the young volcanoes Mt. Suswa, Longonot, and Menengai. Ar dates by Al Deino on K-feldspar phenocrysts show a strong correlation between older Ar ages and decreasing 230Th/232Th, which we interpret to reflect the age of eruption. This system has been the subject of recent research done by several UTEP alumni including Antony Wamalwa using potential field and magnetotelluric (MT) data to identify and characterize fractures and hydrothermal fluids. Also research on geochemical modeling done by John White, Vanessa Espejel and Peter Omenda led to the hypothesis of possible disequilibrium in these young, mainly obsidian samples in their post eruptive history. A pilot study of 8 samples, (also including W-2a USGS standard and a blank) establish the correlation that was seen between the ages found by Deino along with the 230/232Th ratios. All 8 samples from Mt. Suswa showed a 234U/238U ratio of (1) which indicates secular equilibrium or unity and that these are very fresh samples with no post-eruptive decay or leaching of U isotopes. The pilot set was comprised of four samples from the ring-trench group (RTG) with ages ranging from 7ka-present, two samples from the post-caldera stage ranging from 31-10ka, one sample from the syn-caldera stage dated at 41ka, and one sample from the pre-caldera stage dated at 112ka. The young RTG had a 230/232Th fractionation ratio of 0.8 ranging to the older pre-caldera stage with a 230/232Th ratio of 0.6. From this current data and research of 14C ages by Nick Rogers, the data from Longonot volcano was also similar to the 230/232Th ratio we found. Rogers' data places Longonot volcano ages to be no more than 20ka with the youngest samples also roughly around 0.8 disequilibrium. These strong correlations between the pilot study done for Mt. Suswa, 40Ar ages by Deino, along with 14C ages from Rogers have led to the

  14. Comparisons between thorium isotopes in seawater and marine sediments for reconstructing dissolved and total detrital inputs to the ocean

    NASA Astrophysics Data System (ADS)

    Hsieh, Y.; Henderson, G. M.; Williams, R. H.; McGee, D.

    2012-12-01

    Thorium-232, the most abundant Th isotope in the continental crust, has been widely used in seawater and marine sediments to evaluate continental inputs to the ocean. Seawater 232Th concentrations combined with estimates of Th residence time in the surface ocean derived from measurements of 230Th (or 234Th or 228Th) have been used to assess the dissolved 232Th removal flux. Assuming a constant 232Th concentration in detritus and dust Th solubility in seawater, 232Th removal flux can be converted to atmospheric dust input to the ocean. In marine sediments, 232Th concentrations have been normalized by 230Th to estimate total 232Th sinking flux to the seafloor. Similarly, this flux can also be used to estimate dust input to the ocean. Comparisons between dissolved 232Th removal flux in seawater and total 232Th sinking flux in sediments are crucial, because the discrepancy between these two fluxes could provide insights into several important issues, including uncertain dust Th solubility, potential advective Th inputs, inaccurate 230Th-derived sediment accumulation rates, and unknown lateral sediment transport. However, comparisons between these two fluxes have rarely been made in the same core-top sediments and water columns above. In this study, we compile several seawater and marine sediment Th data from different regions of the ocean, with a focus on the tropical North Atlantic Ocean. The data are used to estimate 232Th removal and sinking fluxes, and hence the dissolved and total detrital inputs to the ocean. The results are also compared with other dust tracers (e.g. Al and Ti) and modeled dust deposition to improve our understanding of Th and dust in the ocean. This work offers an important test for the use of Th isotopes in reconstructing paleo dust input to the ocean and the impacts of dust flux changes on marine productivity and climate change in the past.

  15. Uranium-thorium series radionuclides in brines and reservoir rocks from two deep geothermal boreholes in the Salton Sea Geothermal Field, southeastern California

    NASA Astrophysics Data System (ADS)

    Zukin, Jeffrey G.; Hammond, Douglas E.; Teh-Lung, Ku; Elders, Wilfred A.

    1987-10-01

    Naturally occurring U and Th series radionuclides have been analyzed in high temperature brines (~300°C, 25 wt% dissolved solids) and associated rocks from two deep geothermal wells located on the northeastern margin of the Salton Sea Geothermal Field (SSGF). These data are part of a study of the SSGF as a natural analog of possible radionuclide behavior near a nuclear waste repository constructed in salt beds, and permit evaluation of some characteristics of water-rock interaction in the SSGF. Rock/Brine concentration ratios ( Rc = (dpm/ g) rock/(dpm/ g) brine) were found to vary from near unity for isotopes of Ra, Pb and Rn to about 5 × 10 5 for 232Th. The high sorptivity of 232Th is closely followed by that of 238U and 234U ( Rc ~ 5 × 10 4), suggesting that U is retained in the +4 oxidation state by the reducing conditions in the brines. The relatively high solubility of 210Pb and 212Pb is attributed to formation of chloride complexes, while the high Ra solubility is attributed to chloride complexing, a lack of suitable adsorption sites due to the high brine salinity and temperature, and the reducing conditions that prevent MnO 2 and RaSO 4 from forming. The 228Ra /226Ra ratios in the brines are approximately equal to those of their parents ( 232Th /230Th ) in associated rocks, indicating that Ra equilibration in the brine-rock system is achieved within the mean life of 228Ra (8.3 years). The 224Ra /228Ra ratios in these brines are about 0.7, indicating that either (1) brine composition is not homogeneous and 224Ra decays in fracture zones deficient in Ra and Th as the brine travels to the wellhead or (2) Ra equilibration in the brine-host rock system is not complete within the mean life of 224Ra (5.2 days) because the desorption of 224Ra from the solid phase is impeded. The 228Ac /228Ra activity ratio in the SSGF brines studied is <0.1, and from this ratio the residence time of 228Ac in the brine before sorption onto solid surfaces is estimated to be <70

  16. Thorium isotopes in human tissues

    SciTech Connect

    Stehney, A.F.; Lucas, H.F.

    1991-12-31

    Concentrations of {sup 232}Th and activity ratios of {sup 228}Th to {sup 232}Th and {sup 230}Th to {sup 232}Th were determined in autopsy samples from five former employees of a thorium refinery. The ranges of {sup 232}Th activity concentrations (mBq g{sup {minus}1}) were 0.17--94 in lungs, 3.9--1210 in pulmonary lymph nodes, 0.14--1.19 in bones, 0.015--0.68 in liver, 0.97--5.8 in spleen, and 0.009--0.068 in kidneys. These concentrations are 10 to 1000 times greater than have been reported for persons not occupationally exposed to Th. In most of the samples, the ratios of {sup 230}Th to {sup 232}Th and {sup 228}Th to {sup 232}Th activity at death of the subject were 0.1--0.2 and 0.2--0.4, respectively. Thorium-228 to {sup 228}Ra activity ratios ({plus_minus} standard errors) of 0.86 {plus_minus} 0.11 in lungs and 1.18 {plus_minus} 0.13 in lymph nodes of one subject were obtained by calculation from ratios of {sup 228}Th to {sup 232}Th.

  17. Extreme U-Th disequilibrium in rift-related basalts, rhyolites and granophyric granite and the timescale of rhyolite generation, intrusion and crystallization at Alid volcanic center, Eritrea

    USGS Publications Warehouse

    Lowenstern, J. B.; Charlier, B.L.A.; Clynne, M.A.; Wooden, J.L.

    2006-01-01

    Rhyolite pumices and co-erupted granophyric (granite) xenoliths yield evidence for rapid magma generation and crystallization prior to their eruption at 15·2 ± 2·9 ka at the Alid volcanic center in the Danikil Depression, Eritrea. Whole-rock U and Th isotopic analyses show 230Th excesses up to 50% in basalts <10 000 years old from the surrounding Oss lava fields. The 15 ka rhyolites also have 30–40% 230Th excesses. Similarity in U–Th disequilibrium, and in Sr, Nd, and Pb isotopic values, implies that the rhyolites are mostly differentiated from the local basaltic magma. Given the (230Th/232Th) ratio of the young basalts, and presumably the underlying mantle, the (230Th/232Th) ratio of the rhyolites upon eruption could be generated by in situ decay in about 50 000 years. Limited (∼5%) assimilation of old crust would hasten the lowering of (230Th/232Th) and allow the process to take place in as little as 30 000 years. Final crystallization of the Alid granophyre occurred rapidly and at shallow depths at ∼20–25 ka, as confirmed by analyses of mineral separates and ion microprobe data on individual zircons. Evidently, 30 000–50 000 years were required for extraction of basalt from its mantle source region, subsequent crystallization and melt extraction to form silicic magmas, and final crystallization of the shallow intrusion. The granophyre was then ejected during eruption of the comagmatic rhyolites.

  18. Thorium isotopes in colloidal fraction of water from San Marcos Dam, Chihuahua, Mexico

    NASA Astrophysics Data System (ADS)

    Cabral-Lares, M.; Melgoza, A.; Montero-Cabrera, M. E.; Renteria-Villalobos, M.

    2013-07-01

    The main interest of this stiidy is to assess the contents and distribution of Th-series isotopes in colloidal fraction of surface water from San Marcos dam, because the suspended particulate matter serves as transport medium for several pollutants. The aim of this work was to assess the distribution of thorium isotopes (232Th and 230Th) contained in suspended matter. Samples were taken from three surface points along the San Marcos dam: water input, midpoint, and near to dam wall. In this last point, a depth sampling was also carried out. Here, three depth points were taken at 0.4, 8 and 15 meters. To evaluate the thorium behavior in surface water, from every water sample the colloidal fraction was separated, between 1 and 0.1 μm. Thorium isotopes concentraron in samples were obtained by alpha spectrometry. Activity concentrations obtained of 232Th and 230Th in surface points ranged from 0.3 to 0.5 Bq ṡ L-1, whereas in depth points ranged from 0.4 to 3.2 Bq ṡ L-1, respectively. The results show that 230Th is in higher concentration than 232Th in colloidal fraction. This can be attributed to a preference of these colloids to adsorb uranium. Thus, the activity ratio 230Th/232Th in colloidal fraction showed values from 2.3 to 10.2. In surface points along the dam, 230Th activity concentration decreases while 232Th concentration remains constant. On the other hand, activity concentrations of both isotopes showed a pointed out enhancement with depth. The results have shown a possible lixiviation of uranium from geological substrate into the surface water and an important fractionation of thorium isotopes, which suggest that thorium is non-homogeneously distributed along San Marcos dam.

  19. Can calcretes be used to date pedogenic processes in soil profiles under semi arid climate ? An example from U-Th isochrons in calcretes from South India.

    NASA Astrophysics Data System (ADS)

    Durand, Nicolas; Hamelin, Bruno; Deschamps, Deschamps; Gunnel, Yanni; Curmi, Pierre

    2015-04-01

    Pedogenic carbonates, such as calcretes, have often been questioned as possible markers of the pedogenetic evolution of soil profiles under semi-arid climate. However, providing precise chronological constraints on their formation is a perequisite to determine the climatic and paleo-environmental conditions prevailing during and after their formation, and to improve our understanding of the physical and chemical conditions that promoted their development and preservation. On the other hand, these authigenic calcium carbonate precipitates provide us with an interesting test of the U-Th radioactive disequilibrium dating method, the reliability of which has been demonstrated extensively in aragonitic marine formations, and calcitic continental speleothems, but remain much more questionable in highly porous and chemically complex media such as soil profiles. In this study, we combined U-Th systematics with detailed micromorphologic observations of calcretes from South India, investigated at different spatial scales, from the landscape to the soil profile, down to the micro-fabrics of the samples. The U-Th analyses were performed by Thermo-Ionization Mass Spectrometry. Since calcretes are impure carbonates, mixed with various amounts of parent rock and weathered minerals, all ages had to be computed using the isochron technique to correct for the detrital component. This method involves the extraction of several coeval subsamples from a single soil horizon and their U-Th analyses after total dissolution (TDS method). The isochron age is derived from the slope of the mixing line between the pure authigenic carbonate and the detrital phase, and the precision established statistically using the probability of fit and weighted mean deviations (MSWD). Our results show that each set of samples taken from decimetric blocks is characterized by a well defined isochron line, clearly distinct from each other in the 3D Osmond diagram (232Th/238U; 230Th/238U ; 234U/238U). The

  20. 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.

  1. Impact of vegetation change on the mobility of uranium- and thorium-series nuclides in soils

    NASA Astrophysics Data System (ADS)

    Gontier, A.; Rihs, S.; Turpault, M.-P.; Chabaux, F.

    2012-04-01

    The effect of land cover change on chemical mobility and soil response was investigated using short- and long-lived nuclides from the U- and Th series. Indeed, the matching of these nuclides half-live to the pedogenic processes rates make these nuclides especially suitable to investigate either time or mechanism of transfers within a soil-water-plant system. This study was carried out from the experimental Breuil-Chenue site (Morvan mountains, France). The native forest (150 year-old) was partially clear-felled and replaced in 1976 by mono-specific plantations distributed in different stands. Following this cover-change, some mineralogical changes in the acid brown soil were recognized (Mareschal, 2008). Three soil sections were sampled under the native forest and the replanted oak and Douglas spruce stands respectively. The (238U), (234U), (230Th), (226Ra), (232Th) and (228Ra) activities were analysed by thermal ionization mass spectrometry (TIMS), inductively coupled plasma mass spectrometry (MC-ICPMS) and gamma spectrometry. Significant differences in U, Th, and Ra activities were observed between the soils located under the native forest or the replanted-trees stands, mostly dominated by a large uranium mobilization from the replanted soils. Moreover, all the investigated U and Th-series activity ratios show a contrasted trend between the shallowest horizons (0-50cm) and the deepest one (below 50cm), demonstrating the chemical effect of the vegetation change on the shallow soil layers. Using a continuous open-system leaching model, the coupled radioactive disequilibria measured in the different soil layers permit to quantify the rate of the radionuclides mobilities. Reference: Mareschal, L., 2008. Effet des substitutions d'essences forestières sur l'évolution des sols et de leur minéralogie : bilan après 28 ans dans le site expérimental de Breuil (Morvan) Université Henri Poincaré, Nancy-I.

  2. Distribution of natural radionuclides in the production and use of phosphate fertilizers in Brazil.

    PubMed

    Saueia, C H R; Mazzilli, B P

    2006-01-01

    The Brazilian phosphate fertilizer is obtained by wet reaction of igneous phosphate rock with concentrated sulphuric acid, giving as final product, phosphoric acid and dehydrated calcium sulphate (phosphogypsum) as by-products. Phosphoric acid is the starting material for triple superphosphate (TSP), single superphosphate (SSP), monoammonium phosphate (MAP) and diammonium phosphate (DAP). The phosphate rock used as raw material presents in its composition radionuclides of the U and Th natural series. Taking this into account, the main aim of this paper is to evaluate the fluxes of natural radionuclides and radioactive disequilibria involved in the Brazilian industrial process of phosphoric acid production; to determine the content of radioactivity in several commercial fertilizers produced by this industry; to estimate their radiological impact in crop soils and the long term exposure due to their application. Radiological characterization of phosphate rock, phosphogypsum and phosphate fertilizers was performed by alpha and gamma spectrometry. The fertilizer samples, which are derived directly from phosphoric acid, MAP and DAP, presented in their composition low activity concentrations for 226Ra, 228Ra and 210Pb. As for U and Th, the concentrations found in MAP and DAP are more significant, up to 822 and 850Bqkg(-1), respectively. SSP and TSP, which are obtained by mixing phosphoric acid with different amounts of phosphate rock, presented higher concentrations of radionuclides, up to 1158Bqkg(-1) for (238)U, 1167Bqkg(-1) for (234)U, 1169Bqkg(-1) for 230Th, 879Bqkg(-1) for 226Ra, 1255Bqkg(-1) for 210Pb, 521Bqkg(-1) for 232Th, 246Bqkg(-1) for 228Ra and 302Bqkg(-1) for 228Th. Long term exposure due to successive fertilizer applications was evaluated. Internal doses due to the application of phosphate fertilizer for 10, 50 and 100 years were below 1mSvy(-1), showing that the radiological impact of such practice is negligible.

  3. Radionuclides transfer into halophytes growing in tidal salt marshes from the Southwest of Spain.

    PubMed

    Luque, Carlos J; Vaca, Federico; García-Trapote, Ana; Hierro, Almudena; Bolívar, Juan P; Castellanos, Eloy M

    2015-12-01

    Estuaries are sinks of materials and substances which are released directly into them or transported from rivers that drain the basin. It is usual to find high organic matter loads and fine particles in the sediments. We analyzed radionuclide concentrations ((210)Po, (230)Th, (232)Th, (234)U, (238)U, (226)Ra, (228)Th, (228)Ra, (40)K) in sediments and three different organs (roots, stems and leaves) of three species of halophytes plants (Spartina maritima, Spartina densiflora and Sarcocornia perennis). The study was carried out in two tidal salt marshes, one polluted by U-series radionuclides and another nearby that was unpolluted and was used as a control (or reference) area. The Tinto River salt marsh shows high levels of U-series radionuclides coming from mining and industrial discharges. On the contrary, the unperturbed Piedras River salt marsh is located about 25 km from the Tinto marsh, and shows little presence of contaminants and radionuclides. The results of this work have shown that natural radionuclide concentrations (specially the U-isotopes) in the Tinto salt marsh sediments are one order of magnitude higher than those in the Piedras marsh. These radionuclide enhancements are reflected in the different organs of the plants, which have similar concentration increases as the sediments where they have grown. Finally, the transfer factor (TF) of the most polluted radionuclides (U-isotopes and (210)Po) in the Tinto area are one order of magnitude higher than in the Piedras area, indicating that the fraction of each radionuclide in the sediment originating from the pollution is more available for the plants than the indigenous fraction. This means that the plants of the salt marshes are unhelpful as bioindicators or for the phytoremediation of radionuclides.

  4. Measurement and calculation of high-actinide burnup in the prototype fast reactor

    SciTech Connect

    Broadhead, B.L.; Raman, S.; Dickens, J.K. )

    1991-01-01

    An agreement was signed in May 1979 as a part of a long-term cooperative program between the United Kingdom and the US under the liquid-metal fast breeder reactor agreement of 1976. This agreement included an experiment to carry out irradiations of physics specimens of fissile and fertile actinides to improve our knowledge of basic nuclear physics phenomena. Three fuel pins were prepared by the US to contain the actinide physics samples; two of these pins were irradiated at the Dounreay prototype fast reactor (PFR) for a total irradiation of 63 full-power days. The third pin has only recently been removed from the PFT, following an irradiation of > 500 full-power days. Each pin houses 35 capsules containing milligram quantities of actinide oxides of {sup 231}Pa, {sup 230}Th, {sup 232}Th, {sup 233}U, {sup 234}U, {sup 235}U, {sup 236}U, {sup 238}U, {sup 237}Np, {sup 238}Pu, {sup 239}Pu, {sup 240}Pu, {sup 241}Pu, {sup 242}Pu, {sup 244}Pu, {sup 241}Am, {sup 243}Am, {sup 243}Cm, {sup 244}Cm, {sup 246}Cm, and {sup 248}Cm. Following the return of the first fuel pin (FP-1) to the United States in May 1984, the actinide samples were prepared for studies of fission product yields, isotopics, and material concentrations. The measurements were repeated for the second fuel pin (FP-2) to remedy several problems encountered in the processing of the FP-1 pin. A brief description of the measured and calculated {sup 137}Cs yields for both FP-1 and FP-2 are included in this paper.

  5. Characterization of contaminant transport using naturally-occurring U-series disequilibria. 1998 annual progress report

    SciTech Connect

    Murrell, M.; Ku, T.L.

    1998-06-01

    'The goal of the research is to study the migratory behavior of contaminants in subsurface fractured systems using naturally occurring uranium- and thorium-series radionuclides as tracers under in-situ physico-chemical and hydrogeologic conditions. Naturally occurring U- and Th-series disequilibria can provide information on the rates of adsorption-desorption and transport of contaminants as well as on fluid transport and rock dissolution in a natural setting. The authors are developing a realistic model of contaminant migration in the Snake River Plain Aquifer beneath the INEEL by evaluating the retardation processes involved in the rock/water interaction. The major tasks are to: (1) determine the natural distribution of U, Th, Pa and Ra isotopes in the groundwater as well as in rock minerals and sorbed phases, and (2) study rock/water interaction processes using U/Th series disequilibria and a statistical analysis-based model code for the calculation of in-situ retardation factors of radionuclides and rock/water interaction time scales. This study will also provide an improved understanding of the hydrogeologic features of the site and their impact on the migration of contaminants. This report summarizes results after 20 months of a 36-month project. Studies performed at LANL include analysis of the long-lived nuclides {sup 238}U, {sup 235}U, {sup 234}U, {sup 230}Th, {sup 226}Ra, {sup 232}Th, and {sup 231}Pa by thermal ionization mass spectrometry (TIMS). Studies performed at the Univ. of Southern California include the measurement of short-lived naturally occurring radionuclides by decay-counting techniques and the development of models to predict the migration behavior of these radionuclides. Initial efforts began with analysis of 31, 0.5L water samples obtained through routine sampling by USGS and INEEL personnel. One significant observation from these data is that {sup 234}U/{sup 238}U activity ratios are highest in waters that emanate from local recharge

  6. Determination of thorium isotopes in mineral and environmental water and soil samples by alpha-spectrometry and the fate of thorium in water.

    PubMed

    Jia, Guogang; Torri, G; Ocone, R; Di Lullo, A; De Angelis, A; Boschetto, R

    2008-10-01

    A method has been developed for determination of thorium isotopes in water and soil samples by alpha-spectrometry. After fusion with Na(2)CO(3) and Na(2)O(2) at 600 degrees C, soil samples were leached with HNO(3) and HCl. Thorium in water sample or in soil leaching solution was coprecipitated together with iron (III) as hydroxides and/or carbonates at pH 9 with ammonia solution, separated from uranium and other alpha-emitters by a Microthene-TOPO (tri-octyl-phosphine oxide) chromatographic column, electrodeposited on a stainless steel disk, and measured by alpha-spectrometry. The method was checked with two certified reference materials supplied by the IAEA, and reliable results were obtained. The detection limits of the method for water (soil) samples are 0.44 microBq l(-1) (0.070 Bq kg(-1)) for (232)Th, 0.80 microBq l(-1) (0.13 Bq kg(-1)) for (230)Th and 1.0 microBq l(-1) (0.16 Bq kg(-1)) for (228)Th, respectively, if 100 l of water (0.50 g) for each sample are analysed. A variety of water or soil samples were analysed using this procedure and giving average thorium yields of 75.5+/-14.2% for water and 93.4+/-4.5% for soil. The obtained concentrations of thorium isotopes in water samples are in the range of 0.0007-0.0326 mBq l(-1) for (232)Th, 230)Th and 0.0014-1.32 mBq l(-1) for (228)Th. The (230)Th/(232)Th and (228)Th/(232)Th ratios are in the range of 232)Th and (228)Th activity in water is observed and the fate of thorium isotopes in water was studied. The exposure impact due to intake of thorium in the analysed drinking water was evaluated, showing a negligible amount of dose contribution. The concentrations of (232)Th, (230)Th and (228)Th in the analysed soil samples are in the range of 30.2-48.6, 32.5-60.5 and 31.0-53.0 Bq kg(-1), respectively. The obtained mean ratio is 1.04+/-0.05 for (228)Th/(232)Th and 1.20+/-0.41 for (230)Th/(232)Th.

  7. Natural thorium isotopes in marine sediment core off Labuan port

    SciTech Connect

    Hafidz, B. Y.; Asnor, A. S.; Terence, R. C.; Mohamed, C. A. R.

    2014-02-12

    Sediment core was collected from Labuan port and analyzed to determine the radioactivity of thorium (Th) isotopes. The objectives of this study are to determine the possible sources of Th isotopes at Labuan port and estimates the sedimentation rate based on {sup 228}Th/{sup 232}Th model. The results suggest the {sup 230}Th and {sup 232}Th might be originated from terrestrial sedimentary rock while {sup 228}Th originated by authigenic origin. High ratio value of {sup 230}Th/{sup 232}Th detected at the top surface sediment indicates the increasing of {sup 230}Th at the recent years which might be contributed from the anthropogenic sources. The sedimentation rate of core sediment from Labuan Port was successfully estimated by using {sup 228}Th/{sup 232}Th model. The result show high sedimentation rate with 4.67 cm/year indicates rapid deposition occurred at this study area due to the high physical activity at the Labuan port. By assume the constant sedimentation rate at this area; we estimated the age of 142 cm core sediment obtained from Labuan port is 32 years started from 1981 to 2012. This chronology will be used in forthcoming research to investigate the historical profile of anthropogenic activities affecting the Labuan port.

  8. Thorium-uranium disequilibrium dating of Late Quaternary ferruginous concretions and rinds

    NASA Astrophysics Data System (ADS)

    Short, Stephen A.; Lowson, Richard T.; Ems, John; Price, David M.

    1989-06-01

    Radioactive ferruginous nodules from the Alligator Rivers Uranium Province, Northern Territory, Australia, were systematically examined by optical microscopy, XRD, alpha- and fission-track autoradiography, and analysed for U, Th, Ra and major stable elements. Correlation of autoradiographs with microscopic structure and analyses of selective extractions confirmed that U and Th were strongly associated with Fe oxides. Fission-track autoradiography showed no concentration gradient evidence for postdepositional leaching of uranium. Strong acid leaching studies showed that irreversibly adsorbed U, and authigenic 234U and 230Th, but not 226Ra, are quantitatively retained by accumulated oxide/oxyhydroxide. Correlation of the groundwater activity ratio with oxidic 234U/ 238U activity ratios indicated the latter was radiogenically consistent with oxidic 230Th/ 234U activity ratios < 1. Dense, accumulated Fe/Mn oxide matrices are apparently capable of forming radiogenic closed systems in respect of the 230U → 234U230Th decay set. 234U/ 238U and 230Th/ 234U activity ratios were used to derive similar mean ages of rinds for four nodules in the same horizon. Th/U ages were also determined, using a Th-index detrital correction method previously used for impure carbonates, of pedogenic Fe/Mn accumulations having background concentrations of U and Th from other locations in Australia. These ages were compared with TL and 14C ages of the-host sediments. The comparisions suggest that Th/U dating could be used to age indurated layers of Fe/Mn oxides in soil horizons < 350 ka old.

  9. Mapping Dust Input to the Global Ocean using Thorium Isotope Measurements in Surface Sediments

    NASA Astrophysics Data System (ADS)

    Kienast, S. S.; Winckler, G.; Lippold, J.; Mahowald, N. M.

    2012-12-01

    Dust input into the ocean-atmosphere system has significant ramifications for biogeochemical cycles and global climate. Thorium-232, sometimes referred to as primordial Thorium, is the longest lived (1.4 1010 yrs) isotope in the U-Th decay chain. It is greatly enriched in upper continental crust compared to oceanic crust and mid-ocean ridge basalt (MORB) like volcanogenic material. In remote areas of the ocean, away from hemipelagic sources of continental material, it is assumed to be of aeolian origin. In conjunction with 230Th-flux normalization, 232Th measurements are thus becoming a promising new proxy for dust accumulation in the present and past ocean. Here, we present a pilot data compilation of previously published 230Th-normalized fluxes of 232Th from a large set of surface sediments originating from the equatorial Pacific, equatorial Atlantic, Southern Ocean, and other areas, complemented by unpublished data. We compare these 232Th fluxes with estimates of present day dust accumulation derived from a coupled atmosphere, land, ocean, and sea-ice model (CCSM-SMOB1). There is excellent agreement between sedimentary and model derived dust fluxes in e.g. the equatorial Atlantic and eastern equatorial Pacific. In the western equatorial Pacific, we observe differences between the sedimentary 232Th record and model estimates. Potential reasons for these discrepancies, and implications for the use of 232Th as dust proxy will be discussed. 1Mahowald et al. . J. Geosphys.Res.111, 2006

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

    SciTech Connect

    Bard, E. Columbia Univ., Palisades, NY ); Fairbanks, R.G.; Zindler, A. ); Hamelin, B. Univ. Aix-Marseille III ); Hoang, C.T. )

    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 that 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.

  11. 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

  12. 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.

  13. Uranium-thorium-protactinium dating systematics

    SciTech Connect

    Cheng, H.; Edwards, R.L.; Murrell, M.T.; Benjamin, T.M.

    1998-11-01

    With precise {sup 234}U, {sup 230}Th, and {sup 231}Pa data available, {sup 230}Th and {sup 231}Pa ages can now be tested rigorously for concordancy. If the material is not concordant, the isotope characteristics of this material may be examined in some detail. Here, models similar to those used to describe the U-Pb system are evaluated for use in U-Th-Pa studies, for the case in which initial {sup 230}Th and {sup 231}Pa concentrations are effectively zero. The systematics of concordia plots in relation to models of variation in {delta}{sup 234}U, episodic U or loss or gain, continuous U loss or gain, and continuous {sup 234}U, {sup 230}Th and {sup 231}Pa gain or loss are considered for the case in which initial U concentration is significant (for example, in many carbonate deposits). The authors also examine linear U uptake models for the case in which initial U concentration is effectively zero (for example, in teeth and bones). Such models should prove useful in interpreting data from materials that have behaved as open-systems. In particular, these models may help constrain the nature of diagenetic processes, and in some situations it may be possible to determine or constrain true ages with materials that have behaved as open-systems.

  14. Environmental consequences of uranium atmospheric releases from fuel cycle facility: II. The atmospheric deposition of uranium and thorium on plants.

    PubMed

    Pourcelot, L; Masson, O; Renaud, P; Cagnat, X; Boulet, B; Cariou, N; De Vismes-Ott, A

    2015-03-01

    Uranium and thorium isotopes were measured in cypress leaves, wheat grains and lettuce taken in the surroundings of the uranium conversion facility of Malvési (South of France). The comparison of activity levels and activity ratios (namely (238)U/(232)Th and (230)Th/(232)Th) in plants with those in aerosols taken at this site and plants taken far from it shows that aerosols emitted by the nuclear site (uranium releases in the atmosphere by stacks and (230)Th-rich particles emitted from artificial ponds collecting radioactive waste mud) accounts for the high activities recorded in the plant samples close to the site. The atmospheric deposition process onto the plants appears to be the dominant process in plant contamination. Dry deposition velocities of airborne uranium and thorium were measured as 4.6 × 10(-3) and 5.0 × 10(-3) m s(-1), respectively.

  15. U-series constraints on the Holocene human presence in the Cuatro Cienegas basin, Mexico

    NASA Astrophysics Data System (ADS)

    Noble, S. R.; Felstead, N.; Gonzalez, S.; Leng, M. J.; Metcalfe, S. E.; Patchett, P. J.

    2010-12-01

    tracer calibrated against gravimetric solutions prepared from Ames high-purity Th metal crystal and CRM 112a U metal ingot rather than natural materials of assumed secular equilibrium. ICP-MS mass bias and Faraday-SEM gain was monitored using CRM 112a and an in-house 229Th-230Th-232Th solution. Most samples have relatively high U contents (~2 ppm U), moderate [230Th/232Th] = 29-44, and initial [234U/238U] ~ 1.92. We obtain an age of 7.24 ± 0.13 ka BP for this trackway based on an average of two samples of the uppermost tufa surface. Depth profiling of one sample shows consistently increasing age downwards (~370 a/cm). [1] Gonzalez, A.H.G. et al., 2006, Ichnos 16, 12-24;[2] Souza, V. et al., 2006, PNAS 103, 6565-6570; [3] Johannesson, K.H. et al., 2004, J.S.Am.Earth Sci. 17, 171-180; [4] Meyer, E. 1973, Ecology 54, 982-995; [5] Minckley, T.A. & Jackson, S. 2008. J. Biogeography 35, 188-190; [6] Edwards, R.L. et al., 1987, EPSL 81, 175-192; [8] Cheng, H. et al., 2000, Chem. Geol. 169, 17-33; [8] Potter, E.K. et al., 2005, EPSL 247, 10-17.

  16. Modelling the effect of boundary scavenging on Thorium and Protactinium profiles in the ocean

    NASA Astrophysics Data System (ADS)

    Roy-Barman, M.

    2009-07-01

    The "boundary scavenging" box model is a cornerstone of our understanding of the particle-reactive radionuclide fluxes between the open ocean and the ocean margins. However, it does not describe the radionuclide profiles in the water column. Here, I present the transport-reaction equations for radionuclides transported vertically by reversible scavenging on settling particles and laterally by horizontal currents between the margin and the open ocean. Analytical solutions of these equations are compared with existing data. In the Pacific Ocean, the model produces "almost" linear 230Th profiles (as observed in the data) despite lateral transport. However, omitting lateral transport biased the 230Th based particle flux estimates by as much as 50%. 231Pa profiles are well reproduced in the whole water column of the Pacific Margin and from the surface down to 3000 m in the Pacific subtropical gyre. Enhanced bottom scavenging or inflow of 231Pa-poor equatorial water may account for the model-data discrepancy below 3000 m. The lithogenic 232Th is modelled using the same transport parameters as 230Th but a different source function. The main source of 232Th scavenged in the open Pacific is advection from the ocean margin, whereas a net flux of 230Th produced in the open Pacific is advected and scavenged at the margin, illustrating boundary exchange. In the Arctic Ocean, the model reproduces 230Th measured profiles that the uni-dimensional scavenging model or the scavenging-ventilation model failed to explain. Moreover, if lateral transport is ignored, the 230Th based particle settling speed may by underestimated by a factor 4 at the Arctic Ocean margin. The very low scavenging rate in the open Arctic Ocean combined with the enhanced scavenging at the margin accounts for the lack of high 231Pa/230Th ratio in arctic sediments.

  17. Modelling the effect of boundary scavenging on Thorium and Protactinium profiles in the ocean

    NASA Astrophysics Data System (ADS)

    Roy-Barman, M.

    2009-12-01

    The "boundary scavenging" box model is a cornerstone of our understanding of the particle-reactive radionuclide fluxes between the open ocean and the ocean margins. However, it does not describe the radionuclide profiles in the water column. Here, I present the transport-reaction equations for radionuclides transported vertically by reversible scavenging on settling particles and laterally by horizontal currents between the margin and the open ocean. Analytical solutions of these equations are compared with existing data. In the Pacific Ocean, the model produces "almost" linear 230Th profiles (as observed in the data) despite lateral transport. However, omitting lateral transport biaises the 230Th based particle flux estimates by as much as 50%. 231Pa profiles are well reproduced in the whole water column of the Pacific Margin and from the surface down to 3000 m in the Pacific subtropical gyre. Enhanced bottom scavenging or inflow of 231Pa-poor equatorial water may account for the model-data discrepancy below 3000 m. The lithogenic 232Th is modelled using the same transport parameters as 230Th but a different source function. The main source of the 232Th scavenged in the open Pacific is advection from the ocean margin, whereas a net flux of 230Th produced in the open Pacific is advected and scavenged at the margin, illustrating boundary exchange. In the Arctic Ocean, the model reproduces 230Th measured profiles that the uni-dimensional scavenging model or the scavenging-ventilation model failed to explain. Moreover, if lateral transport is ignored, the 230Th based particle settling speed may by underestimated by a factor 4 at the Arctic Ocean margin. The very low scavenging rate in the open Arctic Ocean combined with the enhanced scavenging at the margin accounts for the lack of high 231Pa/230Th ratio in arctic sediments.

  18. Thorium isotope evidence for melting of the mafic oceanic crust beneath the Izu arc

    NASA Astrophysics Data System (ADS)

    Freymuth, Heye; Ivko, Ben; Gill, James B.; Tamura, Yoshihiko; Elliott, Tim

    2016-08-01

    We address the question of whether melting of the mafic oceanic crust occurs beneath ordinary volcanic arcs using constraints from U-Series (238U/232Th, 230Th/232Th and 226Ra/230Th) measurements. Alteration of the top few hundred meters of the mafic crust leads to strong U enrichment. Via decay of 238U to 230Th, this results in elevated (230Th/232Th) (where brackets indicate activity ratios) over time-scales of ∼350 ka. This process leads to the high (230Th/232Th), between 2.6 and 11.0 in the mafic altered oceanic crust (AOC) sampled at ODP Sites 801 and 1149 near the Izu-Bonin-Mariana arc. Th activity ratios in the Izu arc lavas range from (230Th/232Th) = 1.2-2.0. These values are substantially higher than those in bulk sediment subducting at the Izu trench and also extend to higher values than in mid-ocean ridge basalts and the Mariana arc. We show that the range in Th isotope ratios in the Izu arc lavas is consistent with the presence of a slab melt from a mixed source consisting of AOC and subducted sediments with an AOC mass fraction of up to approximately 80 wt.% in the component added to the arc lava source. The oceanic plate subducting at the Izu arc is comparatively cold which therefore indicates that temperatures high enough for fluid-saturated melting of the AOC are commonly achieved beneath volcanic arcs. The high ratio of AOC/sediments of the slab melt component suggested for the Izu arc lavas requires preferential melting of the AOC. This can be achieved when fluid-saturated melting of the slab is triggered by fluids derived from underlying subducted serpentinites. Dehydration of serpentinites and migration of the fluid into the overlying crust causes melting to start within the AOC. The absence of a significant sediment melt component suggests there was insufficient water to flux both AOC and overlying sediments.

  19. 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

  20. Fractionation of natural radionuclides in soils from the vicinity of a former uranium mine Zirovski vrh, Slovenia.

    PubMed

    Strok, Marko; Smodis, Borut

    2010-01-01

    As a result of former uranium mining and milling activities at Zirovski vrh, Slovenia, 0.6 million tons of uranium mill tailings (UMT) were deposited onto a nearby waste pile Borst. Resulting enhanced levels of natural radionuclides in UMT could pose threat for the surrounding environment. Therefore, sequential extraction protocol was performed to assess mobility and bioavailability of (238)U, (234)U, (230)Th and (226)Ra in soils from the waste pile and its surrounding. The radionuclides associated with exchangeable, organic, carbonate, Fe/Mn oxides and residual fraction, respectively, were determined. Results showed that the highest activity concentrations for the studied radionuclides were on the bottom of the waste pile. In non-contaminated locations, about 80% of all radionuclides were in the residual fraction. Considering activity concentrations in the UMT, (238)U and (234)U are the most mobile. Mobility of (226)Ra is suppressed by high sulphate concentrations and is similar to mobility of (230)Th.

  1. HEU age determination

    SciTech Connect

    Moorthy, A.R.; Kato, W.Y.

    1995-08-01

    A technique has been developed to determine the Highly Enriched Uranium (HEU) Age which is defined as the time since the HEU was produced in an enrichment process. The HEU age is determined from the ratios of relevant uranium parents and their daughters viz {sup 230}Th/{sup 234}U and {sup 231}Pa/{sup 235}U. Uranium isotopes are quantitatively measured by their characteristic gammas and their daughters by alpha spectroscopy. In some of the samples where HEU is enriched more than 99%, the only mode of HEU age determination is by the measurement of {sup 231}Pa since there is negligible quantity of {sup 230}Th due to very low atom concentrations of {sup 234}U in the sample. In this paper we have presented data and methodology of finding the age of two HEU samples.

  2. Angular momentum of fission fragments in low energy fission of actinides

    SciTech Connect

    Naik, H.; Dange, S.P.; Singh, R.J.

    2005-01-01

    Independent isomeric yield ratios (IYR) of {sup 128}Sb, {sup 130}Sb, {sup 132}Sb, {sup 131}Te, {sup 133}Te, {sup 132}I, {sup 134}I, {sup 136}I, {sup 135}Xe, and {sup 138}Cs have been determined in fast neutron induced fission of {sup 232}Th, {sup 238}U, {sup 240}Pu, and {sup 244}Cm as well as in thermal neutron induced fission of {sup 232}U and {sup 238}Pu using radiochemical and offline {gamma}-ray spectrometric techniques. From the IYR, fragment angular momenta (J{sub rms}) have been deduced using a spin-dependent statistical model analysis. These data along with the literature data for {sup 230}Th*, {sup 234}U*, {sup 236}U*, {sup 240}Pu*, {sup 242}Pu*, {sup 244}Cm(SF), {sup 246}Cm*, {sup 250}Cf*, and {sup 252}Cf(SF) for fifteen even-Z fissioning systems show the following important features: (i) The J{sub rms} of the odd-Z fission products are higher than those of the even-Z fission products, indicating the odd-even effect. For both the odd-Z and even-Z fission products, the J{sub rms} increase with Z{sub F}{sup 2}/A{sub F}. (ii) The J{sub rms} of fragments with spherical 50-p and 82-n shells are lower compared to those of fragments outside the spherical shell, indicating the effect of shell closure proximity. (iii) The J{sub rms} of the fission products increase with mass number in spite of fluctuations in shell closure proximity and odd-even effects but do not show any correlation with the neutron emission curve. (iv) In all fifteen even-Z fissioning systems from Th to Cf, the yield-weighted J{sub rms} values show an anticorrelation with the elemental yields. (v) The odd-even fluctuation on J{sub rms} does not change drastically from Th to Cf, unlike the proton odd-even effect ({delta}{sub p}) which decreases significantly with the increase of Coulomb parameter (Z{sub F}{sup 2}/A{sub F}{sup 1/3})

  3. Indirect (n,γ) cross sections of thorium cycle nuclei using the surrogate method

    NASA Astrophysics Data System (ADS)

    Wilson, J. N.; Gunsing, F.; Bernstein, L. A.; Bürger, A.; Görgen, A.; Guttormsen, M.; Larsen, A.-C.; Mansouri, P.; Renstrøm, T.; Rose, S. J.; Semchenkov, A.; Siem, S.; Syed, N. U. H.; Toft, H. K.; Wiedeking, M.; Wiborg-Hagen, T.

    2012-03-01

    Indirect neutron capture (n,γ) cross sections have been extracted for the key thorium cycle nuclei 232Th, 231Pa, and 230Th using the surrogate reaction method. Final nucleus γ-decay probabilities were measured between the neutron binding energy and around 1 MeV above it using the 232Th(d,p)233Th, 232Th(3He,t)232Pa, and 232Th(3He,α)231Th reactions in experiments with the CACTUS γ-detector array and Silicon Ring charged-particle detectors at the Oslo Cyclotron Laboratory. Because the neutron capture cross section for 232Th is already well known from direct measurements a comparison with these results provides a stringent test of the applicability of the surrogate method in the actinide region for indirect (n,γ) cross-section measurements. In addition, a new technique for correcting measured γ-ray decay probabilities below the neutron emission energy threshold is proposed and used. We find good agreement between indirect and direct (n,γ) cross-section measurements in the range 500 keV-1 MeV, but large discrepancies outside this range. Explanations for the observed differences are proposed.

  4. Uranium series disequilibrium and high thorium and radium enrichments in Karst formations

    SciTech Connect

    Gunten, H.R. von; Roessler, E.; Surbeck, H.

    1996-04-01

    We found, in limestone Karst soils of the Jura Mountains and of the mountains in the central part of Switzerland, an enrichment up to a factor 20 of {sup 230}Th and {sup 226}Ra with respect to the activities of their progenitors, {sup 234}U and {sup 238}U. Thus, a significant radioactive disequilibrium exists between {sup 238/234}U and {sup 230}Th and {sup 226}Ra. The enrichment of {sup 226}Ra leads to locally high concentrations of its decay product, the noble gas {sup 222}Rn. We propose continuous chemical weathering of limestone (calcite) fragments within the soil column as a plausible cause for the high {sup 230}Th, {sup 226}Ra, and {sup 222}Rn activities. Uranium, contained within calcite, is released during weathering and migrates as stable uranyl carbonate complexes through the soil column. In contrast, its decay products ({sup 230}Th and {sup 226}Ra) hydrolyze, are strongly sorbed to soil particles, and/or form insoluble compounds that become more and more enriched in the soil as this process continues in time. 39 refs., 3 figs., 5 tabs.

  5. Calibration of fossil scleraxonian Southern Ocean deep-sea corals for U-series dating

    NASA Astrophysics Data System (ADS)

    Gutjahr, M.; Vance, D.; Hoffmann, D.; Hillenbrand, C.; Kuhn, G.

    2008-12-01

    The deep Southern Ocean has been pinpointed as candidate reservoir capable of storing the additional respired carbon that was drawn from the atmosphere during the Last Glacial Maximum compared with the present-day. In this context the determination of deep ocean ventilation ages is a commonly applied tool, potentially identifying radiocarbon depletion in glacial deep water and enhanced ocean stratification. In order to derive deep-sea ventilation ages most studies to date have used either radiocarbon age differences between paired planktic and benthic foraminifera samples or coupled U-Th and radiocarbon dates obtained from aragonitic deep-sea corals. Results from both these approaches are, however, as yet very scarce for the Southern Ocean. We present calendar ages for a set of deep-sea scleraxonian corals from the Marie Byrd Seamounts in the Amundsen Sea sector of the Southern Ocean (~123°W, ~69°S, 2500 m to 1430 m water depth) employing the 230Th/U-dating method. The aim of our study is to evaluate whether these calcitic octocorals can be used for ventilation age determinations. Our corals have significantly lower uranium concentrations than aragonitic deep-sea corals, ranging from 80 to 250 ng/g. Most corals of Holocene age reproduced the present-day seawater 234U/238U. Pre-Holocene corals, however, show a systematic enrichment of 234U, leading to slightly elevated deglacial initial 234U/238U and significantly higher 234U/238U for ~MIS5 sub-samples. These corals also appear to grow very slowly, on the order of only few μm/year, making it essential to sample as little coral material as possible for combined 230Th/U- and radiocarbon dating purposes. One coral, sampled at high-resolution in various sections returned ages that scatter around 10 ka BP and the early deglaciation, though several significantly older ages were obtained as well. The present-day (234U/238U) ACT in different sections of this coral is very homogenous (1.155 ± 0.003) and more or less

  6. U-Th and ESR dating of drilled cores from a giant hydrothermal mounds in South Mariana

    NASA Astrophysics Data System (ADS)

    Takamasa, A.; Nakai, S.; Sato, F.; Toyoda, S.; Ishibashi, J.

    2012-12-01

    The time scale for hydrothermal activity is an important factor controlling the size of hydrothermal ore deposits and the evolution of chemosynthesis-based communities in a submarine hydrothermal system. We determined the age of hydrothermal deposits samples, both collected samples by submersible and drilled core samples from South Mariana Trough. Samples were collected from four hydrothermal sites, Snail (near the spreading axis), Archean ( 1.5km from the axis), Pika ( 4.9km from the axis) and Urashima ( 4.9km from the axis). 230Th-234U radioactive disequilibrium dating was applied to hydrothermal sufide minerals consisting of pyrite and sphalerite while electron spin resonance (ESR) dating was applied to barite. For 230Th-234U radioactive disequilibrium dating, we carried out magnetic separation for bulk samples, then we digested samples with nitric acid. U and Th were purified by two-step column separations, and isotopic compositions of spiked and unspiked U and Th were measured by a MC-ICP-MS. Analytical methods for ESR age determination were described in a companion abstract by Toyoda et al. We found that the magnetic fractions had significantly higher U/Th ratios, which enabled 230Th-234U age determinations as precise as ±2% (2σ). This probably reflects that pyrite enriched in magnetic fractions has high U/Th ration. In a sulfide crust sample collected from Archean site, the 230Th-234U ages of the sulfide minerals (0.3-2.2 ka) were compared with ESR ages of barites separated from 12 subsamples of the same sulfide crust. ESR ages (0.27 - 1.7 ka) show a spatial pattern broadly resembling that observed in 230Th-234U dating method. While there are some significant offsets, these results illustrate the potential of the two methods for use in provide information on evolution history of a hydrothermal system. Samples from Pika, Archean and Snail sites yield from 0.5 to ~9 ka, from 0.1 to 3 ka and < ~90 a, respectively. The oldest ages from each site are correlated

  7. 238U, 232Th profiling and U-series isotope analysis of fossil teeth by laser ablation-ICPMS

    NASA Astrophysics Data System (ADS)

    Eggins, Stephen; Grün, Rainer; Pike, Alistair W. G.; Shelley, Michael; Taylor, Lois

    2003-05-01

    U and Th concentration profiles in fossil hominid and faunal teeth have been measured by laser ablation ICPMS. These profiles record diverse modes of U and Th uptake, particularly within enamel, that can be broadly related to the state of sample preservation. Observed U profiles are in general inconsistent with existing diffusion-adsorption models developed for U-uptake in bone and teeth. Where the models appear applicable, calculated diffusion rates are several orders of magnitude smaller than previous estimates. Laser ablation ICPMS offers a means of rapidly characterizing U and Th distributions in the enamel and dentine components of teeth as a precursor to ESR and U-series dating. In particular, it should allow the identification of teeth (and also bone) samples that have simple U-uptake histories and are amenable to precise dating by time-consuming and expensive Th-U and Pa-U TIMS techniques. We also demonstrated the use of laser ablation ICPMS to measure U-series isotopes in dentine and enamel samples with relatively high U concentrations (>20 ppm). These results, obtained using a quadrupole ICPMS, illustrate significant promise for in situ U-series isotope analysis, particularly when combined with the greater sensitivity and multi-collection capabilities of new sector ICPMS instrumentation. The latter may permit precise isotope ratio measurements on samples containing only a few ppm of U.

  8. Fission Product Yields from 232Th, 238U, and 235U Using 14 MeV Neutrons

    NASA Astrophysics Data System (ADS)

    Pierson, B. D.; Greenwood, L. R.; Flaska, M.; Pozzi, S. A.

    2017-01-01

    Neutron-induced fission yield studies using deuterium-tritium fusion-produced 14 MeV neutrons have not yet directly measured fission yields from fission products with half-lives on the order of seconds (far from the line of nuclear stability). Fundamental data of this nature are important for improving and validating the current models of the nuclear fission process. Cyclic neutron activation analysis (CNAA) was performed on three actinide targets-thorium-oxide, depleted uranium metal, and highly enriched uranium metal-at the University of Michigan's Neutron Science Laboratory (UM-NSL) using a pneumatic system and Thermo-Scientific D711 accelerator-based fusion neutron generator. This was done to measure the fission yields of short-lived fission products and to examine the differences between the delayed fission product signatures of the three actinides. The measured data were compared against previously published results for 89Kr, -90, and -92 and 138Xe, -139, and -140. The average percent deviation of the measured values from the Evaluated Nuclear Data Files VII.1 (ENDF/B-VII.1) for thorium, depleted-uranium, and highly-enriched uranium were -10.2%, 4.5%, and -12.9%, respectively. In addition to the measurements of the six known fission products, 23 new fission yield measurements from 84As to 146La are presented.

  9. Chemistry and chronology of magmatic processes, Central Kenya Peralkaline province, East African Rift

    NASA Astrophysics Data System (ADS)

    Anthony, E.; Deino, A. L.; White, J. C.; Omenda, P. A.

    2014-12-01

    We report here a synthesis of the geochemistry of magma evolution correlated with 40Ar/39Ar, 14 C, and U-series chronology for volcanoes in the Central Kenya Peralkaline Province (CKPP). The volcanic centers - Menengai, Eburru, Olkaria, Longonot, and Suswa - are at the apex of the Kenya Dome, and consist of trachyte, phonolite, comendite, and pantellerite. These volcanic centers are within the graben of the EARS and are characterized by a shield-building phase followed by caldera collapse and subsequent post-caldera eruptions. Geochemical modeling demonstrates that the magmas are the result of fractional crystallization of alkali basaltic magmas and magma mixing. Longonot and Suswa have the most chronologic data -14 C, Ar/Ar and U-series - and they show that the youngest eruptions have 230 Th/232Th of 0.8, which was inherited from the magma system prior to eruption. Subsequent changes in 230 Th/232 Th are due to post-eruptive decay of 230 Th and correlate well with 14 C and Ar/Ar.

  10. The behavior of the uranium decay chain nuclides and thorium during the flank eruptions of Kilauea (Hawaii) between 1983 and 1985

    SciTech Connect

    Reinitz, I.M.; Turekian, K.K. )

    1991-12-01

    The concentrations of members of the {sup 238}U decay chain and {sup 232}Th have been determined for the lavas that erupted on the East Rift Zone of Kilauea Volcano, Hawaii (Puu Oo) between January 1983 and January 1985. There was a decrease during the first 180 days in the abundances of all nuclides, following the behavior of the incompatible elements. ({sup 230}Th/{sup 238}U) varies with ({sup 232}Th/{sup 238}U) yielding a batch process age for the source magma of 127,800 {plus minus} 28,500 (2{omega}) y, similar to East Pacific Rise basalts. No ({sup 226}Ra/{sup 230}Th) disequilibrium was evident at Puu Oo although Haleakala and Loihi show significant excesses of ({sup 226}Ra) over ({sup 230}Th). The initial ({sup 210}Pb) excess relative to ({sup 226}Ra) implies strong incompatibility of {sup 210}Pb probably with the help of chloride complexing, and the deficiency in later episodes indicates volatilization from the melt mediated by the formation of volatile chloride compounds.

  11. 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.

  12. Testing the Concept of Drift Shadow at Yucca Mountain, Nevada

    SciTech Connect

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

    2006-03-10

    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 {sup 238}U-{sup 234}U-{sup 230}Th) have been analyzed in samples of rock from beneath four naturally occurring lithophysal cavities. All samples show {sup 234}U depletion relative to parent {sup 238}U, indicating varying degrees of water-rock interaction over the past million years. Variations in {sup 234}U/{sup 238}U activity ratios indicate that depletion of {sup 234}U relative to {sup 238}U 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 {sup 234}U/{sup 238}U 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.

  13. The relationship between riverine U-series disequilibria and erosion rates in a basaltic terrain

    NASA Astrophysics Data System (ADS)

    Vigier, N.; Burton, K. W.; Gislason, S. R.; Rogers, N. W.; Duchene, S.; Thomas, L.; Hodge, E.; Schaefer, B.

    2006-09-01

    U-series isotopes have been measured in the dissolved phase, suspended load and bedload of the main rivers draining basaltic catchments in Iceland. For the dissolved phase, ( 234U/ 238U) and ( 238U/ 230Th) range between 1.08 and 2.2, and 7.4 and 516, respectively. For the suspended load and bedload, ( 234U/ 238U) and ( 238U/ 230Th) range from 0.97 to 1.09 and from 0.93 to 1.05, respectively. Chemical erosion rates, calculated from dissolved major elements, range between 13 and 333 t km - 2 yr - 1 . Physical erosion rates have also been estimated, from existing data, and range between 21 and 4864 t/km 2/yr, with an average of 519 t km - 2 yr - 1 . U-series disequilibria indicate that weathering in Iceland operates at close to steady-state conditions. A model of continuous weathering indicates a maximum weathering timescale of 10 kyr, with an average rate of uranium release into water of 1.6 · 10 - 4 yr - 1 , which is significant when compared to granitic terrains located at similar latitudes and to tropical basaltic terrains. All river waters display ( 234U/ 238U) greater than secular equilibrium, consistent with the effects of alpha-recoil. The same dissolved phase ( 234U/ 238U) exhibit a negative trend with physical erosion rates, explained by the dominant effect of close-to-congruent chemical weathering of hyaloclastites in the younger basaltic terrains. Therefore, chemical erosion rate and mineral weathering susceptibility play a major role in determining 234U- 238U disequilibria in basaltic river waters. Comparison of global data for river basins in which weathering was recently strongly limited indicates a negative correlation between silicate weathering rates estimated with major elements and the age of weathering estimated with U-series disequilibria. This strongly suggests a key role of time and soil thickness on the chemical erosion of silicates.

  14. Level Densities in the actinide region and indirect n,y cross section measurements using the surrogate method

    NASA Astrophysics Data System (ADS)

    Wilson, J. N.; Gunsing, F.; Bernstein, L.; Bürger, A.; Görgen, A.; Thompson, I. J.; Guttormssen, M.; Larsen, A.-C.; Mansouri, P.; Renstrøm, T.; Rose, S. J.; Siem, S.; Wiedeking, M.; Wiborg, T.

    2012-02-01

    Results from a program of measurements of level densities and gamma ray strength functions in the actinide region are presented. Experiments at the Oslo cyclotron involving the Cactus/Siri detectors and 232Th(d,x) and 232Th(3He,x) reactions were carried out to help answer the question of which level density model is the most appropriate for actinide nuclei, since it will have an impact on cross section calculations important for reactor physics simulations. A new technique for extracting level densities and gamma ray strength functions from particle-gamma coincidence data is proposed and results from the development of this technique are presented. In addition, simultaneous measurements of compound nuclear gamma decay probabilities have been performed for the key thorium cycle nuclei 233Th, 231Th and 232Pa up to around 1MeV above the neutron binding energy and have enabled extraction of indirect neutron induced capture cross sections for the 232Th, 231Pa and 230Th nuclei using the surrogate reaction method. Since the neutron capture cross section for 232Th is already well known from direct measurements a comparison provides a stringent test of the applicability of the surrogate technique in the actinide region.

  15. 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

  16. Uranium-series dating of actinide decay series mobility at Pena Blanca

    SciTech Connect

    Dixon, P.R.; Goldstein, S.J.; Murrell, M.T.

    1997-12-31

    Studies of U-series disequilibria near uranium ore deposits can provide valuable information on the mobility of actinides and their daughters over the range of timescales needed to assess the stability of proposed waste repositories. We have applied highly sensitive TIMS methods to obtain 238U-234U-230Th dates for three whole rock samples within a {approximately}30 in long fracture emanating into surrounding tuff from the deposit at Pena Blanca, Mexico. The 238U-234U-230Th data lie on a whole-rock isochron that requires closed-system behavior for the last 380 ka. Preliminary 231Pa-235U data for the U-rich vein also indicates closed system behavior for at least the last 100 ka. In contrast, 226Ra/230Th activity ratios range from 0.76-0.99 which indicates more recent Ra mobility within the fracture most likely due to surface water infiltration. Our results require uranium, thorium and protactinium stability despite recent radium mobility and provide important constraints on repository stability over {approximately}100 ka timescales.

  17. Tracing dust input to the global ocean using thorium isotopes in marine sediments: ThoroMap

    NASA Astrophysics Data System (ADS)

    Kienast, S. S.; Winckler, G.; Lippold, J.; Albani, S.; Mahowald, N. M.

    2016-10-01

    Continental dust input into the ocean-atmosphere system has significant ramifications for biogeochemical cycles and global climate, yet direct observations of dust deposition in the ocean remain scarce. The long-lived isotope thorium-232 (232Th) is greatly enriched in upper continental crust compared to oceanic crust and mid-ocean ridge basalt-like volcanogenic material. In open ocean sediments, away from fluvial and ice-rafted sources of continental material, 232Th is often assumed to be of predominantly eolian origin. In conjunction with flux normalization based on the particle reactive radioisotope thorium-230 (230Th), 232Th measurements in marine sediments are a promising proxy for dust accumulation in the modern and past ocean. Here we present ThoroMap, a new global data compilation of 230Th-normalized fluxes of 232Th. After careful screening, we derive dust deposition estimates in the global ocean averaged for the late Holocene (0-4 ka) and the Last Glacial Maximum (LGM, 19-23 ka). ThoroMap is compared with dust deposition estimates derived from the Community Climate System Model (CCSM3) and CCSM4, two coupled atmosphere, land, ocean, and sea ice models. Model-data correlation factors are 0.63 (CCSM3) and 0.59 (CCSM4) in the late Holocene and 0.82 (CCSM3) and 0.83 (CCSM4) in the LGM. ThoroMap is the first compilation that is built on a single, specific proxy for dust and that exclusively uses flux-normalization to derive dust deposition rates.

  18. Boron, Thorium and Oxygen Isotopes in Icelandic Tephra

    NASA Astrophysics Data System (ADS)

    Rose-Koga, E. F.; Sigmarsson, O.

    2006-12-01

    Important Th-isotope variations in silicic rocks from Iceland have been interpreted in terms of partial melting of a metabasic crust. This hypothesis was tested by boron systematics, since both the B-isotope ratios and their concentration are significantly different in the altered oceanic crust and the underlying mantle. Here we present new boron isotope compositions and concentrations measured by ion microprobe (3f, Nancy, France) on Holocene tephra samples from 6 Icelandic volcanoes. The B concentrations vary by more than a factor 20, from 1.48±0.03 to 36.38±4.46 ppm in basaltic tholeiite and trachytes, respectively. A large range is also observed for B isotope compositions, between - 9.8±2.0 in a trachyte to +7.6±2.6‰ in a subalkaline rhyolite from Askja volcano. Furthermore, the δ^{11}B correlates positively with Th/B (0.26 < Th/B < 2.90) and negatively with 230Th/232Th (0.940 < (230Th/232Th) < 1.067) and with δ18O (-0.2 to +5.3‰). The variations of B isotope compositions in the Icelandic tephra and the correlations with both δ18O and (230Th/232Th) strongly support the crustal melting model for most Icelandic rhyolites. In fact, the co-variation is interpreted as a mixing between mantle derived basalts and crustal melts derived from the anatexis of hydrothermally altered basaltic crust. The highest δ^{11}B (+7.6±2.6 and +7.1±2.1‰) measured in rhyolites from the rift-related Askja and Krafla volcanoes represent the B-isotope composition for the altered Icelandic crust. These values are indeed well within the range of values proposed for altered oceanic crust (between +0.1 and +9.2‰, Spivack and Edmond, 1987 ; +3.4±1.1‰, Smith et al., 1995). In contrast, the lowest δ^{11}B values (-9.8 to -5.7‰) are observed in samples with the highest δ18O (+4.95 to +5.30‰) and (230Th/232Th; 0.990 to 1.067) corresponding to a "normal-mantle" signature (δ^{11}B =- 9.9±1.3‰; Chaussidon and Marty, 1995).

  19. 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.

  20. Scavenging of Thorium and Protactinium by Particles from the East Pacific Rise Hydrothermal Plume

    NASA Astrophysics Data System (ADS)

    Anderson, R. F.; Fleisher, M. Q.; Pavia, F. J.; Vivancos, S. M.; Lu, Y.; Cheng, H.; Edwards, R. L.

    2014-12-01

    Concentrations of dissolved 230Th, 231Pa and 232Th measured along the US GEOTRACES Eastern Pacific Zonal Transect between Peru and Tahiti illustrate the enhanced scavenging of trace elements by particles derived from the hydrothermal plume that spreads westward from the East Pacific Rise (EPR). Concentrations of dissolved 230Th and 231Pa increase linearly with depth in the upper 2 km of the water column, consistent with their removal by reversible scavenging. The intensity of scavenging by plume particles is quantified by comparing the predicted (extrapolated) concentration of dissolved 230Th at the core depth of the plume (30 to 35 fg/kg) with measured concentrations. Within the core of the plume, measured concentrations of dissolved 230Th are 8 fg/kg at a distance of approx. 1200 km to the west of the EPR, and 12 fg/kg at a distance approx 2500 km to the west of the ridge, much less than the predicted value. Particles derived from the EPR plume potentially impact the scavenging and removal of many trace elements from the deep ocean over a broad area of the eastern tropical South Pacific.

  1. Chemical weathering rates in deep-sea sediments: Comparison of multicomponent reactive transport models and estimates based on 234U

    NASA Astrophysics Data System (ADS)

    Maher, K.; Steefel, C. I.; Depaolo, D. J.

    2004-12-01

    Chemical weathering rates in natural systems are typically much slower than expected based on experiments and theory. There are several possible explanations. However, because it has been difficult to determine what effects in particular reduce the rates in specific settings, natural rates remain difficult to predict. Silicate-rich deep-sea sediments provide an ideal in-situ laboratory for investigating weathering rates because certain potentially important factors, such as advective transport through heterogeneous media, limitations on the availability of reactive surface area due to low porosity and/or cementation, unsaturated flow conditions, and seasonal variations in fluid flux and temperature, do not occur in this setting. Geochemical profiles from Site 984 in the North Atlantic are modeled using a multi-component reactive transport model (CRUNCH) to determine in-situ rates of plagioclase dissolution and other diagenetic processes, including sulfate reduction and anaerobic methane oxidation. Various possible processes which might contribute to slower rates in the field are considered, including the effect of mineral saturation state, secondary precipitation of clays, inhibition by dissolved aluminum, and the availability of reactive surface area. The reactive transport model includes an isotopic solid-solution formulation that tracks the isotopic composition of precipitating (calcite) and dissolving (plagioclase and calcite) phases, thus allowing the determination of plagioclase dissolution rates. The rate constants for plagioclase determined by geochemical transport modeling of major element profiles are within the same range determined from U-series calculations and suggest that natural weathering rates for this system are on the order of 10-17.5 to 10-17.7 mol/m2/sec assuming estimates of reactive surface area are correct, several orders of magnitude slower than laboratory-derived rates. The slow plagioclase rates are most likely due to the fact that dissolution takes place close to equilibrium, but the close to equilibrium conditions require either slow clay precipitation or precipitation of soluble clays. Unavailability of reactive surface area could also explain the slow rates, but this is considered less likely because of the very high porosity (about 80%) and the low cementation.

  2. The role of the particle size spectrum in estimating POC fluxes from Th234/U238 disequilibrium

    NASA Astrophysics Data System (ADS)

    Burd, Adrian B.; Jackson, George A.; Moran, S. B.

    2007-06-01

    Thorium-234 is increasingly being used as a tracer for particulate organic carbon (POC) export in the oceans. In particular, POC fluxes are being estimated using disequilibrium between Th234 and its parent radionuclide, U238, and estimates of the POC/Th234 ratio of particles settling out of the water column. We have investigated the effect of variations in the particle size distribution on these estimates by using model particle size spectra and size distributions of organic carbon and Th234. Simulations indicate that the POC/Th234 ratio is sensitive to differences in the distributions of organic carbon and Th234 with particle size. If these size distributions differ, then the POC/Th234 ratio is a function of particle size and estimates of the POC/Th234 ratio using size-fractioned samples are inaccurate. Consequently, size fractioning techniques, such as filtration, yield biased estimates if the quantity being measured varies with particle size. We used a model with phytoplankton, fecal pellets and aggregates to examine the assumption that the particles responsible for the Th234 flux are also responsible for the POC flux. We found that variations in the size distributions of these three populations affected POC and Th234 fluxes differently, suggesting that changes in biological interactions can lead to a preferential increase in POC or Th234 flux. We suggest that further examination of the distributions of organic carbon and Th234 with particle size and type is required to refine our understanding of the factors affecting the POC/Th234 ratio.

  3. Biogeography in 231Pa/230Th ratios and a balanced 231Pa budget for the Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Hayes, Christopher T.; Anderson, Robert F.; Fleisher, Martin Q.; Serno, Sascha; Winckler, Gisela; Gersonde, Rainer

    2014-04-01

    The ratio of unsupported protactinium-231 to thorium-230 in marine sediments, (Pa/Th)xs, is potentially sensitive to several processes of oceanographic and climatological interest: deep ocean circulation, marine biological productivity (as it relates to total particle flux) and particle composition (specifically, biogenic opal and authigenic Mn). In order to attribute variations in (Pa/Th)xs observed in sediment records to changes in specific processes through time, a better understanding of the chemical cycling of these elements in the modern ocean is necessary. To this end, a survey was undertaken of (Pa/Th)xs in surface sediments from the subarctic Pacific (SO202-INOPEX expedition) in combination with a Pacific-wide compilation of published data. Throughout the Pacific, (Pa/Th)xs is robustly correlated with the opal content of sediments. In the North and equatorial Pacific, simultaneous positive correlations with productivity indicators suggest that boundary scavenging and opal scavenging combine to enhance the removal of Pa in the eastern equatorial Pacific and subarctic Pacific. Deep ocean water mass ageing (>3.5 km) associated with the Pacific overturning appears to play a secondary role in determining the basin scale distribution of (Pa/Th)xs. A basin-wide extrapolation of Pa removal is performed which suggests that the Pacific Pa budget is nearly in balance. We hypothesize that through time (Pa/Th)xs distributions in the Pacific could define the evolving boundaries of contrasting biogeographic provinces in the North Pacific, while the influence of hydrothermal scavenging of Pa potentially confounds this approach in the South Pacific.

  4. Modelling the role of marine particle on large scale 231Pa, 230Th, Iron and Aluminium distributions

    NASA Astrophysics Data System (ADS)

    Dutay, J.-C.; Tagliabue, A.; Kriest, I.; van Hulten, M. M. P.

    2015-04-01

    The distribution of trace elements in the ocean is governed by the combined effects of various processes, and by exchanges with external sources. Modelling these represents an opportunity to better understand and quantify the mechanisms that regulate the oceanic tracer cycles. Observations collected during the GEOTRACES program provide an opportunity to improve our knowledge regarding processes that should be considered in biogeochemical models to adequately represent the distributions of trace elements in the ocean. Here we present a synthesis about the state of the art for simulating selected trace elements in biogeochemical models: Protactinium, Thorium, Iron and Aluminium. In this contribution we pay particular attention on the role of particles in the cycling of these tracers and how they may provide additional constraints on the transfer of matter in the ocean.

  5. Ultrafast source-to-surface movement of melt at island arcs from 226Ra-230Th systematics.

    PubMed

    Turner, S; Evans, P; Hawkesworth, C

    2001-05-18

    Island arc lavas have radium-226 excesses that extend to higher values than those observed in mid-ocean ridge or ocean island basalts. The initial ratio of radium-226 to thorium-230 is largest in the most primitive lavas, which also have the highest barium/thorium ratios, and decreases with increasing magmatic differentiation. Therefore, the radium-226 excesses appear to have been introduced into the base of the mantle melting column by fluids released from the subducting plate. Preservation of this signal requires transport to the surface arguably in only a few hundreds of years and directly constrains the average melt velocity to the order of 1000 meters per year. Thus, melt segregation and channel formation can occur rapidly in the mantle.

  6. 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.

  7. Uranium-series nuclides in the Golden fault, Colorado, U.S.A.: dating latest fault displacement and measuring recent uptake of radionuclides by fault-zone materials

    USGS Publications Warehouse

    Szabo, B. J.; Rosholt, J.N.

    1989-01-01

    Concentrations and isotopic ratios of U, Th and Ra were measured in a fault zone near Golden, Colorado where major displacement occurred between about 190 and 615 ka. Faulting created new surfaces for leaching and provided the pathways for U-rich ground water. Uranium and 230Th, the latter produced by the decay of dissolved 234U, are adsorbed by fault gouge, hematite-stained sand and brecciated sand- and claystones. The observed U enrichment is as much as six times baseline value and the simultaneous enrichment of 230Th is estimated at about ninefold relative to 238U. The adsorption of radionuclides chemically analogous to Th, such as Pu (IV) and Np, and 237Np decay products, on fault-zone materials would contribute to the immobilization of high-level radioactive waste in the vicinity of a repository in the event of leakage from engineered barriers into fractured rock-mass. ?? 1989.

  8. Precise timing of the last interglacial period from mass spectrometric determination of thorium-230 in corals.

    PubMed

    Edwards, R L; Chen, J H; Ku, T L; Wasserburg, G J

    1987-06-19

    The development of mass spectrometric techniques for determination of (230)Th abundance has made it possible to reduce analytical errors in (238)U-(234)U-(230)Th dating of corals even with very small samples. Samples of 6 x 10(8) atoms of (230)Th can be measured to an accuracy of +/-3 percent (2sigma) and 3 x 10(10) atoms of (230)Th can be measured to an accuracy of +/-0.2 percent. The time range over which useful age data on corals can be obtained now ranges from about 50 to about 500,000 years. For young corals, this approach may be preferable to (14)C dating. The precision with which the age of a coral can now be determined should make it possible to critically test the Milankovitch hypothesis concerning Pleistocene climate fluctuations. Analyses of a number of corals that grew during the last interglacial period yield ages of 122,000 to 130,000 years. The ages coincide with, or slightly postdate, the summer solar insolation high at 65 degrees N latitude which occurred 128,000 years ago. This supports the idea that changes in Pleistocene climate can be the result of variations in the distribution of solar insolation caused by changes in the geometry of the earth's orbit and rotation axis.

  9. Radiochemical dates obtained by alpha spectrometry on fossil mollusk shell from the 5e Atlantic shoreline of the High Atlas, Morocco.

    PubMed

    Choukri, A; Hakam, O-K; Reyss, J-L; Plaziat, J-C

    2007-08-01

    The reported radiochemical results obtained on 77 samples collected from Moroccan fossil beaches assumed to be deposited during the above present sea-level high stands corresponding to 5e climatic stage, and on 12 present and Holocene samples, are discussed in order to judge the age validity. Contrary to the Holocene shells where (238)U contents are low and (234)U/(238)U are in agreement with sea-water ratio, the 5e results vary considerably irrespective of species and calcite content of samples. Because of the open-system possibility, the (230)Th/(234)U ages based on shell samples should be interpreted as minima for any studied shoreline discussed in the light of geological data and several shells analyses.

  10. Disequilibrium of the 238U series in basalt

    USGS Publications Warehouse

    Somayajulu, B.L.K.; Tatsumoto, M.; Rosholt, J.N.; Knight, R.J.

    1966-01-01

    Radioisotope analyses of basalt samples from Hawaii, Japan, and Iwo Jima show that: (1) 234U and 238U are virtually in radioactive equilibrium, (2) 230Th exceeds equilibrium values in all these samples, (3) 210Pb concentrations range from 10-200% of the equilibrium values and average 30% deficient, and (4) 226Ra is probably not in equilibrium with 234U. The source regions of the basalts or magma forming processes are open systems, chemically. The enrichment of some of the uranium-daughter nuclides is insufficient to account for the excess 206Pb in volcanic rocks. The isotopic composition of lead and specific activity of 210Pb in sublimates from Showa-shinzan, Japan are also reported. ?? 1966.

  11. Monitoring the fate of radionuclides released to the environment: May 1991 report

    SciTech Connect

    Bauer, L.R.

    1992-08-13

    A review of the radiological effluent and environmental monitoring practices in use at Mound has been conducted. The radionuclides under consideration were HT, Pu-239, U-233,234, U-238, Th-230, Th-232, Co-60, Cs-137, and Ac-227. It is concluded from this analysis that additional continuous monitoring programs are not warranted. Dose contributions from these radionuclides are negligible. Further, in many cases environmental surveillance would not be practical due to the extremely low concentrations encountered in the offsite environment. For these reasons, it is believed that no additional action is required in response to DOE Tiger Team Finding R/CF-1.

  12. 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.

  13. Electron spin resonance (ESR) dating of hominid-bearing deposits in the Caverna delle Fate, Ligure, Italy

    NASA Astrophysics Data System (ADS)

    Falgueres, Christophe; Yokoyama, Yuji; Bibron, Roland

    1990-07-01

    Stalagmitic floors interstratified with Mousterian deposits from the Caverna delle Fate (Italy) have been dated by the electron spin resonance (ESR) method. Three samples dated fall between 60,000 and 74,000 yr and indicate the age of the Mousterian deposits. They are in good agreement with ages determined by nondestructive γ-ray spectrometry of the human remains from 231Pa/ 235U and 230Th /234U ratios, which are, respectively, 75,000 -14,000+21,000 and 82,000 -25,000+36,000 yr. These dates are consistent with the morphological characteristics of the bones as Neanderthal remains.

  14. New data on the Hyrkkoelae native copper mineralization: A natural analogue for the long-term corrosion of copper canisters

    SciTech Connect

    Marcos, N.; Ahonen, L.; Bros, R.; Roos, P.; Suksi, J.; Oversby, V.

    1999-07-01

    The Hyrkkoelae U-Cu mineralization located in southwestern Finland is reassessed with reference to the corrosion mechanisms affecting the stability of native copper and the time-scales of corrosion processes. The mineral assemblage native copper--copper sulfide occurs in open fractures at several depth intervals within granite pegmatites (GP). The surfaces of these open fractures have accumulations of uranophane crystals and other unidentified uranyl compounds. The secondary uranium minerals are mainly distributed around copper sulfide grains. Microscopic intergrowths of copper sulfides and uranyl compounds also have been observed. Groundwater samples were collected from the vicinity of the Cu samples. The hydrogeochemical features of these samples indicate that the present conditions are oxidizing. The minimum age of U(VI) transport and deposition is about 200,000 years. This age is indicated by {sup 234}U/{sup 238}U and {sup 230}Th/{sup 234}U activity ratios of uranophane. The age of the hexavalent uranium precipitation may be somewhat later than the last influxes and/or demobilization of sulfur. The mineral assemblage native copper--copper oxide (cuprite) occurs only at one depth interval within altered granite pegmatite. The fracture surface was coated by smectite. The content of uranium in smectite was 69--75 ppm U. The {sup 234}U/{sup 238}U and {sup 230}Th/{sup 234}U activity ratios of smectite showed that it has been exposed to recent groundwaters (e.g., during the last million years). The pH of the groundwater at this interval was near neutral (6.9). The copper grains present at this fracture surface were as large as 1 mm in diameter and had rims of cuprite of 0.01 to 0.1 mm thick. The smallest grains were totally oxidized.

  15. Internal [sup 238]U-series systematics of pumice from the November 13, 1985, eruption of Nevado de Ruiz, Colombia

    SciTech Connect

    Schaefer, S.J.; Williams, S.N. ); Sturchio, N.C. ); Murrell, M.T. )

    1993-03-01

    High-precision mass spectrometer and alpha scintillation measurements of [sup 238]U-series nuclides were obtained for whole-rock pumice and constituent mineral and glass separates to help interpret the timing and nature of magmatic processes that led up to the 1985 eruption of Nevado de Ruiz volcano. Internal isochron diagrams for [sup 226]Ra/Ba vs. [sup 230]Th/Ba and [sup 230]Th/[sup 232]Th vs. [sup 238]U/[sup 232]Th show that data define linear arrays, indicating an average crystallization age of 6.1 [+-] 0.5 ka (Ra-Th isochron) and 7 [+-] 6 ka (Th-U isochron). Stratigraphic, petrographic geochemical, repose time, and eruption volume data for the Holocene eruptive sequence of Nevado del Ruiz indicate that significant changes occurred in the subvolcanic magma chamber between eruptions R9 ([approx]8.6 ka) and R8 ([approx]3.0 ka). This coincides with the average crystallization age derived from the U-series data and may represent the injection of a new batch (or batches) of mantle-derived magma into the subvolcanic magma chamber. 26 refs., 4 figs., 2 tabs.

  16. Daily intakes of naturally occurring radioisotopes in typical Korean foods.

    PubMed

    Choi, Min-Seok; Lin, Xiu-Jing; Lee, Sun Ah; Kim, Wan; Kang, Hee-Dong; Doh, Sih-Hong; Kim, Do-Sung; Lee, Dong-Myung

    2008-08-01

    The concentrations of naturally occurring radioisotopes ((232)Th, (228)Th, (230)Th, (228)Ra, (226)Ra, and (40)K) in typical Korean foods were evaluated. The daily intakes of these radioisotopes were calculated by comparing concentrations in typical Korean foods and the daily consumption rates of these foods. Daily intakes were as follows: (232)Th, 0.00-0.23; (228)Th, 0.00-2.04; (230)Th, 0.00-0.26; (228)Ra, 0.02-2.73; (226)Ra, 0.01-4.37 mBq/day; and (40)K, 0.01-5.71 Bq/day. The total daily intake of the naturally occurring radioisotopes measured in this study from food was 39.46 Bq/day. The total annual internal dose resulting from ingestion of radioisotopes in food was 109.83 muSv/y, and the radioisotope with the highest daily intake was (40)K. These values were same level compiled in other countries.

  17. A Reassessment of U-Th and 14C Ages for Late-Glacial High-Frequency Hydrological Events at Searles Lake, California

    USGS Publications Warehouse

    Lin, J.C.; Broecker, W.S.; Hemming, S.R.; Hajdas, I.; Anderson, Robert F.; Smith, G.I.; Kelley, M.; Bonani, G.

    1998-01-01

    U-Th isochron ages of tufas formed on shorelines suggest that the last pluvial event in Lake Lahontan and Searles Lake was synchronous at about 16,500 cal yr B.P. (equivalent to a radiocarbon age of between 14,000 and 13,500 yr B.P.), whereas the timing of this pluvial event determined by radiocarbon dating is on the order of 1000 yr younger. The timing of seven distinct periods of near desiccation in Searles Lake during late-glacial time has been reinvestigated for U-Th age determination by mass spectrometry. U-Th dating of evaporite layers in the interbedded mud and salt unit called the Lower Salt in Searles Lake was hampered by the uncertainty in assessing the initial 230Th/232Th of the samples. The resulting ages, corrected by a conservative range of initial 230Th/ 232Th ratios, suggest close correlation of the abrupt changes recorded in Greenland ice cores (Dansgaard-Oeschger events) and wet-dry conditions in Searles Lake between 35,000 and 24,000 Cal yr B.P. ?? 1998 University of Washington.

  18. Correcting for initial Th in speleothems to obtain the age of calcite nucleation after a growth hiatus

    NASA Astrophysics Data System (ADS)

    Richards, D. A.; Nita, D. C.; Moseley, G. E.; Hoffmann, D. L.; Standish, C. D.; Smart, P. L.; Edwards, R.

    2013-12-01

    In addition to the many U-Th dated speleothem records (δ18O δ13C, trace elements) of past environmental change based on continuous phases of calcite growth, discontinuous records also provide important constraints for a wide range of past states of the Earth system, including sea levels, permafrost extent, regional aridity and local cave flooding. Chronological information about human activity or faunal evolution can also be obtained where calcite can be seen to overlie cave art or mammalian bones, for example. Among the important considerations when determining the U-Th age of calcite that nucleates on an exposed surface are (1) initial 230Th/232Th, which can be elevated and variable in some settings, and (2) growth rate and sub-sample density, where extrapolation is required. By way of example, we present sea level data based on U-Th ages of vadose speleothems (i.e. formed above the water table and distinct from 'phreatic' examples) from caves of the circum-Caribbean , where calcite growth was interrupted by rising sea levels and then reinitiated after regression. These estimates demand large corrections and derived sea level constraints are compared with alternative data from coral reef terraces, phreatic overgrowths on speleothems or indirect, proxy evidence from oxygen isotopes to constrain rates of ice volume growth. Flowstones from the Bahamas provide useful sea level constraints because they present the longest and most continuous records in such settings (a function of preservation potential in addition to hydrological routing) and also earliest growth post-emergence after sea level fall. We revisit estimates for sea level regression at the end of MIS 5 at ~ 80 ka (Richards et al, 1994; Lundberg and Ford, 1994) and make corrections for non-Bulk Earth initial Th contamination (230Th/232Th activity ratio > 10), based on isochron analysis of alternative stalagmites from the same settings and recent high resolution analysis. We also present new U-Th ages for

  19. Distribution of long-lived radionuclides of the 238U series in the sediments of a small river in a uranium mineralized region of Spain.

    PubMed

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

    2002-01-01

    A study is presented on the distribution and mobilization of the natural U isotopes (238U and 234U), 230Th, and 226Ra in the sediments of a small river crossing an uranium mineralized zone where a disused uranium mine is located. Due to the preferential directions for surface run-off waters and to the mine's situation, one sampling point along the river bed was identified as a point of accumulation of radionuclides. The average values of the activity concentrations (Bq/kg) in this sediment sample were 5,025, 5,055, 5,915 and 1,694 for 238U, 234U, 230Th and 226Ra, respectively, while the respective average values of the activity concentrations (Bq/kg) for the sediment sample considered to give the background level were 125, 124, 131 and 370. Isotopic ratios between the descendants of 238U served to clarify some paths of distribution, involving the soils nearest to the sampling points and the location of these points with respect to the disused mine. The differences in behaviour found between the uranium, thorium and radium isotopes were associated to the mobility of these radionuclides in the fluvial system studied. Correlations between the radionuclide activity concentration ratios and stable element concentrations in the sediment samples were also investigated.

  20. HEU age determination

    SciTech Connect

    Moorthy, A.R.; Kato, W.Y.

    1997-07-01

    A new technique has been developed to determine the age of highly enriched uranium (HEU) in solids. Uranium age is defined as the time since the uranium-containing material was last subjected to a process capable of separating uranium from its radioactive-decay daughters. [Most chemical processing, uranium enrichment, volatilization processes, and phase transformations (especially relevant for uranium hexafluoride) can result in separation of the uranium parent material from the decay-product daughters.] Determination of the uranium age, as defined here, may be relevant in verifying arms-control agreements involving uranium-containing nuclear weapons. The HEU age is determined from the ratios of relevant uranium daughter isotopes and their parents, viz {sup 230}Th/{sup 234}U and {sup 231}Pa/{sup 235}U. Uranium isotopes are quantitatively measured by their characteristic gamma rays and their daughters by alpha spectroscopy. In some of the samples, where HEU is enriched more than 99%, the only mode of HEU age determination is by the measurement of {sup 231}Pa since there is negligible quantity of {sup 230}Th due to very low atom concentrations of {sup 234}U in the samples. In this report the methodology and the data for determining the age of two HEU samples are presented.

  1. Large Scale Accelerator Production of 225Ac: Effective Cross sections for 78-192 MeV Protons Incident on 232Th Targets

    DOE PAGES

    Griswold, Justin R; Medvedev, Dmitri G.; Engle, Jonathan W.; ...

    2016-09-28

    Actinium-225 and 213Bi have been used successfully in targeted alpha therapy (TAT) in preclinical and clinical research. This paper is a continuation of research activities aiming to expand the availability of 225Ac. The high energy proton spallation reaction on natural thorium metal target has been utilized to produce millicurie quantities of 225Ac. The results of sixteen irradiation experiments of Th metal at beam energies between 78 and 200 MeV are summarized in this work. Irradiations have been conducted at Brookhaven National Laboratory (BNL) and Los Alamos National Laboratory (LANL), while target dissolution and processing was carried out at Oak Ridgemore » National Laboratory (ORNL). Excitation functions for actinium and thorium isotopes as well as for some of the fission products are presented. The cross sections for production of 225Ac range from 3.6 to 16.7 mb in the incident proton energy range of 78 to 192 MeV. Based on these data, production of Curie quantities of 225Ac is possible by irradiating a 5.0 g cm-2232Th target for 10 days in either BNL or LANL proton irradiation facilities.« less

  2. Preliminary Results on Direct Observation of True Ternary fission in the reaction {sup 232}Th+d (10 MeV)

    SciTech Connect

    Pyatkov, Yu.; Kamanin, D.; Alexandrov, A.; Alexandrova, I.; Kondratyev, N.; Kuznetsova, E.; Tyukavkin, A.; Zhuchko, V.; Krasznohorkay, A.; Csatlos, M.; Csige, L.; Gulyas, J.; Naqvi, F.; Tornyi, T.

    2010-04-30

    Results of the first direct observation of the true ternary fission of {sup 234}Pa* nucleus are presented. The yield of the effect depending of the experimental geometry is about 10{sup -5}/binary fission. Mass of the lightest fragment in the triplet lies mainly in the range of (20 divide 40) a.m.u. Connection between the effect and known heavy ion or lead radioactivity is discussed.

  3. U-Sries Disequilibra in Soils, Pena Blanca Natural Analog, Chihuahua, Mexico

    SciTech Connect

    D. French; E. Anthony; P. Goodell

    2006-03-16

    The Nopal I uranium deposit located in the Sierra Pena Blanca, Mexico. The deposit was mined in the early 1980s, and ore was stockpiled close by. This stockpile area was cleared and is now referred to as the Prior High Grade Stockpile (PHGS). Some of the high-grade boulders from the site rolled downhill when it was cleared in the 1990s. For this study soil samples were collected from the alluvium surrounding and underlying one of these boulders. A bulk sample of the boulder was also collected. Because the Prior High Grade Stockpile had no ore prior to the 1980s a maximum residence time for the boulder is about 25 years, this also means that the soil was at background as well. The purpose of this study is to characterize the transport of uranium series radionuclides from ore to the soil. Transport is characterized by determining the activities of individual radionuclides and daughter to parent ratios. Isotopes of the uranium series decay chain detected include {sup 210}Pb, {sup 234}U, {sup 230}Th, {sup 226}Ra, {sup 214}Pb, and {sup 214}Bi. Peak areas for each isotope are determined using gamma-ray spectroscopy with a Canberra Ge (Li) detector and GENIE 2000 software. The boulder sample is close to secular equilibrium when compared to the standard BL-5 (Beaver Lodge Uraninite from Canada). Results for the soils, however, indicate that some daughter/parent pairs are in secular disequilibrium. These daughter/parent (D/P) ratios include {sup 230}Th/{sup 234}U, which is greater than unity, {sup 226}Ra/{sup 230}Th, which is also greater than unity, and {sup 210}Pb/{sup 214}Bi, which is less than unity. The gamma-ray spectrum for organic material lacks {sup 230}Th peaks, but contains {sup 234}U and {sup 226}Ra, indicating that plants preferentially incorporate {sup 226}Ra. Our results, combined with previous studies require multistage history of mobilization of the uranium series radionuclides. Earlier studies at the ore zone could limit the time span for mobilization only

  4. 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

  5. The Relative Importance of Terrestrial Versus Marine Sediment Sources to the Nueces- Corpus Christi Estuary, Texas: An Isotopic Approach

    NASA Astrophysics Data System (ADS)

    Yeager, K. M.; Santschi, P. H.; Schindler, K. J.; Andres, M. J.; Weaver, E. A.

    2006-05-01

    Determining principle sources of sediment to coastal systems is an important and complex problem that figures prominently in a myriad of geological, geomorphological, geochemical and biological processes. Lithogenic (226Ra, 228Ra, 228Th, 230Th, 232Th) and fallout (137Cs, 210Pb) isotopes were used in conjunction with sedimentological methods to determine rates of sedimentation in the Nueces Delta and Nueces-Corpus Christi Estuary and to assess the relative importance of marine versus terrestrial sediment sources to the estuary. Sampling focused primarily on the lower Nueces River, Nueces Delta, Nueces Bay, Corpus Christi Bay, Gulf Intracoastal Waterway (GIW) and Gulf of Mexico (GOM). Gain size data show GIW and GOM sediments to be dominantly sands, Corpus Christi Bay sediments to be dominantly clays and sediments from all other sampled areas to be more homogenized in grain size, suggesting that near shore oceanic sediments are sands derived predominantly from long shore transport in the littoral zone. Bed load and suspended sediments sourced from the Nueces River provide sand and fines to the Nueces Delta and Bay, where the coarser size fractions are effectively retained. Similarity of lithogenic isotope ratios in surface sediment types throughout the system precluded a numeric approach to discerning the importance of each of the two large scale sediment source areas (terrestrial and marine). A stepwise, graphical examination of discrete lithogenic isotope activity concentrations shows more promise. Terrestrial, marine and bay sediment means for 226Ra v. 232Th, 226Ra v. 230Th and 228Ra v. 232Th show that terrestrial and marine sediment sources have different signatures, despite having a similar grain size distribution (sands), and that sediment deposited in Nueces and Corpus Christi Bays are indistinguishable from the terrestrial component. Supporting evidence is provided by thorium isotopes, 230Th v. 232Th, 228Th v. 232Th and 228Th v. 230Th. Nueces Delta

  6. Sediment transport time measured with U-Series isotopes: Resultsfrom ODP North Atlantic Drill Site 984

    SciTech Connect

    DePaolo, Donald J.; Maher, Kate; Christensen, John N.; McManus,Jerry

    2006-06-05

    High precision uranium isotope measurements of marineclastic sediments are used to measure the transport and storage time ofsediment from source to site of deposition. The approach is demonstratedon fine-grained, late Pleistocene deep-sea sediments from Ocean DrillingProgram Site 984A on the Bjorn Drift in the North Atlantic. The sedimentsare siliciclastic with up to 30 percent carbonate, and dated by sigma 18Oof benthic foraminifera. Nd and Sr isotopes indicate that provenance hasoscillated between a proximal source during the last three interglacialperiods volcanic rocks from Iceland and a distal continental sourceduring glacial periods. An unexpected finding is that the 234U/238Uratios of the silicate portion of the sediment, isolated by leaching withhydrochloric acid, are significantly less than the secular equilibriumvalue and show large and systematic variations that are correlated withglacial cycles and sediment provenance. The 234U depletions are inferredto be due to alpha-recoil loss of234Th, and are used to calculate"comminution ages" of the sediment -- the time elapsed between thegeneration of the small (<_ 50 mu-m) sediment grains in the sourceareas by comminution of bedrock, and the time of deposition on theseafloor. Transport times, the difference between comminution ages anddepositional ages, vary from less than 10 ky to about 300 to 400 ky forthe Site 984A sediments. Long transport times may reflect prior storagein soils, on continental shelves, or elsewhere on the seafloor. Transporttime may also be a measure of bottom current strength. During the mostrecent interglacial periods the detritus from distal continental sourcesis diluted with sediment from Iceland that is rapidly transported to thesite of deposition. The comminution age approach could be used to dateQuaternary non-marine sediments, soils, and atmospheric dust, and may beenhanced by concomitant measurement of 226Ra/230Th, 230Th/234U, andcosmogenic nuclides.

  7. A procedural manual for measurement of uranium and thorium isotopes utilizing the USGS-Stanford Finnegan Mat 262

    USGS Publications Warehouse

    Shamp, Donald D.

    2001-01-01

    Over the past several decades investigators have extensively examined the 238U-234U- 230Th systematics of a variety of geologic materials using alpha spectroscopy. Analytical uncertainty for 230Th by alpha spectroscopy has been limited to about 2% (2σ). The advantage of thermal ionization mass spectroscopy (TIMS), introduced by Edwards and co-workers in the late 1980’s is the increased detectability of these isotopes by a factor of ~200, and decreases in the uncertainty for 230Th to about 5‰ (2σ) error. This report is a procedural manual for using the USGS-Stanford Finnegan-Mat 262 TIMS to collect and isolate Uranium and Thorium isotopic ratio data. Chemical separation of Uranium and Thorium from the sample media is accomplished using acid dissolution and then processed using anion exchange resins. The Finnegan-Mat262 Thermal Ionization Mass Spectrometer (TIMS) utilizes a surface ionization technique in which nitrates of Uranium and Thorium are placed on a source filament. Upon heating, positive ion emission occurs. The ions are then accelerated and focused into a beam which passes through a curved magnetic field dispersing the ions by mass. Faraday cups and/or an ion counter capture the ions and allow for quantitative analysis of the various isotopes.

  8. Behaviour of nuclides and U-series disequilibrium in clayey sediments: application to the Late Jurassic record from the eastern Paris basin

    NASA Astrophysics Data System (ADS)

    Casanova, J.; Négrel, Ph.; Innocent, C.; Brulhet, J.

    2003-04-01

    We present a record of U-series disequilibrium covering the Callovo-Oxfordian-Thitonian times of the Late Jurassic carbonated platform from the eastern part of the Paris basin. The Callovo-Oxfordian clayey layer is the potential host rock for reconnaissance work carried out by Andra (e.g., Agence Nationale de Gestion des Déchets Radioactifs) in eastern France, the objective of which is the designing and building of an underground research laboratory to study the aptitude of the clay-marl Callovo-Oxfordian layer for the storage of radioactive wastes. We analyse U and Th trace elements on both the labile fraction (extracted by cold HCl) and the total bulk sediments. The Th contents are extremely low in the Oxfordian shelf reef carbonates (<10 ppb) with respect to the Kimmeridgian-Tithonian clayey marls and the Callovian-Oxfordian argilites (up to 10 ppm). In contrast, the uranium contents are much more homogenous (1 ppm ±0.8) along the section. With respect to bulk concentrations, the nuclide contents in the labile component are particularly low in the Callovian-Oxfordian argilites. This behaviour suggests that given the extremely low permeability of the rock, any groundwater circulation of solutes could only have taken place by diffusion - a very slow mechanism that favours water-rock interactions. For U-series analyses (measured by alpha-spectrometry), a total of 43 bulk-rock samples were preferentially microdrilled from the fine-grained lithologies, although the heterogeneity of carbonate facies within sections necessitated occasional sampling of coarser grained lithologies. Within the carbonate-rich part (Oxfordian to Tithonian) of the section, the 234U/238U ratios slightly fluctuate from secular equilibrium and are interpreted as preferential 234U-solution processes related to groundwater circulation. Preferential removal of 234U in this zone is also indicated by some 230Th/234U activity ratios higher than unity. In contrast, most of the samples from the

  9. Accurate fast method with high chemical yield for determination of uranium isotopes (234U, 235U, 238U) in granitic samples using alpha spectroscopy

    NASA Astrophysics Data System (ADS)

    Guirguis, Laila A.; Farag, Nagdy M.; Salim, Adham K.

    2015-03-01

    The present study aims to use the α-spectroscopy at Nuclear Materials Authority (NMA) of Egypt. A radiochemical technique for analysis uranium isotopes was carried out for ten mineralized granitic samples together with the International standards RGU-1 (IAEA) and St4 (NMA). Several steps of sample preparation, radiochemical separation and source preparation were performed before analysis. Uranium was separated from sample matrix with 0.2 M TOPO in cyclohexane as an extracting agent with a chemical yield 98.95% then uranium was purified from lanthanides and actinides present with 0.2 M TOA in xylene as an extracting agent. The pure fraction was electrodeposited on a mirror-polished copper disc from buffer solution (NaHSO4+H2SO4+NH4OH). Rectangle pt-electrode with an anode-cathode distance of 2 cm was used. Current was 900 mA and the electrodeposition time reach up to 120 min. The achieved results show that the chemical yield ranged between 87.9±6.8 and 98±8.6.

  10. High precision thorium-230 ages of corals and the timing of sea level fluctuations in the late Quaternary

    SciTech Connect

    Edwards, R.L.

    1988-01-01

    Mass spectrometric techniques for the measurement of {sup 230}Th and {sup 234}U have been developed. These techniques have made it possible to reduce the analytical errors in {sup 230}Th dating of corals using very small samples (10{sup 7} to 10{sup 10} atoms). The time range over which useful data on corals can now be obtained ranges from 15 to 500,000 years. For young corals, this approach may be preferable to {sup 14}C dating. The precision with which the age of a coral can not be determined makes it possible to determine the timing of sea level fluctuations in the late Quaternary. Analyses of a number of corals that grew during the last interglacial period yield ages of 122 to 130 ky. The ages coincide with or slightly postdate the summer solar insolation high at 65{degree}N latitude, which occurred 128 ky ago. This supports the idea that changes in Pleistocene climate can be the result of orbital forcing. Coral ages may allow us to resolve the ages of individual coseismic uplift events and thereby date prehistoric earthquakes. This possibility has been examined at two localities, northwest Santo Island and north Malekula Island, Vanuatu. The {sup 230}Th growth dates of the surfaces of adjacent emerged coral heads, collected from the same elevation on northwest Santo Island, were, within analytical error, identical (A.D. 1866 {plus minus} 4 and A.D. 1864 {plus minus} 4). This indicates that the corals died at the same time and is consistent with the idea that they were killed by coseismic uplift. Similar adjacent coral heads on north Malekula Island yielded {sup 230}Th growth dates of A.D. 1729 {plus minus} 3 and A.D. 1718 {plus minus} 5. The ages are similar but analytically distinguishable. The difference may be due to erosion of the outer, younger, portion of the latter coral head.

  11. Determination of thorium concentrations and activity ratios in silicate rocks by alpha spectrometry.

    PubMed

    dos Santos, R N; Marques, L S; Nicolai, S H A; Ribeiro, F B

    2004-01-01

    A detailed radiochemical procedure for alpha spectrometry measurements of thorium concentrations and of 230Th/232Th activity ratios in silicates is presented. The Th behaviour, during each step of the chemical process, was investigated by using a 234Th tracer, which is a gamma-ray emitter. The described chemical processing provides relatively high thorium yields, which varied between 56% and 88%, in the analysis of GB-1 (granite) and BB-1 (basalt) Brazilian geological standards. Also, the application of the established radiochemical method allowed a determination of both Th concentrations and activity ratios with high reproducibility, on the order of 2%. The estimation of the concentration result accuracy is also about 2%, which was calculated by using published data obtained from neutron activation analysis as reference values.

  12. Origin of silicic magma in Iceland revealed by Th isotopes

    SciTech Connect

    Sigmarsson, O.; Condomines, M. ); Hemond, C. ); Fourcade, S. ); Oskarsson, N. )

    1991-06-01

    Th, Sr, Nd, and O isotopes have been determined in a suite of volcanic rocks from Hekla and in a few samples from Askja and Krafla volcanic centers in Iceland. Although {sup 87}Sr/{sup 86}Sr and {sup 143}Nd/{sup 144}Nd ratios are nearly the same for all compositions at Hekla, the ({sup 230}Th/{sup 232}Th) ratios differ and thus clearly show that the silicic rocks cannot be derived from fractional crystallization of a more primitive magma. Similar results are obtained for the Krafla and Askja volcanic centers, where the {delta}{sup 18}O values are much lower in the silicic magma than in the mafic magma. These data suggest that large volumes of silicic rocks in central volcanoes of the neovolcanic zones in Iceland are produced by partial melting of the underlying crust.

  13. Total half-lives for selected nuclides

    SciTech Connect

    Holden, N.E.

    1989-01-01

    Measurements of the half-lives of {sup 3}H, {sup 10}Be, {sup 14}C, {sup 26}Al, {sup 40}K, {sup 39}Ar, {sup 53}Mn, {sup 87}Rb, {sup 92}Nb, {sup 129}I, {sup 138}La, {sup 147}Sm, {sup 176}Lu, {sup 174}Hf, {sup 180}Ta, {sup 187}Re, {sup 186}Os, {sup 190}Pt, {sup 204}Pb, {sup 210}Pb, {sup 210}Po, {sup 222}Rn, {sup 224}Th, {sup 226}Ra, {sup 227}Ac, {sup 228}Ra, {sup 228}Th, {sup 230}Th, {sup 232}Th, {sup 231}Pa have been compiled and evaluated. The effect of the {sup 14}C half-life value on carbon dating ages is discussed as well as the stability of {sup 204}Pb. 237 refs., 30 tabs.

  14. Thorium: Determination by CDTN, Brazil

    NASA Astrophysics Data System (ADS)

    Menezes, M. A. B. C.; Sabino, C. V. S.

    1999-01-01

    One of the tasks of the Radiochemical Sector, CDTN/CNEN, Brazil, is to meet the clients' analytical needs. The Sector has been facing the challenges of determining several elements in diversified matrixes from all over the country since the sixties. It has been giving analytical support to universities, industries, environmental monitoring programs, research institutes. Due to the growing need to determine thorium isotopes through the years it was necessary to work out a routine procedures. Nowadays the determination of thorium consists of a well established routine whose procedures are applied to grouped samples according to their kind, physical state, matrix interference, detection limits and number of samples. This paper describes the methods used by CDTN to determine232Th by neutron activation analysis and230Th and228Th by radiochemical separations and alpha spectrometry in several matrixes.

  15. Recycling of crystal mush-derived melts and short magma residence times revealed by U-series disequilibria at Stromboli volcano

    NASA Astrophysics Data System (ADS)

    Bragagni, Alessandro; Avanzinelli, Riccardo; Freymuth, Heye; Francalanci, Lorella

    2014-10-01

    The presence of crystal mushes in the feeding system of active volcanoes is generally revealed by antecrysts, representing the crystalline portion of old magmas recycled in the juvenile material, but very little is known about the fate of interstitial liquid hosted within the crystal-rich mush (i.e. antemelt). U-series disequilibria measured in magmas erupted in the past 18 years at Stromboli volcano provide the first geochemical evidence of the involvement of antemelt and help constraining the timescales of the processes occurring in the plumbing system of the volcano. Despite almost constant major and trace element composition, significant variations in isotope ratios are observed. (230Th/232Th) decreases with time, whilst (238U/232Th), (226Ra/230Th) and 87Sr/86Sr are different in the two types of magma erupted. Magma with low phenocryst content (lp) is erupted as pumices during paroxysm and is thought to belong to a deep reservoir. Highly porphyritic magma (hp) is erupted during the normal “Strombolian” activity as scoria and during the effusive events as lavas, and it is considered to derive from the former one within a shallow reservoir through degassing-driven crystallisation, mixing and incorporation of antecrysts. The distinct (238U/232Th) of lp and hp magma requires the involvement of a component with high 87Sr/86Sr and (238U/232Th) deriving from older magmas erupted earlier in the volcano history (up to 2.5 ka). The incompatibility of U and Th in major mineral phases limits the possible effect of antecrysts, hence requiring the involvement of a U- and Th-rich antemelt. The decrease of 226Ra-excess from lp to hp magmas provides further and independent evidence for the involvement of a few thousands years old antemelt. The variation with time of (230Th/232Th) within lp and hp magmas is exploited to constrain the residence time of magmas in the deep and shallow reservoir of the volcano to <55 yrs (inferred reservoir volume <0.5 km) and 2-10 yrs (inferred

  16. U-238-U-234-Th-230-Th-232 systematics and the precise measurement of time over the past 500,000 years

    NASA Technical Reports Server (NTRS)

    Edwards, R. Lawrence; Chen, J. H.; Wasserburg, G. J.

    1987-01-01

    A method is presented for the high-precision measurement of the Th-230 abundance in corals by isotope-dilution mass spectrometry using techniques developed by Chen and Wasserburg (1980, 1981) and Chen et al. (1986). It is shown that 6 x 10 to the 8th atoms of Th-230 can be measured to + or - 30 percent (2 sigma) and 2 x 10 to the 10th atoms of Th-230 to + or - 2 percent. The time over which useful age data on corals can be obtained ranges from a few years to about 500 ky, with the uncertainty in age ranging from 5 y for a 180-y-old coral, to 44 y for a 8294-y-old coral, to 1.1 ky for a 123.1-ky-old coral. Ages were determined with high analytical precision for several corals that grew during high sea-level stands about 120 ky ago, supporting the view that the dominant cause of Pleistocene climate change was Milankovitch forcing.

  17. Uranium series disequilibrium in a young surficial uranium deposit, northeastern Washington, U.S.A.

    USGS Publications Warehouse

    Zielinski, R.A.; Bush, C.A.; Rosholt, J.N.

    1986-01-01

    A recently discovered ore-grade accumulation of U in organic-rich sediments of late Quaternary age provides an opportunity for studying the early association of U, U-daughters, and organic matter in a natural setting. The U occurs in valley-fill sediments of peat, peaty clay, silt, and sand along the north fork of Flodelle Creek, Stevens County, Washington. Radiometric techniques (delayed neutron, high-resolution gamma-ray spectrometry, thin-source alpha spectrometry) were employed to determine the abundance and distribution of U-series nuclides, the extent of secular equilibrium within the U decay series, and the apparent U-series ages of U incorporation. Sixteen lithologically distinct intervals were sampled from a 292 cm core. Uranium contents range from 140 to 2790 ppm and are positively correlated with organic contents. Measured alpha activity ratios of 234U/238U (1.31-1.38) are very similar to those reported in coexisting waters, suggesting a rather constant isotopic composition of introduced U. Much lower Th contents of <10-40 ppm are controlled by the type and abundance of silicate detritus. The youth of the host sediments (<15 000 a) and the paucity of associated radioactivity suggested large excesses of U relative to radioactive daughters and such excesses were observed, particularly in the shallowest intervals. Apparent ages of U emplacement determined by the (alpha) activity ratio of 230Th daughter to 234U parent show a general increase with depth and fair agreement with estimated depositional ages. This observation suggests dominantly syndepositional or early post depositional emplacement of U followed by decay-generated buildup of 230Th daughter with time. However, interval by interval comparisons of the relative abundances of other daughters, particularly 226Ra and 210Pb, indicate variability caused by processes other than closed-system growth and decay, probably because chemically diverse daughters that are decay-generated in situ have differing

  18. Response of the Indo-Australian Monsoon System to Heinrich Events: Evidence from Marine and Terrestrial Sediments

    NASA Astrophysics Data System (ADS)

    Muller, J.; McManus, J. F.; Oppo, D.; Francois, R. H.

    2012-12-01

    The biannual Asian monsoon dominates the climate of tropical and subtropical regions, bringing a strong seasonal rainfall contrast in these areas. In recent years computer models and paleoclimate records from various tropical locations have demonstrated the sensitivity of the tropical monsoon system to Northern Hemisphere abrupt climate change events. This study presents data from a somewhat underrepresented region, the Australian and southern Indonesian region. Here we compare a new deep-sea sediment record for the Flores Sea, with a terrestrial peat core record from Lynch's Crater, NE Queensland Australia. In the Flores Sea we use the long-lived nuclide 232Th as a novel proxy for detrital riverine input and 230Th normalization to estimate the history of preserved fluxes reaching the seafloor in the Flores Sea. The 230Th normalized burial fluxes of lithogenic and biogenic matter demonstrate that both detrital and biogenic fluxes in the Flores Sea were higher during Heinrich Stadial 1 (HS1) than any other period in the past 22 kyr. High detrital fluxes indicate enhanced precipitation runoff from surrounding landmasses during a period of maximum southward shift of the Intertropical Convergence Zone (ITCZ). The enhanced precipitation associated with HS1 over the Flores Sea is in good timing with a previously interpreted wet event over Lynch's Crater, NE Australia. Our results provide strong evidence for a southward migration of the ITCZ during HS1 and a return northward during the Bølling-Allerød interstadial. This work highlights the sensitivity of Australasian rainfall patterns to high latitude climate change in the Northern Hemisphere. In addition, our work constrains both the northern and southern limits of enhanced rainfall associated with a southward shift of the monsoon belt at the time of HS1 and highlights the value of 232Th as a proxy for continental input to deep-sea sediment records.

  19. Cryptic young zircon and young plagioclase in the Kaharoa Rhyolite, Tarawera, New Zealand: Implications for crystal recycling in magmatic systems

    NASA Astrophysics Data System (ADS)

    Klemetti, E. W.; Cooper, K. M.

    2007-12-01

    We measured in-situ 238U-230Th zircon and bulk plagioclase 238U-230Th-226Ra disequilibria in rhyolite lava and tephra from the ~1315 AD Kaharoa eruption of Tarawera Volcano, New Zealand in order to constrain its history of chemical evolution. These data suggest that zircon records a protracted history (10s of kyr) whereas plagioclase is dominantly young (few kyr), but both phases crystallize up to the eruption. The Kaharoa eruptive period at Tarawera consists of ~2.5 km3 of crystal-rich rhyolite (74-75 wt% silica) lava and ~5 km3 of coeval tephra deposits, making it the largest silicic eruption in New Zealand in the last 1,000 years. 238U-230Th disequilibria measurements of zircon determined via SHRIMP-RG analyses produce an array of ages, with three main populations: (1) within error of eruption age; (2) 15-80 k.y.; (3) 100-175 k.y. Very few analyzed zircon fall within error of eruption age and little difference is seen in the age distribution of zircon between the lava and tephra. In contrast, 238U-230Th and 230Th-226Ra plagioclase ages appear to be within error of eruption age however this age is complicated zircon inclusions in the plagioclase. This contamination by zircon is seen in the 238U-230Th disequilibria and trace element data, where the addition of zircon pushes the bulk plagioclase separate towards more U-enriched values and high Zr values. However, the (230Th)/(232Th) ratios for the separates are the same as the whole rock values, indicating that any zircon in the bulk separate must be young (eruption age). This finding is also borne out in 230Th-226Ra disequilibria, where zero-age zircon contamination is reflected in increased (230Th)/[Ba] with no change in (226Ra)/[Ba]. In both cases, as little as 1 ppm of zero-age zircon contamination is needed to create these patterns. This signal of young plagioclase and zircon growth is in contrast to the protracted history seen in the SHRIMP-RG zircon data. This suggests that young zircon growth in the Kaharoa

  20. 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.

  1. Age of the moon: an isotopic study of uranium-thorium-lead systematics of lunar samples.

    PubMed

    Tatsumoto, M; Rosholt, J N

    1970-01-30

    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 (207)Pb/(206)Pb, (206)Pb/(238)U, (207)Pb/(235U), and(208)Pb/(232)Th 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 (238)U/(235)U ratio is the same as that in earth rocks, and (234)U is in radioactive equilibrium with parent (238)U.

  2. 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.

  3. Helium and thorium isotope constraints on African dust transport to the Bahamas over recent millennia

    NASA Astrophysics Data System (ADS)

    Hayes, Christopher T.; McGee, David; Mukhopadhyay, Sujoy; Boyle, Edward A.; Maloof, Adam C.

    2017-01-01

    Despite its potential linkages with North Atlantic climate, the variability in Saharan dust transport to the western North Atlantic over the past two millennia has not been well-characterized. A factor of 4 increase in dust production in sub-Saharan Africa has been attributed to the onset of Sahelian agriculture 200 yr ago. The regional extent of this anthropogenic dust increase, however, remains uncertain. Additionally, while millennial-scale cold periods of the last deglaciation have been associated with strong increases in North African dust emissions, few adequate records exist to observe dustiness during the Little Ice Age, a century-scale cooling of the North Atlantic (AD 1400-1800). In this study, we develop a new technique for the paired use of 230Th-normalized 232Th fluxes and 3He-normalized 4He fluxes in Bahamian tidal flat sediments. After justifying the fact that 230Th and 3He have had relatively constant sources to tidal flat and banktop waters, and accounting for the smoothing effect of bioturbation, a factor of 4 change in far-field dust transport to the western North Atlantic between the pre-industrial and modern era is not supported by our dust proxies over the past 2000 yr. Furthermore, we speculate why the response of western North Atlantic dust deposition associated with the Little Ice Age climate anomalies may have been modest compared to prior climatic events of the early Holocene or the last deglaciation.

  4. 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

  5. Generation and mobility of radon in soils. Final report

    SciTech Connect

    Rose, A.W.

    1997-06-30

    This report emphasizes research since 1993, but includes some description of previous work which has been discussed in prior reports and publications. The research has the objectives of answering the following questions: (1) How are Rn emanation coefficients related to the form of Ra and other U-series decay products? (2) How do Ra and Rn in soil depend on the form and behavior of their ancestors {sup 234}U and {sup 230}Th? (3) Under what conditions can thermally driven convection in soil have significant effects on radon transport in soil? (4) Under what conditions do soil moisture and soil air convection affect Rn in homes, and how are these variables relevant in mitigation?

  6. Estimated dose to man from uranium milling via the beef/milk food-chain pathway.

    PubMed

    Rayno, D R

    1983-12-01

    One of the major pathways of radiological exposure to man from uranium milling operations is through the beef/milk food chain. Studies by various investigators have shown the extent of uptake and distribution of 238U, 234U, 230Th, 226Ra, 210Pb, and 210Po in plants and cattle. These long-lived natural radioisotopes, all nuclides of the uranium decay series, are found in concentrated amounts in uranium mill tailings. In this paper, data from these investigations are used to estimate the dose to man from consumption of beef and milk from cattle that have fed on forage contaminated with the tailings. The estimated doses from this technologically enhanced source are compared with those resulting from average dietary intake of these radionuclides from natural sources.

  7. Use of strontium isotopes to constrain the timing and mode of dolomitization of upper Cenozoic sediments in a core from San Salvador, Bahamas

    USGS Publications Warehouse

    Swart, Peter K.; Ruiz, Joaquin; Holmes, Charles W.

    1985-01-01

    The 87Sr/86Sr ratios and the activity ratios of 234U/238U and 230Th/238U have been measured in dolomites from a 168-m-deep core taken on the island of San Salvador, Bahamas. These data suggest two periods of dolomitization. The first episode dolomitized Miocene age sediments during the latest Miocene, and the second dolomitized the Pliocene portion of the core and was still active as recently as 150 ka. The late timing of the second episode argues against penecontemporaneous models of dolomitization for the Pliocene sediments. Instead, dolomitization is favored either as a result of mixing-zone development during the large Pleistocene sea-level changes or by movement of seawater through the platform.

  8. 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 information about nuclide migration during uranium processing.

  9. Protactinium-231 measurement and application to a uranium series transport model

    NASA Astrophysics Data System (ADS)

    Golian, C.; Nightingale, T.; Airey, P. L.

    1984-06-01

    Precise measurements of small deviations of 230Th/ 234U and 231Pa/ 235U contribute to the modelling of the geochemical transport of uranium series nuclides. The use of alpha-spectrometry to measure the second-order daughter product 227Th was the analytical technique chosen. It was thereby assumed that the intermediate 227Ac is immobile. Complete methematical expressions for the count rate in various regions of the spectrum have been developed. They allow calculation of the initial yield from the cumulative counts of 227Th and the interfering 223Ra. 224Ra and 212Bi for extended time periods. The resulting increase in precision is particularly useful at low levels. The approach to modelling the transport of uranium series nuclides down-gradient of deposits within the Alligator Rivers Uranium Province of the Northern Territory of Australia is outlined. Some preliminary data are presented which call into question the assumption of the immobility of the 227Ac.

  10. Special Analysis for the Disposal of the Idaho National Laboratory Unirradiated Light Water Breeder Reactor Rods and Pellets Waste Stream at the Area 5 Radioactive Waste Management Site, Nevada National Security Site, Nye County, Nevada

    SciTech Connect

    2014-08-31

    The purpose of this special analysis (SA) is to determine if the Idaho National Laboratory (INL) Unirradiated Light Water Breeder Reactor (LWBR) Rods and Pellets waste stream (INEL103597TR2, Revision 2) is suitable for disposal by shallow land burial (SLB) at the Area 5 Radioactive Waste Management Site (RWMS). The INL Unirradiated LWBR Rods and Pellets waste stream consists of 24 containers with unirradiated fabricated rods and pellets composed of uranium oxide (UO2) and thorium oxide (ThO2) fuel in zirconium cladding. The INL Unirradiated LWBR Rods and Pellets waste stream requires an SA because the 229Th, 230Th, 232U, 233U, and 234U activity concentrations exceed the Nevada National Security Site (NNSS) Waste Acceptance Criteria (WAC) Action Levels.

  11. Uranium-series dating of some pleistocene marine deposits in Southern California

    USGS Publications Warehouse

    Szabo, B. J.; Vedder, J.G.

    1971-01-01

    Analyses of uranium isotopes and their long-lived daughter products showed evidence of uranium migration in most of the 22 fossil mollusk shell samples from marine terrace deposits in southern California. Two samples, however, remained an ideal closed system as indicated by concordant 230Th/234U and 231Pa/235U dates. The closed-system age of the lowest exposed marine terrace deposit along part of the mainland coast of southern California is 69 000 ?? 10 000 yr, and correlation of this discontinuous deposit is afforded between the Newport Beach-Laguna Beach area and the Palos Verdes Hills. Some mollusk shell samples were dated by the open-system model; the remaining samples were found to be unsuitable for uranium-series dating. ?? 1971.

  12. U-series evidence for two high Last Interglacial sea levels in southeastern Tunisia

    NASA Astrophysics Data System (ADS)

    Jedoui, Younes; Reyss, Jean-Louis; Kallel, Nejib; Montacer, Mabrouk; Ismaı̈l, Hedi Ben; Davaud, Eric

    2003-02-01

    Pleistocene raised marine deposits in southeastern Tunisia consist of a siliciclastic unit that culminates at +3 m asl, overlain by a carbonate-rich unit with Strombus bubonius that culminates at +5 m asl. 234U/ 238U ratios on fossil Ostraea shells from both units are compatible with a marine origin from the uranium incorporated into the shells and show narrowly clustered 230Th-ages, respectively, between 147 and 110 ka and 141 and 100 ka. The two units were therefore developed during Marine Isotopic Substage 5e (MISs 5e, Last Interglacial). Their heights are comparable to those of contemporaneous marine deposits found in many tectonically stable areas of the world such as in the Bahamas and in Bermuda and can therefore be used as indicators of eustatic changes during the Last Interglacial. It is argued that on the basis of this evidence, the Last Interglacial was characterised by two eustatic maxima.

  13. Late Pleistocene-Holocene acceleration of uplift rate in southwest Erromango Island, Southern Vanuatu, South Pacific: relation to the growth of the Vanuatuan Mid Sedimentary Basin

    SciTech Connect

    Neef, G.; Hendy, C.

    1988-07-01

    Late Quaternary and Holocene raised coral reefs are well developed in southwestern Erromango Island, which lies in the frontal arc area of the Vanuatuan Island Arc. Eight uranium series ages and one /sup 14/C age from samples from coral reefs at three localities range in age from 4800 B.P. to about 320,000 B.P. Six of the samples dated are from the Matiwo Point area. Here the youngest reef has given a /sup 230/Th//sup 234/U age of 4800 B.P. and a slightly older reef, 4.3 m higher in elevation, has a /sup 14/C age of 5270 B.P. Inland of a cliff the youngest three of four northeastward-tilted raised reefs have given /sup 230/Th//sup 234/U ages ranging from 104,000 B.P. to about 320,000 B.P. These data indicate accelerating uplift rates for southwest Erromango: during the periods 320,000-133,000 B.P., 133,000-6000 B.P., and 6000 - 0 B.P. average uplift rates were 0.33 mm/yr, 0.65 mm/yr, and about 1 mm/yr respectively. These data are interpreted to indicate the growth of the Mid Sedimentary Basin, which lies within the frontal and volcanic arc part of the island arc complex. This increase in uplift/eastward-tilting could represent a Quaternary-Late Pleistocene increase in the subduction rate of the Australian Plate beneath Erromango.

  14. The chronology for the d18O record from Devils Hole, Nevada, extended into the Mid-Holocene

    USGS Publications Warehouse

    Landwehr, J.M.; Sharp, W.D.; Coplen, T.B.; Ludwig, K. R.; Winograd, I.J.

    2011-01-01

    This report presents the numeric values for the chronology of the paleoclimatically relevant mid-to-late Pleistocene record of the ratios of stable oxygen isotope (delta18O) in vein calcite from Devils Hole, Nev., which recently had been extended into the mid-Holocene. Dating was obtained using 230Th-234U-238U thermal ionization mass spectrometry. Devils Hole is a subaqueous cave of tectonic origin, which developed in the discharge zone of a regional aquifer in south-central Nevada. The primary groundwater recharge source area is the Spring Mountains, the highest mountain range in southern Nevada [altitude 3,630 meters (m)], approximately 80 kilometers to the east of the cavern. The walls of the open fault zone comprising the cave system are coated with dense vein calcite precipitated from the through-flowing groundwater. The calcite, up to 40 centimeters (cm) thick, contains a continuous record of the sequential variation of the composition of stable oxygen isotopes in the ground water over time. The vein calcite has also proven to be a suitable material for precise uranium-series dating via thermal ionization mass spectrometry utilizing the 230Th-234U-238U decay clock. Earlier work has presented data from the Devils Hole core DH-11, a 36-cm-long core of vein calcite recovered from a depth of about 30 m below the water table (about 45 m beneath the ground surface). The DH-11 core provided a continuous record of isotopic oxygen variation from 567,700 to 59,800 years before present. Recent work has extended this record up to 4,500 years before present, into the mid-Holocene epoch.

  15. Radiogenic and Radioactive Isotopic Evidence for a Dynamic Residence Time of the Athabasca Glacier Subglacial Water

    NASA Astrophysics Data System (ADS)

    Arendt, C. A.; Aciego, S.; Sims, K. W.; Aarons, S. M.

    2011-12-01

    Little is known about the time it takes precipitation, input of water from reservoirs, surface melt, and basal melt to migrate to the base of a glacier and discharge. Previous work on the residence time of subglacial water has proven to be either inconclusive or inconsistent. Our research will address the primary subglacial water questions; the flux of subglacial water correlates directly to the mass balance of a glacier but what role does subglacial water storage play in that mass balance? Can we determine residence time of subglacial water? And, how variable is residence time seasonally and on longer time scales? The regional focus of our research is the Athabasca Glacier, part of the Columbia Icefield located in Jasper National Park, Alberta, Canada. Uranium-series (U-series) dating methods based on the ingrowth of daughter isotopes from parents (234U, 230Th and 222Rn from the primary parent 238U) have been used to study the residence time of aquifer systems. Here we show the feasibility of applying these techniques to subglacial water. Samples were collected over two 25-day field periods to account for hydrological and chemical fluctuations between the onset of melt and peak melt. Daily physical observations, 222Rn concentrations (from a Durridge RAD7), conductivity, total alkalinity, pH, maximum velocity, and discharge measurements were taken. Fifty daily 10-40L subglacial water and filtered sediment samples were collected and filtered at our collection site in the main channel at the toe of the Athabasca Glacier. The 238U /234U and 87Sr/86Sr isotopic compositions and U, Th, and Sr concentrations of the filtrate and captured sediments is pending. We will extrapolate the residence time of the water based on the accumulation of 234U and 230Th in our samples from alpha decay, which can be coupled to a radiometric timescale. Given that the 238U /234U and 234U/230Th isotopic composition of subglacial water is dependent on recoil and sediment dissolution processes

  16. Uranium and radium diffusion in organic-rich sediments (sapropels)

    NASA Astrophysics Data System (ADS)

    Gourgiotis, A.; Reyss, J.-L.; Frank, N.; Guihou, A.; Anagnostou, C.

    2011-09-01

    Among the late Quaternary Mediterranean sapropels, the S5 (125 ka) is one of the best preserved due to its high organic carbon content that has limited postdepositional oxidation. The high uranium content in this sapropel, >40 dpm g-1, makes this layer interesting for studying uranium series disequilibrium in organic-rich sediments. For this reason, the present work provides isotopic measurements of the U decay series in a S5 sapropel by applying more precise mass spectrometric methods, TIMS/MC-ICPMS, and gamma spectrometry. Assuming that U in the sapropel mostly originated from seawater the (234U/238U), (230Th/238U), (226Ra/230Th) and (231Pa/235U) activity ratios show systematic deviations from the theoretical values for a closed-system evolution of the U series over the 125 ka since sapropel formation. The radiogenic 234Urad and 226Ra show clear evidence of migration in the sapropel with modeled diffusion coefficients of (7.1 ± 1.1) × 10-12 cm2 s-1 and (1.6 ± 0.2) × 10-10 cm2 s-1, respectively. The diffusion of 234Urad cannot explain the high (230Th/238U) and (231Pa/235U) activity ratios observed in the sapropel. Two possible mechanisms or a combination of both are proposed for explaining the irregular (230Th/238U) and (231Pa/235U) activity profiles in sapropel S5. The first one is an enhanced export flux of 230Thxs and 231Paxs excesses exceeding the production rate in seawater, during the time of sapropel formation, and the second one is diffusion of authigenic Uauth in the sapropel. However, the ambiguous determination of 230Thxs and 231Paxs in the sapropel and the poorly understood processes that might lead to Uauth migration in anoxic sediments still limit a final explanation for the deviation of (230Th/238U) and (231Pa/235U) activity ratios from their expected theoretical values.

  17. Uranium-series dating of carbonate (tufa) deposits associated with quaternary fluctuations of Pyramid Lake, Nevada

    USGS Publications Warehouse

    Szabo, B. J.; Bush, C.A.; Benson, L.V.

    1996-01-01

    Uranium-series dating of dense tufa deposited in a small cave, at former lake margins, and in large tufa mounds clarifies the timing of lake-level variation during the past 400,000 yr in the Pyramid Lake basin. A moderate-sized lake occasionally overflowed the Emerson Pass sill at elevation of ???1207 m between ca. 400,000 and 170,000 and from ca. 60,000 to 20,000 yr B.P., as shown by 230Th/234U ages of the cave samples, 230Th-excess ages of tubular tufas, and average isochron-plot ages of shoreline-deposited tufas. (By comparison, modern Pyramid Lake is ???50 m below this sill). There is a lack of tufa record during the intervening period from ca. 170,000 to 60,000 yr B.P. After ca. 20,000 yr, Pyramid Lake underwent abrupt changes in level and, based on previous 14C ages, reached its highest elevation (ca 1335 m) at ca. 14,000 yr B.P. The youngest uranium-series ages are comparable with previously reported 14C ages. ?? 1996 University of Washington.

  18. Fixation of radionuclides in the 238U decay series in the vicinity of mineralized zones: 1. The Austatom Uranium Prospect, Northern Territory, Australia

    NASA Astrophysics Data System (ADS)

    Shirvington, P. J.

    1983-03-01

    The minimum age of a zone of secondary uranium mineralization, located at the Austatom Prospect in the Alligator Rivers region of Australia, is estimated to be 3.6 × 10 5y. This is derived from a geochronological model based on retarded leaching of 234U with respect to 238U and on ratios within the ore of these members of the 238U decay series. Although kaolinite is a dominant mineral in the weathered schist-host-rocks, retarded dissolution of 234U occurs only in the presence of the clay minerals illite and montmorillonite. In their absence the reverse occurs. A model is proposed to explain the results. Ratios of 230Th to 238U indicate that the mineralization has probably remained stationary within the weathered schist for at least 1 to 2 × 10 5y. Future use of clay minerals as buffers in radioactive waste repositories is supported by the excellent long-term retention obtained for oxidized uranium, probably due in part to isomorphic substitution into the clay crystal lattice.

  19. Using Uranium-series isotopes to understand processes of rapid soil formation in tropical volcanic settings: an example from Basse-Terre, French Guadeloupe

    NASA Astrophysics Data System (ADS)

    Ma, Lin

    2015-04-01

    Lin Ma1, Yvette Pereyra1, Peter B Sak2, Jerome Gaillardet3, Heather L Buss4 and Susan L Brantley5, (1) University of Texas at El Paso, El Paso, TX, United States, (2) Dickinson College, Carlisle, PA, United States, (3) Institute de Physique d Globe Paris, Paris, France, (4) University of Bristol, Bristol, United Kingdom, (5) Pennsylvania State University Main Campus, University Park, PA, United States Uranium-series isotopes fractionate during chemical weathering and their activity ratios can be used to determine timescales and rates of soil formation. Such soil formation rates provide important information to understand processes related to rapid soil formation in tropical volcanic settings, especially with respect to their fertility and erosion. Recent studies also highlighted the use of U-series isotopes to trace and quantify atmospheric inputs to surface soils. Such a process is particularly important in providing mineral nutrients to ecosystems in highly depleted soil systems such as the tropical soils. Here, we report U-series isotope compositions in thick soil profiles (>10 m) developed on andesitic pyroclastic flows in Basse-Terre Island of French Guadeloupe. Field observations have shown heterogeneity in color and texture in these thick profiles. However, major element chemistry and mineralogy show some general depth trends. The main minerals present throughout the soil profile are halloysite and gibbsite. Chemically immobile elements such as Al, Fe, and Ti show a depletion profile relative to Th while elements such as K, Mn, and Si show a partial depletion profile at depth. Mobile elements such as Ca, Mg, and Sr have undergone intensive weathering at depths, and an addition profile near the surface, most likely related to atmospheric inputs. (238U/232Th) activity ratios in one soil profile from the Brad David watershed in this study ranged from 0.374 to 1.696, while the (230Th/232Th) ratios ranged from 0.367 to 1.701. A decrease of (238U/232Th) in the

  20. Absolute calibration of the Greenland time scale: implications for Antarctic time scales and for Δ 14C

    NASA Astrophysics Data System (ADS)

    Shackleton, N. J.; Fairbanks, R. G.; Chiu, Tzu-chien; Parrenin, F.

    2004-07-01

    We propose a new age scale for the two ice cores (GRIP and GISP2) that were drilled at Greenland summit, based on accelerator mass spectrometry 14C dating of foraminifera in core MD95-2042 (Paleoceanography 15 (2000) 565), calibrated by means of recently obtained paired 14C and 230Th measurements on pristine corals (Marine radiocarbon calibration curve spanning 10,500 to 50,000 years BP (thousand years before present) Based on paired 230Th/ 234U/ 238U and 14C dates on Pristine Corals Geological Society of America Bulletin, 2003, submitted for publication). The record of core MD95-2042 can be correlated very precisely to the Greenland ice cores. Between 30 and 40 ka BP our scale is 1.4 ka older than the GRIP SS09sea time scale (Journal of Quaternary Science 16 (2001) 299). At the older end of Marine Isotope Stage 3 we use published 230Th dates from speleothems to calibrate the record. Using this scale we show a Δ 14C record that is broadly consistent with the modelled record (Earth Planet. Sci. Lett. 200 (2002) 177) and with the data of Hughen et al. (Science 303 (2004) 202), but not consistent with the high values obtained by Beck et al. (Science 292 (2001) 2453) or by Voelker et al. (Radiocarbon 40 (1998) 517). We show how a set of age scales for the Antarctic ice cores can be derived that are both fully consistent with the Greenland scale, and glaciologically reasonable.

  1. Fluxes of 238U decay series radionuclides in a dicalcium phosphate industrial plant.

    PubMed

    Casacuberta, N; Masqué, P; Garcia-Orellana, J

    2011-06-15

    The production of dicalcium phosphate (DCP) is part of the phosphate industry, which has been recently included in the positive list of the NORM industries defined in the revised version of the EU-BSS (Euratom 29/96). The objective of the present work is to study specific concentrations and fluxes of (238,234)U, (230)Th, (226)Ra, (210)Pb and (210)Po at the different stages of the DCP production. Results showed highest activities of (238)U and (210)Pb were found in DCP (1500-2000 Bq kg(-1)); (230)Th and (210)Po were released together with the sludges (1600-2000 Bq kg(-1)) and (226)Ra presented particularly high activities in water (48 × 10(3) Bq m(-3)) and in the reactor scales (115 × 10(3) Bq kg(-1)). Fluxes of radionuclides showed that (238)U outflows were equally distributed between sludges (16 × 10(3) kBq h(-1)) and dicalcium phosphate (20 × 10(3) kBq h(-1)); (230)Th and (210)Po were almost entirely released in the sludges (30 × 10(3)kBq h(-1)) and the greatest (210)Pb outflow was the DCP current (25 × 10(3) kBq h(-1)). (226)Ra was mainly discharged through the water effluent (12 × 10(3) kBq h(-1)). This work highlights the importance of studying the industrial processes involving NORM, as minor changes in the production steps lead to different radionuclide distribution in the process.

  2. Initial and Diagenetic Behaviour of U Isotopes in Corals: Implications for U-series Dating

    NASA Astrophysics Data System (ADS)

    Robinson, L. F.; Adkins, J. F.; Fernandez, D.; Burnett, D.; Gagnon, A.; Krakauer, N.; Wang, S.

    2005-12-01

    U-series isotopes in corals are one of the most powerful tools for chronometry in Quaternary Paleoceanography. Modern mass spectrometric techniques routinely reach 1 permil precision for the isotopic ratios of uranium and thorium. However, the corals themselves are often found to be open systems for U-series dating. The most widely used metric for diagenetic alteration of the age is the deviation of the δ234U ratio from the seawater value of 146‰. In this study we use deep-sea corals that live and are preserved in a constant seawater environment to investigate the causes of this diagenetic alteration. Coral thin-sections display complex visible banding patterns based on the crystal morphology. Fission track maps and MC-ICP-MS measurements performed on micro-milled sub-samples reveal a primary [U]-variability that has a spatial distribution closely related to the visible banding. Sub-samples from fossil corals, ranging in age from 11 ka to 218 ka, have variable δ234Uinitial with the highest δ234Uinitial values in areas of low [U]. A model shows that most of the variability can be explained by two simple processes, direct transfer of alpha recoil 230Th and 234Th and, more importantly, preferential movement of alpha-decay mobilised 234U. Coupling this preferential movement with a high [U] coating such as an organic film provides a source of 234U to the coral lattice that can account for large δ234Uinitial elevations, with little change to the final age. As surface corals also have large initial [U] gradients, our results demonstrate that many elevated δ234Uinitial values are a natural consequence of the coral's initial [U] gradient. These gradients are biologically induced at the time of calcification and are an example of how better understanding the effects of biomineralization can improve our interpretation of paleotracers.

  3. 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

  4. 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.

  5. Preliminary results of calculations for heavy-water nuclear-power-plant reactors employing {sup 235}U, {sup 233}U, and {sup 232}Th as a fuel and meeting requirements of a nonproliferation of nuclear weapons

    SciTech Connect

    Ioffe, B. L.; Kochurov, B. P.

    2012-02-15

    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 {sup 235}U. It operates in the open-cycle mode involving {sup 233}U 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.

  6. Computational simulation of (nat)UO2, (232)ThO2 and U3O8-Al pills to estimate (p,fission) (99)Mo yield in the modeled targets irradiated by CYCLONE30 accelerator.

    PubMed

    Jozvaziri, Atieh; Gholamzadeh, Zohreh; Yousefi, Kamran; Mirvakili, Seyed Mohammad; Alizadeh, Masoomeh; Aboudzadeh, Mohammadreza

    2017-03-01

    (99)Mo is important for both therapy and imaging purposes. Accelerator and reactor-based procedures are applied to produce it. Newly proton-fission method has been taken in attention by some research centers. In the present work, computationally investigation of the (99)Mo yield in different fissionable targets irradiated by proton was aimed. The results showed UO2 pill target could be efficiently used to produce 11.12Ci/g-U saturation yield of (99)Mo using 25MeV proton irradiation of the optimized-dimension target with 70µA current.

  7. Trace element and U-series systematics for 1963-1965 tephras from Irazú Volcano, Costa Rica: implications for magma generation processes and transit times

    NASA Astrophysics Data System (ADS)

    Clark, S. K.; Reagan, M. K.; Plank, T.

    1998-08-01

    In order to investigate fluid fluxing and the time-scales of magma genesis in the mantle below Costa Rica, basaltic andesites erupted in 1963-1965 from Irazú volcano were analyzed for major and trace element compositions as well as thorium isotope and 226Ra abundances. The 1963-65 eruption of Irazú produced two groups of tephras termed high-Ra, with ( 226Ra)/( 230Th) = 1.13-1.21 and low-Ra with near equilibrium ( 226Ra)/( 230Th) values. Low-Ra and high-Ra samples have similar overall compositions. For example, barium and HSF element concentrations are about the same in the two magma groups, and all tephras have ( 230Th)/( 232Th) ratios of about 1.20 and ( 238U)/( 230Th) ≅ 0.9. However, low-Ra samples have 6-16 % higher concentrations of many highly incompatible elements compared to high-Ra samples, whereas REE, Sr, and P 2O 5, concentrations are higher by about 3-8% in the high-Ra samples. These compositional differences can be explained by variations in the degree of melting and in the compositions of fluids involved in magma genesis. Low-Ra magmas were generated by dehydration partial melting of garnet-bearing mantle that had been enriched previously by a slab fluid. High-Ra magmas were generated by a similar mechanism, but involved an additional mantle-derived fluid. Trace element compositions of the high-Ra magmas suggest that this fluid was similar to a carbonatite. The temperature and pressures during melting were appropriate for carbonatite-silicate melt miscibility, and the carbonatitic fluid was consumed or partly consumed during melting. The lower concentrations of many highly incompatible trace elements in the high-Ra samples resulted from a higher degree of partial melting of its mantle source caused by fluid-silicate melt miscibility. The approximately equal HFS element and Ba concentrations in the low- and high-Ra samples, and the relatively high REE, Sr, and P 2O 5 concentrations in the high-Ra samples reflects the addition of these elements to

  8. Climatic and Tectonic Controls on Alluvial Fan Evolution: The Lost River Range, Idaho

    NASA Astrophysics Data System (ADS)

    Phillips, R. J.; Pierce, J. L.; Sharp, W. D.; Pierce, K. L.

    2006-12-01

    In the northern Basin &Range, alluvial fans developed along the Lost River range-front consist of several distinct inset fan segments with concave-up radial profiles. Multiple large radius (>5 km), shallow (2- 3°), alluvial fans extend across and beyond the active, ~140-km-long, normal Lost River fault. These large fans are relict features, formed by major sheetfloods that occurred intermittently between ~15-180 ka. More recent deposition has been dominated by debris-flows that form small-radius (<2 km), steep (8- 17°), fans closely confined to the mountain front [1,2]. In order to determine the timing of fan surface stabilization, we have undertaken precise mass spectrometric 230Th/U dating of pedogenic carbonate from calcic soils that mantle fan surfaces on the Arco fault segment. Careful selection of mg-size samples of dense soil carbonate pebble coats, from within a trench that cuts through gravelly fan deposits, indicates that the fan soils are geochemically suitable for uranium-series dating (median U=7ppm, 232Th=0.09ppm, 232Th/230Th=154). 230Th/U analysis of these calcic soils can thus provide precise temporal constraints on intervals of surface stability and subsequent soil formation. The oldest fan surface (Qfo1, 178+/-8 ka), exposed within the footwall of the trench, suggests an interval of surface stability, indicating that the fan was likely abandoned due to incision early in MIS 6. Incision may have resulted from surface faulting along the Arco segment of the Lost River fault, but could relate to changes in stream power or sediment supply associated with climatic change or with auto-cyclic variations within the drainage basin. A younger incised and faulted fan surface (Qfo2, 69+/-6 ka), likely represents active alluviation at the beginning of MIS 4 and, since it formed as hanging-wall alluvial gravel, provides age limits on an episode of fault displacement between Qfo1 and Qfo2. In situ pedogenic carbonate coats on sub-angular gravels within the

  9. Uranium-series disequilibria of inflated sections of the Juan de Fuca Ridge: Implications for mantle melting

    NASA Astrophysics Data System (ADS)

    Dreyer, B. M.; Gill, J. B.; Ramos, F. C.; Clague, D. A.; Scott, S. R.

    2010-12-01

    diversity in Endeavour basalts, Th/U variance is low, as in Axial basalts. However, there are differences in (230Th)/(232Th). Seventeen samples from Axial Seamount have (230Th)/(232Th) <1.22, the lowest on the JdFR axis. The range at Endeavour is 1.26-1.35, and highest in N-MORB. (230Th)-excesses [(230Th)/(238U) >1] are much higher at Endeavour (20-30%) than Axial Seamount (5-20%) and the rest of the JdFR (8-14%) but more similar to values of the adjacent Gorda Ridge to the south (up to ~25%). If differences in melt column characteristics (i.e., porosity, lithology, potential temperature) are similar along the JdFR, then ingrowth melt models predict slower upwelling of mantle-derived melts (e.g., longer residence time in the melt column) at Endeavour. Alternatively, Endeavour lavas may be generated from a more pyroxenitic (lherzolite) mantle where large degrees of disequilibria can be generated.

  10. Intakes of thorium while using thoriated tungsten electrodes for TIG welding.

    PubMed

    Ludwig, T; Schwass, D; Seitz, G; Siekmann, H

    1999-10-01

    Thoriated electrodes are used in TIG welding. TIG welders, along with persons who grind thoriated electrodes and persons located near relevant welding and grinding sites, might be at risk of thorium intake. The isotopes of radiological relevance are 232Th, 230Th, and 228Th. The studies described in the literature do not provide a consistent picture of the actual hazards, and changes in European and German radiological protection laws have now made it necessary to determine the risks. To accomplish this, a field test was conducted under real working conditions in 26 different welding shops. The airborne activity generated through welding, and through grinding of electrodes, was measured using personal air samplers. Stationary samplers were also used. The filters' samples were evaluated by means of direct alpha spectrometry with proportional counting and by means of gamma spectrometry following neutron activation. The results clearly showed that considerable intake can occur during both alternating-current welding and electrode grinding, if no suction systems are used. The range of 232Th intakes to welders were estimated from 0.1 Bq y(-1) to 144 Bq y(-1) during welding and from 0.02 Bq y(-1) to 30.2 Bq y(-1) during grinding. In 6 of the 26 cases the recent annual limit on intake derived from the most recent ICRP publications was exceeded--in the worst case it was exceeded by a factor of 10--if it is assumed that the persons studied were not exposed workers (not routinely monitored for radiation exposure). When the significantly more restrictive German limits are applied, the amounts by which the limits were exceeded were even greater. Because many qualified welders have very long careers, the risks can thus be considerable. The paper also discusses parameters that influence exposure, and it presents a catalogue of recommended measures for dosage reduction.

  11. Measurements of (234)U and (238)U in hair, urine, and drinking water among drilled bedrock well water users for the evaluation of hair as a biomonitor of uranium intake.

    PubMed

    Israelsson, Axel; Pettersson, Håkan

    2014-08-01

    Hair is evaluated and compared with urine as a biomonitor for human intake of uranium. Concentrations of U and U and the activity ratio between them are measured in the hair, urine, and drinking water of 24 drilled bedrock well water users in Östergötland, Sweden. The samples are measured with α-spectrometry after radiochemical preparation using liquid-liquid separation with tributylphosphate. The results show that there is a stronger correlation between the uranium concentrations in the drinking water of each subject and the hair of the subject (r = 0.50) than with the urine (r = 0.21). There is also a stronger correlation between the activity ratios of water and hair (r = 0.91) than between water and urine (r = 0.56). These results imply that hair may serve as a robust indicator of chronic uranium intake. One obvious advantage over sampling urine is that hair samples reflect a much longer excretion period: weeks compared to days. The absorbed fraction of uranium, the f value, is calculated as the ratio between the excreted amount of uranium in urine and hair per day and the daily drinking water intake of uranium. The f values stretch from 0.002 to 0.10 with a median of 0.023.

  12. Treatment methods and comparative risks of thorium removal from waste residues

    SciTech Connect

    Porter, R.D.; Hamby, D.M.; Martin, J.E.

    1997-07-01

    This study was done to examine the risks of remediation and the effectiveness of removal methods for thorium and its associated radioactive decay products from various soils and wastes associated with DOE`s Formerly Utilized Sites Remedial Action Program (FUSRAP). Removal of {sup 230}Th from uranium process residues would significantly reduce the buildup of {sup 226}Ra (half-life of 1600 years), and since {sup 230}Th concentrations at most of the important sites greatly exceed the {sup 226}Ra concentrations, such removal would reduce the accumulation of additional radiation risks associated with {sup 226}Ra and its products; and, if treatment also removed {sup 226}Ra, these risks could be mitigated even further. Removal of {sup 232}Th from thorium process residues would remove the source material for {sup 228}Ra, and since {sup 228}Ra has a half-life of 5.76 years, its control at FUSRAP sites could be done with land use controls for the 30--50 years required for {sup 228}Ra and the risks associated with its decay products to decay away. It must be recognized, however, that treatment methods invariably require workers to process residues and waste materials usually with bulk handling techniques. These processes expose workers to the radioactivity in the materials, therefore, workers would incur radiological risks in addition to industrial accident risks. An important question is whether the potential reduction of future radiological risks to members of the public justifies the risks that are incurred by remediation workers due to handling materials. This study examines, first, the effectiveness of treatment and then the risks that would be associated with remediation.

  13. Radionuclide concentrations in raw and purified phosphoric acids from Brazil and their processing wastes: implications for radiation exposures.

    PubMed

    da Conceição, Fabiano Tomazini; Antunes, Maria Lúcia Pereira; Durrant, Steven F

    2012-02-01

    Radionuclides from the U and Th natural series are present in alkaline rocks, which are used as feedstock in Brazil for the production of raw phosphoric acid, which can be considered as a NORM (naturally occurring radioactive material). As a result of the purification of raw phosphoric acid to food-grade phosphoric acid, two by-products are generated, i.e., solid and liquid wastes. Taking this into account, the main aim of this study was to evaluate the fluxes of natural radionuclide in the production of food-grade phosphoric acids in Brazil, to determine the radiological impact caused by ingestion of food-grade phosphoric acid, and to evaluate the solid waste environmental hazards caused by its application in crop soils. Radiological characterization of raw phosphoric acid, food-grade phosphoric acid, solid waste, and liquid waste was performed by alpha and gamma spectrometry. The (238)U, (234)U, (226)Ra, and (232)Th activity concentrations varied depending on the source of raw phosphoric acid. Decreasing radionuclides activity concentrations in raw phosphoric acids used by the producer of the purified phosphoric acid were observed as follows: Tapira (raw phosphoric acid D) > Catalão (raw phosphoric acids B and C) > Cajati (raw phosphoric acid A). The industrial purification process produces a reduction in radionuclide activity concentrations in food-grade phosphoric acid in relation to raw phosphoric acid produced in plant D and single raw phosphoric acid used in recent years. The most common use of food-grade phosphoric acid is in cola soft drinks, with an average consumption in Brazil of 72 l per person per year. Each liter of cola soft drink contains 0.5 ml of food-grade phosphoric acid, which gives an annual average intake of 36 ml of food-grade phosphoric acid per person. Under these conditions, radionuclide intake through consumption of food-grade phosphoric acid per year per person via cola soft drinks is not hazardous to human health in Brazil

  14. 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, 210

  15. Theoretical studies of {sup 238}U-{sup 230}Th-{sup 226}Ra and {sup 235}U-{sup 231}Pa disequilibria in young lavas produced by mantle melting

    SciTech Connect

    Zou, H.; Zindler, A.

    2000-05-01

    This paper provides ready-to-use equations to describe variations in uranium-series (U-series) disequilibrium as a function of elemental distribution coefficients, melting porosity, melting rate, and melting time. The effects of these melting parameters on U-series disequilibria are quantitatively evaluated in both an absolute and relative sense. The importance of net elemental fractionation and ingrowth of daughter nuclides are also described and compared in terms of their relative contributions to total U-series disequilibrium. In addition, the authors compare the production of U-series disequilibrium during mantle melting to trace element fractionations produced by melting in a similar context. Trace element fractionations depend externally on the degree to which a source is melted, whereas U-series disequilibrium depends upon both the degree and rate of melting. In contrast to previous models, their approach to modeling U-series disequilibrium during dynamic melting collapses simply to a description of trace element behavior during dynamic melting when the appropriate decay terms are omitted. Their formulation shows that extremely small degrees of melting, sometimes called upon to explain observed extents of U-series disequilibrium, are not always required.

  16. 210Pb and 210Po Abundances in Dacites Erupted May, 2003 From Anatahan Volcano: Implications for the Time-scales of Magma Generation and Degassing

    NASA Astrophysics Data System (ADS)

    Reagan, M. K.; Matthew, W.; Brian, H.

    2003-12-01

    Six samples of dacite pumice and scoria erupted in May, 2003 and collected from a number of sites around Anathan by Tobias Fischer and David Hilton were analyzed for 210Po activities on three occasions between early June and the time of this writing. With two exceptions, all scoria and pumice samples have 210Po activities that plot on a single growth curve indicating initial (210Po)=0.15 +/-0.07 (1σ ) dpm/g and (210Pb)=1.08+/-0.20 dpm/g. More precise values for these initial activities will be presented at the meeting after further analyses are performed in November. Preliminary alpha spectrometry analyses for U and Th, and ICPMS analyses distributed by Terry Plank suggest that the average (238U) is about 0.53 dpm/g. Equilibrium (228Th)/( 232Th) ratios indicate that these samples do not have excess 228Ra. Assuming that (210Pb )< (226Ra) because of minor degassing of 210Pb (see Gauthier and Condomines, 1999, EPSL, v. 172), the degassing efficiency factor for 210Po is greater than or equal to about 0.85, which is identical to the value calculated for a basaltic andesitic lava from Arenal volcano in Costa Rica (Gill et al., 1985, GRL, v. 12). This is surprising, as the May 10 plinian eruption of Anatahan should have resulted in more closed-system degassing than a lava eruption. This and the similar 210Po values for the scoria and pumice samples suggest that the shallow-level degassing history has little impact on the efficiency of polonium degassing. The scoria and pumice samples from sample 8-1e both have significant excesses of 210Po over the calculated initial (210Pb) value for the other samples. These excesses were partially leachable, indicating that 210Po was sublimated onto these samples, and that these ejecta resided in the vent before being ejected and redeposited The high inferred (226Ra)/( 230Th) for the Anatahan dacites despite the nearly equilibrium (238U)/( 230Th) value measured for one sample contrasts with the values for these ratios in more mafic

  17. Subalkaline andesite from Valu Fa Ridge, a back-arc spreading center in southern Lau Basin: petrogenesis, comparative chemistry, and tectonic implications

    USGS Publications Warehouse

    Vallier, T.L.; Jenner, G.A.; Frey, F.A.; Gill, J.B.; Davis, A.S.; Volpe, A.M.; Hawkins, J.W.; Morris, J.D.; Cawood, Peter A.; Morton, J.L.; Scholl, D. W.; Rautenschlein, M.; White, W.M.; Williams, Ross W.; Stevenson, A.J.; White, L.D.

    1991-01-01

    Tholeiitic andesite was dredged from two sites on Valu Fa Ridge (VFR), a back-arc spreading center in Lau Basin. Valu Fa Ridge, at least 200 km long, is located 40-50 km west of the active Tofua Volcanic Arc (TVA) axis and lies about 150 km above the subducted oceanic plate. One or more magma chambers, traced discontinuously for about 100 km along the ridge axis, lie 3-4 km beneath the ridge. The mostly aphyric and glassy lavas had high volatile contents, as shown by the abundance and large sizes of vesicles. An extensive fractionation history is inferred from the high SiO2 contents and FeO* MgO ratios. Chemical data show that the VFR lavas have both volcanic arc and back-arc basin affinities. The volcanic arc characteristics are: (1) relatively high abundances of most alkali and alkaline earth elements; (2) low abundances of high field strength elements Nb and Ta; (3) high U/Th ratios; (4) similar radiogenic isotope ratios in VFR and TVA lavas, in particular the enrichment of 87Sr 86Sr relative to 206Pb 204Pb; (5) high 238U 230Th, 230Th 232Th, and 226Ra 230Th activity ratios; and (6) high ratios of Rb/Cs, Ba/Nb, and Ba/La. Other chemical characteristics suggest that the VFR lavas are related to MORB-type back-arc basin lavas. For example, VFR lavas have (1) lower 87Sr 86Sr ratios and higher 143Nd 144Nd ratios than most lavas from the TVA, except samples from Ata Island, and are similar to many Lau Basin lavas; (2) lower Sr/REE, Rb/Zr, and Ba/Zr ratios than in arc lavas; and (3) higher Ti, Fe, and V, and higher Ti/V ratios than arc lavas generally and TVA lavas specifically. Most characteristics of VFR lavas can be explained by mixing depleted mantle with either small amounts of sediment and fluids from the subducting slab and/or an older fragment of volcanic arc lithosphere. The eruption of subalkaline andesite with some arc affinities along a back-arc spreading ridge is not unique. Collision of the Louisville and Tonga ridges probably activated back-arc extension

  18. 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.

  19. Radioactivity contents in dicalcium phosphate and the potential radiological risk to human populations.

    PubMed

    Casacuberta, N; Masqué, P; Garcia-Orellana, J; Bruach, J M; Anguita, M; Gasa, J; Villa, M; Hurtado, S; Garcia-Tenorio, R

    2009-10-30

    Potentially harmful phosphate-based products derived from the wet acid digestion of phosphate rock represent one of the most serious problems facing the phosphate industry. This is particularly true for dicalcium phosphate (DCP), a food additive produced from either sulphuric acid or hydrochloric acid digestion of raw rock material. This study determined the natural occurring radionuclide concentrations of 12 DCP samples and 4 tricalcium phosphate (TCP) samples used for animal and human consumption, respectively. Metal concentrations (Al, Fe, Zn, Cd, Cr, As, Hg, Pb and Mg) were also determined. Samples were grouped into three different clusters (A, B, C) based on their radionuclide content. Whereas group A is characterized by high activities of 238U, 234U (approximately 10(3) Bq kg(-1)), 210Pb (2 x 10(3) Bq kg(-1)) and (210)Po ( approximately 800 Bq kg(-1)); group B presents high activities of (238)U, (234)U and (230)Th (approximately 10(3) Bq kg(-1)). Group C was characterized by very low activities of all radionuclides (< 50 Bq kg(-1)). Differences between the two groups of DCP samples for animal consumption (groups A and B) were related to the wet acid digestion method used, with group A samples produced from hydrochloric acid digestion, and group B samples produced using sulphuric acid. Group C includes more purified samples required for human consumption. High radionuclide concentrations in some DCP samples (reaching 2 x 10(3) and 10(3) Bq kg(-1) of 210Pb and 210Po, respectively) may be of concern due to direct or indirect radiological exposure via ingestion. Our experimental results based on 210Pb and 210Po within poultry consumed by humans, suggest that the maximum radiological doses are 11 +/- 2 microSv y(-1). While these results suggest that human health risks are small, additional testing should be conducted.

  20. 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.

  1. Estimation of ground water residence times in the Critical zone: insight from U activity ratios

    NASA Astrophysics Data System (ADS)

    Chabaux, Francois; Ackerer, Julien; Lucas, Yann; viville, Daniel

    2016-04-01

    The use of radioactive disequilibria as tracers and chronometers of weathering processes and related mass transfers has been recognized since the 60'. The development, over the last two decades, of analytical methods for measuring very precisely U-series nuclides (especially, 234U, 230Th and 226Ra) in environmental samples has opened up new scientific applications in Earth Surface Sciences. Here, we propose to present the potential of U activity ratios in surface waters as chronometer of water transfers at a watershed scale. This will be illustrated from studies performed at different scales, with the analysis of U activity ratios in surface waters from small watersheds (Strengbach and Ringelbach watersheds in the Vosges Mountain, France) but also from watersheds of much more regional extension (e.g., the Upper Rhine basin or the Ganges basin). These various studies show that variations of U activity ratios in surface waters are mainly associated with 234U-238U fractionations occurring during the water transfer within the bedrock, which intensity depends on two main parameters: the petro-physical characteristics of the aquifer, principally the geometry of water-rock interfaces and the duration of the water-rock interactions. This readily explains why different U activity ratios (UAR) can be observed in the different aquifers of a continental hydrosystem and hence why UAR can be used to trace the source of river waters. For a hydrological system developed on a substratum marked by fairly homogeneous petro-physical characteristics, the main parameter controlling the UAR in waters draining such a system would be the duration of the water-rock interactions. Variations of UAR in stream or spring waters of such a system can therefore be modeled using simple reactive transport model, which allows the estimation of both the dissolution rate of the bedrock and the residence time of the waters within the aquifer.

  2. U Pb dating of fossil enamel from the Swartkrans Pleistocene hominid site, South Africa

    NASA Astrophysics Data System (ADS)

    Balter, Vincent; Blichert-Toft, Janne; Braga, José; Telouk, Philippe; Thackeray, Francis; Albarède, Francis

    2008-03-01

    We demonstrate that young fossil enamel older than the range of the U-series (˜ 300 ka) can be dated by the U-Pb methods using new models of U and Pb loss and uptake. Contrary to the current hypothesis of U uptake that only considers the adsorption/diffusion mechanism, we here develop a complete time-dependent model which takes gains and losses of the most critical nuclides (238U, 234U, and 230Th) into account, both during chemical (dissolved U) and physical (Th and U α-recoil) processes. Lead is assumed to be a mixture between two components of common Pb and a radiogenic component; the proportions of these components are calculated from the Pb isotope abundances and U/Pb ratios. We apply this new U-Pb method to bovid enamel from the Swartkrans Cave (Gauteng Province, South Africa). This cave has yielded abundant early Pleistocene hominid remains attributed to Paranthropus and Homo as well as various associated archaeological vestiges. Biochronological comparisons with East Africa have provided age estimates ranging between 1.8 and 1.0 Ma, which, however, remain poorly constrained. After correction for initial 234U disequilibrium and further 238U loss, the U and Pb isotope data yield ages of 1.83 ± 1.38, 1.36 ± 0.29, and 0.83 ± 0.21 Ma for the three stratigraphic units, Members 1, 2, and 3, respectively. We discuss the consequences of these radiometric results for hominid evolution in South Africa.

  3. [Evaluation of the partial contribution of naturally occurring radionuclides and nonradioactive chemically toxic elements in formation of biological effects within the Vicia cracca population inhabiting the area contaminated with uranium-radium production wastes in the Komi Republic].

    PubMed

    Evseeva, T I; Geras'kin, S A; Vakhrusheva, O M

    2014-01-01

    The site contaminated with uranium-radium production wastes in the Komi Republic was studied. The activity concentration of naturally occurring radionuclides (226Ra, 228Th, 238U, 230Th, 232Th, 210Po, and 210Pb), as well as concentrations of nonradioactive chemically toxic elements (Pb, Zn, Cu, As, V, Mo, Sr, Y, and Ba) in the soil samples from the experimental site is 10-183 times higher than reference levels. A chronic exposure to alpha-emitters and nonradioactive chemically toxic elements causes adverse effects in tufted vetch (Vacia cracca L.) both at the cellular (aberration of chromosomes) and population (decrease in the reproductive ability) levels. Radionuclides are the main contributors to the decrease in the reproductive capacity and an increase in the level of the cytogenetic damage in root tip cells of tufted vetch seedlings. As and Pb significantly influence the reproductive capacity of plants. Sr, Zn, Y and P modify the biological effects caused by exposure to radionuclides. Moreover, P and Zn reduce the adverse effects of radionuclides; however, Sr and Y enhance these effects.

  4. 226Ra and other radionuclides in water, vegetation, and tissues of beavers (Castor canadensis) from a watershed containing U tailings near Elliot Lake, Canada.

    PubMed

    Clulow, F V; Mirka, M A; Davé, N K; Lim, T P

    1991-01-01

    Radionuclide levels were measured in tissues, gut contents, diet items, and water at site of capture, of adult beavers from the Serpent River drainage basin which contains U tailings at Elliot Lake, Ontario, and from nearby control sites. Levels of (226)Ra in beaver bone, muscle and kidney were highest in animals from locations close to U tailings; liver levels did not vary by site. Environmental (226)Ra levels were within ranges previously reported at these or similar locations elsewhere; levels in beaver gut contents reflected levels in diet items. Concentration ratios exceeded unity only between some vegetation items and beaver bone at the Elliot Lake site and were less than 0.19 between vegetation and other tissues. In two beavers with tissue levels of (226)Ra higher than other sampled, neither (232)Th nor (230)Th were detected in bone, muscle or liver tissues. U-238 was measurable in bone, muscle and liver, (228)Th in bone, (210)Po bone, muscle and liver; and (210)Pb was measurable only in bone. Estimated yearly intakes of radionuclides by people eating beavers were calculated to be below current allowable levels set by the Canadian regulatory authorities.

  5. Studies of transport pathways of Th, rare earths, Ra-228, and Ra-226 from soil to plants and farm animals. Progress report, April 1, 1985-February 28, 1986

    SciTech Connect

    Linsalata, P.

    1986-02-01

    The field study is to assess the soil-to-plant and soil-to-animal concentration factors of the naturally occurring radionuclides /sup 226/Ra, /sup 228/Ra, /sup 232/Th, /sup 230/Th, and /sup 228/Th, as well as of the light rare earth elements (REE), La, Ce and Nd. Farms situated near the center of a deeply weathered alkalic intrusive known as the Pocos de Caldas (PC) plateau were selected for study because of their proximity (i.e., within a few kilometers) to what may be the largest single near-surface deposit of Th (approx.30,000 tonnes) and REE's (>100,000 tonnes) situated near the summit of a hill (the Morro do Ferro (MF)). An ancillary field study is being conducted in Orange County, New York, where a local cattleman has permitted sampling members of the herd as well as soil and feeds which are all grown on the premises. Vegetable samples and soil have also been analyzed from five additional farms in Orange County, NY. 64 refs., 25 figs., 45 tabs.

  6. The Fission Programme at the CERN n_TOF Facility

    NASA Astrophysics Data System (ADS)

    Tsinganis, A.; Barbagallo, M.; Berthoumieux, E.; Calviani, M.; Chiaveri, E.; Colonna, N.; Diakaki, M.; Duran, I.; Guerrero, C.; Gunsing, F.; Leal-Cidoncha, E.; Leong, L.-S.; Paradela, C.; Tarrio, D.; Tassan-Got, L.; Vlastou, R.

    Since 2001, the scientific programme of the CERN n_TOF facility has focused mainly on the study of radiative neutron capture reactions, which are of great interest to nuclear astrophysics and on neutron-induced fission reactions, which are of relevance for nuclear technology, as well as essential for the development of theoretical models of fission. In particular, taking advantage of the high instantaneous neutron flux and high energy resolution of the facility, as well as of high-performance detection and acquisition systems, accurate new measurements on several long-lived major and minor actinides, from 232Th to 245Cm, have been performed so far. Data on these isotopes are needed in order to improve the safety and efficiency of conventional reactors, as well as to develop new systems for nuclear energy production and treatment of nuclear waste, such as Generation IV reactors, Accelerator Driven Systems and reactors based on innovative fuel cycles. A review of the most important results on fission cross-sections and fragment properties obtained at n_TOF for a variety of (radioactive) isotopes is presented along with the perspectives arising from the coming on line in the second half of 2014 of a new 19 m flight-path, which will allow n_TOF to expand its measurement capabilities to even more rare or short-lived isotopes, such as 230Th, 232U, 238,240Pu and 244Cm.

  7. [Radiation risk assessment for plant reference species (Pinus sylvestris and Vicia cracca) from the area of radium production waste storage].

    PubMed

    Evseeva, T I; Geras'kin, S A; Belykh, E S; Maĭstrenko, T A; Vakhrusheva, O M

    2012-01-01

    The risk of an enhanced level of radionuclides of the uranium and thorium decay series in the environment for reference plant species (Pinus sylvestris and Vicia cracca) was assessed. 238U, 230Th, 226Ra, 210Po, 232Th and 228Th concentration factors for plants were found to be lower than one. The aboveground parts of Vicia cracca sampled from the area of the radium production waste storage mainly accumulated 22Ra, Pinus sylvestris branches--210Pb, 226Ra and 210Po. LOEDR calculated for the chromosome aberration frequency in both plant studies was 17-71 microGy/h. LOERD values for the reproductive capacity decrease in P. sylvestris and V. cracca were 17-71 microGy/h and 116-258 microGy/h, correspondingly. EDR10 for the chromosome aberration frequency in P. sylvestris and V. cracca were 148 and 347 microGy/h, that is, correspondingly, 255 and 708 times higher that background values. EDR10 for the plant reproductive capacity was 11-34 microGy/h, which 19-69 times increases the background values.

  8. Coupling of Uranium and Thorium Series Isotope Systematics for Age Determination of Late Pleistocene Zircons using LA-ICP-MS

    NASA Astrophysics Data System (ADS)

    Sakata, S.; Hirakawa, S.; Iwano, H.; Danhara, T.; Hirata, T.

    2014-12-01

    Zircon U-Th-Pb dating method is one of the most important tools for estimating the duration of magmatism by means of coupling of uranium, actinium and thorium decay series. Using U-Pb dating method, its reliability is principally guaranteed by the concordance between 238U-206Pb and 235U-207Pb ages. In case of dating Quaternary zircons, however, the initial disequilibrium effect on 230Th and 231Pa should be considered. On the other hands, 232Th-208Pb dating method can be a simple but powerful approach for investigating the age of crystallization because of negligible influence from initial disequilibrium effect. We have developed a new correction model for accurate U-Pb dating of the young zircon samples by taking into consideration of initial disequilibrium and a U-Pb vs Th-Pb concordia diagram for reliable age calibration was successfully established. Hence, the U-Th-Pb dating method can be applied to various zircons ranging from Hadean (4,600 Ma) to Quaternary (~50 ka) ages, and this suggests that further detailed information concerning the thermal history of the geological sequences can be made by the coupling of U-Th-Pb, fission track and Ar-Ar ages. In this presentation, we will show an example of U-Th-Pb dating for zircon samples from Sambe Volcano (3 to 100 ka), southwest Japan and the present dating technique using LA-ICP-MS.

  9. U&z.sbnd;Th isotopic systematics at 13°N east Pacific Ridge segment

    NASA Astrophysics Data System (ADS)

    Ben Othman, D.; Allègre, C. J.

    Fresh basaltic glasses have been analyzed for U&z.sbnd;Th disequilibrium systematics as part of an extensive study on the East Pacific Rise (EPR) at 12°45'N. These samples are well described in terms of major and trace elements as well as in Nd, Pb and Sr isotopes. Our results show significant heterogeneities in the mantle source at a small scale, and show heterogeneities at larger scales also when compared to other EPR data. U and Th concentration and isotopic data rule out fractional crystallization as a main process and support a mixing model in agreement with the marble cake model developed by Alle`gre and Turcotte and constrained by trace elements and Nd, Sr and Pb isotopes on the same samples by Prinzhofer et al. Based on the high ( 230Th/ 232Th ) isotopic ratios on recent tholeiites especially the Th/U values inferred for their sources clearly show that the upper mantle Th/U has decreased with time.

  10. Depositional behaviors of plutonium and thorium isotopes at Tsukuba and Mt. Haruna in Japan indicate the sources of atmospheric dust.

    PubMed

    Hirose, K; Igarashi, Y; Aoyama, M; Inomata, Y

    2010-02-01

    Monthly plutonium and thorium depositions at Tsukuba (28m asl) and Mt. Haruna (1370m asl) were measured during 2006 and 2007 (Jan 2006-Dec 2007 at Tsukuba, Nov 2006-Dec 2007 at Mt. Haruna). The monthly (239,240)Pu depositions ranged from 0.044 to 2.67mBq m(-2) at Tsukuba and from 0.05 to 0.9mBq m(-2) at Mt. Haruna during the measurement periods. Monthly (239,240)Pu deposition did not differ markedly between the two sites except in April 2007. Seasonal pattern of monthly (239,240)Pu depositions at both sites showed high in spring and low in summer, and typical of seasonal variations in northeastern Asia. Thorium deposition at Tsukuba was higher than that at Mt. Haruna except in May and June 2007. (230)Th/(232)Th activity ratios were used to partition deposition samples into locally and remotely derived fractions. The results revealed that a major proportion of total (239,240)Pu and Th deposits are derived from remote sources, especially in spring.

  11. Health Effects Due to Radionuclides Content of Solid Minerals within Port of Richards Bay, South Africa

    PubMed Central

    Masok, Felix B.; Masiteng, Paulus L.; Mavunda, Risimati D.; Maleka, Peane P.

    2016-01-01

    This study assessed the radiological health hazards to various body organs of workers working within Transnet Precinct in Richards Bay in Kwazulu-Natal, South Africa due to radionuclide content of mineral ores often stored within the facility. Thirty samples were collected from five mineral ores (rock phosphate, rutile, zircon, coal and hematite) and analyzed for 238U, 234U, 226Ra, 210Pb, 235U, 232Th, 228Ra, 228Th and 40K using delayed neutron activation analysis and low energy gamma spectroscopy. Rutile was found to be the most radioactive mineral ore within the facility with 210Pb concentration of 759.00 ± 106.00 Bq·kg−1. Effective annual dose rate in (mSv·y−1) delivered to different organs of the body: testes, bone marrow, whole body, lungs and ovaries from mineral ores were such that dose from mineral ores decreased in the order coal > rutile > rock phosphate > hematite > zircon. The organs with the highest received dose rate were the testes and this received dose was from coal. However, all of the calculated absorbed dose rates to organs of the body were below the maximum permissible safety limits. PMID:27898013

  12. Modern U-Pb chronometry of meteorites: advancing to higher time resolution reveals new problems

    USGS Publications Warehouse

    Amelin, Y.; Connelly, J.; Zartman, R.E.; Chen, J.-H.; Gopel, C.; Neymark, L.A.

    2009-01-01

    In this paper, we evaluate the factors that influence the accuracy of lead (Pb)-isotopic ages of meteorites, and may possibly be responsible for inconsistencies between Pb-isotopic and extinct nuclide timescales of the early Solar System: instrumental mass fractionation and other possible analytical sources of error, presence of more than one component of non-radiogenic Pb, migration of ancient radiogenic Pb by diffusion and other mechanisms, possible heterogeneity of the isotopic composition of uranium (U), uncertainties in the decay constants of uranium isotopes, possible presence of "freshly synthesized" actinides with short half-life (e.g. 234U) in the early Solar System, possible initial disequilibrium in the uranium decay chains, and potential fractionation of radiogenic Pb isotopes and U isotopes caused by alpha-recoil and subsequent laboratory treatment. We review the use of 232Th/238U values to assist in making accurate interpretations of the U-Pb ages of meteorite components. We discuss recently published U-Pb dates of calcium-aluminum-rich inclusions (CAIs), and their apparent disagreement with the extinct nuclide dates, in the context of capability and common pitfalls in modern meteorite chronology. Finally, we discuss the requirements of meteorites that are intended to be used as the reference points in building a consistent time scale of the early Solar System, based on the combined use of the U-Pb system and extinct nuclide chronometers.

  13. Uranium, plutonium, and thorium isotopes in the atmosphere and the lithosphere

    SciTech Connect

    Essien, I.O.

    1983-01-01

    Concentration of /sup 238/U in rain and snow collected at Fayetteville (36/sup 0/N, 94/sup 0/W), Arkansas, showed a marked increase during the summer months of 1980, while Mount St. Helens remained active. This observed increase of /sup 238/U can be explained as due to the fallout of natural uranium from the eruption of Mount St. Helens. Large increases in the concentration of thorium isotopes detected in rain and snow samples during the last months of 1982 and early months of 1983 probably originated from the eruption of El Chichon volcano, which occurred on 28 March 1982. About 450 Ci of /sup 232/Th is estimated to have been injected into the atmosphere by this eruption. Isotopic anomalies were observed in atmospheric samples such as rain and snow. These anomalies can be attributed to various natural as well as man-made sources: nuclear weapon tests, nuclear accidents involving the burn-up of nuclear powered satellites, and volcanic eruptions. The variation of /sup 234/U//sup 238/U ratios in radioactive minerals when leached with nitric acid were also noticed and this variation, while /sup 235/U//sup 238/U remained fairly constant, can be explained in terms of the ..cap alpha..-recoil effect and changes in oxidation state of uranium. Difference found in /sup 239/Pu//sup 238/U ratios in terrestrial samples and uranium minerals can be explained as due to fallout contamination.

  14. Sr-Nd and Uranium-series isotopic constraints on weathering and erosion using suspended and overbank river sediments from recent floodwaters in Australia

    NASA Astrophysics Data System (ADS)

    Turner, S.; Handley, H. K.; Dosseto, A.; Schaefer, B.; Turner, M. B.

    2011-12-01

    Suspended sediments carried by high magnitude floodwaters within major river catchments provide a representative sample of the lithological and chemical variety of the Earth's surface and permit estimation of the average geochemical and isotopic composition of the Earth's upper crust. Uranium-series disequilibria in suspended sediments and their deposits can also be used to constrain the timescales of sediment residence within major catchments. New trace element, Sr-Nd radiogenic isotope and Uranium-series isotope data are presented for suspended particulate river sediments and overbank sediment deposits collected from the Cooper Creek and Darling River during the 2009 and 2010 widespread flooding events in Australia. A mud drape deposited by waning floodwater after a localised and rare (average recurrence interval between 200-500 years) 2007 flood event at Hookina Creek, South Australia was also analysed. PAAS normalised rare earth element (REE) distribution patterns for all samples are generally flat, but show a slight enrichment in the mid- to heavy-REEs relative to light-REEs and a positive Eu anomaly. The Darling River and Hookina Creek samples contain higher overall abundances of trace elements compared to the Cooper Creek samples. The Sr-Nd isotope data form a negative linear array. The Cooper Creek samples display the highest ɛNd values (-2.1 to 3.5) and lowest 87Sr/86Sr isotopic ratios (0.707506-0.707907). The Hookina Creek sample displays a significantly lower ɛNd value and higher 87Sr/86Sr isotopic ratio (more similar to average upper continental crust). These differences are attributed to variations in the composition and age of source rocks. U concentrations (ppm) range from 0.32-0.95 in the Cooper Creek samples, 1.32-2.31 in the Darling river sediments and 2.73 was measured in the Hookina Creek sample. All sediments show the expected activity ratio pattern (for residual products of weathering) of (234U/238U) < 1 and (230Th/234U) >1, apart from an

  15. D/H ratios in speleothem fluid inclusions: A guide to variations in the isotopic composition of meteoric precipitation?

    USGS Publications Warehouse

    Harmon, R.S.; Schwarcz, H.P.; O'Neil, J.R.

    1979-01-01

    D/H ratios of fluid inclusion waters extracted from 230Th/234U-dated speleothems that were originally deposited under conditions of isotopic equilibrium should provide a direct estimate of the hydrogen isotopic composition of ancient meteoric waters. We present here D/H ratios for 47 fluid inclusion samples from thirteen speleothems deposited over the past 250,000 years at cave sites in Iowa, West Virginia, Kentucky and Missouri. At each site glacial-age waters are depleted in deuterium relative to those of interglacial age. The average interglacial/glacial shift in the hydrogen isotopic composition of meteoric precipitation over ice-free areas of east-central North America is estimated to be -12???. This shift is consistent with the present climatic models and can be explained in terms of the prevailing pattern of atmospheric circulation and an increased ocean-continent temperature gradient during glacial times which more than compensated for the increase in deuterium content of the world ocean. ?? 1979.

  16. Radiochronological Age of a Uranium Metal Sample from an Abandoned Facility

    SciTech Connect

    Meyers, L A; Williams, R W; Glover, S E; LaMont, S P; Stalcup, A M; Spitz, H B

    2012-03-16

    A piece of scrap uranium metal bar buried in the dirt floor of an old, abandoned metal rolling mill was analyzed using multi-collector inductively coupled plasma mass spectroscopy (MC-ICP-MS). The mill rolled uranium rods in the 1940s and 1950s. Samples of the contaminated dirt in which the bar was buried were also analyzed. The isotopic composition of uranium in the bar and dirt samples were both the same as natural uranium, though a few samples of dirt also contained recycled uranium; likely a result of contamination with other material rolled at the mill. The time elapsed since the uranium metal bar was last purified can be determined by the in-growth of the isotope {sup 230}Th from the decay of {sup 234}U, assuming that only uranium isotopes were present in the bar after purification. The age of the metal bar was determined to be 61 years at the time of this analysis and corresponds to a purification date of July 1950 {+-} 1.5 years.

  17. Evidence from U-Th dating against Northern Hemisphere forcing of the penultimate deglaciation

    PubMed

    Henderson; Slowey

    2000-03-02

    Milankovitch proposed that summer insolation at mid-latitudes in the Northern Hemisphere directly causes the ice-age climate cycles. This would imply that times of ice-sheet collapse should correspond to peaks in Northern Hemisphere June insolation. But the penultimate deglaciation has proved controversial because June insolation peaks 127 kyr ago whereas several records of past climate suggest that change may have occurred up to 15 kyr earlier. There is a clear signature of the penultimate deglaciation in marine oxygen-isotope records. But dating this event, which is significantly before the 14C age range, has not been possible. Here we date the penultimate deglaciation in a record from the Bahamas using a new U-Th isochron technique. After the necessary corrections for alpha-recoil mobility of 234U and 230Th and a small age correction for sediment mixing, the midpoint age for the penultimate deglaciation is determined to be 135 +/- 2.5 kyr ago. This age is consistent with some coral-based sea-level estimates, but it is difficult to reconcile with June Northern Hemisphere insolation as the trigger for the ice-age cycles. Potential alternative driving mechanisms for the ice-age cycles that are consistent with such an early date for the penultimate deglaciation are either the variability of the tropical ocean-atmosphere system or changes in atmospheric CO2 concentration controlled by a process in the Southern Hemisphere.

  18. On the limits of using combined U-series/ESR method to date fossil teeth from two Early Pleistocene archaeological sites of the Orce area (Guadix-Baza basin, Spain)

    NASA Astrophysics Data System (ADS)

    Duval, Mathieu; Falguères, Christophe; Bahain, Jean-Jacques; Grün, Rainer; Shao, Qingfeng; Aubert, Maxime; Dolo, Jean-Michel; Agustí, Jordi; Martínez-Navarro, Bienvenido; Palmqvist, Paul; Toro-Moyano, Isidro

    2012-05-01

    The combined U-series/electron spin resonance (ESR) dating method was applied to nine teeth from two Early Pleistocene archaeological sites located in the Orce area (Guadix-Baza Basin, Southern Spain): Fuente Nueva-3 (FN-3) and Barranco León (BL). The combination of biostratigraphy and magnetostratigraphy places both sites between the Olduvai and Jaramillo subchrons (1.78-1.07 Ma). Our results highlight the difficulty of dating such old sites and point out the limits of the combined U-series/ESR dating method based on the US model. We identified several sources of uncertainties that may lead to inaccurate age estimates. Seven samples could not be dated because the dental tissues had (230Th/234U) activity ratios higher than equilibrium, indicating that uranium had probably leached from these tissues. It was however possible to calculate numerical estimates for two of the teeth, both from FN-3. One yielded a Middle Pleistocene age that seems to be strongly underestimated; the other provided an age of 1.19 ± 0.21 Ma, in agreement with data obtained from independent methods. The latter result gives encouragement that there are samples that can be used for routine dating of old sites.

  19. AIR AND RADON PATHWAY MODELING FOR THE F AREA TANK FARM

    SciTech Connect

    Dixon, K.; Phifer, M.

    2010-07-30

    An air and radon pathways analysis was conducted for the F-Area Tank Farm (FTF) to estimate the flux of volatile radionuclides and radon at the ground surface due to residual waste remaining in the tanks following closure. This analysis was used as the basis to estimate the dose to the maximally exposed individual (MEI) for the air pathway per Curie (Ci) of each radionuclide remaining in the combined FTF waste tanks. For the air pathway analysis, several gaseous radionuclides were considered. These included carbon-14 (C-14), chlorine-36 (Cl-36), iodine-129 (I-129), selenium-79 (Se-79), antimony-125 (Sb-125), tin-126 (Sn-126), tritium (H-3), and technetium-99 (Tc-99). The dose to the MEI was estimated at the SRS Boundary during the 100 year institutional control period. For the 10,000 year post closure compliance period, the dose to the MEI was estimated at the 100 m compliance point. Additionally, the dose to the MEI was estimated at a seepage outcrop located 1600 m from the facility. For the radon pathway analysis, five parent radionuclides and their progeny were analyzed. These parent radionuclides included uranium-238 (U-238), plutonium-238 (Pu-238), uranium-234 (U-234), thorium-230 (Th-230), and radium-226 (Ra-226). The peak flux of radon-222 due to each parent radionuclide was estimated for the simulation period of 10,100 years.

  20. Status report on the geology of the Lawrence Livermore National Laboratory site and adjacent areas. Volume I. Text and appendices A-E

    SciTech Connect

    Carpenter, D.W.; Puchlik, K.P.; Ramirez, A.L.; Wagoner, J.L.; Knauss, K.G.; Kasameyer, P.W.

    1980-10-01

    In April, 1979, geoscience personnel at Lawrence Livermore National Laboratory (LLNL) initiated comprehensive geologic, seismologic, and hydrologic investigations of the LLNL site and nearby areas. These investigations have two objectives: 1. to obtain data for use in preparing a Final Environmental Impact Report for LLNL, pursuant to the National Environmental Policy Act; 2. to obtain data for use in improving the determination of a design basis earthquake for structural analysis of LLNL facilities. The first phases of these investigations have been completed. Work completed to date includes a comprehensive literature review, analyses of three sets of aerial photographs, reconnaissance geophysical surveys, examination of existing LLNL site borehole data, and the logging of seven exploratory trenches, segments of two sewer trenches, a deep building foundation excavation, a road cut, and an enlarged creek bank exposure. One absolute age date has been obtained by the /sup 14/C method and several dates of pedogenic carbonate formation have been obtained by the /sup 230/Th//sup 234/U method. A seismic monitoring network has been established, and planning for a site hydrologic monitoring program and strong motion instrument network has been completed. The seismologic and hydrologic investigations are beyond the scope of this report and will be discussed separately in future documents.

  1. The paleomagnetism of clastic and precipitate deposits in limestone and dolomite caves

    SciTech Connect

    Latham, A.G. ); Ford, D.C. )

    1991-03-01

    Clastic sediments and calcite precipitates (stalagmites, flowstones, etc.) are abundant in modern limestone caves and normally are the dominant infillings in buried (paleokarst) caves. Clastic sediment fillings are chiefly of fluviatile or local breakdown origin, but lacustrine, colluvial, eolian, and glacial deposits are known. Paleomagnetism has been studied in the fluviatile and lacustrine types: (1) reversal stratigraphy aids dating of geomorphic and paleoclimatic events in the late Pliocene/Pleistocene; (2) fine magnetostratigraphy has yielded estimates of the westward drift. Calcite precipitates (speleothems) may display natural remanent magnetism of either depositional (DRM) or chemical (CRM) origin. NRMs of modern speleothems are primary, not diagenetic; CRMs are invariably associated with the degradation of surface organic matter. (1) Coarse reversal stratigraphy dates geomorphic, etc., events and erosion rates. (2) Fine stratigraphy combined with {sup 230}Th:{sup 234}U dating gives high precision estimates of secular variation, westward drift, and rate of change of geomagnetic anomalies in upper Pleistocene and Holocene deposits. Magnetostratigraphy of paleokarst speleothem fillings associated with hydrocarbons in Ordovician limestones suggest a Permian age for the karstification. Potential applications of magnetostratigraphy to paleokarst deposits of many different scales are considerable.

  2. Generic performance assessment for a deep repository for low and intermediate level waste in the UK--a case study in assessing radiological impacts on the natural environment.

    PubMed

    Jones, S R; Patton, D; Copplestone, D; Norris, S; O'Sullivan, P

    2003-01-01

    Concentrations of radionuclides in soil and surface water, taken from a generic performance assessment of a repository for low and intermediate level radioactive waste, assumed to be located in the UK, have been used as the basis for a case study in assessing radiological impacts on the natural environment. Simplified descriptions of the terrestrial and aquatic ecosystem types likely to be impacted have been developed. A scoping assessment has identified (226)Ra, (210)Po, (234)U, (230)Th and (238)U as having the highest potential for impact, with doses from internally incorporated alpha emitters as being potentially of particular importance. These nuclides, together with (36)Cl and (129)I (which have proved to be of importance in radiological risk assessments for humans) were included in a more detailed dose assessment. A basic methodology for dose assessment of ecosystems is described, and has been applied for the defined impacted ecosystems. Paucity of published data on concentration factors prevented a more detailed assessment for terrestrial ecosystems. For the aquatic ecosystem, a more detailed assessment was possible and highest calculated absorbed dose rates (weighted for the likely higher biological effectiveness of alpha radiation) were about 6.5 microGy h(-1). We conclude that harm to the impacted ecosystems is unlikely and make the observation that the lack of concentration factor or transfer factor data for a sufficiently wide range of species, ecosystems and nuclides appears to be the principal obstacle to establishing a comprehensive framework for the application of radiological protection to ecosystems.

  3. Precise dating of Dansgaard-Oeschger climate oscillations in western Europe from stalagmite data.

    PubMed

    Genty, D; Blamart, D; Ouahdi, R; Gilmour, M; Baker, A; Jouzel, J; Van-Exter, Sandra

    2003-02-20

    The signature of Dansgaard-Oeschger events--millennial-scale abrupt climate oscillations during the last glacial period--is well established in ice cores and marine records. But the effects of such events in continental settings are not as clear, and their absolute chronology is uncertain beyond the limit of (14)C dating and annual layer counting for marine records and ice cores, respectively. Here we present carbon and oxygen isotope records from a stalagmite collected in southwest France which have been precisely dated using 234U/230Th ratios. We find rapid climate oscillations coincident with the established Dansgaard-Oeschger events between 83,000 and 32,000 years ago in both isotope records. The oxygen isotope signature is similar to a record from Soreq cave, Israel, and deep-sea records, indicating the large spatial scale of the climate oscillations. The signal in the carbon isotopes gives evidence of drastic and rapid vegetation changes in western Europe, an important site in human cultural evolution. We also find evidence for a long phase of extremely cold climate in southwest France between 61.2 +/- 0.6 and 67.4 +/- 0.9 kyr ago.

  4. Structural compartmentalisation of a geothermal system, the Torre Alfina field (central Italy)

    NASA Astrophysics Data System (ADS)

    Vignaroli, Gianluca; Pinton, Annamaria; De Benedetti, Arnaldo A.; Giordano, Guido; Rossetti, Federico; Soligo, Michele; Berardi, Gabriele

    2013-11-01

    Recent surging of renewed industrial interest in the exploration of low and medium enthalpy geothermal fields makes the accurate assessment of the geothermal potential essential to minimise uncertainties during both exploration and exploitation. The Torre Alfina field is a case of abandoned, but promising, geothermal field of central Italy where the roles of the internal structural setting and of the recharge areas on the hydrothermal circulation are largely unconstrained. In this paper, field structural data integrated with geomorphic lineament analysis document the occurrence of post-orogenic deformation structures controlling the compartmentalisation of the Torre Alfina geothermal field. Strike-slip and subordinate normal fault systems (with associated network fractures) cut and dislocate the internal architecture of the reservoir and prevent its hydraulic connection with Mount Cetona, considered to be the recharge area and where hydrothermal manifestation, including travertine deposition, occurs. 230Th/234U radiometric dating of superposed travertine units gives 200, 120 and 90 ka respectively, inferred to correspond to the age of the fossil hydrothermal circulation during tectonic activity. The results have been used for illustrating a new geological conceptual model for the Torre Alfina area where the geothermal system is composed of different compartments. Tectonic structures define the main boundaries between compartments, helping the understanding of why productive and non-productive wells were found in apparently similar structural settings within the Torre Alfina field.

  5. Multidimensionally constrained relativistic mean-field study of triple-humped barriers in actinides

    NASA Astrophysics Data System (ADS)

    Zhao, Jie; Lu, Bing-Nan; Vretenar, Dario; Zhao, En-Guang; Zhou, Shan-Gui

    2015-01-01

    Background: Potential energy surfaces (PES's) of actinide nuclei are characterized by a two-humped barrier structure. At large deformations beyond the second barrier, the occurrence of a third barrier was predicted by macroscopic-microscopic model calculations in the 1970s, but contradictory results were later reported by a number of studies that used different methods. Purpose: Triple-humped barriers in actinide nuclei are investigated in the framework of covariant density functional theory (CDFT). Methods: Calculations are performed using the multidimensionally constrained relativistic mean field (MDC-RMF) model, with the nonlinear point-coupling functional PC-PK1 and the density-dependent meson exchange functional DD-ME2 in the particle-hole channel. Pairing correlations are treated in the BCS approximation with a separable pairing force of finite range. Results: Two-dimensional PES's of 226,228,230,232Th and 232,235,236,238U are mapped and the third minima on these surfaces are located. Then one-dimensional potential energy curves along the fission path are analyzed in detail and the energies of the second barrier, the third minimum, and the third barrier are determined. The functional DD-ME2 predicts the occurrence of a third barrier in all Th nuclei and 238U . The third minima in 230 ,232Th are very shallow, whereas those in 226 ,228Th and 238U are quite prominent. With the functional PC-PK1 a third barrier is found only in 226 ,228 ,230Th . Single-nucleon levels around the Fermi surface are analyzed in 226Th, and it is found that the formation of the third minimum is mainly due to the Z =90 proton energy gap at β20≈1.5 and β30≈0.7 . Conclusions: The possible occurrence of a third barrier on the PES's of actinide nuclei depends on the effective interaction used in multidimensional CDFT calculations. More pronounced minima are predicted by the DD-ME2 functional, as compared to the functional PC-PK1. The depth of the third well in Th isotopes decreases

  6. High-Precision Th-Pb Dating by Isotope-Dilution TIMS+MC-ICPMS - Preliminary Results

    NASA Astrophysics Data System (ADS)

    Ickert, R. B.; Mundil, R.; Sharp, W. D.

    2014-12-01

    Relative to the U-Pb decay series, the Th-Pb decay series has received relatively little attention for geochronology although it offers promising applications in both high-resolution geochronology as well as thermochronology. The limitations are partly because Th measurements by thermal ionization have proven notoriously difficult, and for many geochronological applications, the additional information provided by Th-Pb has not been worth the effort required. However, the current generation of MC-ICPMS instruments provides nearly two orders of magnitude better sensitivity of Th than TIMS, eliminating this barrier to measurement and opening up this chronometer for new use. We have developed a method to measure relative abundances of Th, U and Pb by isotope dilution for high-precision geochronology. This method leverages the strengths of two instruments, the high sensitivity and stable mass fractionation of MC-ICPMS instruments for Th and U, and the low background, lack of isobaric interference, and signal stability of TIMS instruments for Pb. To make these measurements, we have calibrated a new synthetic isotope tracer that comprises a mixture of 229Th-233U-236U-202Pb-205Pb. The analytical strategy developed for accessory minerals is a hybrid of techniques previously developed for U-Pb ID-TIMS and U/230Th ID-MC-ICPMS, with a two-column HCl-HNO3 anion exchange procedure (one to separate U and Pb from matrix+Th, and the other to separate Th from matrix), followed by a recombination of the U and Th fractions for MC-ICPMS analysis while the Pb fraction is measured by TIMS. Th-Pb measurements are complementary to, and potentially as precise as the U-Pb gold standard, and the method will find application in certain geological problems, including (1) precisely determining the relative decay rates of 232Th and 238U, (2) dating materials that are young enough to be substantially affected by 230Th or 231Pa disequilibria, and (3) dating small quantities of high-Th minerals like

  7. Stalagmite reconstructions of western tropical Pacific climate from the last glacial maximum to present

    NASA Astrophysics Data System (ADS)

    Partin, Judson Wiley

    The West Pacific Warm Pool (WPWP) plays an important role in the global heat budget and global hydrologic cycle, so knowledge about its past variability would improve our understanding of global climate. Variations in WPWP precipitation are most notable during El Nino-Southern Oscillation events, when climate changes in the tropical Pacific impact rainfall not only in the WPWP, but around the globe. The stalagmite records presented in this dissertation provide centennial-to-millennial-scale constraints of WPWP precipitation during three distinct climatic periods: the Last Glacial Maximum (LGM), the last deglaciation, and the Holocene. In Chapter 2, the methodologies associated with the generation of U/Th-based absolute ages for the stalagmites are presented. In the final age models for the stalagmites, dates younger than 11,000 years have absolute errors of +/-400 years or less, and dates older than 11,000 years have a relative error of +/-2%. Stalagmite-specific 230Th/ 232Th ratios, calculated using isochrons, are used to correct for the presence of unsupported 230Th in a stalagmite at the time of formation. Hiatuses in the record are identified using a combination of optical properties, high 232Th concentrations, and extrapolation from adjacent U/Th dates. In Chapter 3, stalagmite oxygen isotopic composition (delta18O) records from N. Borneo are presented which reveal millennial-scale rainfall changes that occurred in response to changes in global climate boundary conditions, radiative forcing, and abrupt climate changes. The stalagmite delta18O records detect little change in inferred precipitation between the LGM and the present, although significant uncertainties are associated with the impact of the Sunda Shelf on rainfall delta 18O during the LGM. A millennial-scale drying in N. Borneo, inferred from an increase in stalagmite delta18O, peaks at ˜16.5ka coeval with timing of Heinrich event 1, possibly related to a southward movement of the Intertropical

  8. Field experiment determinations of distribution coefficients of actinide elements in alkaline lake environments

    SciTech Connect

    Simpson, H.J.; Trier, R.M.; Li, Y.-H.; Anderson, R.F.; Herczeg, A.L.

    1984-08-01

    Measurements of the radioisotope concentrations of a number of elements (Am, Pu, U, Pa, Th, Ac, Ra, Po, Pb, Cs, and Sr) in the water and sediments of a group of alkaline (pH = 9-10), saline lakes demonstrate greatly enhanced soluble-phase concentrations of elements with oxidation states of (III)-(VI) as the result of complexing by carbonate ion. Ratios of soluble radionuclide concentrations in Mono Lake to those in seawater ((CO/sub 3//sup 2 -/) in Mono Lake = 200 times that of seawater) were: Pu(approx. =10), /sup 238/U(approx. =150), /sup 231/Pa, /sup 228/Th, /sup 230/Th(approx. =10/sup 3/), and /sup 232/Th(approx. =10/sup 5/). Effective distribution coefficients of these radionuclides in high CO/sub 3//sup 2 -/ environments are several orders of magnitude lower (i.e., less particle reactive) than in most other natural waters. The importance of CO/sub 3//sup 2 -/ ion on effective K/sub d/ values was also strongly suggested by laboratory experiments in which most of the dissolved actinide elements became adsorbed to particles after a water sample normally at a pH of 10 was acidified, stripped of all CO/sub 2/, and then returned to pH 10 by adding NH/sub 4/OH. Furthermore, the effect of complexation by organic ligands is of secondary importance in the presence of appreciable carbonate ion concentration. Neither pure phase solubility calculations nor laboratory scale K/sub d/ determinations accurately predicted the measured natural system concentrations. Therefore, measurements of the distribution of radionuclides in natural systems are essential for assessment of the likely fate of potential releases from high level waste repositories to groundwater. 50 references, 31 figures, 43 tables.

  9. Endeavour basalt geology and petrology

    NASA Astrophysics Data System (ADS)

    Gill, J. B.; Stakes, J.; Ramos, F.; Michael, P.; Stakes, D.

    2005-12-01

    We report major and trace element and isotope data from 250 basalt samples recently collected by submersible from the axial valley and flanks of the Endeavour segment of the Juan de Fuca Ridge. Off-axis volcanism is abundant on both flanks which are mirror images of one another geologically. Axial valley walls up to 1 km off axis appear to be steps of in tact but variably fractured sheet, lobate, and hackly lava flows similar to the youngest lavas seen in collapse features in the axis. Coverage by pillow terrane increases with distance off axis and coverage becomes complete after 1 km. The similarity of the two flanks suggests that the currently asymmetric axial magma chamber (van Ark et al., 2004) may be shorter-lived than the off-axis volcanism. MgO contents range from 6.0-8.5% and generally are lower on the flanks consistent with consistently cooler chamber edges there. La/Yb ratios vary 3-fold within 100 m in the axial valley, with normalized La/Sm = 0.8-2.5 in contrast to constant Sr and Nd isotopes. However, Th/U and 230Th/232Th ratios vary only slightly in the axial valley, which may enable dating of off-axis samples. H2O/Ce is less than 170, typical of values throughout much of the Pacific. Variations in depth and degree of melting, and in source composition, are implied. At times, these heterogeneities escaped homogenization in axial magma chambers. Cl concentrations and Cl/K ratios are surprisingly low considering the active hydrothermal systems in close proximity and the potential for brine incorporation into the magma chamber.

  10. Ra isotopes in trees: Their application to the estimation of heartwood growth rates and tree ages

    NASA Astrophysics Data System (ADS)

    Hancock, Gary J.; Murray, Andrew S.; Brunskill, Gregg J.; Argent, Robert M.

    2006-12-01

    The difficulty in estimating growth rates and ages of tropical and warm-temperate tree species is well known. However, this information has many important environmental applications, including the proper management of native forests and calculating uptake and release of atmospheric carbon. We report the activities of Ra isotopes in the heartwood, sapwood and leaves of six tree species, and use the radial distribution of the 228Ra/226Ra activity ratio in the stem of the tree to estimate the rate of accretion of heartwood. A model is presented in which dissolved Ra in groundwater is taken up by tree roots, translocated to sapwood in a chemically mobile (ion-exchangeable) form, and rendered immobile as it is transferred to heartwood. Uptake of 232Th and 230Th (the parents of 228Ra and 226Ra) is negligible. The rate of heartwood accretion is determined from the radioactive decay of 228Ra (half-life 5.8 years) relative to long-lived 226Ra (half-life 1600 years), and is relevant to growth periods of up to 50 years. By extrapolating the heartwood accretion rate to the entire tree ring record the method also appears to provide realistic estimates of tree age. Eight trees were studied (three of known age, 72, 66 and 35 years), including three Australian hardwood eucalypt species, two mangrove species, and a softwood pine (P. radiata). The method indicates that the rate of growth ring formation is species and climate dependent, varying from 0.7 rings yr-1 for a river red gum (E. camaldulensis) to around 3 rings yr-1 for a tropical mangrove (X. mekongensis).

  11. Thorium isotopes tracing the iron cycle at the Hawaii Ocean Time-series Station ALOHA

    NASA Astrophysics Data System (ADS)

    Hayes, Christopher T.; Fitzsimmons, Jessica N.; Boyle, Edward A.; McGee, David; Anderson, Robert F.; Weisend, Rachel; Morton, Peter L.

    2015-11-01

    The role of iron as a limiting micronutrient motivates an effort to understand the supply and removal of lithogenic trace metals in the ocean. The long-lived thorium isotopes (232Th and 230Th) in seawater can be used to quantify the input of lithogenic metals attributable to the partial dissolution of aerosol dust. Thus, Th can help in disentangling the Fe cycle by providing an estimate of its ultimate supply and turnover rate. Here we present time-series (1994-2014) data on thorium isotopes and iron concentrations in seawater from the Hawaii Ocean Time-series Station ALOHA. By comparing Th-based dissolved Fe fluxes with measured dissolved Fe inventories, we derive Fe residence times of 6-12 months for the surface ocean. Therefore, Fe inventories in the surface ocean are sensitive to seasonal changes in dust input. Ultrafiltration results further reveal that Th has a much lower colloidal content than Fe does, despite a common source. On this basis, we suggest Fe colloids may be predominantly organic in composition, at least at Station ALOHA. In the deep ocean (>2 km), Fe approaches a solubility limit while Th, surprisingly, is continually leached from lithogenic particles. This distinction has implications for the relevance of Fe ligand availability in the deep ocean, but also suggests Th is not a good tracer for Fe in deep waters. While uncovering divergent behavior of these elements in the water column, this study finds that dissolved Th flux is a suitable proxy for the supply of Fe from dust in the remote surface ocean.

  12. Anoxia and possible export production spikes in the Red Sea during Termination II: evidence from U-decay series and organic C concentrations

    NASA Astrophysics Data System (ADS)

    Torfstein, A.; Almogi-Labin, A.; McManus, J. F.

    2014-12-01

    The late Quaternary history of the Red Sea is characterized by sharp increases in sea surface salinity during glacial maxima in response to global sea level drop. These imposed an extremely weak current exchange between the Red Sea and the Indian Ocean through the Bab-el-Mandeb Straits that resulted in temporal changes in stratification, productivity and subsurface oxygenation of the Red Sea. The combined effect of these perturbations has been interpreted to impose extended aplanktonic zones in Red Sea sediments centered at glacial maxima. Yet the dynamics of the transition between glacial and interglacial stages in the Red Sea are still not well understood. Here, we present evidence for the occurrence of a strong anoxic episode during the penultimate transition from Marine Isotope Stage (MIS) 6 to MIS5 (Termination II) based on uranium concentrations, isotopic ratios, and organic carbon concentrations (Corg) studied in core KL23 taken by R/V Meteor from northern Red Sea (24o44.88'N 35o03.28'E) at 702 m water depth. (234U/238U) activity ratios and U concentrations start rising from their MIS6 levels (~1 and 1.9 ppm, respectively) ca. 140 ka, and peak at 135-132 ka (1.08 and 3.1 ppm). These patterns are matched by changes in Corg, and the onset of all slightly precedes sea level rise patterns. Thereafter, uranium and Corg decrease sharply, reaching minima that characterizes the rest of MIS5e, ca. 130 ka. Uranium activity ratios however, decrease gradually from their deglacial peak to a minimum value (~0.94) at 122 ka. In view of the redox sensitive behavior of U, the buildup of U concentrations would support anoxic conditions, rather than a rise in export production, as the most likely explanation for the preservation of Corg in the sediments. Yet, the high (234U/238U) values that imply a dominance of open seawater U in the samples, together with d13C values of foraminifera bracketing the studied interval that display a depletion trend indicating an increase in

  13. Carbon, Oxygen and Uranium Isotopes in Pedothem Carbonates Reveal Anomalous North American Atmospheric Circulation 70,000 to 55,000 Years Ago

    NASA Astrophysics Data System (ADS)

    Oerter, E.; Sharp, W. D.; Oster, J. L.; Ebeling, A.; Valley, J. W.; Kozdon, R.; Orland, I. J.; Hellstrom, J. C.; Woodhead, J. D.; Hergt, J.; Chadwick, O.; Amundson, R.

    2015-12-01

    Climate conditions in North America during the past two glacial cycles remain uncertain in part because long, well-dated, continuous paleoclimate records are limited in number and sparsely distributed. Here we present the first continuous, millennial resolution paleoclimate proxy record derived from C, O and U isotopes in mm-thick pedogenic carbonate clast-coatings (pedothems), which are widely distributed in semi-arid to arid regions worldwide. Carbonate 230Th/U ages were obtained from laser ablation ICP-MS spots of 93um diameter size, which also yielded 234U/238Ui proxy values for soil water infiltration and paleoprecipitation. The U-series transects were coupled to δ13C and δ18O values obtained by ion probe on ~10um diameter spots. Modern soil carbonate in the region has δ18O and δ13C values that are similar to the youngest (early Holocene) samples acquired in the laminations, strengthening the interpretation that the carbonate reflects soil isotopic conditions at the time of formation. Our new record from the Wind River Basin in Wyoming spans the last 120,000 years and confirms a previously hypothesized period of increased transport of Gulf of Mexico moisture northward into the continental interior from 70,000 to 55,000 years ago. Such pronounced meridional moisture transport, which contrasts with the dominant zonal transport of Pacific moisture into the North American interior by westerly winds before and after 70,000 to 55,000 years ago, may have resulted from a persistent anticyclone developed above the North American ice sheet during Marine Isotope Stage 4. Subsequently, the carbonate record suggests that climate in mid-latitude central North America became progressively more arid during the onset of the last glaciation (both δ13C and 234U/238Ui values become more positive), culminating in peak aridity during the LGM. We conclude that pedothems, when analyzed using micro-analytical techniques, can provide unique insights into past terrestrial climates.

  14. Uranium biogeochemistry across the redox transition zone of a permanently stratified fjord: Framvaren, Norway

    USGS Publications Warehouse

    Swarzenski, P.W.; McKee, B.A.; Skei, J.M.; Todd, J.F.

    1999-01-01

    During August 1995, the vertical concentration profile of dissolved and particulate uranium exhibited strong non-conservative characteristics in the upper 30 m of Framvaren Fjord. There was a pronounced peak in both particulate (> 0.2 ??m; 1.09 nM) and dissolved (< 0.2 ??m; 17.06 nM) uranium in the finely stratified waters at the O2/H2S interface which is positioned well within the euphotic zone at about 20-21 m. Such concentration maxima at the redox boundary are also observed for dissolved organic carbon (DEC), Sr and Ba. Dissolved U levels seen in the water column from 18 m down to 30 m exceeded the high salinity (salinity = 35) U concentrations (13.63 ?? 0.84 nM; Chen, J.H., Edwards, R.L., Wasserburg, G.L., 1986. 238U, 234U and 232Th in seawater. Earth Planet Sci. Lett. 80, 241-251.) observed uniformly in the open ocean. A prolific population of S microbes (e.g., Chromatium, Chlorobium sp.) flourishes at the O2/H2S interface. The source of elevated U at the redox boundary must be due to microbial uptake and subsequent release processes rather than dilution from oceanic uranium. Uranium oxidation state determinations in waters from 1, 22 and 30 m depth reveal that reduced U(IV) is not present in significant abundance, and that the chemical and/or biological reduction of hexavalent uranium is largely inhibited. Our results suggest that U and other trace constituents such as DOC, Sr, Ba, Fe(II), Mn(II) are greatly modified by direct and indirect microbial transformation reactions which are most concentrated across the redox transition zone in Framvaren Fjord.

  15. Alpha-emitting isotopes and chromium in a coastal California aquifer

    USGS Publications Warehouse

    Densmore, Jill N.; Izbicki, John A.; Murtaugh, Joseph M.; Swarzenski, Peter W.; Bullen, Thomas D.

    2014-01-01

    The unadjusted 72-h gross alpha activities in water from two wells completed in marine and alluvial deposits in a coastal southern California aquifer 40 km north of San Diego were 15 and 25 picoCuries per liter (pCi/L). Although activities were below the Maximum Contaminant Level (MCL) of 15 pCi/L, when adjusted for uranium activity; there is concern that new wells in the area may exceed MCLs, or that future regulations may limit water use from the wells. Coupled well-bore flow and depth-dependent water-quality data collected from the wells in 2011 (with analyses for isotopes within the uranium, actinium, and thorium decay-chains) show gross alpha activity in marine deposits is associated with decay of naturally-occurring 238U and its daughter 234U. Radon activities in marine deposits were as high as 2230 pCi/L. In contrast, gross alpha activities in overlying alluvium within the Piedra de Lumbre watershed, eroded from the nearby San Onofre Hills, were associated with decay of 232Th, including its daughter 224Ra. Radon activities in alluvium from Piedra de Lumbre of 450 pCi/L were lower than in marine deposits. Chromium VI concentrations in marine deposits were less than the California MCL of 10 μg/L (effective July 1, 2014) but δ53Cr compositions were near zero and within reported ranges for anthropogenic chromium. Alluvial deposits from the nearby Las Flores watershed, which drains a larger area having diverse geology, has low alpha activities and chromium as a result of geologic and geochemical conditions and may be more promising for future water-supply development.

  16. Simultaneous determination of gross alpha, gross beta and ²²⁶Ra in natural water by liquid scintillation counting.

    PubMed

    Fons, J; Zapata-García, D; Tent, J; Llauradó, M

    2013-11-01

    The determination of gross alpha, gross beta and (226)Ra activity in natural waters is useful in a wide range of environmental studies. Furthermore, gross alpha and gross beta parameters are included in international legislation on the quality of drinking water [Council Directive 98/83/EC]. In this work, a low-background liquid scintillation counter (Wallac, Quantulus 1220) was used to simultaneously determine gross alpha, gross beta and (226)Ra activity in natural water samples. Sample preparation involved evaporation to remove (222)Rn and its short-lived decay daughters. The evaporation process concentrated the sample ten-fold. Afterwards, a sample aliquot of 8 mL was mixed with 12 mL of Ultima Gold AB scintillation cocktail in low-diffusion vials. In this study, a theoretical mathematical model based on secular equilibrium conditions between (226)Ra and its short-lived decay daughters is presented. The proposed model makes it possible to determine (226)Ra activity from two measurements. These measurements also allow determining gross alpha and gross beta simultaneously. To validate the proposed model, spiked samples with different activity levels for each parameter were analysed. Additionally, to evaluate the model's applicability in natural water, eight natural water samples from different parts of Spain were analysed. The eight natural water samples were also characterised by alpha spectrometry for the naturally occurring isotopes of uranium ((234)U, (235)U and (238)U), radium ((224)Ra and (226)Ra), (210)Po and (232)Th. The results for gross alpha and (226)Ra activity were compared with alpha spectrometry characterization, and an acceptable concordance was obtained.

  17. OSMOSE program : statistical review of oscillation measurements in the MINERVE reactor R1-UO2 configuration.

    SciTech Connect

    Stoven, G.; Klann, R.; Zhong, Z.; Nuclear Engineering Division

    2007-08-28

    The OSMOSE program is a collaboration on reactor physics experiments between the United States Department of Energy and the France Commissariat Energie Atomique. At the working level, it is a collaborative effort between the Argonne National Laboratory and the CEA Cadarache Research Center. The objective of this program is to measure very accurate integral reaction rates in representative spectra for the actinides important to future nuclear system designs, and to provide the experimental data for improving the basic nuclear data files. The main outcome of the OSMOSE measurement program will be an experimental database of reactivity-worth measurements in different neutron spectra for the heavy nuclides. This database can then be used as a benchmark to verify and validate reactor analysis codes. The OSMOSE program (Oscillation in Minerve of isotopes in Eupraxic Spectra) aims at improving neutronic predictions of advanced nuclear fuels through oscillation measurements in the MINERVE facility on samples containing the following separated actinides: {sup 232}Th, {sup 233}U, {sup 234}U, {sup 235}U, {sup 236}U, {sup 238}U, {sup 237}Np, {sup 238}Pu, {sup 239}Pu, {sup 240}Pu, {sup 241}Pu, {sup 242}Pu, {sup 241}Am, {sup 243}Am, {sup 244}Cm, and {sup 245}Cm. The first part of this report provides an overview of the experimental protocol and the typical processing of a series of experimental results which is currently performed at CEA-Cadarache. In the second part of the report, improvements to this technique are presented, as well as the program that was created to process oscillation measurement results from the MINERVE facility in the future.

  18. 210Po-210Pb Dating and U-Series Disequilibria of a Young Basaltic Flow at 10° 44'N EPR

    NASA Astrophysics Data System (ADS)

    van der Zander, I.; Rubin, K. H.; Zierenberg, R. A.; Voight, J. R.; von Damm, K.; McClain, J.

    2004-12-01

    Divers in the submersible Alvin observed and sampled a very young appearing lava flow at 10° 44'N on the East Pacific Rise (EPR) during a November 2003 biodiversity-funded dive series (DEB-0072695 to J.R. Voight) to the area. The occurrence of the glassy, unsedimented, low-lying graben filling lava flow was unexpected on this magma-starved ridge segment just north of the Clipperton Transform Fault and so 3 dives were used to investigate a 4 km long segment of the flow. Measurements (in progress) of 210Po-210Pb disequilibrium in 4 samples of this lava flow confirm that it is likely extremely young (0-2 months old when the samples were collected). Such age dating is critical here because although this area of the EPR is covered by the SOSUS hydrophone array, data are not available in real time and will not be downloaded until November 2004. The 210Po-210Pb geochronometer (T1/2 =138.4 d) involves a time series of 3 or 4 210Po analyses over the course of 1 year or more, so that our analyses are still ongoing (just 2 data per sample so far) and our results quite preliminary. By meeting time we will have better constrained eruption ages with the addition of more data to the ingrowth curves. Results of other chemical analyses on these same samples are being used to compositionally characterize the lavas and to constrain magmatic process timescales. All 13 of the lavas sampled in Nov 2003 are low MgO (6.5-6.7 wt%) basalts, displaying inter-sample compositional variations (lava flow heterogeneity) at the higher end of the known MORB flow catalogue, in contrast to mafic (8 wt% MgO) and compositionally homogeneous lava flows erupted at the nearby and well-studied 9° 50'N EPR site. 230Th-238U disequilibria in the young 10° 44'N flow clusters around 14-15% 230Th-excesses, which overlaps the high end of the data range from "zero-age" MORB flows at 9° 50'N EPR and the Juan De Fuca Ridge (JDF). Slightly higher excesses, lower (230Th/232Th ), and higher Th/U ratios (2

  19. SUPPLEMENTARY COMPARISON: Activity measurements of a suite of radionuclides (90Sr, 137Cs, 210Pb, 210Po, 228Ra, 234U, 235U, 238U, 238Pu, 239,240Pu) in soil reference material (Rocky Flats II): CCRI(II)-S2

    NASA Astrophysics Data System (ADS)

    Nour, S.; Inn, K. G. W.; Karam, L. R.

    2009-01-01

    In 2005, the CCRI decided that a comparison undertaken from 2002 to 2007 by the NIST (SIM) in the development of a new soil (Rocky Flats II) standard reference material (SRM) was sufficiently well constructed that it could be converted into a supplementary comparison under CCRI(II), with comparison identifier CCRI(II)-S2, so as to support calibration and measurement capability (CMC) claims for radionuclide measurements in reference material (specifically, low calcium-content soils). Previous comparisons of radionuclides have been of single or multiple nuclides in non-complex matrices and results of such could not be extended to support capabilities to measure the same nuclides in reference materials. The results of this comparison have been reported to the participants, and have been used to determine the certified reference value of the SRM. The key comparison working group (KCWG) of the CCRI(II) has approved this approach as a mechanism to link all the results to certified 'reference values' in lieu of the key comparison reference value (KCRV) of these specified radionuclides in this type of matrix (soil) so as to support CMCs of similar materials. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCRI Section II, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

  20. URANIUM-SERIES DISEQUILIBRIUM IN TUFF AND GRANITE:HYDROGEOLOGICAL IMPLICATIONS

    SciTech Connect

    M. Gasscoyne; N.H. Miller

    2000-10-27

    radionuclide involved. Depending on the analytical precision obtained, the observation of a {sup 234}U/{sup 238}U activity ratio that is less than or greater than 1.000 clearly shows that an isotope of uranium has migrated within the rock in the last 1-2 million years. Other daughter/parent activity ratios can be used to detect radionuclide migration over shorter time-scales, such as {sup 230}Th/{sup 234}U (300,000 years) and {sup 226}Ra/{sup 230}Th (8,000 years). Uranium-series disequilibrium is, therefore, a useful technique for application to site evaluation for nuclear fuel waste disposal because it can be used to: (1) show that so-called ''intact rock'' is indeed intact (i.e. radionuclides are in secular equilibrium and are immobile), (2) determine the principal flow regimes in a rock mass by analysis of rock matrix, fracture material, etc., (3) estimate the time period of recent radionuclide migration in the rock, and (4) proxy as a natural analogue for the potential mobility of uranium at the site. Several examples of these applications have been reported. This paper describes the use of uranium-series disequilibrium in the comparison of two North American sites: the water-saturated Lac du Bonnet granite batholith on the Canadian Shield and the unsaturated tuffs from the Exploratory Studies Facility (ESF) and Cross-Drift Tunnels at Yucca Mountain, Nevada. In particular, the fact that unfractured rock should be at secular equilibrium is applied to both sites to determine if the rock matrix is a significant flow path for groundwater.

  1. The mobility of uranium and other elements during alteration of rhyolite ash to montmorillonite: A case study in the Troublesome Formation, Colorado, U.S.A.

    USGS Publications Warehouse

    Zielinski, R.A.

    1982-01-01

    An unusual occurrence of juxtaposed glassy and clay-altered ash was sampled to estimate the degree and type of element mobility during alteration of glass to montmorillonite. The results are particularly interesting in that major mobilization of uranium is indicated. Closely spaced samples of glassy and montmorillonitic ash were collected from the same 20-50 cm thick stratigraphic horizon in the Troublesome Formation (Miocene) of northwestern Colorado. Sharp contacts exist between glassy ash and underlying pink montmorillonite and indicate that water-saturated conditions were restricted to basal ash layers. Formation of montmorillonite instead of zeolites suggests that the water was not highly saline or alkaline. Isotopic and chemical analyses of glassy and clay-altered samples indicate the following: 1. (1) Montmorillonite has U concentrations which are only 10-15% of the concentrations in coexisting glass. Similarly depleted elements include Cs, Rb, Na and K. Much smaller depletions of these elements in some glassy samples serve as sensitive indicators of incipient alteration of glass to montmorillonite. 2. (2) Abundances of relatively insoluble elements such as Th, Ta, Hf and Al are slightly higher (5-50%) in clay-altered ash and serve as indicators of the maximum levels of enrichment in residual material. Greater enrichment of elements such as Ca, Mg, Sr, Sc, P, Cr and Co indicate structural incorporation, adsorption, or ion-exchange uptake by clay or secondary hydrous oxides of Fe and Mn. 3. (3) The rare-earth-element patterns and abundances in glass are sufficiently mimicked by detritus-free montmorillonite to document the compositional equivalency of the two. 4. (4) Radioactive equilibrium exists between 238U and its decay products 234U and 230Th. This documents minimal open-system mobility of U within the last ??? 0.3 Ma. ?? 1982.

  2. 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.

  3. Natural attenuation reactions at a uranium mill tailings site, western U.S.A.

    PubMed

    Zhu, Chen; Anderson, Greg M; Burden, David S

    2002-01-01

    This paper presents a modeling analysis of the geochemical evolution of a contaminated sandy aquifer at a uranium mill tailings site in the western United States. The tailings pond contains fluids having a pH of 1.5 to 3.5 and high levels of As, Be, Cd, Cr, Pb, Mo, Ni, Se, 226Ra, 228Ra, 230Th, 238U, and 234U. Seepage of tailings fluids into the aquifer has formed a low-pH ground water plume. The reclamation plan is to install a low-permeability cover on the tailings pond to stop the seepage and allow the plume to be attenuated by reactions with the aquifer matrix and flushed by uncontaminated upgradient ground water. To evaluate this reclamation scenario, ground water and sediment core samples were analyzed along one flowpath. Speciation-solubility and mass-transfer modeling revealed two sets of chemical reactions for acid seepage and flushing, respectively. The current concentrations and distribution of ground water constituents can be interpreted as being controlled by stepwise pH-buffer reactions with calcite, amorphous aluminum hydroxide, and amorphous iron hydroxides. These buffer reactions divide the aquifer into zones of near-constant pH, separated by interface zones. For the flushing stage, it is predicted that reactions with surface-bound species will dominate the reaction paths, and more pore volumes are required to neutralize the plume than predicted by models that do not consider surface reactions. Direct mineralogical and surface analysis is needed to substantiate this assertion.

  4. GAMMA-RAY CHARACTERIZATION OF THE U-SERIES INTERMEDIATE DAUGHTERS FROM SOIL SAMPLES AT THE PENA BLANCA NATURAL ANALOG, CHIHUAHUA, MEXICO

    SciTech Connect

    D.C. French; E.Y. Anthony; P.C. Goodell

    2005-07-18

    The Pena Blanca natural analog is located in the Sierra Pena Blanca, approximately 50 miles north of Chihuahua City, Mexico. The Sierra Pena Blanca is composed mainly of ash-flow tuffs, and the uranium in the region is contained in the brecciated zones of these tuffs. The Pena Blanca site is considered a natural analog to the proposed Yucca Mountain Nuclear Waste Repository because they share similar characteristics of structure, volcanic lithology, tectonic activity, and hydrologic regime. One of the mineralized zones, the Nopal I deposit, was mined in the early 1980s and the ore was stockpiled close to the mine. This stockpile area has subsequently been cleared and is referred to as the prior high-grade stockpile (PHGS) site. Soil surrounding boulders of high-grade ore associated with the PHGS site have been sampled. The purpose of this study is to characterize the transport of uranium series radioisotopes from the boulder to the soil during the past 25 years. Transport is characterized by determining the activities of individual radionuclides and daughter to parent ratios. The daughter to parent ratios are used to establish whether the samples are in secular equilibrium. Activities are determined using gamma-ray spectroscopy. Isotopes of the uranium series decay chain detected by gamma-ray spectroscopy include {sup 210}Pb, {sup 234}U, {sup 234}Th, {sup 230}Th, {sup 226}Ra, {sup 214}Pb, {sup 214}Bi, and {sup 234}Pa. Preliminary results indicate that some daughter to parent pairs appear to be in secular disequilibrium. Thorium is in excess relative to uranium, and radium is in excess relative to thorium. A deficiency appears to exist for {sup 210}Pb relative to {sup 214}Bi and {sup 214}Pb. If these results are borne out by further analysis, they would suggest transport of nuclides from the high-grade boulder into its surroundings, followed by continued leaching of uranium and lead from the environment.

  5. Radon loss from barite in submarine hydrothermal sulfide deposits

    NASA Astrophysics Data System (ADS)

    Uchida, A.; Toyoda, S.; Ishibashi, J.

    2012-12-01

    Determining the ages of the hydrothermal deposit will greatly contribute the studies of temporal change of submarine hydrothermal activities, as they are essential factors for ore formation and for the biological systems sustained by the chemical species arising from hydrothermal activities. The dating methods available for this purpose includes disequilibrium among 238U, 234U, and 230Th in sufide minerals, between 226Ra and 210Pb, and 228Ra and 228Th in barite (BaSO4) contained in the deposits, and ESR (electron spin resonance) using SO3- radical in barite. In applying these dating methods, a closed system is assumed, where radioactive nuclei decay following the law of physics but are not mobile out of the mineral. However, White and Rood (2001) reported that 3 to 20% of 222Rn is lost from barite crystal, which are used for casing of mining on the land. As 222Rn loss in barite greatly affects the dating results of 226}Ra-{210Pb method and ESR dating method in which radioactive equilibrium is assumed to calculate the dose rate, in the present paper, we investigated {222}Rn loss from the barite crystals contained in hydrothermal sulfide deposits. The radioactive nuclei, 210Pb and 214Bi were measured by the low background pure germanium gamma ray spectrometer at Okayama University of Science. A Pitchblend Uraninite (UO2) mixed with NaCl was used as the equilibrated standard. The barite crystals extracted from hydrothermal sulfide deposits taken in South Mariana Trough are also crused and mixed with NaCl. The mixed powder was packed in a thin stainless container which prevent from Rn loss, before the measurements. The measurements for 24 hours were repeated every day for 20 days. As results, it was found that the peak intensities of 210Pb and 214Bi did not change with time, meaning no Rn loss.

  6. Neanderthal skeleton from Tabun: U-series data by gamma-ray spectrometry.

    PubMed

    Schwarcz, H P; Simpson, J J; Stringer, C B

    1998-12-01

    The Neanderthal hominid Tabun C1, found in Israel by Garrod & Bate, was attributed to either layer B or C of their stratigraphic sequence. We have used gamma-ray spectrometry to determine the 230Th/234U and 231Pa/235U ratios of two bones from this skeleton, the mandible and a femur. The ages calculated from these ratios depend on the uranium uptake history of the bones. Assuming a model of early U (EU) uptake the age of the Tabun C1 mandible is 34+/-5 ka. The EU age of the femur is 19+/-2 ka. The femur may have experienced continuous (linear) U uptake which would give an age of 33+/-4 ka, in agreement with the mandible's EU age, but implies marked inhomogeneity in U uptake history at the site. These new age estimates for the skeleton suggest that it was younger than deposits of layer C. This apparent age is less than those of other Neanderthals found in Israel, and distinctly younger than the ages of the Skhul and Qafzeh burials. This suggests that Neanderthals did not necessarily coexist with the earliest modern humans in the region. All of the more complete Neanderthal fossils from Israel are now dated to the cool period of the last glacial cycle, suggesting that Neanderthals may have arrived in this region as a result of the southward expansion of their habitable range. The young age determined for the Tabun skeleton would suggest that Neanderthals survived as late in the Levant as they did in Europe.

  7. Extended Late Pleistocene Sea Level Record

    NASA Astrophysics Data System (ADS)

    Fairbanks, R. G.; Cao, L.; Mortlock, R. A.

    2006-12-01

    Several hundred new closed system 230Th/234U and radiocarbon dates and the addition of more cores and coral samples from the islands of Barbados, Kiritimati and Araki contribute to an enhanced sea level record for the late Pleistocene ranging from the present to 240,000 yrs BP. Application of more rigorous sample screening criteria, including redundant 231Pa/235U dates have resulted in more closed system ages and better sea level resolution. In addition, a multibeam survey has mapped an extensive glacial lowstand reef on a ridge south of Barbados that is capped by a set of pinnacle reefs that grew during the early deglaciation. Among our new observations, the more detailed Barbados sea level record now resolves a Younger Dryas still- stand and a sea level drop between 16,140 and 14,690, overlapping the timing of H1 by some age estimates. The coral ages bracketing melt water pulse 1A have been further refined to 14,082 +/- 28 yrs BP and 13,632 +/- 32 yrs BP (2-sigma). The Isotope Stage 3 interstadial ended with sea level near 87.5 meters below present at 29,500 years ago before dropping to full glacial levels. The last glacial sea level lowstand began as early as 26,000 yrs BP. Extensive dating of Marine Isotope Stage 3 interstadial reefs on the islands of Araki and Barbados have added considerable resolution to this time interval and reliably bracket lowstand intervals separating the interstadials. A new diagenesis model has improved our prospecting success for closed system ages from older reefs and added some critical dates to the sparse closed-system data set for MIS-5 and MIS-7 high stand reefs..

  8. Improved spatial resolution for U-series dating of opal at Yucca Mountain, Nevada, USA, using ion-microprobe and microdigestion methods

    USGS Publications Warehouse

    Paces, J.B.; Neymark, L.A.; Wooden, J.L.; Persing, H.M.

    2004-01-01

    Two novel methods of in situ isotope analysis, ion microprobe and microdigestion, were used for 230Th/U and 234U/238U dating of finely laminated opal hemispheres formed in unsaturated felsic tuff at Yucca Mountain, Nevada, proposed site for a high-level radioactive waste repository. Both methods allow analysis of layers as many as several orders of magnitude thinner than standard methods using total hemisphere digestion that were reported previously. Average growth rates calculated from data at this improved spatial resolution verified that opal grew at extremely slow rates over the last million years. Growth rates of 0.58 and 0.69 mm/m.y. were obtained for the outer 305 and 740 ??m of two opal hemispheres analyzed by ion microprobe, and 0.68 mm/m.y. for the outer 22 ??m of one of these same hemispheres analyzed by sequential microdigestion. These Pleistocene growth rates are 2 to 10 times slower than those calculated for older secondary calcite and silica mineral coatings deposited over the last 5 to 10 m.y. dated by the U-Pb method and may reflect differences between Miocene and Pleistocene seepage flux. The microdigestion data also imply that opal growth rates may have varied over the last 40 k.y. These data are the first indication that growth rates and associated seepage in the proposed repository horizon may correlate with changes in late Pleistocene climate, involving faster growth during wetter, cooler climates (glacial maximum), slower growth during transition climates, and no growth during the most arid climate (modern). Data collected at this refined spatial scale may lead to a better understanding of the hydrologic variability expected within the thick unsaturated zone at Yucca Mountain over the time scale of interest for radioactive waste isolation. ?? 2004 Elsevier Ltd.

  9. Time-scales of sedimentary transfer and weathering processes from U-series nuclides: Clues from the Himalayan rivers

    NASA Astrophysics Data System (ADS)

    Granet, M.; Chabaux, F.; Stille, P.; France-Lanord, C.; Pelt, E.

    2007-09-01

    In order to define time-scales of erosion and sedimentary transfer in the Himalaya, 238U- 234U- 230Th disequilibria have been analysed in river bank sediments and in bedloads collected along the Kali Gandaki river, one of the main Nepalese rivers, and in the Ghaghara and Gandak rivers, two major plain tributaries of the Ganges. The Th activity ratios and U/Th ratios in river sediments of the two Ganges tributaries constantly decrease from upstream to downstream. This is related to the maturation of sediments by weathering during their transfer to the plain. The U-series data allow to calculate a transfer time for the sediments in the alluvial Gangetic plain from the chain front to the confluence with the Ganges of about 100 kyr for both rivers. The Kali Gandaki river sediment data highlight a decrease of both the Th isotopic and U/Th ratios which is explained by a mixing between two sources with similar U/Th ratios but having suffered a different U-Th fractionation history. Interpretation of the U-series data in the frame of this scenario gives long time-scales of weathering of several 100's kyr for the Himalayan terranes. The results imply that Himalayan bedrocks are submitted to a long in situ stage of weathering before their erosion and transfer into the rivers. In addition, occurrence of similar U-Sr signatures in dissolved (i.e. < 0.1-0.2 μm) and sediment phases of the Kali Gandaki river suggests that "dissolved" uranium could be carried by colloids constituted by sedimentary microparticles. This precludes the use of U-series disequilibria in this river to calculate weathering budgets and to assess whether the erosion is working at steady-state or not.

  10. Migration of radionuclides through backfill in a nuclear waste repository

    SciTech Connect

    Lung, H.

    1986-01-01

    Four models are analyzed to predict the performance of a backfill layer as part of the waste package emplacement in a nuclear waste repository. The corresponding computer code for each model is also developed. The time-dependent mass transfer analysis on a spherical waste-backfill geometry indicates that the radioactive decay effect can enhance the mass transfer rate from the backfill instead of reducing it. The analysis yields the breakthrough time of the backfill layer, which in turn characterizes the backfill performance. A non-linear (Langmuir) sorption isotherm is used to describe the sorption saturation in the backfill. The steady state mass transport analysis through a prolate spheroidal waste-backfill geometry shows that a simple formula can be used to calculate the individual resistances to mass transport in backfill and in host rock. A general, non-recursive analytical solution is derived for a radioactive decay chain of arbitrary length in either a finite or a semi-infinite medium. Numerical examples are given for different boundary conditions and for different decay chains. The results justify that for a backfill layer made of low permeability material, a zero water velocity can be used in the backfill analysis. It is also shown that under normal repository conditions, the mass transfer rate from the backfill is quite small. For the daughter member with a smaller retardation coefficient than that of the mother nuclide, such as /sup 226/Ra in the /sup 234/U ..-->.. /sup 230/Th ..-->.. /sup 226/Ra chain, an interior maximum in the concentration profile appears in the backfill. This phenomenon can be seen only in a chain calculation.

  11. Radionuclide activities, geochemistry, and accumulation rates of sediments in the Gulf of Thailand

    NASA Astrophysics Data System (ADS)

    Srisuksawad, Kanitha; Porntepkasemsan, Boonsom; Nouchpramool, Sunun; Yamkate, Pathom; Carpenter, Roy; Peterson, Michael L.; Hamilton, Terry

    1997-07-01

    Downcore concentration profiles of 210Pb, U, and Th isotopes, Al, Fe, Ti, Mn and Sc were measured in sediment box cores collected at 22 stations (16-70 m water depth) covering most of the Thai zone of the Gulf of Thailand. Distributions of excess 210Pb and the detrital elements were used to study spatial variations in sedimentary processes, mineralogy, and geochemistry between different regions of the gulf. Steady-state depositional concentrations and fluxes of excess 210Pb are 3-10 times lower in Gulf of Thailand sediments than in sediments from mid-latitudes in the northern hemisphere, reflecting lower 210Pb inputs from atmospheric fallout at 6-13°N latitude and from lower production of 210Pb from 226Ra in the shallower waters of the Gulf. U and Th concentrations are approximately 2-3 times higher than those in shelf sediments from mid-latitudes of North America, consistent with a higher proportion of granitic source rocks in the Thai environment. Downcore variations in 228Th/ 232Th activity ratios and in U activities reveal that exchange of interstitial and overlying waters and their dissolved chemicals occurs down to 20 cm in 8 of 10 cores. This benthic exchange may be important in budgets of fluxes of other soluble chemicals in this shallow shelf sea. A net flux of U isotopes from overlying water into Gulf of Thailand sediments occurs, in contrast to their release from sediments of the tropical Amazon shelf. Detectable levels of 137Cs were found only in sediments near the mouth of the largest river, the Chao Phraya. The detrital elements 232Th, 230Th, Al, Ti, and Sc all show relatively uniform downcore concentration profiles. This supports a key assumption in calculations of sediment accumulation rates from downcore profiles of 210Pb activity, that steady-state depositional conditions exist and that basic sediment mineralogy and grain size does not change. 210Pb model derived mass accumulation rates vary between 270 and 490 mg/cm 2 per year in the upper Gulf

  12. Stalagmite geochemistry and the timing of the last interglacial-glacial transition in Central Europe (NE Hungary)

    NASA Astrophysics Data System (ADS)

    Siklosy, Z.; Demeny, A.; Pilet, S.; Leel-Ossy, Sz.; Lin, K.; Shen, C.-C.

    2009-04-01

    Speleothems can provide accurate chronologies for reconstructions of climate change by combination of U/Th dating and climate-related geochemical compositions. Geochemical studies of speleothems from Central Europe are mostly based on stable C and O isotope analyses, thus, complex geochemical studies combining isotope and trace element measurements are needed for more reliable climate models for this transitional area between oceanic and continental regions. We present stable H-C-O isotope and trace element records obtained on speleothems covering the Last Interglacial (MIS 5e) and the transition to MIS 5d. A stalagmite from Baradla Cave grew from 127.5 to 110 ka. Accelerated growth rates have been detected by U/Th age data in the 127 to 126 ka and 119 to 117 ka parts. Trace element compositions and 230Th/232Th ratios suggest changes in the hydrological regime, whereby early calcite precipitates formed in fissures during the dry and cold glacial period were dissolved by the starting flux of infiltrating meteoric water (producing elevated dissolved ion concentration but low detrital Th component), then the increasing amount of dripwater during the interglacial period resulted in trace element dilution. Temperature and precipitation amount variations are also reflected by the stable isotope compositions. Oxygen isotope composition shows a continuous increase from 127.5 ka until about 118 ka most probably related to temperature rise, whereas C isotope values are shifted in negative direction suggesting increasing humidity in accordance with trace element contents. The presumably warmest period at ca. 118 ka is associated with rather arid climate as indicated by peak d18O values coinciding with the highest dD values of fluid inclusion water. This is followed by a pronounced negative shift in both O and H isotope values, similarly to recent Alpine studies (Meyer et al., 2008), most probably related to cooling. Hydrogen isotope compositions of fluid inclusion water

  13. Eolian dust input to the Subarctic North Pacific

    NASA Astrophysics Data System (ADS)

    Serno, Sascha; Winckler, Gisela; Anderson, Robert F.; Hayes, Christopher T.; McGee, David; Machalett, Björn; Ren, Haojia; Straub, Susanne M.; Gersonde, Rainer; Haug, Gerald H.

    2014-02-01

    Eolian dust is a significant source of iron and other nutrients that are essential for the health of marine ecosystems and potentially a controlling factor of the high nutrient-low chlorophyll status of the Subarctic North Pacific. We map the spatial distribution of dust input using three different geochemical tracers of eolian dust, 4He, 232Th and rare earth elements, in combination with grain size distribution data, from a set of core-top sediments covering the entire Subarctic North Pacific. Using the suite of geochemical proxies to fingerprint different lithogenic components, we deconvolve eolian dust input from other lithogenic inputs such as volcanic ash, ice-rafted debris, riverine and hemipelagic input. While the open ocean sites far away from the volcanic arcs are dominantly composed of pure eolian dust, lithogenic components other than eolian dust play a more crucial role along the arcs. In sites dominated by dust, eolian dust input appears to be characterized by a nearly uniform grain size mode at ∼4 μm. Applying the 230Th-normalization technique, our proxies yield a consistent pattern of uniform dust fluxes of 1-2 g/m2/yr across the Subarctic North Pacific. Elevated eolian dust fluxes of 2-4 g/m2/yr characterize the westernmost region off Japan and the southern Kurile Islands south of 45° N and west of 165° E along the main pathway of the westerly winds. The core-top based dust flux reconstruction is consistent with recent estimates based on dissolved thorium isotope concentrations in seawater from the Subarctic North Pacific. The dust flux pattern compares well with state-of-the-art dust model predictions in the western and central Subarctic North Pacific, but we find that dust fluxes are higher than modeled fluxes by 0.5-1 g/m2/yr in the northwest, northeast and eastern Subarctic North Pacific. Our results provide an important benchmark for biogeochemical models and a robust approach for downcore studies testing dust-induced iron fertilization of

  14. No iron fertilization in the equatorial Pacific Ocean during the last ice age.

    PubMed

    Costa, K M; McManus, J F; Anderson, R F; Ren, H; Sigman, D M; Winckler, G; Fleisher, M Q; Marcantonio, F; Ravelo, A C

    2016-01-28

    The equatorial Pacific Ocean is one of the major high-nutrient, low-chlorophyll regions in the global ocean. In such regions, the consumption of the available macro-nutrients such as nitrate and phosphate is thought to be limited in part by the low abundance of the critical micro-nutrient iron. Greater atmospheric dust deposition could have fertilized the equatorial Pacific with iron during the last ice age--the Last Glacial Period (LGP)--but the effect of increased ice-age dust fluxes on primary productivity in the equatorial Pacific remains uncertain. Here we present meridional transects of dust (derived from the (232)Th proxy), phytoplankton productivity (using opal, (231)Pa/(230)Th and excess Ba), and the degree of nitrate consumption (using foraminifera-bound δ(15)N) from six cores in the central equatorial Pacific for the Holocene (0-10,000 years ago) and the LGP (17,000-27,000 years ago). We find that, although dust deposition in the central equatorial Pacific was two to three times greater in the LGP than in the Holocene, productivity was the same or lower, and the degree of nitrate consumption was the same. These biogeochemical findings suggest that the relatively greater ice-age dust fluxes were not large enough to provide substantial iron fertilization to the central equatorial Pacific. This may have been because the absolute rate of dust deposition in the LGP (although greater than the Holocene rate) was very low. The lower productivity coupled with unchanged nitrate consumption suggests that the subsurface major nutrient concentrations were lower in the central equatorial Pacific during the LGP. As these nutrients are today dominantly sourced from the Subantarctic Zone of the Southern Ocean, we propose that the central equatorial Pacific data are consistent with more nutrient consumption in the Subantarctic Zone, possibly owing to iron fertilization as a result of higher absolute dust fluxes in this region. Thus, ice-age iron fertilization in the

  15. Chronology of Late Pleistocene glacier advances in the Rı´o Mendoza Valley, Argentina

    NASA Astrophysics Data System (ADS)

    Espizua, Lydia E.

    1999-10-01

    The Rı´o Mendoza valley at 33°S latitude has been repeatedly invaded by glaciers during the Late Pleistocene. Relative-age criteria, U-series ages, and thermoluminescense dating, permitted the glacial deposits to be separated into three mappable units, each less extensive than its predecessor, designed from oldest to youngest, Penitentes, Horcones and Almacenes drifts. Previous studies have shown that during the Penitentes advance the glacier system terminated at 2500 m, while during the subsequent Horcones advance, ice terminated at 2750 m and the Almacenes moraine reached 3250 m. A travertine layer overlying Penitentes till yielded 230Th/ 232Th ages of 38,300±5300, 24,200±2000 and 22,800±3100 yr B.P. This study focuses on dating interstadial sediments in the upper Rı´o Mendoza valley in order to constrain the ages of the drifts. A date was obtained from a composite stratigraphic profile based on exposures along the east side of the Rı´o de los Horcones Inferior valley, a tributary of the Rı´o de las Cuevas valley, which includes the Penitentes and Horcones tills separated by nonglacial sediments (silt, fine sand and clay), and are interpreted as representing the Penitentes-Horcones nonglacial interval. The fine quartz grains (4-11 μm) of these sediments were TL dated as 31,000±3100 yr. All these dates, which are minimum ages for the underlying Penitentes till, imply that the Penitentes ice advanced prior to the last glacial maximum and sometime before ca. 40,000 years ago. A minimum date for Horcones till comes from an exposure on the east side of the Rı´o de los Horcones Inferior valley where the Horcones and Almacenes tills are separated by sediments of nonglacial origin. The fine quartz grains (4-11 μm) of these sediments have been dated by TL as 15,000±2100 years ago. Almacenes till is inferred to represent a standstill or a readvance that occurred late during the Horcones glacier advance. These dates imply that the Penitentes advance may

  16. Mapping South American Summer Monsoon Changes during Heinrich Event 1 and the LGM: Insights from New Paleolake Records from the Central Andes

    NASA Astrophysics Data System (ADS)

    Chen, C. Y.; McGee, D.; Quade, J.

    2015-12-01

    Cave stalagmite records show strong evidence of abrupt changes in summer monsoons during Heinrich events, but we lack rigorous constraints on the amount of wetting or drying occurring in monsoon regions. Studies on shoreline deposits of closed-basin lakes can establish quantitative bounds on water balance changes through mapping-based estimates of lake volume variations. We present new dating constraints on lake level variations in Agua Caliente I and Laguna Loyoques, two closed-basin, high-altitude paleolakes on the Altiplano-Puna plateau of the Central Andes (23.1°S, 67.4°W, 4250 masl). Because this area receives >70% of its total annual precipitation during austral summer, the region is ideally suited to capture a pure response to changes in the South American summer monsoon (SASM). The plateau is home to several small (<40 km2) lakes surrounded by well-preserved paleoshorelines that indicate past wetter conditions. Agua Caliente I is unique, having multiple shorelines encrusted with biologically-mediated calcium carbonate "tufa" deposits. Initial U-Th dating of these massive shoreline tufas reveals that these deposits are dateable to within ±50 to 300 years due to high U concentrations and low initial Th content (as indicated by high 230Th/232Th). Our U-Th dates show that Agua Caliente I was greater in lake surface area during two periods: 17.5-14.5 kyrs BP, coincident with Heinrich Event 1 (HE1), and 24-23 kyrs BP, roughly coincident with the Last Glacial Maximum (LGM). At these times, Agua Caliente I also overflowed into a neighboring lake basin (Loyoques) through an 8-km long southeast-trending stream channel. Thus, during HE1 and the LGM, the lake was ~9 times larger in surface area relative to modern. Hydrologic modeling constrained by paleotemperature estimates is used to provide bounds for these past precipitation changes. We also tentatively explore physical mechanisms linking Heinrich events and the regional hydroclimate by comparing freshwater

  17. Widespread Lake Highstands in the Southernmost Andean Altiplano during Heinrich Event 1: Implications for the South American Summer Monsoon

    NASA Astrophysics Data System (ADS)

    Chen, C. Y.; McGee, D.; Quade, J.

    2014-12-01

    Speleothem-based oxygen isotope records provide strong evidence of anti-phased behavior of the northern and southern hemisphere summer monsoons during Heinrich events, but we lack rigorous constraints on the amount of wetting or drying occurring in monsoon regions. Studies centered on shoreline deposits of closed-basin lakes are well suited for establishing such quantitative controls on water balance changes by providing unequivocal evidence of lake volume variations. Here we present new dating constraints on the highstands of several high-altitude (3800-4350 m) paleolakes in the southern Andean Altiplano, an outlying arid region of the Atacama Desert stretching across the Chilean-Bolivian-Argentinian border east of the Andes (20-25°S). These lakes once occupied the closed basins where only phreatic playas, dry salars, and shallow ponds exist today. Initial U-Th dating of massive shoreline tufas reveals that these deposits are dateable to within ±150 to 300 yrs due to high U concentrations and low initial Th content (as indicated by high 230Th/232Th). Our U-Th and 14C dates show that lake highstands predominantly occur between 18.5 and 14.5 kyrs BP, coinciding with Heinrich Event 1 (HE1) and the expansion of other nearby lakes, such as Lake Titicaca. Because of their (1) location at the modern-day southwestern edge of the summer monsoon, (2) intact shoreline preservation, and (3) precise age control, these lakes may uniquely enable us to reconstruct the evolution of water balance (P-E) changes associated with HE1. Hydrologic modeling constrained by temperature estimates provided by local glacial records is used to provide bounds for past precipitation changes. We also examine North Atlantic cooling as the mechanism for these changes by comparing a compilation of S. American lake level records with various hosing experiments and transient climate simulations at HE1. Our results lend us confidence in expanding our U-Th work to other shoreline tufas in the

  18. The Last Interglacial sea level change: new evidence from the Abrolhos islands, West Australia

    NASA Astrophysics Data System (ADS)

    Eisenhauer, A.; Zhu, Z. R.; Collins, L. B.; Wyrwoll, K. H.; Eichstätter, R.

    U-series ages measured by thermal ionisation mass spectrometry (TIMS) are reported for a Last Interglacial (LI) fossil coral core from the Turtle Bay, Houtman Abrolhos islands, western Australia. The core is 33.4m long the top of which is approximately 5ma.p.s.l. (above present sea level). From the 232Th concentrations and the reliability of the U-series ages, two sections in the core can be distinguished. Calculated U/Th ages in core sectionI (3.3ma.p.s.l to 11mb.p.s.l) vary between 124+/-1.7kaBP (3.3ma.p.s.l.) and 132.5+/-1.8ka (4mb.p.s.l., i.e. below present sea level), and those of sectionII (11-23mb.p.s.l.) between 140+/-3 and 214+/-5kaBP, respectively. The ages of core sectionI are in almost perfect chronological order, whereas for sectionII no clear age-depth relationship of the samples can be recognised. Further assessments based on the ∂234U(T) criteria reveal that none of the samples of core sectionII give reliable ages, whereas for core sectionI several samples can be considered to be moderately reliable within 2ka. The data of the Turtle Bay core complement and extend our previous work from the Houtman Abrolhos showing that the sea level reached a height of approximately 4mb.p.s.l at approximately 134kaBP and a sea level highstand of at least 3.3ma.p.s.l. at approximately 124kaBP. Sea level dropped below its present position at approximately 116kaBP. Although the new data are in general accord with the Milankovitch theory of climate change, a detailed comparison reveals considerable differences between the Holocenand LI sea level rise as monitored relative to the Houtman Abrolhos islands. These observation apparently add further evidence to the growing set of data that the LI sea level rise started earlier than recognised by SPECMAP chronology. A reconciliation of these contradictionary observations following the line of arguments presented by Crowley (1994) are discussed with respect to the Milankovitch theory.

  19. Tables of Neutron-Induced Fission Cross Section for Various Pu, U, and Th Isotopes, Deduced from Measured Fission Probabilites

    SciTech Connect

    Younes, W; Britt, H C

    2003-03-31

    Cross sections for neutron-induced fission of {sup 231,233}Th, {sup 234,235,236,237,239}U, and {sup 240,241,243}Pu are presented in tabular form for incident neutron energies of 0.1 {le} E{sub n}(MeV) {le} 2.5. The cross sections were obtained by converting measured fission probabilities from (t,pf) reactions on mass-A targets to (n,f) cross sections on mass-A + 1 neutron targets, by using modeling to compensate for the differences in the reaction mechanisms. Data from Britt et al. were used for the {sup 234}U(t,pf) reaction, from Cramer et al. for the {sup 230,232}Th(t,pf), {sup 236,238}U(t,pf), and {sup 240,242}Pu(t,pf) reactions, and from Britt et al. for the {sup 233,235}U(t,pf) and {sup 239}Pu(t,pf) reactions. The fission probabilities P{sub (t,pf)}(E{sub x}), measured as a function of excitation energy E{sub x} of the compound system formed by the (t,p) reaction, are listed in the tables with the corresponding deduced cross sections as a function of incident neutron energy E{sub n}, {sigma}{sub (n,f)}(E{sub n}). The excitation energy and incident neutron energy are related by E{sub x} = E{sub n} + B{sub n}, where B{sub n}, where B{sub n} is the neutron binding energy. Comparison with ENDF/B-VI evaluations of the well-measured {sup 234,235,236}U(n,f) and {sup 240,241}Pu(n,f) cross sections confirms the accuracy of the present results within a 10% standard deviation above E{sub n} = 1 MeV. Below E{sub n} = 1 MeV, localized deviations of at most {+-} 20% are observed.

  20. Modeling report of the CEA cadarache MINERVE reactor for the OSMOSE project.

    SciTech Connect

    Klann, R.; Perret, G.; Hudelot, J. P.; Antony, M.

    2005-02-25

    The OSMOSE program (Oscillation in Minerve of isotopes in ''Eupraxic'' spectra) is a collaboration between the U.S. Department of Energy (DOE) and the Commissariat a l' Energie Atomique (CEA). It aims at measuring integral absorption rates of minor actinides by the oscillation technique in the MINERVE experimental facility located at the CEA Cadarache Research Center. The OSMOSE program also includes a complete analytical program to understand and resolve potential discrepancies between calculated and measured values. The OSMOSE program began in 2001 and will continue until 2013. The Argonne National Laboratory has developed Monte Carlo and deterministic calculation models of the MINERVE facility to determine core and safety parameters such as axial and radial fission rate distributions, control rod worth, spectral indices, and the reactivity worth of oscillated samples. Oscillation samples include calibration samples with different uranium enrichments and boron concentrations and the OSMOSE samples--separated actinides including {sup 232}Th, {sup 233}U, {sup 234}U, {sup 235}U, {sup 236}U, {sup 238}U, {sup 237}Np, {sup 238}Pu, {sup 239}Pu, {sup 240}Pu, {sup 241}Pu, {sup 242}Pu, {sup 241}Am, {sup 243}Am, {sup 244}Cm and {sup 245}Cm. Seven different neutron spectra will be created in the MINERVE facility: an overmoderated UO{sub 2} matrix (representative of a fuel processing plant or flooded storage cask), a UO{sub 2} matrix in water (representative of LWRs), a mixed oxide fuel matrix (representative of cores containing MOX fuels), two epithermal spectra (representative of under-moderated reactors), a moderated fast spectrum (representative of fast reactors which have some slowing down due to moderators such as lead-bismuth or sodium), and a very hard spectrum (representative of fast reactors with little moderation from reactor coolant). The different spectra are achieved by changing the experimental lattice within the MINERVE reactor. The currently investigated core

  1. 10 CFR 110.22 - General license for the export of source material.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... country not listed in § 110.28: (1) Uranium or thorium, other than U-230, U-232, Th-227, and Th-228, in any substance in concentrations of less than 0.05 percent by weight. (2) Thorium, other than Th-227... thorium, other than U-230, U-232, Th-227, or Th-228, in individual shipments of 10 kilograms or less...

  2. U-Pb Ages of Secondary Silica at Yucca Mountain, Nevada: Implications for the Paleohydrology of the Unsaturated Zone

    SciTech Connect

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

    2001-08-20

    U, Th, and Pb isotopes were analyzed in layers of opal and chalcedony from individual millimeter- to centimeter-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 {sup 206}Pb/{sup 204}Pb (up to 53,806), thus making them suitable for U-Pb age determinations. Interpretations of U-Pb isotopes in opal samples at Yucca Mountain are complicated by the incorporation of excess {sup 234}U at the time of mineral formation, resulting in reverse discordance of U-Pb ages. However, the {sup 207}Pb/{sup 235}U 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, {sup 207}Pb/{sup 235}U 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. {sup 234}U and {sup 230}Th in most silica layers deeper in the coatings are in secular equilibrium with {sup 238}U, which is consistent with their old age and closed system behavior during the past 0.5 m.y. U-Pb 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 depositional rates of 1 to 5 mm/m.y. These data imply that the deeper

  3. 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

  4. The Late Quaternary Seismic Stratigraphy of the Southern Shelf of the Strait of Istanbul (Sea of Marmara, Turkey)

    NASA Astrophysics Data System (ADS)

    Deniz Abuş, Eren

    2013-04-01

    The sea level changes in the northern shelf (Istanbul) of the Sea of Marmara and the sources of sedimentary packages at the southern exist of the Strait of Istanbul have been an ongoing debate the past decade. This study aims to enlighten both the sea level oscillations since ~125 ky before present and the structure of aforesaid sedimentary sequence, Unit 2, near Kurbaǧalı River observed in high resolution sparker seismic sections using global sea level change curves. Contary to Hiscott et al. (2002), Gökaşan et al. (2005), and Eriş et al. (2007) preferring the global sea level change curve in Fairbanks (1989) so as to explain the age interval of the sequence, we introduced the curve in Bard et al. (1990) presented the 230Th - 234U ages of Acropora palmata samples collected from the offshore of the island of Barbados, where Fairbanks (1989) submits the first chronology using the limited 14C ages. Therefore, the deposition of the Unit 2 was considered as 10 - 9 ky before present by Hiscott et al. (2002), as 12 - 11±1.1 ky BP by Gökaşan et al. (2005), and as 6.4 - 3.2 ky BP by Eriş et al. (2007). Having applied this calibration to our study, the age interval of the Unit 2 was calculated as 11.5 ky before present. In previous studies, Unit 2 was presented as prograding deltaic deposits of the Kurbaǧalı River yet our studies illustrates that the stream current of Kurbaǧalı River is not capable of supporting adequate sediment input, which is about 1.5 x 8.5 kilometers when the thickness and rate of propagation of Unit 2 are considered. Thanks to high resolution seismic sections and bathymetry, we firstly introduce that the Unit 2 is a point-bar structure forming as a product of the meandering regime at the southern exit of the Bosphorus.

  5. Regolith evolution on the millennial timescale from combined U-Th-Ra isotopes and in situ cosmogenic 10Be analysis in a weathering profile (Strengbach catchment, France)

    NASA Astrophysics Data System (ADS)

    Ackerer, J.; Chabaux, F.; Van der Woerd, J.; Viville, D.; Pelt, E.; Kali, E.; Lerouge, C.; Ackerer, P.; di Chiara Roupert, R.; Négrel, P.

    2016-11-01

    U-Th-Ra disequilibria, cosmogenic in situ 10Be concentrations and major and trace element concentrations have been analyzed in a 2 m-deep weathering profile sampled at the summit of the granitic Strengbach catchment (France). The data have been used to independently estimate both the long-term regolith production and denudation rates and the weathering and erosion rates. Modeling of the 238U-234U-230Th-226Ra disequilibrium variations in the lower part of the profile yields a regolith production rate of 12 ± 4 mm/kyr (30 ± 10 T/km2/yr), while modeling of the high-resolution 10Be concentration profile leads to an exposure age of 19.7 ± 2.2 kyr, an inherited concentration of 15,000 ± 1,000 at/g in quartz and a mean denudation rate of 22 ± 10 mm/kyr (37 ± 15 T/km2/yr). The consistency between production and denudation rates suggests that, on a millennial timescale, the regolith mass balance at the summit of the catchment is close to a steady state, even if the watershed may have been impacted by Quaternary climatic changes and by recent anthropogenic perturbations (e.g., 20th century acid rain and recent afforestation efforts). The results also indicate that physical erosion is likely the dominant long-term process of regolith denudation in the catchment. Furthermore, the comparison of the long-term production and denudation rates and of weathering and erosion rates determined from the depth profile analyses with the current weathering and erosion rates estimated at the outlet of the watershed based on monitoring of the water chemistry and sediment fluxes suggests that physical erosion may have varied more than the chemical weathering flux during the last 150 kyr. Although very few other sites with U-series, in situ 10Be and stream monitoring data are available for comparison, the current data suggest that (1) the mass balance steady state of regolith might be commonly achieved in soil mantled landscapes, and (2) physical erosion has varied much more than

  6. Time scale and conditions of weathering under tropical climate: Study of the Amazon basin with U-series

    NASA Astrophysics Data System (ADS)

    Dosseto, A.; Bourdon, B.; Gaillardet, J.; Allègre, C. J.; Filizola, N.

    2006-01-01

    The Rio Solimões/Amazonas (Amazon River) and its major tributaries have been analyzed for U-series nuclides. 238U- 234U- 230Th- 226Ra disequilibria have been measured in the dissolved (<0.2 μm) and suspended loads (>0.2 μm) as well as bed sands. U-series disequilibria are closely related to major and trace element compositions and therefore reflect elemental fractionation during chemical weathering. Moreover, while the dissolved load records present-day weathering, suspended particles integrate the erosion history over much longer time scales (>100 ka). Lowland rivers are characterized by long time scales of chemical erosion (⩾100 ka) resulting in a high weathering intensity. Moreover, exchange between suspended particles and the dissolved load may explain the U-series signature for these rivers. By combining U-series and Pb isotopes in suspended particles, we show that erosion in the Rio Madeira basin occurred as a multi-step process, whereby the pristine continental crust was eroded several hundreds of Ma ago to produce sediments that have then been integrated in the Cordillera by crustal shortening and are currently eroded. In contrast, recent erosion of a pristine crust is more likely for the Rio Solimões/Amazonas (<10 ka). The suspended particles of the rivers draining the Andes (Solimões/Amazonas, Madeira) suggest time scales of weathering ranging between 4 and 20 ka. This indicates that suspended particles transported by those rivers are not stored for long periods in the Andean foreland basin and the tropical plain. The sediments delivered to the ocean have resided only a few ka in the Amazon basin (6.3 ± 1 ka for the Rio Amazonas at Óbidos). Nevertheless, a large fraction of the sediments coming out from the Andes are trapped in the foreland basin and may never reach the ocean. Erosion in the Andes is not operating in steady state. U-series systematics shows unambiguously that rivers are exporting a lot more sediments than predicted by steady

  7. Quaternary tectonic stability of the Bahamian archipelago: evidence from fossil coral reefs and flank margin caves

    NASA Astrophysics Data System (ADS)

    Carew, James L.; Mylroie, John E.

    Throughout the islands of the Bahamian archipelago fossil coral reefs are found from current sea level up to a maximum elevation of +4 m. {234U}/{230Th} radiometric dates obtained from in situ corals from these reefs, by both alpha-count and mass-spectrometric techniques, indicates that they were all formed during Oxygen Isotope Substage 5e (ca. 125,000 years ago). Those data are consistent with a maximum sea-level highstand of +6 m during Substage 5e, and either no vertical motion of the Bahamas, or possible isostatic subsidence of up to 2 m during the past 120,000 years. No older in situ fossil corals, or other subtidal deposits, have been found subaerially exposed anywhere in the Bahamas. That finding suggests that late Quaternary (at least the past 300,000 years) isostatic subsidence has occurred at a rate of 1-2 m per hundred thousand years, and/or no pre-5e highstands were above modern sea level. An independent corroboration of the conclusions drawn about sea level amplitude and tectonic stability of the Bahamas from the coral reef data is available from examination of abundant flank margin caves (horizontal, phreatic dissolution caves) found above modern sea level throughout the Bahamas. These horizontally extensive air-filled caves have dissolutional ceilings with elevations that are restricted to +1 to +7 m, which is consistent with formation at the margin of a thin freshwater lens elevated by a past +6 m sea-level highstand. The restricted cave elevations, and the lack of stalagmites in these caves that are older than 100,000 years, are also consistent with cave formation during Substage 5e, and possible subsequent isostatic subsidence of a few metres. The subsurface geology of the southeastern Bahamas contains a long-term record (millions of years) that has been attributed to past tectonic activity along the North American/Caribbean plate boundary. While that record suggests differential subsidence across the Bahamas in the Tertiary Period, the data from

  8. Climate and environmental changes during the past millennium in central western Guizhou, China as recorded by Stalagmite ZJD-21

    NASA Astrophysics Data System (ADS)

    Kuo, Tz-Shing; Liu, Zi-Qi; Li, Hong-Chun; Wan, Nai-Jung; Shen, Chuan-Chou; Ku, Teh-Lung

    2011-04-01

    Stalagmite ZJD-21 (12.3-cm long) was collected from Zhijin Cave in Zhijin County, Guizhou, China. Its 210Pb profile and seven 230Th/ 234U dates indicate that the stalagmite has grown continuously for the past 1100 years. The δ18O record of ZJD-21 indicates that δ18O in the stalagmite was mainly influenced by rainfall amount and/or summer/winter rain ratio, with lighter values corresponding to wetter climatic conditions and/or more summer monsoonal rains. The ZJD-21 δ18O record suggests: (1) dry/warm climates during AD 950-1100 (overlapping with most of the Medieval Warm Period, MWP, in Europe); (2) strengthening of the summer monsoon from the MWP toward the beginning of the Little Ice Age (LIA) at AD 1250; (3) relatively wet/cold conditions occurred between AD 1250 and 1500, shown by relatively light δ18O values; (4) the summer monsoon intensity strongly declined referred by the increase δ18O trend from AD 1500 to AD 1600, perhaps resulting in dry/cold conditions; and (5) a strongly enhancement of the summer monsoon intensity appeared from AD 1700 to 1950, reflecting wet/cold conditions during the late period of the LIA. On decadal scales the monsoonal climate of central western Guizhou can be either warm/wet and cold/dry, or warm/dry and cold/wet. The δ13C variations in ZJD-21 on decadal-to-centennial scales respond mainly to vegetation changes with heavier values reflecting lesser amount of forest coverage. Prior to AD 1700, the δ13C generally co-varied with δ18O reflecting the expected more extensive vegetation growth (lighter δ13C) under wetter climate (lighter δ18O). However, during the past 300 years the δ13C increased sharply showing an opposite trend to that of δ18O. This observation strongly suggests that a decline of surface vegetation due to an artificial deforestation might have occurred - an occurrence coincident with the large-scale immigration into central western Guizhou in connection with copper-mining activities during the reign of

  9. The Pech-de-l'Azé I Neandertal child: ESR, uranium-series, and AMS 14C dating of its MTA type B context.

    PubMed

    Soressi, M; Jones, H L; Rink, W J; Maureille, B; Tillier, A-M

    2007-04-01

    The Pech-de-l'Azé I skull and mandible are included in the juvenile Neandertal remains from Europe. However, some preserved features in the cranial skeleton seem to distinguish the specimen from other Neandertal children. Unfortunately, the stratigraphic position and dating of this child has never been clear. Our recent work on unpublished archives show that the Pech-de-l'Azé I Neandertal child was discovered at the bottom of layer 6, attributed to the Mousterian of Acheulean tradition type B. These skull and mandible are the first diagnostic human remains (aside from an isolated tooth) attributed to the Mousterian of Acheulian tradition (MTA) type B. Consequently, we confirm that Neandertals were the makers of this Mousterian industry, which is characterized by unusual high frequencies of Upper Paleolithic type tools, elongated blanks and blades. We were able to date the context of the hominid remains by dating layer 6 and the layers above and beneath it using ESR, coupled ESR/(230)Th/(234)U (coupled ESR/U-series), and AMS (14)C. Coupled ESR/U-series results on 16 mammalian teeth constrain the age of the uppermost layer 7 to 41-58ka, and layer 6 to 37-51ka. The wide spread in each age estimate results mainly from uncertainties in the gamma-dose rate. These ages are concordant with AMS (14)C ages of two bones coming from the top of layer 6, which provide dates of about 41.7-43.6ka cal BP. A combination of stratigraphic arguments and dating results for layers 6 and 7 show that the Neandertal child cannot be older than 51ka or younger than 41ka. The lowermost layer 4 is shown to be older than 43ka by the principle of superposition and ESR dating in the immediately overlying layer 5. This study shows that the MTA type B had been manufactured by Neandertals before the arrival of anatomically modern humans in the local region. Additionally, by providing a firm chronological framework for the specific morphometric the features of Pech-de-l'Azé I Neandertal child, this

  10. The Late Pleistocene Duoi U'Oi cave in northern Vietnam: palaeontology, sedimentology, taphonomy and palaeoenvironments

    NASA Astrophysics Data System (ADS)

    Bacon, Anne-Marie; Demeter, F.; Duringer, P.; Helm, C.; Bano, M.; Vu, The Long; Kim Thuy, Nguyen Thi; Antoine, P.-O.; Thi Mai, Bui; Huong, Nguyen Thi Mai; Dodo, Y.; Chabaux, F.; Rihs, S.

    2008-08-01

    This paper describes new fossil materials recovered at the Duoi U'Oi site, in December 2003, by a Vietnamese-French-Japanese team. The Duoi U'Oi cave is located in Man Duc village, 25 km of Hoà Binh city in northern Vietnam. It belongs to a karstic network developed in a dark grey micritic marine limestone dated from the Lower to the Middle Triassic. The sedimentary fill produced a rich mammalian fauna, essentially composed of isolated teeth of middle- to large-sized mammals (Artiodactyla, Perissodactyla, Proboscidea, Carnivora, Rodentia, Primates), and characteristic of Late Pleistocene. The results of the Duoi U'Oi fieldwork are of great interest for the following reasons: (1) the biochronological age of the fauna is consistent with 230Th/ 234U/ 238U dating from the calcitic floors (66±3 ka). The Duoi U'Oi fauna is thus the oldest well-dated modern fauna known for the Southeast Asian mainland; (2) in terms of sedimentology, the analysis of the formation of the fossiliferous breccia and that of the processes of deposits shows a close relation between the karstic deposits inside the cave and the deposits in the alluvial terraces. The observation of three levels of alluvial terraces associated with three caves situated at 62, 10 and 3 m above the present alluvial plain suggests that exokarstic and endokarstic sediments evolved together; (3) in terms of palaeobiogeography, Duoi U'Oi is the continental fauna showing the strongest resemblance with the Late Pleistocene faunas from Indonesian islands (Punung, Gunung Dawung, Lida Ajer, Sibrambang and Djambu caves); this implies that, at the time of Duoi U'Oi, ca 70 ka, the Sundaland was mainly characterised by faunas of modern aspect; (4) the analysis of major taphonomic factors that led to the mammal assemblage reveals a combination of selective agents (selective role of predators and porcupines, selective destruction of age classes for some species, selective preservation of fossils due to the deposition processes in

  11. Inner gorge-slot canyon system produced by repeated stream incision (eastern Alps): Significance for development of bedrock canyons

    NASA Astrophysics Data System (ADS)

    Sanders, Diethard; Wischounig, Lukas; Gruber, Alfred; Ostermann, Marc

    2014-06-01

    Many inner bedrock gorges of the Alps show abrupt downstream changes in gorge width, as well as channel type and gradient, as a result of epigenetic incision of slot canyons. Many slot canyons also are associated with older gorge reaches filled with Quaternary deposits. The age of slot canyons and inner bedrock gorges, however, commonly is difficult to constrain. For the inner-bedrock gorge system of the Steinberger Ache catchment (eastern Alps), active slot canyons as well as older, abandoned gorge reaches filled with upper Würmian proglacial deposits record three phases of gorge development and slot-canyon incision. A 234U/230Th age of cement of 29.7 ± 1.8 ka in fluvial conglomerates onlapping the flank of an inner gorge fits with late Würmian valley-bottom aggradation shortly before pleniglacial conditions; in addition, the age indicates that at least the corresponding canyon reach must be older. During advance of ice streams in the buildup of the Last Glacial Maximum (LGM), the catchment was blocked, and a proglacial lake formed. Bedrock gorges submerged in that lake were filled with fluviolacustrine deposits. During the LGM, the entire catchment was overridden by ice. During post-glacial reincision, streams largely found again their preexisting inner bedrock canyons. In some areas, however, the former stream course was 'missed', and a slot canyon formed. The distribution of Pleistocene deposits, the patterns of canyon incision, and the mentioned U/Th cementation age, however, together record a further discrete phase of base-level rise and stream incision well before the LGM. The present course of Steinberger Ache and its tributaries is a patchwork of (1) slot canyons incised during post-glacial incision; (2) vestiges of slot canyons cut upon an earlier (middle to late Würmian?) cycle of base-level rise and fall; (3) reactivated reaches up to ~ 200 m in width of inner bedrock gorge that are watershed at present, and more than at least ~ 30 ka in age; and (4

  12. Calcite precipitation on glass substrates and active stalagmites in Katerloch Cave (Austria): Constraints from environmental monitoring

    NASA Astrophysics Data System (ADS)

    Sakoparnig, Marlene; Boch, Ronny; Wang, Xianfeng; Lin, Ke; Spötl, Christoph; Leis, Albrecht; Gollowitsch, Anna; Dietzel, Martin

    2016-04-01

    Located near Graz at the SE-rim of the Alps Katerloch is well-known for its impressive dripstone decoration, e.g. several metres tall and relatively fast growing (0.2-0.7 mm/yr on average) candle-stick-type stalagmites. In the course of an ongoing multi-annual and partially high-resolution cave monitoring program we study modern (active) sites of carbonate deposition focusing on the site-specific growth dynamics and connection of modern regional and cave environmental conditions with petrographic, chemical and stable isotopic information captured in the speleothems. Fresh calcite precipitates on artificial (glass) substrates underneath active drip sites were collected continuously from 2006 to 2014 (eight years!). The samples (up to 7 mm thick) represent cave sections of different temperature and drip sites of partially different characteristics (e.g. drip rate). We also recovered short drill cores (up to 3 cm length, 1 cm diameter) from the top of active stalagmites probably representing the last decades to centuries of calcite crystallization. Moreover, an actively growing stalagmite (K10) comprising both modern and past calcite deposition was collected. 238U-234U-230Th dating using MC-ICP-MS of K10 (71 cm long) revealed several distinct growth intervals (separated by growth interruptions) starting at 129.1 ±1.2 kyr BP (Last Interglacial) up to now, mostly reflecting warm and humid climate intervals. High-resolution (100 μm) isotope profiles micromilled from the multi-annual modern calcite precipitates on artificial substrates revealed low δ13C values of -12.8 to -8.3 ‰ (VPDB) and relatively high δ18O of -6.9 to -4.9 ‰Ṫhe δ18O curves from all collection sites (different growth rate) record a pronounced decrease during their most recent growth period most likely corresponding to a significant decrease towards lower oxygen isotope values observed in drip waters collected in the year 2014 compared with samples from 2005 to 2007. Drip water δ2H /δ18O

  13. Quantification soil production and erosion using isotopic techniques

    NASA Astrophysics Data System (ADS)

    Dosseto, Anthony; Suresh, P. O.

    2010-05-01

    Soil is a critical resource, especially in the context of a rapidly growing world's population. Thus, it is crucial to be able to quantify how soil resources evolve with time and how fast they become depleted. Over the past few years, the application of cosmogenic isotopes has permitted to constrain rates of soil denudation. By assuming constant soil thickness, it is also possible to use these denudation rates to infer soil production rates (Heimsath et al. 1997). However, in this case, it is not possible to discuss any imbalance between erosion and production, which is the core question when interested in soil resource sustainability. Recently, the measurement of uranium-series isotopes in soils has been used to quantify the residence time of soil material in the weathering profile and to infer soil production rates (Dequincey et al. 2002; Dosseto et al. 2008). Thus, the combination of U-series and cosmogenic isotopes can be used to discuss how soil resources evolve with time, whether they are depleting, increasing or in steady-state. Recent work has been undertaken in temperate southeastern Australia where a several meters thick saprolite is developed over a graniodioritc bedrock and underlains a meter or less of soil (Dosseto et al., 2008) and in tropical Puerto Rico, also in a granitic catchment. Results show that in an environment where human activity is minimal, soil and saprolite are renewed as fast as they are destroyed through denudation. Further work is investigating these processes at other sites in southeastern Australia (Frogs Hollow; Heimsath et al. 2001) and Puerto Rico (Rio Mameyes catchment; andesitic bedrock). Results will be presented and a review of the quantification of the rates of soil evolution using isotopic techniques will be given. Dequincey, O., F. Chabaux, et al. (2002). Chemical mobilizations in laterites: Evidence from trace elements and 238U-234U-230Th disequilibria. Geochim. Cosmochim. Acta 66(7): 1197-1210. Dosseto, A., S. P

  14. Late-Quaternary Speleothem Records from the Balkan Peninsula - Potential, Objectives and First Results

    NASA Astrophysics Data System (ADS)

    John, I.; McCoy, W. D.; Markovic, S.; Endlicher, W.

    2010-12-01

    Mid-latitude speleothems often contain detailed, high-resolution records of local and regional interglacial climate changes. Many speleothem records of Holocene (MIS 1) and Eemian (MIS 5e) climate evolution have been investigated, but there is very little work being done in the Balkan region, despite the fact that the area is very rich in limestone caves with speleothems. Situated at the interface between temperate-continental and Mediterranean climates, present-day climate on the Balkan Peninsula is determined by two major upper-level jet streams, the polarfront jet (PFJ) and the subtropical jet (STJ). On a seasonal scale, both features exert varying influence and determine frontogenesis processes, cyclonic activity and precipitation. On decadal to millennial time-scales, changes and fluctuations in the position and permanency of these atmospheric circulation features influence the isotope signature in rainfall and ultimately in cave drip waters and related speleothems. We are investigating speleothems from Serbia, Montenegro and Bosnia-Herzegovina to study Late Quaternary climatic changes and to learn how both synoptic-scale systems were linked during the Holocene and previous interglacial periods. By example of a stalagmite collected in Vernjikica Cave, Serbia (Carpatho-Balkans), the project's potential to address important aspects of paleoclimatic research in the Mediterranean realm is discussed. The first studied, fine-laminated calcite stalagmite is about 50 cm tall and extends conically from the base to the top, presenting at least two visible growth discontinuities. Four preliminary uranium-series ages (234U/230Th) constrain the general period of growth to MIS 5d to MIS 5b. Preliminary results suggest that the stable oxygen isotope profile obtained from the axial zone largely reflects the unaltered isotopic composition of the cave drip water. The observed shifts in the isotope records display long-term changing climate conditions from temperate warm and

  15. A Record of Changes in the Indian Monsoon From ~29 ka to 11 ka Based on a Stalagmite from Socotra Island, Yemen

    NASA Astrophysics Data System (ADS)

    Shakun, J. D.; Burns, S. J.; Fleitmann, D.; Kramers, J.; Matter, A.; Al-Subary, A.

    2005-12-01

    Stalagmite M1-5 from Socotra Island, Yemen in the northwest Indian Ocean provides a robust, high-resolution paleoclimate record from 28.5-11.1 ka based on 681 stable isotope and 28 234U/ 230Th measurements. Variations in M1-5 oxygen isotope ratios are interpreted to be primarily driven by an amount effect and to principally reflect changes in the mean position and/or intensity of convection of the intertropical convergence zone. Migration of the ITCZ over the region is the island's source of precipitation. The M1-5 d18O time series is strongly correlated to the Greenland ice cores, similar to an earlier Socotra speleothem record from 53-40 ka (Burns et al., 2003), indicating a North Atlantic-Indian Ocean cold-dry/warm-wet teleconnection persisted through the end of the last glacial period. D/O events 1, 2, 3, Heinrich events 0 and 1, and the Holocene onset are well expressed in M1-5, and the Last Glacial Maximum occurs at ~23 ka, consistent with northern hemisphere ice volume and temperature forcing. M1-5 correlates well with Arabian Sea monsoon-driven productivity and denitrification records as well as the Hulu and Dongge Cave speleothem records from China over decadal to millennial timescales, indicating the entire East African-Asian monsoon system behaved as a cohesive unit during the last deglaciation. M1-5 is also highly coherent with records from the Cariaco Basin during the Bolling/Allerod period, and generally coherent over longer timescales as well, suggesting the intertropical convergence zone fluctuated in unison in the Indian and Atlantic Ocean basins. Significant antiphasing is seen between M1-5 and the Byrd ice core from Antarctica throughout the entire length of the speleothem record, implying the operation of the bipolar seesaw during this interval. In fact, M1-5 is more strongly anticorrelated with Antarctica than is Greenland, suggesting a potential bipolar seesaw mechanism (or feedback) other than the Atlantic thermohaline circulation, perhaps

  16. Corrigendum to "Deep water provenance and dynamics of the (de)glacial Atlantic meridional overturning circulation" [Earth Planet. Sci. Lett. 445 (2016) 68-78

    NASA Astrophysics Data System (ADS)

    Lippold, Jörg; Gutjahr, Marcus; Blaser, Patrick; Christner, Emanuel; de Carvalho Ferreira, Maria Luiza; Mulitza, Stefan; Christl, Marcus; Wombacher, Frank; Böhm, Evelyn; Antz, Benny; Cartapanis, Olivier; Vogel, Hendrik; Jaccard, Samuel L.

    2017-01-01

    We have reconstructed past modes of the Atlantic Meridional Overturning Circulation (AMOC) by combining two sedimentary proxies, Nd isotopes (εNd) and the 231Pa/230Th ratio over the last deglaciation. Combined down-core 231Pa/230Th and εNd records from six Atlantic Ocean sediment archives are presented (Lippold et al., 2016).

  17. Extraction of protactinium-233 and separation from thermal neutron-irradiated thorium-232 using crown ethers

    SciTech Connect

    Jalhoom, Moayyed G.; Mohammed, Dawood A.; Khalaf, Jumah S.

    2008-07-01

    A new method was developed for the extraction and separation of {sup 233}Pa from thermal neutron-irradiated {sup 232}Th. Solutions of Pa{sup 233} were prepared in LiCI-HCl solutions from which appreciable extraction was obtained using dibenzo-18-crown-6 in 1,2-dichloroethane. The effects of cavity size, substitutions on the crown ring, type of the organic solvent, and temperature on extraction are discussed. Very high separation factors were obtained for the pairs {sup 233}Pa/{sup 232}Th (>105), {sup 233}Pa/{sup 233}U (> 1000), and {sup 232}U/{sup 232}Th (>60). (authors)

  18. Interactions of secondary particles with thorium samples in the setup QUINTA irradiated with 6 GeV deuterons

    NASA Astrophysics Data System (ADS)

    Khushvaktov, J.; Adam, J.; Baldin, A. A.; Chilap, V. V.; Furman, V. I.; Sagimbaeva, F.; Solnyshkin, A. A.; Stegailov, V. I.; Tichy, P.; Tsoupko-Sitnikov, V. M.; Tyutyunnikov, S. I.; Vespalec, R.; Vrzalova, J.; Yuldashev, B. S.; Wagner, V.; Zavorka, L.; Zeman, M.

    2016-08-01

    The natural uranium assembly, QUINTA, was irradiated with 6 GeV deuterons. The 232Th samples were placed at the central axis of the setup QUINTA. The spectra of gamma rays emitted by the activated 232Th samples have been analysed and more than one hundred nuclei produced have been identified. For each of those products, reaction rates have been determined. The ratio of the weight of produced 233U to 232Th is presented. Experimental results were compared with the results of Monte Carlo simulations by FLUKA code.

  19. Natural radioactivity content of granite tiles used in Greece.

    PubMed

    Papaefthymiou, H

    2008-01-01

    Measurements of (226)Ra, (232)Th and (40)K activity concentrations in commercial granite tiles imported in Greece were performed using gamma-ray spectrometry. The activity concentration of (226)Ra, (232)Th and (40)K ranged from 1 to 434, 2 to 239 and 71 to 1576 Bq kg(-1), respectively. The calculated activity concentration index (I) values for all granite samples examined were found to be within the EC limit values for superficial and other materials with restricted use.

  20. Petrological variability in recent magmatism at Axial Seamount

    NASA Astrophysics Data System (ADS)

    Dreyer, B. M.; Clague, D. A.; Gill, J. B.

    2011-12-01

    Axial Seamount is known for its compositional homogeneity. We report on petrological variability in lavas from the summit caldera and rims of Axial Seamount during the last ~1.2ka and its implications for shallow crustal magma dynamics. AUVs have mapped the summit at ~1 m resolution, and ROVs have collected numerous lavas and volcaniclastic cores. Geospatial, superpositional, compositional, and age constraint data were used to outline flow units and construct geologic maps. Nearly 200 glasses from summit lavas were analyzed for major elements. A subset of ~20 samples were analyzed for selected trace elements, Pb-, U-, and Th- isotope ratios, and 226Ra and 210Pb. The results a) confirm a high degree compositional homogeneity, b) demonstrate a more restricted range in Pb-isotope ratios than previous data, c) indicate uniform compositional source component(s) genetically linked to that of the Cobb-Eickelberg seamount chain, and d) expand the dataset of distinctly-low 230Th/232Th lavas and subdivide them into geospatial groups. Hundreds of volcaniclastic grains collected from subsurface depths of up to several tens of cm analyzed for major elements extend the record of summit magmatism beyond what is exposed. Summit lava glasses are compositionally N-MORB. Summit volcaniclastics range to higher MgO (+1%); thus, magmatism likely included more mafic episodes than is recorded in the flows as yet sampled or that volcaniclastics preferentially sample higher temperature lavas. Negative correlation of CaO/Al2O3 with MgO in all glasses suggests fractionation from parental melt(s) of plag ± ol but not cpx. K2O/TiO2 ranges are typical for much of the JdFR. Summit lavas range from aphyric to ~35% plag phyric ± a few % ol. Plag-phyric summit lavas tend to have greater MgO (>7.5%), lower CaO/Al2O3 (<0.80), and lower K2O/TiO2 (<0.10) compared to aphyric lavas. For ~18 caldera flows with absolute or relative age control, plag-phyric lavas are older than aphyric lavas, the oldest of

  1. Constrains on the Uranium Isotopic Composition of Seawater and Implications for Coral U/Th Geochronology

    NASA Astrophysics Data System (ADS)

    Chutcharavan, P. M.; Dutton, A.; Ellwood, M. J.

    2015-12-01

    Coral U-series geochronology is an important tool for calibrating records of sea level change during the late Quaternary and coral 14C dates for the radiocarbon timescale. However, coralline aragonite is highly susceptible to diagenesis, and samples must be carefully screened to ensure a specimen is unaltered. One method used to accept or reject U-series ages is the initial coral 234U/238U activity ratio, which reflects the 234U/238U activity of seawater at the time of coral skeleton formation. Due to the long residence time of uranium in the ocean (~400,000 years), researchers often assume that seawater 234U/238U has remained constant throughout the late Pleistocene. Coral specimens whose U-series ages yield an initial 234U/238U value that is significantly different than modern seawater are considered altered. Several studies have demonstrated that coral initial 234U/238U and, hence, seawater 234U/238U may have varied significantly on glacial-interglacial timescales, but the cause of this variability is subject to debate. To evaluate the pattern and mechanisms of 234U/238U variability in seawater over the last glacial cycle, we draw upon a compilation of U-series measurements of shallow and deep water corals to better define the observed variability. Observed trends from the coral record will be assessed using a simple two-box model of the ocean to determine how changes to the ocean's uranium isotope budget during glacial cycles can explain shifts in seawater 234U/238U. An improved understanding the evolution of seawater 234U/238U composition will enable more robust interpretations of both closed-system and open-system ages for corals. Such interpretations of U-series ages are essential to the development of robust chronologies for climate and sea level change and for improving the calibration of the radiocarbon timescale.

  2. Prompt Fission Neutron Spectra of Actinides

    SciTech Connect

    Capote, R; Chen, Y J; Hambsch, F J; Kornilov, N V; Lestone, J P; Litaize, O; Morillon, B; Neudecker, D; Oberstedt, S; Ohsawa, T; Smith, D. L.

    2016-01-01

    The energy spectrum of prompt neutrons emitted in fission (PFNS) plays a very important role in nuclear science and technology. A Coordinated Research Project (CRP) “Evaluation of Prompt Fission Neutron Spectra of Actinides”was established by the IAEA Nuclear Data Section in 2009, with the major goal to produce new PFNS evaluations with uncertainties for actinide nuclei. The following technical areas were addressed: (i) experiments and uncertainty quantification (UQ): New data for neutron-induced fission of 233U, 235U, 238U, and 239Pu have been measured, and older data have been compiled and reassessed. There is evidence from the experimental work of this CRP that a very small percentage of neutrons emitted in fission are actually scission neutrons; (ii) modeling: The Los Alamos model (LAM) continues to be the workhorse for PFNS evaluations. Monte Carlo models have been developed that describe the fission phenomena microscopically, but further development is needed to produce PFNS evaluations meeting the uncertainty targets; (iii) evaluation methodologies: PFNS evaluations rely on the use of the least-squares techniques for merging experimental and model data. Considerable insight was achieved on how to deal with the problem of too small uncertainties in PFNS evaluations. The importance of considering that all experimental PFNS data are “shape” data was stressed; (iv) PFNS evaluations: New evaluations, including covariance data, were generated for major actinides including 1) non-model GMA evaluations of the 235U(nth,f), 239Pu(nth,f), and 233U(nth,f) PFNS based exclusively on experimental data (0.02 ≤ E ≤ 10 MeV), which resulted in PFNS average energies E of 2.00±0.01, 2.073±0.010, and 2.030±0.013 MeV, respectively; 2) LAM evaluations of neutron-induced fission spectra on uranium and plutonium targets with improved UQ for incident energies from thermal up to 30 MeV; and 3) Point-by-Point calculations for 232Th, 234U and 237Np targets; and (v) data

  3. Protactinium neutron-induced fission up to 200 MeV

    NASA Astrophysics Data System (ADS)

    Maslov, V.

    2010-03-01

    The theoretical evaluation of 230-233Pa(n,F) cross sections is based on direct data, 230-234Pa fission probabilities and ratios of fission probabilities in first-chance and emissive fission domains, surrogate for neutroninduced fission. First chance fission cross sections trends of Pa are based on consistent description of 232Th(n,F), 232Th(n,2n) and 238U(n,F), 238U(n,xn) data, supported by the ratio surrogate data by Burke et al., 2006, for the 237U(n,F) reaction. Ratio surrogate data on fission probabilities of 232Th(6 Li,4 He)234Pa and 232 Th(6 Li,d)236U by Nayak et al., 2008, support the predicted 233Pa(n, F) cross section at En=11.5-16.5 MeV. The predicted trends of 230-232Pa(n, F) cross section up to En=20 MeV, are consistent with fissilities of Pa nuclides, extracted by 232Th(p,F) (Isaev et al., 2008) and 232Th(p,3n) (Morgenstern et al., 2008) data analysis. The excitation energy and nucleon composition dependence of the transition from asymmetric to symmetric scission for fission observables of Pa nuclei is defined by analysis of p-induced fission of 232Th at Ep=1-200 MeV. Predominantly symmetric fission in 232Th(p,F) at En( p)=200 MeV as revealed by experimental branching ratios (Dujvestijn et al., 1999) is reproduced. Steep transition from asymmetric to symmetric fission with increase of nucleon incident energy is due to fission of neutron-deficient Pa (A≤229) nuclei. A structure of the potential energy surface (a drop of f f symmetric and asymmetric fission barriers difierence (EfSYM - EfASYM) from ~3.5 MeV to ~1 MeV) of N-deficient Pa nuclides (A≤226) and available phase space at outer fission saddles, are shown to be responsible for the sharp increase with En( p) of the symmetric fission component contribution for 232Th(p,F) and 230-233 Pa(n, F) reactions. That is a strong evidence of emissive fission nature of moderately excited Pa nuclides, reliably quantified only up to En( p)~20(30) MeV. Predicted fission cross section of 232Pa(n,F) coincides

  4. Protactinium-thorium ratio as a proxy for ocean circulation

    NASA Astrophysics Data System (ADS)

    Balcerak, Ernie

    2011-12-01

    The Atlantic meridional overturning circulation (AMOC) transports water and heat over long distances in the Atlantic Ocean and is believed to have an important effect on Earth's climate. Knowing how strong the AMOC was in the past is essential to understanding past climate. One proxy researchers have used to assess the past strength of the AMOC is the sedimentary protactinium- thorium ratio (231Pa/230Th). Both 231Pa and 230Th are produced through decay of uranium at a constant rate in the ocean water column, but 230Th does not last long enough in the water to be transported away from the location where it was produced, while 231Pa has a longer residence time in the water. Therefore, sedimentary 231Pa/230Th ratios could provide information about the strength of past ocean circulation.

  5. The natural flux of greenhouse gases in the case of monitoring the flux of juvenile carbon dioxide in the Hranice Karst

    NASA Astrophysics Data System (ADS)

    Geršl, Milan; Stepišnik, Uroš; Mareček, Jan; Geršlová, Eva; Hammerschmiedt, Michal

    2015-04-01

    Rn, groundwater levels, and influence of the ambient conditions on the cave system and the operation of the visitor trail. The data obtained are an exceptional source of information about the behaviour of natural emissions of a greenhouse gas in the form of juvenile carbon dioxide. The hydrothermal speleothems carry unique information about production of carbon dioxide in the studied area. Based on their dating using the 230Th/234U method it can be deduced indirectly that the carbon dioxide emissions occurred as early as 84-127 thousand years ago in the area. The research was conducted with the support of the project entitled "Postdoc contracts at MENDELU technical and ekonomical research' (CZ.1.07/2.3.00/30.0031). Geršl, M. - Geršlová, E. - Šimečková, B. (2012): Subcrustal CO2 flux measurement in the Hranice hydrothermal Karst, methodology and first results. - Geoscience research reports for 2011, 45, D, 162-166. Praha. Meyberg, M. - Rinne, B. (1995): Messung des 3He/4He-Isotopenverhältnisses im Hranicka Propast (Tschechische Republik). - Die Höhle. Zeitschrift für Karst- und Höhlenkunde, 46, 1, 5-8. Wien.

  6. High-Resolution Speleothem Records of the Indian Ocean Monsoon Variability of the Last 6 ka and 0,5 ka From Soqotra Island, Yemen

    NASA Astrophysics Data System (ADS)

    de Geest, P.; Verheyden, S.; Cheng, H.; Edwards, L. R.; Keppens, E.

    2004-12-01

    Soqotra is an arid tropical island in the Indian Ocean, situated between the Horn of Africa and the Arabian Peninsula. The inter-tropical convergence zone (ITCZ) passes there twice each year, resulting in a bi-annual rainy season. High-resolution \\delta18O and \\delta13C ratios of speleothems from two different caves are used to reconstruct changes in the Monsoon intensity and/or variability. Based on 10 TIMS 234U/230Th dating, two active speleothems from Hoq (S-STM1) and Kazekas Caves (S-STM5) have formed over a period of 6 ka BP and 0,5 ka BP, respectively. To obtain a detailed climate reconstruction more than 1000 \\delta13C and \\delta18O measurements were carried out, providing a time resolution between 2,5 and 10 years. In S-STM1 \\delta18O -values range between -4,5\\permil and -1,5\\permil and \\delta13C -values between -10,5\\permil and -5,5\\permil; while for S-STM5 these values range respectively between -4\\permil and -2\\permil and -7\\permil and -3\\permil (vs VPDB). Based on the comparison between \\delta18O excursions and historical meteorological data, the amount of precipitation is reflected in the \\delta18O signal. Different mechanisms for the \\delta13C are considered, such as a diminution of the C4-type vegetation during droughts, resulting in more positive \\delta13C -value or kinetic effects during the calcification process itself. Throughout the time series, co-variation occur between \\delta13C and \\delta18O -values (R2= 0,69) exhibiting long term (millennial) and short term (decadal) variations. In both stalagmites, layers of white porous calcite (WPC) (0,1-0,5mm) and dark dense calcite (DDC) (0,01-0,1mm) alternate, most probably due to seasonal variations. The WPC has more positive \\delta13C and \\delta18O -values, while the DDC shows more negative values, clearly demonstrated by high-resolution micro sampling up to a monthly to bi-weekly resolution. A positive correlation between the greyscale variations in the calcite fabric, the

  7. Coupling data from U-series and 10Be CRN to evaluate soil steady-state in the Betic Cordillera

    NASA Astrophysics Data System (ADS)

    Schoonejans, Jerome; Vanacker, Veerle; Opfergelt, Sophie; Granet, Mathieu; Chabaux, François

    2015-04-01

    The regolith mantel is produced by weathering of bedrock through physical and biochemical processes. At the same time, the upper part of the regolith is eroded by gravity mass movements, water and wind erosion. Feedback's between production and erosion of soil material are important for soil development, and are essential to reach long-term steady-state in soil chemical and physical properties. Nowadays, long-term denudation rates of regolith can be quantified by using in-situ cosmogenic nuclides (CRN). If the soil thickness remains constant over sufficiently long time, soil production rates can be determined. However, the a priori assumption of long-term steady-state can be questionable in highly dynamic environments. In this study, we present analytical data from two independent isotopic techniques, in-situ cosmogenic nuclides and Uranium series disequilibrium. The disequilibrium of Uranium isotopes (238U, 234U, 230Th, 226Ra) is an alternative method that allows assessing soil formation rates through isotopic analysis of weathering products. Nine soil profiles were sampled in three different mountain ranges of the Betic Cordillera (SE Spain): Sierra Estancias, Filabres, Cabrera. All soils overly fractured