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1

Quantum description of quaternary nuclear fission  

Microsoft Academic Search

The quantum theory of binary and ternary fission is generalized to the case of recently observed quaternary nuclear fission.\\u000a Formulas for the amplitudes of partial fission widths and angular and energy distributions of quaternary fission products\\u000a are derived with allowance for strong channel coupling. The nonevaporation mechanism for formation of light particles is used\\u000a to explain the experimentally observed decrease

S. G. Kadmensky; O. V. Smolyansky

2007-01-01

2

P-odd, P-even, and T-odd asymmetries in true quaternary fission of nuclei  

NASA Astrophysics Data System (ADS)

The coefficients of P-odd, P-even, and T -odd asymmetries for a third and a fourth prescission particle emitted in the true quaternary fission of nuclei that was induced by polarized cold neutrons were studied on the basis of quantum-mechanical fission theory. By using non-evaporation (nonadiabatic) mechanisms of light-particle emission, these coefficients were compared with the analogous coefficients for prescission third particles emitted in the ternary fission of nuclei.

Kadmensky, S. G.; Titova, L. V.

2013-04-01

3

P-odd, P-even, and T-odd asymmetries in true quaternary fission of nuclei  

SciTech Connect

The coefficients of P-odd, P-even, and T -odd asymmetries for a third and a fourth prescission particle emitted in the true quaternary fission of nuclei that was induced by polarized cold neutrons were studied on the basis of quantum-mechanical fission theory. By using non-evaporation (nonadiabatic) mechanisms of light-particle emission, these coefficients were compared with the analogous coefficients for prescission third particles emitted in the ternary fission of nuclei.

Kadmensky, S. G., E-mail: kadmensky@phys.vsu.ru; Titova, L. V. [Voronezh State University (Russian Federation)] [Voronezh State University (Russian Federation)

2013-04-15

4

Study of ternary and quaternary spontaneous fission of sup 2 sup 5 sup 2 Cf with the NESSI detector  

E-print Network

Ternary and quaternary spontaneous decay of sup 2 sup 5 sup 2 Cf was studied with the NESSI detector, a combination of two 4 pi detectors for charged particles, neutrons and gamma-rays. The applied method of particle identification by measuring the energies and relative time-of-flights of the decay products is shown to be very effective for the study of rare decay modes. The energy and angular distributions of the decay products, the associated neutron multiplicities, the total energy of the prompt gamma-radiation as well as correlations between the various observables were measured for the first time in a single full-scale experiment. The characteristics of ternary fission known from previous investigations are confirmed in the frame of a methodically independent experiment. Preliminary estimates of the quaternary fission yield are presented. An attempt is made to determine the mechanism of quaternary fission.

Tishchenko, V G; Hilscher, D; Jahnke, U

2002-01-01

5

Probabilities for the emission of light particles and their energy and angular distributions for true quaternary nuclear fission  

NASA Astrophysics Data System (ADS)

On the basis of quantum-mechanical fission theory, the features of true quaternary nuclear fission are studied by treating this fission process as a sequence of three processes following one another in the course of time. The first two processes are the escape of the first and then the second of the two light particles emitted from the neck of a fissioning nucleus because of a nonadiabatic character of the collective deformation motion of this nucleus. Finally, the third process is the separation of the fissioning nucleus into two rather heavy fission fragments. The differences that arise in the emission probabilities and in the angular and energy distributions upon going over from the first emitted to the second emitted prescission third and fourth particles are analyzed by invoking experimental data on the spontaneous and thermalneutron-induced fission of nuclei, and it is shown that these differences are caused by the changes both in the geometric configuration of the fissioning nucleus and in the shell structure of its neck after the first prescission particle is emitted from it.

Kadmensky, S. G.; Titova, L. V.

2013-01-01

6

Probabilities for the emission of light particles and their energy and angular distributions for true quaternary nuclear fission  

SciTech Connect

On the basis of quantum-mechanical fission theory, the features of true quaternary nuclear fission are studied by treating this fission process as a sequence of three processes following one another in the course of time. The first two processes are the escape of the first and then the second of the two light particles emitted from the neck of a fissioning nucleus because of a nonadiabatic character of the collective deformation motion of this nucleus. Finally, the third process is the separation of the fissioning nucleus into two rather heavy fission fragments. The differences that arise in the emission probabilities and in the angular and energy distributions upon going over from the first emitted to the second emitted prescission third and fourth particles are analyzed by invoking experimental data on the spontaneous and thermalneutron-induced fission of nuclei, and it is shown that these differences are caused by the changes both in the geometric configuration of the fissioning nucleus and in the shell structure of its neck after the first prescission particle is emitted from it.

Kadmensky, S. G., E-mail: kadmensky@phys.vsu.ru; Titova, L. V. [Voronezh State University (Russian Federation)] [Voronezh State University (Russian Federation)

2013-01-15

7

The occurrence and fission-track ages of late neogene and quaternary volcanic sediments, Siwalik group, Northern Pakistan  

USGS Publications Warehouse

Volcanic sediments, now mostly bentonites and bentonitic mudstones, occur throughout the Late Neogene and Quaternary Siwalik Group of northern Pakistan. A number of these deposits have been dated by the fission-track method, utilizing zircon phenocrysts from these deposits, and provide the chronometric constraints upon which a paleomagnetic stratigraphy is developed for the Siwalik Group. Notable in the occurrence of these altered tuff horizons is an apparent mode in their stratigraphic development from approximately 3.0 to 1.5 m.y. B.P. which coincides with the period of activity of the Dacht-e-Nawar volcanic complex of east-central Afghanistan. Fission-track ages of certain tuffs for critical areas of northern Pakistan are reported herein. ?? 1982.

Johnson, G.D.; Zeitler, P.; Naeser, C.W.; Johnson, N.M.; Summers, D.M.; Frost, C.D.; Opdyke, N.D.; Tahirkheli, R.A.K.

1982-01-01

8

Fission-track evidence for Quaternary uplift of the Nanga Parbat region, Pakistan  

USGS Publications Warehouse

The north-striking Nanga Parbat-Haramosh Massif protrudes into the northwestern Himalaya along the axis of a great syntaxis1,2 (Fig. 1), where the Hindu Kush, Karakorum, and Himalayan ranges converge. As the Indus Suture Zone3 enters this region from the east it bifurcates into two branches, encircling what may be a docked island-arc terrane4. The southern branch (the Main Mantle Thrust) crops out on both flanks of the Nanga Parbat massif, forming a tight structural loop5. This massif and the adjacent terrane contain some of the highest peaks in the Himalaya; Nanga Parbat and the Indus River (located just 20km away) define the world's greatest continental relief (6,930 m). We report here the discovery of unexpectedly young sphene, zircon and apatite fission-track dates from the Nanga Parbat-Haramosh Massif. These dates (as low as 1.3 Myr for zircon and 0.4 Myr for apatite) imply that during the Pleistocene the Nanga Parbat region was uplifted and eroded at nearly 1 cm yr-1. ?? 1982 Nature Publishing Group.

Zeitler, P.K.; Johnson, N.M.; Naeser, C.W.; Tahirkheli, R.A.K.

1982-01-01

9

Quaternary Studies  

NSDL National Science Digital Library

First, the Irish Quaternary Association (IQUA) website publicizes its aim "to promote Quaternary studies in Ireland through its publications, and the organization of field meetings and conferences" (1). Visitors can learn about the importance of quaternary studies as well as find out the latest news and upcoming meetings. At the second website, the University of Wisconsin-Madison describes the current and recent studies dealing with "basic and applied problems in glacial geology, surficial geology, palynology, sedimentology, geologic mapping, hydrogeology, soils, and environmental geology "(2). The website offers abstracts of publications of members of the Department of Geology and Geophysics and the Wisconsin Geological and Natural History Survey along with descriptions of the lab, a shaded relief map of the Wisconsin area, and amusing glacial songs. Next, the Godwin Institute of Quaternary Research (GIQR) presents the University of Cambridge's history in quaternary research and the seven current research groups and four recent research projects (3 ). The website furnishes news from the research groups, a gallery of historical images of the East Anglia excursion, and summaries of the Institute's reference collections. Fourth, the International Union for Quaternary Research (INQUA) discusses quaternary scientists' investigations "to interpret the changing world of the glacial ages and their impact on our planet's surface environments" (4). Researchers can find out about INQUA-funded projects, meetings, and scientific commissions. Next, the Quaternary Research Association explains that it "exists to promote understanding of the Quaternary Period by publishing field guides, technical guides, and an international journal as well as holding field meetings and speaker meetings" (5). Students and researchers can discover employment, research, grant, meetings, and educational opportunities. Sixth, the University of Wales presents its investigations in the Remote Sensing Laboratory, Palaeoecology Laboratory, and the Luminescence Laboratory (6 ). Users can find concise descriptions of individual researchers' successes, abstracts of published papers, and links to conference information. The seventh website illustrates the Alaska Quaternary Center's commitment "to the promotion of interdisciplinary research and the enhancement of interdisciplinary instruction in Quaternary sciences" (7). Users can view images of the field work and learn how to obtain quaternary data from the Geographic Information Network of Alaska (GINA). Lastly, Rutgers University promotes its Graduate Certificate in Quaternary Studies where students take part in geology, geography, meteorology, and other disciplines interested in the last couple of million years of Earth's history (8). Students and educators can find information on the researchers involved with the program and the necessary course work.

10

Quaternary investigation  

SciTech Connect

The primary purpose of the Quaternary investigation is to provide information on the location and age of Quaternary deposits for use in evaluating the presence or absence of neotectonic deformation or paleoliquefaction features within the Savannah River Site (SRS) region. The investigation will provide a basis for evaluating the potential for capable faults and associated deformation in the SRS vicinity. Particular attention will be paid to the Pen Branch fault.

Stieve, A.

1991-05-15

11

Nuclear fission  

Microsoft Academic Search

Nuclear fission is reviewed. The value of a channel analysis is noted in determining fission cross sections, fluctuations in fission widths and fission asymmetry. The importance of barrier height in any fission mode is emphasized. The difficulty of obtaining the mass distribution of fission fragments by a statistical theory is noted; this situation arises because the result is a strong

J. A. Wheeler

1956-01-01

12

The Alaska Quaternary Center  

NSDL National Science Digital Library

This website illustrates the Alaska Quaternary Center's (at the University of Alaska, Fairbanks) commitment "to the promotion of interdisciplinary research and the enhancement of interdisciplinary instruction in Quaternary sciences." Users can view images of the field work and learn how to obtain quaternary data from the AQC Quaternary Research Geodatabase.

13

Irish Quaternary Association (IQUA)  

NSDL National Science Digital Library

The Irish Quaternary Association (IQUA) website publicizes its aim "to promote Quaternary studies in Ireland through its publications, and the organization of field meetings and conferences." Visitors can learn about the importance of quaternary studies, find out the latest news and upcoming meetings, and find links to Quaternary studies journals.

14

Quaternary and Geomorphology.  

ERIC Educational Resources Information Center

Highlights conferences and meetings of organizations involved with quaternary geology and geomorphology, including International Union of Quaternary Research Conference held in Moscow. The impetus of a revision of "The Quaternary of the United States" resulted from this conference. Includes activities/aims of "Friends of the Pleistocene"…

Andrews, J. T.; Graf, W. L.

1983-01-01

15

Superasymmetric Fission  

NASA Astrophysics Data System (ADS)

The existence of superasymmetric fission mode connected with Z = 28 and N = 50 nuclear shells is analysed in the framework of the scission point model. Calculations of PES near the scission point had shown that the 78Ni fission mode would be manifested in fission of neutron-rich compound nuclei. In the case of fission of superheavy nucleus the superasymmetric fission mode is enhanced by influence of the Z = 82 and N = 126 nuclear shells in heavy fragment. Enhancement of highly asymmetric mass and charge division in the proton and neutron fission of 238U at intermediate energy in comparison with thermal neutron induced fission was described by the model developed for calculating the product yields with inclusion of superasymmetric fission mode. This model was used for the prediction of the formation cross sections of neutron-rich nuclides in fission.

Rubchenya, V. A.

2001-10-01

16

Quaternary Research Association  

NSDL National Science Digital Library

The Quaternary Research Association explains that it "exists to promote understanding of the Quaternary Period by publishing field guides, technical guides, and an international journal as well as holding field meetings and speaker meetings." Students and researchers can discover employment, research, grant, meetings, and educational opportunities.

17

Nuclear fission  

Microsoft Academic Search

The object of the book is to provide a comprehensive account of present ; understanding of nuclear fission. While it is written at an introductory level ; for students of the physics and chemistry of fission, it also attempts to cover ; recent developments at a sufficient depth to make the volume valuable to research ; scientists. The theoretical framework

R. Vandenbosch; J. R. Huizenga

1973-01-01

18

Benchmarking Nuclear Fission Theory  

E-print Network

We suggest a small set of fission observables to be used as test cases for validation of theoretical calculations. The purpose is to provide common data to facilitate the comparison of different fission theories and models. The proposed observables are chosen from fission barriers, spontaneous fission lifetimes, fission yield characteristics, and fission isomer excitation energies.

G. F. Bertsch; W. Loveland; W. Nazarewicz; P. Talou

2015-02-20

19

Benchmarking Nuclear Fission Theory  

E-print Network

We suggest a small set of fission observables to be used as test cases for validation of theoretical calculations. The purpose is to provide common data to facilitate the comparison of different fission theories and models. The proposed observables are chosen from fission barriers, spontaneous fission lifetimes, fission yield characteristics, and fission isomer excitation energies.

Bertsch, G F; Nazarewicz, W; Talou, P

2015-01-01

20

Bimodal fission  

SciTech Connect

In recent years, we have measured the mass and kinetic-energy distributions from the spontaneous fission of /sup 258/Fm, /sup 259/Md, /sup 260/Md, /sup 258/No, /sup 262/No, and /sup 260/(104). All are observed to fission with a symmetrical division of mass, whereas the total-kinetic-energy (TKE) distributions strongly deviated from the Gaussian shape characteristically found in the fission of all other actinides. When the TKE distributions are resolved into two Gaussians the constituent peaks lie near 200 and near 233 MeV. We conclude two modes or bimodal fission is occurring in five of the six nuclides studied. Both modes are possible in the same nuclides, but one generally predominates. We also conclude the low-energy but mass-symmetrical mode is likely to extend to far heavier nuclei; while the high-energy mode will be restricted to a smaller region, a region of nuclei defined by the proximity of the fragments to the strong neutron and proton shells in /sup 132/Sn. 16 refs., 7 figs., 1 tab.

Hulet, E.K.

1989-04-19

21

Quaternary Faunal Environments  

NSDL National Science Digital Library

Students collect information the environments associated with a list of presently living mammals. Students use FAUNMAP to explore the spatial patterns associated with these living mammals during the late Quaternary. They compare these distributions for living mammals to the distribution patterns for a set of extinct mammals. Students answer a set of questions that provide a basis for a summary report.

Christopher Hill

22

Fission meter  

DOEpatents

A neutron detector system for discriminating fissile material from non-fissile material wherein a digital data acquisition unit collects data at high rate, and in real-time processes large volumes of data directly into information that a first responder can use to discriminate materials. The system comprises counting neutrons from the unknown source and detecting excess grouped neutrons to identify fission in the unknown source.

Rowland, Mark S. (Alamo, CA); Snyderman, Neal J. (Berkeley, CA)

2012-04-10

23

Ternary Fission Studies by Correlation Measurements with Ternary Particles  

NASA Astrophysics Data System (ADS)

The rare ternary fission process has been studied mainly by inclusive measurements of the energy distributions and fractional yields of the light charged particles (LCPs) from fission, or by experiments on the angular and energy correlation between LCPs and fission fragments (FFs). The present contribution presents a brief overview of more elaborate correlation measurements that comprise the emission of neutrons and ? rays with LCPs and FFs, or the coincident registration of two LCPs. These measurements have permitted identification of new modes of particle-accompanied fission, such as the population of excited states in LCPs, the formation of neutron-unstable nuclei as short-lived intermediate LCPs, as well as the sequential decay of particle-unstable LCPs and quaternary fission. Furthermore, the neutron multiplicity numbers bar ? (A) and distributions of fragment masses A, measured for the ternary fission modes with various LCP isotopes, give a valuable hint of the role played by nuclear shell structure in the fission process near scission. Finally, two different hitherto unknown asymmetries in ternary ?-particle emission with respect to the fission axis, called the TRI and ROT effect, were studied in fission reactions induced by polarised cold neutrons.

Mutterer, Manfred

2011-10-01

24

Seminar on Fission VI  

NASA Astrophysics Data System (ADS)

Topical reviews. Angular momentum in fission / F. Gönnenwein ... [et al.]. The processes of fusion-fission and quasi-fission of heavy and super-heavy nuclei / M. G. Itkis ... [et al.] -- Fission cross sections and fragment properties. Minor-actinides fission cross sections and fission fragment mass yields via the surrogate reaction technique / B. Jurado ... [et al.]. Proton-induced fission on actinide nuclei at medium energy / S. Isaev ... [et al.]. Fission cross sections of minor actinides and application in transmutation studies / A. Letourneau ... [et al.]. Systematics on even-odd effects in fission fragments yields: comparison between symmetric and asymmetric splits / F. Rejmund, M Caamano. Measurement of kinetic energy distributions, mass and isotopic yields in the heavy fission products region at Lohengrin / A. Bail ... [et al.] -- Ternary fission. On the Ternary [symbol] spectrum in [symbol]Cf(sf) / M. Mutterer ... [et al.]. Energy degrader technique for light-charged particle spectroscopy at LOHENGRIN / A. Oberstedt, S. Oberstedt, D. Rochman. Ternary fission of Cf isotopes / S. Vermote ... [et al.]. Systematics of the triton and alpha particle emission in ternary fission / C. Wagemans, S. Vermote, O. Serot -- Neutron emission in fission. Scission neutron emission in fission / F.-J. Hambsch ... [et al.]. At and beyond the Scission point: what can we learn from Scission and prompt neutrons? / P. Talou. Fission prompt neutron and gamma multiplicity by statistical decay of fragments / S. Perez-Martin, S. Hilaire, E. Bauge -- Fission theory. Structure and fission properties of actinides with the Gogny force / H. Goutte ... [et al.]. Fission fragment properties from a microscopic approach / N. Dubray, H. Goutte, J.-P. Delaroche. Smoker and non-smoker neutron-induced fission rates / I. Korneev ... [et al.] -- Facilities and detectors. A novel 2v2E spectrometer in Manchester: new development in identification of fission fragments / I. Tsekhanovich ... [et al.]. Development of PSD and ToF + PSD techniques for fission experiments / M. Sillanpää ... [et al.]. MYRRHA, a new fast spectrum facility / H. Aït Abderrahim, P. D'hondt, D. De Bruyn. The BR1 reactor: a versatile tool for fission experiments / J. Wagemans -- "Special" fission processes. Shape isomers - a key to fission barriers / S. Oberstedt ... [et al.]. Fission in spallation reactions / J. Cugnon, Th. Aoust, A. Boudard -- Conference photo -- List of participants.

Wagemans, Cyriel; Wagemans, Jan; D'Hondt, Pierre

2008-04-01

25

Quaternary GIS Laboratory  

NSDL National Science Digital Library

This is the home page of the Quaternary Geographic Information System (GIS) Laboratory at the Institute of Arctic and Alpine Research (INSTAAR) at the University of Colorado. The laboratory supports quantitative spatial analysis of glacier, climate, coastal, and other environmental relationships at high latitudes. Users can access a collection of climate animations for the State of Alaska which show seasonal variation in monthly temperature and precipitation. There is also a set of high-resolution imagery and terrain models for Barrow, Alaska, an animation of the land bridge between Asia and North America, an atlas of paleoglaciation for the state, and links to a variety of other projects involving climatology, paleoclimatology, and glacial geomorphology in the Sate of Alaska.

26

ChemTeacher: Fission  

NSDL National Science Digital Library

ChemTeacher compiles background information, videos, articles, demonstrations, worksheets and activities for high school teachers to use in their classrooms. The Fission page includes resources for teaching students about the discovery and applications of fission.

2011-01-01

27

Geometry of membrane fission.  

PubMed

Cellular membranes define the functional geometry of intracellular space. Formation of new membrane compartments and maintenance of complex organelles require division and disconnection of cellular membranes, a process termed membrane fission. Peripheral membrane proteins generally control membrane remodeling during fission. Local membrane stresses, reflecting molecular geometry of membrane-interacting parts of these proteins, sum up to produce the key membrane geometries of fission: the saddle-shaped neck and hour-glass hemifission intermediate. Here, we review the fundamental principles behind the translation of molecular geometry into membrane shape and topology during fission. We emphasize the central role the membrane insertion of specialized protein domains plays in orchestrating fission in vitro and in cells. We further compare individual to synergistic action of the membrane insertion during fission mediated by individual protein species, proteins complexes or membrane domains. Finally, we describe how local geometry of fission intermediates defines the functional design of the protein complexes catalyzing fission of cellular membranes. PMID:25062896

Frolov, Vadim A; Escalada, Artur; Akimov, Sergey A; Shnyrova, Anna V

2015-01-01

28

THEORY OF NUCLEAR FISSION  

Microsoft Academic Search

sion. In the first section calculations of the fission barrier are ; reviewed. The second section considers fission probability. Qualitative ; considerations concerning the fourth section is devoted to work on the mass, ; charge, and angular distributions of fission fragments. 76 references. ; (J.S.R.);

Geilikman

1957-01-01

29

Numerical Simulations of Fission  

NASA Astrophysics Data System (ADS)

In this paper, we use the term fission to refer to the breakup of an equilibrium celestial body driven by rapid rotation. Historically, it was conjectured that fission would lead to splitting of a body directly into two or more pieces. Numerical hydrodynamic simulation techniques have now become sufficiently powerful to study the outcome of dynamic fission instabilities. We summarize recent work and present new simulations spanning a range of rotation rates and fluid compressibility. In the best resolved cases dynamic fission instability always leads to ejection of a ring or disk of debris rather thin one or a few discrete bodies. In this case, just as in most other lunar origin theories, a fission-product Moon must accrete out of a geocentric swarm of material. Intrinsic nonaxisymmetry of the remnant Earth after fission would prevent rapid recollapse of the swarm. The revised picture aleviates some of the problems associated with earlier versions of the fission theory. The two most serious remaining objections are that it is difficult to make the proto-Earth rotate fast enough to undergo fission and that the proto-Earth must be largely molten at the time it fissions. To overcome the first objection, it may be necessary to combine fission with the planetesimal impact theory. Some advantages of such a hybrid theory are discussed. The second objection cannot be fully assessed until more is known about the fission history and accretion of the proto-Earth.

Durisen, Richard H.; Gingold, Robert A.

1987-01-01

30

Quaternary Glaciers of New Zealand  

Microsoft Academic Search

Located in the southwestern Pacific Ocean, New Zealand's record of Quaternary glaciations, preserved in landforms and near-surface deposits, begins at the margins of modern glaciers and extends outwards geographically and backwards in time, to the last glaciation and beyond. The record becomes increasingly fragmentary into the Middle and Early Pleistocene.

D. J. A. Barrell

2011-01-01

31

Quaternary uplift of southern Italy  

Microsoft Academic Search

Dramatic coastline changes demonstrate rapid Quaternary uplift of Calabria in southern Italy. Because most of the west (Tyrrhenian Sea) coast is normal fault bounded, previous work has asserted that its uplift is local footwall uplift related to extension. However, the east (Ionian Sea) coast is also uplifting but is not normal fault bounded. This reanalysis, based on original field work

Rob Westaway

1993-01-01

32

Modernizing the Fission Basis  

NASA Astrophysics Data System (ADS)

A recent Fission Product Review Panel study has identified important issues associated with the possible neutron energy dependence of the fission product isotope ^147Nd. As a result, we initiated a program at TUNL to obtain high-precision and self-consistent data for the energy dependence of fission product yields in the 1 to 15 MeV energy range. Three dual fission ionization chambers dedicated to ^235U, ^238U, and ^239Pu thick target foils and thin monitor foils, respectively, were exposed to neutron beams produced via the reactions ^2H(d,n)^3He and ^3H(d,n)^4He. After irradiation, the characteristic ? rays from specific fission products were recorded over a period of many weeks using HPGe detectors in a low-background environment. Results for the yield of seven fission isotopes obtained at 4.6, 9.0 and 14.8 MeV are reported.

Bhatia, C.; Fallin, B.; Howell, C.; Tornow, W.; Gooden, M.; Kelley, J.; Arnold, C.; Bond, E.; Bredeweg, T.; Fowler, M.; Moody, W.; Rundberg, R.; Rusev, G.; Vieira, D.; Wilhemy, J.; Becker, J.; Macri, R.; Ryan, C.; Sheets, S.; Stoyer, M.; Tonchev, A.

2012-10-01

33

Relativistic Coulomb Fission  

NASA Technical Reports Server (NTRS)

Nuclear fission reactions induced by the electromagnetic field of relativistic nuclei are studied for energies relevant to present and future relativistic heavy ion accelerators. Cross sections are calculated for U-238 and Pu-239 fission induced by C-12, Si-28, Au-197, and U-238 projectiles. It is found that some of the cross sections can exceed 10 b.

Norbury, John W.

1992-01-01

34

Relativistic Coulomb fission  

NASA Astrophysics Data System (ADS)

Nuclear fission reactions induced by the electromagnetic field of relativistic nuclei are studied for energies relevant to present and future relativistic heavy ion accelerators. Cross sections are calculated for U-238 and Pu-239 fission induced by C-12, Si-28, Au-197, and U-238 projectiles. It is found that some of the cross sections can exceed 10 b.

Norbury, John W.

35

Fission Xenon on Mars  

NASA Technical Reports Server (NTRS)

Fission Xe components due to Pu-244 decay in the early history of Mars have been identified in nakhlites; as in the case of ALH84001 and Chassigny the fission gas was assimilated into indigenous solar-type Xe. Additional information is contained in the original extended abstract.

Mathew, K. J.; Marti, K.; Marty, B.

2002-01-01

36

Fission gas detection system  

DOEpatents

A device for collecting fission gas released by a failed fuel rod which device uses a filter to pass coolant but which filter blocks fission gas bubbles which cannot pass through the filter due to the surface tension of the bubble.

Colburn, Richard P. (Pasco, WA)

1985-01-01

37

Biomodal spontaneous fission  

SciTech Connect

Investigations of mass and kinetic-energy distributions from spontaneous fission have been extended in recent years to an isotope of element 104 and, for half-lives, to an isotope of element 108. The results have been surprising in that spontaneous fission half-lives have turned out to be much longer than expected and mass and kinetic- energy distributions were found to abruptly shift away from those of the lighter actinides, showing two modes of fission. These new developments have caused a re-evaluation of our understanding of the fission process, bringing an even deeper appreciation of the role played by nuclear shell effects upon spontaneous fission properties. 16 refs., 10 figs.

Hulet, E.K. (Lawrence Livermore National Lab., CA (USA))

1989-09-26

38

Quaternary ecology: A paleoecological perspective  

SciTech Connect

This book considers issues and problems in ecology which may be illuminated, if not solved, by considering paleoecology. The five central chapters include a discussion of application of Quaternary ecology to future global climate change, including global warming. Other areas presented include: population dispersal, invasions, expansions, and migrations; plant successions; ecotones; factors in community structure; ecosystem patterns and processes. Published case studies are numerous. The role played by continuing climatic change in vegetation change is acknowledged but not stressed.

Delcourt, H.R.; Delcourt, P.A.

1991-01-01

39

21 CFR 172.165 - Quaternary ammonium chloride combination.  

Code of Federal Regulations, 2010 CFR

...2009-04-01 true Quaternary ammonium chloride combination. 172.165 ...Preservatives § 172.165 Quaternary ammonium chloride combination. The food additive, quaternary ammonium chloride combination, may be...

2010-04-01

40

40 CFR 721.10511 - Quaternary ammonium salts (generic).  

Code of Federal Regulations, 2014 CFR

...2014-07-01 false Quaternary ammonium salts (generic). 721.10511 Section 721...Substances § 721.10511 Quaternary ammonium salts (generic). (a) Chemical substance...identified generically as quaternary ammonium salts (PMNs P-07-320,...

2014-07-01

41

Fission yields for thermal-neutron fission of plutonium-241  

Microsoft Academic Search

Cumulative fission yeilds for 17 fission products (16 mass chains) created by thermal-neutron fission of ²⁴¹Pu were determined from analysis of gross fission product gamma-ray spectra obtained using a large-volume Ge(Li) detector. Uncertainties assigned to nine of the measured yields are smaller than existing evaluated uncertainties. 25 references.

Dickens

1979-01-01

42

Statistical Theory of Nuclear Fission: Asymmetric Fission  

Microsoft Academic Search

A statistical theory is developed, according to which the relative probability of a mode of fission is determined by the total excitation energy of its two fragments calculated at the moment just before separation. In order to calculate the excitation energy, the well known semiempirical atomic mass formula is corrected for its deviations known to be attributed to the effects

Peter Fong

1956-01-01

43

Isomers in Fission Fragments  

SciTech Connect

The structure of neutron-rich nuclei produced as secondary fission fragments was investigated using the EUROGAM and GAMMASPHERE ACS arrays, the LOHENGRIN fission-fragment mass separator and the FIFI fission-fragment identifier. Fission products were populated in spontaneous fission of {sup 248}Cm and {sup 252}Cf and in thermal neutron-induced fission of {sup 233}U, {sup 235}U and {sup 241}Pu at ILL Grenoble. Particularly useful in such studies are isomeric states, well populated in fission due to their yrast character, easy to detect due to their long half lives and easy to interpret because of their relatively simple composition. We discuss their role in studies of neutron-rich nuclei, giving examples of isomers found in our recent experiments. A special type of K-isomers, resulting from 'crossing' of extruder and intruder orbitals plays a role in the mechanism of a sudden onset of deformation in the A = 100 and A = 150 regions. We present evidence for these isomers in both regions. Possible further studies in this field are proposed.

Urban, W.; Faust, H.; Jentschel, M.; Koester, U.; Krempel, J.; Materna, Th.; Mutti, P.; Soldner, T. [Institut Laue-Langevin, B.P. 156, F-38042 Grenoble Cedex 9 (France); Genevey, J.; Pinston, J. A.; Simpson, G. [Laboratoire de Physique Subatomique et de Cosmologie, IN2P3-CNRS/Universite J. Fourier, F-38026 Grenoble Cedex (France); Rzaca-Urban, T.; Zlomaniec, A.; Lukasiewicz, M. [Faculty of Physics, University of Warsaw, PL-00681 Warsaw (Poland); Sieja, K. [Gesellschaft fuer Schwerionenforschung, D-64291 Darmstadt (Germany); Nowacki, F.; Dorvaux, O.; Gall, B. J. P.; Roux, B. [Institut Pluridisciplinaire Hubert Curien, F-67037 Strasbourg Cedex (France); Dare, J. A. [Department of Physics and Astronomy, The University of Manchester, M13 9PL Manchester (United Kingdom)] (and others)

2009-01-28

44

Dynamical theory of nuclear fission  

Microsoft Academic Search

The asymmetric fission problem is investigated from the dynamical theory point of view under a variety of conditions which cover most cases encountered in practice. Quantitative and qualitative results are obtained. In all the cases studied the dynamical theory cannot explain the experimental results of asymmetric mass distribution of fission products. NUCLEAR REACTION Fission. Asymmetric fission.

Peter Fong

1976-01-01

45

Antiproton-induced nuclear fission  

Microsoft Academic Search

A dynamical model, which takes into account all stages of fission induced by stopped antiprotons (atomic cascade, intranuclear cascade, evaporation cascade, fission of a compound nucleus, and evaporation from fission fragments), has been formulated. In particular, the dynamics of the descent of fissioning nuclei from the saddle point to the scission point has been described by the diffusion model. The

A. S. Iljinov; M. V. Mebel; H. Daniel; T. von Egidy; F. J. Hartmann; P. Hofmann; Y. S. Kim

1994-01-01

46

Fission induced plasmas  

NASA Technical Reports Server (NTRS)

The possibility of creating a plasma from fission fragments was investigated, as well as the probability of utilizing the energy of these particles to create population inversion leading to laser action. Eventually, it is hoped that the same medium could be used for both fissioning and lasing, thus avoiding inefficiences in converting one form of energy to the other. A central problem in understanding a fission induced plasma is to obtain an accurate model of the electron behavior; some calculations are presented to this end. The calculations are simple, providing a compendium of processes for reference.

Harries, W. L.

1977-01-01

47

Fission Systems for Mars Exploration  

NASA Technical Reports Server (NTRS)

Fission systems are used extensively on earth, and 34 such systems have flown in space. The energy density of fission is over 10 million times that of chemical reactions, giving fission the potential to eliminate energy density constraints for many space missions. Potential safety and operational concerns with fission systems are well understood, and strategies exist for affordably developing such systems. By enabling a power-rich environment and highly efficient propulsion, fission systems could enable affordable, sustainable exploration of Mars.

Houts, Michael G.; Kim, T.; Dorney, D. J.; Swint, Marion Shayne

2012-01-01

48

Singlet fission photovoltaics  

E-print Network

The efficiency of a solar cell is restricted by the "single junction limit," whereby photons with energy higher than the bandgap lose energy by thermalization. Singlet exciton fission splits a high-energy molecular excitation ...

Lee, Jiye

2013-01-01

49

Quasi-fission  

SciTech Connect

Recent experimental and theoretical investigations have led to the characterization of a new reaction mechanism called quasi-fission. This process is characterized by the emergence of fission-like fragments, which do not originate from the fission decay of a compound nucleus formed by heavy-ion fusion, but rather from the break up of a short-lived intermediate complex. The occurrence of quasi-fission processes appear to be limited to heavy reaction systems and/or large angular momenta, although the present work demonstrates that such reactions occur for somewhat lighter projectiles than previously believed. It is thus shown that measurements of fragment angular distributions provide a signature for quasifission by being sensitive to whether or not a compound nucleus was formed during the reaction. From an analysis of such data it is concluded that the possibilities for synthesizing super-heavy elements in the range Z=112-116 are reduced considerably over previous estimates.

Back, B.B.

1983-01-01

50

Stereoselective Synthesis of Quaternary Proline Analogues  

PubMed Central

This review describes available methods for the diastereoselective and asymmetric synthesis of quaternary prolines. The focus is on the preparation of ?-functionalized prolines with the pyrrolidine moiety not embedded in a polycyclic frame. The diverse synthetic approaches are classified according to the bond which is formed to complete the quaternary skeleton. PMID:19655047

Calaza, M. Isabel

2009-01-01

51

Singlet exciton fission photovoltaics.  

PubMed

Singlet exciton fission, a process that generates two excitons from a single photon, is perhaps the most efficient of the various multiexciton-generation processes studied to date, offering the potential to increase the efficiency of solar devices. But its unique characteristic, splitting a photogenerated singlet exciton into two dark triplet states, means that the empty absorption region between the singlet and triplet excitons must be filled by adding another material that captures low-energy photons. This has required the development of specialized device architectures. In this Account, we review work to develop devices that harness the theoretical benefits of singlet exciton fission. First, we discuss singlet fission in the archetypal material, pentacene. Pentacene-based photovoltaic devices typically show high external and internal quantum efficiencies. They have enabled researchers to characterize fission, including yield and the impact of competing loss processes, within functional devices. We review in situ probes of singlet fission that modulate the photocurrent using a magnetic field. We also summarize studies of the dissociation of triplet excitons into charge at the pentacene-buckyball (C60) donor-acceptor interface. Multiple independent measurements confirm that pentacene triplet excitons can dissociate at the C60 interface despite their relatively low energy. Because triplet excitons produced by singlet fission each have no more than half the energy of the original photoexcitation, they limit the potential open circuit voltage within a solar cell. Thus, if singlet fission is to increase the overall efficiency of a solar cell and not just double the photocurrent at the cost of halving the voltage, it is necessary to also harvest photons in the absorption gap between the singlet and triplet energies of the singlet fission material. We review two device architectures that attempt this using long-wavelength materials: a three-layer structure that uses long- and short-wavelength donors and an acceptor and a simpler, two-layer combination of a singlet-fission donor and a long-wavelength acceptor. An example of the trilayer structure is singlet fission in tetracene with copper phthalocyanine inserted at the C60 interface. The bilayer approach includes pentacene photovoltaic cells with an acceptor of infrared-absorbing lead sulfide or lead selenide nanocrystals. Lead selenide nanocrystals appear to be the most promising acceptors, exhibiting efficient triplet exciton dissociation and high power conversion efficiency. Finally, we review architectures that use singlet fission materials to sensitize other absorbers, thereby effectively converting conventional donor materials to singlet fission dyes. In these devices, photoexcitation occurs in a particular molecule and then energy is transferred to a singlet fission dye where the fission occurs. For example, rubrene inserted between a donor and an acceptor decouples the ability to perform singlet fission from other major photovoltaic properties such as light absorption. PMID:23611026

Lee, Jiye; Jadhav, Priya; Reusswig, Philip D; Yost, Shane R; Thompson, Nicholas J; Congreve, Daniel N; Hontz, Eric; Van Voorhis, Troy; Baldo, Marc A

2013-06-18

52

Process for treating fission waste  

DOEpatents

A method is described for the treatment of fission waste. A glass forming agent, a metal oxide, and a reducing agent are mixed with the fission waste and the mixture is heated. After melting, the mixture separates into a glass phase and a metal phase. The glass phase may be used to safely store the fission waste, while the metal phase contains noble metals recovered from the fission waste.

Rohrmann, Charles A. (Kennewick, WA); Wick, Oswald J. (Richland, WA)

1983-01-01

53

Student Experiments in Spontaneous Fission.  

ERIC Educational Resources Information Center

Advanced undergraduate experiments utilizing a commercially available, thin spontaneous fission source are described, including studies of the energy and mass distribution of the fission fragments and their energy and angular correlation. The experiments provide a useful introduction to fission, nuclear mass equations, heavy-ion physics, and…

Becchetti, F. D.; Ying, J. S.

1981-01-01

54

The Mechanism of Nuclear Fission  

Microsoft Academic Search

On the basis of the liquid drop model of atomic nuclei, an account is given of the mechanism of nuclear fission. In particular, conclusions are drawn regarding the variation from nucleus to nucleus of the critical energy required for fission, and regarding the dependence of fission cross section for a given nucleus on energy of the exciting agency. A detailed

Niels Bohr; John Archibald Wheeler

1939-01-01

55

Microscopic Description of Induced Fission  

E-print Network

Selected aspects of the description of neutron-induced fission in 240Pu in the framework of the nuclear energy density functional theory at finite temperature are presented. In particular, we discuss aspects pertaining to the choice of thermodynamic state variables, the evolution of fission barriers as function of the incident neutron energy, and the temperatures of the fission fragments.

N. Schunck

2013-02-22

56

Ice Age refugia and Quaternary extinctions: An issue of Quaternary evolutionary palaeoecology  

NASA Astrophysics Data System (ADS)

Quaternary palaeoecology, as a discipline, involves the analysis of a large range of fossil organisms from the last ca. 2 million years. This paper considers the role that these Quaternary records can take in better understanding the evolution of those organisms. We also discuss the surprisingly low uptake of evolutionary biology in Quaternary palaeoecological studies. This leads us to encourage an advance on both these fronts with a greater degree of collaboration with phylogeographic and ancient DNA researchers. These discussions accompany a summary of a special issue of Quaternary Science Reviews representing the proceedings of the XVII INQUA held in Cairns Australia in 2007. This special issue includes papers on a wide variety of Quaternary evolutionary palaeoecological and population dynamic subjects including extinct Pacific Island palm trees, Beringian beetles, Scandinavian trees, and the effects on human and animal populations of an extraterrestrial impact event in the Late Glacial of North America.

Stewart, John R.; Cooper, Alan

2008-12-01

57

Anisotropies in Quaternary Intermetallic Compounds  

NASA Astrophysics Data System (ADS)

From the high-temperature series expansion of magnetic susceptibilities and the anisotropic Weiss temperatures, the first Steven's parameter, B2^0 , and the magnetic exchange interaction constant Jex^ll of each R^=3 ions magnetic sublattice in quaternary intermetallic compounds, RNi2B2C B(R= Tm, Er, Ho, Dy, and Tb) were obtained. The R =Dy system shows the biggest B2^0 value and the R = Tb system does the smallest one. Also we have measured and analyzed the anisotropic M(H) isotherms as a function of applied magnetic fields for H perpendicular and parallel to the c-axis for each compounds to check out our crystalline electric field (CEF) results obtained from the previous mentioned method by using the anisotropic Weiss temperatures. It turned out that most of the temperature dependence of magnetization curve M (T) for H perpendicular the c-axis at low temperature comes from the temperature dependent population of the singlet ground state in group L among groups L(low-lying levels of ground states), H(high levels of ground states), and M(first excited states).

Lee, W. C.

2008-03-01

58

Quaternary glaciation of Mount Everest  

NASA Astrophysics Data System (ADS)

The Quaternary glacial history of the Rongbuk valley on the northern slopes of Mount Everest is examined using field mapping, geomorphic and sedimentological methods, and optically stimulated luminescence (OSL) and 10Be terrestrial cosmogenic nuclide (TCN) dating. Six major sets of moraines are present representing significant glacier advances or still-stands. These date to >330 ka (Tingri moraine), >41 ka (Dzakar moraine), 24-27 ka (Jilong moraine), 14-17 ka (Rongbuk moraine), 8-2 ka (Samdupo moraines) and ˜1.6 ka (Xarlungnama moraine), and each is assigned to a distinct glacial stage named after the moraine. The Samdupo glacial stage is subdivided into Samdupo I (6.8-7.7 ka) and Samdupo II (˜2.4 ka). Comparison with OSL and TCN defined ages on moraines on the southern slopes of Mount Everest in the Khumbu Himal show that glaciations across the Everest massif were broadly synchronous. However, unlike the Khumbu Himal, no early Holocene glacier advance is recognized in the Rongbuk valley. This suggests that the Khumbu Himal may have received increased monsoon precipitation in the early Holocene to help increase positive glacier mass balances, while the Rongbuk valley was too sheltered to receive monsoon moisture during this time and glaciers could not advance. Comparison of equilibrium-line altitude depressions for glacial stages across Mount Everest reveals asymmetric patterns of glacier retreat that likely reflects greater glacier sensitivity to climate change on the northern slopes, possibly due to precipitation starvation.

Owen, Lewis A.; Robinson, Ruth; Benn, Douglas I.; Finkel, Robert C.; Davis, Nicole K.; Yi, Chaolu; Putkonen, Jaakko; Li, Dewen; Murray, Andrew S.

2009-07-01

59

Fission-induced plasmas  

NASA Technical Reports Server (NTRS)

The possibility of creating a plasma from fission fragments, and to utilize the energy of the particles to create population inversion that would lead to laser action is investigated. An investigation was made of various laser materials which could be used for nuclear-pumped lasing. The most likely candidate for a fissioning material in the gaseous form is uranium hexafluoride - UF6, and experiments were performed to investigate materials that would be compatible with it. One of the central problems in understanding a fission-induced plasma is to obtain a model of the electron behavior, and some preliminary calculations are presented. In particular, the rates of various processes are discussed. A simple intuitive model of the electron energy distribution function is also shown. The results were useful for considering a mathematical model of a nuclear-pumped laser. Next a theoretical model of a (3)He-Ar nuclear-pumped laser is presented. The theory showed good qualitative agreement with the experimental results.

Harries, W. L.; Shiu, Y. J.

1979-01-01

60

A REVIEW OF NUCLEAR FISSION. PART ONE. FISSION PHENOMENA AT LOW ENERGY. Revised Edition  

Microsoft Academic Search

The discovery of fission is described, and fission theory is outlined. ; The probability of fission is discussed. Distribution of mass and nuclear charge ; in fission is considered. Measurements of the kinetic energy of fission ; fragments are described. The emission of prompt neutrons, delayed neutrons, and ; gamma rays in fission is discussed. (M.C.G.);

Hyde

1962-01-01

61

40 CFR 721.10569 - Tricyclic quaternary amine salt (generic).  

Code of Federal Regulations, 2013 CFR

...2013-07-01 false Tricyclic quaternary amine salt (generic). 721.10569 Section 721...721.10569 Tricyclic quaternary amine salt (generic). (a) Chemical substance...generically as tricyclic quaternary amine salt (PMN P-08-471) is subject to...

2013-07-01

62

Catalytic enantioselective synthesis of quaternary carbon stereocentres  

NASA Astrophysics Data System (ADS)

Quaternary carbon stereocentres--carbon atoms to which four distinct carbon substituents are attached--are common features of molecules found in nature. However, before recent advances in chemical catalysis, there were few methods of constructing single stereoisomers of this important structural motif. Here we discuss the many catalytic enantioselective reactions developed during the past decade for the synthesis of single stereoisomers of such organic molecules. This progress now makes it possible to incorporate quaternary stereocentres selectively in many organic molecules that are useful in medicine, agriculture and potentially other areas such as flavouring, fragrances and materials.

Quasdorf, Kyle W.; Overman, Larry E.

2014-12-01

63

Catalytic enantioselective synthesis of quaternary carbon stereocentres.  

PubMed

Quaternary carbon stereocentres-carbon atoms to which four distinct carbon substituents are attached-are common features of molecules found in nature. However, before recent advances in chemical catalysis, there were few methods of constructing single stereoisomers of this important structural motif. Here we discuss the many catalytic enantioselective reactions developed during the past decade for the synthesis of single stereoisomers of such organic molecules. This progress now makes it possible to incorporate quaternary stereocentres selectively in many organic molecules that are useful in medicine, agriculture and potentially other areas such as flavouring, fragrances and materials. PMID:25503231

Quasdorf, Kyle W; Overman, Larry E

2014-12-11

64

Measurement of Fission Product Yields from Fast-Neutron Fission  

NASA Astrophysics Data System (ADS)

One of the aims of the Stockpile Stewardship Program is a reduction of the uncertainties on fission data used for analyzing nuclear test data [1,2]. Fission products such as 147Nd are convenient for determining fission yields because of their relatively high yield per fission (about 2%) and long half-life (10.98 days). A scientific program for measuring fission product yields from 235U,238U and 239Pu targets as a function of bombarding neutron energy (0.1 to 15 MeV) is currently underway using monoenergetic neutron beams produced at the 10 MV Tandem Accelerator at TUNL. Dual-fission chambers are used to determine the rate of fission in targets during activation. Activated targets are counted in highly shielded HPGe detectors over a period of several weeks to identify decaying fission products. To date, data have been collected at neutron bombarding energies 4.6, 9.0, 14.5 and 14.8 MeV. Experimental methods and data reduction techniques are discussed, and some preliminary results are presented.

Arnold, C. W.; Bond, E. M.; Bredeweg, T. A.; Fowler, M. M.; Moody, W. A.; Rusev, G.; Vieira, D. J.; Wilhelmy, J. B.; Becker, J. A.; Henderson, R.; Kenneally, J.; Macri, R.; McNabb, D.; Ryan, C.; Sheets, S.; Stoyer, M. A.; Tonchev, A. P.; Bhatia, C.; Bhike, M.; Fallin, B.; Gooden, M. E.; Howell, C. R.; Kelley, J. H.; Tornow, W.

2014-09-01

65

Fission and Fusion Game  

NSDL National Science Digital Library

In this activity, students play a board game where they learn the characteristics of and differences between fission and fusion, as well as the real world applications of these energy-releasing reactions. Reproducible game cards and and game board are included in the resource. The investigation supports material presented in chapter 3, "What Heats the Earth's Interior?" in the textbook, Energy flow, part of the Global System Science, an interdisciplinary course for high school students that emphasizes how scientists from a wide variety of fields work together to understand significant problems of global impact.

66

Isotopic Distributions of Fission Fragments from Transfer-induced Fission  

NASA Astrophysics Data System (ADS)

Fissioning systems from U to Cm as well as 250Cf were produced by 238U+12C transfer and fusion reactions. The detection of the target-like transfer partner made the characterization of the fissioning systems in (Z,A) and excitation energy possible. The isotopic identification of the fission fragments was achieved by using the VAMOS spectrometer combined to with reactions in inverse kinematics. Results regarding the populated transfer channels and excitation of the target-like transfer partner are presented, as well as the 240Pu fission probability. Isotopic yields of the fission-fragments for 240,241Pu and 250Cf, having excitation energies of about 10 and 45 MeV, respectively, are discussed.

Rodríguez-Tajes, C.; Caamaño, M.; Delaune, O.; Farget, F.; Audouin, L.; Bacri, C.-O.; Benlliure, J.; Casarejos, E.; Clement, E.; Cortina, D.; Derkx, X.; Dijon, A.; Doré, D.; Fernández-Domínguez, B.; Gaudefroy, L.; Golabek, C.; Heinz, A.; Jurado, B.; Lemasson, A.; Navin, A.; Paradela, C.; Ramos, D.; Roger, T.; Salsac, M. D.; Schmitt, C.; Schmidt, K.-H.; Shrivastava, A.; Taieb, J.

67

Observation of cold fission in 242Pu spontaneous fission  

NASA Astrophysics Data System (ADS)

Coincidence ?-ray data from the spontaneous fission of 242Pu were collected at the Lawrence Berkeley Laboratory high purity Ge (HPGe) array, GAMMASPHERE. Data from several cold-fission (0 neutron emission) isotopic pairs were observed and are presented. An interesting trend in the fractional population of cold-fission events was observed and is discussed. Relative yields of Zr-Xe, Sr-Ba, and Mo-Te pairs were measured. The Zr-Xe system has the most complete data set. Some speculations on the trend in the number of neutrons emitted as a function of the mass of the Xe isotope populated are presented. Comparisons between the yields from the spontaneous fission of 242Pu and the yields from thermal-neutron-induced fission of 241Pu are also presented.

Dardenne, Y. X.; Aryaeinejad, R.; Asztalos, S. J.; Babu, B. R.; Butler-Moore, K.; Chu, S. Y.; Cole, J. D.; Drigert, M. W.; Gregorich, K. E.; Hamilton, J. H.; Kormicki, J.; Lee, I. Y.; Lougheed, R. W.; Lu, Q. H.; Ma, W.-C.; Mohar, M. F.; Moody, K. J.; Prussin, S. G.; Ramayya, A. V.; Rasmussen, J. O.; Stoyer, M. A.; Wild, J. F.

1996-07-01

68

Interference effects in nuclear fission  

Microsoft Academic Search

Various interference effects governing the character of angular distributions of binary and ternary nuclear fission products\\u000a and P-odd, P-even, and T-odd asymmetries in these angular distributions have been studied within the quantum theory of spontaneous and low-energy\\u000a induced nuclear fission.

S. G. Kadmensky; L. V. Titova

2007-01-01

69

Transient times in nuclear fission  

Microsoft Academic Search

Heavy-ion induced fission at excitation energies of 100 MeV or more shows deviations from the statistical model in the numbers of light particles emitted prior to fission. A quantitative theory is presented which assumes that slow relaxation times of collective nuclear degrees of freedom and the transients associated therewith are responsible for such departures. Numerical results show encouraging agreement with

Hans A. Weidenmüller

1987-01-01

70

Nuclear fission and spatial chaos  

Microsoft Academic Search

Nuclear fission is the most fundamental reaction between neutrons and atomic nuclei of nuclear fuel in a reactor. In this paper, according to the nonlinear dynamical behavior of the neutron transport system in space (or the distribution behavior of neutrons in the reactor) which reveals this essential reaction, we investigate the relation between nuclear fission and spatial chaos, neutron multiplication

Shu Tang Liu

2006-01-01

71

Fission modes of mercury isotopes  

E-print Network

Background: Recent experiments on beta-delayed fission in the mercury-lead region and the discovery of asym- metric fission in 180 Hg [1] have stimulated theoretical interest in the mechanism of fission in heavy nuclei. Purpose: We study fission modes and fusion valleys in 180 Hg and 198 Hg to reveal the role of shell effects in pre-scission region and explain the experimentally observed fragment mass asymmetry and its variation with A. Methods: We use the self-consistent nuclear density functional theory employing Skyrme and Gogny energy density functionals. Results: The potential energy surfaces in multi-dimensional space of collective coordinates, including elongation, triaxiality, reflection-asymmetry, and necking, are calculated for 180 Hg and 198 Hg. The asymmetric fission valleys - well separated from fusion valleys associated with nearly spherical fragments - are found in in both cases. The density distributions at scission configurations are studied and related to the experimentally observed mass splits. Conclusions: The energy density functionals SkM\\ast and D1S give a very consistent description of the fission process in 180 Hg and 198 Hg. We predict a transition from asymmetric fission in 180 Hg towards more symmetric distribution of fission fragments in 198 Hg. For 180 Hg, both models yield 100 Ru/80 Kr as the most probable split. For 198 Hg, the most likely split is 108 Ru/90 Kr in HFB-D1S and 110 Ru/88 Kr in HFB-SkM\\ast.

M. Warda; A. Staszczak; W. Nazarewicz

2012-07-17

72

Antibacterial and Hemolytic Activities of Quaternary Pyridinium  

E-print Network

bacteria but not mammalian cells.[2­4] Polymers have been used as antimicrobial agents due commonly used as biocidal agents.[6­15] A number of polymeric disinfectants based on quaternary pyridinium bacteria. Recently, Gao and coworkers synthesized random copolymers of acrylamide and vinyl pyridine

73

Enantioselective construction of remote quaternary stereocentres  

NASA Astrophysics Data System (ADS)

Small molecules that contain all-carbon quaternary stereocentres--carbon atoms bonded to four distinct carbon substituents--are found in many secondary metabolites and some pharmaceutical agents. The construction of such compounds in an enantioselective fashion remains a long-standing challenge to synthetic organic chemists. In particular, methods for synthesizing quaternary stereocentres that are remote from other functional groups are underdeveloped. Here we report a catalytic and enantioselective intermolecular Heck-type reaction of trisubstituted-alkenyl alcohols with aryl boronic acids. This method provides direct access to quaternary all-carbon-substituted ?-, ?-, ?-, ?- or ?-aryl carbonyl compounds, because the unsaturation of the alkene is relayed to the alcohol, resulting in the formation of a carbonyl group. The scope of the process also includes incorporation of pre-existing stereocentres along the alkyl chain, which links the alkene and the alcohol, in which the stereocentre is preserved. The method described allows access to diverse molecular building blocks containing an enantiomerically enriched quaternary centre.

Mei, Tian-Sheng; Patel, Harshkumar H.; Sigman, Matthew S.

2014-04-01

74

Quaternary Geochronology 2 (2007) 290295 Research paper  

E-print Network

at the beginning of the Last Interglacial. These are in good agreement with the 10 Be cosmogenic dates obtained of the strongest ever recorded intracontinental earthquakes (magnitude 8.3 on Richter scale). PreviousQuaternary Geochronology 2 (2007) 290­295 Research paper Luminescence dating of a gigantic

Long, Bernard

75

Quaternary geology of the Amazonian Lowland  

Microsoft Academic Search

The Quaternary history of the Amazon lowlands is characterized by deposition of sediments of Andean provenance and by the influences of changing sea levels. Areas well above the present water tables were not reached by Pleistocene high-water stages. These areas have been intensively weathered since the Tertiary, forming hard lateritic weathering horizons. These weathering horizons are best explained by the

Georg Irion; Jens Müller; Jose Nunes de Mello; Wolfgang J. Junk

1995-01-01

76

Nuclear Fission Research at IRMM  

SciTech Connect

The Institute for Reference Materials and Measurements (IRMM) will celebrate its 45th anniversary in 2005. With its 150-MeV Geel Electron Linear Accelerator (GELINA) and 7-MV Van de Graaff accelerator as multi-purpose neutron sources, it served the nuclear physics community for this period.The research in the field of nuclear fission was focused in recent years on both the measurement and calculation of fission cross sections, and the measurement of fission fragment properties.Fission cross sections were determined for 233Pa and 234U; the fission process was studied in the resolved resonance region of 239Pu(n,f) and for 251Cf(nth,f). These measurements derive their interest from accelerator driven systems, the thorium fuel cycle, high temperature reactors, safety issues of current reactors, and basic physics. The measurements are supported by several modeling efforts that aim at improving model codes and nuclear data evaluation.

Hambsch, Franz-Josef [EC-JRC-Institute for Reference Materials and Measurements, Retieseweg 111, B-2440 Geel (Belgium)

2005-05-24

77

Call Title: Nuclear Fission and Radiation Protection Call Identifier: FP7-Fission-2009  

E-print Network

Call Title: Nuclear Fission and Radiation Protection · Call Identifier: FP7-Fission-2009 · Date repartition (EUR million) 1 Fission-1 5.5 2 Fission-2 20.0 (of which EUR 1.0 million is reserved for topic Fission-2009-2.2.2) 3 Fission-3 18.0 4 Fission-5 & -7 5.405 Total 48.905 All budgetary figures

De Cindio, Fiorella

78

Fission Time Distributions in Fusion-Fission Reactions  

NASA Astrophysics Data System (ADS)

The fission time distributions have been analysed using the comparison between measured and calculated characteristics of neutrons, protons and ?-particles for compound nuclei near 182Pt, 220Th and 239Np, formed in the heavy ion and proton induced fission. Theoretical calculations were carried out taking into account effects of nuclear friction which increases with nuclear temperature. The form of the extracted fission time distributions consits of short and long time components. The center position of both components decreases slowly with increasing of excitation energy of compound nucleus.

Rubchenya, V. A.; Alexandrov, A. A.; Alkhazov, I. D.; Äystö, J.; Evsenin, A.; Khlebnikov, S. V.; Kuznetsov, A. V.; Lyapin, V. G.; Mutterer, M.; Penionzhkevich, Yu. E.; Osetrov, O. I.; Radivojevich, Z.; Sobolev, Yu. G.; Tiourin, G. P.; Trzaska, W. H.; Vakhtin, D. N.

2002-12-01

79

Dynamical Aspects of Nuclear Fission  

NASA Astrophysics Data System (ADS)

Fission dynamics. Dependence of scission-neutron yield on light-fragment mass for [symbol]=1/2 [et al.]. Dynamics of capture quasifission and fusion-fission competition / L. Stuttgé ... [et al.] -- Fission-fission. The processes of fusion-fission and quasi-fission of superheavy nuclei / M. G. Itkis ... [et al.]. Fission and quasifission in the reactions [symbol]Ca+[symbol]Pb and [symbol]Ni+[symbol]W / G. N. Knyazheva ... [et al.]. Mass-energy characteristics of reactions [symbol]Fe+[symbol][symbol][symbol]266Hs and [symbol]Mg+[symbol]Cm[symbol][symbol]Hs at Coulomb barrier / L. Krupa ... [et al.]. Fusion of heavy ions at extreme sub-barrier energies / ?. Mi?icu and H. Esbensen. Fusion and fission dynamics of heavy nuclear system / V. Zagrebaev and W. Greiner. Time-dependent potential energy for fusion and fission processes / A. V. Karpov ... [et al.] -- Superheavy elements. Advances in the understanding of structure and production mechanisms for superheavy elements / W. Greiner and V. Zagrebaev. Fission barriers of heaviest nuclei / A. Sobiczewski ... [et al.]. Possibility of synthesizing doubly magic superheavy nuclei / Y Aritomo ... [et al.]. Synthesis of superheavy nuclei in [symbol]Ca-induced reactions / V. K. Utyonkov ... [et al.] -- Fragmentation. Production of neutron-rich nuclei in the nucleus-nucleus collisions around the Fermi energy / M. Veselský. Signals of enlarged core in [symbol]Al / Y. G. Ma ... [et al.] -- Exotic modes. New insight into the fission process from experiments with relativistic heavy-ion beams / K.-H. Schmidt ... [et al.]. New results for the intensity of bimodal fission in binary and ternary spontaneous fission of [symbol]Cf / C. Goodin ... [et al.]. Rare fission modes: study of multi-cluster decays of actinide nuclei / D. V. Kamanin ... [et al.]. Energy distribution of ternary [symbol]-particles in [symbol]Cf(sf) / M. Mutterer ... [et al.]. Preliminary results of experiment aimed at searching for collinear cluster tripartition of [symbol]Pu / Y. V. Pyatkov. Comparative study of the ternary particle emission in [symbol] and [symbol]Cm(SF) / S. Vermote ... [et al.] -- Structure of fission fragments and neurton rich nuclei / manifestation of average y-ray multiplicity in the fission modes of [symbol]Cf(sf) and the proton-induced fission of [symbol]Pa, [symbol]Np, and [symbol]Am / M. Berešová ... [et al.]. Yields of correlated fragment pairs and average gamma-ray multiplicities and energies in [symbol]Pb([symbol]O, f) / A. Bogachev ... [et al.]. Recent experiments at gammasphere intended to the study of [symbol]Cf spontaneous fission / A. V. Daniel ... [et al.]. Nuclear structure studies of microsecond isomers near A =100 / J. Genevey ... [et al.]. Covariant density functional theory: isospin properties of nuclei far from stability / G. A. Lalazisis. Relativistic mean-field description of light nuclei / J. Leja and Š. Gmuca. Energy nucleon spectra from reactions at intermediate energies / O. Grudzevich ... [et al.] -- Developments in experimental techniques. Analysis, processing and visualization of multidimensional data using DaqProVis system / M. Morhá? ... [et al.].

Kliman, J.; Itkis, M. G.; Gmuca, Š.

2008-11-01

80

The Fission Vision  

NSDL National Science Digital Library

Leo Szilard, a Hungarian physicist, imagined the two steps needed to free the energy in an atom's nucleus: one, a nuclear chain reaction, and two, a critical mass of the right element to set off and sustain it. Does he envision the process we now call "fission," the splitting of nuclei? Yes, he seems to, but Szilard's ideas are not yet clearly expressed. And he doesn't know which element will provide nuclei that can be easily split. This chapter describes his quest and that of his contemporaries, to identify this missing element--which ultimately unleashed nuclear energy into the world. In addition, this compelling chapter clearly illustrates the nature of science and science as a human endeavor as recommended in the National Science Education Standards.

Joy Hakim

2007-08-17

81

Fission fragment angular momentum in ODD-Z fissioning systems  

NASA Astrophysics Data System (ADS)

Independent isomeric yield ratios of 128Sb, 130Sb, 132, 131Te, 133Te, 132I, 134I, 136I, 135Xe and 138Cs have been determined in the fast neutron induced fission of 237Np and 241Am using radiochemical and gamma spectrometric technique. From the independent isomeric yield ratios, fragment angular momenta (Jrms) have been deduced using spin-dependent statistical model analysis. Comparison of these data with the literature data for even-Z fissioning systems shows the following important features: (i) Angular momenta for fragments with spherical 82n shell and even-Z products are lower compared to the fragments with out the 82n shell and odd-Z products indicating the effect of nuclear structure. (ii) Angular momentum of even-Z products in all the fissioning systems are comparable where as for odd-Z products it is slightly higher in the odd-Z fissioning systems than in the adjacent even-Z fissioning systems. This indicates the role of single particle on fragment angular momentum in odd-Z fissioning systems.

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

82

40Ar/39Ar dating of Quaternary feldspar: examples from the Taupo Volcanic Zone, New Zealand  

USGS Publications Warehouse

Using a continuous laser and resistance furnace, we have measured ages on Quaternary plagioclase with an absolute precision of about ??30 ka and on Quaternary sanidine with a relative precision of better than 1%. Such precision was achieved by using low-temperature heating steps to remove much of the nonradiogenic argon contamination. Plagioclase is one of the most common mineral phases in volcanic rocks; thus, these procedures will be widely applicable to many problems for which precise radiometric age control has not been available. We studied plagioclase and plagioclase-sanidine concentrates from the oldest and the three largest silicic ash-flow deposits of the Taupo Volcanic Zone, New Zealand, one of the world's largest and most active volcanic systems. The results are in close agreement with new magnetostratigraphic data, suggesting that existing fission-track age determinations significantly underestimate the age of older units, and shift the inception of Taupo Vaolcanic Zone volcanism back to at least 1600 ka. -from Authors

Pringle, M.S.; McWilliams, M.; Houghton, B.F.; Lanphere, M.A.; Wilson, C.J.N.

1992-01-01

83

Background radiation from fission pulses  

SciTech Connect

Extensive source terms for beta, gamma, and neutrons following fission pulses are presented in various tabular and graphical forms. Neutron results from a wide range of fissioning nuclides (42) are examined and detailed information is provided for four fuels: /sup 235/U, /sup 238/U, /sup 232/Th, and /sup 239/Pu; these bracket the range of the delayed spectra. Results at several cooling (decay) times are presented. For ..beta../sup -/ and ..gamma.. spectra, only /sup 235/U and /sup 239/Pu results are given; fission-product data are currently inadequate for other fuels. The data base consists of all known measured data for individual fission products extensively supplemented with nuclear model results. The process is evolutionary, and therefore, the current base is summarized in sufficient detail for users to judge its quality. Comparisons with recent delayed neutron experiments and total ..beta../sup -/ and ..gamma.. decay energies are included. 27 refs., 47 figs., 9 tabs.

England, T.R.; Arthur, E.D.; Brady, M.C.; LaBauve, R.J.

1988-05-01

84

?-delayed fission of 180Tl  

NASA Astrophysics Data System (ADS)

The detailed analysis of the ?-delayed fission data of 180Tl is presented. The experiment was performed by producing a pure beam of 180Tl by means of highly selective resonance laser ionization followed by mass separation with the ISOLDE (CERN, Geneva) isotope separator. A surprising asymmetric mass distribution of fission fragments from 180Hg, the daughter of 180Tl ? decays, was observed. Here, the energy calibration of the silicon detectors, which is crucial for a proper determination of the fission fragments’ energy and mass split, is presented and the total kinetic energy and its dependence on the mass split ratio is discussed. A more precise ?-delayed fission probability P?DF(180Tl)=3.2(2)×10-3% was deduced.

Elseviers, J.; Andreyev, A. N.; Huyse, M.; Van Duppen, P.; Antalic, S.; Barzakh, A.; Bree, N.; Cocolios, T. E.; Comas, V. F.; Diriken, J.; Fedorov, D.; Fedosseev, V. N.; Franchoo, S.; Ghys, L.; Heredia, J. A.; Ivanov, O.; Köster, U.; Marsh, B. A.; Nishio, K.; Page, R. D.; Patronis, N.; Seliverstov, M. D.; Tsekhanovich, I.; Van den Bergh, P.; Van De Walle, J.; Venhart, M.; Vermote, S.; Veselský, M.; Wagemans, C.

2013-10-01

85

Quantum Relaxation in Singlet Fission  

NASA Astrophysics Data System (ADS)

Singlet fission is a multielectron process in organic chromophores, where an initially excited singlet state decays into two independent triplets. First observed in organic semiconductors almost 40 years ago, the phenomenon may be a promising route for increasing yields in next-generation photovoltaics. Early theories that ignored quantum coherence between excited states were capable of explaining the fission process on nanosecond timescales, but recent observations of fission on sub picosecond timescales call several tenants of those theories into question. We present a theory of optical dephasing and decoherence in singlet fission, drawing on ideas from quantum information theory to establish conditions for decoherence and disentanglement between the relevant quantum states on the picosecond timescale.

Teichen, Paul; Eaves, Joel

2013-03-01

86

Advanced Space Fission Propulsion Systems  

NASA Technical Reports Server (NTRS)

Fission has been considered for in-space propulsion since the 1940s. Nuclear Thermal Propulsion (NTP) systems underwent extensive development from 1955-1973, completing 20 full power ground tests and achieving specific impulses nearly twice that of the best chemical propulsion systems. Space fission power systems (which may eventually enable Nuclear Electric Propulsion) have been flown in space by both the United States and the Former Soviet Union. Fission is the most developed and understood of the nuclear propulsion options (e.g. fission, fusion, antimatter, etc.), and fission has enjoyed tremendous terrestrial success for nearly 7 decades. Current space nuclear research and technology efforts are focused on devising and developing first generation systems that are safe, reliable and affordable. For propulsion, the focus is on nuclear thermal rockets that build on technologies and systems developed and tested under the Rover/NERVA and related programs from the Apollo era. NTP Affordability is achieved through use of previously developed fuels and materials, modern analytical techniques and test strategies, and development of a small engine for ground and flight technology demonstration. Initial NTP systems will be capable of achieving an Isp of 900 s at a relatively high thrust-to-weight ratio. The development and use of first generation space fission power and propulsion systems will provide new, game changing capabilities for NASA. In addition, development and use of these systems will provide the foundation for developing extremely advanced power and propulsion systems capable of routinely and affordably accessing any point in the solar system. The energy density of fissile fuel (8 x 10(exp 13) Joules/kg) is more than adequate for enabling extensive exploration and utilization of the solar system. For space fission propulsion systems, the key is converting the virtually unlimited energy of fission into thrust at the desired specific impulse and thrust-to-weight ratio. This presentation will discuss potential space fission propulsion options ranging from first generation systems to highly advanced systems. Ongoing research that shows promise for enabling second generation NTP systems with Isp greater than 1000 s will be discussed, as will the potential for liquid, gas, or plasma core systems. Space fission propulsion systems could also be used in conjunction with simple (water-based) propellant depots to enable routine, affordable missions to various destinations (e.g. moon, Mars, asteroids) once in-space infrastructure is sufficiently developed. As fuel and material technologies advance, very high performance Nuclear Electric Propulsion (NEP) systems may also become viable. These systems could enable sophisticated science missions, highly efficient cargo delivery, and human missions to numerous destinations. Commonalities between NTP, fission power systems, and NEP will be discussed.

Houts, Michael G.; Borowski, Stanley K.

2010-01-01

87

Quaternary glaciations in the Northern Hemisphere  

SciTech Connect

This volume presents the final report of Project 24 of the International Geological Correlation Programme. The publication is drawn from the contributions of leading individual scientist as well as from scientific research teams. It reflects the present state of knowledge of the Quaternary Glaciations in the Northern Hemisphere and their correlation in space and time, as well as providing a unique summary of climatic change.

Sibrava, V.; Bowen, D.Q.; Richmond, G.M.

1987-01-01

88

Late Quaternary Environments in the Nile Basin  

Microsoft Academic Search

The Late Quaternary history of the Nile has been reconstructed using well-dated sedimentary, stable isotope and fossil records\\u000a and associated archaeological remains. The White Nile flows over the bed of an ancient lake dating to ~ 400 ka (Marine Isotope\\u000a Stage 11). High flood levels in the White Nile since that time appear to coincide with times of sapropel accumulation

Martin A. J. Williams; Michael R. Talbot

89

Palladium-catalyzed asymmetric quaternary stereocenter formation.  

PubMed

An efficient palladium catalyst is presented for the formation of benzylic quaternary stereocenters by conjugate addition of arylboronic acids to a variety of ?,?-disubstituted carbocyclic, heterocyclic, and acyclic enones. The catalyst is readily prepared from PdCl(2), PhBOX, and AgSbF(6), and provides products in up to 99% enantiomeric excess, with good yields. Based on this strategy, (-)-?-cuparenone has been prepared in only two steps. PMID:22532469

Gottumukkala, Aditya L; Matcha, Kiran; Lutz, Martin; de Vries, Johannes G; Minnaard, Adriaan J

2012-05-29

90

The Microscopic Theory of Fission  

SciTech Connect

Fission-fragment properties have been calculated for thermal neutron-induced fission on a {sup 239}Pu target, using constrained Hartree-Fock-Bogoliubov calculations with a finite-range effective interaction. A quantitative criterion based on the interaction energy between the nascent fragments is introduced to define the scission configurations. The validity of this criterion is benchmarked against experimental measurements of the kinetic energies and of multiplicities of neutrons emitted by the fragments.

Younes, W; Gogny, D

2009-06-09

91

Semiclassical theory of nuclear fission  

Microsoft Academic Search

The semiclassical approach recently developed for large-amplitude collective oscillations is extended to tunneling phenomena in order to obtain a microscopic description of nuclear fission. For this purpose the imaginary-time partition function is evaluated via its euclidean path integral representation. The stationary phase condition leads to the imaginary-time-dependent Hartree-Fock equation. Its classical solution gives a dynamical picture of the fission process.

H. Reinhardt

1981-01-01

92

The microscopic theory of fission  

E-print Network

Fission-fragment properties have been calculated for thermal neutron-induced fission on a $^{239}\\textrm{Pu}$ target, using constrained Hartree-Fock-Bogoliubov calculations with a finite-range effective interaction. A quantitative criterion based on the interaction energy between the nascent fragments is introduced to define the scission configurations. The validity of this criterion is benchmarked against experimental measurements of the kinetic energies and of multiplicities of neutrons emitted by the fragments.

W. Younes; D. Gogny

2009-10-09

93

Fission Modes of Mercury Isotopes  

SciTech Connect

Background: Recent experiments on -delayed fission in the mercury-lead region and the discovery of asymmetric fission in 180Hg [A. N. Andreyev et al., Phys. Rev. Lett. 105, 252502 (2010)] have stimulated theoretical interest in the mechanism of fission in heavy nuclei.

Purpose: We study fission modes and fusion valleys in 180Hg and 198Hg to reveal the role of shell effects in the prescission region and explain the experimentally observed fragment mass asymmetry and its variation with A.

Methods: We use the self-consistent nuclear density functional theory employing Skyrme and Gogny energy density functionals.

Results: The potential energy surfaces in multidimensional space of collective coordinates, including elongation, triaxiality, reflection-asymmetry, and necking, are calculated for 180Hg and 198Hg. The asymmetric fission valleys well separated from fusion valleys associated with nearly spherical fragments are found in both cases. The density distributions at scission configurations are studied and related to the experimentally observed mass splits.

Conclusions: The energy density functionals SkM and D1S give a very consistent description of the fission process in 180Hg and 198Hg. We predict a transition from asymmetric fission in 180Hg toward a more symmetric distribution of fission fragments in 198Hg. For 180Hg, both models yield 100Ru/80Kr as the most probable split. For 198Hg, the most likely split is 108Ru/90Kr in HFB-D1S and 110Ru/88Kr in HFB-SkM .

Warda, M. [Maria Curie-Sk?odowska University-Poland; Staszczak, A. [Maria Curie-Sklodowska University; Nazarewicz, Witold [UTK/ORNL/University of Warsaw

2012-01-01

94

Aleksis Dreimanis: a legacy in Quaternary science  

NASA Astrophysics Data System (ADS)

Aleksis Dreimanis was born and raised in Latvia. His interest in Quaternary and glacial geology began early and developed into a career that has spanned 7 decades. At age 20 he published his first paper in glacial geology and soon after began teaching at the University of Latvia. Teaching and research were interrupted by World War II but resumed at the Baltic University (Pinneberg, Germany), then at the University of Western Ontario where he has been ever since. Throughout his career, Dreimanis has successfully balanced the twin disciplines of Quaternary history and glacial geology. He was among the first to study quantitatively the relationship between till lithology and till formation and to study how glacial transport and dynamics affect till texture and deformation. With co-workers he developed the well-known stratigraphic scheme of the last glaciation in the Great Lakes region of North America. Aleksis became world-renowned through his committee work, especially as President of the INQUA Commission on Genesis and Lithology of Glacial Quaternary Deposits. His diplomacy, enthusiasm, and passion for his subject have inspired students and colleagues around the globe and resulted in remarkable international dialogue, cooperation, and consensus. Professor Aleksis Dreimanis is an honest scientist, a gentleman, and a true scholar who has left a rich legacy for future Quaternarists.

Hicock, Stephen R.; Menzies, John

2000-12-01

95

Late quaternary sequence stratigraphy, South Florida margin  

SciTech Connect

Late Quaternary sea-level change and the Florida Current have combined to produce a progradational shelf-slope margin along the western portion of the south Florida Platform facing the Straits of Florida. Analysis of high resolution seismic reflection profiles suggest at least eight 5th order late Quaternary sequences downlap onto the Pourtales Terrace at 250 m water depth. Along most of the south Florida margin, this Late Quaternary section is very thin, and only where significant accumulations occur can the stratigraphic patterns produced by sea-level change be clearly observed. Recognition of systems tracts and their boundaries from high-resolution seismic data is important for prediction of sedimentary facies and stratigraphic development of margins. Many south Florida seismic boundaries can be fit to the Exxon sequence stratigraphy model. Others appear to reflect the added effect of bottom-current erosion that complicates the signal produced by sea-level change. Overall, the sea-level signal appears to dominate the stratigraphic record, especially from the 2-dimensional perspective of dip-oriented seismic profiles. However, the 3-dimensional geometry of deposits are strongly influenced by along slope accumulation patterns controlled by the Florida Current. This study provides new insight on the importance of both geostrophic boundary currents and sea-level change in controlling stratigraphic development of a carbonate platform margin. Similar anomalously thick slope deposits in ancient sequences may indicate similar controls on accumulation and could lend to predictions of related paleo-platform configurations.

Locker, S.D.; Hine, A.C. [Univ. of South Florida, St. Petersburg, FL (United States). Dept. of Marine Science

1995-12-01

96

40 CFR 721.9075 - Quaternary ammonium salt of fluorinated alkylaryl amide.  

Code of Federal Regulations, 2010 CFR

...2010-07-01 false Quaternary ammonium salt of fluorinated alkylaryl amide. 721...Substances § 721.9075 Quaternary ammonium salt of fluorinated alkylaryl amide. ...identified generically as quaternary ammonium salt of fluorinated alkylaryl amide...

2010-07-01

97

40 CFR 721.9075 - Quaternary ammonium salt of fluorinated alkylaryl amide.  

Code of Federal Regulations, 2011 CFR

...2011-07-01 false Quaternary ammonium salt of fluorinated alkylaryl amide. 721...Substances § 721.9075 Quaternary ammonium salt of fluorinated alkylaryl amide. ...identified generically as quaternary ammonium salt of fluorinated alkylaryl amide...

2011-07-01

98

Gravity anomalies, Quaternary vents, and Quaternary faults in the southern Cascade Range, Oregon and California: Implications for arc and backarc evolution  

Microsoft Academic Search

Isostatic residual gravity anomalies in the southern Cascade Range of northern California and southern Oregon are spatially correlated with broad zones of Quaternary magmatism as reflected by the total volume of Quaternary volcanic products, the distribution of Quaternary vents, and the anomalously low teleseismic P wave velocities in the upper 30 km of crust. The orientation of Quaternary faults also

Richard J. Blakely; Robert L. Christiansen; Marianne Guffanti; Ray E. Wells; Julie M. Donnelly-Nolan; L. J. Patrick Muffler; Michael A. Clynne; James G. Smith

1997-01-01

99

Quaternary Geologic Map of Connecticut and Long Island Sound Basin  

USGS Publications Warehouse

The Quaternary geologic map (sheet 1) and explanatory figures and cross sections (sheet 2) portray the geologic features formed in Connecticut during the Quaternary Period, which includes the Pleistocene (glacial) and Holocene (postglacial) Epochs. The Quaternary Period has been a time of development of many details of the landscape and of all the surficial deposits. At least twice in the late Pleistocene, continental ice sheets swept across Connecticut. Their effects are of pervasive importance to the present occupants of the land. The Quaternary geologic map illustrates the geologic history and the distribution of depositional environments during the emplacement of glacial and postglacial surficial deposits and the landforms resulting from those events.

Stone, Janet Radway; Schafer, John P.; London, Elizabeth Haley; DiGiacomo-Cohen, Mary L.; Lewis, Ralph S.; Thompson, Woodrow B.

2005-01-01

100

Compact fission counter for DANCE  

SciTech Connect

The Detector for Advanced Neutron Capture Experiments (DANCE) consists of 160 BF{sub 2} crystals with equal solid-angle coverage. DANCE is a 4{pi} {gamma}-ray calorimeter and designed to study the neutron-capture reactions on small quantities of radioactive and rare stable nuclei. These reactions are important for the radiochemistry applications and modeling the element production in stars. The recognition of capture event is made by the summed {gamma}-ray energy which is equivalent of the reaction Q-value and unique for a given capture reaction. For a selective group of actinides, where the neutron-induced fission reaction competes favorably with the neutron capture reaction, additional signature is needed to distinguish between fission and capture {gamma} rays for the DANCE measurement. This can be accomplished by introducing a detector system to tag fission fragments and thus establish a unique signature for the fission event. Once this system is implemented, one has the opportunity to study not only the capture but also fission reactions. A parallel-plate avalanche counter (PPAC) has many advantages for the detection of heavy charged particles such as fission fragments. These include fast timing, resistance to radiation damage, and tolerance of high counting rate. A PPAC also can be tuned to be insensitive to {alpha} particles, which is important for experiments with {alpha}-emitting actinides. Therefore, a PPAC is an ideal detector for experiments requiring a fast and clean trigger for fission. A PPAC with an ingenious design was fabricated in 2006 by integrating amplifiers into the target assembly. However, this counter was proved to be unsuitable for this application because of issues related to the stability of amplifiers and the ability to separate fission fragments from {alpha}'s. Therefore, a new design is needed. A LLNL proposal to develop a new PPAC for DANCE was funded by NA22 in FY09. The design goal is to minimize the mass for the proposed counter and still be able to maintain a stable operation under extreme radioactivity and the ability to separate fission fragments from {alpha}'s. In the following sections, the description is given for the design and performance of this new compact PPAC, for studying the neutron-induced reactions on actinides using DANCE at LANL.

Wu, C Y; Chyzh, A; Kwan, E; Henderson, R; Gostic, J; Carter, D; Bredeweg, T; Couture, A; Jandel, M; Ullmann, J

2010-11-06

101

Thorium-uranium fission radiography  

NASA Technical Reports Server (NTRS)

Results are described for studies designed to develop routine methods for in-situ measurement of the abundance of Th and U on a microscale in heterogeneous samples, especially rocks, using the secondary high-energy neutron flux developed when the 650 MeV proton beam of an accelerator is stopped in a 42 x 42 cm diam Cu cylinder. Irradiations were performed at three different locations in a rabbit tube in the beam stop area, and thick metal foils of Bi, Th, and natural U as well as polished silicate glasses of known U and Th contents were used as targets and were placed in contact with mica which served as a fission track detector. In many cases both bare and Cd-covered detectors were exposed. The exposed mica samples were etched in 48% HF and the fission tracks counted by conventional transmitted light microscopy. Relative fission cross sections are examined, along with absolute Th track production rates, interaction tracks, and a comparison of measured and calculated fission rates. The practicality of fast neutron radiography revealed by experiments to data is discussed primarily for Th/U measurements, and mixtures of other fissionable nuclei are briefly considered.

Haines, E. L.; Weiss, J. R.; Burnett, D. S.; Woolum, D. S.

1976-01-01

102

Quaternary seismo-tectonic activity of the Polochic Fault, Guatemala  

E-print Network

Quaternary seismo-tectonic activity of the Polochic Fault, Guatemala Christine Authemayou,1 transform boundary between the North American and Caribbean plates in Guatemala and the associated seismic), Quaternary seismo-tectonic activity of the Polochic Fault, Guatemala, J. Geophys. Res., 117, B07403, doi:10

Paris-Sud XI, Université de

103

Applications 1/2 1. Dating Quaternary basalt volcanism  

E-print Network

Radiocarbon dating (if charcoal in between) K-Ar or Ar-Ar dating or: Cosmogenic 3He 1. Dating QuaternaryApplications 1/2 1. Dating Quaternary basalt volcanism 2. Timing of landslides 3. Tectonic displacement 4. Glaciers and ice-sheets 5. Meteorite impacts 6. Sedimentation rates 7. (Ground) water dating 8

Siebel, Wolfgang

104

Late Quaternary history of southern Chesapeake Bay  

SciTech Connect

More than 700 km of high-resolution, seismic-reflection profiles and sidescan-sonar images provide new information about the late Quaternary history of southern Chesapeake Bay. Sidescan-sonar images show that, excluding the nearshore zone, most of the bay bottom has a monotonously smooth surface, except that sand waves, ripples, and other bedforms occur in local areas affected by tidal currents. Seismic-reflection data show that the Quaternary stratigraphy of the southern part of the Bay is related primarily to the last cycle of sea-level change. The Quaternary section overlies an erosion surface cut deeply into gently seaward-dipping marine beds of Neogene age. Fluvial paleochannels, related to the last major low sea-level stand, are characterized by as much as 55 m of incision and by thin, irregular, terrace and channel-bottom deposits. Marine and estuarine deposits related to the Holocene transgression partially or fully bury the fluvial valleys and overlie the interfluves. A prominent feature of the Bay-mouth area is a wedge of sediment that has prograded into the Bay from the inner shelf. The common assumption--that the Chesapeake Bay is the drowned valley of the Pleistocene Susquehanna River--is only partially valid for the southern part of the Bay. The Bay mouth area, in general, is relatively young. The axial channel of the Bay is a modern tidal channel that is actively eroding Tertiary deposits and migrating toward the south and west; it is unrelated to older fluvial channels. Also, the positions of the modern axial channel and the last two fluvial paleochannels indicate long-term southward migration of the Bay mouth.

Colman, S.M.; Hobbs, C.H. III; Halka, J.P.

1985-01-01

105

Singlet exciton fission in solution  

NASA Astrophysics Data System (ADS)

Singlet exciton fission, the spin-conserving process that produces two triplet excited states from one photoexcited singlet state, is a means to circumvent the Shockley-Queisser limit in single-junction solar cells. Although the process through which singlet fission occurs is not well characterized, some local order is thought to be necessary for intermolecular coupling. Here, we report a triplet yield of 200% and triplet formation rates approaching the diffusion limit in solutions of bis(triisopropylsilylethynyl (TIPS)) pentacene. We observe a transient bound excimer intermediate, formed by the collision of one photoexcited and one ground-state TIPS-pentacene molecule. The intermediate breaks up when the two triplets separate to each TIPS-pentacene molecule. This efficient system is a model for future singlet-fission materials and for disordered device components that produce cascades of excited states from sunlight.

Walker, Brian J.; Musser, Andrew J.; Beljonne, David; Friend, Richard H.

2013-12-01

106

Singlet exciton fission in solution.  

PubMed

Singlet exciton fission, the spin-conserving process that produces two triplet excited states from one photoexcited singlet state, is a means to circumvent the Shockley-Queisser limit in single-junction solar cells. Although the process through which singlet fission occurs is not well characterized, some local order is thought to be necessary for intermolecular coupling. Here, we report a triplet yield of 200% and triplet formation rates approaching the diffusion limit in solutions of bis(triisopropylsilylethynyl (TIPS)) pentacene. We observe a transient bound excimer intermediate, formed by the collision of one photoexcited and one ground-state TIPS-pentacene molecule. The intermediate breaks up when the two triplets separate to each TIPS-pentacene molecule. This efficient system is a model for future singlet-fission materials and for disordered device components that produce cascades of excited states from sunlight. PMID:24256865

Walker, Brian J; Musser, Andrew J; Beljonne, David; Friend, Richard H

2013-12-01

107

Cranking mass parameters for fission  

E-print Network

A formalism for semi-adiabatic cranking mass parameters is presented. For the fission process of 234U, the time-dependent pairing equations of motion were used to calculate the excitation energy and to extract values of the cranking inertia. A fission barrier is determined by minimizing the action trajectory in a five dimensional configuration space spanned by elongation, necking, deformations of fragments and mass-asymmetry. The deformation energy is computed in the the frame of the microscopic-macroscopic model. The two center shell model with Woods-Saxon potentials is used in this context. Values of the inertia for excited fissioning systems are reported. A dependence between the cranking mass parameters and the intrinsic excitation energy is evidenced.

M. Mirea; R. C. Bobulescu

2009-09-11

108

Quantum efficiency and fission rate in tetracene  

E-print Network

Using singlet fission in a photovoltaic cell, the theoretical energy conversion efficiency limit is larger than the Shockley-Queisser limit due to two excitons produced with one incident photon. In a singlet fission material, ...

Wu, Tony Chang-Chi

2013-01-01

109

DE LA FISSION A LA FUSION  

E-print Network

bas DE LA FISSION A LA FUSION Aspects historiques et perspectives 15 octobre 2008 Gen`eve, Uni, astrophysicien La d´ecouverte de la fission de l'uranium par Bernard Fernandez, physicien nucl´eaire, historien

Schibler, Ueli

110

Search for Singlet Fission Chromophores  

SciTech Connect

Singlet fission, in which a singlet excited chromophore shares its energy with a ground-state neighbor and both end up in their triplet states, is of potential interest for solar cells. Only a handful of compounds, mostly alternant hydrocarbons, are known to perform efficiently. In view of the large number of conditions that a successful candidate for a practical cell has to meet, it appears desirable to extend the present list of high performers to additional classes of compounds. We have (i) identified design rules for new singlet fission chromophores and for their coupling to covalent dimers, (ii) synthesized them, and (iii) evaluated their performance as neat solids or covalent dimers.

Havlas, Z.; Akdag, A.; Smith, M. B.; Dron, P.; Johnson, J. C.; Nozik, A. J.; Michl, J.

2012-01-01

111

Process for treating fission waste. [Patent application  

DOEpatents

A method is described for the treatment of fission waste. A glass forming agent, a metal oxide, and a reducing agent are mixed with the fission waste and the mixture is heated. After melting, the mixture separates into a glass phase and a metal phase. The glass phase may be used to safely store the fission waste, while the metal phase contains noble metals recovered from the fission waste.

Rohrmann, C.A.; Wick, O.J.

1981-11-17

112

Fusion - fission dynamics: fragment mass distribution studies  

NASA Astrophysics Data System (ADS)

Using the major accelerator facilities available in India, detailed experimental studies have been made to understand the mechanism of quasi-fission and role of nuclear shell effect in heavy nuclei. Fission fragment mass distribution has been used as the probe to explore the role of entrance channel effects on fusion-fission and quasifission dynamics. Fission fragment mass distribution has also been demonstrated to be useful to identify the phenomenon of `washing out' of nuclear shell effect with excitation energy.

Bhattacharya, S.; Chaudhuri, A.; Ghosh, T. K..; Banerjee, K.; Bhattacharya, C.; Kundu, S.; Mukherjee, G.; Rana, T. K.; Roy, P.; Pandey, R.; Bhattacharya, P.

2015-01-01

113

The topography of the nuclear fission barrier  

Microsoft Academic Search

Fission theory first developed within the framework of the liquid drop model. Shell model concepts were introduced into fission\\u000a theory much later than they were in nuclear structure theory, but then with spectacular success in explaining striking experimental\\u000a results then emerging in actinide fission. In the last two decades the complex topography of the fission barrier that is the\\u000a result

J E Lynn

1989-01-01

114

Microscopic description of nuclear fission dynamics  

Microsoft Academic Search

We discuss possible avenues to study fission dynamics starting from a time-dependent mean-field approach. Previous attempts to study fission dynamics using the time-dependent Hartree–Fock (TDHF) theory are analyzed. We argue that different initial conditions may be needed to describe fission dynamics depending on the specifics of the fission phenomenon and propose various approaches toward this goal. In particular, we provide

A. S. Umar; V. E. Oberacker; J. A. Maruhn; P.-G. Reinhard

2010-01-01

115

Microscopic description of nuclear fission dynamics  

Microsoft Academic Search

We discuss possible avenues to study fission dynamics starting from a time-dependent mean-field approach. Previous attempts to study fission dynamics using the time-dependent Hartree-Fock (TDHF) theory are analyzed. We argue that different initial conditions may be needed to describe fission dynamics depending on the specifics of the fission phenomenon and propose various approaches toward this goal. In particular, we provide

A. S. Umar; V. E. Oberacker; J. A. Maruhn; P.-G. Reinhard

2010-01-01

116

Neutronics for critical fission reactors and subcritical fission in hybrids  

SciTech Connect

The requirements of future innovative nuclear fuel cycles will focus on safety, sustainability and radioactive waste minimization. Critical fast neutron reactors and sub-critical, external source driven systems (accelerator driven and fusion-fission hybrids) have a potential role to meet these requirements in view of their physics characteristics. This paper provides a short introduction to these features.

Salvatores, Massimo [CEA-Cadarache, DEN-Dir, Bat. 101, St-Paul-Lez-Durance 13108 (France)

2012-06-19

117

Spontaneous fission properties of the heavy elements: Bimodal fission  

SciTech Connect

We have measured the mass and kinetic-energy distributions from the spontaneous fission of SVYFm, SVYNo, SVZMd, SWMd, SW(104), and SWSNo. All are observed to fission with a symmetrical division of mass, whereas the total-kinetic-energy (TKE) distributions strongly deviated from the Gaussian shape characteristically found in the fission of all other actinides. When the TKE distributions are resolved into two Gaussian's, the constituent peaks lie near 200 and near 233 MeV. We conclude two modes or bimodal fission is occurring in five of the six nuclides studied. Both modes are possible in the same nuclide, but one generally predominates. We also conclude the low-energy but mass-symmetrical mode is likely to extend to far heavier nuclei; while the high-energy mode will be restricted to a smaller region, a region of nuclei defined by the proximity of the fragments to the strong neutron and proton shells in TSSn. 21 refs., 7 figs., 1 tab.

Hulet, E.K.

1988-11-11

118

Uranium235 Thermal Neutron Fission Yields  

Microsoft Academic Search

The absolute yields of six nuclides in the thermal neutron fission of U235 have been determined to better than 6 percent, using fission counting and radiochemical techniques. The results are in good agreement with earlier determinations of lower accuracy. They support mass spectrometric indications of fine structure in the yield-mass curve in low-energy nuclear fission.

George W. Reed; Anthony Turkevich

1953-01-01

119

Fission for Program Comprehension Jeremy Gibbons  

E-print Network

Fission for Program Comprehension Jeremy Gibbons Oxford University Computing Laboratory Wolfson at the cost of clarity. Fission is the same transformation, in reverse: creating structure, ex nihilo. We explore the use of fission for program comprehension, that is, for reconstructing the design of a program

Gibbons, Jeremy

120

Space Fission System Test Effectiveness  

SciTech Connect

Space fission technology has the potential to enable rapid access to any point in the solar system. If fission propulsion systems are to be developed to their full potential, however, near-term customers need to be identified and initial fission systems successfully developed, launched, and utilized. One key to successful utilization is to develop reactor designs that are highly testable. Testable reactor designs have a much higher probability of being successfully converted from paper concepts to working space hardware than do designs which are difficult or impossible to realistically test. ''Test Effectiveness'' is one measure of the ability to realistically test a space reactor system. The objective of this paper is to discuss test effectiveness as applied to the design, development, flight qualification, and acceptance testing of space fission systems. The ability to perform highly effective testing would be particularly important to the success of any near-term mission, such as NASA's Jupiter Icy Moons Orbiter, the first mission under study within NASA's Project Prometheus, the Nuclear Systems Program.

Houts, Mike [Los Alamos National Laboratory, MS-K575, Los Alamos, NM 87545 (United States); Schmidt, Glen L. [New Mexico Tech, Institute for Engineering Research and Applications, 901 University Blvd SE, Albuquerque, NM 87109-4339 (United States); Van Dyke, Melissa; Godfroy, Tom; Martin, James; Bragg-Sitton, Shannon; Dickens, Ricky; Salvail, Pat; Harper, Roger [NASA MSFC, TD40, Marshall Space Flight Center, AL, 35812 (United States)

2004-02-04

121

Fifty years with nuclear fission  

Microsoft Academic Search

The news of the discovery of nuclear fission, by Otto Hahn and Fritz Strassmann in Germany, was brought to the United States by Niels Bohr in January 1939. Since its discovery, the United States, and the world for that matter, has never been the same. It therefore seemed appropriate to acknowledge the fifieth anniversary of its discovery by holding a

J. W. Behrens; A. D. Carlson

1989-01-01

122

Etching fission tracks in zircons  

USGS Publications Warehouse

A new technique has been developed whereby fission tracks can be etched in zircon with a solution of sodium hydroxide at 220??C. Etching time varied between 15 minutes and 5 hours. Colored zircon required less etching time than the colorless varieties.

Naeser, C.W.

1969-01-01

123

Space Fission Propulsion System Development Status  

NASA Technical Reports Server (NTRS)

The world's first man-made self-sustaining fission reaction was achieved in 1942. Since then fission has been used to propel submarines, generate tremendous amounts of electricity, produce medical isotopes, and provide numerous other benefits to society. Fission systems operate independently of solar proximity or orientation, and are thus well suited for deep spare or planetary surface missions. In addition, the fuel for fission systems (enriched uranium) is virtually non-radioactive. The primary safety issue with fission systems is avoiding inadvertent system start - addressing this issue through proper system design is straightforward. Despite the relative simplicity and tremendous potential of space fission systems, the development and utilization of these systems has proven elusive. The first use of fission technology in space occurred 3 April 1965 with the US launch of the SNAP-10A reactor. There have been no additional US uses of space fission system. While space fission system were used extensively by the former Soviet Union, their application was limited to earth-orbital missions. Early space fission systems must be safely and affordably utilized if Ae are to reap the benefits of advanced space fission systems.

Houts, Mike; VanDyke, Melissa; Godfroy, Tom; Pedersen, Kevin; Martin, James; Dickens, Ricky; Williams, Eric; Harper, Roger; Salvail, Pat; Hrbud, Ivana; Rodgers, Stephen L. (Technical Monitor)

2001-01-01

124

Antimicrobial Polymeric Materials with Quaternary Ammonium and Phosphonium Salts  

PubMed Central

Polymeric materials containing quaternary ammonium and/or phosphonium salts have been extensively studied and applied to a variety of antimicrobial-relevant areas. With various architectures, polymeric quaternary ammonium/phosphonium salts were prepared using different approaches, exhibiting different antimicrobial activities and potential applications. This review focuses on the state of the art of antimicrobial polymers with quaternary ammonium/phosphonium salts. In particular, it discusses the structure and synthesis method, mechanisms of antimicrobial action, and the comparison of antimicrobial performance between these two kinds of polymers. PMID:25667977

Xue, Yan; Xiao, Huining; Zhang, Yi

2015-01-01

125

Biocide comparison: Aldehyde versus mixture of aldehyde and quaternary amine  

SciTech Connect

Glutaraldehyde and quaternary ammonium chloride salts are widely used biocides in oil field systems to control microbiologically influenced corrosion (MIC). These biocides and others were evaluated for their efficacy to control sessile and planktonic sulfate reducing bacteria (SRB) and aerobic bacteria. The efficacy of these biocides was then compared. In addition to laboratory evaluation, all the biocides were evaluated against SRB and acid producing bacteria in two different field waters. It was found that the blend containing aldehyde and quaternary amino was, in general, a more effective biocide than either glutaraldehyde or quaternary amine alone.

Prasad, R. [Champion Technologies, Inc., Houston, TX (United States)

1994-12-31

126

Space Fission Propulsion System Development Status  

NASA Technical Reports Server (NTRS)

The world's first man-made self-sustaining fission reaction was achieved in 1942. Since then fission has been used to propel submarines, generate tremendous amounts of electricity, produce medical isotopes, and provide numerous other benefits to society. Fission systems operate independently of solar proximity or orientation, and are thus well suited for deep space or planetary surface missions. In addition, the fuel for fission systems (enriched uranium) is virtually non-radioactive. The primary safety issue with fission systems is avoiding inadvertent system start. Addressing this issue through proper system design is straight-forward. Despite the relative simplicity and tremendous potential of space fission systems, the development and utilization of these systems has proven elusive. The first use of fission technology in space occurred 3 April 1965 with the US launch of the SNAP-10A reactor. There have been no additional US uses of space fission systems. While space fission systems were used extensively by the former Soviet Union, their application was limited to earth-orbital missions. Early space fission systems must be safely and affordably utilized if we are to reap the benefits of advanced space fission systems. NASA's Marshall Space Flight Center, working with Los Alamos National Laboratory (LANL), Sandia National Laboratories, and others, has conducted preliminary research related to a Safe Affordable Fission Engine (SAFE). An unfueled core has been fabricated by LANL, and resistance heaters used to verify predicted core thermal performance by closely mimicking heat from fission. The core is designed to use only established nuclear technology and be highly testable. In FY01 an energy conversion system and thruster will be coupled to the core, resulting in an 'end-to-end' nuclear electric propulsion demonstrator being tested using resistance heaters to closely mimic heat from fission. Results of the SAFE test program will be presented. The applicability of a SAFE-powered electric propulsion system to outer planet science missions will also be discussed.

Houts, M.; Van Dyke, M. K.; Godfroy, T. J.; Pedersen, K. W.; Martin, J. J.; Dickens, R.; Williams, E.; Harper, R.; Salvail, P.; Hrbud, I.

2001-01-01

127

A fission fragment detector for correlated fission output studies  

NASA Astrophysics Data System (ADS)

A digital data acquisition system has been combined with a double Frisch gridded ionization chamber for use at both moderated and unmoderated neutron sources at the Los Alamos Neutron Science (LANSCE) facility. The high efficiency of the instrument combined with intense LANSCE beams and new acquisition system permits fission output measurements across 11 orders of magnitude incident neutron energy. The acquisition and analysis system is presented along with the first in-beam performance tests of the setup.

Mosby, S.; Tovesson, F.; Couture, A.; Duke, D. L.; Kleinrath, V.; Meharchand, R.; Meierbachtol, K.; O'Donnell, J. M.; Perdue, B.; Richman, D.; Shields, D.

2014-09-01

128

Quaternary coral reef refugia preserved fish diversity.  

PubMed

The most prominent pattern in global marine biogeography is the biodiversity peak in the Indo-Australian Archipelago. Yet the processes that underpin this pattern are still actively debated. By reconstructing global marine paleoenvironments over the past 3 million years on the basis of sediment cores, we assessed the extent to which Quaternary climate fluctuations can explain global variation in current reef fish richness. Comparing global historical coral reef habitat availability with the present-day distribution of 6316 reef fish species, we find that distance from stable coral reef habitats during historical periods of habitat loss explains 62% of the variation in fish richness, outweighing present-day environmental factors. Our results highlight the importance of habitat persistence during periods of climate change for preserving marine biodiversity. PMID:24876495

Pellissier, Loïc; Leprieur, Fabien; Parravicini, Valeriano; Cowman, Peter F; Kulbicki, Michel; Litsios, Glenn; Olsen, Steffen M; Wisz, Mary S; Bellwood, David R; Mouillot, David

2014-05-30

129

Dimeric quaternary structure of human laforin.  

PubMed

The phosphatase laforin removes phosphate groups from glycogen during biosynthetic activity. Loss-of-function mutations in the gene encoding laforin is the predominant cause of Lafora disease, a fatal form of progressive myoclonic epilepsy. Here, we used hybrid structural methods to determine the molecular architecture of human laforin. We found that laforin adopts a dimeric quaternary structure, topologically similar to the prototypical dual specificity phosphatase VH1. The interface between the laforin carbohydrate-binding module and the dual specificity phosphatase domain generates an intimate substrate-binding crevice that allows for recognition and dephosphorylation of phosphomonoesters of glucose. We identify novel molecular determinants in the laforin active site that help decipher the mechanism of glucan phosphatase activity. PMID:25538239

Sankhala, Rajeshwer S; Koksal, Adem C; Ho, Lan; Nitschke, Felix; Minassian, Berge A; Cingolani, Gino

2015-02-20

130

DSP Algorithms for Fission Fragment and Prompt Fission Neutron Spectroscopy  

SciTech Connect

Digital signal processing (DSP) algorithms are in high demand for modern nuclear fission investigation due to importance of increase the accuracy of fissile nuclear data for new generation of nuclear power stations. DSP algorithms for fission fragment (FF) and prompt fission neutron (PFN) spectroscopy are described in the present work. The twin Frisch-grid ionization chamber (GTIC) is used to measure the kinetic energy-, mass- and angular distributions of the FF in the {sup 252}Cf(SF) reaction. Along with the neutron time-of-flight (TOF) measurement the correlation between neutron emission and FF mass and energy is investigated. The TOF is measured between common cathode of the GTIC and the neutron detector (ND) pulses. Waveform digitizers (WFD) having 12 bit amplitude resolution and 100 MHz sampling frequency are used for the detector pulse sampling. DSP algorithms are developed as recursive procedures to perform the signal processing, similar to those available in various nuclear electronics modules, such as constant fraction discriminator (CFD), pulse shape discriminator (PSD), peak-sensitive analogue-to-digital converter (pADC) and pulse shaping amplifier (PSA). To measure the angle between FF and the cathode plane normal to the GTIC a new algorithm is developed having advantage over the traditional analogue pulse processing schemes. Algorithms are tested by comparing the numerical simulation of the data analysis of the {sup 252}Cf(SF) reaction with data available from literature.

Zeynalova, O. [Moscow State Institute of Radioengineering, Electronics and Automation 78, Vernadski Avenue, 119454 Moscow (Russian Federation); Joint Institute for Nuclear Research, Joliot Curie 6, Dubna, Moscow region (Russian Federation); Zeynalov, Sh. [Joint Institute for Nuclear Research, Joliot Curie 6, Dubna, Moscow region (Russian Federation); European Commission, Joint Research Centre, Institute for Reference Materials and Measurements, Retieseweg 111, 2440 Geel (Belgium); Hambsch, F.-J.; Oberstedt, S.; Fabry, I. [European Commission, Joint Research Centre, Institute for Reference Materials and Measurements, Retieseweg 111, 2440 Geel (Belgium)

2009-10-29

131

Nuclear-fission studies with relativistic secondary beams: analysis of fission channels  

E-print Network

Nuclear fission of several neutron-deficient actinides and pre-actinides from excitation energies around 11 MeV was studied at GSI Darmstadt by use of relativistic secondary beams. The characteristics of multimodal fission of nuclei around 226Th are systematically investigated and interpreted as the superposition of three fission channels. Properties of these fission channels have been determined for 15 systems. A global view on the properties of fission channels including previous results is presented. The positions of the asymmetric fission channels are found to be constant in element number over the whole range of systems investigated.

C. Boeckstiegel; S. Steinhaeuser; K. -H. Schmidt; H. -G. Clerc; A. Grewe; A. Heinz; M. de Jong; A. R. Junghans; J. Mueller; B. Voss

2007-12-21

132

The newsletter of the CAMBRIDGE QUATERNARY ISSUE 32 MICHAELMAS 2005  

E-print Network

sheets during the 20th century" November Tues 15th ESC Don Canfield (Odense, Denmark) "Neoproterozoic://www.quaternary.group.cam.ac.uk/ #12;Dates for your Diary Michaelmas 2005 October Tue 25th ESC Jake Lowenstern (Yellowstone Volcano

de Gispert, Adrià

133

Catalytic asymmetric synthesis of all-carbon quaternary stereocenters  

PubMed Central

Only a few catalytic asymmetric C—C bond-forming reactions have been shown to be useful for constructing all-carbon quaternary stereocenters. This Perspective examines the current state of such methods. PMID:14724294

Douglas, Christopher J.; Overman, Larry E.

2004-01-01

134

Fission Properties for R-Process Nuclei  

SciTech Connect

We present a systematics of fission barriers and fission lifetimes for the whole landscape of superheavy elements (SHE), i.e., nuclei with Z 100. The fission lifetimes are also compared with the -decay half-lives. The survey is based on a self-consistent description in terms of the Skyrme-Hartree-Fock (SHF) approach. Results for various different SHF parametrizations are compared to explore the robustness of the predictions. The fission path is computed by quadrupole constrained SHF. The computation of fission lifetimes takes care of the crucial ingredients of the large-amplitude collective dynamics along the fission path, as self-consistent collective mass and proper quantum corrections. We discuss the different topologies of fission landscapes which occur in the realm of SHE (symmetric versus asymmetric fission, regions of triaxial fission, bimodal fission, and the impact of asymmetric ground states). The explored region is extended deep into the regime of very neutron-rich isotopes as they are expected to be produced in the astrophysical r process.

Erler, J. [Inst. fur Theoretische Physik II, Univ. Erlangen-Numberg, Germany/UTK/ORNL; Langanke, K. [GSI-Darmstadt/Tech. Univ. Darmstadt, Inst. Phys./Frankfurt Inst. Advanced Studies, Germany; Loens, H. P. [GSI-Darmstadt/Tech. Univ. Darmstadt, Inst. Phys.; Martinez-Pinedo, G. [GSI-Darmstadt/Tech. Univ. Darmstadt, Inst. Phys.; Reinhard, P.-G. [Inst. fur Theoretische Physik II, Univ. Erlangen-Numberg, Germany

2012-01-01

135

Fission properties for r-process nuclei  

E-print Network

We present a systematics of fission barriers and fission lifetimes for the whole landscape of super-heavy elements (SHE), i.e. nuclei with Z>100. The fission lifetimes are also compared with the alpha-decay half-lives. The survey is based on a self-consistent description in terms of the Skyrme-Hartree-Fock (SHF) approach. Results for various different SHF parameterizations are compared to explore the robustness of the predictions. The fission path is computed by quadrupole constrained SHF. The computation of fission lifetimes takes care of the crucial ingredients of the large-amplitude collective dynamics along the fission path, as self-consistent collective mass and proper quantum corrections. We discuss the different topologies of fission landscapes which occur in the realm of SHE (symmetric versus asymmetric fission, regions of triaxial fission, bi-modal fission, and the impact of asymmetric ground states). The explored region is extended deep into the regime of very neutron-rich isotopes as they are expected to be produced in the astrophysical r process.

J. Erler; K. Langanke; H. P. Loens; G. Martínez-Pinedo; P. -G. Reinhard

2011-12-05

136

Binary fission via lnviscid Trajectories  

NASA Astrophysics Data System (ADS)

We sketch an evolutionary picture which, unlike the classical picture, appears favorable to the hypothesis that close binary stars originate in the fission of a single slowly contracting protostar. The main differences from the classical picture are (1) evolution proceeds along certain families of Riemann ellipsoids, rather than along the Jacobi family and (2) the critical ellipsoid on the evolutionary trajectory suffers a deformation given by an ellipsoidal harmonic of order four, rather than of order three.

Lebovitz, N. R.

137

The VERDI fission fragment spectrometer  

NASA Astrophysics Data System (ADS)

The VERDI time-of-flight spectrometer is dedicated to measurements of fission product yields and of prompt neutron emission data. Pre-neutron fission-fragment masses will be determined by the double time-of-flight (TOF) technique. For this purpose an excellent time resolution is required. The time of flight of the fragments will be measured by electrostatic mirrors located near the target and the time signal coming from silicon detectors located at 50 cm on both sides of the target. This configuration, where the stop detector will provide us simultaneously with the kinetic energy of the fragment and timing information, significantly limits energy straggling in comparison to legacy experimental setup where a thin foil was usually used as a stop detector. In order to improve timing resolution, neutron transmutation doped silicon will be used. The high resistivity homogeneity of this material should significantly improve resolution in comparison to standard silicon detectors. Post-neutron fission fragment masses are obtained form the time-of-flight and the energy signal in the silicon detector. As an intermediary step a diamond detector will also be used as start detector located very close to the target. Previous tests have shown that poly-crystalline chemical vapour deposition (pCVD) diamonds provides a coincidence time resolution of 150 ps not allowing complete separation between very low-energy fission fragments, alpha particles and noise. New results from using artificial single-crystal diamonds (sCVD) show similar time resolution as from pCVD diamonds but also sufficiently good energy resolution.

Frégeau, M. O.; Bry?, T.; Gamboni, Th.; Geerts, W.; Oberstedt, S.; Oberstedt, A.; Borcea, R.

2013-12-01

138

A novel Voltage-mode CMOS quaternary logic design  

Microsoft Academic Search

This brief presents a novel kind of voltage-mode CMOS design that uses multiple threshold voltage transistors and three power supply lines to implement quaternary logic gates, showing lower power dissipation and using less area than the present voltage-mode quaternary circuits. Inverter, NMIN, and NMAX gates are simulated with the Spice tool using TSMC 0.18-?m technology. The proposed logic circuits overcome

R. C. G. da Silva; H. Boudinov; L. Carro

2006-01-01

139

The tempo of avian diversification during the Quaternary  

Microsoft Academic Search

It is generally assumed that the Quaternary was a period of heightened diversification in temperate ver- tebrate organisms. Previous molecular systematics studies have challenged this assertion. We re-examined this issue in north temperate birds using log-lineage plots and distributions of sister-taxon distances. Log- lineage plots support earlier conclusions that avian diversification slowed during the Quaternary. To test plots of empirical

Robert M. Zink; John Klicka; Brian R. Barber

2004-01-01

140

Technical Application of Nuclear Fission  

NASA Astrophysics Data System (ADS)

The chapter is devoted to the practical application of the fission process, mainly in nuclear reactors. After a historical discussion covering the natural reactors at Oklo and the first attempts to build artificial reactors, the fundamental principles of chain reactions are discussed. In this context chain reactions with fast and thermal neutrons are covered as well as the process of neutron moderation. Criticality concepts (fission factor ?, criticality factor k) are discussed as well as reactor kinetics and the role of delayed neutrons. Examples of specific nuclear reactor types are presented briefly: research reactors (TRIGA and ILL High Flux Reactor), and some reactor types used to drive nuclear power stations (pressurized water reactor [PWR], boiling water reactor [BWR], Reaktor Bolshoi Moshchnosti Kanalny [RBMK], fast breeder reactor [FBR]). The new concept of the accelerator-driven systems (ADS) is presented. The principle of fission weapons is outlined. Finally, the nuclear fuel cycle is briefly covered from mining, chemical isolation of the fuel and preparation of the fuel elements to reprocessing the spent fuel and conditioning for deposit in a final repository.

Denschlag, J. O.

141

Synthesis and anticoagulant activity of the quaternary ammonium chitosan sulfates.  

PubMed

Quaternary ammonium chitosan sulfates with diverse degrees of substitution (DS) ascribed to sulfate groups between 0.52 and 1.55 were synthesized by reacting quaternary ammonium chitosan with an uncommon sulfating agent (N(SO(3)Na)(3)) that was prepared from sodium bisulfite (NaHSO(3)) through reaction with sodium nitrite (NaNO(2)) in the aqueous system homogeneous. The structures of the derivatives were characterized by FTIR, (1)H NMR and (13)C NMR. The factors affecting DS of quaternary ammonium chitosan sulfates which included the molar ratio of NaNO(2) to quaternary ammonium chitosan, sulfated temperature, sulfated time and pH of sulfated reaction solution were investigated in detail. Its anticoagulation activity in vitro was determined by an activated partial thromboplastin time (APTT) assay, a thrombin time (TT) assay and a prothrombin time (PT) assay. Results of anticoagulation assays showed quaternary ammonium chitosan sulfates significantly prolonged APTT and TT, but not PT, and demonstrated that the introduction of sulfate groups into the quaternary ammonium chitosan structure improved its anticoagulant activity obviously. The study showed its anticoagulant properties strongly depended on its DS, concentration and molecular weight. PMID:21996571

Fan, Lihong; Wu, Penghui; Zhang, Jinrong; Gao, Song; Wang, Libo; Li, Mingjia; Sha, Mingming; Xie, Weiguo; Nie, Min

2012-01-01

142

New fission track ages of tektites and related glasses  

Microsoft Academic Search

Fission track dating is applied to a large number of australites, Muong Nong type tektites, Darwin glasses and Libyan Desert glasses. It is found that these glasses often have lowered fission track ages due to annealing effects. The same specimens have also smaller fission track etch pits. According to the diminishing percentage of etched fossil fission track diameters, lowered fission

W. Gentner; D. Storzer; G. A. Wagner

1969-01-01

143

Comparative evaluation of solar, fission, fusion, and fossil energy resources. Part 2: Power from nuclear fission  

NASA Technical Reports Server (NTRS)

Different types of nuclear fission reactors and fissionable materials are compared. Special emphasis is placed upon the environmental impact of such reactors. Graphs and charts comparing reactor facilities in the U. S. are presented.

Clement, J. D.

1973-01-01

144

Fission dynamics within time-dependent Hartree-Fock: deformation-induced fission  

E-print Network

Background: Nuclear fission is a complex large-amplitude collective decay mode in heavy nuclei. Microscopic density functional studies of fission have previously concentrated on adiabatic approaches based on constrained static calculations ignoring dynamical excitations of the fissioning nucleus, and the daughter products. Purpose: To explore the ability of dynamic mean-field methods to describe fast fission processes beyond the fission barrier, using the nuclide $^{240}$Pu as an example. Methods: Time-dependent Hartree-Fock calculations based on the Skyrme interaction are used to calculate non-adiabatic fission paths, beginning from static constrained Hartree-Fock calculations. The properties of the dynamic states are interpreted in terms of the nature of their collective motion. Fission product properties are compared to data. Results: Parent nuclei constrained to begin dynamic evolution with a deformation less than the fission barrier exhibit giant-resonance-type behaviour. Those beginning just beyond the ...

Goddard, P M; Rios, A

2015-01-01

145

A Quaternary Geomagnetic Instability Time Scale  

NASA Astrophysics Data System (ADS)

Reversals and excursions of Earth's geomagnetic field create marker horizons that are readily detected in sedimentary and volcanic rocks worldwide. An accurate and precise chronology of these geomagnetic field instabilities is fundamental to understanding several aspects of Quaternary climate, dynamo processes, and surface processes. For example, stratigraphic correlation between marine sediment and polar ice records of climate change across the cryospheres benefits from a highly resolved record of reversals and excursions. The temporal patterns of dynamo behavior may reflect physical interactions between the molten outer core and the solid inner core or lowermost mantle. These interactions may control reversal frequency and shape the weak magnetic fields that arise during successive dynamo instabilities. Moreover, weakening of the axial dipole during reversals and excursions enhances the production of cosmogenic isotopes that are used in sediment and ice core stratigraphy and surface exposure dating. The Geomagnetic Instability Time Scale (GITS) is based on the direct dating of transitional polarity states recorded by lava flows using the 40Ar/39Ar method, in parallel with astrochronologic age models of marine sediments in which O isotope and magnetic records have been obtained. A review of data from Quaternary lava flows and sediments yields a GITS comprising 10 polarity reversals and 27 excursions during the past 2.6 million years. Nine of the ten reversals bounding chrons and subchrons are associated with 40Ar/39Ar ages of transitionally-magnetized lava flows. The tenth, the Guass-Matuyama chron boundary, is tightly bracketed by 40Ar/39Ar dated ash deposits. Of the 27 well-documented excursions, 14 occurred during the Matuyama chron and 13 during the Brunhes chron; 19 have been dated directly using the 40Ar/39Ar method on transitionally-magnetized volcanic rocks and form the backbone of the GITS. Excursions are clearly not the rare phenomena once thought. Rather, during the Quaternary period, they occur nearly three times as often as full polarity reversals. I will address analytical issues, including the size and consistency of system blanks, that have led to the recognition of minor (1%) discrepencies between the 40Ar/39Ar age for a particular reversal or excursion and the best astrochronologic estimates from ODP sediment cores. For example, re-analysis of lava flows from Haleakala volcano, Maui that record in detail the Matuyama-Brunhes polarity reversal have been undertaken with blanks an order of magntitude smaller and more stable than was common a decade ago. Using the modern astrochronologic calibration of 28.201 Ma for the age of the Fish Canyon sanidine standard, results thus far yield an 40Ar/39Ar age of 772 × 11 ka for the reversal that is identical to the most precise and accurate astrochronologic age of 773 × 2 ka for this reversal from ODP cores. Similarly, new dating of sanidine in the Cerro Santa Rosa I rhyolite dome, New Mexico reveals an age of 932 × 5 ka for the excursion it records, in perfect agreement with astrochronologically dated ODP core records. Work underway aims at refining the 40Ar/39Ar ages that underpin the entire GITS by further eliminating the bias between the radioisotopic and astrochronologically determined ages for several reversals and excursions.

Singer, B. S.

2013-12-01

146

Fission product yields for thermal-neutron fission of plutonium-239  

Microsoft Academic Search

Absolute cumulative yields have been determined for 49 fission products representing 36 mass chains created during thermal-neutron fission of ²³⁹Pu, including 3 mass chains for which no prior data exist. Using Ge(Li) spectroscopy, spectra were obtained of gamma rays from decay of fission products between 1550 s and 31 days after a 100-s irradiation. Data were obtained for all fission

J. K. Dickens; J. W. McConnell

1980-01-01

147

Fission yields of In isotopes in the thermal neutron fission of 235 U  

Microsoft Academic Search

Fission yields of124–132In in the thermal neutron fission of235U were determined for the first time. Charge displacements?Z=Zp-ZUCD were calculated for the corresponding mass chains. Both fission yields and charge displacement values were compared with those obtained by systematics by Wahl et al. and Wolfsberg. It was found that the fission yields of the In isotopes obey the gaussian distribution. The

M. Shmid; G. Engler

1983-01-01

148

Experimental investigation into Quaternary badland geomorphic development  

NASA Astrophysics Data System (ADS)

Badland morphology is commonly linked to lithological properties of the bedrock. However, recent investigations indicate that the geomorphic development is sensitive to climate and in particular to precipitation characteristics. In this study, the precipitation characteristics that are critical for the Quaternary landscape development in the Dinosaur Badlands in Alberta, Canada, and Zin Valley Badlands, Negev Desert, Israel are investigated. Runoff, erosion and weathering were simulated in the field and the laboratory to determine rates for modeling different precipitation regimes. Currently, the geomorphic development in the Dinosaur badlands is characterized by weathering/supply limited conditions, leading to slope retreat independent of lithology. In the Negev, transport limited conditions cause frequent runoff discontinuity, creating a pattern of areas dominated by erosion or deposition. The results of the weathering and erosion experiments show that the balance between snowmelt induced weathering in the spring and summer rainfall and erosion determine the rate of slope retreat in the Dinosaur Badlands. In the Zin Valley, on the other hand, the magnitude of the individual rainstorms determines whether a slope section is eroded or acts as a sediment sink. The experiments illustrate that the badland slopes experienced an auto-stabilization during the Quaternary in the Zin Valley. In the Dinosaur Badlands Holocene climatic variations have not caused a permanent differentiation of patterns of erosion and deposition. Based on these results the reaction of badland slopes to changing precipitation characteristics was modeled. In their current state, both badland slope systems appear to be fairly stable against climate change in the range of those occurring during the Holocene. However, the stability is achieved in different ways. In the Dinosaur Badlands, weathering rates are low compared to erosion capacity, maintaining continuous evacuation of sediment from slopes to the flood planes of the Red Deer River system. Only a very pronounced contrast between winter weathering and drier summers would generate a colluvium and thus change slope hydrology. In the Zin Valley the development of a thick colluvium at the foot of the slopes has increased infiltration capacity, reducing runoff and sediment yield into the floodplain. Here, only an increase in rainfall magnitude would improve runoff continuity and induce the erosion of the colluvium. This would in turn reduce infiltration capacity and thus initiate a positive feedback on runoff and sediment yield into the Zin River. Overall, Holocene climate change appears to be insufficient to change the geomorphic development in both badlands. However, this stability is achieved not despite of climate, but because of the specific history of geomorphic development. In addition, the combination of erosion and weathering experiments with numerical modeling demonstrates the versatility of Experimental Geomorphology in landscape evolution studies.

Kasanin-Grubin, Milica; Kuhn, Nikolaus; Yair, Aaron; Bryan, Rorke; Schwanghart, Wolfgang

2010-05-01

149

Theoretical Description of the Fission Process  

NASA Astrophysics Data System (ADS)

Spontaneous fission is one the oldest decay modes known, but is still not fully understood. On the one hand, various nuclear structure models have been applied to fission barriers, lifetimes, and mass/charge distributions, and they provide a good overall description of the phenomenon and, in many cases, detailed predictions. On the other hand, the full-fledged, non-adiabatic description of fission, based on effective nucleon-nucleon interactions, still does not exist. The aim of our project on ``Theoretical Description of the Fission Process,'' supported by NNSA (www.phys.utk.edu/witek/fission/fission.html), is to attack the problem of spontaneous fission using modern theoretical methods and state-of-the-art computational tools. During the first stage of the project, we have studied static fission barriers of the even-even actinide and transactinide nuclei within the self-consistent Density Functional Theory. The computations are carried out applying a code that makes it possible to break all self-consistent symmetries of the nuclear mean field, including axial symmetry and reflection symmetry. Particular attention has been paid to symmetry-breaking effects along the fission path.

Nazarewicz, Witold

2006-10-01

150

Some Fission Problems Circa 1950 and 2008  

NASA Astrophysics Data System (ADS)

In the first part of the talk I will recall conversations with Niels Bohr and John Wheeler concerning the puzzle of the asymmetric mass division in nuclear fission. In 1950 this was the outstanding problem in fission theory, and for a brief period I foolishly believed to have found the solution by relaxing the incompressibility assumption in the liquid drop model of fission. In the second part I will describe recent progress in the formulation and streamlining of the transition-state formulae for the competition between the disintegration of an excited compound nucleus by particle emission and fission.

?wiatecki, W. J.

151

Yields of fission products produced by thermal-neutron fission of 243Cm  

Microsoft Academic Search

On the basis of measured yields for 72 gamma rays and known nuclear data, cumulative fission-product yields were deduced for 69 fission products having half-lives between 36 seconds and 65 days representing 41 mass chains created during thermal-neutron fission of 243Cm.

J. K. Dickens; J. W. McConnell

1986-01-01

152

Yields of fission products produced by thermal-neutron fission of 243Cm  

NASA Astrophysics Data System (ADS)

On the basis of measured yields for 72 gamma rays and known nuclear data, cumulative fission-product yields were deduced for 69 fission products having half-lives between 36 seconds and 65 days representing 41 mass chains created during thermal-neutron fission of 243Cm.

Dickens, J. K.; McConnell, J. W.

1986-08-01

153

Quaternary ammonium biocides: efficacy in application.  

PubMed

Quaternary ammonium compounds (QACs) are among the most commonly used disinfectants. There has been concern that their widespread use will lead to the development of resistant organisms, and it has been suggested that limits should be place on their use. While increases in tolerance to QACs have been observed, there is no clear evidence to support the development of resistance to QACs. Since efflux pumps are believe to account for at least some of the increased tolerance found in bacteria, there has been concern that this will enhance the resistance of bacteria to certain antibiotics. QACs are membrane-active agents interacting with the cytoplasmic membrane of bacteria and lipids of viruses. The wide variety of chemical structures possible has seen an evolution in their effectiveness and expansion of applications over the last century, including non-lipid-containing viruses (i.e., noroviruses). Selection of formulations and methods of application have been shown to affect the efficacy of QACs. While numerous laboratory studies on the efficacy of QACs are available, relatively few studies have been conducted to assess their efficacy in practice. Better standardized tests for assessing and defining the differences between increases in tolerance versus resistance are needed. The ecological dynamics of microbial communities where QACs are a main line of defense against exposure to pathogens need to be better understood in terms of sublethal doses and antibiotic resistance. PMID:25362069

Gerba, Charles P

2015-01-01

154

Quaternary structure of hemoglobin in solution  

NASA Astrophysics Data System (ADS)

Many important proteins perform their physiological functions under allosteric control, whereby the binding of a ligand at a specific site influences the binding affinity at a different site. Allosteric regulation usually involves a switch in protein conformation upon ligand binding. The energies of the corresponding structures are comparable, and, therefore, the possibility that a structure determined by x-ray diffraction in the crystalline state is influenced by its intermolecular contacts, and thus differs from the solution structure, cannot be excluded. Here, we demonstrate that the quaternary structure of tetrameric human normal adult carbonmonoxy-hemoglobin can readily be determined in solution at near-physiological conditions of pH, ionic strength, and temperature by NMR measurement of 15N-1H residual dipolar couplings in weakly oriented samples. The structure is found to be a dynamic intermediate between two previously solved crystal structures, known as the R and R2 states. Exchange broadening at the subunit interface points to a rapid equilibrium between different structures that presumably include the crystallographically observed states.

Lukin, Jonathan A.; Kontaxis, Georg; Simplaceanu, Virgil; Yuan, Yue; Bax, Ad; Ho, Chien

2003-01-01

155

Late Quaternary mammalian zoogeography of eastern Washington  

NASA Astrophysics Data System (ADS)

The late Quaternary mammalian zoogeographic history of eastern Washington as revealed by archaeological and paleontological research conforms to a set of past environmental conditions inferred from botanical data. During the relatively cool and moist late Pleistocene and early Holocene, Cervus cf. elaphus, Ovis canadensis, Vulpes vulpes, Martes americana, Alopex lagopus, and perhaps Rangifer sp., taxa with ecological preferences for mesic steppe habitats, were present in the now xeric Columbia Basin. As the climate became progressively warmer and drier during the late Pleistocene and early Holocene, Antilocapra americana, Onychomys leucogaster, Spermophilus townsendii, and Neotoma cinerea, taxa with ecological preferences for xeric steppe habitats, appear in the Columbia Basin. Bison sp. and Taxidea taxus may have been present in eastern Washington for the last 20,000 yr. Middle and late Holocene records for Oreamnos americanus, Spermophilus columbianus, S. townsendii, Lagurus curtatus, and Urocyon cinereoargenteus in central eastern Washington suggest fluctuations in the ranges of these taxa that conform to a middle Holocene period of less effective precipitation and a ca. 3500-yr-old period of more effective precipitation before essentially modern environmental conditions prevailed.

Lyman, R. Lee; Livingston, Stephanie D.

1983-11-01

156

Centric fission consequences in man.  

PubMed

The authors summarise the consequences of centric fission in man as follows: classical (monocentric) isochromosomes; usually either for p or q, exceptionally for both arms; stable telocentrics for either one or both arms; isochromosome for one arm, stable telocentric for the other; isochromosome for one arm concurring with translocation of the telocentric for the other; telocentric/isochromosome mosaicism for the same arm; stable telocentric for a part of one arm, the remaining of the chromosome forming a smaller element (obviously this rearrangement requires an additional break outside the centromere), and whole-arm translocations. These events are discussed in the light of current notions about centromere structure and function. PMID:3495221

Rivera, H; Cantú, J M

1986-01-01

157

Fission dynamics within time-dependent Hartree-Fock: deformation-induced fission  

E-print Network

Background: Nuclear fission is a complex large-amplitude collective decay mode in heavy nuclei. Microscopic density functional studies of fission have previously concentrated on adiabatic approaches based on constrained static calculations ignoring dynamical excitations of the fissioning nucleus, and the daughter products. Purpose: To explore the ability of dynamic mean-field methods to describe fast fission processes beyond the fission barrier, using the nuclide $^{240}$Pu as an example. Methods: Time-dependent Hartree-Fock calculations based on the Skyrme interaction are used to calculate non-adiabatic fission paths, beginning from static constrained Hartree-Fock calculations. The properties of the dynamic states are interpreted in terms of the nature of their collective motion. Fission product properties are compared to data. Results: Parent nuclei constrained to begin dynamic evolution with a deformation less than the fission barrier exhibit giant-resonance-type behaviour. Those beginning just beyond the barrier explore large amplitude motion but do not fission, whereas those beginning beyond the two-fragment pathway crossing fission to final states which differ according to the exact initial deformation. Conclusions: Time-dependent Hartree-Fock is able to give a good qualitative and quantitative description of fast fission, provided one begins from a sufficiently deformed state.

P. M. Goddard; P. D. Stevenson; A. Rios

2015-04-03

158

Nuclear Power from Fission Reactors. An Introduction.  

ERIC Educational Resources Information Center

The purpose of this booklet is to provide a basic understanding of nuclear fission energy and different fission reaction concepts. Topics discussed are: energy use and production, current uses of fuels, oil and gas consumption, alternative energy sources, fossil fuel plants, nuclear plants, boiling water and pressurized water reactors, the light…

Department of Energy, Washington, DC. Technical Information Center.

159

Options for Affordable Fission Surface Power Systems  

NASA Technical Reports Server (NTRS)

Fission surface power systems could provide abundant power anywhere on free surface of the moon or Mars. Locations could include permanently shaded regions on the moon and high latitudes on Mars. To be fully utilized; however, fission surface power systems must be safe, have adequate performance, and be affordable. This paper discusses options for the design and development of such systems.

Houts, Mike; Gaddis, Steve; Porter, Ron; VanDyke, Melissa; Martin Jim; Godfroy, Tom; Bragg-Sitton, Shannon; Garber, Anne; Pearson, Boise

2006-01-01

160

Independent Isotopic Fission Yield Studies with Jyfltrap  

NASA Astrophysics Data System (ADS)

A technique to determine the independent isotopic fission yields utilizing the ability of a Penning trap to unambiguously identify the isotopes based on their mass has recently been developed at the IGISOL facility in the University of Jyväskylä. The analysis of proton induced fission of 238U at 25 MeV energy has been finalized. The results will be compared with theoretical models.

Penttilä, H.; Elomaa, V.-V.; Eronen, T.; Gorelov, D.; Hakala, J.; Jokinen, A.; Kankainen, A.; Karvonen, P.; Kolhinen, V. S.; Moore, I. D.; Rahaman, S.; Rinta-Antila, S.; Rissanen, J.; Rubchenya, V.; Saastamoinen, A.; Sonoda, T.; Weber, C.; Äystö, J.

2014-09-01

161

Theory of nuclear fission by stopped pions  

Microsoft Academic Search

Nuclear fission by stopped pions is analyzed in a two-step model in which the pion is absorbed on a nucleon pair, followed by the prompt emission of one nucleon and compound nucleus formation by the other. This simple picture yields agreement with observed prompt neutron spectra and average nucleon multiplicities. The analysis of nuclear fission in a statistical framework is

Nimai C. Mukhopadhyay; Jörg Hadermann; Klaus Junker

1979-01-01

162

Statistical model investigation of nuclear fission  

Microsoft Academic Search

To assist in the improvement of fission product yield data libraries, the statistical theory of fission was investigated. Calculation of the theory employs a recent nuclear mass formula and nuclear density of states expression. Yields computed with a simple statement of the theory do not give satisfactory results. A slowly varying empirical parameter is introduced to improve agreement between measured

Pepping

1979-01-01

163

Induced-Fission Imaging of Nuclear Material  

SciTech Connect

This paper presents initial results from development of the induced-fission imaging technique, which can be used for the purpose of measuring or verifying the distribution of fissionable material in an unopened container. The technique is based on stimulating fissions in nuclear material with 14 MeV neutrons from an associated-particle deuterium-tritium (D-T) generator and counting the subsequent induced fast fission neutrons with an array of fast organic scintillation detectors. For each source neutron incident on the container, the neutron creation time and initial trajectory are known from detection of the associated alpha particle of the d + t {yields} {alpha} + n reaction. Many induced fissions will lie along (or near) the interrogating neutron path, allowing an image of the spatial distribution of prompt induced fissions, and thereby fissionable material, to be constructed. A variety of induced-fission imaging measurements have been performed at Oak Ridge National Laboratory with a portable, low-dose D-T generator, including single-view radiographic measurements and three-dimensional tomographic measurements. Results from these measurements will be presented along with the neutron transmission images that have been performed simultaneously. This new capability may have applications to a number of areas in which there may be a need to confirm the presence or configuration of nuclear materials, such as nuclear material control and accountability, quality assurance, treaty confirmation, or homeland security applications.

Hausladen, Paul [ORNL] [ORNL; Blackston, Matthew A [ORNL] [ORNL; Mullens, James Allen [ORNL] [ORNL; McConchie, Seth M [ORNL] [ORNL; Mihalczo, John T [ORNL] [ORNL; Bingham, Philip R [ORNL] [ORNL; Ericson, Milton Nance [ORNL] [ORNL; Fabris, Lorenzo [ORNL] [ORNL

2010-01-01

164

Get Close to a Nuclear Fission Reaction!  

NSDL National Science Digital Library

This animation-enhanced essay from the FRONTLINE Web site details what happens inside a nuclear reactor core. Learn how engineers and technicians have designed nuclear facilities to control fission activity, regulate the tremendous heat released during fission, contain radiation, and process electricity.

2004-01-29

165

Nuclear Fission and Fission{minus}Product Spectroscopy: Second International Workshop. Proceedings  

SciTech Connect

These proceedings represent papers presented at the Second International Workshop on Nuclear Fission and Fission{minus}Product Spectroscopy held in Seyssins, France in April, 1998. The objective was to bring together the specialists in the field to overview the situation and to assess our present understanding of the fission process. The topics presented at the conference included nuclear waste management, incineration, neutron driven transmutation, leakage etc., radioactive beams, neutron{minus}rich nuclei, neutron{minus}induced and spontaneous fission, ternary fission phenomena, angular momentum, parity and time{minus}reversal phenomena, and nuclear fission at higher excitation energy. Modern spectroscopic tools for gamma spectroscopy as applied to fission were also discussed. There were 53 papers presented at the conference,out of which 3 have been abstracted for the Energy,Science and Technology database.(AIP)

Fioni, G. [Commissariat Energie Atomique, Saclay (France); Faust, H.; Oberstedt, S. [Institut Laue-Langevin, Grenoble (France); Hambsch, F. [Institute for Reference Materials and Measurements, Geel (Belgium)

1998-10-01

166

Theoretical Description of the Fission Process  

SciTech Connect

Advanced theoretical methods and high-performance computers may finally unlock the secrets of nuclear fission, a fundamental nuclear decay that is of great relevance to society. In this work, we studied the phenomenon of spontaneous fission using the symmetry-unrestricted nuclear density functional theory (DFT). Our results show that many observed properties of fissioning nuclei can be explained in terms of pathways in multidimensional collective space corresponding to different geometries of fission products. From the calculated collective potential and collective mass, we estimated spontaneous fission half-lives, and good agreement with experimental data was found. We also predicted a new phenomenon of trimodal spontaneous fission for some transfermium isotopes. Our calculations demonstrate that fission barriers of excited superheavy nuclei vary rapidly with particle number, pointing to the importance of shell effects even at large excitation energies. The results are consistent with recent experiments where superheavy elements were created by bombarding an actinide target with 48-calcium; yet even at high excitation energies, sizable fission barriers remained. Not only does this reveal clues about the conditions for creating new elements, it also provides a wider context for understanding other types of fission. Understanding of the fission process is crucial for many areas of science and technology. Fission governs existence of many transuranium elements, including the predicted long-lived superheavy species. In nuclear astrophysics, fission influences the formation of heavy elements on the final stages of the r-process in a very high neutron density environment. Fission applications are numerous. Improved understanding of the fission process will enable scientists to enhance the safety and reliability of the nation’s nuclear stockpile and nuclear reactors. The deployment of a fleet of safe and efficient advanced reactors, which will also minimize radiotoxic waste and be proliferation-resistant, is a goal for the advanced nuclear fuel cycles program. While in the past the design, construction, and operation of reactors were supported through empirical trials, this new phase in nuclear energy production is expected to heavily rely on advanced modeling and simulation capabilities.

Witold Nazarewicz

2009-10-25

167

Fission Surface Power Technology Development Status  

NASA Technical Reports Server (NTRS)

Power is a critical consideration in planning exploration of the surfaces of the Moon, Mars, and beyond. Nuclear power is an important option, especially for locations in the solar system where sunlight is limited in availability or intensity. NASA is maintaining the option for fission surface power for the Moon and Mars by developing and demonstrating technology for an affordable fission surface power system. Because affordability drove the determination of the system concept that this technology will make possible, low development and recurring costs result, while required safety standards are maintained. However, an affordable approach to fission surface power also provides the benefits of simplicity, robustness, and conservatism in design. This paper will illuminate the multiplicity of benefits to an affordable approach to fission surface power, and will describe how the foundation for these benefits is being developed and demonstrated in the Exploration Technology Development Program s Fission Surface Power Project.

Palac, Donald T.; Mason, Lee S.; Houts, Michael G.; Harlow, Scott

2010-01-01

168

Fission dynamics at low excitation energy  

NASA Astrophysics Data System (ADS)

The mass asymmetry in the fission of 236U at low excitation energy is clarified by the analysis of the trajectories obtained by solving the Langevin equations for the shape degrees of freedom. It is demonstrated that the position of the peaks in the mass distribution of fission fragments is determined mainly by the saddle point configuration originating from the shell correction energy. The width of the peaks, on the other hand, results from the shape fluctuations close to the scission point caused by the random force in the Langevin equation. We have found out that the fluctuations between elongated and compact shapes are essential for the fission process. According to our results the fission does not occur with continuous stretching in the prolate direction, similarly to that observed in starch syrup, but is accompanied by the fluctuations between elongated and compact shapes. This picture presents a new viewpoint of fission dynamics and the splitting mechanism.

Aritomo, Y.; Chiba, S.; Ivanyuk, F.

2014-11-01

169

Superfluid dynamics of 258Fm fission  

E-print Network

Theoretical description of nuclear fission remains one of the major challenges of quantum many-body dynamics. The slow, mostly adiabatic motion through the fission barrier is followed by a fast, non-adiabatic descent of the potential between the fragments. The latter stage is essentially unexplored. However, it is crucial as it generates most of the excitation energy in the fragments. The superfluid dynamics in the latter stage of fission is obtained with the time-dependent Hartree-Fock theory including BCS dynamical pairing correlations. The fission modes of the 258Fm nucleus are studied. The resulting fission fragment characteristics show a good agreement with experimental data. Quantum shell effects are shown to play a crucial role in the dynamics and formation of the fragments. The importance of quantum fluctuations beyond the independent particle/quasi-particle picture is underlined and qualitatively studied.

Scamps, Guillaume; Lacroix, Denis

2015-01-01

170

Fission dynamics at low excitation energy. 2  

E-print Network

The mass asymmetry in the fission of U-236 at low excitation energy is clarified by the analysis of the trajectories obtained by solving the Langevin equations for the shape degrees of freedom. It is demonstrated that the position of the peaks in the mass distribution of fission fragments is determined mainly by the saddle point configuration originating from the shell correction energy. The width of the peaks, on the other hand, results from the shape fluctuations close to the scission point caused by the random force in the Langevin equation. We have found out that the fluctuations between elongated and compact shapes are essential for the fission process. According to our results the fission does not occur with continuous stretching in the prolate direction, similarly to that observed in starch syrup, but is accompanied by the fluctuations between elongated and compact shapes. This picture presents a new viewpoint of fission dynamics and the splitting mechanism.

Y. Aritomo; S. Chiba; F. A. Ivanyuk

2014-11-01

171

Superfluid dynamics of 258Fm fission  

E-print Network

Theoretical description of nuclear fission remains one of the major challenges of quantum many-body dynamics. The slow, mostly adiabatic motion through the fission barrier is followed by a fast, non-adiabatic descent of the potential between the fragments. The latter stage is essentially unexplored. However, it is crucial as it generates most of the excitation energy in the fragments. The superfluid dynamics in the latter stage of fission is obtained with the time-dependent Hartree-Fock theory including BCS dynamical pairing correlations. The fission modes of the 258Fm nucleus are studied. The resulting fission fragment characteristics show a good agreement with experimental data. Quantum shell effects are shown to play a crucial role in the dynamics and formation of the fragments. The importance of quantum fluctuations beyond the independent particle/quasi-particle picture is underlined and qualitatively studied.

Guillaume Scamps; Cédric Simenel; Denis Lacroix

2015-01-15

172

Systematics of Fission-Product Yields  

SciTech Connect

Empirical equations representing systematics of fission-product yields have been derived from experimental data. The systematics give some insight into nuclear-structure effects on yields, and the equations allow estimation of yields from fission of any nuclide with atomic number Z{sub F} = 90 thru 98, mass number A{sub F} = 230 thru 252, and precursor excitation energy (projectile kinetic plus binding energies) PE = 0 thru {approx}200 MeV--the ranges of these quantities for the fissioning nuclei investigated. Calculations can be made with the computer program CYFP. Estimates of uncertainties in the yield estimates are given by equations, also in CYFP, and range from {approx} 15% for the highest yield values to several orders of magnitude for very small yield values. A summation method is used to calculate weighted average parameter values for fast-neutron ({approx} fission spectrum) induced fission reactions.

A.C. Wahl

2002-05-01

173

The isotope hydrology of Quaternary climate change.  

PubMed

Understanding the links between climate change and human migration and culture is an important theme in Quaternary archaeology. While oxygen and hydrogen stable isotopes in high-latitude ice cores provide the ultimate detailed record of palaeoclimate extending back to the Middle Pleistocene, groundwater can act as a climate archive for areas at lower latitudes, permitting a degree of calibration for proxy records such as lake sediments, bones, and organic matter. Not only can oxygen and hydrogen stable isotopes be measured on waters, but the temperature of recharge can be calculated from the amount of the atmospheric noble gases neon, argon, krypton, and xenon in solution, while residence time can be estimated from the decay of the radioisotopes carbon-14, chlorine-36, and krypton-81 over timescales comparable to the ice core record. The Pleistocene-Holocene transition is well characterised in aquifers worldwide, and it is apparent that isotope-temperature relationships of the present day are not necessarily transferable to past climatic regimes, with important implications for the interpretation of proxy isotope data. Groundwaters dating back to one million years, i.e., to beyond the Middle Pleistocene, are only found in major aquifer basins and information is relatively sparse and of low resolution. Speleothem fluid inclusions offer a way of considerably increasing this resolution, but both speleothem formation and large-scale groundwater recharge requires humid conditions, which may be relatively infrequent for areas currently experiencing arid climates. Both types of record therefore require caution in their interpretation when considering a particular archaeological context. PMID:21051074

Darling, W G

2011-04-01

174

Fission-energy release for 16 fissioning nuclides. Final report  

SciTech Connect

Results are presented of a least-squares evaluation of the components of energy release per fission in /sup 232/Th, /sup 233/U, /sup 235/U, /sup 238/U, /sup 239/Pu, and /sup 241/Pu. For completeness, older (1978) results based on systematics are presented for these and ten other isotopes of interest. There have been recent indications that the delayed energy components may be somewhat higher than those used previously, but the LSQ results do not seem to change significantly when modest (approx. 1 MeV) increases in the total delayed energy are included in the inputs. Additional measurements of most of the energy components are still needed to resolve remaining discrepancies.

Sher, R.

1981-03-01

175

Quaternary naltrexone reverses radiogenic and morphine-induced locomotor hyperactivity  

SciTech Connect

The present study attempted to determine the relative role of the peripheral and central nervous system in the production of morphine-induced or radiation-induced locomotor hyperactivity of the mouse. Toward this end, we used a quaternary derivative of an opiate antagonist (naltrexone methobromide), which presumably does not cross the blood-brain barrier. Quaternary naltrexone was used to challenge the stereotypic locomotor response observed in these mice after either an i.p. injection of morphine or exposure to 1500 rads /sup 60/Co. The quaternary derivative of naltrexone reversed the locomotor hyperactivity normally observed in the C57BL/6J mouse after an injection of morphine. It also significantly attenuated radiation-induced locomotion. The data reported here support the hypothesis of endorphin involvement in radiation-induced and radiogenic behaviors. However, these conclusions are contingent upon further research which more fully evaluates naltrexone methobromide's capacity to cross the blood-brain barrier.

Mickley, G.A.; Stevens, K.E.; Galbraith, J.A.; White, G.A.; Gibbs, G.L.

1984-04-01

176

Tertiary and Quaternary Research with Remote Sensing Methods  

NASA Technical Reports Server (NTRS)

Problems encountered in mapping the Quaternary section of the Wind River Region using remote sensing methods are discussed. Analysis of the stratigraphic section is a fundamental aspect of the geologic study of sedimentary basins. Stratigraphic analysis of post-Cretaceous rocks in the Wind River Basin encounters problems of a distinctly different character from those involved in studying the pre-Cretaceous section. The interior of the basin is predominantly covered by Tertiary and Quaternary sediments. These rocks, except on the basin margin to the north, are mostly flat lying or gently dipping. The Tertiary section consists of sandstones, siltstones, and tuffaceous sediments, some variegated, but in general poorly bedded and of great lithologic similarity. The Quaternary sediments consist of terrace, fan, and debris tongue deposits, unconsolidated alluvium occupying the bottoms of modern watercourses, deposits of eolian origin and tufa. Terrace and fan deposits are compositionally diverse and reflect the lithologic diversity of the source terranes.

Conel, J. E.

1985-01-01

177

Tertiary and quaternary research with remote sensing methods  

NASA Astrophysics Data System (ADS)

Problems encountered in mapping the Quaternary section of the Wind River Region using remote sensing methods are discussed. Analysis of the stratigraphic section is a fundamental aspect of the geologic study of sedimentary basins. Stratigraphic analysis of post-Cretaceous rocks in the Wind River Basin encounters problems of a distinctly different character from those involved in studying the pre-Cretaceous section. The interior of the basin is predominantly covered by Tertiary and Quaternary sediments. These rocks, except on the basin margin to the north, are mostly flat lying or gently dipping. The Tertiary section consists of sandstones, siltstones, and tuffaceous sediments, some variegated, but in general poorly bedded and of great lithologic similarity. The Quaternary sediments consist of terrace, fan, and debris tongue deposits, unconsolidated alluvium occupying the bottoms of modern watercourses, deposits of eolian origin and tufa. Terrace and fan deposits are compositionally diverse and reflect the lithologic diversity of the source terranes.

Conel, J. E.

1985-08-01

178

The tempo of avian diversification during the Quaternary.  

PubMed Central

It is generally assumed that the Quaternary was a period of heightened diversification in temperate vertebrate organisms. Previous molecular systematics studies have challenged this assertion. We re-examined this issue in north temperate birds using log-lineage plots and distributions of sister-taxon distances. Log-lineage plots support earlier conclusions that avian diversification slowed during the Quaternary. To test plots of empirical sister-taxon distances we simulated three sets of phylogenies: constant speciation and extinction, a pulse of recent speciation, and a pulse of recent extinction. Previous opinions favour the model of recent speciation although our empirical dataset on 74 avian comparisons failed to reject a distribution derived from the constant and extinction models. Hence, it does not appear that the Quaternary was a period of exceptional rates of diversification, relative to the background rate. PMID:15101578

Zink, Robert M; Klicka, John; Barber, Brian R

2004-01-01

179

40 CFR 721.8658 - Modified polymer of vinyl acetate and quaternary ammonium compound (generic).  

Code of Federal Regulations, 2013 CFR

...2013-07-01 2013-07-01 false Modified polymer of vinyl acetate and quaternary ammonium...Chemical Substances § 721.8658 Modified polymer of vinyl acetate and quaternary ammonium...substance identified generically as modified polymer of vinyl acetate and quaternary...

2013-07-01

180

40 CFR 721.8658 - Modified polymer of vinyl acetate and quaternary ammonium compound (generic).  

Code of Federal Regulations, 2010 CFR

...2010-07-01 2010-07-01 false Modified polymer of vinyl acetate and quaternary ammonium...Chemical Substances § 721.8658 Modified polymer of vinyl acetate and quaternary ammonium...substance identified generically as modified polymer of vinyl acetate and quaternary...

2010-07-01

181

Quaternary tectonics of the southeastern coastal area, Korea: subsidence of marine terrace and late Quaternary faults  

NASA Astrophysics Data System (ADS)

Strong earthquake has rarely occurred in Korean peninsula and a few events were recorded since 27 A.D. Historical and recent earthquakes are concentrated in the southeastern area of Korean peninsula, where more than 30 Quaternary fault exposures have recently been founded. The southern tip of the southeastern coastal area has been known as a stable block: quaternary fault and micro-earthquakes haven’t occurred. To clarify whether the active tectonic movement is or not, digital marine terrace mapping and fracture mapping have been done for the southeastern coastal area. The area is composed of the Late Cretaceous volcanic rocks, sedimentary rocks and the Early Tertiary granite. Wave-cut platform in the area is comparatively smaller and narrower than that of other southeastern parts. Most of platforms have no Quaternary sediments and or very thin sediments. Platforms except the Holocene are generally divided into three steps. The lowest platform has a height of 8-11m. The middle one is broad with a height of 17 to 22m. The highest is narrowly scattered with a height of 33-41m. The lowest platform is correlated to the 2nd terrace of the northern area, which has been attributed to the isotopic substage, 5a. The uplift rate based on the altimetrical and indirect chronological data ranges from 0.072-0.108 m/ky. Such a low uplift rate indicates that the area is very stable because of belonging to intra-plate or continental block. The elevation of platform is getting lower from the north to the south. Reducing altitude of platform towards the south might be interpreted to a local block tilting within Yangsan Fault Belt during the Latest Pleistocene or an active tectonic subsidence to the south throughout the whole Korean peninsula. Several Quaternary faults supporting the active tectonic movement have been found from marine terrace feature mapping. Two sites have been proved the presence of fault by geophysical survey and cut-slope. Flight of marine terrace at two fault sites inclines slowly to the inland side and shows topographically vertical offset with small amount. Local block tilting and subsiding platforms from the north to the south are both due to the active tectonic fault movement of the Latest Pleistocene. Accompanied reverse Pleistocene faults dip to the east and show the top-up-to-the-west reverse movement sense. GPS measurement revealed the west of northwestern vector. Differential tectonic stress regime to the west has occurred to Korean peninsula during the Latest Pleistocene. Stronger tectonic force from the Pacific Ocean Plate gave an effect of high platform to the northern area. Weaker dynamic force due to the Philippine Plate caused low elevation to the southern area.

Choi, S.-J.; Ota, Y.; Chwae, U.

2003-04-01

182

Prompt mass distributions in fission  

NASA Astrophysics Data System (ADS)

A previously developed structure-sensitive statistical model, incorporating the nuclear structure and deformation effects, has been utilised to study the prompt mass distributions in fision and other related characteristics. The principle of detailed balance has been applied to calculate the yield probabilities. The fusion barriers and the penetrabilities of the fragments were estimated from a nuclear plus Coulomb interaction potential. The prompt fragment mass yields were then obtained as a product of three quantities: the product level densities of the conjugates at their most probable excitation energies, the barrier penetrabilities and the isobaric charge yields. The calculations are free from any arbitrary parameters. Comparison with experimental data for226Ra( p, f) at E p =11.1MeV,232Th( n, f) at E n =1.0 MeV,235U( n, f) and239Pu( n, f) at thermal neutron energies and for the spontaneous fission of252Cf shows fairly good agreement.

Majumdar, Harashit; Chatterjee, A.

1982-03-01

183

Recent advances in singlet fission.  

PubMed

A survey is provided of recent progress in the understanding of singlet fission, a spin-allowed process in which a singlet excited molecule shares its energy with a ground-state neighbor to produce two triplet excited molecules. It has been observed to occur in single-crystal, polycrystalline, and amorphous solids, on timescales from 80 fs to 25 ps, producing triplet yields as high as 200%. Photovoltaic devices using the effect have shown external quantum efficiencies in excess of 100%. Almost all the efficient materials are alternant hydrocarbons of the acene series or their simple derivatives, and it is argued that a wider structural variety would be desirable. The current state of the development of molecular structure design rules, based on first-principles theoretical considerations, is described along with initial examples of implementation. PMID:23298243

Smith, Millicent B; Michl, Josef

2013-01-01

184

Recent Advances in Singlet Fission  

NASA Astrophysics Data System (ADS)

A survey is provided of recent progress in the understanding of singlet fission, a spin-allowed process in which a singlet excited molecule shares its energy with a ground-state neighbor to produce two triplet excited molecules. It has been observed to occur in single-crystal, polycrystalline, and amorphous solids, on timescales from 80 fs to 25 ps, producing triplet yields as high as 200%. Photovoltaic devices using the effect have shown external quantum efficiencies in excess of 100%. Almost all the efficient materials are alternant hydrocarbons of the acene series or their simple derivatives, and it is argued that a wider structural variety would be desirable. The current state of the development of molecular structure design rules, based on first-principles theoretical considerations, is described along with initial examples of implementation.

Smith, Millicent B.; Michl, Josef

2013-04-01

185

Summary: Our 50-year odyssey with fission  

NASA Astrophysics Data System (ADS)

On the occasion of this International Conference on Fifty Years Research in Nuclear Fission, we summarize our present understanding of the fission process and the challenges that lie ahead. The basic properties of fission arise from a delicate competition between disruptive Coulomb forces, cohesive nuclear forces and fluctuating shell and pairing forces. These static forces are primarily responsible for such experimental phenomena as deformed ground-state nuclear shapes, fission into fragments of unequal size, sawtooth neutron yields, spontaneously fissioning isomers, broad resonances and narrow intermediate structure in fission cross sections and cluster radioactivity. However, inertial and dissipative forces also play decisive roles in the dynamical evolution of a fissioning nucleus. The energy dissipated between the saddle and scission points is small for low initial excitation energy at the saddle point and increases with increasing excitation energy. At moderate excitation energies, the dissipation of collective energy into internal single-particle excitation energy proceeds largely through the interaction of nucleons with the mean field and with each other in the vicinity of the nuclear surface, as well as through the transfer of nucleons between the two portions of the evolving dumbbell-like system. These unique dissipation mechanisms arise from the Pauli exclusion principle for fermions and the details of the nucleon-nucleon interaction, which make the mean free path of a nucleon near the Fermi surface at low excitation energy longer than the nuclear radius. With its inverse process of heavy-ion fusion reactions, fission continues to yield surprises in the study of large-amplitude collective nuclear motion. Future challenges include devising experiments to unambiguously distinguish dissipative effects from analogous effects caused by collective degrees of freedom and computing fission directly from the underlying hadronic interaction.

Nix, J. Rayford

1989-10-01

186

Recovery and use of fission product noble metals  

SciTech Connect

Noble metals in fission products are of strategic value. Market prices for noble metals are rising more rapidly than recovery costs. A promising concept has been developed for recovery of noble metals from fission product waste. Although the assessment was made only for the three noble metal fission products (Rh, Pd, Ru), there are other fission products and actinides which have potential value. (DLC)

Jensen, G.A.; Rohmann, C.A.; Perrigo, L.D.

1980-06-01

187

Statistical Estimation of Distributions of Physical Quantities in Nuclear Fission  

Microsoft Academic Search

Making use of a model based on the statistical theory, calculations were performed to obtain the mass yields, the most probable charges, the kinetic energies and the prompt neutron yields of fission fragments, and the mass yields of fission products from thermal-neutron-induced fission of U, U, Pu, Pu and from the spontaneous fission of Cf. The calculations are further extended

Toru YAMAMOTO; Kazusuke SUGIYAMA

1974-01-01

188

Future challenges for nuclear data research in fission (u)  

SciTech Connect

I describe some high priority research areas in nuclear fission, where applications in nuclear reactor technologies and in modeling criticality in general are demanding higher accuracies in our databases. We focus on fission cross sections, fission neutron spectra, and fission product data.

Chadwick, Mark B [Los Alamos National Laboratory

2010-01-01

189

Fission Track Analysis and Its Applications to Geological Problems  

Microsoft Academic Search

Fission track analysis as a geological dating tool was first proposed in the early 1960s. The past 10 years has seen a major expansion in application to more general geological problems. This reflects advances in understanding the temperature dependence of fission track annealing and of the information contained in fission track length distributions. Fission track analysis provides detailed information on

Kerry Gallagher; Roderick Brown; Christopher Johnson

1998-01-01

190

Fission induced by nucleons at intermediate energies  

NASA Astrophysics Data System (ADS)

Monte Carlo calculations of fission of actinides and pre-actinides induced by protons and neutrons in the energy range from 100 MeV to 1 GeV are carried out by means of a recent version of the Liège Intranuclear Cascade Model, INCL++, coupled with two different evaporation-fission codes, GEMINI++ and ABLA07. In order to reproduce experimental fission cross sections, model parameters are usually adjusted on available (p , f) cross sections and used to predict (n , f) cross sections for the same isotopes.

Lo Meo, S.; Mancusi, D.; Massimi, C.; Vannini, G.; Ventura, A.

2015-01-01

191

Fission induced by nucleons at intermediate energies  

E-print Network

Monte Carlo calculations of fission of actinides and pre-actinides induced by protons and neutrons in the energy range from 100 MeV to 1 GeV are carried out by means of a recent version of the Li\\`ege Intranuclear Cascade Model, INCL++, coupled with two different evaporation-fission codes, GEMINI++ and ABLA07. In order to reproduce experimental fission cross sections, model parameters are usually adjusted on available (p,f) cross sections and used to predict (n,f) cross sections for the same isotopes.

Sergio Lo Meo; Davide Mancusi; Cristian Massimi; Gianni Vannini; Alberto Ventura

2014-09-17

192

Ternary Fission Induced by Polarized Neutrons  

SciTech Connect

P-odd and T-odd asymmetries in the emission of fragments and light particles have been investigated in ternary fission induced by polarized neutrons. P-odd asymmetries unambiguously point to a violation of parity in the fission process. By contrast, T-odd asymmetries do not necessarily imply a violation of time reversal invariance. The asymmetries observed are rather due to a final state interaction between the light ternary particle and the nucleus from which they are ejected. New results with interesting information on the ternary fission process are presented.

Goennenwein, F.; Jesinger, P. [Physikalisches Institut, Universitaet Tuebingen, 72076 Tuebingen (Germany); Gagarski, A.; Petrov, G.; Bunakov, V. [Petersburg Nuclear Physics Institute, 188300 Gatchina (Russian Federation); Mutterer, M. [Institut fuer Kernphysik, Technische Universitaet, 64289 Darmstadt (Germany); Trzaska, W. [Department of Physics, Jyvaeskylae University, 40351 Jyvaeskylae (Finland); Nesvizhevsky, V.; Lelievre-Berna, E. [Institut Laue Langevin, 38042 Grenoble (France)

2005-05-24

193

Fission Matrix Capability for MCNP Monte Carlo  

SciTech Connect

In a Monte Carlo criticality calculation, before the tallying of quantities can begin, a converged fission source (the fundamental eigenvector of the fission kernel) is required. Tallies of interest may include powers, absorption rates, leakage rates, or the multiplication factor (the fundamental eigenvalue of the fission kernel, k{sub eff}). Just as in the power iteration method of linear algebra, if the dominance ratio (the ratio of the first and zeroth eigenvalues) is high, many iterations of neutron history simulations are required to isolate the fundamental mode of the problem. Optically large systems have large dominance ratios, and systems containing poor neutron communication between regions are also slow to converge. The fission matrix method, implemented into MCNP[1], addresses these problems. When Monte Carlo random walk from a source is executed, the fission kernel is stochastically applied to the source. Random numbers are used for: distances to collision, reaction types, scattering physics, fission reactions, etc. This method is used because the fission kernel is a complex, 7-dimensional operator that is not explicitly known. Deterministic methods use approximations/discretization in energy, space, and direction to the kernel. Consequently, they are faster. Monte Carlo directly simulates the physics, which necessitates the use of random sampling. Because of this statistical noise, common convergence acceleration methods used in deterministic methods do not work. In the fission matrix method, we are using the random walk information not only to build the next-iteration fission source, but also a spatially-averaged fission kernel. Just like in deterministic methods, this involves approximation and discretization. The approximation is the tallying of the spatially-discretized fission kernel with an incorrect fission source. We address this by making the spatial mesh fine enough that this error is negligible. As a consequence of discretization we get a spatially low-order kernel, the fundamental eigenvector of which should converge faster than that of continuous kernel. We can then redistribute the fission bank to match the fundamental fission matrix eigenvector, effectively eliminating all higher modes. For all computations here biasing is not used, with the intention of comparing the unaltered, conventional Monte Carlo process with the fission matrix results. The source convergence of standard Monte Carlo criticality calculations are, to some extent, always subject to the characteristics of the problem. This method seeks to partially eliminate this problem-dependence by directly calculating the spatial coupling. The primary cost of this, which has prevented widespread use since its inception [2,3,4], is the extra storage required. To account for the coupling of all N spatial regions to every other region requires storing N{sup 2} values. For realistic problems, where a fine resolution is required for the suppression of discretization error, the storage becomes inordinate. Two factors lead to a renewed interest here: the larger memory available on modern computers and the development of a better storage scheme based on physical intuition. When the distance between source and fission events is short compared with the size of the entire system, saving memory by accounting for only local coupling introduces little extra error. We can gain other information from directly tallying the fission kernel: higher eigenmodes and eigenvalues. Conventional Monte Carlo cannot calculate this data - here we have a way to get new information for multiplying systems. In Ref. [5], higher mode eigenfunctions are analyzed for a three-region 1-dimensional problem and 2-dimensional homogenous problem. We analyze higher modes for more realistic problems. There is also the question of practical use of this information; here we examine a way of using eigenmode information to address the negative confidence interval bias due to inter-cycle correlation. We apply this method mainly to four problems: 2D pressurized water reactor (PWR) [6],

Carney, Sean E. [Los Alamos National Laboratory; Brown, Forrest B. [Los Alamos National Laboratory; Kiedrowski, Brian C. [Los Alamos National Laboratory; Martin, William R. [Los Alamos National Laboratory

2012-09-05

194

Fission yields at different fission-product kinetic energies for thermal-neutron-induced fission of 239Pu  

Microsoft Academic Search

At the recoil spectrometer ``Lohengrin'' of the Institut Laue-Langevin in Grenoble, the yields of the light fission products from the thermal-neutron-induced fission of 239Pu were measured as a function of A, Z, the kinetic energy E and the ionic charge states q. The nuclear charge and mass distributions summed over all ionic charge states were determined for different light fissionproduct

C. Schmitt; A. Guessous; J. P. Bocquet; H.-G. Clerc; R. Brissot; D. Engelhardt; H. R. Faust; F. Gönnenwein; M. Mutterer; H. Nifenecker; J. Pannicke; Ch. Ristori; J. P. Theobald

1984-01-01

195

Fission-product formation in the thermal-neutron-induced fission of odd Cm isotopes  

Microsoft Academic Search

Thermal-neutron-induced fission of 243Cm was studied at the Lohengrin mass separator. The light-mass peak of the fission-yield curve was investigated, and yields of masses from A=72 to A=120 were obtained. Independent-product yields were determined for nuclear charges Z=28 37 . The yield of masses in the superasymmetric region was found to be identical to other fission reactions studied at Lohengrin.

I. Tsekhanovich; N. Varapai; V. Rubchenya; D. Rochman; G. S. Simpson; V. Sokolov; G. Fioni; Ilham Al Mahamid

2004-01-01

196

QUELQUES RSULTATS SUR LA FISSION ET LA FRAGMENTATION C 1 -127 QUELQUES RSULTATS SUR LA FISSION ET LA FRAGMENTATION  

E-print Network

QUELQUES R�SULTATS SUR LA FISSION ET LA FRAGMENTATION C 1 - 127 QUELQUES R�SULTATS SUR LA FISSION Nucléaires, Strasbourg Résumé. -On donne quelques résultats sur la fragmentation, la fission double et triple report some results on fragmentation, binary and ternary fission reactions, induced by 3, 18and 24 Ge

Paris-Sud XI, Université de

197

LATE QUATERNARY EVOLUTION OF THE NORTHEAST FAN, OFFSHORE NOVA SCOTIA  

E-print Network

LATE QUATERNARY EVOLUTION OF THE NORTHEAST FAN, OFFSHORE NOVA SCOTIA Matthew Robichaud Submitted of Earth Sciences Dalhousie University, Halifax, Nova Scotia March 2006 #12;jt Dalhousie University Department of Earth Sciences Halifax, Nova Scotia Canada B3H 3|5 (902) 494-2358 FAX 1902) 494-f>8«9 DATE

Beaumont, Christopher

198

Application of quaternary phase diagrams to compound semiconductor processing  

SciTech Connect

Isobaric, isothermal phase diagrams are a molar representation of condensed phases in equilibrium with each other at a fixed temperature, pressure, and composition. Since three or four elements are usually involved at a fabricated interface in a semiconductor device, knowledge of the appropriate ternary or quaternary phase diagram is important for optimizing the processing parameters and designing long term stability of devices. While the use of phase diagrams is well-established in the fields of metallurgy, ceramics and mineralogy, only recently have phase diagrams been employed to provide a framework for understanding thin film reactions on a substrate, encountered in semiconductor processing. Even though there are many examples of applications of ternary phase diagrams in the semiconductor literature (for instance, metallization of GaAs, the use of refractory metal silicides for metallization layers in VLSI devices and oxidation of III-V compounds), the same is not true for quaternary phase diagrams. To date, the only application is oxidation of mercury cadmium telluride. This lack of examples is not warranted, as four elements are often involved at a critical interface in compound semiconductor processing and devices. This paper reports on the progress made to remedy this situation by considering the application of quaternary phase diagrams to understanding and predicting the behavior of II-VI thin film interfaces in photovoltaic devices under annealing conditions. Moreover, for the first time, solid solubility is taken into account for quaternary phase diagrams of semiconductor systems.

Sinclair, R.

1994-10-01

199

Future climate change and the British Quaternary research community  

Microsoft Academic Search

The uncertainty surrounding estimates of future global warming, even given a single scenario for increasing greenhouse gas emissions, is unacceptably large and has not declined substantially over the last three decades. The Quaternary science community is uniquely placed to constrain the array of possible futures by providing reconstructions of past climate that can be used, together with instrumental data, to

Danny McCarroll

2010-01-01

200

Quaternary research in Poland: selected achievements and prospects  

Microsoft Academic Search

A b s t r a c t . During the last thirty years there were several turnouts in Quaternary studies that increasingly accelerated our under- standing of natural processes and opened new research fields. Among others, they included complex reconstruction of palaeoclimatic phenomena, studies of deep-sea and long-term continental record, and extensive application of reliable dating methods. In Poland

Leszek Marks

201

Application of Analytic Geometry to Ternary and Quaternary Diagrams.  

ERIC Educational Resources Information Center

Advantages of representing ternary and quaternary composition diagrams by means of rectangular coordinates were pointed out in a previous paper (EJ 288 693). A further advantage of that approach is that analytic geometry, based on rectangular coordinates, is directly applicable as demonstrated by the examples presented. (JN)

MacCarthy, Patrick

1986-01-01

202

8 | Quaternary AUSTRALASIA 26 (2) The PAGES 3rd  

E-print Network

8 | Quaternary AUSTRALASIA 26 (2) The PAGES 3rd Open Science Meeting (OSM) and 1st Young Scientists key topics such as public awareness of palaeoclimate research, the involvement of young scientists in the palaeoclimate community, and access to published data. Each group reported back the following day, giving

Phipps, Steven J.

203

Quaternary Paleoecology and Climate Change, Bladen County, NC  

NSDL National Science Digital Library

Students analyze a Quaternary pollen diagram from lakes in Bladen County, NC. This diagram contains (from the top down) the current deglaciation, the last glacial, and the previous interglacial. Students These lakes occur in Carolina Bays and students also evaluate a proposal that meteorite impact created the Bays.

Martin Farley

204

The Croonian Lecture: Radiocarbon Dating and Quaternary History in Britain  

Microsoft Academic Search

The lecture is an attempt to show the way in which research upon the Quaternary Period in Britain is being affected by the application to it of radiocarbon dating. Mild interstadial periods during the last glaciation can be distinguished, set in sequence and related to similar European interstadials. It is shown that a brief climatic oscillation occurs widely in the

H. Godwin

1961-01-01

205

Quaternary history and contemporary patterns in a currently expanding species  

Microsoft Academic Search

BACKGROUND: Quaternary climatic oscillations had dramatic effects on species evolution. In northern latitudes, populations had to survive the coldest periods in refugial areas and recurrently colonized northern regions during interglacials. Such a history usually results in a loss of genetic diversity. Populations that did not experience glaciations, in contrast, probably maintained most of their ancestral genetic diversity. These characteristics dramatically

Carole Kerdelhué; Lorenzo Zane; Mauro Simonato; Paola Salvato; Jérôme Rousselet; Alain Roques; Andrea Battisti

2009-01-01

206

Range Shifts and Adaptive Responses to Quaternary Climate Change  

Microsoft Academic Search

Tree taxa shifted latitude or elevation range in response to changes in Quaternary climate. Because many modern trees display adaptive differentiation in relation to latitude or elevation, it is likely that ancient trees were also so differentiated, with environmental sensitivities of populations throughout the range evolving in conjunction with migrations. Rapid climate changes challenge this process by imposing stronger selection

Margaret B. Davis; Ruth G. Shaw

2001-01-01

207

Late Quaternary vegetational and climatic changes in Brazil  

Microsoft Academic Search

Brazil comprises about 50% of the South American continent including prominent ecosystems like the Amazon and the Atlantic rain forests, semideciduous forests, cerrado, Araucaria forests and campos (grasslands). Detailed palynological studies on new sediment cores located on a transect from southern to northern Brazil allow a regional reconstruction of late Quaternary vegetation and climate history. This paper presents an overview

Hermann Behling

1998-01-01

208

Quaternary Glacial Mapping in Western Wisconsin Using Soil Survey Information  

ERIC Educational Resources Information Center

The majority of soils in the western Wisconsin have developed from glacial sediments deposited during the Quaternary Period (2.6 million years before present). In many regions, multiple advances and retreats have left a complex landscape of diverse glacial sediments and landforms. The soils that have developed on these deposits reflect the nature…

Oehlke, Betsy M.; Dolliver, Holly A. S.

2011-01-01

209

Prompt Fission Gamma-ray Spectra and Multiplicities for Various Fissioning Systems  

NASA Astrophysics Data System (ADS)

The prompt fission gamma spectra (PFGS) and multiplicities (PFGM) are investigated from a Monte Carlo simulation of the fission fragment deexcitation. The fission fragment characteristics are sampled from mass, charge, kinetic energy, spin and parity distributions from experimental data or theoretical models. Initial excitation energy is shared between the two complementary fragments using a mass dependent temperature ratio law and a level density parameter law based on Ignatyuk's prescription. Details can be found elsewhere in the literature. The deexcitation process can be performed with different calculation schemes. The first one is based on a Weisskopf model for neutron evaporation and nuclear transition sampling (from level density and strength function models) for gamma evaporation. In this case, the competition between neutrons and gammas is taken into account by using a spin dependent excitation energy limit under which gamma emission takes place. The second one is based on an Hauser-Feshbach model for neutron/gamma evaporation based on neutron transmission coefficients (from optical model calculations) and the same model as above for gammas. The n/? competition is then automatically taken into account at the very beginning of the primary fission fragments evaporation process. Fission observables, especially related to prompt fission gammas are presented and discussed for spontaneous fission (252Cf, 240Pu), thermal fission (235U+nth) and fast fission (238U+n1.8MeV). Comparisons with experimental data are shown when available.

Litaize, Olivier; Regnier, David; Serot, Olivier

210

Microscopic description of complex nuclear decay: Multimodal fission  

NASA Astrophysics Data System (ADS)

Our understanding of nuclear fission, a fundamental nuclear decay, is still incomplete due to the complexity of the process. In this paper, we describe a study of spontaneous fission using the symmetry-unrestricted nuclear density functional theory. Our results show that the observed bimodal fission can be explained in terms of pathways in multidimensional collective space corresponding to different geometries of fission products. We also predict a new phenomenon of trimodal spontaneous fission for some rutherfordium, seaborgium, and hassium isotopes.

Staszczak, A.; Baran, A.; Dobaczewski, J.; Nazarewicz, W.

2009-07-01

211

Evolution of isotopic fission-fragment yields with excitation energy  

NASA Astrophysics Data System (ADS)

Two fission experiments have been performed at GANIL using 238U beams at different energies and light targets. Different fissioning systems were produced with excitation energies from 10 to 230 MeV and their decay by fission was investigated with GANIL spectrometers. Preliminary fission-fragment isotopic distributions have been obtained. The evolution with impinging energy of their properties, the neutron excess and the width of the neutron-number distributions, gives important insights into the dynamics of fusion-fission mechanism.

Delaune, O.; Caamaño, M.; Derkx, X.; Farget, F.; Schmidt, K.-H.; Tarasov, O. B.; Audouin, L.; Amthor, A. M.; Bacri, C.-O.; Barreau, G.; Bastin, B.; Bazin, D.; Benlliure, J.; Blank, B.; Cacères, L.; Casarejos, E.; Fernández-Domínguez, B.; Gaudefroy, L.; Golabek, C.; Grévy, S.; Jurado, B.; Kamalou, O.; Lemasson, A.; Lukyanov, S. M.; Mittig, W.; Morrissey, D. J.; Navin, A.; Pereira, J.; Perrot, L.; Rejmund, M.; Roger, T.; Saint-Laurent, M. G.; Savajols, H.; Schmitt, C.; Sherrill, B. M.; Stodel, C.; Taieb, J.; Thomas, J. C.; Villari, A. C. C.

2012-07-01

212

Nuclear fissions in r and r -cooling processes  

Microsoft Academic Search

The effect of nuclear fissions occurring during ther-cooling stage is investigated. The initial conditions for ther-cooling process are derived from the final conditions of the dynamicalr-process. Neutron-excess nuclides in the region ofZ?80 are all assumed to have finite probabilities for spontaneous fission, neutron-induced fission and ß-decay-induced fission. For the evaluation of the rates for delayed neutron emission, ß-decay-induced fission and

Teruaki Ohnishi

1978-01-01

213

Microscopic description of complex nuclear decay: multimodal fission  

E-print Network

Our understanding of nuclear fission, a fundamental nuclear decay, is still incomplete due to the complexity of the process. In this paper, we describe a study of spontaneous fission using the symmetry-unrestricted nuclear density functional theory. Our results show that the observed bimodal fission can be explained in terms of pathways in multidimensional collective space corresponding to different geometries of fission products. We also predict a new phenomenon of trimodal spontaneous fission for some rutherfordium, seaborgium, and hassium isotopes.

A. Staszczak; A. Baran; J. Dobaczewski; W. Nazarewicz

2009-06-23

214

Porous fission fragment tracks in fluorapatite  

SciTech Connect

Fission tracks caused by the spontaneous fission of {sup 238}U in minerals, as revealed by chemical etching, are extensively used to determine the age and thermal history of Earth's crust. Details of the structure and annealing of tracks at the atomic scale have remained elusive, as the original track is destroyed during chemical etching. By combining transmission electron microscopy with in situ heating, we demonstrate that fission tracks in fluorapatite are actually porous tubes, instead of having an amorphous core, as generally assumed. Direct observation shows thermally induced track fragmentation in fluoapatite, in clear contrast to the amorphous tracks in zircon, which gradually ''fade'' without fragmentation. Rayleigh instability and the thermal emission of vacancies control the annealing of porous fission tracks in fluorapatite.

Li Weixing; Ewing, Rodney C. [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2104 (United States); Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, Michigan 48109-2104 (United States); Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109-1005 (United States); Wang Lumin [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2104 (United States); Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, Michigan 48109-2104 (United States); Sun Kai [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2104 (United States); Lang, Maik [Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109-1005 (United States); Trautmann, Christina [GSI Helmholtz Centre for Heavy Ion Research, Planckstr. 1, 64291 Darmstadt (Germany)

2010-10-01

215

Electron spectra from decay of fission products  

SciTech Connect

Electron spectra following decay of individual fission products (72 less than or equal to A less than or equal to 162) are obtained from the nuclear data given in the compilation using a listed and documented computer subroutine. Data are given for more than 500 radionuclides created during or after fission. The data include transition energies, absolute intensities, and shape parameters when known. An average beta-ray energy is given for fission products lacking experimental information on transition energies and intensities. For fission products having partial or incomplete decay information, the available data are utilized to provide best estimates of otherwise unknown decay schemes. This compilation is completely referenced and includes data available in the reviewed literature up to January 1982.

Dickens, J K

1982-09-01

216

Fast fission of {sup 238}U  

SciTech Connect

Independent and cumulative yields of about 150 products from fast fission of {sup 238}U, many of them with half-lives of the order of seconds, have been measured at Studsvik. Some results are reported here.

Rudstam, G.; Johansson, P.I.; Aleklett, K. [Studsvik Neutron Research Lab., Nykoeping (Sweden)

1994-12-31

217

Charge transfer-mediated singlet fission.  

PubMed

Singlet fission, the splitting of a singlet exciton into two triplet excitons in molecular materials, is interesting not only as a model many-electron problem, but also as a process with potential applications in solar energy conversion. Here we discuss limitations of the conventional four-electron and molecular dimer model in describing singlet fission in crystalline organic semiconductors, such as pentacene and tetracene. We emphasize the need to consider electronic delocalization, which is responsible for the decisive role played by the Mott-Wannier exciton, also called the charge transfer (CT) exciton, in mediating singlet fission. At the strong electronic coupling limit, the initial excitation creates a quantum superposition of singlet, CT, and triplet-pair states, and we present experimental evidence for this interpretation. We also discuss the most recent attempts at translating this mechanistic understanding into design principles for CT state-mediated intramolecular singlet fission in oligomers and polymers. PMID:25648486

Monahan, N; Zhu, X-Y

2015-04-01

218

Aqueous cutting fluid for machining fissionable materials  

DOEpatents

The present invention is directed to a cutting fluid for machining fissionable material. The cutting fluid is formed of glycol, water and boron compound in an adequate concentration for effective neutron attenuation so as to inhibit criticality incidents during machining.

Duerksen, Walter K. (Norris, TN); Googin, John M. (Oak Ridge, TN); Napier, Jr., Bradley (Powell, TN)

1984-01-01

219

Reactor power history from fission product signatures  

E-print Network

The purpose of this research was to identify fission product signatures that could be used to uniquely identify a specific spent fuel assembly in order to improve international safeguards. This capability would help prevent and deter potential...

Sweeney, David J.

2009-05-15

220

Fission Barriers of Compound Superheavy Nuclei  

E-print Network

The dependence of fission barriers on the excitation energy of the compound nucleus impacts the survival probability of superheavy nuclei synthesized in heavy-ion fusion reactions. In this work, we investigate the isentropic ...

Sheikh, J. A.

221

Nuclear fission as resonance-mediated conductance  

E-print Network

For 75 years the theory of nuclear fission has been based on the existence of a collective coordinate associated with the nuclear shape, an assumption required by the Bohr-Wheeler formula as well as by the R-matrix theory of fission. We show that it is also possible to formulate the theory without the help of collective coordinates. In the new formulation, fission is facilitated by individual states in the barrier region rather than channels over the barrier. In a certain limit the theory reduces to a formula closely related to the formula for electronic conductance through resonant tunneling states. In contrast, conduction through channels gives rise to a staircase excitation function that is well-known in nanoscale electronics but has never been seen in nuclear fission.

G. F. Bertsch

2014-12-18

222

Comparative Functional Genomics of the Fission Yeasts  

E-print Network

The fission yeast clade—comprising Schizosaccharomyces pombe, S. octosporus, S. cryophilus, and S. japonicus—occupies the basal branch of Ascomycete fungi and is an important model of eukaryote biology. A comparative ...

Regev, Aviv

223

Advanced modeling of prompt fission neutrons  

SciTech Connect

Theoretical and numerical studies of prompt fission neutrons are presented. The main results of the Los Alamos model often used in nuclear data evaluation work are reviewed briefly, and a preliminary assessment of uncertainties associated with the evaluated prompt fission neutron spectrum for n (0.5 MeV)+{sup 239}Pu is discussed. Advanced modeling of prompt fission neutrons is done by Monte Carlo simulations of the evaporation process of the excited primary fission fragments. The successive emissions of neutrons are followed in the statistical formalism framework, and detailed information, beyond average quantities, can be inferred. This approach is applied to the following reactions: {sup 252}Cf (sf), n{sub th} + {sup 239}Pu, n (0.5 MeV)+{sup 235}U, and {sup 236}Pu (sf). A discussion on the merits and present limitations of this approach concludes this presentation.

Talou, Patrick [Los Alamos National Laboratory

2009-01-01

224

A new neutron counter for fission research  

NASA Astrophysics Data System (ADS)

A new neutron counter for research experiments on nuclear fission has been developed. This instrument is designed for the detection of prompt fission neutrons within relatively high levels of gamma and neutron background. It is composed of a set of 3He proportional counters arranged within a block of polyethylene which serves as moderator. The detection properties have been studied by means of Monte Carlo simulations and experiments with radioactive sources. These properties are confirmed by an experiment on neutron-induced fission of 238U at the WNR facility of the Los Alamos Neutron Science Center during which the mean prompt fission neutron multiplicity, or ?¯ has been measured from 1 to 20 MeV of incident neutron energy.

Laurent, B.; Granier, T.; Bélier, G.; Chatillon, A.; Martin, J.-F.; Taieb, J.; Hambsch, F.-J.; Tovesson, F.; Laptev, A. B.; Haight, R. C.; Nelson, R. O.; O'Donnell, J. M.

2014-05-01

225

Hollow fission fragment tracks in fluorapatite  

NASA Astrophysics Data System (ADS)

Spontaneous fission of uranium in minerals creates a damaged "track" along the trajectory of the fission fragments. Fission tracks in fluorapatite, enlarged by chemical etching, are widely used in geologic age-dating and the reconstruction of the thermal history of Earth's crust. However, despite this wide spread application, there have been no systematic studies of the internal structure of unetched fission tracks or the atomic-scale process of track annealing. In this research, fission tracks in fluorapatite are demonstrated to be nano-channels instead of amorphous cores as had been assumed. The formation of hollow tracks is ascribed to the highly ionizing energy deposition of fission fragments inducing radiolytic decomposition of fluorapatite accompanied by the loss of volatile elements. The mechanism for thermal annealing of hollow tracks in fluorapatite is shown to be entirely different from that of amorphous tracks in zircon. The discontinuity of fission tracks, in addition to the shrinkage, prevents chemicals from entering into the hollow tracks for further etching, and then significantly reduces the etched length. The shrinkage of hollow fission tracks results from thermo-emission of vacancies or gaseous species from the cavities to surrounding solids instead of atomic-scale recovery of the amorphous core. The high diffusivity of atoms on the surface of hollow tracks causes the discontinuity of tracks either by Rayleigh instability, by Brownian motion, or by preferential motion of track segments. The preferential motion of atoms along c-axis causes more rapid annealing of fission tracks perpendicular to the c-axis. Under the electron beam, the hollow tracks segment into droplets and the track segments randomly move at room temperature or preferentially move along c-axis at high temperatures. The radiolytic annealing results from beam-enhanced diffusion, which is similar to thermally enhanced diffusion. The similarity in the morphology of fission tracks and electron beam-induced bubbles and their preferential elongation along c-axis at high temperatures further confirm that the tracks are actually hollow channels. The radius profile of fission track along its trajectory has been calculated. These data will be critical to developing an atomic-scale model of track fading as it applied to geologic age-dating.

Li, Weixing

226

I-NERI ANNUAL TECHNICAL PROGRESS REPORT: 2006-002-K, Separation of Fission Products from Molten LiCl-KCl Salt Used for Electrorefining of Metal Fuels  

SciTech Connect

An attractive alternative to the once-through disposal of electrorefiner salt is to selectively remove the active fission products from the salt and recycle the salt back to the electrorefiner (ER). This would allow salt reuse for some number of cycles before ultimate disposal of the salt in a ceramic waste form. Reuse of ER salt would, thus, greatly reduce the volume of ceramic waste produced during the pyroprocessing of spent nuclear fuel. This final portion of the joint I-NERI research project is to demonstrate the separation of fission products from molten ER salt by two methods previously selected during phase two (FY-08) of this project. The two methods selected were salt/zeolite contacting and rare-earth fission product precipitation by oxygen bubbling. The ER salt used in these tests came from the Mark-IV electrorefiner used to anodically dissolved driver fuel from the EBR-II reactor on the INL site. The tests were performed using the Hot Fuel Dissolution Apparatus (HFDA) located in the main cell of the Hot Fuels Examination Facility (HFEF) at the Materials and Fuels complex on the INL site. Results from these tests were evaluated during a joint meeting of KAERI and INL investigators to provide recommendations as to the future direction of fission product removal from electrorefiner salt that accumulate during spent fuel treatment. Additionally, work continued on kinetic measurements of surrogate quaternary salt systems to provide fundamental kinetics on the ion exchange system and to expand the equilibrium model system developed during the first two phases of this project. The specific objectives of the FY09 I-NERI research activities at the INL include the following: • Perform demonstration tests of the selected KAERI precipitation and INL salt/zeolite contacting processes for fission product removal using radioactive, fission product loaded ER salt • Continue kinetic studies of the quaternary Cs/Sr-LiCl-KCl system to determine the rate of ion exchange during the salt/zeolite contacting process • Compare the adsorption models to experimentally obtained, ER salt results • Evaluate results obtained from the oxygen precipitation and salt/zeolite ion exchange studies to determine the best processes for selective fission-product removal from electrorefiner salt.

S. Frank

2009-09-01

227

The mean field description of nuclear fission  

Microsoft Academic Search

Potential energy surfaces for fission studies of a model rare-earth nucleus are calculated in a constrained, static Hartree-Fock approximation using both single-centre and two-centre trial functions. Difficulties in interpreting the results in terms of a fission barrier are discussed. The time evolution of the static configurations boosted by a quadrupole velocity field is studied within the framework of the time-dependent

J. Okolowicz; J. M. Irvine; J. Nemeth

1983-01-01

228

Modeling Fission Product Sorption in Graphite Structures  

SciTech Connect

The goal of this project is to determine changes in adsorption and desorption of fission products to/from nuclear-grade graphite in response to a changing chemical environment. First, the project team will employ principle calculations and thermodynamic analysis to predict stability of fission products on graphite in the presence of structural defects commonly observed in very high- temperature reactor (VHTR) graphites. Desorption rates will be determined as a function of partial pressure of oxygen and iodine, relative humidity, and temperature. They will then carry out experimental characterization to determine the statistical distribution of structural features. This structural information will yield distributions of binding sites to be used as an input for a sorption model. Sorption isotherms calculated under this project will contribute to understanding of the physical bases of the source terms that are used in higher-level codes that model fission product transport and retention in graphite. The project will include the following tasks: Perform structural characterization of the VHTR graphite to determine crystallographic phases, defect structures and their distribution, volume fraction of coke, and amount of sp2 versus sp3 bonding. This information will be used as guidance for ab initio modeling and as input for sorptivity models; Perform ab initio calculations of binding energies to determine stability of fission products on the different sorption sites present in nuclear graphite microstructures. The project will use density functional theory (DFT) methods to calculate binding energies in vacuum and in oxidizing environments. The team will also calculate stability of iodine complexes with fission products on graphite sorption sites; Model graphite sorption isotherms to quantify concentration of fission products in graphite. The binding energies will be combined with a Langmuir isotherm statistical model to predict the sorbed concentration of fission products on each type of graphite site. The model will include multiple simultaneous adsorbing species, which will allow for competitive adsorption effects between different fission product species and O and OH (for modeling accident conditions).

Szlufarska, Izabela [University of Wisconsin, Madison, WI (United States); Morgan, Dane [University of Wisconsin, Madison, WI (United States); Allen, Todd [University of Wisconsin, Madison, WI (United States)

2013-04-08

229

Our 50-year odyssey with fission: Summary  

SciTech Connect

On the occasion of this International Conference on Fifty Years Research in Nuclear Fission, we summarize our present understanding of the fission process and the challenges that lie ahead. The basic properties of fission arise from a delicate competition between disruptive Coulomb forces, cohesive nuclear forces, and fluctuating shell and pairing forces. These static forces are primarily responsible for such experimental phenomena as deformed ground-state nuclear shapes, fission into fragments of unequal size, sawtooth neutron yields, spontaneously fissioning isomers, broad resonances and narrow intermediate structure in fission cross sections, and cluster radioactivity. However, inertial and dissipative forces also play decisive roles in the dynamical evolution of a fissioning nucleus. The energy dissipated between the saddle and scission points is small for low initial excitation energy at the saddle point and increases with increasing excitation energy. At moderate excitation energies, the dissipation of collective energy into internal single-particle excitation energy proceeds largely through the interaction of nucleons with the mean field and with each other in the vicinity of the nuclear surface, as well as through the transfer of nucleons between the two portions of the evolving dumbell-like system. These unique dissipation mechanisms arise from the Pauli exclusion principle for fermions and the details of the nucleon-nucleon interaction, which make the mean free path of a nucleon near the Fermi surface at low excitation energy longer than the nuclear radius. With its inverse process of heavy-ion fusion reactions, fission continues to yield surprises in the study of large-amplitude collective nuclear motion. 87 refs., 12 figs.

Nix, J.R.

1989-01-01

230

Calculating Quaternary glacial erosion rates in northeast Scotland  

NASA Astrophysics Data System (ADS)

Northeast Scotland is an area exhibiting selective erosion by Quaternary ice sheets. In this area both glacial and preglacial landforms exist in close proximity. The depths of erosion which this modification represents are calculated on the assumption of various depths of preglacial weathering. A depth of erosion of between 34 and 62 m per unit area is indicated. Calculated rates of erosion are 0.021 mm a -1 for the entire 2.3 m.y. of the Quaternary, and between 0.1 and 0.5 mm a -1 on the assumption that glacial conditions existed in this area for 500,000 years and 100,000 years, respectively. These figures are compared to the offshore sedimentary record in the adjacent west-central North Sea. The volume of sediment deposited offshore is equivalent to a depth of erosion of 195 m per unit area, yielding an average erosion rate of 0.085 mm a -1 over the entire Quaternary. Rates of erosion were low in the preglacial Pliocene (0.049 mm a -1) and early Quaternary (0.063 mm a -1). The expansion of ice sheets across the area in the middle Quaternary was associated with a sharp increase in the rates of erosion (> 0.13 mm a -1) but the last (late Devensian) ice sheet in the area was less erosive (< 0.095 mm a -1). The estimated rates of erosion represented by the offshore sedimentary record therefore exceed the estimated rates of glacial erosion from the onshore geomorphological reconstruction.

Glasser, Neil F.; Hall, Adrian M.

1997-09-01

231

Novel roles for actin in mitochondrial fission.  

PubMed

Mitochondrial dynamics, including fusion, fission and translocation, are crucial to cellular homeostasis, with roles in cellular polarity, stress response and apoptosis. Mitochondrial fission has received particular attention, owing to links with several neurodegenerative diseases. A central player in fission is the cytoplasmic dynamin-related GTPase Drp1, which oligomerizes at the fission site and hydrolyzes GTP to drive membrane ingression. Drp1 recruitment to the outer mitochondrial membrane (OMM) is a key regulatory event, which appears to require a pre-constriction step in which the endoplasmic reticulum (ER) and mitochondrion interact extensively, a process termed ERMD (ER-associated mitochondrial division). It is unclear how ER-mitochondrial contact generates the force required for pre-constriction or why pre-constriction leads to Drp1 recruitment. Recent results, however, show that ERMD might be an actin-based process in mammals that requires the ER-associated formin INF2 upstream of Drp1, and that myosin II and other actin-binding proteins might be involved. In this Commentary, we present a mechanistic model for mitochondrial fission in which actin and myosin contribute in two ways; firstly, by supplying the force for pre-constriction and secondly, by serving as a coincidence detector for Drp1 binding. In addition, we discuss the possibility that multiple fission mechanisms exist in mammals. PMID:25217628

Hatch, Anna L; Gurel, Pinar S; Higgs, Henry N

2014-11-01

232

Atypical mitochondrial fission upon bacterial infection  

PubMed Central

We recently showed that infection by Listeria monocytogenes causes mitochondrial network fragmentation through the secreted pore-forming toxin listeriolysin O (LLO). Here, we examine factors involved in canonical fusion and fission. Strikingly, LLO-induced mitochondrial fragmentation does not require the traditional fission machinery, as Drp1 oligomers are absent from fragmented mitochondria following Listeria infection or LLO treatment, as the dynamin-like protein 1 (Drp1) receptor Mff is rapidly degraded, and as fragmentation proceeds efficiently in cells with impaired Drp1 function. LLO does not cause processing of the fusion protein optic atrophy protein 1 (Opa1), despite inducing a decrease in the mitochondrial membrane potential, suggesting a unique Drp1- and Opa1-independent fission mechanism distinct from that triggered by uncouplers or the apoptosis inducer staurosporine. We show that the ER marks LLO-induced mitochondrial fragmentation sites even in the absence of functional Drp1, demonstrating that the ER activity in regulating mitochondrial fission can be induced by exogenous agents and that the ER appears to regulate fission by a mechanism independent of the canonical mitochondrial fission machinery. PMID:24043775

Stavru, Fabrizia; Palmer, Amy E.; Wang, Chunxin; Youle, Richard J.; Cossart, Pascale

2013-01-01

233

Accurate fission data for nuclear safety  

E-print Network

The Accurate fission data for nuclear safety (AlFONS) project aims at high precision measurements of fission yields, using the renewed IGISOL mass separator facility in combination with a new high current light ion cyclotron at the University of Jyvaskyla. The 30 MeV proton beam will be used to create fast and thermal neutron spectra for the study of neutron induced fission yields. Thanks to a series of mass separating elements, culminating with the JYFLTRAP Penning trap, it is possible to achieve a mass resolving power in the order of a few hundred thousands. In this paper we present the experimental setup and the design of a neutron converter target for IGISOL. The goal is to have a flexible design. For studies of exotic nuclei far from stability a high neutron flux (10^12 neutrons/s) at energies 1 - 30 MeV is desired while for reactor applications neutron spectra that resembles those of thermal and fast nuclear reactors are preferred. It is also desirable to be able to produce (semi-)monoenergetic neutrons for benchmarking and to study the energy dependence of fission yields. The scientific program is extensive and is planed to start in 2013 with a measurement of isomeric yield ratios of proton induced fission in uranium. This will be followed by studies of independent yields of thermal and fast neutron induced fission of various actinides.

A. Solders; D. Gorelov; A. Jokinen; V. S. Kolhinen; M. Lantz; A. Mattera; H. Penttila; S. Pomp; V. Rakopoulos; S. Rinta-Antila

2013-04-08

234

Theoretical descriptions of neutron emission in fission  

SciTech Connect

Brief descriptions are given of the observables in neutron emission in fission together with early theoretical representations of two of these observables, namely, the prompt fission neutron spectrum N(E) and the average prompt neutron multiplicity {bar {nu}}{sub p}. This is followed by summaries, together with examples, of modern approaches to the calculation of these two quantities. Here, emphasis is placed upon the predictability and accuracy of the new approaches. In particular, the dependencies of N(E) and {bar {nu}}{sub p} upon the fissioning nucleus and its excitation energy are discussed. Then, recent work in multiple-chance fission and other recent work involving new measurements are presented and discussed. Following this, some properties of fission fragments are mentioned that must be better known and better understood in order to calculate N(E) and {bar {nu}}{sub p} with higher accuracy than is currently possible. In conclusion, some measurements are recommended for the purpose of benchmarking simultaneous calculations of neutron emission and gamma emission in fission. 32 refs., 26 figs.

Madland, D.G.

1990-01-01

235

Anatomy of neck configuration in fission decay  

E-print Network

The anatomy of neck configuration in the fission decay of Uranium and Thorium isotopes is investigated in a microscopic study using Relativistic mean field theory. The study includes $^{236}U$ and $^{232}Th$ in the valley of stability and exotic neutron rich isotopes $^{250}U$, $^{256}U$, $^{260}U$, $^{240}Th$, $^{250}Th$, $^{256}Th$ likely to play important role in the r-process nucleosynthesis in stellar evolution. Following the static fission path, the neck configurations are generated and their composition in terms of the number of neutrons and protons are obtained showing the progressive rise in the neutron component with the increase of mass number. Strong correlation between the neutron multiplicity in the fission decay and the number of neutrons in the neck is seen. The maximum neutron-proton ratio is about 5 for $^{260}$U and $^{256}$Th suggestive of the break down of liquid-drop picture and inhibition of the fission decay in still heavier isotopes. Neck as precursor of a new mode of fission decay like multi-fragmentation fission may also be inferred from this study.

S. K. Patra; R. K. Choudhury; L. Satpathy

2010-05-10

236

Accurate Fission Data for Nuclear Safety  

NASA Astrophysics Data System (ADS)

The Accurate fission data for nuclear safety (AlFONS) project aims at high precision measurements of fission yields, using the renewed IGISOL mass separator facility in combination with a new high current light ion cyclotron at the University of Jyväskylä. The 30 MeV proton beam will be used to create fast and thermal neutron spectra for the study of neutron induced fission yields. Thanks to a series of mass separating elements, culminating with the JYFLTRAP Penning trap, it is possible to achieve a mass resolving power in the order of a few hundred thousands. In this paper we present the experimental setup and the design of a neutron converter target for IGISOL. The goal is to have a flexible design. For studies of exotic nuclei far from stability a high neutron flux (1012 neutrons/s) at energies 1 - 30 MeV is desired while for reactor applications neutron spectra that resembles those of thermal and fast nuclear reactors are preferred. It is also desirable to be able to produce (semi-)monoenergetic neutrons for benchmarking and to study the energy dependence of fission yields. The scientific program is extensive and is planed to start in 2013 with a measurement of isomeric yield ratios of proton induced fission in uranium. This will be followed by studies of independent yields of thermal and fast neutron induced fission of various actinides.

Solders, A.; Gorelov, D.; Jokinen, A.; Kolhinen, V. S.; Lantz, M.; Mattera, A.; Penttilä, H.; Pomp, S.; Rakopoulos, V.; Rinta-Antila, S.

2014-05-01

237

Spontaneous fission properties of 258Fm, 259Md, 260Md, 258No, and 260]: Bimodal fission  

NASA Astrophysics Data System (ADS)

We have measured the mass and kinetic-energy distributions from the spontaneous fission of 258Fm, 258No, 259Md, 260Md, and 260]. All are observed to fission with a symmetrical division of mass. The total-kinetic-energy distributions strongly deviated from the Gaussian shape characteristically found in the fission of all other actinides. When the total-kinetic-energy distributions are resolved into two Gaussians, the constituent peaks lie near 200 and 233 MeV. We conclude that both low- and high-energy fission modes occur in four of the five nuclides studied. We call this property ``bimodal fission.'' Even though both modes are possible in the same nuclide, one generally predominates. We offer an explanation for each mode based on shell structures of the fissioning nucleus and of its fragments. The appearance of both modes of fission in this region of the nuclide chart seems to be a coincidence in that the opportunity to divide into near doubly magic Sn fragments occurs in the same region where the second fission barrier is expected to drop in energy below the ground state of the fissioning nucleus. Appropriate paths on the potential-energy surface of deformation have been found by theorists, but no physical grounds have been advanced that would allow the near equal populations we observe traveling each path. We suggest that this failure to find a reason for somewhat equal branching may be a fundamental flaw of current fission models. Assuming the proposed origins of these modes are correct, we conclude the low-energy, but also mass-symmetrical mode is likely to extend to far heavier nuclei. The high-energy mode will be restricted to a smaller region, a realm of nuclei defined by the proximity of the fragments to the strong neutron and proton shells in 132Sn. We present some concluding remarks on the present state of fission theory and indicate a potential redirection that might be taken.

Hulet, E. K.; Wild, J. F.; Dougan, R. J.; Lougheed, R. W.; Landrum, J. H.; Dougan, A. D.; Baisden, P. A.; Henderson, C. M.; Dupzyk, R. J.; Hahn, R. L.; Schädel, M.; Sümmerer, K.; Bethune, G. R.

1989-08-01

238

Isotopic fission fragment distributions as a deep probe to fusion-fission dynamics  

E-print Network

During the fission process, the nucleus deforms and elongates up to the two fragments inception and their final separation at scission deformation. The evolution of the nucleus energy with deformation is determined by the macroscopic properties of the nucleus, and is also strongly influenced by the single-particle structure of the nucleus. The fission fragment distribution is a direct consequence of the deformation path the nucleus has encountered, and therefore is the most genuine experimental observation of the potential energy landscape of the deforming nucleus. Very asymmetric fusion-fission reactions at energy close to the Coulomb barrier, produce well-defined conditions of the compound nucleus formation, where processes such as quasi-fission, pre-equilibrium emission and incomplete fusion are negligible. In the same time, the excitation energy is sufficient to reduce significantly structural effects, and mostly the macroscopic part of the potential is responsible for the formation of the fission fragments. We use inverse kinematics combined with spectrometers to select and identify the fission fragments produced in $^{238}$U+$^{12}$C at a bombarding energy close to and well-above the Coulomb barrier. For the first time, the isotopic yields are measured over the complete atomic-number distribution, between Z=30 and Z=63. The experimental set-up also allows to identify transfer-induced reactions, which lead to low-energy fission where the nuclear shell structure shows a strong influence on the fission-fragment distributions. The resulting set of data gives the possibility to observe the fission fragment properties over a wide range of excitation energy, and they reveal the vanishing of the shell effects in the potential energy of the fissioning nucleus, as well as the influence of fission dynamics.

F. Farget; M. Caamano; O. Delaune; O. B. Tarasov; X. Derkx; K. -H. Schmidt; A. M. Amthor; L. Audouin; C. -O. Bacri; G. Barreau; B. Bastin; D. Bazin; B. Blank; J. Benlliure; L. Caceres; E. Casarejos; A. Chibihi; B. Fernandez-Dominguez; L. Gaudefroy; C. Golabek; S. Grevy; B. Jurado; O. Kamalou; A. Lemasson; S. Lukyanov; W. Mittig; D. J. Morrissey; A. Navin; J. Pereira; L. Perrot; M. Rejmund; T. Roger; M. -G. Saint-Laurent; H. Savajols; C. Schmitt; B. M. Sherill; C. Stodel; J. Taieb; J. -C. Thomas; A. C. Villari

2012-09-24

239

Fission neutron source in Rome  

NASA Astrophysics Data System (ADS)

A fission neutron source is operating in Rome at the ENEA Casaccia Research Center since 1971, consisting of a low power fast reactor named RSV-Tapiro. it is employed for a variety of experiments, including dosimetry, material testing, radiation protection and biology. In particular, application to experimental radiobiology includes studies of the biological action of neutrons in the whole-body irradiated animal, or in specialized systems in vivo or in vitro. For his purpose a vertical irradiation facility was originally constructed. Recently, a new horizontal irradiation facility has been designed to allow the exposure of larger samples or larger sample batches at one time. Dosimetry at the sample irradiation positions is routinely carried out by the conventional method of using two ion chambers. This physical dosimetry has recently been compared with the results of biological dosimetry based on the detection of chromosomal aberrations in peripheral blood human lymphocytes irradiated in vitro. A characterization of the radiation quality in the two configurations has been carried out by tissue equivalent proportional counter microdosimetry measurements. Information about the main characteristics of the reactor and the two irradiation facilities is provided and relevant results of the various measurements are summarized. Radiobiological results obtained using this neutron source are also briefly outlined.

Coppola, Mario; Di Majo, V.; Ingrao, G.; Rebessi, S.; Testa, A.

1997-02-01

240

Fission fragment K x-ray emission and nuclear charge distribution for thermal neutron fission of 233U, 235U, 239Pu and spontaneous fission of 252Cf  

Microsoft Academic Search

The emission of K X-rays by fission fragments within ~ 1 nsec after fission has been studied as a function of fragment mass and nuclear charge for thermal neutron-induced fission of 233U, 235U, 239Pu and spontaneous fission of 252Cf. This work is based on a simultaneous measurement of the fragment kinetic energies to obtain the fragment masses and high-resolution measurement

W. Reisdorf; J. P. Unik; H. C. Griffin; L. E. Glendenin

1971-01-01

241

Characterization of Quaternary and suspected Quaternary faults, regional studies, Nevada and California  

SciTech Connect

This report presents the results of geologic studies that help define the Quaternary history of selected faults in the region around Yucca Mountain, Nevada. These results are relevant to the seismic-design basis of a potential nuclear waste repository at Yucca Mountain. The relevancy is based, in part, on a need for additional geologic data that became apparent in ongoing studies that resulted in the identification of 51 relevant and potentially relevant individual and compound faults and fault zones in the 100-km-radius region around the Yucca Mountain site. Geologic data used to characterize the regional faults and fault zones as relevant or potentially relevant seismic sources includes age and displacement information, maximum fault lengths, and minimum distances between the fault and the Yucca Mountain site. For many of the regional faults, no paleoseismic field studies have previously been conducted, and age and displacement data are sparse to nonexistent. In November 1994, the Branch of Earthquake and Landslide Hazards entered into two Memoranda of Agreement with the Yucca Mountain Project Branch to conduct field reconnaissance, analysis, and interpretation of six relevant and six potentially relevant regional faults. This report describes the results of study of those faults exclusive of those in the Pahrump-Stewart Valley-Ash Meadows-Amargosa Valley areas. We also include results of a cursory study of faults on the west flank of the Specter Range and in the northern part of the Last Chance Range. A four-phase strategy was implemented for the field study.

Anderson, R.E.; Bucknam, R.C.; Crone, A.J.; Haller, K.M.; Machette, M.N.; Personius, S.F.; Barnhard, T.P.; Cecil, M.J.; Dart, R.L.

1995-12-31

242

The cumulative fission yields of light mass fragments in the thermal neutron fission of Pu239  

Microsoft Academic Search

The relative cumulative yields of 19 light mass fragments or rubidium, ; strontium, yttrium, zirconium. molybdenum, and ruthenium formed in the thermal ; neutron fission of Pu²³⁹ have been determined with a mass spectrometer ; using the isotope dilution technique. The yields of the fission product isotopes ; of these elements, together with the previously published relative yields of ;

H. R. Fickel; R. H. Tomlinson

1959-01-01

243

Independent fission yields of Rb and Cs from thermal-neutron-induced fission of 239Pu  

Microsoft Academic Search

The relative independent fission yields of Rb and Cs from thermal-neutron-induced fission of 239Pu have been measured on line using a mass spectrograph and thermalized neutrons from a burst reactor. Independent yields were derived by normalizing the measurements to products of chain yields and fractional independent yields, estimating the latter from measured cumulative yields of Kr and Xe. Comparing the

Silvio J. Balestrini; Leon Forman

1975-01-01

244

Nuclear charge distribution of heavy fission fragments from thermal-neutron-induced fission of 235 U  

Microsoft Academic Search

Fragments from thermal-neutron induced fission of235U have been separated by a mass spectrometer with respect to their masses and kinetic energies within 1 µsec. The separation principles are briefly described. For masses 130 to 139 amu the charge distributions have been determined by counting the number of beta tracks emitted from the individual mass selected fission fragments in a nuclear

Ewald Konecny; Helmut Gunther; Helmut Rösler; Günter Siegert; Heinz Ewald

1970-01-01

245

Yields of rare earth fission products in the spontaneous fission of californium-252  

Microsoft Academic Search

Cumulative fission yields of rare earth isotopes have been determined in the spontaneous fission of252Cf by fast radiochemical separation and gamma-ray spectrometry. The determined yield values are compared with the available literature data. The yield values for147Nd,151Nd and151Pm differ from the reported values. The yield for145Ce is determined for the first time.

B. S. Tomar; H. Naik; A. Ramaswamy; Satya Prakash

1985-01-01

246

Microscopic Description of Nuclear Fission:. Fission Barrier Heights of Even-Even Actinides  

NASA Astrophysics Data System (ADS)

We evaluate the performance of modern nuclear energy density functionals for predicting inner and outer fission barrier heights and energies of fission isomers of even-even actinides. For isomer energies and outer barrier heights, we find that the self-consistent theory at the HFB level is capable of providing quantitative agreement with empirical data.

McDonnell, J.; Schunck, N.; Nazarewicz, W.

2014-09-01

247

Dual-fission chamber and neutron beam characterization for fission product yield measurements using monoenergetic neutrons  

NASA Astrophysics Data System (ADS)

A program has been initiated to measure the energy dependence of selected high-yield fission products used in the analysis of nuclear test data. We present out initial work of neutron activation using a dual-fission chamber with quasi-monoenergetic neutrons and gamma-counting method. Quasi-monoenergetic neutrons of energies from 0.5 to 15 MeV using the TUNL 10 MV FM tandem to provide high-precision and self-consistent measurements of fission product yields (FPY). The final FPY results will be coupled with theoretical analysis to provide a more fundamental understanding of the fission process. To accomplish this goal, we have developed and tested a set of dual-fission ionization chambers to provide an accurate determination of the number of fissions occurring in a thick target located in the middle plane of the chamber assembly. Details of the fission chamber and its performance are presented along with neutron beam production and characterization. Also presented are studies on the background issues associated with room-return and off-energy neutron production. We show that the off-energy neutron contribution can be significant, but correctable, while room-return neutron background levels contribute less than <1% to the fission signal.

Bhatia, C.; Fallin, B.; Gooden, M. E.; Howell, C. R.; Kelley, J. H.; Tornow, W.; Arnold, C. W.; Bond, E. M.; Bredeweg, T. A.; Fowler, M. M.; Moody, W. A.; Rundberg, R. S.; Rusev, G.; Vieira, D. J.; Wilhelmy, J. B.; Becker, J. A.; Macri, R.; Ryan, C.; Sheets, S. A.; Stoyer, M. A.; Tonchev, A. P.

2014-09-01

248

Yield of the fission products in the fission of 238 Np by thermal neutrons  

Microsoft Academic Search

Obviously, new experimental information on the features of the fission of nuclides with odd Z must provide a clearer picture of the anomalies noted and should explain them. The present paper reports on the results of experimental determinations of the relative and absolute yields of heavy products of the fission effected by thermal neutrons of a shortlived nuclide with odd

A. A. Solonkin; V. F. Teplykh; E. V. Platygina; K. A. Petrzhak; A. V. Mosesov

1988-01-01

249

Yields of fission products produced by thermal-neutron fission of 229Th  

NASA Astrophysics Data System (ADS)

Absolute yields have been determined for 47 gamma rays emitted in the decay of 37 fission products representing 25 mass chains created during thermal-neutron fission of 229Th. Using a Ge(Li) detector, spectra were obtained of gamma rays emitted between 15 min and 0.4 yr after very short irradiations by thermal neutrons of a 15-?g sample of 229Th. On the basis of measured gamma-ray yields and known nuclear data, yields for cumulative production of 37 fission products were deduced. The absolute overall normalization uncertainty is <8%. The results are compared with fission-product yields previously measured, with generally good agreement. On this basis, and using other measurements for masses not observed in the present experiment, a complete mass distribution for A between 76 and 152 was deduced. The measured A-chain cumulative yields from the present program make up 84% of the total light-mass (A<=115) yield and 77% of the total heavy-mass yield. The data were analyzed to obtain values of most-probable charge (Zp) and charge-dispersion (?) parameters. Based upon insight gained from study of similar data obtained for thermalneutron fission of 235U, we postulate a simple functional dependence ?=?(Zp), and using this dependence obtain values of Zp(A) for 15 mass chains created during fission of 229Th. Values of Zp(A) were estimated for other mass chains based upon results of a recent study of Zp(A). Charge distributions determined using the deduced mass distribution and the deduced sets of Zp(A) and ?(Zp) are in very good agreement with recent measurements, exhibiting a pronounced even-odd effect in elemental yields. These results may be used to predict unmeasured yields for 229Th fission. NUCLEAR REACTIONS Fission 209Th(nth, f), measured fission product gamma-ray yields; deduced fission-product yields and element and mass yields.

Dickens, J. K.; McConnell, J. W.

1983-01-01

250

Options For Development of Space Fission Propulsion Systems  

NASA Technical Reports Server (NTRS)

Fission technology can enable rapid, affordable access to any point in the solar system. Potential fission-based transportation options include high specific power continuous impulse propulsion systems and bimodal nuclear thermal rockets. Despite their tremendous potential for enhancing or enabling deep space and planetary missions, to date space fission system have only been used in Earth orbit. The first step towards utilizing advanced fission propulsion systems is development of a safe, near-term, affordable fission system that can enhance or enable near-term missions of interest. An evolutionary approach for developing space fission propulsion systems is proposed.

Houta, Mike; VanDyke, Melissa; Godfroy, Tom; Pedersen, Kevin; Martin, James; Dickens, Ricky; Salvail, Pat; Hrbud, Ivana; Rodgers, Stephen L. (Technical Monitor)

2001-01-01

251

Bimodal fission in the Skyrme-Hartree-Fock approach  

E-print Network

Spontaneous-fission properties of 256Fm, 258Fm, and 260Fm isotopes are studied within the Skyrme-Hartree-Fock+BCS framework. In the particle-hole channel we take the Skyrme SkM* effective force, while in the particle-particle channel we employ the seniority pairing interaction. Three static fission paths for all investigated heavy fermium isotopes are found. The analysis of these fission modes allows to describe observed asymmetric fission of 256Fm, as well as bimodal fission of 258Fm and symmetric fission in 260Fm.

A. Staszczak; J. Dobaczewski; W. Nazarewicz

2006-12-04

252

Fission Surface Power Technology Development Update  

NASA Technical Reports Server (NTRS)

Power is a critical consideration in planning exploration of the surfaces of the Moon, Mars, and places beyond. Nuclear power is an important option, especially for locations in the solar system where sunlight is limited or environmental conditions are challenging (e.g., extreme cold, dust storms). NASA and the Department of Energy are maintaining the option for fission surface power for the Moon and Mars by developing and demonstrating technology for a fission surface power system. The Fission Surface Power Systems project has focused on subscale component and subsystem demonstrations to address the feasibility of a low-risk, low-cost approach to space nuclear power for surface missions. Laboratory demonstrations of the liquid metal pump, reactor control drum drive, power conversion, heat rejection, and power management and distribution technologies have validated that the fundamental characteristics and performance of these components and subsystems are consistent with a Fission Surface Power preliminary reference concept. In addition, subscale versions of a non-nuclear reactor simulator, using electric resistance heating in place of the reactor fuel, have been built and operated with liquid metal sodium-potassium and helium/xenon gas heat transfer loops, demonstrating the viability of establishing system-level performance and characteristics of fission surface power technologies without requiring a nuclear reactor. While some component and subsystem testing will continue through 2011 and beyond, the results to date provide sufficient confidence to proceed with system level technology readiness demonstration. To demonstrate the system level readiness of fission surface power in an operationally relevant environment (the primary goal of the Fission Surface Power Systems project), a full scale, 1/4 power Technology Demonstration Unit (TDU) is under development. The TDU will consist of a non-nuclear reactor simulator, a sodium-potassium heat transfer loop, a power conversion unit with electrical controls, and a heat rejection system with a multi-panel radiator assembly. Testing is planned at the Glenn Research Center Vacuum Facility 6 starting in 2012, with vacuum and liquid-nitrogen cold walls to provide simulation of operationally relevant environments. A nominal two-year test campaign is planned including a Phase 1 reactor simulator and power conversion test followed by a Phase 2 integrated system test with radiator panel heat rejection. The testing is expected to demonstrate the readiness and availability of fission surface power as a viable power system option for NASA's exploration needs. In addition to surface power, technology development work within this project is also directly applicable to in-space fission power and propulsion systems.

Palac, Donald T.; Mason, Lee S.; Houts, Michael G.; Harlow, Scott

2011-01-01

253

Singlet fission in linear chains of molecules  

NASA Astrophysics Data System (ADS)

We develop a model configuration interaction Hamiltonian to study the electronic structure of a chain of molecules undergoing singlet fission. We first consider models for dimer and trimer and then we use a matrix partitioning technique to build models of arbitrary size able to describe the relevant electronic structure for singlet fission in linear aggregates. We find that the multi-excitonic state (ME) is stabilized at short inter-monomer distance and the extent of this stabilization depends upon the size of orbital coupling between neighboring monomers. We also find that the coupling between ME states located on different molecules is extremely small leading to bandwidths in the order of ˜10 meV. This observation suggests that multi-exciton states are extremely localized by electron-phonon coupling and that singlet fission involves the transition between a relatively delocalized Frenkel exciton and a strongly localized multi-exciton state. We adopt the methodology commonly used to study non-radiative transitions to describe the singlet fission dynamics in these aggregates and we discuss the limit of validity of the approach. The results indicate that the phenomenology of singlet fission in molecular crystals is different in many important ways from what is observed in isolated dimers.

Ambrosio, Francesco; Troisi, Alessandro

2014-11-01

254

Decreasing mitochondrial fission prevents cholestatic liver injury.  

PubMed

Mitochondria frequently change their shape through fission and fusion in response to physiological stimuli as well as pathological insults. Disrupted mitochondrial morphology has been observed in cholestatic liver disease. However, the role of mitochondrial shape change in cholestasis is not defined. In this study, using in vitro and in vivo models of bile acid-induced liver injury, we investigated the contribution of mitochondrial morphology to the pathogenesis of cholestatic liver disease. We found that the toxic bile salt glycochenodeoxycholate (GCDC) rapidly fragmented mitochondria, both in primary mouse hepatocytes and in the bile transporter-expressing hepatic cell line McNtcp.24, leading to a significant increase in cell death. GCDC-induced mitochondrial fragmentation was associated with an increase in reactive oxygen species (ROS) levels. We found that preventing mitochondrial fragmentation in GCDC by inhibiting mitochondrial fission significantly decreased not only ROS levels but also cell death. We also induced cholestasis in mouse livers via common bile duct ligation. Using a transgenic mouse model inducibly expressing a dominant-negative fission mutant specifically in the liver, we demonstrated that decreasing mitochondrial fission substantially diminished ROS levels, liver injury, and fibrosis under cholestatic conditions. Taken together, our results provide new evidence that controlling mitochondrial fission is an effective strategy for ameliorating cholestatic liver injury. PMID:25342755

Yu, Tianzheng; Wang, Li; Lee, Hakjoo; O'Brien, Dawn K; Bronk, Steven F; Gores, Gregory J; Yoon, Yisang

2014-12-01

255

Singlet fission in linear chains of molecules.  

PubMed

We develop a model configuration interaction Hamiltonian to study the electronic structure of a chain of molecules undergoing singlet fission. We first consider models for dimer and trimer and then we use a matrix partitioning technique to build models of arbitrary size able to describe the relevant electronic structure for singlet fission in linear aggregates. We find that the multi-excitonic state (ME) is stabilized at short inter-monomer distance and the extent of this stabilization depends upon the size of orbital coupling between neighboring monomers. We also find that the coupling between ME states located on different molecules is extremely small leading to bandwidths in the order of ?10?meV. This observation suggests that multi-exciton states are extremely localized by electron-phonon coupling and that singlet fission involves the transition between a relatively delocalized Frenkel exciton and a strongly localized multi-exciton state. We adopt the methodology commonly used to study non-radiative transitions to describe the singlet fission dynamics in these aggregates and we discuss the limit of validity of the approach. The results indicate that the phenomenology of singlet fission in molecular crystals is different in many important ways from what is observed in isolated dimers. PMID:25429953

Ambrosio, Francesco; Troisi, Alessandro

2014-11-28

256

Correlation of recent fission product release data  

SciTech Connect

For the calculation of source terms associated with severe accidents, it is necessary to model the release of fission products from fuel as it heats and melts. Perhaps the most definitive model for fission product release is that of the FASTGRASS computer code developed at Argonne National Laboratory. There is persuasive evidence that these processes, as well as additional chemical and gas phase mass transport processes, are important in the release of fission products from fuel. Nevertheless, it has been found convenient to have simplified fission product release correlations that may not be as definitive as models like FASTGRASS but which attempt in some simple way to capture the essence of the mechanisms. One of the most widely used such correlation is called CORSOR-M which is the present fission product/aerosol release model used in the NRC Source Term Code Package. CORSOR has been criticized as having too much uncertainty in the calculated releases and as not accurately reproducing some experimental data. It is currently believed that these discrepancies between CORSOR and the more recent data have resulted because of the better time resolution of the more recent data compared to the data base that went into the CORSOR correlation. This document discusses a simple correlational model for use in connection with NUREG risk uncertainty exercises. 8 refs., 4 figs., 1 tab.

Kress, T.S.; Lorenz, R.A.; Nakamura, T.; Osborne, M.F.

1989-01-01

257

Unexpected primitive rodents in the Quaternary of Argentina  

NASA Astrophysics Data System (ADS)

This article describes the first fossils recorded in the Hernandarias Formation (Pleistocene) in Entre Ríos province (eastern Argentina). They are represented by three teeth assigned to the caviomorph rodents (Rodentia, Mammalia) Aenigmys diamantensis gen. et sp. nov. and Eumysops. To establish the phylogenetic affinities of the two most enigmatic teeth, their enamel microstructure was studied. Aenigmys diamantensis is considered the most primitive taxon of a clade formed by Dinomyidae-Neoepiblemidae-Heptaxodontidae. Evidence of the close relationships among these families also is presented herein. The new fossils reinforce previous hypotheses about the survival of primitive Brazilian taxa after their extinction in the Pampas and Patagonia of southern South America. They also show that the diversity of caviomorph rodents during the Quaternary was greater than supposed and that an important Quaternary extinction, not previously detected, affected several lineages. With the available evidence, it is not possible to determine if these rodents indicate a warm pulse or a particular biogeographic situation in Entre Ríos.

Vucetich, María G.; Vieytes, Emma C.; Verzi, Diego H.; Noriega, Jorge I.; Tonni, Eduardo P.

2005-10-01

258

Late-quaternary vegetational dynamics and community stability reconsidered  

NASA Astrophysics Data System (ADS)

Defining the spatial and temporal limits of vegetational processes such as migration and invasion of established communities is a prerequisite to evaluating the degree of stability in plant communities through the late Quaternary. The interpretation of changes in boundaries of major vegetation types over the past 20,000 yr offers a complementary view to that provided by migration maps for particular plant taxa. North of approximately 43°N in eastern North America, continual vegetational disequilibrium has resulted from climatic change, soil development, and species migrations during postglacial times. Between 33° and 39°N, stable full-glacial vegetation was replaced by a relatively unstable vegetation during late-glacial climatic amelioration; stable interglacial vegetation developed there after about 9000 yr B.P. Late-Quaternary vegetation has been in dynamic equilibrium, with a relatively constant flora, south of 33°N on upland interfluves along the northern Gulf Coastal Plain, peninsular Florida, and west-central Mexico.

Delcourt, Paul A.; Delcourt, Hazel R.

1983-03-01

259

Quaternary ammonium polyethylenimine nanoparticles for treating bacterial contaminated water.  

PubMed

This study highlights the potential application of antimicrobial quaternary ammonium nanomaterials for water disinfection. Quaternary ammonium polyethylenimine (QA-PEI) nanoparticles (NPs) were synthesized by polyethylenimine crosslinking and alkylation with octyl iodide followed by methyl iodide quaternization. Particles modified with octyldodecyl alkyl chains were also prepared and evaluated. The antimicrobial activity of QA-PEI NPs was studied after anchoring in non-leaching polymeric coatings and also in aqueous suspension. Particles at different loadings (w/w) were embedded in polyethylene vinyl acetate and polyethylene methacrylic acid coatings and tested for antimicrobial activity against four representative strains of bacteria in static and dynamic modes. Coatings embedded with fluorescent labelled particles tracked by Axioscope fluorescence microscope during the antimicrobial test indicates no particles leaching out. Coatings loaded with 5% w/w QA-PEI exhibited strong antibacterial activity. Aqueous suspension was tested and found effective for bacterial decontamination at 0.1ppm and maintains its activity for several weeks. PMID:25800358

Farah, Shady; Aviv, Oren; Laout, Natalia; Ratner, Stanislav; Beyth, Nurit; Domb, Abraham J

2015-04-01

260

Fission yields at different fission-product kinetic energies for thermal-neutron-induced fission of 239Pu  

NASA Astrophysics Data System (ADS)

At the recoil spectrometer "Lohengrin" of the Institut Laue-Langevin in Grenoble, the yields of the light fission products from the thermal-neutron-induced fission of 239Pu were measured as a function of A, Z, the kinetic energy E and the ionic charge states q. The nuclear charge and mass distributions summed over all ionic charge states were determined for different light fissionproduct kinetic energies between 93 and 112 MeV. The proton odd-even effect which was measured to be (11.6 ± 0.6)% causes considerable fine structure in the yields. The average kinetic energy of even- Z elements in the light fission-product group is 0.3 ± 0.1 MeV larger than for odd- Z elements. The neutron odd-even effect is (6.5 ± 0.7)%. The comparison with previously published data 1) for thermal-neutron-induced fission of 235U reveals a correlation between the proton odd-even effect in the yield and in the kinetic energy of the elements. The dependence of the proton odd-even effect on the fragmentation is very similar for 235U and 239Pu when it is considered as a function of the nuclear charge of the heavy fission products. The isobaric variances ?z2. for thermal-neutron fission of 235U and 239Pu coincide at all kinetic energies if the influence of the proton odd-even effect is averaged out. This supports the hypothesis that the magnitude of ?z2 is determined only by quantum-mechanical zero-point fluctuations. The influence of the spherical shells Z = 50 and N = 82 on the fragmentation is discussed.

Schmitt, C.; Guessous, A.; Bocquet, J. P.; Clerc, H.-G.; Brissot, R.; Engelhardt, D.; Faust, H. R.; Gönnenwein, F.; Mutterer, M.; Nifenecker, H.; Pannicke, J.; Ristori, CH.; Theobald, J. P.

1984-11-01

261

Sorption of Polymeric Quaternary Ammonium Compounds to Humic Acid  

Microsoft Academic Search

Polymeric quaternary ammonium salts or polyquaterniums are used not only in the water and wastewater industry but also in\\u000a cosmetics. The former have been extensively studied with sorption to wastewater treatment plant (WWTP) biosolids an important\\u000a factor in their fate, mitigating release to the environment. Compounds of cosmetic origin have not received the same scrutiny\\u000a as those used in other

Janet Cumming; Darryl William Hawker; Heather Chapman; Kerry Nugent

2011-01-01

262

Synthesis and performance of ester quaternary biodegradable softeners  

Microsoft Academic Search

Reaction of hydroxyethylpiperazine with two moles of fatty acid, followed by quaternization with methyl chloride, methyl bromide\\u000a or dimethyl sulfate, resulted in new quaternaries useful as biodegradable fabric softeners. Additional softeners were synthesized\\u000a from hard tallow propane diamine by reaction with butyrolactone, followed by ethoxylation, esterification with one mole of\\u000a fatty acid and quaternization.

R. Lagerman; S. Clancy; D. Tanner; N. Johnston; B. Callian; F. Friedli

1994-01-01

263

Vegetation ecotone dynamics in Southwest Alaska during the Late Quaternary  

Microsoft Academic Search

To examine Late Quaternary vegetation change across the modern vegetation gradient from continuous boreal forest (central Alaska) to Betula shrub tundra (Bristol Bay region), pollen records from Idavain and Snipe Lakes are described and compared to those of four other sites in southwest Alaska. Major features of the vegetation history at Idavain Lake include herb-dominated tundra (ca 14–12kaBP), mixed herb\\/Betula

Linda B. Brubaker; Patricia M. Anderson; Feng Sheng Hu

2001-01-01

264

Quaternary TL Surveys: A Guide to Thermoluminescence (TL) Date Measurement  

NSDL National Science Digital Library

Quaternary TL Surveys, a company that provides date measurement services to archaeologists and geologists, offers this comprehensive tutorial on archaeometric dating techniques. The tutorial contains a general overview as well as specific information on dating flint and stone, stalagmitic calcite, sediments, and methods of interpreting and using TL dates. For ease of use, portions of the guide are marked to alert users to their relative importance.

265

Preparation of bis -quaternary ammonium salts from epichlorohydrin  

Microsoft Academic Search

A novelbis-quaternary ammonium salt was prepared conveniently and almost quantitatively fromN,N-dimethyldodecylamine, its hydrochloride, and epichlorohydrin. Reaction ofN,N-dimethyldodecylamine with epichlorohydrin (in the presence of the amine hydrochloride) or various dichloro compounds was\\u000a investigated by using1H nuclear magnetic resonance. The reaction route was studied by examining the reactivity of reagents with the amine and the\\u000a effect of reaction temperature. The ease of

Tae-Seong Kim; Toshikazu Hirao; Isao Ikeda

1996-01-01

266

Petrogenesis of Plio-Quaternary basalts in Mahabad, NW Iran  

NASA Astrophysics Data System (ADS)

The Mahabad1:100000 sheet is located mostly in the Kurdestan district on southern part of west Azerbijan province between east Longitude 45? 30'- 46 ?, and northern Latitude 36? 30'- 37?. Geographic position, geological and structural setting as well as general geological characters of this zone is very similar to Sanandaj-Sirjan zone. Topography is dominated by mountainous terrain with an average elevation around 1800 meters. The oldest rocks belong to intrusive rocks, Mahabad Rhyolite. The younger ones include Plio-Quaternary basalt to alkali basalt, andesite, trachyte and alluvium terraces and salt marsh. The young quaternary volcanoes occur in the southern range east and east of mahabad map sheet. The Plio-Quaternary volcanic lava are seen in the Borhan village? It is built almost entirely of fluid lava flows?. The volcanic rocks are basic in composition (basalt, tephrit basanite). The petrographic and geochemical evidences, related diagrams show fractionation. By studying the major and trace elements variation diagrams, a trend of normal crystallization can be seen crustal contamination in extensional environments. It seems that the original magma has an ultrabasic composition. Some of the phenocrysts of olivine, pyroxene & plagioclase are seen in thin sections. These rocks have microlitic porphyritic? hyallo microlithic porphyritic textures in thin sections. On the basis of chemical analysis? magma that has formed the rocks had alkaline nature. The ratio of nephelin norm is around 5.3 in this rocks. A primitive mantle- normalized incompatible trace element diagram shows close similarity to typical OIB pattern. All of documents denote that magma originated from an enriched asthenospheric mantle and low degree of partial melting in source. Key words: alkali basalt, Quaternary, Volcanic, Compression. asthenospher

Shojaei, Masoomeh; Kheirkhah, Monireh; Hashem Emami, Mohamad; Maleki, Glavig

2010-05-01

267

Quaternary fluvial archives: achievements of the Fluvial Archives Group  

NASA Astrophysics Data System (ADS)

In their geomorphological and sedimentary records, rivers provide valuable archives of environments and environmental change, at local to global scales. In particular, fluvial sediments represent databanks of palaeoenvironment and palaeoclimatic (for example) of fossils (micro- and macro-), sedimentary and post-depositional features and buried soils. Well-dated sequences are of the most value, with dating provided by a wide range of methods, from radiometric (numerical) techniques to included fossils (biostratigraphy) and/or archaeological material. Thus Quaternary fluvial archives can also provide important data for studies of Quaternary biotic evolution and early human occupation. In addition, the physical disposition of fluvial sequences, be it as fragmented terrace remnants or as stacked basin-fills, provides valuable information about geomorphological and crustal evolution. Since rivers are long-term persistent features in the landscape, their sedimentary archives can represent important frameworks for regional Quaternary stratigraphy. Fluvial archives are distributed globally, being represented on all continents and across all climatic zones, with the exception of the frozen polar regions and the driest deserts. In 1999 the Fluvial Archives Group (FLAG) was established, as a working group of the Quaternary Research Association (UK), aimed at bringing together those interested in such archives. This has evolved into an informal organization that has held regular biennial combined conference and field-trip meetings, has co-sponsored other meetings and conference sessions, and has presided over two International Geoscience Programme (IGCP) projects: IGCP 449 (2000-2004) 'Global Correlation of Late Cenozoic Fluvial Deposits' and IGCP 518 (2005-2007) 'Fluvial sequences as evidence for landscape and climatic evolution in the Late Cenozoic'. Through these various activities a sequence of FLAG publications has appeared, including special issues in a variety of journals, amassing a substantial volume of information on fluvial archives worldwide. This presentation will highlight some of these data and will describe important patterns observed and interpretations arising therefrom.

Bridgland, David; Cordier, Stephane; Herget, Juergen; Mather, Ann; Vandenberghe, Jef; Maddy, Darrel

2013-04-01

268

The impact of Quaternary Ice Ages on mammalian evolution.  

PubMed Central

The Quaternary was a time of extensive evolution among mammals. Most living species arose at this time, and many of them show adaptations to peculiarly Quaternary environments. The latter include continental northern steppe and tundra, and the formation of lakes and offshore islands. Although some species evolved fixed adaptations to specialist habitats, others developed flexible adaptations enabling them to inhabit broad niches and to survive major environmental changes. Adaptation to short-term (migratory and seasonal) habitat change probably played a part in pre-adapting mammal species to the longer-term cyclical changes of the Quaternary. Fossil evidence indicates that environmental changes of the order of thousands of years have been sufficient to produce subspeciation, but speciation has typically required one hundred thousand to a few hundred thousand years, although there are both shorter and longer exceptions. The persistence of taxa in environments imposing strong selective regimes may have been important in forcing major adaptive change. Individual Milankovitch cycles are not necessarily implicated in this process, but nor did they generally inhibit evolutionary change among mammals: many evolutionary divergences built over multiple climatic cycles. Deduction of speciation timing requires input from fossils and modern phenotypic and breeding data, to complement and constrain mitochondrial DNA coalescence dates which appear commonly to overestimate taxic divergence dates and durations of speciation. Migrational and evolutionary responses to climate change are not mutually exclusive but, on the contrary, may be synergistic. Finally, preliminary analysis suggests that faunal turnover, including an important element of speciation, was elevated in the Quaternary compared with the Neogene, at least in some biomes. Macroevolutionary species selection or sorting has apparently resulted in a modern mammalian fauna enriched with fast-reproducing and/or adaptively generalist species. PMID:15101579

Lister, Adrian M

2004-01-01

269

Efficient formation of benzylic quaternary centers via palladium catalysis.  

PubMed

Four's a crowd: An efficient protocol for the formation of benzylic quaternary centers via arylation of enones using a catalyst made from Pd(O2 CCF3 )2 and 2,2'-bipyridine is developed. For cyclic substrates, catalyst loadings as low as 1 mol % Pd are enough to afford excellent yields (>90%) using a variety of arylboronic acids. In case of acyclic substrates, the addition of KSbF6 was found to improve conversions and yields. PMID:23821532

Gottumukkala, Aditya L; Suljagic, Jasmin; Matcha, Kiran; de Vries, Johannes G; Minnaard, Adriaan J

2013-09-01

270

Quaternary freshwater Ostracoda from the Great Salt Lake Basin  

E-print Network

THE UNIVERSITY OF KANSAS PALEONTOLOGICAL CONTRIBUTIONS October 23, 1975 Paper 78 QUATERNARY FRESHWATER OSTRACODA FROM THE GREAT SALT LAKE BASIN, UTAH' KENNETH H. LISTER Department of Geology, The University of Kansas, Lawrence; present address: 317... Via Anita, Redondo Beach, California ABSTRACT Ostracodes are described from two cores, each more than 200 m long taken in Quater- nary sediments of the Great Salt Lake Basin, Utah. Thirty-one species of Ostracoda in thirteen genera have been identified...

Lister, K. H.

1975-10-23

271

Multiple sources of alkanes in Quaternary oceanic sediment of Antarctica  

USGS Publications Warehouse

Normal alkanes (n-C13n-C36), isoprenoid hydrocarbons (i-C15, i-C16, i-C18, i-C19, and i-C20) triterpanes (C27C32), and (C27C29) are present in low concentrations offshore Antarctica in near-surface, Quaternary sediment of the Wilkes Land continental margin and of the western Ross Sea. The distributions of these hydrocarbons are interpreted relative to possible sources and processes. The hydrocarbons appear to be mixtures of primary and recycled material from marine and terrigenous sources. The n-alkanes are most abundant and are characterized by two distinct populations, one of probable marine origin and the other likely from terrigenous, vascular plant sources. Because the continent of Antarctica today is devoid of higher plants, the plant-derived hydrocarbons in these offshore sediments probably came from wind-blown material and recycled Antarctic sediment that contains land-plant remains from an earlier period of time. Isoprenoid hydrocarbons are partially recycled and mainly of marine origin; the dominance of pristane over phytane suggests oxic paleoenvironmental conditions. Both modern and ancient triterpanes and steranes are present, and the distribution of these indicates a mixture of primary and recycled bacterial, algal, and possible higher-plant materials. Although the sampled sediments were deposited during the Quaternary, they apparently contain a significant component of hydrocarbons of pre-Quaternary age. ?? 1987.

Kvenvolden, K.A.; Rapp, J.B.; Golan-Bac, M.; Hostettler, F.D.

1987-01-01

272

Simulation of Quaternary glacial cycles with fully interactive carbon cycle  

NASA Astrophysics Data System (ADS)

Although it is generally accepted that, as postulated by the Milankovitch theory, Earth's orbital variations play an important role in Quaternary climate dynamics, the mechanism of glacial cycles still not fully understood. Among major scientific challenges remains the understanding of the nature of 100 kyr cycles that dominated climate variability over the late part of Quaternary and a strong link between ice volume and atmospheric CO2 concentration. Here using the Earth system model of intermediate complexity CLIMBER-2 which includes all major components of the Earth system - atmosphere, ocean, land surface, northern hemisphere ice sheets, terrestrial biota and soil carbon, aeolian dust and marine biogeochemistry - we performed simulations of the Quaternary climate cycles using variations in the Earth's orbital parameters as the only prescribed climate forcing. Thanks to high computational efficiency of the CLIMBER-2 model we performed a large suite of model simulations aimed on better understanding the role of individual processes. We found that the main drivers of atmospheric CO2 evolve with time: changes in sea surface temperature and volume of bottom water of southern origin exert CO2 control during glacial inception and deglaciation, while changes in carbonate chemistry and marine biology are dominant during the first and second parts of the glacial cycles, respectively. Changes in terrestrial carbon pool play significant role during deglaciation. We also discus how paleoclimate records, such as atmospheric and deep oceanic d13C, can help to constrain model parameters and test hypotheses on the mechanism of glacial-interglacial CO2 variations.

Ganopolski, Andrey; Brovkin, Victor

2014-05-01

273

Ecological impacts of the late Quaternary megaherbivore extinctions.  

PubMed

As a result of the late Quaternary megafaunal extinctions (50,000-10,000 before present (BP)), most continents today are depauperate of megaherbivores. These extinctions were time-transgressive, size- and taxonomically selective, and were caused by climate change, human hunting, or both. The surviving megaherbivores often act as ecological keystones, which was likely true in the past. In spite of this and extensive research on the causes of the Late Quaternary Extinctions, the long-term ecological consequences of the loss of the Pleistocene megafauna remained unknown until recently, due to difficulties in linking changes in flora and fauna in paleorecords. The quantification of Sporormiella and other dung fungi have recently allowed for explicit tests of the ecological consequences of megafaunal extirpations in the fossil pollen record. In this paper, I review the impacts of the loss of keystone megaherbivores on vegetation in several paleorecords. A growing number of studies support the hypothesis that the loss of the Pleistocene megafauna resulted in cascading effects on plant community composition, vegetation structure and ecosystem function, including increased fire activity, novel communities and shifts in biomes. Holocene biota thus exist outside the broader evolutionary context of the Cenozoic, and the Late Quaternary Extinctions represent a regime shift for surviving plant and animal species. PMID:24649488

Gill, Jacquelyn L

2014-03-01

274

Isotopic fission fragment distributions as a deep probe to fusion-fission dynamics  

NASA Astrophysics Data System (ADS)

During the fission process, the atomic nucleus deforms and elongates up to the two fragments inception and their final separation at the scission deformation. The evolution of the nucleus energy with deformation defines a potential energy landscape in the multidimensional deformation space. It is determined by the macroscopic properties of the nucleus, and is also strongly influenced by the single-particle structure of the nucleus, which modifies the macroscopic energy minima. The fission fragment distribution is a direct consequence of the deformation path the nucleus has encountered, and therefore is the most genuine experimental observation of the potential energy landscape of the deforming nucleus. Very asymmetric fusion-fission reactions at energy close to the Coulomb barrier, produce well-defined conditions of the compound nucleus formation, where processes such as quasi-fission, pre-equilibrium emission and incomplete fusion are negligible. In the same time, the excitation energy is sufficient to reduce significantly structural effects, and mostly the macroscopic part of the potential is responsible for the formation of the fission fragments. We use inverse kinematics combined with a spectrometer to select and identify the fission fragments produced in 238U+12C at a bombarding energy close to and well-above the Coulomb barrier. For the first time, the isotopic yields are measured over the complete atomic-number distribution, between Z=30 and Z=63. In the experimental set-up, it is also possible to identify transfer-induced reactions, which lead to low-energy fission

Farget, F.; Caamaño, M.; Delaune, O.; Tarasov, O. B.; Derkx, X.; Schmidt, K.-H.; Amthor, A. M.; Audouin, L.; Bacri, C.-O.; Barreau, G.; Bastin, B.; Bazin, D.; Blank, B.; Benlliure, J.; Cacéres, L.; Casarejos, E.; Chbihi, A.; Fernàndez-Dominguez, B.; Gaudefroy, L.; Golabek, C.; Grévy, S.; Jurado, B.; Kamalou, O.; Lemasson, A.; Lukyanov, S.; Mittig, W.; Morrissey, D. J.; Navin, A.; Pereira, J.; Perrot, L.; Rejmund, M.; Roger, T.; Saint-Laurent, M.-G.; Savajols, H.; Schmitt, C.; Sherill, B. M.; Stodel, C.; Taieb, J.; Thomas, J.-C.; Villari, A. C.

2013-03-01

275

Study on fission blanket fuel cycling of a fusion-fission hybrid energy generation system  

NASA Astrophysics Data System (ADS)

This paper presents a preliminary study on neutron physics characteristics of a light water cooled fission blanket for a new type subcritical fusion-fission hybrid reactor aiming at electric power generation with low technical limits of fission fuel. The major objective is to study the fission fuel cycling performance in the blanket, which may possess significant impacts on the feasibility of the new concept of fusion-fission hybrid reactor with a high energy gain (M) and tritium breeding ratio (TBR). The COUPLE2 code developed by the Institute of Nuclear and New Energy Technology of Tsinghua University is employed to simulate the neutronic behaviour in the blanket. COUPLE2 combines the particle transport code MCNPX with the fuel depletion code ORIGEN2. The code calculation results show that soft neutron spectrum can yield M > 20 while maintaining TBR >1.15 and the conversion ratio of fissile materials CR > 1 in a reasonably long refuelling cycle (>five years). The preliminary results also indicate that it is rather promising to design a high-performance light water cooled fission blanket of fusion-fission hybrid reactor for electric power generation by directly loading natural or depleted uranium if an ITER-scale tokamak fusion neutron source is achievable.

Zhou, Z.; Yang, Y.; Xu, H.

2011-10-01

276

Fission-product formation in the thermal-neutron-induced fission of odd Cm isotopes  

NASA Astrophysics Data System (ADS)

Thermal-neutron-induced fission of 243Cm was studied at the Lohengrin mass separator. The light-mass peak of the fission-yield curve was investigated, and yields of masses from A=72 to A=120 were obtained. Independent-product yields were determined for nuclear charges Z=28 37 . The yield of masses in the superasymmetric region was found to be identical to other fission reactions studied at Lohengrin. The multimodal approach to fission and the macroscopic-microscopic method for the calculation of charge-distribution parameters in isobaric chains were used to analyze experimental results from the fission of 243Cm and 245Cm . A systematics on fission modes was derived from the analysis and extended to the 247Cm case. The weight of the 132Sn mode was found to decrease in 243Cm , relative to the 245Cm nucleus. A prediction of the 78Ni yield in the fission of Cm isotopes was made. The feasibility of the study of 78Ni at Lohengrin has been demonstrated.

Tsekhanovich, I.; Varapai, N.; Rubchenya, V.; Rochman, D.; Simpson, G. S.; Sokolov, V.; Fioni, G.; Mahamid, Ilham Al

2004-10-01

277

Low-mass fission detector for the fission neutron spectrum measurement  

SciTech Connect

For the fission neutron spectrum measurement, the neutron energy is determined in a time-of-flight experiment by the time difference between the fission event and detection of the neutron. Therefore, the neutron energy resolution is directly determined by the time resolution of both neutron and fission detectors. For the fission detection, the detector needs not only a good timing response but also the tolerance of radiation damage and high {alpha}-decay rate. A parallel-plate avalanche counter (PPAC) has many advantages for the detection of heavy charged particles such as fission fragments. These include fast timing, resistance to radiation damage, and tolerance of high counting rate. A PPAC also can be tuned to be insensitive to particles, which is important for experiments with - emitting actinides. Therefore, a PPAC is an ideal detector for experiments requiring a fast and clean trigger for fission. In the following sections, the description will be given for the design and performance of a new low-mass PPAC for the fission-neutron spectrum measurements at LANL.

Wu, C Y; Henderson, R; Gostic, J; Haight, R C; Lee, H Y

2010-10-20

278

Fission and geosynchronous release of the moon  

NASA Astrophysics Data System (ADS)

The paper considers the origin, fission, and geosynchronous release of the moon. The fission theory was discarded on the basis of energy considerations; however, the accretion of the earth and the radial segregation of heavy chemicals toward the center led to a differential rotation of the different layers so that during the geostationary period the moon was synchronous with respect to the surface layer and the earth-moon system has a correct angular momentum and large stability. It is possible to explain the formation of the one original earth continent and the lunar maria by a half-billion-year geosynchronous phase of the lunar motion; such a phase is possible if the moon was created by fission and if a long period of differential rotation of the earth had existed, the moon being in synchronism with the earth surface.

Grjebine, T.; Marchal, C.

1980-05-01

279

?-delayed fission and ? decay of 178Tl  

NASA Astrophysics Data System (ADS)

A detailed nuclear-decay spectroscopy study of the neutron-deficient isotope 178Tl has been performed using the highly selective Resonance Ionization Laser Ion Source and ISOLDE mass separator (CERN), which allowed a unique isobarically pure beam of 178Tl to be produced. The first identification of the ?-delayed fission of this isotope was made and its probability P?DF(178Tl)=0.15(6)% was determined. An asymmetric fission fragment mass distribution of the daughter isotope 178Hg (populated by the ? decay of 178Tl) was deduced based on the measured fission fragment energies. The fine-structure ?-decay pattern of 178Tl allowed the low-energy states in the daughter nucleus 174Au to be studied.

Liberati, V.; Andreyev, A. N.; Antalic, S.; Barzakh, A.; Cocolios, T. E.; Elseviers, J.; Fedorov, D.; Fedoseeev, V. N.; Huyse, M.; Joss, D. T.; Kalaninová, Z.; Köster, U.; Lane, J. F. W.; Marsh, B.; Mengoni, D.; Molkanov, P.; Nishio, K.; Page, R. D.; Patronis, N.; Pauwels, D.; Radulov, D.; Seliverstov, M.; Sjödin, M.; Tsekhanovich, I.; Van den Bergh, P.; Van Duppen, P.; Venhart, M.; Veselský, M.

2013-10-01

280

Energy partition in low energy fission  

E-print Network

The intrinsic excitation energy of fission fragments is dynamically evaluated in terms of the time dependent pairing equations. These equations are corroborated with two conditions. One of them fixes the number of particles and the another separates the pairing active spaces associated to the two fragments in the vicinity of the scission configuration. The fission path is obtained in the frame of the macroscopic-microscopic model. The single particle level schemes are obtained within the two center Woods-Saxon shell model. It is shown that the available intrinsic dissipated energy is not shared proportionally to the masses of the two fission fragments. If the heavy fragment possesses nucleon numbers close to the magic ones, the accumulated intrinsic excitation energy is lower than that of the light fragment.

M. Mirea

2011-02-14

281

Prompt Fission ?-rays Measured Using Liquid Scintillators  

NASA Astrophysics Data System (ADS)

The prompt ?-ray spectra from 235U(n,f) at incident energies of 1 to 20 MeV and for 235Cf(s.f.) were measured up to 4 MeV in coincidence with two parallel plate avalanche counters and the liquid scintillator array FIGARO. The unfolded ?-ray spectra from 1-4 MeV using the single value decomposition and iterative Bayesian techniques for the incident neutron energy regions corresponding to the first, second and third chance fissions were found to nearly identical and similar to the distribution from the spontaneous fission of 252Cf. General agreement with the ?-ray distributions from fission was also found with previous measurements.

Kwan, E.; Wu, C. Y.; Haight, R. C.; Lee, H. Y.; Bredeweg, T. A.; Chyzh, A.; Devlin, M.; Fotiades, N.; Gostic, J. M.; Henderson, R. A.; Jandel, M.; Laptev, A.; Nelson, R. O.; O'Donnell, J. M.; Perdue, B. A.; Taddeucci, T. N.; Ullmann, J. L.; Wender, S. A.

2014-05-01

282

A microscopic model of singlet fission.  

PubMed

Singlet fission, where an electronically excited singlet on one chromophore converts into a doubly excited state on two, has gone from a curiosity in organic photophysics to a potential pathway for increasing solar energy conversion efficiencies. Focusing on the role of solvent-induced energy level fluctuations that would be present in a dye-sensitized solar cell, we present a microscopic model for singlet fission. Starting from an electronic model Hamiltonian, we construct diabatic states in a manifold of single and double excitations with total singlet multiplicity and then develop a multilevel non-Markovian theory of dynamics for electronic populations in the presence of energy level fluctuations. Depending on the energy scales, energy gap fluctuations can either facilitate or hinder interconversion steps that lead to singlet fission. We critically assess the Markovian approximation that leads to golden rule rates and study the role of intramolecular solvation dynamics and electron transfer. PMID:22587487

Teichen, Paul E; Eaves, Joel D

2012-09-20

283

Comparative Functional Genomics of the Fission Yeasts  

PubMed Central

The fission yeast clade, comprising Schizosaccharomyces pombe, S. octosporus, S. cryophilus and S. japonicus, occupies the basal branch of Ascomycete fungi and is an important model of eukaryote biology. A comparative annotation of these genomes identified a near extinction of transposons and the associated innovation of transposon-free centromeres. Expression analysis established that meiotic genes are subject to antisense transcription during vegetative growth, suggesting a mechanism for their tight regulation. In addition, trans-acting regulators control new genes within the context of expanded functional modules for meiosis and stress response. Differences in gene content and regulation also explain why, unlike the Saccharomycotina, fission yeasts cannot use ethanol as a primary carbon source. These analyses elucidate the genome structure and gene regulation of fission yeast and provide tools for investigation across the Schizosaccharomyces clade. PMID:21511999

Rhind, Nicholas; Chen, Zehua; Yassour, Moran; Thompson, Dawn A; Haas, Brian J; Habib, Naomi; Wapinski, Ilan; Roy, Sushmita; Lin, Michael F.; Heiman, David I; Young, Sarah K; Furuya, Kanji; Guo, Yabin; Pidoux, Alison; Chen, Huei Mei; Robbertse, Barbara; Goldberg, Jonathan M.; Aoki, Keita; Bayne, Elizabeth H.; Berlin, Aaron M; Desjardins, Christopher A.; Dobbs, Edward; Dukaj, Livio; Fan, Lin; FitzGerald, Michael G; French, Courtney; Gujja, Sharvari; Hansen, Klavs; Keifenheim, Dan; Levin, Joshua Z.; Mosher, Rebecca A.; Müller, Carolin A.; Pfiffner, Jenna; Priest, Margaret; Russ, Carsten; Smialowska, Agata; Swoboda, Peter; Sykes, Sean M; Vaughn, Matthew; Vengrova, Sonya; Yoder, Ryan; Zeng, Qiandong; Allshire, Robin; Baulcombe, David; Birren, Bruce W.; Brown, William; Ekwall, Karl; Kellis, Manolis; Leatherwood, Janet; Levin, Henry; Margalit, Hanah; Martienssen, Rob; Nieduszynski, Conrad A.; Spatafora, Joseph W.; Friedman, Nir; Dalgaard, Jacob Z.; Baumann, Peter; Niki, Hironori; Regev, Aviv; Nusbaum, Chad

2011-01-01

284

Solution-processable singlet fission photovoltaic devices.  

PubMed

We demonstrate the successful incorporation of a solution-processable singlet fission material, 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene), into photovoltaic devices. TIPS-pentacene rapidly converts high-energy singlet excitons into pairs of triplet excitons via singlet fission, potentially doubling the photocurrent from high-energy photons. Low-energy photons are captured by small-bandgap electron-accepting lead chalcogenide nanocrystals. This is the first solution-processable singlet fission system that performs with substantial efficiency with maximum power conversion efficiencies exceeding 4.8%, and external quantum efficiencies of up to 60% in the TIPS-pentacene absorption range. With PbSe nanocrystal of suitable bandgap, its internal quantum efficiency reaches 170 ± 30%. PMID:25517654

Yang, Le; Tabachnyk, Maxim; Bayliss, Sam L; Böhm, Marcus L; Broch, Katharina; Greenham, Neil C; Friend, Richard H; Ehrler, Bruno

2015-01-14

285

Fission of pre-actinide nuclei  

E-print Network

A study of photofission on 181Ta nucleus induced by bremsstrahlung photons with endpoint energies of 50 and 3500 MeV has been performed. The fission yields have been measured by using the induced-activity method in an off-line analysis. The absolute photofission cross sections for the tantalum target at 50 and 3500 MeV are found to be 5.4 \\pm 1.1 microb and 0.77\\pm0.11 mb, respectively, and the corresponding deduced fissilities are (0.23\\pm0.05) x 10^{-3} and (2.9 \\pm 0.9) x 10^{-3}. Mass- and charge-yield distributions were derived from the data. The results were compared with the simulated results from CRISP code for multi-modal fission by assuming symmetrical fission mode.

A. Deppman; G. S. Karapetyan; V. Guimarães; C. Gonzales; A. R. Balabekyan; N. A. Demekhina

2014-12-12

286

Lunar surface fission power supplies: Radiation issues  

SciTech Connect

A lunar space fission power supply shield that uses a combination of lunar regolith and materials brought from earth may be optimal for early lunar outposts and bases. This type of shield can be designed such that the fission power supply does not have to be moved from its landing configuration, minimizing handling and required equipment on the lunar surface. Mechanisms for removing heat from the lunar regolith are built into the shield, and can be tested on earth. Regolith activation is greatly reduced compared with a shield that uses only regolith, and it is possible to keep the thermal conditions of the fission power supply close to these seen in free space. For a well designed shield, the additional mass required to be brought fro earth should be less than 1000 kg. Detailed radiation transport calculations confirm the feasibility of such a shield.

Houts, M.G.; Lee, S.K.

1994-07-01

287

Energy Dependence of Plutonium Fission-Product Yields  

NASA Astrophysics Data System (ADS)

A method is developed for interpolating between and/or extrapolating from two pre-neutron-emission first-chance mass-asymmetric fission-product yield curves. Measured 240Pu spontaneous fission and thermal-neutron-induced fission of 239Pu fission-product yields (FPY) are extrapolated to give predictions for the energy dependence of the n + 239Pu FPY for incident neutron energies from 0 to 16 MeV. After the inclusion of corrections associated with mass-symmetric fission, prompt-neutron emission, and multi-chance fission, model calculated FPY are compared to data and the ENDF/B-VII.1 evaluation. The ability of the model to reproduce the energy dependence of the ENDF/B-VII.1 evaluation suggests that plutonium fission mass distributions are not locked in near the fission barrier region, but are instead determined by the temperature and nuclear potential-energy surface at larger deformation.

Lestone, J. P.

2011-12-01

288

Database and Map of Quaternary Faults and Folds in Peru and its Offshore Region  

USGS Publications Warehouse

This publication consists of a main map of Quaternary faults and fiolds of Peru, a table of Quaternary fault data, a region inset map showing relative plate motion, and a second inset map of an enlarged area of interest in southern Peru. These maps and data compilation show evidence for activity of Quaternary faults and folds in Peru and its offshore regions of the Pacific Ocean. The maps show the locations, ages, and activity rates of major earthquake-related features such as faults and fault-related folds. These data are accompanied by text databases that describe these features and document current information on their activity in the Quaternary.

Machare, Jose; Fenton, Clark H.; Machette, Michael N.; Lavenu, Alain; Costa, Carlos; Dart, Richard L.

2003-01-01

289

SEDIMENTOLOGY AND GEOMORPHOLOGY OF QUATERNARY ALLUVIAL FANS WITH IMPLICATIONS TO GROWTH STRATA, LOST RIVER RANGE,  

E-print Network

SEDIMENTOLOGY AND GEOMORPHOLOGY OF QUATERNARY ALLUVIAL FANS WITH IMPLICATIONS TO GROWTH STRATA......................................................................................14 5. UPPER CEDAR CREEK ALLUVIAL FAN.............................................. 19 Surface 6. JONES CREEK ALLUVIAL FAN......................................................... 67 Surface

Lawrence, Rick L.

290

Italian hybrid and fission reactors scenario analysis  

SciTech Connect

Italy is a country where a long tradition of studies both in the fission and fusion field is consolidated; nevertheless a strong public opinion concerned with the destination of the Spent Nuclear Fuel hinders the development of nuclear power. The possibility to a severe reduction of the NSF mass generated from a fleet of nuclear reactors employing an hypothetical fusionfission hybrid reactor has been investigated in the Italian framework. The possibility to produce nuclear fuel for the fission nuclear reactors with the hybrid reactor was analyzed too.

Ciotti, M.; Manzano, J.; Sepielli, M. [ENEA CR Frascati, Via Enrico Fermi, 45, 00044, Frascati, Roma (Italy); ENEA CR casaccia, Via Anguillarese, 301, 00123, Santa Maria di Galeria, Roma (Italy)

2012-06-19

291

Angular Momentum Distribution of Fission Fragments  

NASA Astrophysics Data System (ADS)

Latest generation fission experiments provide an excellent testing ground for theoretical models. In this contribution we compare the measurements obtained with the DANCE calorimeter at LANSCE with our full-scale simulation of the primary fragment de-excitation, using the recently developed CGMF code, based on a Monte-Carlo implementation of the Hauser-Feshbach theoretical model. We compute the isomeric ratios as a function of the initial angular momentum of the fission fragments. Comparison with the available experimental data allows us to determine the initial spin distribution. Finally, we study the sensitivity to the discrete spectra input.

Stetcu, I.; Talou, P.; Kawano, T.; Jandel, M.

2014-04-01

292

Fission Theory and Semiempirical Mass Formula  

Microsoft Academic Search

The fission theory of Bohr and Wheeler employs the semiempirical mass formula with the following constants: Es(=surface energy)=14A23 Mev; x=ECoulomb2Es=(147.8)(Z2A); nuclear radius=Coulomb radius=1.47×10-13A13 cm. The experimental masses deviate systematically from the values calculated using this formula. In the present note it is shown that these differences may severely influence the results of the fission theory. A reduction of the standard

Th. A. Maris

1956-01-01

293

Reexamination of fission fragment angular distributions and the fission process: Formalism  

NASA Astrophysics Data System (ADS)

The theory of fission fragment angular distributions is examined and the universally used expression is found to be valid only under restrictive assumptions. A more general angular distribution formula is derived and applied to recent data of high spin systems. At the same time it is shown that the strong anisotropies observed from such systems can be understood without changing the essential basis of standard fission theory. The effects of reaction mechanisms other than complete fusion on fission fragment angular distributions are discussed and possible angular distribution signatures of noncompound nucleus formation are mentioned.

Bond, P. D.

1985-08-01

294

Fission-gas release from uranium nitride at high fission rate density  

NASA Technical Reports Server (NTRS)

A sweep gas facility has been used to measure the release rates of radioactive fission gases from small UN specimens irradiated to 8-percent burnup at high fission-rate densities. The measured release rates have been correlated with an equation whose terms correspond to direct recoil release, fission-enhanced diffusion, and atomic diffusion (a function of temperature). Release rates were found to increase linearly with burnups between 1.5 and 8 percent. Pore migration was observed after operation at 1550 K to over 6 percent burnup.

Weinstein, M. B.; Kirchgessner, T. A.; Tambling, T. N.

1973-01-01

295

New fission mode of the {sup 252}Cf spontaneous fission obtained with modern HPGE detectors  

SciTech Connect

The data of Independent yields of secondary fission fragment pairs (emerging after prompt neutron emission from primary fragment pairs) obtained by detecting coincidences between {gamma} rays following the spontaneous fission of {sup 252}Cf have been expanded. Our approach to estimate characteristics of the primary fragments pairs (mass and excitation energy distributions) by unfolding the yields of secondary fragment pairs is discussed. Mew model parameters were introduced and results are presented here. The new results confirmed our old assumption that in case of Mo-Ba charge split the two fission modes differing with average total kinetic energy on {approx}36 MeV are realized.

Daniel, A. V.; Ter-Akopian, G. M.; Oganessian, Yu. Ts.; Popeko, G. S. [Flerov Laboratory of Nuclear Reactions, JINR, Dubna 141980 (Russian Federation); Hamilton, J. H.; Kormicki, J.; Ramayya, A. V.; Babu, B. R. S.; Ginter, T.; Zhu, S. J. [Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235 (United States); Ma, W.-C. [Department of Physics, Mississippi State University, Mississippi State, Mississippi 39762 (United States); Rasmussen, J.; Stoyer, M. A.; Lee, I. Y.; Asztalos, S.; Chu, S. Y.; Gregorich, K. E.; Macchiavelli, A. O.; Mohar, M. F.; Prussin, S. G. [Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)] (and others)

1998-02-15

296

Fission Decay Widths for Heavy-Ion Fusion-Fission Reactions  

E-print Network

Cross-section and neutron-emission data from heavy-ion fusion-fission reactions are consistent with a Kramers-modified statistical model which takes into account the collective motion of the system about the ground state; the temperature dependence of the location of fission transition points; and the orientation degree of freedom. We see no evidence to suggest that the nuclear viscosity departs from the surface-plus-window dissipation model. The strong increase in the nuclear viscosity above a temperature of ~1 MeV deduced by others is an artifact generated by an inadequate fission model.

S. G. McCalla; J. P. Lestone

2008-01-30

297

Quaternary coastal evolution of Oman (Arabian Peninsula) - a quantitative approach  

NASA Astrophysics Data System (ADS)

The paper reviews the Quaternary coastal evolution of Oman. Emphasise is put on quantifying the different forcing factors. The plate tectonic setting, the Quaternary climate evolution, the sea-level history and the impact of natural hazards are identified as key factors of coastal evolution. The Arabian Plate is characterized by a northward movement forming a continent-continent collision zone in the west and the Makran Subduction Zone in the east. As a result differential land movement is observable in Oman. The Quaternary climate evolution is well understood. Besides other proxies notably spelothems and aeolian deposits allow to draw a consistent picture. It is understood that changes in the position of the intertropical convergence zone result in intensity-changes of the summer monsoon. These changes are related to global atmospheric circulation patterns. Data on the sea-level history are sparse; despite general assumptions of a sea-level lowstand, correlating with the last glacial maximum, resulting in terrestrial conditions within the Arabian Gulf. Furthermore, a mid-Holocene sea level highstand in the range of +2m is documented in several locations. The coastlines of Oman are affected by tsunami and hurricanes. However, almost no instrumental or historical data on the impact of such natural hazards are available due to the isolation of the country in the past. Several Quaternary deposits have been investigated in a reconnaissance survey. There is sound geological evidence for a tsunami to have affected the coastline in 1945, with the possibility of older tsunami events being also recorded in the geological record. There is strong evidence of differential land movement along the coastline; locally indicated by marine terraces in elevations of up to 400m (Rupprechter at al. 2012). By quantifying the differential land movement for numerous sites, the sea-level history will be revealed. Ultimately the data will be utilized to form the base of a modeling approach. Furthermore, a sedimentary archive of past precipitation events is documented which will allow reconstructing frequency and intensity of precipitation events and may indicate the impact of past hurricanes. It is concluded that the geological archives are suitable to quantify the forcing factors of Quaternary coastal evolution on different time scales and that the recurrence intervals of natural hazards will be revealed. Proxy data will be gained in subsequent investigations. This allows a scientific based holistic approach for an integrated coastal zone management that helps to formulate adaptation strategies with regard to global warming and expected environmental changes.

Hoffmann, G.; Rupprechter, M.; Roepert, A.; Quraishi, K. Al; Balushi, N. Al; Grützner, C.; Reicherter, K.

2012-04-01

298

Unravelling sediment pathways and volcanic spikes in the East Carpathians: a fission track thermochronology provenance study  

NASA Astrophysics Data System (ADS)

Single grain age dating of detrital sediments is a well established technique to obtain constraints on thermal history and sediment provenance of source areas. The reconstruction of major changes in the source area, due to past and ongoing tectonic activity, is of paramount importance since these changes control transport and deposition in the adjacent sinks. Since the late Neogene an unusual exhumation history has been seen in most of European orogens. Most of the current research has inferred the coupling between tectonics, climate and surface processes as responsible for topographic changes. In the same time, the Neogene volcanic activity in the Carpatho-Pannonian, with a west-to-east age progression, has major implications in basins connectivity within the source to sink Danube system. In the SE Carpathians, in an environment setting that is marked by tectonic, climatic and volcanic overprint, we apply the robust detrital zircon fission track method to constrain the sediment pathways and temporal resolution of the source area and adjacent basins. The river system draining the SE Carpathians shows a grain age distribution similar to that in the source areas. Zircon fission-track provenance ages from the foreland basin correlates to specific tectonic events in the orogen. All our zircon fission-track samples have non-reset age peaks and suggest uplifting and eroding of the more internal nappes. An eastward decreasing pattern of individual peaks has been seen, with age clusters of about 60 Ma, 100 Ma and also well defined older ones. Strong volcanic age peaks have been found for the latest Miocene samples, where the youngest age components are almost identical to the stratigraphic age of sediments. Moreover, analyzed grains clearly show inclusions, euhedral morphometry and zonations. They are likely derived from the Neogene volcanism situated in eastern margin of Transylvanian basin, and dated by K-Ar method as young as Quaternary up to 10.5 Ma. In this study we provide significant constraints on the timing of basin connectivity within the Paratethys domains that had bordered the East Carpathians Mountains. Moreover, our well defined zircon fission track age clusters are of importance for better understanding of the dynamic source to sink Danube system that controls most of the current topography of central Europe.

Trifan, Catalin; Andriessen, Paul; Matenco, Liviu

2014-05-01

299

Development and Utilization of Space Fission Power Systems  

NASA Technical Reports Server (NTRS)

Space fission power systems could enable advanced civilian space missions. Terrestrially, thousands of fission systems have been operated since 1942. In addition, the US flew a space fission system in 1965, and the former Soviet Union flew 33 such systems prior to the end of the Cold War. Modern design and development practices, coupled with 65 years of experience with terrestrial reactors, could enable the affordable development of space fission power systems for near-term planetary surface applications.

Houts, Michael; Mason, Lee S.; Palac, Donald T.; Harlow, Scott E.

2008-01-01

300

Development and Utilization of Space Fission Power Systems  

NASA Technical Reports Server (NTRS)

Space fission power systems could enable advanced civilian space missions. Terrestrially, thousands of fission systems have been operated since 1942. In addition, the US flew a space fission system in 1965, and the former Soviet Union flew 33 such systems prior to the end of the Cold War. Modern design and development practices, coupled with 65 years of experience with terrestrial reactors, could enable the affordable development of space fission power systems for near-term planetary surface applications.

Houts, Michael G.; Mason, Lee S.; Palac, Donald T.; Harlow, Scott E.

2009-01-01

301

Fission barriers in a macroscopic-microscopic model  

SciTech Connect

In the framework of the macroscopic-microscopic model, this study investigates fission barriers in the region of actinide nuclei. A very effective four-dimensional shape parametrization for fissioning nuclei is proposed. Taking, in particular, the left-right mass asymmetric and nonaxial shapes into account is demonstrated to have a substantial effect on fission barrier heights. The influence of proton versus neutron deformation differences on the potential energy landscape of fissioning nuclei is also discussed.

Dobrowolski, A.; Pomorski, K.; Bartel, J. [Theoretical Nuclear Physics Division, Marie-Curie-Sklodowska University, Lublin (Poland); Katedra Fizyki Teoretycznej, Uniwersytet M. C. Sklodowskiej, Lublin (Poland); Institut Pluridisciplinaire Hubert Curien, Universite Louis Pasteur, Strasbourg (France)

2007-02-15

302

Nuclear fissions in R and r-cooling processes  

Microsoft Academic Search

The initial condition for the r-cooling process is determined using a model of the dynamical r-process. All nuclides with Z of at least 80 on the neutron-rich side of the beta-stable line are assumed to have finite probabilities for spontaneous fission, neutron-induced fission, and beta-decay-induced fission. Rates for beta decay, neutrino energy loss, beta-decay-induced fission, and delayed neutron emission are

T. Ohnishi

1978-01-01

303

T -odd asymmetries for evaporation neutrons in nuclear fission  

Microsoft Academic Search

T-odd asymmetries in the angular distributions of evaporation neutrons emitted by thermalized fission fragments in the fission\\u000a of axially symmetric deformed nuclei by cold polarized neutrons are investigated within the quantum theory of fission. The\\u000a asymmetries in question are due to the anisotropy of angular distributions of evaporation neutrons in the center-of-mass systems\\u000a of the fission fragments, and this anisotropy

S. G. Kadmenskii; S. S. Kadmenskii; D. E. Lyubashevskii

2010-01-01

304

Fissile and fusile breeding in the thorium fusion fission hybrid  

Microsoft Academic Search

The thorium fuel cycle fissile and fusile breeding in a molten salt and a solid fuel blanket for a system consisting of fusion fuel factories coupled to fission satellites burners, is considered. The use of the thorium cycle in a fusion fission hybrid could bypass the stage of fourth generation fission breeder reactors in that the energy multiplication in the

Magdi Ragheb; Ayman Nour Eldin

2010-01-01

305

Fission-suppressed blankets for fissile fuel breeding fusion reactors  

Microsoft Academic Search

Two blanket concepts for deuterium-tritium (DT) fusion reactors are presented which maximize fissile fuel production while at the same time suppress fission reactions. By suppressing fission reactions, the reactor will be less hazardous, and therefore easier to design, develop, and license. A fusion breeder operating a given nuclear power level can produce much more fissile fuel by suppressing fission reactions.

J. D. Lee; R. W. Moir

1981-01-01

306

Enabling the Use of Space Fission Propulsion Systems  

SciTech Connect

This paper gives brief descriptions of advantages of fission technology for reaching any point in the solar system and of earlier efforts to develop space fission propulsion systems, and gives a more detailed description of the safe, affordable fission engine (SAFE) concept being pursued at the National Aeronautics and Space Administration's Marshall Space Flight Center.

Mike Houts; Melissa Van Dyke; Tom Godfroy; James Martin; Kevin Pedersen; Ricky Dickens; Ivana Hrbud; Leo Bitteker; Bruce Patton; Suman Chakrabarti; Joe Bonometti

2000-06-04

307

Multiphonon Relaxation Slows Singlet Fission in Crystalline Erik Busby,,,  

E-print Network

Multiphonon Relaxation Slows Singlet Fission in Crystalline Hexacene Erik Busby,,, Timothy C: Singlet fission, the conversion of a singlet excitation into two triplet excitations, is a viable route to improved solar-cell efficiency. Despite active efforts to understand the singlet fission mechanism, which

Hone, James

308

Fifty years of nuclear fission: Nuclear data and measurements series  

Microsoft Academic Search

This report is the written version of a colloquium first presented at Argonne National Laboratory in January 1989. The paper begins with an historical preamble about the events leading to the discovery of nuclear fission. This leads naturally to an account of early results and understanding of the fission phenomena. Some of the key concepts in the development of fission

Lynn

1989-01-01

309

SOME NEW INSIGHTS ON THE THEORY OF NUCLEAR FISSION  

Microsoft Academic Search

Experimental developments which in recent years have shown the ; deficiencies of the liquid drop model in the explanation of nuclear fission are ; summarized. The angular and mass distributions in the fission products are ; considered with respect to the collective model. The effect of individual ; particles on spontaneous fission is shown. (J.S.R.);

van der Woude

1960-01-01

310

Microscopic description of complex nuclear decay: Multimodal fission  

Microsoft Academic Search

Our understanding of nuclear fission, a fundamental nuclear decay, is still incomplete due to the complexity of the process. In this paper, we describe a study of spontaneous fission using the symmetry-unrestricted nuclear density functional theory. Our results show that the observed bimodal fission can be explained in terms of pathways in multidimensional collective space corresponding to different geometries of

A. Staszczak; A. Baran; J. Dobaczewski; Witold Nazarewicz

2009-01-01

311

PASSAGE OF FISSION PRODUCTS THROUGH THE SKIN OF TUNA  

E-print Network

PASSAGE OF FISSION PRODUCTS THROUGH THE SKIN OF TUNA SPECIAL SCIENTIFIC REPORT- FISHERIES No. 167 and Wildlife Service, John L. Farley, Director PASSAGE OF FISSION PRODUCTS THROUGH THE SKIN OF TUNA by Walter A was slow. PASSAGE OF FISSION PRODUCTS THROUGH THE SKIN OF TUNA In relation to "fallout" from nuclear -bomb

312

Protein-driven membrane stresses in fusion and fission  

E-print Network

Protein-driven membrane stresses in fusion and fission Michael M. Kozlov1 , Harvey T. McMahon2 fusion and fission become more evident if we disregard the accompanying biological processes and consider fusion or fission come from proteins andin most cases from membrane-bound proteins. In this review, we

McMahon, Harvey

313

Fission of Entangled Spins: An Electronic Structure Perspective Xintian Feng,  

E-print Network

Fission of Entangled Spins: An Electronic Structure Perspective Xintian Feng, Anatoliy V. Luzanov 61001, Ukraine *S Supporting Information ABSTRACT: Electronic structure aspects of singlet fission of singlet fission are explained. Based on the Cauchy-Schwarz inequality, we propose using the norm of one

Krylov, Anna I.

314

Fission Yeast Tel1ATM and Rad3ATR  

E-print Network

Fission Yeast Tel1ATM and Rad3ATR Promote Telomere Protection and Telomerase Recruitment Bettina A organisms, including budding and fission yeasts, Arabidopsis, Drosophila, and mammals. However, such as fission yeast and humans. Here, we demonstrate by quantitative chromatin immunoprecipitation (ChIP) assays

Nakamura, Toru M.

315

Interleaved Preparation and Output in the COMIC Fission Module  

E-print Network

Interleaved Preparation and Output in the COMIC Fission Module Mary Ellen Foster Institute, Edinburgh EH8 9LW United Kingdom M.E.Foster@ed.ac.uk Abstract We give a technical description of the fission the robust- ness of the fission module, and how it can be con- figured to support a variety of requirements

Foster, Mary Ellen

316

Membrane Fission Is Promoted by Insertion of Amphipathic Helices and  

E-print Network

Membrane Fission Is Promoted by Insertion of Amphipathic Helices and Is Restricted by Crescent BAR membrane curva- ture. Here, we investigate membrane fission by shallow hydrophobic insertions- brane fission driven by hydrophobic insertions. A quantitative assay for vesiculation reveals an antag

McMahon, Harvey

317

Fission of actinides through quasimolecular shapes Guy Royer1a  

E-print Network

Fission of actinides through quasimolecular shapes Guy Royer1a , Hongfei Zhang2 , Philippe Eudes1 the most probable fission path. The potential barrier heights agree with the experimental data, while the smaller one changes from oblate to prolate shapes. 1 Introduction The analysis of the fission

Paris-Sud XI, Université de

318

Physical, semantic and pragmatic levels for multimodal fusion and fission  

E-print Network

Physical, semantic and pragmatic levels for multimodal fusion and fission Fr´ed´eric Landragin, multimodal fission is linked to the repartition of information among several communication modalities System (IMMPS). The term `fission' is sometimes used in input, for instance when the user's utterance has

Paris-Sud XI, Université de

319

Fission barrier heights and lifetimes for heavy and superheavy nuclei  

E-print Network

Fission barrier heights and lifetimes for heavy and superheavy nuclei J. Bartel*, A. Dobrowolski for Nuclear Research, Kiev, Ukraine Abstract. Ground-state masses, fission barrier heights and a lifetimes with the Yukawa folding procedure. Fission barrier height are nicely reproduced in our approach which contains

Pomorski, Krzysztof

320

Uncertainties and Covariances of the Fission Cross Sections and the Fission Neutron Multiplicities for Actinides  

SciTech Connect

Experimental data on the fission cross sections and the fission-neutron multiplicities of actinides are analyzed on the basis of the unrecognized error-estimation method. Such an approach allows us to estimate reasonable systematic uncertainties of available data, which are underestimated by authors of most measurements as a rule. The corresponding uncertainties and covariances of evaluated data are obtained for the most important actinides in the 15-energy group representation. Differences between the present evaluations and the recent BOLNA results are discussed for the main actinides. It is shown that the fission cross section uncertainties are overestimated essentially in the BOLNA analysis for minor actinides. Uncertainties of the cross sections and the neutron multiplicities averaged over the Cf-252 fission-neutron spectrum are considered.

Gai, E.V. [Institute of Physics and Power Engineering, 239033 Obninsk (Russian Federation); Ignatyuk, A.V. [Institute of Physics and Power Engineering, 239033 Obninsk (Russian Federation)], E-mail: ignatyuk@ippe.ru

2008-12-15

321

Fission barriers and probabilities of spontaneous fission for elements with Z$\\geq$100  

E-print Network

This is a short review of methods and results of calculations of fission barriers and fission half-lives of even-even superheavy nuclei. An approvable agreement of the following approaches is shown and discussed: The macroscopic-microscopic approach based on the stratagem of the shell correction to the liquid drop model and a vantage point of microscopic energy density functionals of Skyrme and Gogny type selfconsistently calculated within Hartree-Fock-Bogoliubov method. Mass parameters are calculated in the Hartree-Fock-Bogoliubov cranking approximation. A short part of the paper is devoted to the nuclear fission dynamics. We also discuss the predictive power of Skyrme functionals applied to key properties of the fission path of $^{266}$Hs. It applies the standard techniques of error estimates in the framework of a $\\chi^2$ analysis.

Baran, A; Reinhard, P -G; Robledo, L M; Staszczak, A; Warda, M

2015-01-01

322

Fission barriers and probabilities of spontaneous fission for elements with Z$\\geq$100  

E-print Network

This is a short review of methods and results of calculations of fission barriers and fission half-lives of even-even superheavy nuclei. An approvable agreement of the following approaches is shown and discussed: The macroscopic-microscopic approach based on the stratagem of the shell correction to the liquid drop model and a vantage point of microscopic energy density functionals of Skyrme and Gogny type selfconsistently calculated within Hartree-Fock-Bogoliubov method. Mass parameters are calculated in the Hartree-Fock-Bogoliubov cranking approximation. A short part of the paper is devoted to the nuclear fission dynamics. We also discuss the predictive power of Skyrme functionals applied to key properties of the fission path of $^{266}$Hs. It applies the standard techniques of error estimates in the framework of a $\\chi^2$ analysis.

A. Baran; M. Kowal; P. -G. Reinhard; L. M. Robledo; A. Staszczak; M. Warda

2015-03-05

323

Constraining the age and magnitude of uplift in the northern National Petroleum Reserve in Alaska (NPRA)-apatite fission-track analysis of samples from three wells  

USGS Publications Warehouse

A broad, post-mid-Cretaceous uplift is defined in the northern National Petroleum Reserve in Alaska (NPRA) by regional truncation of Cretaceous strata, thermal maturity patterns, and amounts of exhumation estimated from sonic logs. Apatite fission-track (AFT) analysis of samples from three wells (South Meade No. 1, Topagoruk No. 1, and Ikpikpuk No. 1) across the eastern flank of the uplift indicates Tertiary cooling followed by Quaternary heating. Results from all three wells indicate that cooling, presumably caused by uplift and erosion, started about 75-65 Ma (latest Cretaceous-earliest Tertiary) and continued through the Tertiary Period. Data from South Meade indicate more rapid cooling after about 35-15 Ma (latest Eocene-middle Miocene) followed by a significant increase in subsurface temperature during the Quaternary, probably the result of increased heat flow. Data from Topagoruk and Ikpikpuk include subtle evidence of accelerated cooling starting in the latest Eocene-middle Miocene and possible evidence of increased temperature during the Quaternary. Subsurface temperature perturbations related to the insulating effect of permafrost may have been responsible for the Quaternary temperature increase at Topagoruk and Ikpikpuk and may have been a contributing factor at South Meade. Multiple lines of geologic evidence suggest that the magnitude of exhumation resulting from uplift and erosion is 5,000-6,500 ft at South Meade, 4,000-5,500 ft at Topagoruk, and 2,500-4,000 ft at Ikpikpuk. The results from these wells help to define the broad geometry of the uplift, which increases in magnitude from less than 1,000 ft at the Colville River delta to perhaps more than 7,000 ft along the northwestern coast of NPRA, between Point Barrow and Peard Bay. Neither the origin nor the offshore extent of the uplift, west and north of the NPRA coast, have been determined.

Houseknecht, David W.; Bird, Kenneth J.; O'Sullivan, Paul

2011-01-01

324

A Novel Route to Recognizing Quaternary Ammonium Cations Using Electrospray Mass Spectrometry  

NASA Astrophysics Data System (ADS)

Characterizing and elucidating structures is a commonplace and necessary activity in the pharmaceutical industry with mass spectrometry and NMR being the primary tools for analysis. Although many functional groups are readily identifiable, quaternary ammonium cations have proven to be difficult to unequivocally identify using these techniques. Due to the lack of an N-H bond, quaternary ammonium groups can only be detected in the 1H NMR spectra by weak signals generated from long-range 14N-H coupling, which by themselves are inconclusive evidence of a quaternary ammonium functional group. Due to their low intensity, these signals are frequently not detected. Additionally, ions cannot be differentiated in a mass spectrum as an M+ or [M + H]+ ion without prior knowledge of the compound's structure. In order to utilize mass spectrometry as a tool for determining this functionality, ion cluster formation of quaternary ammonium cations and non-quaternary amines was studied using electrospray ionization. Several mobile phase modifiers were compared; however, the addition of small amounts of trifluoroacetic acid proved superior in producing characteristic and intense [M +2TFA]- clusters for compounds containing quaternary ammonium cations when using negative electrospray. By fragmenting this characteristic ion using CID, nearly all compounds studied could be unambiguously identified as containing a quaternary ammonium cation or a non-quaternary amine attributable to the presence (non-quaternary amine) or absence (quaternary ammonium cation) of the resulting [2TFA + H]- ion in the product spectra. This method of analysis provides a rapid, novel, and reliable technique for indicating the presence of quaternary ammonium cations in order to aid in structural elucidation.

Shackman, Holly M.; Ding, Wei; Bolgar, Mark S.

2015-01-01

325

Nondestructive fission gas release measurement and analysis  

Microsoft Academic Search

Siemens Power Corporation (SPC) has performed reactor poolside gamma scanning measurements of fuel rods for fission gas release (FGR) detection for more than 10 yr. The measurement system has been previously described. Over the years, the data acquisition system, the method of spectrum analysis, and the means of reducing spectrum interference have been significantly improved. A personal computer (PC)-based multichannel

P. M. OLeary; D. R. Packard

1993-01-01

326

Search for other natural fission reactors  

Microsoft Academic Search

Precambrian uranium ores have been surveyed for evidence of other natural fission reactors. The requirements for formation of a natural reactor direct investigations to uranium deposits with large, high-grade ore zones. Massive zones with volumes approximately greater than 1 m³ and concentrations approximately greater than 20 percent uranium are likely places for a fossil reactor if they are approximately greater

K. E. Apt; J. P. Balagna; E. A. Bryant; G. A. Cowan; W. R. Daniels; R. J. Vidale

1977-01-01

327

FISSION REACTORS KEYWORDS: high-temperature  

E-print Network

conversion system, and the progress in the electrolysis cell materials field can help the econom- icalFISSION REACTORS KEYWORDS: high-temperature steam electrolysis, advanced gas reactor, supercritical CO2 cycle HYDROGEN PRODUCTION USING HIGH-TEMPERATURE STEAM ELECTROLYSIS SUPPORTED BY ADVANCED GAS

Yildiz, Bilge

328

Fission in intermediate energy heavy ion reactions  

SciTech Connect

A systematic study of reaction mechanisms at intermediate energies (50--100 MeV/A) has been performed at the Lawrence Berkeley Laboratory's BeValac using medium weight projectiles on medium and heavy element targets. A gas and plastic phoswich detector system was employed which gave large geometric coverage and a wide dynamic response. The particles identified with the gas detectors could be characterized into three components - intermediate mass fragments (IMF), fission fragments (FF) and heavy residues (HR). Major observed features are: the reaction yields are similar in the 50 to 100 MeV/A range, central collisions have high multiplicity of IMF's with broad angular correlations consistent with a large participant region, effects of final state Coulomb interactions are observed and give information on the size and temporal behavior of the source, true fission yields are dependent on target fissility and correlated with relatively peripheral collisions. Analysis of fission and evaporation yields implies limiting conditions for which fission decay remains a viable deexcitation channel. 7 figs.

Wilhelmy, J.B.; Begemann-Blaich, M.; Blaich, T.; Boissevain, J.; Fowler, M.M.; Gavron, A.; Jacak, B.V.; Lysaght, P.S.; Britt, H.C.; Fields, D.J.

1989-01-01

329

Theory of Binary and Ternary Cold Fission  

Microsoft Academic Search

We give a description of cold fision processes from 252Cf within the stationary scattering formalism. A strong dependence of binary decay widths upon the internal structure of the considered resonant state is predicted. We describe the angular distribution of 4He, 10Be and 14C in the spontaneous ternary cold fission.

D. S. Delion; A. Sandulescu; S. Misicu; W. Greiner

2003-01-01

330

Fission-fragment gamma-ray multiplicities  

SciTech Connect

The gamma ray multiplicity (M{gamma}) of fission fragments is a valuable experimental clue to the physics of the fission process in particular and the dynamics of heavy-ion collisions in general. Apparatus for measuring M{gamma} as a function of mass asymmetry was constructed and commissioned. The apparatus consisted of a time-of-flight telescope with a time resolution for fission fragments of {approx}1.5 ns and a solid angle of some 0.04 strad. The telescope was constructed using a micro-channel plate start detector and a parallel plate avalanche counter as a stop detector. Gamma rays from the fragments were detected in an array of three 5{double prime} {times} 6{double prime} NaI(Tl) detectors placed approximately 55 cm from the target. When used in beam this apparatus provided sufficient mass resolution for the detected fission fragments and allowed excellent separation of the {gamma}-rays and neutrons from the reaction on the basis of their time-of-flight.

Hook, D.E.

1987-01-01

331

MCNP6 Fission Multiplicity with FMULT Card  

Microsoft Academic Search

With the merger of MCNPX and MCNP5 into MCNP6, MCNP6 now provides all the capabilities of both codes allowing the user to access all the fission multiplicity data sets. Detailed in this paper is: (1) the new FMULT card capabilities for accessing these different data sets; (2) benchmark calculations, as compared to experiment, detailing the results of selecting these separate

Trevor Wilcox; Michael Lorne Fensin; John S. Hendricks; Michael R. James; Gregg W. McKinney

2012-01-01

332

Energy dependence of optically induced exciton fission  

Microsoft Academic Search

A general discussion of the kinematics of optically induced fission in organic crystals is presented. Explanations are given for the nonoccurrence of this phenomenon in certain systems, and a theoretical interpretation is offered for the photon energy dependence of the magnetic field effect on the prompt fluorescence of solid tetracene at 77°K. The structure observed by Moller and Pope below

C. E. Swenberg; M. A. Ratner; N. E. Geacintov

1974-01-01

333

Singlet exciton fission in a hexacene derivative.  

PubMed

Hexacene, an acene with six benzene rings, is notable for its exceptionally small triplet energy, around one third of the singlet energy. Herein, singlet fission, i.e., conversion of a singlet exciton into two triplets, is demonstrated in a thin film of hexacene derivative, employing both transient absorption spectroscopy and magnetic field effects on photocurrent. PMID:23293054

Lee, Jiye; Bruzek, Matthew J; Thompson, Nicholas J; Sfeir, Matthew Y; Anthony, John E; Baldo, Marc A

2013-03-13

334

Observe an Animation of Nuclear Fission  

NSDL National Science Digital Library

Teachers could use this resource with students to help them visualize the process of nuclear fission. Students could be encouraged to use the movie control buttons to view and review the animation, pausing whenever necessary. Although this resource was designed to supplement a specific Earth science textbook, it can be used without that text.

2010-01-01

335

Theory of Charge Dispersion in Nuclear Fission  

Microsoft Academic Search

By introducing charge asymmetry as a new dynamical collective coordinate in the asymmetric two-center shell model, the nuclear charge dispersion in the fission of 236U is calculated without using any free parameter. The agreement between theory and experiment is quite good.

Raj K. Gupta; Werner Scheid; Walter Greiner

1975-01-01

336

Random Fluctuations in a Nuclear Fission Reactor  

Microsoft Academic Search

THE theory of the stochastic dynamics of a nuclear fission reactor has been formulated by Moore1. The present investigation is concerned with the measurement of time-dependent reactor parameters, using a spectral analysis technique and the formulation of both theory and experiment for the correlation analysis and measurement of spatially dependent reactor parameters.

L. G. Kemeny; Samaun

1961-01-01

337

Fifty years with nuclear fission. Volume 1  

Microsoft Academic Search

The news of the discovery of nuclear fission, by Otto Hahn and Fritz Strassmann in Germany, was brought to the United States by Niels Bohr in January 1939. Since its discovery, the United States, and the world for that matter, has never been the same. It therefore seemed appropriate to acknowledge the fifieth anniversary of its discovery by holding a

J. W. Behrens; A. D. Carlson

1989-01-01

338

Macroscopic and microscopic aspects in nuclear fission  

Microsoft Academic Search

Nuclear macroscopic properties are determined as statistical averages and it is then recognized that several levels of macroscopic descriptions may exist. By zooming the averaging scale the gross shell structures are distinguished from the macroscopic background and a theory can be formed consistently combining both the macroscopic and microscopic features. The shell structure varies in the fissioning nucleus on its

V. Strutinsky

1989-01-01

339

THE INDUSTRIAL UTILISATION OF FISSION PRODUCTS  

Microsoft Academic Search

Industrial applications of fussion products are reviewed. In addition ; to the economic aspects of salvaging uranium fission products the increasing ; problem of storage will be partially solved. It is estimated that by 1975, 18.5 ; tons of U²³⁵ will be used in power plants of Great Britian alone each year. ; This would mean an almost equal mass

1955-01-01

340

Liquid uranium alloy-helium fission reactor  

DOEpatents

This invention teaches a nuclear fission reactor having a core vessel and at least one tandem heat exchanger vessel coupled therewith across upper and lower passages to define a closed flow loop. Nuclear fuel such as a uranium alloy in its liquid phase fills these vessels and flow passages. Solid control elements in the reactor core vessel are adapted to be adjusted relative to one another to control fission reaction of the liquid fuel therein. Moderator elements in the other vessel and flow passages preclude fission reaction therein. An inert gas such as helium is bubbled upwardly through the heat exchanger vessel operable to move the liquid fuel upwardly therein and unidirectionally around the closed loop and downwardly through the core vessel. This helium gas is further directed to heat conversion means outside of the reactor vessels to utilize the heat from the fission reaction to generate useful output. The nuclear fuel operates in the 1200.degree.-1800.degree. C. range, and even higher to 2500.degree. C., limited only by the thermal effectiveness of the structural materials, increasing the efficiency of power generation from the normal 30-35% with 300.degree.-500.degree. C. upper limit temperature to 50-65%. Irradiation of the circulating liquid fuel, as contrasted to only localized irradiation of a solid fuel, provides improved fuel utilization.

Minkov, Vladimir (Skokie, IL)

1986-01-01

341

On statistical models for fission track counts  

Microsoft Academic Search

The statistical basis for the usual analysis of fission track counts obtained by the external detector method is discussed and illustrated with examples. A consequence is that if any observed correlation between counts of spontaneous and induced tracks is due to heterogeneity in the density of uranium, then the model proposed by McGee and Johnson (1979)for assessing the experimental error

R. F. Galbraith

1981-01-01

342

Fission Energy and Other Sources of Energy  

ERIC Educational Resources Information Center

Discusses different forms of energy sources and basic reasons for the opposition to the use of atomic energy. Suggests that research efforts should also be aimed toward the fission technology to make it acceptable besides major research studies conducted in the development of alternative energy sources. (CC)

Alfven, Hannes

1974-01-01

343

After Apollo: Fission Origin of the Moon  

ERIC Educational Resources Information Center

Presents current ideas about the fission process of the Moon, including loss of mass. Saturnian rings, center of the Moon, binary stars, and uniformitarianism. Indicates that planetary formation may be best explained as a destructive, rather than a constructive process. (CC)

O'Keefe, John A.

1973-01-01

344

Liquid uranium alloy-helium fission reactor  

DOEpatents

This invention describes a nuclear fission reactor which has a core vessel and at least one tandem heat exchanger vessel coupled therewith across upper and lower passages to define a closed flow loop. Nuclear fuel such as a uranium alloy in its liquid phase fills these vessels and flow passages. Solid control elements in the reactor core vessel are adapted to be adjusted relative to one another to control fission reaction of the liquid fuel therein. Moderator elements in the other vessel and flow passages preclude fission reaction therein. An inert gas such as helium is bubbled upwardly through the heat exchanger vessel operable to move the liquid fuel upwardly therein and unidirectionally around the closed loop and downwardly through the core vessel. This helium gas is further directed to heat conversion means outside of the reactor vessels to utilize the heat from the fission reaction to generate useful output. The nuclear fuel operates in the 1200 to 1800/sup 0/C range, and even higher to 2500/sup 0/C.

Minkov, V.

1984-06-13

345

The Fission Vision: Teacher and Student Editions  

NSDL National Science Digital Library

Although they may have heard the term many times, students often have difficulty conceptualizing the process of nuclear fission. The kinesthetic simulation, as wellas the two suggested applets, are worthwhile activities for clarifying the process of nuclearfission. This free selection includes the Table of Contents, A Note from Joy Hakim, Resources for Integration and Implementation, the corresponding National Science Education Standards, and the Index.

Juliana Texley

2008-11-01

346

Angular momentum of fission fragments in low energy fission of actinides  

NASA Astrophysics Data System (ADS)

Independent isomeric yield ratios (IYR) of 128Sb, 130Sb, 132Sb, 131Te, 133Te, 132I, 134I, 136I, 135Xe, and 138Cs have been determined in fast neutron induced fission of 232Th, 238U, 240Pu, and 244Cm as well as in thermal neutron induced fission of 232U and 238Pu using radiochemical and offline ?-ray spectrometric techniques. From the IYR, fragment angular momenta (Jrms) have been deduced using a spin-dependent statistical model analysis. These data along with the literature data for 230Th?, 234U?, 236U?, 240Pu?, 242Pu?, 244Cm(SF), 246Cm?, 250Cf?, and 252Cf(SF) for fifteen even-Z fissioning systems show the following important features: (i) The Jrms 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 Jrms increase with Z2F/AF. (ii) The Jrms 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 Jrms 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 Jrms values show an anticorrelation with the elemental yields. (v) The odd-even fluctuation on Jrms does not change drastically from Th to Cf, unlike the proton odd-even effect (?p) which decreases significantly with the increase of Coulomb parameter (Z2F/A1/3F).

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

2005-01-01

347

Yields of fission products produced by thermal-neutron fission of 245Cm  

Microsoft Academic Search

Absolute yields have been determined for 105 gamma rays emitted in the decay of 95 fission products representing 54 mass chains created during thermal-neutron fission of 245Cm. These results include 17 mass chains for which no prior yield data exist. Using a Ge(Li) detector, spectra were obtained of gamma rays between 30 sec and 0.3 yr after very short irradiations

J. K. Dickens; J. W. McConnell

1981-01-01

348

Yields of fission products produced by thermal-neutron fission of 229Th  

Microsoft Academic Search

Absolute yields have been determined for 47 gamma rays emitted in the decay of 37 fission products representing 25 mass chains created during thermal-neutron fission of 229Th. Using a Ge(Li) detector, spectra were obtained of gamma rays emitted between 15 min and 0.4 yr after very short irradiations by thermal neutrons of a 15-mug sample of 229Th. On the basis

J. K. Dickens; J. W. McConnell

1983-01-01

349

Yields of fission products produced by thermal-neutron fission of ²⁴⁹Cf  

Microsoft Academic Search

Absolute yields have been determined for 107 gamma rays emitted in the decay of 97 fission products representing 54 mass chains created during thermal-neutron fission of ²⁴⁹Cf. These results include 14 mass chains for which no prior yield data exist. Using a Ge(Li) detector, spectra were obtained of gamma rays emanating from a 0.4 ..mu..g sample of ²⁴⁹Cf between 45

J. K. Dickens; J. W. McConnell

1981-01-01

350

Fission fragment energy correlation measurements for the thermal neutron fission of 239Pu and 235U  

Microsoft Academic Search

Fission fragment mass and kinetic energy distributions and mass-versus-energy correlations have been measured for the thermal neutron induced fission of 239Pu and 235U. Unwanted events were eliminated by a coherence test based on time of flight. The global mass distribution for 239Pu shows much weaker fine structure than 235U. However, for events with high total kinetic energy this fine structure

M. Asghar; F. Caïtucoli; P. Perrin; C. Wagemans

1978-01-01

351

Yields of fission products produced by thermal-neutron fission of 249Cf  

Microsoft Academic Search

Absolute yields have been determined for 107 gamma rays emitted in the decay of 97 fission products representing 54 mass chains created during thermal-neutron fission of 249Cf. These results include 14 mass chains for which no prior yield data exist. Using a Ge(Li) detector, spectra were obtained of gamma rays emanating from a 0.4 mug sample of 249Cf between 45

J. K. Dickens; J. W. McConnell

1981-01-01

352

Fission track dating of kimberlitic zircons  

USGS Publications Warehouse

The only reliable method for dating kimberlites at present is the lengthy and specialized hydrothermal procedure that extracts 206Pb and 238U from low-uranium zircons. This paper describes a second successful method by fission track dating of large single-crystal zircons, 1.0-1.5 cm in dimension. The use of large crystals overcomes the limitations imposed in conventional fission track analysis which utilizes crushed fragments. Low track densities, optical track dispersion, and the random orientation of polished surfaces in the etch and irradiation cycle are effectively overcome. Fission track ages of zircons from five African kimberlites are reported, from the Kimberley Pool (90.3 ?? 6.5 m.y.), Orapa (87.4 ?? 5.7 and 92.4 ?? 6.1 m.y.), Nzega (51.1 ?? 3.8 m.y.), Koffiefontein (90.0 ?? 8.2 m.y.), and Val do Queve (133.4 ?? 11.5 m.y.). In addition we report the first radiometric ages (707.9 ?? 59.6 and 705.5 ?? 61.0 m.y.) of crustal zircons from kimberlites in northwest Liberia. The fission track ages agree well with earlier age estimates. Most of the zircons examined in this study are zoned with respect to uranium but linear correlations are established (by regression analysis) between zones of variable uranium content, and within zones of constant uranium content (by analysis of variance). Concordance between the fission track method and the U/Pb technique is established and we concluded that track fading from thermal annealing has not taken place. Kimberlitic zircons dated in this study, therefore, record the time of eruption. ?? 1983.

Haggerty, S.E.; Raber, E.; Naeser, C.W.

1983-01-01

353

Induction of nuclear fission by high-voltage application  

E-print Network

In nuclear power generation, fissile materials are mainly used. For example, $U^{235}$ is fissile and therefore quite essential for use of nuclear energy. However, the material $U^{235}$ has very small natural abundance less than 1 %. We should seek possibility of utilizing fissionable materials such as $U^{238}$ because natural abundance of such fissionable materials is generally much larger than fissile ones. In this paper, we show that thermal neutrons with vanishing kinetic energy can induce nuclear fission when high voltage is applied to fissionable materials. To obtain this result, we use the liquid-drop model for nuclei. Finally, we propose how fissionable materials can be utilized.

Hirokazu Maruyama

2007-11-20

354

The behavior of fission products during nuclear rocket reactor tests  

SciTech Connect

Fission product release from nuclear rocket propulsion reactor fuel is an important consideration for nuclear rocket development and application. Fission product data from the last six reactors of the Rover program are collected in this paper to provide as basis for addressing development and testing issues. Fission product loss from the fuel will depend on fuel composition and reactor design and operating parameters. During ground testing, fission products can be contained downstream of the reactor. The last Rover reactor tested, the Nuclear Furnance, was mated to an effluent clean-up system that was effective in preventing the discharge of fission products into the atmosphere.

Bokor, P.C.; Kirk, W.L.; Bohl, R.J. (Los Alamos National Laboratory, MS E550, Los Alamos, New Mexico (USA))

1991-01-10

355

Fission Technology for Exploring and Utilizing the Solar System  

NASA Technical Reports Server (NTRS)

Fission technology can enable rapid, affordable access to any point in the solar system. Potential fission-based transportation options include bimodal nuclear thermal rockets, high specific energy propulsion systems, and pulsed fission propulsion systems. In-space propellant re-supply enhances the effective performance of all systems, but requires significant infrastructure development. Safe, timely, affordable utilization of first-generation space fission propulsion systems will enable the development of more advanced systems. First generation space systems will build on over 45 years of US and international space fission system technology development to minimize cost,

Houts, Mike; VanDyke, Melissa; Godfroy, Tom; Pedersen, Kevin; Martin, James; Dickens, Ricky; Salvail, Pat; Hrbub, Ivana; Schmidt, George R. (Technical Monitor)

2000-01-01

356

Fission Yield Measurements by Inductively Coupled Plasma Mass-Spectrometry  

SciTech Connect

Correct prediction of the fission products inventory in irradiated nuclear fuels is essential for accurate estimation of fuel burnup, establishing proper requirements for spent fuel transportation and storage, materials accountability and nuclear forensics. Such prediction is impossible without accurate knowledge of neutron induced fission yields. Unfortunately, the accuracy of the fission yields reported in the ENDF/B-VII.0 library is not uniform across all of the data and much of the improvement is desired for certain isotopes and fission products. We discuss our measurements of cumulative fission yields in nuclear fuels irradiated in thermal and fast reactor spectra using Inductively Coupled Plasma Mass Spectrometry.

Irina Glagolenko; Bruce Hilton; Jeffrey Giglio; Daniel Cummings; Karl Grimm; Richard McKnight

2009-11-01

357

LATE-QUATERNARY VEGETATION DYNAMICS IN NORTH AMERICA: SCALING FROM TAXA TO BIOMES  

Microsoft Academic Search

This paper integrates recent efforts to map the distribution of biomes for the late Quaternary with the detailed evidence that plant species have responded individual- istically to climate change at millennial timescales. Using a fossil-pollen data set of over 700 sites, we review late-Quaternary vegetation history in northern and eastern North America across levels of ecological organization from individual taxa

John W. Williams; Bryan N. Shuman; Thompson Webb; Patrick J. Bartlein; Phillip L. Leduc

2004-01-01

358

Late Quaternary variability of sedimentary nitrogen isotopes in the eastern South Pacific Ocean  

E-print Network

Late Quaternary variability of sedimentary nitrogen isotopes in the eastern South Pacific Ocean), Late Quaternary variability of sedimentary nitrogen isotopes in the eastern South Pacific Ocean) in the water columns of the Arabian Sea (AS) and the eastern North and South Pacific oceans (ENP; ESP) holds

Demouchy, Sylvie

359

Quaternary records of the dire wolf, Canis dirus, in North and South ROBERT G. DUNDAS  

E-print Network

skeletal elements from Rancho La Brea, comparing them with Canis lupus and dire wolf specimens from otherQuaternary records of the dire wolf, Canis dirus, in North and South America ROBERT G. DUNDAS Dundas, R. G. 1999 (September): Quaternary records of the dire wolf, Canis dirus, in North and South

Wang, Zhi "Luke"

360

Recent Progress on the Stereoselective Synthesis of Cyclic Quaternary ?-Amino Acids  

PubMed Central

The most recent papers describing the stereoselective synthesis of cyclic quaternary ?-amino acids are collected in this review. The diverse synthetic approaches are classified according to the size of the ring and taking into account the bond that is formed to complete the quaternary skeleton. PMID:20300486

Cativiela, Carlos; Ordóñez, Mario

2010-01-01

361

Quaternary deposits and landscape evolution of the central Blue Ridge of Virginia  

E-print Network

into Quaternary climatic change and landscape evolution of the central Blue Ridge Mountains. The oldest Science B.V. All rights reserved. Keywords: Landscape evolution; Blue Ridge Mountains; Terraces; DebrisQuaternary deposits and landscape evolution of the central Blue Ridge of Virginia L. Scott Eatona

Eaton, L. Scott

362

Late Quaternary faulting and historic seismicity in the western Lake Mead area, Nevada, Arizona and California  

Microsoft Academic Search

As part of a regional seismic hazard study for Reclamation dams on the northern lower Colorado River, the age and distribution of known and suspected late Quaternary faults were investigated and historic seismicity was analyzed for the western Lake Mead area. Late Quaternary faults in the area consist of the Mead Slope, Black Hills, Frenchman Mountain, and California Wash faults.

L. W. Anderson; D. R. OConnel

1993-01-01

363

Flightless ducks, giant mice and pygmy mammoths: Late Quaternary extinctions on California's Channel Islands  

Microsoft Academic Search

Explanations for the extinction of Late Quaternary megafauna are heavily debated, ranging from human overkill to climate change, disease and extraterrestrial impacts. Synthesis and analysis of Late Quaternary animal extinctions on California's Channel Islands suggest that, despite supporting Native American populations for some 13,000 years, few mammal, bird or other species are known to have gone extinct during the prehistoric

Torben C. Rick; Courtney A. Hofman; Todd J. Braje; Jesús E. Maldonado; T Scott Sillett; Kevin Danchisko; Jon M. Erlandson

2012-01-01

364

A review of Quaternary range shifts in European aquatic Coleopterageb_572 87..100  

E-print Network

of the Quaternary fossil record of Euro- pean water beetles to evaluate their geographical and temporal coverage compiled Quaternary water beetle records from public databases and published references. We included of the species. Results Our final data set included over 9000 records for 259 water beetle species. Fossil

Murcia, Universidad de

365

All-optical quaternary logic gates - An extension of binary logic gates  

NASA Astrophysics Data System (ADS)

All optical multivalued logic processors are of paramount importance in optical computing and signal processing. In this communication, the author proposes a new method of developing all-optical quaternary logic gates which are the extension of binary logic gates. To develop the quaternary logic gate the authors first coverts the quaternary frequency encoded data into equivalent binary intensity encoded data; then binary logic operations are done among the equivalent binary data, and finally the intensity encoded data outputs are converted into frequency encoded quaternary logic output. Simulation result supports the feasibility of the proposed scheme. Novelty of the scheme is that the same optical circuit is dedicated to implement any two-input quaternary logic operation only by changing two basic switches functioning as binary logic gates. Finally, the authors have cascaded these logic gates using "1×2" all-optical switches to develop quaternary logic unit by means of which any kind of quaternary logic operation as proposed in this scheme can be performed. Dense wavelength division demultiplexers (DMUX) are used here for wavelength routing purpose, and switching and frequency conversion characters of semiconductor optical amplifiers are exploited to develop very fast and secure quaternary logic unit.

Garai, Sisir Kumar

2015-04-01

366

Quaternary history of sea ice in the western Arctic Ocean based on foraminifera  

E-print Network

Quaternary history of sea ice in the western Arctic Ocean based on foraminifera Leonid Polyak a xxx Keywords: Western Arctic Ocean Foraminifers Quaternary Mid-Pleistocene Transition Sea ice history a b s t r a c t Sediment cores from the Northwind Ridge, western Arctic Ocean, including uniquely

Long, Bernard

367

Quaternary history of sea ice in the western Arctic Ocean based on foraminifera  

E-print Network

Quaternary history of sea ice in the western Arctic Ocean based on foraminifera Leonid Polyak a 4 February 2013 Keywords: Western Arctic Ocean Foraminifers Quaternary Mid-Pleistocene Transition Sea ice history a b s t r a c t Sediment cores from the Northwind Ridge, western Arctic Ocean

St-Ong, Guillaume

368

Late Quaternary stratigraphy and sedimentation patterns in the western Arctic Ocean Leonid Polyak a,  

E-print Network

Late Quaternary stratigraphy and sedimentation patterns in the western Arctic Ocean Leonid Polyak a Article history: Accepted 17 March 2009 Available online xxxx Keywords: Arctic Ocean sediment stratigraphy sedimentary environments Late Quaternary glaciations Sediment cores from the western Arctic Ocean obtained

Howat, Ian M.

369

Dating late Quaternary planktonic foraminifer Neogloboquadrina pachyderma from the Arctic Ocean by using amino acid racemization  

E-print Network

Dating late Quaternary planktonic foraminifer Neogloboquadrina pachyderma from the Arctic Ocean was determined by using independently dated sediment cores from the Arctic Ocean. The racemization rates calibrated for the last 150 ka using 14 C ages and the emerging Quaternary chronostratigraphy of Arctic Ocean

Howat, Ian M.

370

Shoreline and Lacustrine Records of Late Quaternary Climate Change in the Chihuahuan Desert, Mexico  

Microsoft Academic Search

Spatial and temporal patterns of Quaternary moisture and temperature variability in northern Mexico are difficult to reconstruct given the paucity of continuous, long-term Quaternary climate records from the region. Preliminary shoreline age dates and a pair of lacustrine sediment cores from Laguna Fresnal in northern Chihuahua, Mexico, record climate-driven variations in both lake level and sedimentologic input. Reeves (1969) first

P. J. Castiglia; P. J. Fawcett

2001-01-01

371

Catalytic enantioselective Nazarov cyclization: construction of vicinal all-carbon-atom quaternary stereocenters.  

PubMed

The diastereoselective asymmetric synthesis of vicinal all-carbon-atom quaternary stereocenters is a challenging problem in organic synthesis for which only few solutions have been described. A catalytic asymmetric Nazarov cyclization of fully substituted dienones that provides cyclopentenone derivatives with vicinal quaternary stereocenters in high optical purity and as single diastereoisomers is now reported. PMID:24838340

Jolit, Anais; Walleser, Patrick M; Yap, Glenn P A; Tius, Marcus A

2014-06-10

372

An aminostratigraphy for the British Quaternary based on Bithynia opercula  

PubMed Central

Aminostratigraphies of Quaternary non-marine deposits in Europe have been previously based on the racemization of a single amino acid in aragonitic shells from land and freshwater molluscs. The value of analysing multiple amino acids from the opercula of the freshwater gastropod Bithynia, which are composed of calcite, has been demonstrated. The protocol used for the isolation of intra-crystalline proteins from shells has been applied to these calcitic opercula, which have been shown to more closely approximate a closed system for indigenous protein residues. Original amino acids are even preserved in bithyniid opercula from the Eocene, showing persistence of indigenous organics for over 30 million years. Geochronological data from opercula are superior to those from shells in two respects: first, in showing less natural variability, and second, in the far better preservation of the intra-crystalline proteins, possibly resulting from the greater stability of calcite. These features allow greater temporal resolution and an extension of the dating range beyond the early Middle Pleistocene. Here we provide full details of the analyses for 480 samples from 100 horizons (75 sites), ranging from Late Pliocene to modern. These show that the dating technique is applicable to the entire Quaternary. Data are provided from all the stratotypes from British stages to have yielded opercula, which are shown to be clearly separable using this revised method. Further checks on the data are provided by reference to other type-sites for different stages (including some not formally defined). Additional tests are provided by sites with independent geochronology, or which can be associated with a terrace stratigraphy or biostratigraphy. This new aminostratigraphy for the non-marine Quaternary deposits of southern Britain provides a framework for understanding the regional geological and archaeological record. Comparison with reference to sites yielding independent geochronology, in combination with other lines of evidence, allows tentative correlation with the marine oxygen isotope record. PMID:23396683

Penkman, Kirsty E.H.; Preece, Richard C.; Bridgland, David R.; Keen, David H.; Meijer, Tom; Parfitt, Simon A.; White, Tom S.; Collins, Matthew J.

2013-01-01

373

A transferable model for singlet-fission kinetics  

NASA Astrophysics Data System (ADS)

Exciton fission is a process that occurs in certain organic materials whereby one singlet exciton splits into two independent triplets. In photovoltaic devices these two triplet excitons can each generate an electron, producing quantum yields per photon of >100% and potentially enabling single-junction power efficiencies above 40%. Here, we measure fission dynamics using ultrafast photoinduced absorption and present a first-principles expression that successfully reproduces the fission rate in materials with vastly different structures. Fission is non-adiabatic and Marcus-like in weakly interacting systems, becoming adiabatic and coupling-independent at larger interaction strengths. In neat films, we demonstrate fission yields near unity even when monomers are separated by >5 Å. For efficient solar cells, however, we show that fission must outcompete charge generation from the singlet exciton. This work lays the foundation for tailoring molecular properties like solubility and energy level alignment while maintaining the high fission yield required for photovoltaic applications.

Yost, Shane R.; Lee, Jiye; Wilson, Mark W. B.; Wu, Tony; McMahon, David P.; Parkhurst, Rebecca R.; Thompson, Nicholas J.; Congreve, Daniel N.; Rao, Akshay; Johnson, Kerr; Sfeir, Matthew Y.; Bawendi, Moungi G.; Swager, Timothy M.; Friend, Richard H.; Baldo, Marc A.; van Voorhis, Troy

2014-06-01

374

Fifty years of nuclear fission: Nuclear data and measurements series  

SciTech Connect

This report is the written version of a colloquium first presented at Argonne National Laboratory in January 1989. The paper begins with an historical preamble about the events leading to the discovery of nuclear fission. This leads naturally to an account of early results and understanding of the fission phenomena. Some of the key concepts in the development of fission theory are then discussed. The main theme of this discussion is the topography of the fission barrier, in which the interplay of the liquid-drop model and nucleon shell effects lead to a wide range of fascinating phenomena encompassing metastable isomers, intermediate-structure effects in fission cross-sections, and large changes in fission product properties. It is shown how study of these changing effects and theoretical calculations of the potential energy of the deformed nucleus have led to broad qualitative understanding of the nature of the fission process. 54 refs., 35 figs.

Lynn, J.E.

1989-06-01

375

Conservation of Isospin in Neutron-Rich Fission Fragments  

E-print Network

On the occasion of the $75^{th}$ anniversary of the fission phenomenon, we present a surprisingly simple result which highlights the important role of isospin and its conservation in neutron rich fission fragments. We have analysed the fission fragment mass distribution from two recent heavy-ion reactions $^{238}$U($^{18}$O,f) and $^{208}$Pb($^{18}$O,f) as well as a thermal neutron fission reaction $^{245}$Cm(n$^{th}$,f). We find that the conservation of the total isospin explains the overall trend in the observed relative yields of fragment masses in each fission pair partition. The isospin values involved are very large making the effect dramatic. The findings open the way for more precise calculations of fission fragment distributions in heavy nuclei and may have far reaching consequences for the drip line nuclei, HI fusion reactions, and calculation of decay heat in the fission phenomenon.

Jain, Ashok Kumar; Maheshwari, Bhoomika

2014-01-01

376

Conservation of Isospin in Neutron-rich Fission Fragments  

NASA Astrophysics Data System (ADS)

On the occasion of the 75 anniversary of the fission phenomenon, we present a surprisingly simple result which highlights the important role of isospin and its conservation in neutron rich fission fragments. We have analysed the fission fragment mass distribution from two recent heavyion reactions 238U(18O,f) and 208Pb(18O,f) as well as a thermal neutron fission reaction 245Cm(n,f). We find that the conservation of the total isospin explains the overall trend in the observed relative yields of fragment masses in each fission pair partition. The isospin values involved are very large making the effect dramatic. The findings open the way for more precise calculations of fission fragment distributions in heavy nuclei and may have far reaching consequences for the drip line nuclei, HI fusion reactions, and calculation of decay heat in the fission phenomenon.

Jain, A. K.; Choudhury, D.; Maheshwari, B.

2014-06-01

377

A transferable model for singlet-fission kinetics.  

PubMed

Exciton fission is a process that occurs in certain organic materials whereby one singlet exciton splits into two independent triplets. In photovoltaic devices these two triplet excitons can each generate an electron, producing quantum yields per photon of >100% and potentially enabling single-junction power efficiencies above 40%. Here, we measure fission dynamics using ultrafast photoinduced absorption and present a first-principles expression that successfully reproduces the fission rate in materials with vastly different structures. Fission is non-adiabatic and Marcus-like in weakly interacting systems, becoming adiabatic and coupling-independent at larger interaction strengths. In neat films, we demonstrate fission yields near unity even when monomers are separated by >5 Å. For efficient solar cells, however, we show that fission must outcompete charge generation from the singlet exciton. This work lays the foundation for tailoring molecular properties like solubility and energy level alignment while maintaining the high fission yield required for photovoltaic applications. PMID:24848234

Yost, Shane R; Lee, Jiye; Wilson, Mark W B; Wu, Tony; McMahon, David P; Parkhurst, Rebecca R; Thompson, Nicholas J; Congreve, Daniel N; Rao, Akshay; Johnson, Kerr; Sfeir, Matthew Y; Bawendi, Moungi G; Swager, Timothy M; Friend, Richard H; Baldo, Marc A; Van Voorhis, Troy

2014-06-01

378

Multimodal Fission in Heavy-Ion Induced Reactions  

SciTech Connect

Mass, energy and folding angle distributions of the fission fragments as well as multiplicities of neutron and gamma-quanta emissions accompanying the fission process were measured for fission of 226Th, 227Pa and 234Pu compound nuclei produced in reactions with 18O and 26Mg projectiles over a wide energy range. Data were analyzed with respect to the presence of fission modes. Asymmetric fission was observed even at very high initial excitation for all the measured systems. The so-called fission mode S1 (caused by the proton shell Z{approx}50 and neutron shell N{approx}82 in heavy fragment) was found to be dominant in asymmetric fission of 234Pu. Reactions with not full linear momentum transfer were observed in the folding spectra for all the measured systems.

Pokrovskiy, I. V.; Bogachev, A. A.; Iitkis, M. G.; Iitkis, J. M.; Kondratiev, N. A.; Kozulin, E. M. [Flerov Laboratory of Nuclear Reaction, Joint Institute for Nuclear Research, 141980, Dubna (Russian Federation); Dorvaux, O.; Rowley, N.; Schmitt, Ch.; Stuttge, L. [Instutut de Recherches Subatomiques, IN2P3-CNR/, BP28, F-67037, Strasbourg (France); Hanappe, F.; Kinnard, V. [Universite Libre de Bruxelles, B1050, Brussels (Belgium)

2006-08-14

379

Subroutines to Simulate Fission Neutrons for Monte Carlo Transport Codes  

E-print Network

Fortran subroutines have been written to simulate the production of fission neutrons from the spontaneous fission of 252Cf and 240Pu, and from the thermal neutron induced fission of 239Pu and 235U. The names of these four subroutines are getnv252, getnv240, getnv239, and getnv235, respectively. These subroutines reproduce measured first, second, and third moments of the neutron multiplicity distributions, measured neutron-fission correlation data for the spontaneous fission of 252Cf, and measured neutron-neutron correlation data for both the spontaneous fission of 252Cf and the thermal neutron induced fission of 235U. The codes presented here can be used to study the possible uses of neutron-neutron correlations in the area of transparency measurements and the uses of neutron-neutron correlations in coincidence neutron imaging.

J. P. Lestone

2014-09-17

380

Conservation of Isospin in Neutron-Rich Fission Fragments  

E-print Network

On the occasion of the $75^{th}$ anniversary of the fission phenomenon, we present a surprisingly simple result which highlights the important role of isospin and its conservation in neutron rich fission fragments. We have analysed the fission fragment mass distribution from two recent heavy-ion reactions $^{238}$U($^{18}$O,f) and $^{208}$Pb($^{18}$O,f) as well as a thermal neutron fission reaction $^{245}$Cm(n$^{th}$,f). We find that the conservation of the total isospin explains the overall trend in the observed relative yields of fragment masses in each fission pair partition. The isospin values involved are very large making the effect dramatic. The findings open the way for more precise calculations of fission fragment distributions in heavy nuclei and may have far reaching consequences for the drip line nuclei, HI fusion reactions, and calculation of decay heat in the fission phenomenon.

Ashok Kumar Jain; Deepika Choudhury; Bhoomika Maheshwari

2014-08-11

381

Fission fragment energy correlation measurements for the thermal neutron sub-barrier fission of 237Np and above-the-barrier fission of 235U  

Microsoft Academic Search

Fission fragment mass and kinetic energy distributions and mass-versus-energy correlations have been measured at the Grenoble high-flux reactor for the thermal neutron induced sub-barrier fission and above-the-barrier fission of 237Np and 235U, respectively. Unwanted events were eliminated by careful timing. In the case of 237Np(nth, f), the two odd particles (one proton and one neutron) are, on the average, shared

M. Asghar; P. D'Hondt; C. Guet; P. Perrin; C. Wagemans

1977-01-01

382

Strontium isotopes in Quaternary basalts of southeastern California  

USGS Publications Warehouse

Strontium isotopic variations (87Sr/86Sr of 0.7029 to 0.7052) in Quaternary basalts of southeastern California, USA, are not readily explained by assimilation of crustal material similar to that contained as xenoliths in the basalt. Isotopic differences between chrome diopside (0.7016) and olivine (0.7087) from a lherzolite xenolith suggest that the isotopic variations in the basalts may be inherited from the source regions or modified by the upper parts of the mantle that were traversed by the lavas. ?? 1970.

Peterman, Z.E.; Carmichael, I.S.E.; Smith, A.L.

1970-01-01

383

Design of quaternary Ir-Nb-Ni-Al refractory superalloys  

Microsoft Academic Search

We propose a method for developing new quaternary Ir-Nb-Ni-Al refractory superalloys for ultra-high-temperature uses, by mixing\\u000a two types of binary alloys, Ir-20 at. pct Nb and Ni-16.8 at. pct Al, which contain fcc\\/L12 two-phase coherent structures. For alloys of various Ir-Nb\\/Ni-Al compositions, we analyzed the microstructure and measured\\u000a the compressive strengths. Phase analysis indicated that three-phase equilibria—fcc, Ir3Nb-L12, and Ni3Al-L12—existed

X. H. Yu; Y. Yamabe-Mitarai; Y. Ro; H. Harada

2000-01-01

384

Charophytes as lacustrine biomarkers during the quaternary in North Africa  

NASA Astrophysics Data System (ADS)

The use of charophytes as biomarkers is discussed with emphasis on the differences in study methods for cosmopolitan and ecotype species. A first extensive inventory of Quaternary deposits of charophytes in Africa north of the equator comprising 18 sites from Senegal to the Sudan is drawn up with data on spatial and temporal distribution. The existence of relatively deep cold lakes in the Holocene is shown by the frequent presence of specimens of cold flora no longer present in Africa today. All the original data show the complementary nature of the study of fossil Charophyta for the multidisciplinary reconstitution of palaeoenvironments.

Soulié-Märsche, I.

385

Quaternary Fault and Fold Database for the United States: California  

NSDL National Science Digital Library

This interactive map shows the major fault systems of the Quaternary for the State of California. It is subdivided into 1x2 degree sheets, each of which is linked to a more detailed map. Users can select a sheet and see an enlargement of the area. Individual fault systems are numbered and keyed to a legend which provides a link to a written synopsis of information for the fault, including fault type and geologic history. Links are also provided to more extensive reports for the faults, including a "complete" report with references.

386

Arctic-alpine blockfields in northern Sweden: Quaternary not Neogene  

NASA Astrophysics Data System (ADS)

Slowly-eroding, blockfield-mantled, non-glacial surface remnants may serve as markers against which to determine Quaternary glacial erosion volumes in high latitude mountain settings. To investigate this potential utility of these surfaces, chemical weathering, erosion rates, and origins of mountain blockfields are investigated in northern Sweden. This is done, firstly, by assessing the intensity of regolith chemical weathering along altitudinal transects descending from three blockfield-mantled summits. Clay/silt ratios, secondary mineral assemblages determined through X-ray diffraction, and the presence of chemically weathered grains visible on scanning electron microscopy, in fine matrix samples collected from pits excavated along the transects are each used for this purpose. Secondly, erosion rates and total surface histories of two of the summits are inferred from concentrations of in situ-produced cosmogenic 10Be and 26Al in quartz at the blockfield surface. An interpretative model is adopted that includes temporal variations in nuclide production rates through surface burial by glacial ice and glacial isostasy-induced elevation changes of the blockfield surfaces. Together, our data indicate that these blockfields are not derived from remnants of intensely weathered Neogene weathering profiles, as is commonly considered. Evidence for this interpretation includes minor chemical weathering in each of the three examined blockfields, despite some differences according to slope position. In addition, average erosion rates of ∼16.2 mm ka-1 and ∼6.7 mm ka-1, calculated for two blockfield-mantled summits, are low but of sufficient magnitude to remove present blockfield mantles, of up to a few meters in thickness, within a late-Quaternary timeframe. Hence, blockfield mantles appear to be replenished by regolith formation through, primarily physical, weathering processes that have operated during the Quaternary. Erosion rates remain low enough, however, for blockfield-mantled, non-glacial surface remnants to provide reasonable landscape markers against which to contrast Quaternary erosion volumes in surrounding glacial landscape elements. The persistence of blockfield mantles over a number of glacial-interglacial cycles and an apparently low likelihood that they can re-establish on glacially eroded bedrock, also discounts the operation of a "glacial buzz-saw" on surface remnants that are presently perceived as non-glacial. These interpretations are tempered though by outstanding questions concerning the composition of preceding Neogene regoliths and why they have apparently been comprehensively removed from these remnant non-glacial surfaces. It remains possible that periglacial erosion of perhaps more intensely weathered Neogene regoliths was high during the Pliocene-Pleistocene transition to colder conditions and that periglacial processes reshaped non-glacial surface remnants largely before the formation of blockfield armours.

Goodfellow, B. W.; Stroeven, A. P.; Fabel, D.; Fredin, O.; Derron, M.-H.; Bintanja, R.; Caffee, M. W.

2014-02-01

387

Tandem mass spectrometric analysis of quaternary ammonium pesticides.  

PubMed

A detailed MS(n) study on an ion trap instrument of the quaternary ammonium pesticides paraquat, diquat, difenzoquat, mepiquat and chlormequat reveals a number of ions not reported previously, and has allowed examination of the fragmentation pathways. A number of transitions that are highly specific to each quat have been identified. Optimal ion trap operating conditions determined using Simplex optimisation can promote either detection of a particular fragmentation transition or a range of MS/MS product ions with a high overall signal response. Thus, fragmentation conditions were optimised to enhance the specificity or sensitivity of MS/MS methods. PMID:11319792

Evans, C S; Startin, J R; Goodall, D M; Keely, B J

2001-01-01

388

Distribution of Prompt Neutron Emission Probability for Fission Fragments in Spontaneous Fission of 252Cf and 244,248Cm  

SciTech Connect

Neutrons emitted in fission events were measured separately for each complementary fragment in correlation with fission fragment energies. Two high-efficiency Gd-loaded liquid scintillator tanks were used for neutron registration. Fission fragment energies were measured using a twin Frisch gridded ionization chamber with a pinhole collimator. The neutron multiplicity distributions were obtained for each value of the fission fragment mass and energy and corrected for neutron registration efficiency, background, and pile-up. The dependency of these distributions on fragment mass and energy for different energy and mass bins as well as mass and energy distribution of fission fragments are presented and discussed.

Vorobyev, A.S.; Shcherbakov, O.A. [Petersburg Nuclear Physics Institute, Gatchina, Leningrad district, 188300 (Russian Federation); Dushin, V.N.; Jakovlev, V.A.; Kalinin, V.A.; Petrov, B.F. [V.G. Khlopin Radium Institute, St. Petersburg, 194021 (Russian Federation); Hambsch, F.-J. [EC-JRC-Institute for Reference Materials and Measurements Retieseweg 111, B-2440, Geel (Belgium); Laptev, A.B. [Petersburg Nuclear Physics Institute, Gatchina, Leningrad district, 188300 (Russian Federation); Japan Nuclear Cycle Development Institute, Tokai-mura, Naka-gun, Ibaraki, 319-1194 (Japan)

2005-05-24

389

Late Quaternary geomorphology and soils in Crater Flat, Yucca mountain area, southern Nevada  

SciTech Connect

Crater Flat is an alluvium-filled structural basin on the west side of Yucca Mountain, Nevada, which is under consideration for a high-level nuclear waste repository. North-trending, late Quaternary faults offset alluvium in Crater Flat both along the canyons of the western flanks of Yucca Mountain and out on the piedmont slope. We believe the initial lack of young offsets at Yucca Mountain was in part due to unrecognized late Quaternary stratigraphy. We hypothesize that alluviation in the Yucca Mountain region was more active during the late Quaternary than previously thought. Several techniques were tried to test this hypothesis. Results are compared with previous soils and surface-exposure dating studies, and correlated to stratigraphy of other late Quaternary units in the southern Nevada, Death Valley, and Mojave Desert areas, and provide new stratigraphic data relevant to understanding climatic-alluvial processes in the Basin and Range Province during the late Quaternary. 76 refs., 7 figs., 6 tabs.

Peterson, F.F.; Bell, J.W.; Ramelli, A.R. [Univ. of Nevada, Reno, NV (United States)] [Univ. of Nevada, Reno, NV (United States); Dorn, R.I. [Arizona State Univ., Tempe, AZ (United States)] [Arizona State Univ., Tempe, AZ (United States); Ku, T.L. [Univ. of Southern California, Los Angeles, CA (United States)] [Univ. of Southern California, Los Angeles, CA (United States)

1995-04-01

390

Fission studies of secondary beams from relativistic uranium projectiles: The proton even-odd effect in fission fragment charge yields  

SciTech Connect

Nuclear-charge yields of fragments produced by fission of neutron-deficient isotopes of uranium, protactinium, actinium, and radium have been measured. These radioactive isotopes were produced as secondary beams, and electromagnetic fission was induced in a lead target with an average excitation energy around 11 MeV. The local even-odd effect in symmetric and in asymmetric fission of thorium isotopes is found to be independent of Z{sup 2}/A. The charge yields of the fission fragments of the odd-Z fissioning protactinium and actinium show a pronounced even-odd effect. In asymmetric fission the unpaired proton predominantly sticks to the heavy fragment. A statistical model based on the single-particle level density at the Fermi energy is able to reproduce the overall trend of the local even-odd effects both in even-Z and odd-Z fissioning systems.

Junghans, A. R.; Benlliure, J.; Schmidt, K.-H.; Voss, B. [GSI Darmstadt, Planckstrsse 1, D-64291 Darmstadt (Germany); Boeckstiegel, C.; Clerc, H.-G.; Grewe, A.; Heinz, A.; Jong, M. de; Mueller, J.; Steinhaeuser, S. [Institut fuer Kernphysik, Technische Universitaet Darmstadt, Schlossgartenstrasse 9, D-64289 Darmstadt (Germany); Pfuetzner, M. [Institute of Experimental Physics, University of Warsaw, Ul Hoza 69, 00-381 Warszawa (Poland)

1999-09-02

391

A correlated electron view of singlet fission.  

PubMed

Singlet fission occurs when a single exciton splits into multiple electron-hole pairs, and could dramatically increase the efficiency of organic solar cells by converting high energy photons into multiple charge carriers. Scientists might exploit singlet fission to its full potential by first understanding the underlying mechanism of this quantum mechanical process. The pursuit of this fundamental mechanism has recently benefited from the development and application of new correlated wave function methods. These methods-called restricted active space spin flip-can capture the most important electron interactions in molecular materials, such as acene crystals, at low computational cost. It is unrealistic to use previous wave function methods due to the excessive computational cost involved in simulating realistic molecular structures at a meaningful level of electron correlation. In this Account, we describe how we use these techniques to compute single exciton and multiple exciton excited states in tetracene and pentacene crystals in order to understand how a single exciton generated from photon absorption undergoes fission to generate two triplets. Our studies indicate that an adiabatic charge transfer intermediate is unlikely to contribute significantly to the fission process because it lies too high in energy. Instead, we propose a new mechanism that involves the direct coupling of an optically allowed single exciton to an optically dark multiexciton. This coupling is facilitated by intermolecular motion of two acene monomers that drives nonadiabatic population transfer between the two states. This transfer occurs in the limit of near degeneracies between adiabatic states where the Born-Oppenheimer approximation of fixed nuclei is no longer valid. Existing theories for singlet fission have not considered this type of coupling between states and, therefore, cannot describe this mechanism. The direct mechanism through intermolecular motion describes many experimentally observed characteristics of these materials, such as the ultrafast time scale of photobleaching and triplet generation during singlet fission in pentacene. We believe this newly discovered mechanism provides fundamental insight to guide the creation of new solar materials that exhibit high efficiencies through multiple charge generation. PMID:23427823

Zimmerman, Paul M; Musgrave, Charles B; Head-Gordon, Martin

2013-06-18

392

Historical distribution of Sundaland's Dipterocarp rainforests at Quaternary glacial maxima.  

PubMed

The extent of Dipterocarp rainforests on the emergent Sundaland landmass in Southeast Asia during Quaternary glaciations remains a key question. A better understanding of the biogeographic history of Sundaland could help explain current patterns of biodiversity and support the development of effective forest conservation strategies. Dipterocarpaceae trees dominate the rainforests of Sundaland, and their distributions serve as a proxy for rainforest extent. We used species distribution models (SDMs) of 317 Dipterocarp species to estimate the geographic extent of appropriate climatic conditions for rainforest on Sundaland at the last glacial maximum (LGM). The SDMs suggest that the climate of central Sundaland at the LGM was suitable to sustain Dipterocarp rainforest, and that the presence of a previously suggested transequatorial savannah corridor at that time is unlikely. Our findings are supported by palynologic evidence, dynamic vegetation models, extant mammal and termite communities, vascular plant fatty acid stable isotopic compositions, and stable carbon isotopic compositions of cave guano profiles. Although Dipterocarp species richness was generally lower at the LGM, areas of high species richness were mostly found off the current islands and on the emergent Sunda Shelf, indicating substantial species migration and mixing during the transitions between the Quaternary glacial maxima and warm periods such as the present. PMID:25385612

Raes, Niels; Cannon, Charles H; Hijmans, Robert J; Piessens, Thomas; Saw, Leng Guan; van Welzen, Peter C; Slik, J W Ferry

2014-11-25

393

Distribution and metabolism of quaternary amines in salt marshes  

NASA Technical Reports Server (NTRS)

Quaternary amines such as glycine betaine (GBT) are common osmotically active solutes in much of the marine biota. GBT is accumulated by various bacteria, algae, higher plants, invertebrates, and vertebrates in response to salinity or water stresses; in some species, GBT occurs at tens to hundreds of millimolar concentrations and can account for a significant fraction of total nitrogen. Initial studies suggest that GBT is readily converted to two potential methane precursors, trimethylamine (TMA) and acetate, in anoxic sediments. TMA is apparently the most important methane precursor in surface sediments containing sulfate reducing bacteria. In salt marshes, the bulk of the methane formed may be due to the metabolism of TMA rather than other substrates. Current research is focussed on testing this hypothesis and on determining the role of quaternary amino osmoregulatory solutes in methane fluxes from marine environments. Preliminary studies have dealt with several problems: (1) determination of GBT concentrations in the dominant flora and fauna of salt marshes; (2) synthesis of radiolabelled GBT for metabolic studies; and (3) determination of fates of BGT in marine sediments using radiotracers. Both GC and HPLC techniques have been used to assay GBT concentrations in plant and animal tissues. S. alterniflora is probably the only significant source of GBT (and indirectly of methane) since the biomass and distribution of most other species is limited. Current estimates suggest that S. alterniflora GBT could account for most of the methane efflux from salt marshes.

King, Gary M.

1985-01-01

394

Ecostratigraphic datums and sequence stratigraphy: Application to the marine Quaternary  

SciTech Connect

The marine Quaternary is characterized by few evolutionary appearances and extinctions of planktonic foraminifera. Because climatic fluctuations are a fundamental characteristic of Pleistocene, however, better stratigraphic resolution of the marine Quaternary can be gained by the establishment of biozones based on climatically controlled foraminiferal assemblages. Utilizing relative abundances of the warm-water Globorotalia menardii complex and temperature-water G. inflata, supplemented by left- and right-coiling varieties of G. truncatulinoides, the authors have subdivided the prezone-W Pleistocene of the tropical Atlantic (Core V16-205), Caribbean Sea (DSDP Core 502B), and northeast Gulf of Mexico (ODP Core 625B, Eureka Core E67-135) into 17 subzones, each with an average duration of {approximately}100,000 yrs. The subzones appear to reflect water mass shifts and disjunct species distributions resulting from expansion and contraction of northern hemisphere ice sheets. Hence, subzonal boundaries should also reflect change in eustatic sea level and sequence boundaries. Indeed, graphic correlation of the subzones, along with biostratigraphic markers and paleomagnetic and oxygen isotope datums, reveals changes in sediment accumulation rate (especially on the continental slope) and missing section, as well as intervals of deformation (core breaks) that affect the occurrence of subzonal boundaries and biostratigraphic markers.

Martin, R.E. (Univ. of Delaware, Neward (United States)); Neff, E. (Univ. of Rhode Island, Narragansett (United States)); Johnson, G.W. (Hart Environmental Management, Pennsauken, NJ (United States)); Krantz, D. (Univ. of Delaware, Lewes (United States))

1991-03-01

395

Late Quaternary terrestrial vertebrate coprolites from New Zealand  

NASA Astrophysics Data System (ADS)

Over the past decade, concerted efforts to find and study Late Quaternary terrestrial vertebrate coprolites in New Zealand have revealed new insights into the diets and ecologies of New Zealand's prehistoric birds. Here, we provide a broader review of the coprolites found in natural (non-archaeological) Late Quaternary deposits from New Zealand. We summarise the morphological diversity of the coprolites, and discuss the taphonomy of the sites in which they are found. Since the 1870s more than 2000 coprolites have been discovered from 30 localities, all restricted to the South Island. The distribution of coprolite localities appears to reflect the presence of geological and climatic factors that enhance the potential for coprolite preservation; coprolites require dry conditions for preservation, and have been found on the ground surface within drafting cave entrances and at shallow (<300 mm) depths beneath rock overhangs with a northerly aspect. We classify the coprolites into eleven morphotypes, each of which may represent a range of different bird and/or reptile species. A review of genetically identified specimens shows that coprolites of different bird species overlap in size and morphology, reinforcing the need for identifications to be based on ancient DNA analysis.

Wood, Jamie R.; Wilmshurst, Janet M.

2014-08-01

396

Geomorphology and Quaternary geology of the Dakhla Oasis Region, Egypt  

NASA Astrophysics Data System (ADS)

Dakhla Oasis (25.5°N, 29°E) occupies a structurally localized depression at 90-140 m above sea level, ˜1200 km 2 in area, below a 300 m escarpment bordering the Libyan Plateau, Western Desert of Egypt. Semi-arid intervals of the Quaternary period generated eight sedimentary formations, separated by erosion during hyper-arid intervals. Sediments comprise three generations of colluvial/fluvial fanglomerates, two generations of tabular spring-laid clastic and chemical sediments, two generations of mound springs and basinal sediments. of fluvio-lacustrine, evaporitic, pluvio-aeolian and aeolian origins. Discussion of these sediments is organized according to geomorphic region, from north to south, plateau, scarp and piedmont, lowland and cuesta plain. Chronological evidence is restricted to many radiocarbon dates of Holocene cultural material associated with playa sediments (9-4.5 ka), a {Th}/{U} isochron age of ˜62.0 ±7.6 ka for basinal evaporites, and two {Th}/{U} ages of ˜176 and ˜170 ka for a boulder of derived travertine. The regional Quaternary sequence is reconstructed from stratigraphic and geomorphic relationships of the sediments and erosion surfaces. It is broadly similar to sequences earlier reconstructed in the topographically similar Kharga Oasis region 150 km to the east, and Kurkur Oasis, 400 km to the south-southeast. Speculations on chronology and driving mechanism are offered in conclusion.

Brookes, Ian A.

397

Microscopic Calculations of 240Pu Fission  

SciTech Connect

Hartree-Fock-Bogoliubov calculations have been performed with the Gogny finite-range effective interaction for {sup 240}Pu out to scission, using a new code developed at LLNL. A first set of calculations was performed with constrained quadrupole moment along the path of most probable fission, assuming axial symmetry but allowing for the spontaneous breaking of reflection symmetry of the nucleus. At a quadrupole moment of 345 b, the nucleus was found to spontaneously scission into two fragments. A second set of calculations, with all nuclear moments up to hexadecapole constrained, was performed to approach the scission configuration in a controlled manner. Calculated energies, moments, and representative plots of the total nuclear density are shown. The present calculations serve as a proof-of-principle, a blueprint, and starting-point solutions for a planned series of more comprehensive calculations to map out a large set of scission configurations, and the associated fission-fragment properties.

Younes, W; Gogny, D

2007-09-11

398

System Concepts for Affordable Fission Surface Power  

NASA Technical Reports Server (NTRS)

This paper presents an overview of an affordable Fission Surface Power (FSP) system that could be used for NASA applications on the Moon and Mars. The proposed FSP system uses a low temperature, uranium dioxide-fueled, liquid metal-cooled fission reactor coupled to free-piston Stirling converters. The concept was determined by a 12 month NASA/DOE study that examined design options and development strategies based on affordability and risk. The system is considered a low development risk based on the use of terrestrial-derived reactor technology, high efficiency power conversion, and conventional materials. The low-risk approach was selected over other options that could offer higher performance and/or lower mass.

Mason, Lee; Poston, David; Qualls, Louis

2008-01-01

399

Fission Surface Power Technology Development Status  

NASA Technical Reports Server (NTRS)

With the potential future deployment of a lunar outpost there is expected to be a clear need for a high-power, lunar surface power source to support lunar surface operations independent of the day-night cycle, and Fission Surface Power (FSP) is a very effective solution for power levels above a couple 10 s of kWe. FSP is similarly enabling for the poorly illuminated surface of Mars. The power levels/requirements for a lunar outpost option are currently being studied, but it is known that cost is clearly a predominant concern to decision makers. This paper describes the plans of NASA and the DOE to execute an affordable fission surface power system technology development project to demonstrate sufficient technology readiness of an affordable FSP system so viable and cost-effective FSP system options will be available when high power lunar surface system choices are expected to be made in the early 2010s.

Palac, Donald T.; Mason, Lee S.; Harlow, Scott

2009-01-01

400

SABR Fusion-Fission Hybrid Studies  

NASA Astrophysics Data System (ADS)

The Subcritical Advanced Burner Reactor (SABR) concept is a fast reactor comprised of a tokamak fusion neutron source based on ITER surrounded by an annular fission core adapted from Integral Fast Reactor designs. Previous work has examined SABR used to help close the nuclear fuel cycle by fissioning the transuranics from spent nuclear fuel. One focus of the present work is a SABR Breeder Reactor to achieve tritium self-sufficieny and a Pu breeding ratio significantly above 1 in order to provide fuel for SABR as well as for MOX-fueled LWR's and other fast reactors. Another focus of this research is the dynamic safety simulation of lloss-of-flow loss-of-heat-sink, loss-of-power, and positive reactivity accidents in the TRU fuel SABR burner reactor. The reactivity effect of thermal-induced bowing of fuel pins has been modeled, which is expected to provide passive safety.

Stewart, Chris

2012-03-01

401

Nuclear Fission Investigation with Twin Ionization Chamber  

NASA Astrophysics Data System (ADS)

The purpose of the present paper was to report the recent results, obtained in development of digital pulse processing mathematics for prompt fission neutron (PFN) investigation using twin ionization chamber (TIC) along with fast neutron time-of-flight detector (ND). Due to well known ambiguities in literature (see refs. [4, 6, 9 and 11]), concerning a pulse induction on TIC electrodes by FF ionization, we first presented detailed mathematical analysis of fission fragment (FF) signal formation on TIC anode. The analysis was done using Ramo-Shockley theorem, which gives relation between charged particle motion between TIC electrodes and so called weighting potential. Weighting potential was calculated by direct numerical solution of Laplace equation (neglecting space charge) for the TIC geometry and ionization, caused by FF. Formulae for grid inefficiency (GI) correction and digital pulse processing algorithms for PFN time-of-flight measurements and pulse shape analysis are presented and discussed.

Zeynalova, O.; Zeynalov, Sh.; Nazarenko, M.; Hambsch, F.-J.; Oberstedt, S.

2011-11-01

402

Fusion-fission energy systems evaluation  

SciTech Connect

This report serves as the basis for comparing the fusion-fission (hybrid) energy system concept with other advanced technology fissile fuel breeding concepts evaluated in the Nonproliferation Alternative Systems Assessment Program (NASAP). As such, much of the information and data provided herein is in a form that meets the NASAP data requirements. Since the hybrid concept has not been studied as extensively as many of the other fission concepts being examined in NASAP, the provided data and information are sparse relative to these more developed concepts. Nevertheless, this report is intended to provide a perspective on hybrids and to summarize the findings of the rather limited analyses made to date on this concept.

Teofilo, V.L.; Aase, D.T.; Bickford, W.E.

1980-01-01

403

Fusion, fragmentation, and fission of mitochondria.  

PubMed

Individual mitochondria which form the chondriom of eucaryotic cells are highly dynamic systems capable of fusion and fragmentation. These two processes do not exclude one another and can occur concurrently. However, fragmentation and fusion of mitochondria regularly alternate in the cell cycle of some unicellular and multicellular organisms. Mitochondrial shapes are also described which are interpreted as intermediates of their "equational" division, or fission. Unlike the fragmentation, the division of mitochondria, especially synchronous division, is also accompanied by segregation of mitochondrial genomes and production of specific "dumbbell-shaped" intermediates. This review considers molecular components and possible mechanisms of fusion, fragmentation, and fission of mitochondria, and the biological significance of these processes is discussed. PMID:12948383

Polyakov, V Yu; Soukhomlinova, M Yu; Fais, D

2003-08-01

404

Nuclear Fission Investigation with Twin Ionization Chamber  

SciTech Connect

The purpose of the present paper was to report the recent results, obtained in development of digital pulse processing mathematics for prompt fission neutron (PFN) investigation using twin ionization chamber (TIC) along with fast neutron time-of-flight detector (ND). Due to well known ambiguities in literature (see refs. [4, 6, 9 and 11]), concerning a pulse induction on TIC electrodes by FF ionization, we first presented detailed mathematical analysis of fission fragment (FF) signal formation on TIC anode. The analysis was done using Ramo-Shockley theorem, which gives relation between charged particle motion between TIC electrodes and so called weighting potential. Weighting potential was calculated by direct numerical solution of Laplace equation (neglecting space charge) for the TIC geometry and ionization, caused by FF. Formulae for grid inefficiency (GI) correction and digital pulse processing algorithms for PFN time-of-flight measurements and pulse shape analysis are presented and discussed.

Zeynalova, O.; Zeynalov, Sh. [JINR-Joint Institute for Nuclear Research, Dubna, Moscow region (Russian Federation); Nazarenko, M. [Moscow State Institute of Radioengineering and Automation, 78 Vernadski Avenue, 119454 Moscow (Russian Federation); Hambsch, F.-J.; Oberstedt, S. [EC-JRC Institute for Reference Materials and Measurements, Retieseweg 111, 2440 Geel (Belgium)

2011-11-29

405

A New Role for Myosin II in Vesicle Fission  

PubMed Central

An endocytic vesicle is formed from a flat plasma membrane patch by a sequential process of invagination, bud formation and fission. The scission step requires the formation of a tubular membrane neck (the fission pore) that connects the endocytic vesicle with the plasma membrane. Progress in vesicle fission can be measured by the formation and closure of the fission pore. Live-cell imaging and sensitive biophysical measurements have provided various glimpses into the structure and behaviour of the fission pore. In the present study, the role of non-muscle myosin II (NM-2) in vesicle fission was tested by analyzing the kinetics of the fission pore with perforated-patch clamp capacitance measurements to detect single vesicle endocytosis with millisecond time resolution in peritoneal mast cells. Blebbistatin, a specific inhibitor of NM-2, dramatically increased the duration of the fission pore and also prevented closure during large endocytic events. Using the fluorescent markers FM1-43 and pHrodo Green dextran, we found that NM-2 inhibition greatly arrested vesicle fission in a late phase of the scission event when the pore reached a final diameter of ? 5 nm. Our results indicate that loss of the ATPase activity of myosin II drastically reduces the efficiency of membrane scission by making vesicle closure incomplete and suggest that NM-2 might be especially relevant in vesicle fission during compound endocytosis. PMID:24959909

Cabeza, Jose M.; Acosta, Jorge; Ramirez-Ponce, Pilar; Ales, Eva

2014-01-01

406

A new approach to prompt fission neutron TOF data treatment  

NASA Astrophysics Data System (ADS)

The prompt neutron emission in spontaneous fission of 252Cf has been investigated applying digital signal electronics along with associated digital signal processing algorithms. A new mathematical approach, applicable to single events, was developed for prompt fission neutron (PFN) time-offlight distribution unfolding. The main goal was to understand the reasons of the long existing discrepancy between theoretical calculations and the measurements of prompt fission neutron (PFN) emission dependence on the total kinetic energy (TKE) of the fission fragments (FF). Since the 252Cf (sf) reaction is one of the main references for nuclear data the understanding of the PFN emission mechanism is very important both for nuclear fission theory and nuclear data. The experimental data were taken with a twin Frisch-grid ionization chamber and a NE213-equivalent neutron detector in an experimental setup similar to the well known work of C. Budtz-Jorgensen and H.-H. Knitter. About 2.5 × 105 coincidences between fission fragment (FF) and neutron detector response to prompt fission neutron detection have been registered (? 1.6 × 107 of total recorded fission events). Fission fragment kinetic energy, mass and angular distribution, neutron time-of-flight and pulse shape have been investigated using a 12-bit waveform digitizer. The signal waveforms have been analyzed using digital signal processing algorithms. The main goal of this work was a detailed description of the prompt fission neutron treatment.

Zeynalov, Sh.; Zeynalova, O. V.; Hambsch, F.-J.; Oberstedt, S.

407

The analyses of neutron coincidence data to verify both spontaneous-fission and fissionable isotopes  

SciTech Connect

For neutron coincidence counter applications to the assay of plutonium samples, various calibration methods can be used to evaluate the data. The reals (R) and totals (T) rates can be used to predict the induced-fission rate. When this is done, the results give information related to both the spontaneous-fission isotopes and the fissionable isotopes (induced fission). The combination of both approaches is less sensitive to the plutonium isotopic uncertainties than the normal spontaneous-fission approach. Five calibration methods are evaluated for a wide variety of sample types to emphasize the advantages and disadvantages of the methods. For certain sample categories with well-defined geometries, such as light-water reactor and fast breeder reactor mixed-oxide fuel assemblies, a method is presented that allows the verification of the declared isotopics within given constraints. Recommendations are given on analysis procedures to reduce the assay errors for coincidence counting of any type of sample. 15 refs., 11 figs., 15 tabs.

Menlove, H.O.; Abedin-Zadeh, R.; Zhu, R. (Los Alamos National Lab., NM (USA); International Atomic Energy Agency, Vienna (Austria); Academia Sinica, Beijing, BJ (China). Inst. of Atomic Energy)

1989-08-01

408

Featured Organism: Schizosaccharomyces pombe, The Fission Yeast  

PubMed Central

Schizosaccharomyces pombe, the fission yeast, has long been a crucial model for the study of the eukaryote cell cycle. We take a look at this important yeast, whose genome has recently been completed, featuring comments from Valerie Wood, Jürg Bähler, Ramsay McFarlane, Susan Forsburg, Iain Hagan and Paul Nurse on the implications of having the complete sequence and future prospects for pombe genomics. PMID:18628834

2002-01-01

409

Fusion, Fission, and Secretion During Phagocytosis  

NSDL National Science Digital Library

Phagocytosis is essential for the elimination of pathogens and for clearance of apoptotic bodies. The ingestion process entails extensive remodeling of the cellular membranes, particularly when large and/or multiple particles are engulfed. The membrane fusion and fission events that accompany phagocytosis are described. The coordinated sequence of membrane trafficking events required for phagocytosis involves multiple organelles and also serves other cellular functions, such as cytokine secretion.

2007-12-01

410

Scission Configurations in the Cold Fission  

Microsoft Academic Search

The scission configuration in the cold fission is studied in the frame of a molecular model consisting of two aligned fragments interacting by means of Coulomb and nuclear proximity forces. As a study case we choose the binary cold splitting of 252Cf in two even-even nuclei, i.e. 148Ba and 104Mo. Their deformation energies are computed via the constrained Hartree-Fock +

S. Misicu; P. Quentin; N. Pillet

2001-01-01

411

Double fine structure in binary cold fission  

Microsoft Academic Search

We give a description of the binary cold fission process of 252Cf within the stationary scattering formalism. The decay of the dinuclear system (quasi-molecule) consists in the tunnelling of a metastable state from an internal region, where the nucleus-nucleus potential makes a quasi-molecular pocket due to the interplay of repulsive and attractive nuclear forces and the Coulomb force, to the

D. S. Delion; A. Sandulescu; S. Misicu; F. Carstoiu; W. Greiner

2002-01-01

412

Toward singlet fission for excitonic solar cells  

Microsoft Academic Search

Sensitizer dyes capable of producing two triplet excited states from a singlet excited state produced by the absorption of a single photon would allow an increase of the efficiency of photovoltaic cells by up to a factor of 1.5, provided that each triplet injects an electron into a semiconductor such as TiO2. Although singlet fission in certain crystals and polymers

Josef Michl; Arthur J. Nozik; Xudong Chen; Justin C. Johnson; Geeta Rana; Akin Akdag; Andrew F. Schwerin

2007-01-01

413

Nuclear fission with mean-field instantons  

Microsoft Academic Search

We present a description of nuclear spontaneous fission, and generally of quantum tunneling, in terms of instantons, that is, periodic imaginary-time solutions to time-dependent mean-field equations. This description allows comparisons to be made with the more familiar generator coordinate (GCM) and adiabatic time-dependent Hartree-Fock (ATDHF) methods. It is shown that the action functional whose value for the instanton is the

Janusz

2008-01-01

414

Undergraduate Measurements For Fission Reactor Applications  

NASA Astrophysics Data System (ADS)

Undergraduate students at the University of Dallas (UD) have investigated elastic and inelastic neutron scattering cross sections on structural materials important for criticality considerations in nuclear fission processes. Neutrons scattered off of 23Na and NatFe were detected using neutron time-of-flight techniques at the University of Kentucky Low-Energy Nuclear Accelerator Facility. These measurements are part of an effort to increase the efficiency of power generation from existing fission reactors in the US and in the design of new fission systems. Students have learned the basics of how to operate the Model CN Van de Graaff generator at the laboratory, setup detectors and electronics, use data acquisition systems, and they are currently analyzing the angular dependence of the scattered neutrons for incident neutron energies of 3.57 and 3.80 MeV. Most students participating in the project will use the research experience as the material for their undergraduate research thesis required for all Bachelor of Science students at the University of Dallas. The first student projects on this topic were completed during the summer of 2010; an overview of student participation in this investigation and their preliminary results will be presented.

Hicks, S. F.; Kersting, L. J.; Lueck, C. J.; McDonough, P.; Crider, B. P.; McEllistrem, M. T.; Peters, E. E.; Vanhoy, J. R.

2011-06-01

415

Accurate fission data for nuclear safety  

E-print Network

The Accurate fission data for nuclear safety (AlFONS) project aims at high precision measurements of fission yields, using the renewed IGISOL mass separator facility in combination with a new high current light ion cyclotron at the University of Jyvaskyla. The 30 MeV proton beam will be used to create fast and thermal neutron spectra for the study of neutron induced fission yields. Thanks to a series of mass separating elements, culminating with the JYFLTRAP Penning trap, it is possible to achieve a mass resolving power in the order of a few hundred thousands. In this paper we present the experimental setup and the design of a neutron converter target for IGISOL. The goal is to have a flexible design. For studies of exotic nuclei far from stability a high neutron flux (10^12 neutrons/s) at energies 1 - 30 MeV is desired while for reactor applications neutron spectra that resembles those of thermal and fast nuclear reactors are preferred. It is also desirable to be able to produce (semi-)monoenergetic neutrons...

Solders, A; Jokinen, A; Kolhinen, V S; Lantz, M; Mattera, A; Penttila, H; Pomp, S; Rakopoulos, V; Rinta-Antila, S

2013-01-01

416

MAFF - The Munich accelerator for fission fragments  

NASA Astrophysics Data System (ADS)

At the new high flux reactor FRM-II in Munich the accelerator MAFF (Munich accelerator for fission fragments) is under design. In the high neutron flux of 10(14) n/cm(2) s up to 10(14) neutron-rich fission fragments per second are produced in the 1 g U-235 target. Ions with an energy of 30 keV are extracted from the ion source. In the mass seperator two isotopes can be selected. One of the beams is used for low energy experiments, the other one is injected into an ECRIS (or EBIS) for charge breeding to a q/A? 0.16. A gas filled RFQ cooler is used for emittance improvement. The subsequent LINAC delivers beams with an energy ranging from 3.7 MeV/u to 5.9 MeV/u. New IH structures are being developed at the Munich tandem laboratory. A small storage ring is planned in a further stage to recycle the fission fragments. A thin target foil can be placed into this ring, e.g., for synthesis of super-heavy elements. The through-going beam tube has been installed in the heavy water tank of the reactor. Tests of the target ion source in a special oven to test long term stability and safety tests were in progress.

Beck, L.; Habs, D.; Reiter, P.; Thirolf, P.; Sieber, T.; Bongers, H.; Emhofer, S.; Maier, H. J.

2002-12-01

417

New fission mode of the {sup 252}Cf spontaneous fission obtained with modern HPGE detectors  

SciTech Connect

The data of Independent yields of secondary fission fragment pairs (emerging after prompt neutron emission from primary fragment pairs) obtained by detecting coincidences between {gamma} rays following the spontaneous fission of {sup 252}Cf have been expanded. Our approach to estimate characteristics of the primary fragments pairs (mass and excitation energy distributions) by unfolding the yields of secondary fragment pairs is discussed. Mew model parameters were introduced and results are presented here. The new results confirmed our old assumption that in case of Mo-Ba charge split the two fission modes differing with average total kinetic energy {l_angle}TKE{r_angle} on {approximately}36 MeV are realized. {copyright} {ital 1998 American Institute of Physics.}

Daniel, A.V.; Ter-Akopian, G.M.; Oganessian, Y.T.; Popeko, G.S. [Flerov Laboratory of Nuclear Reactions, JINR, Dubna 141980 (Russia); Hamilton, J.H.; Kormicki, J.; Ramayya, A.V.; Babu, B.R.; Ginter, T.; Zhu, S.J. [Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235 (United States); Ma, W. [Department of Physics, Mississippi State University, Mississippi State, Mississippi 39762 (United States); Rasmussen, J.; Stoyer, M.A.; Lee, I.Y.; Asztalos, S.; Chu, S.Y.; Gregorich, K.E.; Macchiavelli, A.O.; Mohar, M.F.; Prussin, S.G. [Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Kliman, J.; Morhac, M. [Institute of Physics, Slovak Academy of Sciences, Bratislava (Slovak Republic); Cole, J.D.; Aryaeinejad, R.; Dardenne, Y.K.; Driger, M. [Idaho National Engineering Laboratory, Idaho Falls, Idaho 83415 (United States)

1998-02-01

418

Exotic fission properties of highly neutron-rich Uranium isotopes  

E-print Network

The series of Uranium isotopes with $N=154 \\sim 172$ around the magic number N=162/164 are identified to be thermally fissile. The thermal neutron fission of a typical representative $^{249}$U of this region amenable to synthesis in the radioactive ion beam facilities is considered here. Semiempirical study of fission barrier height and width shows this nucleus to be infinitely stable against spontaneous fission due to increase in barrier width arising out of excess neutrons. Calculation of probability of fragment mass yields and microscopic study in relativistic mean field theory, show this nucleus to undergo a new mode of thermal fission decay termed {\\it multifragmentation fission} where a number of prompt scission neutrons are simultaneously released along with the two heavy fission fragments.

L. Satpathy; S. K. Patra; R. K. Choudhury

2007-03-05

419

Exotic fission properties of highly neutron-rich Uranium isotopes  

E-print Network

The series of Uranium isotopes with $N=154 \\sim 172$ around the magic number N=162/164 are identified to be thermally fissile. The thermal neutron fission of a typical representative $^{249}$U of this region amenable to synthesis in the radioactive ion beam facilities is considered here. Semiempirical study of fission barrier height and width shows this nucleus to be infinitely stable against spontaneous fission due to increase in barrier width arising out of excess neutrons. Calculation of probability of fragment mass yields and microscopic study in relativistic mean field theory, show this nucleus to undergo a new mode of thermal fission decay termed {\\it multifragmentation fission} where a number of prompt scission neutrons are simultaneously released along with the two heavy fission fragments.

Satpathy, L; Patra, S K

2007-01-01

420

Microscopic theory of singlet exciton fission. I. General formulation.  

PubMed

Singlet fission, a spin-allowed energy transfer process generating two triplet excitons from one singlet exciton, has the potential to dramatically increase the efficiency of organic solar cells. However, the dynamical mechanism of this phenomenon is not fully understood and a complete, microscopic theory of singlet fission is lacking. In this work, we assemble the components of a comprehensive microscopic theory of singlet fission that connects excited state quantum chemistry calculations with finite-temperature quantum relaxation theory. We elaborate on the distinction between localized diabatic and delocalized exciton bases for the interpretation of singlet fission experiments in both the time and frequency domains. We discuss various approximations to the exact density matrix dynamics and propose Redfield theory as an ideal compromise between speed and accuracy for the detailed investigation of singlet fission in dimers, clusters, and crystals. Investigations of small model systems based on parameters typical of singlet fission demonstrate the numerical accuracy and practical utility of this approach. PMID:23534622

Berkelbach, Timothy C; Hybertsen, Mark S; Reichman, David R

2013-03-21

421

Microscopic theory of singlet exciton fission. I. General formulation  

NASA Astrophysics Data System (ADS)

Singlet fission, a spin-allowed energy transfer process generating two triplet excitons from one singlet exciton, has the potential to dramatically increase the efficiency of organic solar cells. However, the dynamical mechanism of this phenomenon is not fully understood and a complete, microscopic theory of singlet fission is lacking. In this work, we assemble the components of a comprehensive microscopic theory of singlet fission that connects excited state quantum chemistry calculations with finite-temperature quantum relaxation theory. We elaborate on the distinction between localized diabatic and delocalized exciton bases for the interpretation of singlet fission experiments in both the time and frequency domains. We discuss various approximations to the exact density matrix dynamics and propose Redfield theory as an ideal compromise between speed and accuracy for the detailed investigation of singlet fission in dimers, clusters, and crystals. Investigations of small model systems based on parameters typical of singlet fission demonstrate the numerical accuracy and practical utility of this approach.

Berkelbach, Timothy C.; Hybertsen, Mark S.; Reichman, David R.

2013-03-01

422

Fractal Model of Fission Product Release in Nuclear Fuel  

NASA Astrophysics Data System (ADS)

A model of fission gas migration in nuclear fuel pellet is proposed. Diffusion process of fission gas in granular structure of nuclear fuel with presence of inter-granular bubbles in the fuel matrix is simulated by fractional diffusion model. The Grunwald-Letnikov derivative parameter characterizes the influence of porous fuel matrix on the diffusion process of fission gas. A finite-difference method for solving fractional diffusion equations is considered. Numerical solution of diffusion equation shows correlation of fission gas release and Grunwald-Letnikov derivative parameter. Calculated profile of fission gas concentration distribution is similar to that obtained in the experimental studies. Diffusion of fission gas is modeled for real RBMK-1500 fuel operation conditions. A functional dependence of Grunwald-Letnikov derivative parameter with fuel burn-up is established.

Stankunas, Gediminas

2012-09-01

423

Fission xenon from extinct Pu-244 in 14,301.  

NASA Technical Reports Server (NTRS)

Xenon extracted in step-wise heating of lunar breccia 14,301 contains a fission-like component in excess of that attributable to uranium decay during the age of the solar system. There seems to be no adequate source for this component other than Pu-244. Verification that this component is in fact due to the spontaneous fission of extinct Pu-244 comes from the derived spectrum which is similar to that observed from artificially produced Pu-244. It thus appears that Pu-244 was extant at the time lunar crustal material cooled sufficiently to arrest the thermal diffusion of xenon. Subsequent history has apparently maintained the isotopic integrity of plutonium fission xenon. Of major importance are details of the storage itself. Either the fission component is the result of in situ fission of Pu-244 and subsequent storage in 14,301 material, or the fission xenon was stored in an intermediate reservoir before incorporation into 14,301.

Drozd, R.; Hohenberg, C. M.; Ragan, D.

1972-01-01

424

Electron-capture delayed fission properties of 244Es  

SciTech Connect

Electron-capture delayed fission was observed in {sup 244}Es produced via the {sup 237}Np({sup 12}C,5n){sup 244}Es reaction at 81 MeV (on target) with a production cross section of 0.31{+-}0.12 {micro}b. The mass-yield distribution of the fission fragments is highly asymmetric. The average preneutron-emission total kinetic energy of the fragments was measured to be 186{+-}19 MeV. Based on the ratio of the number of fission events to the measured number of {alpha} decays from the electron-capture daughter {sup 244}Cf (100% {alpha} branch), the probability of delayed fission was determined to be (1.2{+-}0.4) x 10{sup -4}. This value for the delayed fission probability fits the experimentally observed trend of increasing delayed fission probability with increasing Q value for electron-capture.

Shaughnessy, Dawn A.; Gregorich, Kenneth E.; Adams, Jeb L.; Lane, Michael R.; Laue, Carola A.; Lee, Diana M.; McGrath, Christopher A.; Ninov, Victor; Patin, Joshua B.; Strellis, Dan A.; Sylwester, Eric R.; Wilk, Philip A.; Hoffman, Darleane C.

2001-03-16

425

Early results utilizing high-energy fission product (gamma) rays to detect fissionable material in cargo  

SciTech Connect

A concept for detecting the presence of special nuclear material ({sup 235}U or {sup 239}Pu) concealed in intermodal cargo containers is described. It is based on interrogation with a pulsed beam of 7 MeV neutrons that produce fission events and their {beta}-delayed neutron emission or {beta}-delayed high-energy {gamma}-radiation between beam pulses provide the detection signature. Fission product {beta}-delayed {gamma}-rays above 3 MeV are nearly ten times more abundant than {beta}-delayed neutrons and are distinct from natural radioactivity and from nearly all of the induced activity in a normal cargo. Detector backgrounds and potential interferences with the fission signature radiation have been identified and quantified. An important goal in the US is the detection of nuclear weapons or special nuclear material (SNM) concealed in intermodal cargo containers. This must be done with high detection probability, low false alarm rates, and without impeding commerce, i.e. about one minute for an inspection. The concept for inspection has been described before and its components are now being evaluated. While normal radiations emitted from plutonium may allow its detection, the majority of {sup 235}U {gamma} ray emission is at 186 keV, is readily attenuated by cargo, and thus not a reliable detection signature for passive detection. Delayed neutron detection following a neutron or photon beam pulse has been used successfully to detect lightly or unshielded SNM targets. While delayed neutrons can be easily distinguished from beam neutrons they have relatively low yield in fission, approximately 0.008 per fission in {sup 239}Pu and 0.017 per fission in {sup 235}U, and are rapidly attenuated in hydrogenous materials making that technique unreliable when challenged by thick hydrogenous cargo overburden. They propose detection of {beta}-delayed high-energy {gamma} radiation as a more robust signature characteristic of SNM.

Slaughter, D R; Accatino, M R; Bernstein, A; Church, J A; Descalle, M A; Gosnell, T B; Hall, J M; Loshak, A; Manatt, D R; Mauger, G J; McDowell, M; Moore, T M; Norman, E B; Pohl, B A; Pruet, J A; Petersen, D C; Walling, R S; Weirup, D L; Prussin, S G

2004-09-30

426

Yields of fission products produced by thermal-neutron fission of 245Cm  

NASA Astrophysics Data System (ADS)

Absolute yields have been determined for 105 gamma rays emitted in the decay of 95 fission products representing 54 mass chains created during thermal-neutron fission of 245Cm. These results include 17 mass chains for which no prior yield data exist. Using a Ge(Li) detector, spectra were obtained of gamma rays between 30 sec and 0.3 yr after very short irradiations of thermal neutrons on a 1 ?g sample of 245Cm. On the basis of measured gamma-ray yields and known nuclear data, total chain mass yields and relative uncertainties were obtained for 51 masses between 84 and 156. The absolute overall normalization uncertainty is <8%. The measured A-chain cumulative yields make up 81% of the total light mass (A<=121) yield and 92% of the total heavy mass yield. The results are compared with fission-product yields previously measured with generally good agreement. The mass-yield data have been compared with those for thermal-neutron fission of 239Pu and for 252Cf(s.f.); the influences of the closed shells Z=50, N=82 are not as marked as for thermal-neutron fission of 239Pu but much more apparent than for 252Cf(s.f.). Information on the charge distribution along several isobaric mass chains was obtained by determining fractional yields for 12 fission products. The charge distribution width parameter, based upon data for the heavy masses, A=128 to 140, is independent of mass to within the uncertainties of the measurements. Gamma-ray assignments were made for decay of short-lived fission products for which absolute gamma-ray transition probabilities are either not known or in doubt. Absolute gamma-ray transition probabilities were determined as (51 +/- 8)% for the 374-keV gamma ray from decay of 110Rh, (35 +/- 7)% for the 1096-keV gamma ray from decay of 133Sb, and (21.2 +/- 1.2)% for the 255-keV gamma ray from decay of 142Ba. RADIOACTIVITY, FISSION 245Cm(n,f) En=thermal; measured ?(E?,T12) deduced mass, charge yields.

Dickens, J. K.; McConnell, J. W.

1981-01-01

427

Mass resolved angular distribution of fission fragments for near-barrier fusion-fission reactions  

SciTech Connect

It is shown that K-equilibration fission can explain the decrease of mass resolved fission fragment anisotropy at larger mass asymmetries. Two competing mechanisms contribute to the anisotropy. The effective moment of inertia and K{sub 0}{sup 2} decreases with the increase of mass asymmetry and contribute to the increase of anisotropy. On the other hand, for larger asymmetries, the barriers are higher and lifetimes are longer. Such systems are more K equilibrated and will have smaller anisotropy. {copyright} {ital 1997} {ital The American Physical Society}

Vorkapic, D. [Centre de Recherches Nucleaires, IN2P3-CNRS/Universite Louis Pasteur, BP28, F-67037 Strasbourg Cedex (France)] [Centre de Recherches Nucleaires, IN2P3-CNRS/Universite Louis Pasteur, BP28, F-67037 Strasbourg Cedex (France); Ivanisevic, B. [Vinca Institute of Nuclear Sciences, P.O. Box 522, 11101 Belgrade (Yugoslavia)] [Vinca Institute of Nuclear Sciences, P.O. Box 522, 11101 Belgrade (Yugoslavia)

1997-05-01

428

Sharp change over from compound nuclear fission to shape dependent quasi fission  

E-print Network

Fission fragment mass distribution has been measured from the decay of $^{246}$Bk nucleus populating via two entrance channels with slight difference in mass asymmetries but belonging on either side of the Businaro Gallone mass asymmetry parameter. Both the target nuclei were deformed. Near the Coulomb barrier, at similar excitation energies the width of the fission fragment mass distribution was found to be drastically different for the $^{14}$N + $^{232}$Th reaction compared to the $^{11}$B + $^{235}$U reaction. The entrance channel mass asymmetry was found to affect the fusion process sharply.

T. K. Ghosh; K. Banerjee; C. Bhattacharya; S. Bhattacharya; S. Kundu; P. Mali; J. K. Meena; G. Mukherjee; S. Mukhopadhyay; T. K. Rana; P. Bhattacharya; K. S. Golda

2008-09-17

429

Quaternary history and contemporary patterns in a currently expanding species  

PubMed Central

Background Quaternary climatic oscillations had dramatic effects on species evolution. In northern latitudes, populations had to survive the coldest periods in refugial areas and recurrently colonized northern regions during interglacials. Such a history usually results in a loss of genetic diversity. Populations that did not experience glaciations, in contrast, probably maintained most of their ancestral genetic diversity. These characteristics dramatically affected the present-day distribution of genetic diversity and may influence the ability of species to cope with the current global changes. We conducted a range-wide study of mitochondrial genetic diversity in the pine processionary moth (Thaumetopoea pityocampa/T. wilkinsoni complex, Notodontidae), a forest pest occurring around the Mediterranean Basin and in southern Europe. This species is responding to the current climate change by rapid natural range expansion and can also be accidentally transported by humans. Our aim was to assess if Quaternary climatic oscillations had a different effect across the species' range and to determine if genetic footprints of contemporary processes can be identified in areas of recent introduction. Results We identified three main clades that were spatially structured. In most of Europe, the genetic diversity pattern was typical for species that experienced marked glaciation cycles. Except in refugia, European populations were characterized by the occurrence of one main haplotype and by a strong reduction in genetic diversity, which is expected in regions that were rapidly re-colonized when climatic conditions improved. In contrast, all other sub-clades around the Mediterranean Basin occurred in limited parts of the range and were strongly structured in space, as is expected in regions in which the impact of glaciations was limited. In such places, genetic diversity was retained in most populations, and almost all haplotypes were endemic. This pattern was extreme on remote Mediterranean islands (Crete, Cyprus, Corsica) where highly differentiated, endemic haplotypes were found. Recent introductions were typified by the existence of closely-related haplotypes in geographically distant populations, which is difficult to detect in most of Europe because of a lack of overall genetic structure. Conclusion In regions that were not prone to marked glaciations, recent moth introductions/expansions could be detected due to the existence of a strong spatial genetic structure. In contrast, in regions that experienced the most intense Quaternary climatic oscillations, the natural populations are not genetically structured, and contemporary patterns of population expansion remain undetected. PMID:19732434

Kerdelhué, Carole; Zane, Lorenzo; Simonato, Mauro; Salvato, Paola; Rousselet, Jérôme; Roques, Alain; Battisti, Andrea

2009-01-01

430

Quaternary Reorganization of North American Mid-continent Drainage Systems  

NASA Astrophysics Data System (ADS)

Identification of ancestral drainage systems in the North American mid-continent has been a topic of research and debate among geologists since the middle of the 19th Century. Over time our understanding of the significance of Quaternary glaciations in reshaping drainage patterns has grown. The ancestral Teays River, which drained large areas of the central Appalachians and flowed westward across Indiana and western Illinois, was dammed multiple times by Quaternary glaciers before finally being rerouted to the course of the modern central Ohio River. Similarly, the northward-flowing ancestral Pittsburgh River was dammed by pre-Illinoian glaciers; subsequent stream piracy converted this river system into the modern Allegheny, Monongahela and uppermost Ohio Rivers. Deposits and geomorphic features along the westward-flowing lower Wisconsin River indicate that the modern upper Mississippi River and Wisconsin River may have experienced a similar history of ice blockage, stream piracy, and radical rerouting. Coring into the Bridgeport strath terrace along the lower Wisconsin River reveals that the bedrock surface dips to the east, indicating the valley was cut by an eastward-flowing river. We believe the most likely scenario following this interpretation is that an ancestral river flowing along the modern upper Mississippi River valley made a sharp bend at Prairie du Chien, WI, and flowed eastward along the valley occupied by the modern lower Wisconsin River. This river, referred to here as the Wyalusing River, likely flowed northeastward into the Great Lakes (St. Lawrence) drainage until that path was blocked by ice advancing from the northwest. Subsequent stream piracy immediately south of the modern confluence of the Mississippi and Wisconsin Rivers rerouted these streams, converting them to the headwaters of the greater Mississippi drainage. The combined rerouting of these river systems into entirely different drainage basins necessitates significant fundamental changes to the total discharge of the St. Lawrence and Mississippi Rivers. While it is unclear if the Teays River ever flowed into the St. Lawrence drainage or developed as a westward-flowing tributary to the buried Mahomet valley in Illinois, both the ancestral Pittsburgh and Wyalusing Rivers originated as headwaters of the St. Lawrence basin before being rerouted as part of the Mississippi basin. The areas formerly drained by the Pittsburgh and Wyalusing Rivers comprise ~8% of the modern Mississippi River basin, and modern discharge from those areas represent ~14% of the mean annual discharge of the Mississippi River. The transfer of this drainage area and discharge to the Mississippi basin is mirrored by an equivalent loss from the St. Lawrence system during the Quaternary as a direct result of glacially-driven drainage system reorganization.

Carson, E. C.; Rawling, J. E., III; Attig, J. W.; Bates, B. R.

2013-12-01

431

Neutron flux profile monitor for use in a fission reactor  

DOEpatents

A neutron flux monitor is provided which consists of a plurality of fission counters arranged as spaced-apart point detectors along a delay line. As a fission event occurs in any one of the counters, two delayed current pulses are generated at the output of the delay line. The time separation of the pulses identifies the counter in which the particular fission event occured. Neutron flux profiles of reactor cores can be more accurately measured as a result.

Kopp, Manfred K. (Oak Ridge, TN); Valentine, Kenneth H. (Lenoir City, TN)

1983-01-01

432

Proton induced fission of 181-Ta at relativistic energies  

E-print Network

Total fission cross sections of 181-Ta induced by protons at different relativistic energies have been measured at GSI, Darmstadt. The inverse kinematics technique used together with a dedicated set-up, made it possible to determine these cross sections with high accuracy. The new data obtained in this experiment will contribute to the understanding of the fission process at high excitation energies. The results are compared with data from previous experiments and systematics for proton-induced fission cross sections.

Y. Ayyad; J. Benlliure; E. Casarejos; H. Álvarez-Pol; A. Bacquias; A. Boudard; M. Caamaño; T. Enqvist; V. Föhr; A. Keli?-Heil; K. Kezzar; S. Leray; C. Paradela; D. Pérez-Loureiro; R. Pleska?; D. Tarrío

2012-03-07

433

Violation of Fundamental Symmetries in Resonance Neutron Induced Fission  

NASA Astrophysics Data System (ADS)

It is considered the multimode neutron induced fission going via neutron resonances (NR) as a unique possibility to observe and to study interference phenomena in nuclear fission or quantum mechanical aspects of the process. The P-even and P-odd angular correlations of fission fragments (FF) are discussed in terms of the formal theory of (n,f) reaction in a helicity representation developed recently by authors. Due to the proper account of total space parity in FF channels and specific advantages of the helicity representation for these exit channels it becomes possible to calculate the reduced fission amplitudes and to sum the general expression for the differential cross section of (n,f) - reaction over all non observed characteristics of FF. After the summation the observed angular correlations could be expressed via the reduced S-matrix defined with aid "integral" fission amplitudes specified for the J?K (A.Bohr's) fission channels. The conditions necessary for "survival" of FF angular correlations (after summation over huge number of exit channels with random fission amplitudes) are discussed in connection with a spontaneous violation of the shape symmetry of fissioning nucleus on the way from the normal to scission deformation. In all consideration it is assumed that space parity violation in fission process takes place at the stage of compound nucleus before an "exit" to the transition state of fission. Some examples of theoretical analysis of experimental data relevant to the subject under discussion are presented. The results show possibility to study a dependence of fission barriers on parity and to get more deep insight in the nature of transition states of fissioning nuclei. It means that such study provides some new tools to investigate properties of nuclei at extremely high deformation. In conclusion it is discussed some open problems as the tasks for future experimental and theoretical study.

Barabanov, A.; Furman, W.; Popov, A.

2002-12-01

434

Evaluation of fission neutron spectra for minor actinides  

SciTech Connect

A method of evaluation of fission neutron spectra was developed and applied to minor actinides. The method is based on the Madland-Nix model of fission neutron emission, combined with the Ignatyuk model of the level density, the Moriyama-Ohnishi model of fission fragment mass distribution and the mass formula of Tachibana et al. It was found that the neutron spectra tend to be harder with increasing fissility of the compound nucleus.

Ohsawa, Takaaki; Shibata, Toshikazu [Kinki Univ., Osaka (Japan)

1994-12-31

435

Search for {beta}-delayed fission of {sup 228}Ac  

SciTech Connect

Radium was radiochemically separated from natural thorium. Thin {sup 228}Ra{yields}{beta}{sup -228}Ac sources were prepared and exposed to mica fission track detectors, and measured by an HPGe {gamma}-ray detector. The {beta}-delayed fission events of {sup 228}Ac were observed and its {beta}-delayed fission probability was found to be (5{+-}2)x10{sup -12}.

Xu Yanbing; Ding Huajie; Yuan Shuanggui; Yang Weifan; Niu Yanning; Li Yingjun; Xiao Yonghou [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); Zhang Shengdong [China Institute of Atomic Energy, Beijing 102413 (China); Lu Xiting [School of Physics, Peking University, Beijing 1000871 (China)

2006-10-15

436

T -odd asymmetries for evaporation ?-rays in nuclear fission  

Microsoft Academic Search

T-odd asymmetries in angular distributions of evaporation ?-rays emitted by thermalized fragments resulting from the fission\\u000a of axially symmetric deformed nuclei induced by cold polarized neutrons are investigated within the quantum theory of fission.\\u000a The asymmetries in question are due to the anisotropy of the angular distributions of evaporation ?-rays, caused by zero wriggling\\u000a vibrations of the fissioning nucleus and

S. G. Kadmenskii; V. E. Bunakov; S. S. Kadmenskii

2010-01-01

437

Fission studies with 140 MeV $\\bm?$-Particles  

E-print Network

Binary fission induced by 140 MeV $\\alpha$-particles has been measured for $^{\\rm nat}$Ag, $^{139}$La, $^{165}$Ho and $^{197}$Au targets. The measured quantities are the total kinetic energies, fragment masses, and fission cross sections. The results are compared with other data and systematics. A minimum of the fission probability in the vicinity $Z^2/A=24$ is observed.

A. Buttkewitz; H. H. Duhm; F. Goldenbaum; H. Machner; W. Strauss

2009-07-23

438

Fission studies with 140 MeV {alpha} particles  

SciTech Connect

Binary fission induced by 140 MeV {alpha} particles has been measured for {sup nat}Ag, {sup 139}La, {sup 165}Ho, and {sup 197}Au targets. The measured quantities are the total kinetic energies, fragment masses, and fission cross sections. The results are compared with other data and systematics. A minimum of the fission probability in the vicinity Z{sup 2}/A=24 is observed.

Buttkewitz, A.; Duhm, H. H.; Strauss, W. [I. Institut fuer Experimentalphysik, Universitaet Hamburg, Hamburg (Germany); Goldenbaum, F. [Institut fuer Kernphysik, Forschungszentrum Juelich, Juelich (Germany); Machner, H. [Institut fuer Kernphysik, Forschungszentrum Juelich, Juelich (Germany); Fachbereich Physik, Universitaet Duisburg-Essen, Duisburg (Germany)

2009-09-15

439

The nature of singlet exciton fission in carotenoid aggregates.  

PubMed

Singlet exciton fission allows the fast and efficient generation of two spin triplet states from one photoexcited singlet. It has the potential to improve organic photovoltaics, enabling efficient coupling to the blue to ultraviolet region of the solar spectrum to capture the energy generally lost as waste heat. However, many questions remain about the underlying fission mechanism. The relation between intermolecular geometry and singlet fission rate and yield is poorly understood and remains one of the most significant barriers to the design of new singlet fission sensitizers. Here we explore the structure-property relationship and examine the mechanism of singlet fission in aggregates of astaxanthin, a small polyene. We isolate five distinct supramolecular structures of astaxanthin generated through self-assembly in solution. Each is capable of undergoing intermolecular singlet fission, with rates of triplet generation and annihilation that can be correlated with intermolecular coupling strength. In contrast with the conventional model of singlet fission in linear molecules, we demonstrate that no intermediate states are involved in the triplet formation: instead, singlet fission occurs directly from the initial 1Bu photoexcited state on ultrafast time scales. This result demands a re-evaluation of current theories of polyene photophysics and highlights the robustness of carotenoid singlet fission. PMID:25825939

Musser, Andrew J; Maiuri, Margherita; Brida, Daniele; Cerullo, Giulio; Friend, Richard H; Clark, Jenny

2015-04-22

440

Uncertainties analysis of fission fraction for reactor antineutrino experiments  

E-print Network

Reactor antineutrino experiment are used to study neutrino oscillation, search for signatures of nonstandard neutrino interaction, and monitor reactor operation for safeguard application. Reactor simulation is an important source of uncertainties for a reactor neutrino experiment. Commercial code is used for reactor simulation to evaluate fission fraction in Daya Bay neutrino experiment, but the source code doesn't open to our researcher results from commercial secret. In this study, The open source code DRAGON was improved to calculate the fission rates of the four most important isotopes in fissions, $^{235}$U,$^{238}$U,$^{239}$Pu and $^{241}$Pu, and then was validated for PWRs using the Takahama-3 benchmark. The fission fraction results are consistent with those of MIT's results. Then, fission fraction of Daya Bay reactor core was calculated by using improved DRAGON code, and the fission fraction calculated by DRAGON agreed well with these calculated by SCIENCE. The average deviation less than 5\\% for all the four isotopes. The correlation coefficient matrix between $^{235}$U,$^{238}$U,$^{239}$Pu and $^{241}$Pu were also studied using DRAGON, and then the uncertainty of the antineutrino flux by the fission fraction was calculated by using the correlation coefficient matrix. The uncertainty of the antineutrino flux by the fission fraction simulation is 0.6\\% per core for Daya Bay antineutrino experiment. The uncertainties source of fission fraction calculation need further to be studied in the future.

X. B. Ma; F. Lu; L. Z. Wang; Y. X. Chen; W. L. Zhong; F. P. An

2015-03-17

441

Generalized Energy-Dependent Q Values for Fission  

SciTech Connect

We extend Madland's parameterization of the energy release in fission to obtain the dependence of the fission Q value for major and minor actinides on the incident neutron energies in the range 0 {le} E{sub n} {le} 20 MeV. Our parameterization is based on the actinide evaluations recommended for the ENDF/B-VII.1 release. This paper describes the calculation of energydependent fission Q values based on the calculation of the prompt energy release in fission by Madland. This calculation was adopted for use in the LLNL ENDL database and then generalized to obtain the prompt fission energy release for all actinides. Here the calculation is further generalized to the total energy release in fission. There are several stages in a fission event, depending on the time scale. Neutrons and gammas may be emitted at any time during the fission event.While our discussion here is focussed on compound nucleus creation by an incident neutron, similar parameterizations could be obtained for incident gammas or spontaneous fission.

Vogt, R

2010-03-31

442

Cold (neutronless) {alpha} ternary fission of {sup 252}Cf  

SciTech Connect

The phenomenon of cold (neutronless) alpha ternary fission in spontaneous fission of {sup 252}Cf was experimentally observed by triple gamma coincidence technique with Gammasphere with 72 gamma-ray detectors. Correlated pairs of {sub 36}Kr-{sub 60}Nd, {sub 38}Sr-{sub 58}Ce, {sub 40}Zr-{sub 56}Ba, {sub 42}Mo-{sub 54}Xe, {sub 44}Ru-{sub 52}Te, and {sub 46}Pd-{sub 50}Sn were observed to be associated with {alpha} ternary fission of {sup 252}Cf. Yields of cold {alpha} ternary fission were extracted. {copyright} {ital 1998} {ital The American Physical Society}

Ramayya, A.V.; Hamilton, J.H.; Hwang, J.K.; Peker, L.K.; Kormicki, J.; Babu, B.R.; Ginter, T.N.; Sandulescu, A.; Florescu, A.; Greiner, W.; Ter-Akopian, G.M.; Daniel, A.V.; Zhu, S.J. [Physics Department, Vanderbilt University, Nashville, Tennessee 37235 (United States)] [Physics Department, Vanderbilt University, Nashville, Tennessee 37235 (United States); Sandulescu, A.; Florescu, A.; Greiner, W.; Ter-Akopian, G.M.; Daniel, A.V.; Zhu, S.J. [Joint Institute for Heavy Ion Research, Oak Ridge, Tennessee 37835 (United States)] [Joint Institute for Heavy Ion Research, Oak Ridge, Tennessee 37835 (United States); Sandulescu, A.; Florescu, A.; Carstoiu, F. [Institute for Atomic Physics, Bucharest, P.O. Box MG-6 (Romania)] [Institute for Atomic Physics, Bucharest, P.O. Box MG-6 (Romania); Sandulescu, A.; Greiner, W. [Institute fuer Theoretische Physik der J.W. Goethe Universitaet, D-60054, Frankfurt am Main (Germany)] [Institute fuer Theoretische Physik der J.W. Goethe Universitaet, D-60054, Frankfurt am Main (Germany); Ter-Akopian, G.M.; Oganessian, Y.T.; Daniel, A.V. [Joint Institute for Nuclear Research, Dubna 141980 (Russia)] [Joint Institute for Nuclear Research, Dubna 141980 (Russia); Ma, W.C.; Varmette, P.G. [Department of Physics, Mississippi State University, Mississippi 39762 (United States)] [Department of Physics, Mississippi State University, Mississippi 39762 (United States); Rasmussen, J.O.; Asztalos, S.J.; Chu, S.Y.; Gregorich, K.E.; Macchiavelli, A.O.; Macleod, R.W. [Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)] [Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Cole, J.D.; Aryaeinejad, R.; Butler-Moore, K.; Drigert, M.W. [Idaho National Engineering Laboratory, Idaho Falls, Idaho 83415-2114 (United States)] [Idaho National Engineering Laboratory, Idaho Falls, Idaho 83415-2114 (United States); Stoyer, M.A.; Bernstein, L.A.; Lougheed, R.W.; Moody, K.J. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)] [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Prussin, S.G. [Nuclear Engineering Department, University of California, Berkeley, California 94720 (United States)] [Nuclear Engineering Department, University of California, Berkeley, California 94720 (United States); Zhu, S.J. [Physics Department, Tsinghua University, Beijing, Peoples Republic of (China)] [Physics Department, Tsinghua University, Beijing, Peoples Republic of (China); Griffin, H.C. [University of Michigan, Ann Arbor, Michigan 48104 (United States)] [University of Michigan, Ann Arbor, Michigan 48104 (United States); Donangelo, R. [University Federal do Rio de Janeiro, Rio de Janeiro, CP 68528, RG (Brazil)] [University Federal do Rio de Janeiro, Rio de Janeiro, CP 68528, RG (Brazil)

1998-05-01

443

Magnetic Materials Suitable for Fission Power Conversion in Space Missions  

NASA Technical Reports Server (NTRS)

Terrestrial fission reactors use combinations of shielding and distance to protect power conversion components from elevated temperature and radiation. Space mission systems are necessarily compact and must minimize shielding and distance to enhance system level efficiencies. Technology development efforts to support fission power generation scenarios for future space missions include studying the radiation tolerance of component materials. The fundamental principles of material magnetism are reviewed and used to interpret existing material radiation effects data for expected fission power conversion components for target space missions. Suitable materials for the Fission Power System (FPS) Project are available and guidelines are presented for bounding the elevated temperature/radiation tolerance envelope for candidate magnetic materials.

Bowman, Cheryl L.

2012-01-01

444

Advanced Modeling of Prompt Fission Neutrons and Gamma Rays  

NASA Astrophysics Data System (ADS)

Prompt fission neutrons and gamma rays are computed using a Monte Carlo treatment of the statistical evaporation of the excited primary fission fragments. The assumption of two fragments in thermal equilibrium at the time of neutron emission is addressed by studying the neutron multiplicity as a function of fragment mass. Results for the neutron-induced fission of 235U are discussed, for incident neutron energies from 0.5 to 5.5 MeV. Recent experimental data on the fission fragment yields as a function of mass and total kinetic energy are used as input data.

Talou, P.; Kawano, T.

2010-03-01

445

Exposure to common quaternary ammonium disinfectants decreases fertility in mice.  

PubMed

Quaternary ammonium compounds (QACs) are antimicrobial disinfectants commonly used in commercial and household settings. Extensive use of QACs results in ubiquitous human exposure, yet reproductive toxicity has not been evaluated. Decreased reproductive performance in laboratory mice coincided with the introduction of a disinfectant containing both alkyl dimethyl benzyl ammonium chloride (ADBAC) and didecyl dimethyl ammonium chloride (DDAC). QACs were detected in caging material over a period of several months following cessation of disinfectant use. Breeding pairs exposed for six months to a QAC disinfectant exhibited decreases in fertility and fecundity: increased time to first litter, longer pregnancy intervals, fewer pups per litter and fewer pregnancies. Significant morbidity in near term dams was also observed. In summary, exposure to a common QAC disinfectant mixture significantly impaired reproductive health in mice. This study illustrates the importance of assessing mixture toxicity of commonly used products whose components have only been evaluated individually. PMID:25483128

Melin, Vanessa E; Potineni, Haritha; Hunt, Patricia; Griswold, Jodi; Siems, Bill; Werre, Stephen R; Hrubec, Terry C

2014-12-01

446

Expanded record of Quaternary oceanographic change: Amerasian Arctic Ocean  

USGS Publications Warehouse

Four sediment cores collected from the Northwind and Mendeleyev ridges, Arctic Ocean, from 1089 m to 1909 m water depth, provide an oceanographic record extending back into the Matuyama reversed polarity chron. Benthic foraminiferal analyses show four prominent assemblage zones: Bolivina arctica, Cassidulina teretis, Bulimina aculeata, and Oridorsalis tener from the upper Matuyama reversed polarity chronozone through the Brunhes normal polarity chronozone. These assemblage zones represent depth-dependent benthic foraminiferal biofacies changes associated with oceanographic events that occurred in the Amerasian basin at ??? 780 and 300 ka, and indicate oceanographic influence from the North Atlantic. Recognition of these benthic assemblage zones in Arctic cores from the Alpha Ridge indicates that the benthic foraminiferal zonations in intermediate to deep water (>1000 m) Arctic cores may be more useful than preexisting lithostratigraphic zonations and should provide important information pertaining to the Quaternary paleoceanographic evolution of the Arctic Ocean.

Ishman, S.E.; Polyak, L.V.; Poore, R.Z.

1996-01-01

447

Asynchronous extinction of late Quaternary sloths on continents and islands  

PubMed Central

Whatever the cause, it is extraordinary that dozens of genera of large mammals became extinct during the late Quaternary throughout the Western Hemisphere, including 90% of the genera of the xenarthran suborder Phyllophaga (sloths). Radiocarbon dates directly on dung, bones, or other tissue of extinct sloths place their “last appearance” datum at ?11,000 radiocarbon years before present (yr BP) or slightly less in North America, ?10,500 yr BP in South America, and ?4,400 yr BP on West Indian islands. This asynchronous situation is not compatible with glacial–interglacial climate change forcing these extinctions, especially given the great elevational, latitudinal, and longitudinal variation of the sloth-bearing continental sites. Instead, the chronology of last appearance of extinct sloths, whether on continents or islands, more closely tracks the first arrival of people. PMID:16085711

Steadman, David W.; Martin, Paul S.; MacPhee, Ross D. E.; Jull, A. J. T.; McDonald, H. Gregory; Woods, Charles A.; Iturralde-Vinent, Manuel; Hodgins, Gregory W. L.

2005-01-01

448

Transport phenomena in a reactive quaternary gas mixture  

NASA Astrophysics Data System (ADS)

Quaternary gas mixtures which undergo a binary and reversible chemical reaction of the type A+B?C+D are analyzed within the framework of Boltzmann equation in order to investigate the effects caused by the reactions on the transport coefficients. The gas system is considered close to chemical equilibrium, a state in which the affinity has a small value characterizing the final stage of a chemical reaction. This kind of the reaction is also known in the literature as fast processes, i.e., processes whose frequencies of the interactions due to chemical reactions is of the same order of the elastic interactions between the constituents of the system. The theory is applied for two known reactions: H2+Cl?HCl+H and H+D2?HD+D. The coefficients of reaction rate, shear viscosity, thermal conductivity, diffusion and thermal diffusion ratio are analyzed for both reactions by considering the different parameters which characterize these chemical reactions.

Silva, Adriano W.; Alves, Giselle M.; Kremer, Gilberto M.

2007-02-01

449

Quaternary prevention, an answer of family doctors to overmedicalization  

PubMed Central

In response to the questioning of Health Policy and Management (HPAM) by colleagues on the role of rank and file family physicians in the same journal, the author, a family physician in Belgium, is trying to highlight the complexity and depth of the work of his colleagues and their contribution to the understanding of the organization and economy of healthcare. It addresses, in particular, the management of health elements throughout the ongoing relationship of the family doctor with his/her patients. It shows how the three dimensions of prevention, clearly included in the daily work, are complemented with the fourth dimension, quaternary prevention or prevention of medicine itself, whose understanding could help to control the economic and human costs of healthcare. PMID:25674569

Jamoulle, Marc

2015-01-01

450

Control of Quaternary sea-level changes on gas seeps  

NASA Astrophysics Data System (ADS)

Gas seeping to the seafloor through structures such as pockmarks may contribute significantly to the enrichment of atmospheric greenhouse gases and global warming. Gas seeps in the Gulf of Lions, Western Mediterranean, are cyclical, and pockmark "life" is governed both by sediment accumulation on the continental margin and Quaternary climate changes. Three-dimensional seismic data, correlated to multi-proxy analysis of a deep borehole, have shown that these pockmarks are associated with oblique chimneys. The prograding chimney geometry demonstrates the syn-sedimentary and long-lasting functioning of the gas seeps. Gas chimneys have reworked chronologically constrained stratigraphic units and have functioned episodically, with maximum activity around sea level lowstands. Therefore, we argue that one of the main driving mechanisms responsible for their formation is the variation in hydrostatic pressure driven by relative sea level changes.

Riboulot, Vincent; Thomas, Yannick; Berné, Serge; Jouet, Gwénaël.; Cattaneo, Antonio

2014-07-01

451

Quaternary ammonium poly(diethylaminoethyl methacrylate) possessing antimicrobial activity.  

PubMed

Quaternary ammonium (QA) methacrylate monomers and polymers were synthesized from a N-alkylation of N,N-diethylaminoethyl methacrylate (DEAEM) monomer. Linear copolymers, and for the first time reported crosslinked nanoparticles (NPs), based QA-PDEAEM were prepared by radical polymerization of the quaternized QA-DEAEM monomers with either methyl methacrylate (MMA) or a divinyl monomer. QA-PDEAEM NPs of 50-70nm were embedded in polyethylene vinyl acetate coating. QA-polymers with N-C8 and N-C18 alkyl chains and copolymers with methyl methacrylate were prepared at different molar ratios and examined for their antimicrobial effectiveness. These coatings exhibited strong antibacterial activity against four representative Gram-positive and Gram-negative bacteria. PMID:25686793

Farah, Shady; Aviv, Oren; Laout, Natalia; Ratner, Stanislav; Beyth, Nurit; Domb, Abraham J

2015-04-01

452

Fission-product energy release for times following thermal-neutron fission of ²³U between 2 and 14000 seconds  

Microsoft Academic Search

Fission-product decay energy-releases rates were measured for thermal-neutron fission of ²³U. Samples of mass 1 to 10 ..mu..g were irradiated for 1 to 100 sec by use of the fast pneumatic-tube facility at the Oak Ridge Research Reactor. The resulting beta- and gamma-ray emissions were counted for times-after-fission between 2 and 14,000 seconds. The data were obtained for beta and

J. K. Dickens; J. F. Emery; T. A. Love; J. W. McConnell; K. J. Northcutt; R. W. Peelle; H. Weaver

1977-01-01

453

Fission-fragment charge distributions in thermal-neutron induced fission of 239Pu and 235U  

Microsoft Academic Search

Fission-fragment charge distributions of heavy fragments were investigated for fragment masses 131 <= A <= 140 in the reactions 239Pu(nth, f) and 235U(nth, f). This was done by a correlated observation of beta-tracks and fission-fragment tracks in nuclear emulsions for fission fragments separated with respect to mass and kinetic energy by a recoil mass spectrograph. The average nuclear charges are

H. Gunther; G. Siegert; R. L. Ferguson; H. Ewald; E. Konecny

1972-01-01

454

Heavy-ion versus 3He\\/4He fusion-fission reactions: Angular momentum dependence of dissipation in nuclear fission  

Microsoft Academic Search

The stochastic Langevin model is employed to study dissipation properties in fission in the 16O + 181Ta -->197Tl system by analyzing prescission neutron yields measured in this reaction. It has been found that the 197Tl nuclei undergo fission that is not in accordance with the standard Bohr-Wheeler statistical theory. A detailed comparison with previously published work in which fission excitation

W. Ye

2011-01-01

455

Complex Support Vector Machines for Regression and Quaternary Classification.  

PubMed

The paper presents a new framework for complex support vector regression (SVR) as well as Support Vector Machines (SVM) for quaternary classification. The method exploits the notion of widely linear estimation to model the input-out relation for complex-valued data and considers two cases: 1) the complex data are split into their real and imaginary parts and a typical real kernel is employed to map the complex data to a complexified feature space and 2) a pure complex kernel is used to directly map the data to the induced complex feature space. The recently developed Wirtinger's calculus on complex reproducing kernel Hilbert spaces is employed to compute the Lagrangian and derive the dual optimization problem. As one of our major results, we prove that any complex SVM/SVR task is equivalent with solving two real SVM/SVR tasks exploiting a specific real kernel, which is generated by the chosen complex kernel. In particular, the case of pure complex kernels leads to the generation of new kernels, which have not been considered before. In the classification case, the proposed framework inherently splits the complex space into four parts. This leads naturally to solving the four class-task (quaternary classification), instead of the typical two classes of the real SVM. In turn, this rationale can be used in a multiclass problem as a split-class scenario based on four classes, as opposed to the one-versus-all method; this can lead to significant computational savings. Experiments demonstrate the effectiveness of the proposed framework for regression and classification tasks that involve complex data. PMID:25095266

Bouboulis, Pantelis; Theodoridis, Sergios; Mavroforakis, Charalampos; Evaggelatou-Dalla, Leoni

2014-07-30

456

Quaternary incised valleys in southern Brazil coastal zone  

NASA Astrophysics Data System (ADS)

High-resolution seismic records obtained in the Rio Grande do Sul coastal zone, southern Brazil, revealed that prominent valleys and channels developed in the area before the installation of actual coastal plain. Landwards, the paleoincisions can be linked with the present courses of the main river dissecting the area. Oceanwards, they can be linked with related features previously recognized in the continental shelf and slope by means of seismic and morphostructural studies. Based mainly on seismic, core data and geologic reasoning, it can be inferred that the coastal valleys were incised during forced regression events into the coastal prism deposited during previous sea level highstand events of the Quaternary. Seismic data has revealed paleovalleys up to 10 km wide and, in some places, infilled with up to 40 m thick of sediments. The results indicated two distinct periods of cut-and-fill events in the Patos Lagoon area. The filling of the younger incision system is mainly Holocene and its onset is related to the last main regressive event of the Pleistocene, when the sea level fell about 130 m below the actual position. The older incision and filling event is related to the previous regressive-transgressive events of the Middle and Late Pleistocene. The fluvial discharge fed delta systems on the shelf edge during the sea level lowstands. The subsequent transgressions drowned the incised drainage, infilling it and closing the inlets formerly connecting the coastal river to the ocean. The incised features may have played a significant role on the basin-margin architecture, facies distribution and accommodation space during the multitude of up and down sea level events of the Quaternary.

Weschenfelder, Jair; Baitelli, Ricardo; Corrêa, Iran C. S.; Bortolin, Eduardo C.; dos Santos, Cristiane B.

2014-11-01

457

Are seawater Sr/Ca variations preserved in Quaternary foraminifera?  

SciTech Connect

High precision measurements of Sr/Ca in planktonic foraminifera for the last 150 ka reveal Sr/Ca variations of up to 12% on glacial/interglacial time scales. Although records showing the largest variations appear to be strongly influenced by selective dissolution, other records show Sr/Ca variations of 3--5% that do not covary with indicators of dissolution intensity and that are reproduced in sites of contrasting Quaternary dissolution histories. These systematic variations are characterized by high Sr/Ca ratios during glacial maxima, followed by steep decreases during deglaciation and gradual increases through interstadial periods, closely following {delta}{sup 18}O curves. Foraminiferal Sr/Ca variations may reflect changes in the Sr/Ca ratio of seawater, or they may be due to kinetically or biologically induced changes in Sr partitioning. Coupled numerical models of the Sr and Ca budgets of the ocean reveal that sea level changes, together with large changes in river fluxes and carbonate accumulation rates, can produce seawater Sr/Ca variations that approximate both the shape and amplitude of foraminiferal Sr/Ca variations. However, such extreme changes in river and carbonate fluxes conflict with existing data on carbonate accumulation rates and Sr isotopic constraints on the magnitude of variations in the river flux. Smaller variations (1--3%) in the Sr/Ca ratio of seawater likely characterize Quaternary glacial cycles. Changes in Sr partitioning due to glacial-interglacial changes in the carbonate ion concentration and other environmental factors likely produce additional variation in the Sr/Ca record of planktonic foraminifera.

Stoll, H.M.; Schrag, D.P.; Clemens, S.C.

1999-11-01

458

Fission barrier, damping of shell correction and neutron emission in the fission of A$\\sim$200  

E-print Network

Decay of $^{210}$Po compound nucleus formed in light and heavy-ion induced fusion reactions has been analyzed simultaneously using a consistent prescription for fission barrier and nuclear level density incorporating shell correction and its damping with excitation energy. Good description of all the excitation functions have been achieved with a fission barrier of 21.9 $\\pm$ 0.2 MeV. For this barrier height, the predicted statistical pre-fission neutrons in heavy-ion fusion-fission are much smaller than the experimental values, implying the presence of dynamical neutrons due to dissipation even at these low excitation energies ($\\sim$ 50~MeV) in the mass region A $\\sim$ 200. When only heavy-ion induced fission excitation functions and the pre-fission neutron multiplicities are included in the fits, the deduced best fit fission barrier depends on the assumed fission delay time during which dynamical neutrons can be emitted. A fission delay of (0.8 $\\pm$ 0.1 )$\\times 10^{-19}$ s has been estimated correspondin...

Mahata, K; Kapoor, S S

2015-01-01

459

Fission Product Data Measured at Los Alamos for Fission Spectrum and Thermal Neutrons on 239Pu, 235U, 238U  

NASA Astrophysics Data System (ADS)

We describe measurements of fission product data at Los Alamos that are important for determining the number of fissions that have occurred when neutrons are incident on plutonium and uranium isotopes. The fission-spectrum measurements were made using a fission chamber designed by the National Institute for Standards and Technology (NIST) in the BIG TEN critical assembly, as part of the Inter-laboratory Liquid Metal Fast Breeder Reactor (LMFBR) Reaction Rate (ILRR) collaboration. The thermal measurements were made at Los Alamos' Omega West Reactor. A related set of measurements were made of fission-product ratios (so-called R-values) in neutron environments provided by a number of Los Alamos critical assemblies that range from having average energies causing fission of 400-600 keV (BIG TEN and the outer regions of the Flattop-25 assembly) to higher energies (1.4-1.9 MeV) in the Jezebel, and in the central regions of the Flattop-25 and Flattop-Pu, critical assemblies. From these data we determine ratios of fission product yields in different fuel and neutron environments (Q-values) and fission product yields in fission spectrum neutron environments for 99Mo, 95Zr, 137Cs, 140Ba, 141,143Ce, and 147Nd. Modest incident-energy dependence exists for the 147Nd fission product yield; this is discussed in the context of models for fission that include thermal and dynamical effects. The fission product data agree with measurements by Maeck and other authors using mass-spectrometry methods, and with the ILRR collaboration results that used gamma spectroscopy for quantifying fission products. We note that the measurements also contradict earlier 1950s historical Los Alamos estimates by ˜5-7%, most likely owing to self-shielding corrections not made in the early thermal measurements. Our experimental results provide a confirmation of the England-Rider ENDF/B-VI evaluated fission-spectrum fission product yields that were carried over to the ENDF/B-VII.0 library, except for 99Mo where the present results are about 4%-relative higher for neutrons incident on 239Pu and 235U. Additionally, our results illustrate the importance of representing the incident energy dependence of fission product yields over the fast neutron energy range for high-accuracy work, for example the 147Nd from neutron reactions on plutonium. An upgrade to the ENDF library, for ENDF/B-VII.1, based on these and other data, is described in a companion paper to this work.

Selby, H. D.; Mac Innes, M. R.; Barr, D. W.; Keksis, A. L.; Meade, R. A.; Burns, C. J.; Chadwick, M. B.; Wallstrom, T. C.

2010-12-01

460

CHAMBRES A FISSION MINIATURES POUR LES MESURES DES TAUX DE FISSION DANS LES RACTEURS DE RECHERCHE  

E-print Network

of the pulse spectrum, some recent realizations are described : small diameter chambers, low absorption chamber, and high temperature chamber. Finally, a brief survey of applications is given. REVUE DE PHYSIQUE APPLIQU�E produisent. La chambre d'ionisation à fission à impulsions, à remplissage gazeux, convient bien à ce dernier

Paris-Sud XI, Université de

461

THE THEORY OF NUCLEAR FISSION. IV. THE EFFECT OF THE MAGIC NUMBERS ON NUCLEAR FISSION  

Microsoft Academic Search

German) The concepts of fission theory developed in previous works (Ann. ; Physik (7) 7, 333(1961)) are systematically developed. From the basic conception ; of shell structure dependent deformation of the fragments at the moment of their ; separation, magic effects result in the nuclear force potential between both ; fragments and the mean kinetic energy of the fragments whose

W. Brunner; H. Paul

1961-01-01

462

Toward singlet fission for excitonic solar cells  

NASA Astrophysics Data System (ADS)

Sensitizer dyes capable of producing two triplet excited states from a singlet excited state produced by the absorption of a single photon would allow an increase of the efficiency of photovoltaic cells by up to a factor of 1.5, provided that each triplet injects an electron into a semiconductor such as TiO II. Although singlet fission in certain crystals and polymers was reported long ago, little is known about its efficiency in dyes suitable for use as sensitizers of photoinduced charge separation on semiconductors surfaces. Biradicaloids and large alternant hydrocarbons are desirable parent structures likely to meet the requirement E(T II), E(S I) > 2E(T I) for the excitation energies of the lowest excited singlet (S I) and the two triplet (T I, T II) states. We report results for 1,3-diphenylisobenzofuran, a model compound of the biradicaloid type. Its energy levels satisfy the desired relation, and in solution it shows no triplet formation by intersystem crossing. In the neat solid state, it forms triplets efficiently, and indirect evidence suggests that this is due to singlet fission. This appears to be the first compound displaying SF by design. When two such chromophores were combined into dimers, triplet formation yields of up to 9% were observed in polar solvents, possibly due to singlet fission, but possibly due to intersystem crossing. The triplet formation occurs in two steps, via an intermediate assigned as an intramolecular charge-transfer state and responsible for most of the observed excitation loss.

Michl, Josef; Nozik, Arthur J.; Chen, Xudong; Johnson, Justin C.; Rana, Geeta; Akdag, Akin; Schwerin, Andrew F.

2007-09-01

463

Antiproton Powered Gas Core Fission Rocket  

SciTech Connect

Extensive research in recent years has demonstrated that 'at rest' annihilation of antiprotons in the uranium isotope U238 leads to fission at nearly 100% efficiency. The resulting highly-ionizing, energetic fission fragments can heat a suitable medium to very high temperatures, making such a process particularly suitable for space propulsion applications. Such an ionized medium, which would serve as a propellant, can be confined by a magnetic field during the heating process, and subsequently ejected through a magnetic nozzle to generate thrust. The gasdynamic mirror (GDM) magnetic configuration is especially suited for this application since the underlying confinement principle is that the plasma be of such density and temperature as to make the ion-ion collision mean free path shorter than the plasma length. Under these conditions the plasma behaves like a fluid, and its escape from the system is analogous to the flow of a gas into vacuum from a vessel with a hole. For the system we propose we envisage radially injecting atomic or U238 plasma beam at a pre-determined position and axially pulsing an antiproton beam which upon interaction with the uranium target gives rise to near isotropic ejection of fission fragments with a total mass of 212 amu and total energy of about 160 MeV. These particles, along with the annihilation products (i.e. pions and muons) will heat the background U238 gas - inserted into the chamber just prior to the release of the antiproton - to one keV temperature. Preliminary analysis reveals that such a propulsion system can produce a specific impulse of about 3000 seconds at a thrust of about 50 kN. When applied to a round trip Mars mission, we find that such a journey can be accomplished in about 142 days with 2 days of thrusting and requiring only one gram of antiprotons to achieve it.

Kammash, Terry [Department of Nuclear Engineering and Radiological Sciences, University of Michigan, 2355 Bonisteel Blvd, Ann Arbor, MI 48109 (United States)

2005-02-06

464

Pairing-induced speedup of nuclear spontaneous fission  

NASA Astrophysics Data System (ADS)

Background: Collective inertia is strongly influenced at the level crossing at which the quantum system changes its microscopic configuration diabatically. Pairing correlations tend to make the large-amplitude nuclear collective motion more adiabatic by reducing the effect of these configuration changes. Competition between pairing and level crossing is thus expected to have a profound impact on spontaneous fission lifetimes. Purpose: To elucidate the role of nucleonic pairing on spontaneous fission, we study the dynamic fission trajectories of 264Fm and 240Pu using the state-of-the-art self-consistent framework. Methods: We employ the superfluid nuclear density functional theory with the Skyrme energy density functional SkM* and a density-dependent pairing interaction. Along with shape variables, proton and neutron pairing correlations are taken as collective coordinates. The collective inertia tensor is calculated within the nonperturbative cranking approximation. The fission paths are obtained by using the least action principle in a four-dimensional collective space of shape and pairing coordinates. Results: Pairing correlations are enhanced along the minimum-action fission path. For the symmetric fission of 264Fm, where the effect of triaxiality on the fission barrier is large, the geometry of the fission pathway in the space of the shape degrees of freedom is weakly impacted by pairing. This is not the case for 240Pu, where pairing fluctuations restore the axial symmetry of the dynamic fission trajectory. Conclusions: The minimum-action fission path is strongly impacted by nucleonic pairing. In some cases, the dynamical coupling between shape and pairing degrees of freedom can lead to a dramatic departure from the static picture. Consequently, in the dynamical description of nuclear fission, particle-particle correlations should be considered on the same footing as those associated with shape degrees of freedom.

Sadhukhan, Jhilam; Dobaczewski, J.; Nazarewicz, W.; Sheikh, J. A.; Baran, A.

2014-12-01

465

Excitation energy dependence of fission in the mercury region  

E-print Network

Background: Recent experiments on beta-delayed fission reported an asymmetric mass yield in the neutron-deficient nucleus 180Hg. Earlier experiments in the mass region A=190-200 close to the beta-stability line, using the (p,f) and (\\alpha,f) reactions, observed a more symmetric distribution of fission fragments. While the beta-delayed fission of 180Hg can be associated with relatively low excitation energy, this is not the case for light-ion reactions, which result in warm compound nuclei. Purpose: To elucidate the roles of proton and neutron numbers and excitation energy in determining symmetric and asymmetric fission yields, we compute and analyze the isentropic potential energy surfaces of 174,180,198Hg and 196,210Po. Methods: We use the finite-temperature superfluid nuclear density functional theory, for excitation energies up to E*=30MeV and zero angular momentum. For our theoretical framework, we consider the Skyrme energy density functional SkM* and a density-dependent pairing interaction. Results: For 174,180Hg, we predict fission pathways consistent with asymmetric fission at low excitation energies, with the symmetric fission pathway opening very gradually as excitation energy is increased. For 198Hg and 196Po, we expect the nearly-symmetric fission channel to dominate. 210Po shows a preference for a slightly asymmetric pathway at low energies, and a preference for a symmetric pathway at high energies. Conclusions: Our self-consistent theory suggests that excitation energy weakly affects the fission pattern of the nuclei considered. The transition from the asymmetric fission in the proton-rich nuclei to a more symmetric fission in the heavier isotopes is governed by the shell structure of pre-scission configurations.

J. D. McDonnell; W. Nazarewicz; J. A. Sheikh; A. Staszczak; M. Warda

2014-06-26

466

Pairing-induced speedup of nuclear spontaneous fission  

E-print Network

Collective inertia is strongly influenced at the level crossing at which quantum system changes diabatically its microscopic configuration. Pairing correlations tend to make the large-amplitude nuclear collective motion more adiabatic by reducing the