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Sample records for oklo natural fission

  1. Organic free radicals and micropores in solid graphitic carbonaceous matter at the Oklo natural fission reactors, Gabon

    International Nuclear Information System (INIS)

    The presence, concentration, and distribution of organic free radicals as well as their association with specific surface areas and microporosities help characterize the evolution and behavior of the Oklo carbonaceous matter. Such information is necessary in order to evaluate uranium mineralization, liquid bitumen solidification, and radio nuclide containment at Oklo. In the Oklo ore deposits and natural fission reactors carbonaceous matter is often referred to as solid graphitic bitumen. The carbonaceous parts of the natural reactors may contain as much as 65.9% organic C by weight in heterogeneous distribution within the clay-rich matrix. The solid carbonaceous matter immobilized small uraninite crystals and some fission products enclosed in this uraninite and thereby facilitated radio nuclide containment in the reactors. Hence, the Oklo natural fission reactors are currently the subjects of detailed studies because they may be useful analogues to support performance assessment of radio nuclide containment at anthropogenic radioactive waste repository sites. Seven carbonaceous matter rich samples from the 1968 ± 50 Ma old natural fission reactors and the associated Oklo uranium ore deposit were studied by electron spin resonance (ESR) spectroscopy and by measurements of specific surface areas (BET method). Humic acid, fulvic acid, and fully crystalline graphite standards were also examined by ESR spectroscopy for comparison with the Oklo solid graphitic bitumens. Wwith the Oklo solid graphitic bitumens. With one exception, the ancient Oklo bitumens have higher organic free radical concentrations than the modem humic and fulvic acid samples. The presence of carbon free radicals in the graphite standard could not be determined due to the conductivity of this material. 72 refs., 7 figs., 1 tab

  2. Nuclear fission is no invention of humans: The natural reactor of Oklo two billion years ago

    International Nuclear Information System (INIS)

    On 7 July 1972, in a routine isotopic analysis of a sample of uranium ore that was sent from the west African state of Gabon to the French isotope separation plant Pierrelatte, a content of only 0.7171 atomic per cent (at.%) of 235U, instead of 0.7202, was determined. The technicians who carried out the analyses were very exact, and they checked the analysis records of previous batches from the Oklo mine. They then noticed greater departures (eventually finding contents as low as 0.296 at.%!). These showed that the isotope depletions were greater for higher total uranium contents. Since geochemical isotope effects in such heavy elements are excluded, the only explanation was that nuclear fission was somehow involved. Thereupon analyses were undertaken of associated elements, e.g. neodymium, that is formed in high yield in nuclear fission. Here anomalies in the isotope composition relative to natural neodymium were explained on the basis of their known nuclear fission yields. Clear proofs for nuclear fission were also shown in other elements from zinc (atomic number (Z) = 30) to dysprosium (Z = 66). The clearest is the low abundance of 142Nd, since it is not formed in fission. The uranium content of ores from Oklo was especially high, so one can imagine that the entrance of rainwater could have started a self-sustaining chain reaction, initiated by neutrons from the spontaneous fission of 238U or by neutrons formed by secondary reactionr by neutrons formed by secondary reactions of cosmic radiation. From changes in isotope ratios, however, with modern mass spectrometry one can learn a lot about the migration of fission products. Thus it is possible to obtain a 'glimpse' of a final repository after millions of years, a better picture than any computer simulation has been able to provide. And although no technical barriers and no optimized geological conditions hindered the migration of fission products and plutonium, this picture shows that uranium, neptunium, plutonium, niobium, yttrium, technetium, zirconium and the rare earth metals have remained in their original places. Elements that have migrated are alkali metals, e.g. rubidium and caesium, the alkaline earth metals barium and strontium, the noble gases, molybdenum, cadmium, lead and iodine. It must also be noted that, in this historical final repository, the heat production of approximately 50 W/m2 (through the intermittent chain reaction) was many times higher than in the final repositories planned today for highly radioactive waste

  3. Geochemical and Neutronic Characteristics of the Natural Fossil Fission Reactors at Oklo and Bangombé, Gabon

    Science.gov (United States)

    Hidaka, Hiroshi; Holliger, Philippe

    1998-01-01

    Isotopic studies have been completed on samples from the natural fission reactors at Oklo and Bangombé in order to determine the conditions under which they functioned when critical and to evaluate the retention and migration of fissiogenic radionuclides. The abundances and isotopic compositions of the elements Rb, Sr, Zr, Ru, Pd, Ag, Te, Ba, rare earth elements (REEs), and U have been measured by thermal ionization mass spectrometry (TIMS) and inductively coupled plasma mass spectrometry (ICP-MS). Isotopic analyses and in situ ion imaging have also been performed by using an ion microprobe. Seven samples were taken from the SF84 borehole (zone 10), one from the S2 borehole in gallery SD37 (zone 13), both being zones in the Oklo deposit, and one from the BA145 borehole in the Bangombé deposit. The isotopic data allow for a detailed description of the functional conditions of these reactors, and based on these results, we have calculated the retention rates of the fissiogenic nuclides and nucleogenic Bi and Th. The nuclear parameters of the natural fission reactors are characterized by the isotopic abundances of Ru, Nd, Sm, Gd, Er, Yb, Lu, and U: neutron fluence (n/cm 2), fission proportions of 235U, 238U, and 239Pu, the restitution factor of 235U resulting from 239Pu decay, average temperature (°C) in the reactor, and duration of functioning (yr). In the 70 cm thick reactor core encountered by borehole SF84, the neutron fluence is in the range from 5.3x10 20 to 8.0x10 20 (n/cm 2). The variation in 235U depletion shows a strong positive correlation with the restitution factor and an inverse correlation with neutron fluence, which demonstrates the stability of the reaction zone since the period of criticality. Large depletions of 149Sm, 155Gd, and 157Gd have been detected in a sample of sandstone from 60 cm below this reactor core which also had a normal uranium isotopic ratio ( 235U/ 238U = 0.007254); this resulted from neutron capture reactions. The neutron fluence calculated from these isotopic anomalies is relatively high (6.2x10 18 n/cm 2) and probably shows that nuclear reactions began, but that criticality could never be sustained due to an excess of neutron poisons (e.g., Sm and Gd). The results obtained from SD37 reveal that reactor zone 13 is not similar to the other reactor zones. The proportion of 238U fission as calculated from the isotopic composition of Ru is extremely high (18% of the total), while that of SF84 (zone 10) is at most 5.0% of total fission. This result implies that the duration of criticality in reactor zone 13 was much shorter than in other reactor zones. In the Bangombé reactor zone BA145, the chemical and nuclear characteristics are close to those of SF84. The retentivities of many fission products as compared with fissiogenic Nd have been assessed for the reactor core samples. From the measured and calculated relative retentions, more than 90% of fissiogenic Ru, Rh, Pd, Te, and REEs have been retained in SF84 and SD37. In these same zones, however, the relative retentions of fissiogenic alkaline and alkaline earth elements are less than 20%. The retentions of long-lived radioisotopes, such as 90Sr, 99Tc, 137Cs, 236U, and 237Np have been calculated by reference to their radiogenic daughters 90Zr, 99Ru, 137Ba, 232Th, and 209Bi, respectively. The excess or depletion of isotopic abundances measured in the daughter nuclides has allowed the prediction of the rate of chemical fractionation between the parent and daughter nuclides in the reactor during criticality. These results greatly improve the understanding of the Oklo phenomenon and provide important data for the evaluation of the concept of long-term storage of radioactive wastes in geological formations.

  4. Oklo natural reactors: geological and geochemical conditions

    International Nuclear Information System (INIS)

    Published as well as unpublished material on the Oklo natural reactors in Gabon was evaluated with regard to the long-term aspects of nuclear waste disposal. Even though the vast data base available at present can provide only a site specific description of the phenomenon, already this material gives relevant information on plutonium retention, metamictization, fission product release, hydrogeochemical stability and migration of fission products. Generalized conclusions applicable to other nuclear waste repository would require the quantitative reconstruction of t s coupled thermo-hydrologic-chemical processes. This could be achieved by studying the deviations in the 2H/1H and 18O/16O ratios of minerals at Oklo. A further generalization of the findings from Oklo could be realized by examining the newly-discovered reactor zone 10, which was active under very different thermal conditions than the other reactors. 205 refs

  5. The Oklo natural nuclear reactors: neutron parameters, age and duration of the reactions, uranium and fission products migrations

    International Nuclear Information System (INIS)

    Mass spectrometry and isotopic dilution technique are used in order to carry out, on various samples from the fossil nuclear reactors at Oklo, Gabon, isotopic and chemical analyses of some particular elements involved in the nuclear reactions: uranium, lead, bismuth, thorium, rare gases (krypton, xenon), rare earths (neodymium, samarium, europium, gadolinium, dysprosium), ruthenium and palladium. Interpretations of these analyses lead to the determination of many neutron parameters such as the neutron fluence received by the samples, the spectrum index, the conversion coefficient, and also the percentages of fissions due to uranium-238 and plutonium-239 and the total number of fissions relative to uranium. All these results make it possible to determine the age of the nuclear reactions by measuring the amounts of fission rare earths formed, i.e. 1.97 billion years. This study brings some informations to the general problem of radioactive wastes storage in deep geological formations, the storage of uranium, plutonium and many fission products having been carried out naturally, and for about two billion years

  6. Oklo natural fission reactor program. Progress report, April 1-August 31, 1980

    Energy Technology Data Exchange (ETDEWEB)

    Curtis, D.B. (comp.)

    1980-12-01

    An interim report has been published on the redistribution of uranium, thorium, and lead in samples representing several million cubic meters of sandstone and metamorphosed sediments in the Athabasca Basin which is located in the northwest corner of the Canadian province of Saskatchewan. The region of study includes zones of uranium mineralization at Key Lake. Mineralization occurs at the unconformity between the Athabasca sandstone and the underlying metasediments and in fault zones within the metasediments. Lead isotopes record a radiometric age of 1300 +- 150 m.y. in samples from above and below the unconformity. This age probably reflects the time of deposition of the sandstones and an associated redistribution of uranium and/or lead in the underlying rocks. Many of the samples have been fractionated with respect to radiogenic lead and the actinide parent elements since that time. Sandstones and altered rocks from the region above the unconformity have been a transport path and are a repository for lead. In contrast, mineralized rocks are deficient in radiogenic lead and must be an important source of lead in the local geologic environment. Samples from Oklo reactor zone 9 and nearby host rocks have been prepared for isotopic analyses of ruthenium, molybdenum, uranium and lead.

  7. The analyses of various fissiogenic nuclides from Oklo natural reactor

    International Nuclear Information System (INIS)

    The isotopic compositions of Rb, Sr, Zr, Mo, Ru, Pd, Ag, Te, Ba, rare earth elements (REE) and U in four Oklo uranium ore samples were determined by thermal ionization mass spectrometer. The analyses of these elements make possible the reconstruction of relative fission product yield curves covering mass number range from 85 to 176 of Oklo samples. Relative mobility or retentivity of fissiogenic nuclides in the Oklo ore can be recognized from the deviations between empirical fission yields for uranium fuel and measured ones for Oklo samples. The degree of retention for some fissiogenic nuclides would be discussed. The comparison of empirical fission yields with measured ones suggests that Ru, Pd, Te and most of REE have been retained well in the reactor. On the other hand, considerably large amounts of fissiogenic Rb, Sr and Ba have been removed from the reactor. Fissiogenic Zr, Mo and Aa have been partially removed. (author)

  8. The deposit of Oklo and its natural nuclear reactors

    International Nuclear Information System (INIS)

    In the uranium deposit of Oklo (Republic of Gabon), seven zones have been discovered since 1972, in which natural fission reactions took place. Since 1974, a thorough geological study of these zones has been undertaken. It includes field studies, observations of drilled samples and laboratory studies. These studies permit the authors to define the geological environment of the reactors and to point out the influence of nuclear reactions on the surrounding formations. All this work was completed by a geological and metallogenic study of the deposit of Oklo and of the uraniferous basin of Franceville. The deposit of Oklo is situated in a detrital, sandstone-like and pelitic series belonging to the Francevillian. The Francevillian and the mineralization are dated as Middle Precambrian (1800-2000 M.A.). The ore of Oklo is the result of two concentration stages. In the first, uranium seems to have been fixed by hydrocarbons that were concentrated in oil traps. After a tectonic event, circulations of oxidizing solutions generated reconcentrations that are associated with hematite and have contents of UO2 between 1 and 20%. The fission reactions developed in the high-graded ores which had formed during the last phase of UO2 concentration. A thorough tectonic analysis of the ore deposit shows that high-graded ores and fission reactors are controlled by fractures. The working of nuclear reactors results in a local increase of temperature which gave a rise increase of temperature which gave a rise to circulation of warm water. The results of this hydrothermal circulation and of the neutron bombardment are seen in a succession of facies surrounding the reactors. At the centre of the reactor all sedimentary structures have been destroyed; within the reaction zone the following clays mineral zones are founded: (1) 1 Md illite and ferrous chlorite corresponding to the common Francevillian sediment; (2) 2 Md illite, (3) magnesium chlorite and (4) 1 Md illite and chlorite-vermiculite in the very rich uraninite ore. These dydrothermal circulations also caused removal of silica toward the outer zones which reacted affecting the geometry of the reactors by fracturing

  9. Recent outputs of the Oklo (Gabon) natural analogue study to nuclear waste disposal

    International Nuclear Information System (INIS)

    In the past twenty five years, the natural nuclear reactors of Oklo have been the subject of numerous detailed studies. First investigated for the physical and neutron aspects of the nuclear reaction, they were then reconsidered because they provide a unique opportunity in the world to study the containment of actinides and fission products in a geological formation over a broad timescale (two billion years). Although the sites investigated do not represent a complete analogue of a repository system, many of the processes studied (mass transfer to the surface, transport, migration / retention), the spatial extent of these processes, and the timescales involved, are compatible with processes liable to occur during the lifespan of a repository for the deep geological disposal of spent nuclear fuel. A fresh program was therefore initiated as a European Commission project in 1990, entitled''Oklo as a natural analog for transfer processes in a radioactive waste repository'- phase 7, and then extended by a phase 2 entitled Oklo, Natural Analogue - Behavior of Nuclear Reaction Products in a Natural Environment''. Researches conducted in phase I served to determine the physical conditions of the operation of the natural reactor, reconstruct the geological history of the reactor environment, and decode the behavior of actinides as well as fission products in the surrounding geological formations. Phase N, which ended in June 1999, had three main objectives: i) to assess radionuclide migration and retention processes from the reactor zones to the geological environment, ii) to define the confinement properties and long-term behavior of geological materials; iii) to test models of processes related to radionuclide migration and retention, and eventually to provide suitable data and scenarios for performance assessment of nuclear waste disposal. This paper proposes a synthesis of the main outputs of the Oklo project to the performance assessment of nuclear waste disposal, the study of the long-term evolution of spent fuel and the long-term behavior of geological materials with respect to the containment of actinides and fission products. The Oklo natural analogue displays a number of specific features that make it unique in the world. The Oklo basin is characterized by the occurrence of meter scale uraninite lenses, that were affected by nuclear fission 2 billion years ago. These ''reactor zones'' exist in three sites: Oklo, Okelobondo and Bagombe. By analogy with a repository system, they are considered as representative of the 'Source' term. Numerous isotopic and geochemical tracers are thus available in order to restrict the migration or retention processes of actinides and fission products present in these zones. The near environment of the reactor zones, called ''Near field'' by analogy, is mainly composed of clayey materials (i.e. chlorite, illite, kaolinite). Reactor zones are found at present from the surface (Bagombe under oxidizing and acid conditions, with supergene weathering) to deep (Okelobondo under reducing conditions, with a low groundwater dynamics) conditions. Some reactor zones, e.g. R.Z. 13 in Oklo mine, have been subjected to strong hydrothermal disturbances (with temperatures above 350 deg C), linked to the geological history of the Franceville basin. On the other hand, the old age of the Oklo reactors (2 Ga) implies that pressure, temperature and chemical conditions have evolved during a long geological history, with associated basin scale movements of fluids. The Oklo-natural analogue Phase II project compiled useful information and tools for persons involved in Performance Assessment of waste disposal, wasteform conception or long term behavior [10] in four main areas corresponding to major investigation fields: 1/ ''Source'' term evolution, 2/ Long term containment properties of geological materials, 3/ Migration and retention of actinides and fission or end products, and 4/Geochemical and transport modeling. The main outputs of the European Oklo project to the nuclear waste repository issue are shown. The

  10. Oklo reactors: natural analogs to nuclear waste repositories

    International Nuclear Information System (INIS)

    The 2-billion-year-old fossil reactors at Oklo are ancient natural nuclear waste sites. Isotope dilution mass spectrometric analyses of the fission products in the reactor core uraninite and the peripheral pelitic sandstone provide data for calculating the reactor operating parameters, the quantities of fissiogenic isotopes produced, the fraction of these isotopes retained in the cores, and the location in the peripheral rocks of the fissiogenic fraction lost from the cores. For a duration of criticality of 3 x 105 yrs, the thermal plus resonance neutron fluence ranged between 1020 and 1021 neutrons/cm2. The fraction of technetium (60 to 85%), ruthenium (75 to 90%), and neodymium (85 to 100%) retained is negatively correlated with fluence. The lost fission products are contained within a few tens of meters of their source, the reactor cores. The systematics of the decay of 99Tc (t/sub 1/2/ = 2.13 x 105 yr) to 99Ru limits the period of fissiogenic element migration to approximately 1 million yr at a time 2 billion yr ago. Thermodynamic calculations of the temperature-dependent solubilities indicate that the loss of fissiogenic elements is diffusion controlled, whereas retention in the surrounding rocks is a result of temperature-dependent deposition from an aqueous solution. These results concerning the geochemistry of technetium, ruthenium, and neodymium at a natural waste site support the concept of geologic burial of man-made radioactive wastes

  11. Fine structure in the mass yield curve and the Oklo natural reactors (Preprint No. IT-14)

    International Nuclear Information System (INIS)

    Fission yields can be determined by radiochemical or mass-spectrometric techniques. In the radiochemical method the number of fissions can be determined by direct counting of the radioactive fission products after exposing the fissionable materials to a neutron flux. However, the accuracy of radiochemically determined fission yields, particularly in the symmetric region where the probability of fission is low and uncertainties in isomeric ratios in the many of the nuclides of interest occur, is often poor. Fine structure effects can usually only be detected by the more accurate mass spectrometric technique. An important region in the study of fine structure is the symmetric valley where discontinuities in neutron yield distribution may occur. Although it must be acknowledged that an extrapolation of the results of the Oklo natural reactor to the storage of radioactive wastes in geological repositories is not a straightforward mater, nevertheless the isotopic studies carried out at Oklo have demonstrated that the retention of many fission products in well-preserved crystalline lattices has been achieved on a time scale far longer than is required for practical purposes. (author). 24 refs

  12. Organic matter and containment of uranium and fissiogenic isotopes at the Oklo natural reactors

    Science.gov (United States)

    Nagy, B.; Gauthier-Lafaye, F.; Holliger, P.; Davis, D.W.; Mossman, D.J.; Leventhal, J.S.; Rigali, M.J.; Parnell, J.

    1991-01-01

    SOME of the Precambrian natural fission reactors at Oklo in Gabon contain abundant organic matter1,2, part of which was liquefied at the time of criticality and subsequently converted to a graphitic solid3,4. The liquid organic matter helps to reduce U(VI) to U(IV) from aqueous solutions, resulting in the precipitation of uraninite5. It is known that in the prevailing reactor environments, precipitated uraninite grains incorporated fission products. We report here observations which show that these uraninite crystals were held immobile within the resolidified, graphitic bitumen. Unlike water-soluble (humic) organic matter, the graphitic bituminous organics at Oklo thus enhanced radionu-clide containment. Uraninite encased in solid graphitic matter in the organic-rich reactor zones lost virtually no fissiogenic lan-thanide isotopes. The first major episode of uranium and lead migration was caused by the intrusion of a swarm of adjacent dolerite dykes about 1,100 Myr after the reactors went critical. Our results from Oklo imply that the use of organic, hydrophobic solids such as graphitic bitumen as a means of immobilizing radionuclides in pretreated nuclear waste warrants further investigation. ?? 1991 Nature Publishing Group.

  13. Organic matter and containment of uranium and fissiogenic isotopes at the Oklo natural reactors

    International Nuclear Information System (INIS)

    Some of the Precambrian natural fission reactors at Oklo in Gabon contain abundant organic matter, part of which was liquefied at the time of criticality and subsequently converted to a graphitic solid. The liquid organic matter helps to reduce U(VI) to U(IV) from aqueous solutions, resulting in the precipitation of uraninite. It is known that in the prevailing reactor environments, precipitated uraninite grains incorporated fission products. We report here observations which show that these uraninite crystals were held immobile within the re-solidified, graphitic bituminous organics at Oklo thus enhanced radionuclide containment. Uraninite encased in solid graphitic matter in the organic-rich reactor zones lost virtually no fissiogenic lanthanide isotopes. The first major episode of uranium and lead migration was caused by the intrusion of a swarm of adjacent dolerite dykes about 1,100 Myr after the reactors went critical. Our results from Oklo imply that the use of organic, hydrophobic solids such as graphitic bitumen as a means of immobilizing radionuclides in pre-treated nuclear waste warrants further investigation. (author)

  14. Radiolysis in nature: Evidence from the Oklo natural reactors

    International Nuclear Information System (INIS)

    An examination of the mineralogy of the reactor zones at Oklo shows that they have been significantly altered. The rocks immediately adjacent to these zones are also mineralogically modified with respect to normal uranium bearing rocks. The mineralogic changes appear to be the consequence of radiation damage, changes in the bulk chemistry of the system and increased temperatures. Chemical changes were the consequence of convectively circulating fluids that transported elements in and out of the rocks. There were also changes in the electrochemical conditions in the rocks. These changes can most reasonably be attributed to oxidizing and reducing species produced by the radiolysis of water. We have calculated radiation doses and examined the production of radiolysis products in the fluid phase which lead to the following conclusions: 1) There was a net reduction of iron, probably associated with a net increase in total iron in the rocks of the reactor zones. The reduction of iron was most likely the result of hydrogen produced by the radiolysis of water. 2) Commensurate with the iron reduction, there was an oxidation of uranium and multivalent fission products, resulting in their transport out of the reactor zone. 3) Approximately 10 percent of the uranium and various proportions of these fission products were removed and redeposited in rocks within a few meters of the reactor zones. 4) The calculated radiation doses from alpha radiation and the inferred hydrogen production suggest an effective radiation yield of 0.06 molecules of hydrogen per 100 eV of energy imparted to the fluid phase. Considering radiation from both alpha and beta sources, the G value for hydrogen production is reduced to 0.01 to 0.002 molecules H2/100 eV. (author)

  15. Xenon in oklo al phosphate: implication for operational conditions of natural reactors.

    Science.gov (United States)

    Meshik, A. P.; Hohenberg, C. M.; Pravdivtseva, O. V.

    2003-04-01

    New data for the Oklo natural reactor (Gabon), obtained by laser microprobe extraction and high precision noble gas mass-spectrometry, confirm our previous findings of large amount of anomalous Xe in U-free Al-phosphate adjacent to uraninite [1]. Compared with known fission spectra, the anomalous Xe is enriched in 132Xe, 131Xe and, to a less extent, 129Xe and 134Xe. It was suggested [1] that the observed Xe anomalies are due to chemical fractionation of Xe from ?^ precursors (mainly I and Te) in isobaric decay chains. However, no mechanisms were proposed at that time. In this work, a follow-up to the previous studies, we explore the manner in which these anomalies may be produced. Apparently, under the temperatures present during the active periods of the Oklo reactor (300 - 450^oC), both I and Xe may easily diffuse out of U-oxides. Te in general is less mobile, due to slightly higher ionic radius, and has better retention than I and Xe. When the chain reaction is stopped, the temperature starts dropping and at the certain moment Xe formed from Te starts to retain in the Al-phosphate. Since that moment, accumulation of each Xe isotope must be proportional to decay time of corresponding Te isotope. This may in fact be responsible for the Xe anomalies found in Al-phosphate. 132Te, 131Te and 134Te have different half-lives and therefore ratios of these isotopes will not remain constant after the chain reaction is terminated due to the lack of water. Our calculation demonstrates that to produce the observed Xe anomalies the reactor must have been cycling with about 1frac{3}{4} hour period. Large concentration of fission products found in Al-phosphate also suggests that this material may be suitable for long-term storage of nuclear wastes. We are grateful to Don Bogard and to late Paul K. Kuroda with whom the idea of thermal cycling of Oklo reactor has been discussed. The Oklo sample was provided by Maurice Pagel and Yuri Dymkov. This work is supported by NASA grant NAG5-9442 References: [1] Meshik A. P., Kehm K., and Hohenberg C. M. (2000) GCA 64, No. 9, 1651-1661.

  16. Record of Cycling Operation of the Natural Nuclear Reactor in the Oklo/Okelobondo Area in Gabon

    Science.gov (United States)

    Meshik, A. P.; Hohenberg, C. M.; Pravdivtseva, O. V.

    2004-10-01

    Using selective laser extraction technique combined with sensitive ion-counting mass spectrometry, we have analyzed the isotopic structure of fission noble gases in U-free La-Ce-Sr-Ca aluminous hydroxy phosphate associated with the 2 billion yr old Oklo natural nuclear reactor. In addition to elevated abundances of fission-produced Zr, Ce, and Sr, we discovered high (up to 0.03 cm3 STP/g) concentrations of fission Xe and Kr, the largest ever observed in any natural material. The specific isotopic structure of xenon in this mineral defines a cycling operation for the reactor with 30-min active pulses separated by 2.5h dormant periods. Thus, nature not only created conditions for self-sustained nuclear chain reactions, but also provided clues on how to retain nuclear wastes, including fission Xe and Kr, and prevent uncontrolled runaway chain reaction.

  17. Record of cycling operation of the natural nuclear reactor in the Oklo/Okelobondo area in Gabon

    International Nuclear Information System (INIS)

    Using selective laser extraction technique combined with sensitive ion-counting mass spectrometry, we have analyzed the isotopic structure of fission noble gases in U-free La-Ce-Sr-Ca aluminous hydroxy phosphate associated with the 2 billion yr old Oklo natural nuclear reactor. In addition to elevated abundances of fission-produced Zr, Ce, and Sr, we discovered high (up to 0.03 cm3 STP/g) concentrations of fission Xe and Kr, the largest ever observed in any natural material. The specific isotopic structure of xenon in this mineral defines a cycling operation for the reactor with 30-min active pulses separated by 2.5 h dormant periods. Thus, nature not only created conditions for self-sustained nuclear chain reactions, but also provided clues on how to retain nuclear wastes, including fission Xe and Kr, and prevent uncontrolled runaway chain reaction

  18. What we learn from the nuclear data in Oklo natural reactor

    International Nuclear Information System (INIS)

    We reexamined the constraint for the time variation of the coupling constant of the fundamental interaction by studying the isotropic abundance of Sm observed at Oklo natural reactor. Using the most modern and reliable data, together with the study of the isotropic abundance of Gd, we found that the original finding of Shlyakhter is essentially correct, that is, the Oklo data provides us the most stringent limit for the time variation compared with any other methods. (author)

  19. Fate of the Epsilon Phase in the Oklo Natural Reactors

    International Nuclear Information System (INIS)

    In spent nuclear fuel (SNF), the micron- to submicron-sized epsilon phase (Mo-Ru-Pd-Tc-Rh) is an important host of 99Tc which has a long half life (2.13 x 105 years) and can be an important contributor to dose in safety assessments of nuclear waste repositories. In addition, Tc is predominantly present as TcO4- under oxidizing conditions at wide range of pH, weakly adsorbed onto mineral surfaces, and unlikely to be incorporated into alteration uranyl minerals. In the Oklo natural reactor (2.0 Ga), essentially all of the 99Tc has decayed to 99Ru. Thus, this study focuses on Ru and the other metals of the epsilon phase in order to investigate the occurrence and the fate of the epsilon phase during the corrosion of this natural SNF. Samples from reactor zone (RZ)-10 (836, 819, 687); from RZ-13 (864, 910); were investigated using TEM (transmission electron microscopy). Within the UO2 matrix, a Bi-Pd particle (40-60 nm), fioodite, PdBi2, was observed with trace amounts of As, Fe, and Te surrounded by an amorphous Pb-rich area. (Pd,Rh)2As, palladodymite or rhodarsenide, was observed (400-500 nm in size). Ruthenarsinite, (Ru,Ni)As, was identified in most samples: with a representative composition of As, 59.9: Co, 2.5: Ni, 5.2; Ru, 18.6; Rh, 8.4; Pd, 3.1; Sb, 2.4 in atomic percent. The particles diameters are a few hundred nanometers and, in most cases, surrounded by a Pb-rich phase (400-500 nm). Typically, the ruthenarsenite does not occur as single particle but an aggregate of ?200 nm-sized particles. Some Ru-particles revealed a complex phase separation within the grain such as a Ru-particle (600-700 nm) with Pb at the core of the particle and enrichment of Ni, Co, and As at the rim. Some ruthenarsenite crystals were embedded in chlorite immediately adjacent to uraninite. A few particles were still coated by Pb. These results suggest a history for the epsilon phases: (1) The original epsilon phase was transformed to, in most cases, ruthenarsenite. (2) All Mo and most of the Tc were released from the epsilon phase. Some portion of the other metals was also leached and provided a space for a precipitation of PbS between the ruthenarsenite and uraninite. (3) Once the uraninite matrix dissolved, the epsilon particles were released and sometimes captured within adjacent alteration minerals

  20. Fate of the epsilon phase in the Oklo natural reactors

    International Nuclear Information System (INIS)

    Full text of publication follows: In spent nuclear fuel (SNF), the micron- to submicron-sized epsilon phase (Mo-Ru-Pd-Tc-Rh) is an important host of 99Tc which has a long half life (2.13 x 105 years) and can be an important contributor to dose in safety assessments of nuclear waste repositories. In addition, Tc is predominantly present as TcO4 - under oxidizing conditions at wide range of pH, weakly adsorbed onto mineral surfaces, and unlikely to be incorporated into alteration uranyl minerals. In the Oklo natural reactor (2.0 Ga), essentially all of the 99Tc has decayed to 99Ru. Thus, this study focuses on Ru and the other metals of the epsilon phase in order to investigate the occurrence and the fate of the epsilon phase during the corrosion of this natural SNF. Samples from reactor zone (RZ)-10 (836, 819, 687); from RZ-13 (864, 910); were investigated using TEM (transmission electron microscopy). Within the UO2 matrix, a Bi-Pd particle (40-60 nm), froodite, PdBi2, was observed with trace amounts of As, Fe, and Te surrounded by an amorphous Pb-rich area. (Pd,Rh)2As, palladodymite or rhodarsenide, was observed (400-500 nm in size). Ruthenarsinite, (Ru,Ni)As, was identified in most samples: with a representative composition of As, 59.9: Co, 2.5: Ni, 5.2; Ru, 18.6; Rh, 8.4; Pd, 3.1; Sb, 2.4 in atomic percent. The particles diameters are a few hundred nanometers and, in most cases, sw hundred nanometers and, in most cases, surrounded by a Pb-rich phase (400-500 nm). Typically, the ruthenarsenite does not occur as single particle but an aggregate of ?200 nm-sized particles. Some Ru-particles revealed a complex phase separation within the grain such as a Ru-particle (600-700 nm) with Pb at the core of the particle and enrichment of Ni, Co, and As at the rim. Some ruthenarsenite crystals were embedded in chlorite immediately adjacent to uraninite. A few particles were still coated by Pb. These results suggest a history for the epsilon phases: (i) The original epsilon phase was transformed to, in most cases, ruthenarsenite. (ii) All Mo and most of the Tc were released from the epsilon phase. Some portion of the other metals was also leached and provided a space for a precipitation of PbS between the ruthenarsenite and uraninite. (iii) Once the uraninite matrix dissolved, the epsilon particles were released and sometimes captured within adjacent alteration minerals. (authors)

  1. Geological follow-up of the mining of the Oklo natural rectors

    International Nuclear Information System (INIS)

    The part of the Oklo natural reactors which was still in place after their discovery was mined between September 1975 and February 1977. In the reaction zones 27 faces and 8 outcrops have been surveyed in detail and sampled, approximately 1700 samples having been taken. In the course of these surveys a large number of sedimentological, petrographic and tectonic observations have been made. (author)

  2. Natural Nuclear Reactor Oklo and Variation of Fundamental Constants Part 1: Computation of Neutronics of Fresh Core

    OpenAIRE

    Petrov, Yu V.; Nazarov, A. I.; Onegin, M. S.; Petrov, V. Yu; Sakhnovsky, E. G.

    2005-01-01

    Using modern methods of reactor physics we have performed full-scale calculations of the natural reactor Oklo. For reliability we have used recent version of two Monte Carlo codes: Russian code MCU REA and world wide known code MCNP (USA). Both codes produce similar results. We have constructed a computer model of the reactor Oklo zone RZ2 which takes into account all details of design and composition. The calculations were performed for three fresh cores with different uran...

  3. Knowledge gained from the study of natural fossil reactors at Oklo for radioactive waste disposal

    International Nuclear Information System (INIS)

    The natural reactors of Oklo operated about two thousand million years ago and since then the uranium has remained in place almost in its entirety; this remarkable state of preservation has made it possible to make some interesting observations regarding the containment or, conversely, the dispersion of fission-produced or radiogenic elements in the ground. The geological environment of the reactors is described briefly; the most important fact is that the thermal convection currents associated with the heat release from nuclear reactions have completely desilicated the sandstones which contained uranium, thereby forming argillaceous lenses. The behaviour of the elements studied is described, these being classified into three categories according to their geochemical stability: (1) Elements that have been almost entirely preserved apart from occasional small redistributions. These are mainly the rare earths, zirconium, the elements of platinum ore (Ru, Rh and Pd) and radiogenic thorium. It is moreover fairly certain that the plutonium remained intact in the uranium before decaying; (2) Elements that have migrated but still exist in considerable quantities, notably radiogenic lead and bismuth and molybdenum; and (3) Elements that have been practically eliminated apart from small traces. These are the rare gases (Kr and Xe), iodine, cadmium, the alkali metals (Rb and Cs) and the alkaline-earth metals (Sr and Br). It seems, however, that in certain cases the migration ofer, that in certain cases the migration of these elements from uranium may not have been very rapid. The main conclusion to be drawn from these observations is that uraninite was largely responsible for the preservation; it has exhibited a very remarkable retentive capacity, especially for weakly volatile elements having ionic radii compatible with its crystal lattice. On the other hand, the retentive capacities of argillaceous gangue and of the environment seem to have been rather poor

  4. The Oklo phenomenon as an analogue of radioactive waste disposal. A review

    International Nuclear Information System (INIS)

    This work demonstrates the utility of the Oklo uranium ore deposit and natural fission reactors as a long time scale analogue for man-made radioactive waste repositories. Oklo has opened a new horizon representing an unrivalled opportunity to apply isotopic geochemistry to the study of migrations of fission products after an extremely long cooling and storage time and to define the processes involved in the transport of these elements through geological materials. This is the topic of the first section of this report. In the second section the information available on retention or migration at Oklo of the most interesting fission products is presented trying to illustrate how relevant the Oklo experience is in formulating predictions on the destiny of high activity waste disposed of in stable geological formations

  5. Oklo. A review and critical evaluation of literature

    International Nuclear Information System (INIS)

    The Oklo natural fossil fission reactors in Gabon, Equatorial Africa, have been studied as a natural analogue for spent nuclear fuel in a geological environment. For these studies, it is important to know what has happened to these reactors since they formed. This review is focussed on existing geological and geochronological information concerning the Oklo reactors and the surrounding ore. A sequence of geological and geochemical events in the Oklo area, as described in the literature, is given. The data and the studies behind this established geochronology are discussed and evaluated. Of the regional geology, special attention is given to the dating of the Francevillian sediments, and the intrusion of a dolerite dyke swarm. The processes that led to the mineralisation at Oklo, the subsequent formation of the nuclear reactors and later migration of fission products are described. Further discussion concerns the studies of the dolerite dyke swarm, since this appears to be one of the most important events related to fission product migration. A close look at the data related to this event shows that further study of the age of the dolerite dykes, and their effect on the uraninite in the Oklo reactors, is needed

  6. Oklo. A review and critical evaluation of literature

    Energy Technology Data Exchange (ETDEWEB)

    Zetterstroem, Lena [Swedish Museum of Natural History, Stockholm (Sweden). Lab. for Isotope Geology

    2000-10-01

    The Oklo natural fossil fission reactors in Gabon, Equatorial Africa, have been studied as a natural analogue for spent nuclear fuel in a geological environment. For these studies, it is important to know what has happened to these reactors since they formed. This review is focussed on existing geological and geochronological information concerning the Oklo reactors and the surrounding ore. A sequence of geological and geochemical events in the Oklo area, as described in the literature, is given. The data and the studies behind this established geochronology are discussed and evaluated. Of the regional geology, special attention is given to the dating of the Francevillian sediments, and the intrusion of a dolerite dyke swarm. The processes that led to the mineralisation at Oklo, the subsequent formation of the nuclear reactors and later migration of fission products are described. Further discussion concerns the studies of the dolerite dyke swarm, since this appears to be one of the most important events related to fission product migration. A close look at the data related to this event shows that further study of the age of the dolerite dykes, and their effect on the uraninite in the Oklo reactors, is needed.

  7. The Oklo reactors

    International Nuclear Information System (INIS)

    The Oklo reactors comprise up to nine 235-U depleted zones in an uranium ore in the Republic of Gabon in West Africa. The depletion in fissile U-235 has been proved to have caused by nuclear chain reactions. The study of the Oklo phenomenon indicates that very efficient retardation mechanisms may operate in nature - at least under special conditions. A closer study of these processes ought to be made to establish the limitations to their occurrence. The Oklo sandstone formation today would probably be considered unacceptable as a host rock for a repository. (EG)

  8. Thermohydraulic and nuclear modeling of natural fission reactors

    Science.gov (United States)

    Viggato, Jason Charles

    Experimental verification of proposed nuclear waste storage schemes in geologic repositories is not possible, however, a natural analog exists in the form of ancient natural reactors that existed in uranium-rich ores. Two billion years ago, the enrichment of natural uranium was high enough to allow a sustained chain reaction in the presence of water as a moderator. Several natural reactors occurred in Gabon, Africa and were discovered in the early 1970's. These reactors operated at low power levels for hundreds of thousands of years. Heated water generated from the reactors also leached uranium from the surrounding rock strata and deposited it in the reactor cores. This increased the concentration of uranium in the core over time and served to "refuel" the reactor. This has strong implications in the design of modern geologic repositories for spent nuclear fuel. The possibility of accidental fission events in man-made repositories exists and the geologic evidence from Oklo suggests how those events may progress and enhance local concentrations of uranium. Based on a review of the literature, a comprehensive code was developed to model the thermohydraulic behavior and criticality conditions that may have existed in the Oklo reactor core. A two-dimensional numerical model that incorporates modeling of fluid flow, temperatures, and nuclear fission and subsequent heat generation was developed for the Oklo natural reactors. The operating temperatures ranged from about 456 K to about 721 K. Critical reactions were observed for a wide range of concentrations and porosity values (9 to 30 percent UO2 and 10 to 20 percent porosity). Periodic operation occurred in the computer model prediction with UO2 concentrations of 30 percent in the core and 5 percent in the surrounding material. For saturated conditions and 30 percent porosity, the model predicted temperature transients with a period of about 5 hours. Kuroda predicted 3 to 4 hour durations for temperature transients. The large instantaneous jumps in temperature could be an indication of the violent ejection of water that Kuroda predicted, resulting in ongoing geyser activity. The range of temperatures simulated by the computer model within the Oklo reactors agreed with evidence from the Oklo geology.

  9. Oklo working group meeting

    International Nuclear Information System (INIS)

    Natural analogue studies have been carried out for several years in the framework of the European Community's R and D programme on radioactive waste; and within its recent fourth five-year programme on 'Management and storage of radioactive waste (1990-94)' the Community is participating in the Oklo study, natural analogue for transfer processes in a geological repository. The Oklo project is coordinated by CEA-IPSN (F) and involves laboratories from several CEA directorates (IPSN, DTA and DCC) which collaborate with other institutions from France: CREGU, Nancy; CNRS, Strasbourg and ENSMD, Fontainebleau. Moreover, institutes from non-EC member States are also taking part in the Oklo study. The second joint CEC-CEA progress meeting of the Oklo Working Group was held in April 1992 in Brussels and gave the possibility of reviewing and discussing progress made since its first meeting in February 1991 at CEA in Fontenay-aux-Roses. About 40 participants from 15 laboratories and organizations coming from France, Canada, Gabon, Japan, Sweden and the USA underline the great interest in the ongoing research activities. The meeting focused on the different tasks within the CEC-CEA Oklo project concerning (i) field survey and sampling, (ii) characterization of the source term, (iii) studies of the petrographical and geochemical system, and (iv) studies of the hydrogeological system and hydrodynamic modelling. (author) 17 papers are presented

  10. The epsilon Phase in the UO2 of the Oklo Natural Reactors

    International Nuclear Information System (INIS)

    In spent nuclear fuel (SNF), the metal epsilon phase consists of an alloy of Mo-Ru-Pd-Tc-Rh, occurring at a micron to sub-micron scale. 99Tc has a long half life (2.13 x 105 years) and can be an important contributor to dose in safety assessments of nuclear waste repositories. Under oxidizing conditions, TcO4- is the predominant species of Tc. In this form, Tc is highly soluble and weakly adsorbed onto mineral surfaces. Because the Oklo reactors are 2.0 billion years old, a majority of the 99Tc formed by natural fission reactions has decayed to 99Ru. Thus, this study is focused on Ru and the other constituents of the epsilon phase in order to investigate the occurrence and the fate of epsilon phase elements during the corrosion of this natural SNF. Samples from reactor zone (RZ)-10 (836, 819, 687); from RZ-13 (864, 910); from Okklobondo (943) were studied. High resolution transmission electron microscopy (HRTEM) and high-angle annular dark-field scanning TEM (HAADF-STEM) with energy dispersive X-ray analysis (EDX) were completed on thin foil specimens of uraninite from each reactor zone. Among these samples, no Ru-bearing phase is observed in 910 and 943. A Bi-Pd particle (40-60 nm), froodite, PdBi2, occurs with trace amounts of As, Fe, and Te surrounded by an amorphous Pb-rich area (No.864). A Ru-As particle (?300nm) occurs surrounded by Pb-rich inclusion (400-500 nm) in uraninite (No.819). Based on EDX analysis the composition is: As, 59.9 Co, 2.5: Ni, 5.2; Ru, 18.6; Th, 8.4; Pd, 3.1; Sb, 2.4 in atomic%. The Ru-As phase is not a single particle, but an aggregate of 100-200 nm-sized ruthenarsenite, (Ru,Ni)As, particles. Another Ru-particle (600-700 nm) shows that Pb occurs at the core of the particle, and the rim portion consists of Ni, Co, and As without Ru (No.819). Ru-particles, ruthenarsenite, occur with Ni between the core and the rim. A Mo-particle (2As. All of the Ru-phases are associated with polycrystalline galena. There is a wide variation in the composition of the Ru-phase. The Ru-particles are, in most cases, ruthenarsenite, and do not contain detectable amounts of Mo, although the Mo-concentration for the epsilon phase in SNF is reported to be as high as 40 atomic%. Mo is only observed as a separate nano-scale phase in a nanocrystalline aggregate of galena

  11. Natural Nuclear Reactor Oklo and Variation of Fundamental Constants Part 1: Computation of Neutronic of Fresh Core

    CERN Document Server

    Petrov, Yu V; Onegin, M S; Petrov, V Yu; Sakhnovskii, E G; Petrov, Yu.V.

    2006-01-01

    Using a modern methods of reactor physics we have performed the full-scale calculations of the natural reactor Oklo. For reliability we have used the recent version of two Monte Carlo codes: the Russian code MCU REA and world wide known code MCNP (USA). Both codes produce close results. We constructed computer model of zone RZ2 of reactor Oklo which takes into account all details of design and composition. The calculations were performed for the three fresh cores with different uranium contents. Multiplication factors, reactivities and neutron fluxes were calculated. We estimated also the temperature and void effects for the fresh core. As would be expected, we have found for the fresh core a great difference between reactor spectra and Maxwell's one, which was used before for averaging cross sections in the Oklo reactor. The averaged cross section of Sm and its dependence on the shift of resonance position (due to variation of fundamental constants) are significantly different from previous results. Contrary...

  12. Natural nuclear reactor at Oklo and variation of fundamental constants: Computation of neutronics of a fresh core

    Science.gov (United States)

    Petrov, Yu. V.; Nazarov, A. I.; Onegin, M. S.; Petrov, V. Yu.; Sakhnovsky, E. G.

    2006-12-01

    Using modern methods of reactor physics, we performed full-scale calculations of the Oklo natural reactor. For reliability, we used recent versions of two Monte Carlo codes: the Russian code MCU-REA and the well-known international code MCNP. Both codes produced similar results. We constructed a computer model of the Oklo reactor zone RZ2 which takes into account all details of design and composition. The calculations were performed for three fresh cores with different uranium contents. Multiplication factors, reactivities, and neutron fluxes were calculated. We also estimated the temperature and void effects for the fresh core. As would be expected, we found for the fresh core a significant difference between reactor and Maxwell spectra, which had been used before for averaging cross sections in the Oklo reactor. The averaged cross section of 62149Sm and its dependence on the shift of a resonance position Er (due to variation of fundamental constants) are significantly different from previous results. Contrary to the results of previous papers, we found no evidence of a change of the samarium cross section: a possible shift of the resonance energy is given by the limits -73??Er?62 meV. Following tradition, we have used formulas of Damour and Dyson to estimate the rate of change of the fine structure constant ?. We obtain new, more accurate limits of -4×10-17??·/??3×10-17yr-1. Further improvement of the accuracy of the limits can be achieved by taking account of the core burn-up. These calculations are in progress.

  13. THE FATE OF THE EPSILON PHASE IN UO2 OF THE OKLO NATURAL FISSON REACTORS

    International Nuclear Information System (INIS)

    In spent nuclear fuel (SNF), the micron- to nano-sized epsilon phase (Mo-Ru-Pd-Tc-Rh) is an important host of 99Tc which has a long half life (2.13 x 105 years) and can be an important contributor to dose in safety assessments of nuclear waste repositories. In order to examine the occurrence and the fate of the epsilon phase during the corrosion of SNF over long time periods, samples of uraninite from the Oklo natural reactors (?2.0 Ga) have been investigated using transmission electron microscopy (TEM). Because essentially all of the 99Tc has decayed to 99Ru, this study focuses on 4d-elements of the epsilon phase. Samples were obtained from the research collection at University of Michigan representing reactor zone (RZ) 10 (836, 819,687) and from RZ 13 (864,910). Several phases with 4d-metals have been identified within UO2 matrix at the scale of 50-700 nm; fioodite, PdBi2, with trace amounts of As, Fe, and Te, and palladodymite or rhodarsenide, (Pd,Rh)2As. The most abundant 4d-metal phase is ruthenarsinite, (Ru,Ni)As, which has a representative composition: As, 59.9; Coy 2.5; Ni, 5.2; Ru, 18.6; Rh, 8.4; Pd, 3.1; Sb, 2.4 in atomic%. Ruthenarsenite nanoparticles are typically surrounded by Pb-rich domains, galena in most cases; whereas, some particles reveal a complexly zoned composition within the grain, such as a Pb-rich domain at the core and enrichment of Ni, Co, and As at the rim. Some ruthenarsenites and Rh-Bi-particles are embedded in surrounding alteration products, e.g., chlorite, adjacent to uraninite (no further than ?5 (micro)m). A few of those particles are still coated by a Pb-rich layer. Based on these results, the history that epsilon phases have experienced can be described as follows: (1) The original epsilon phase was changed to, in most cases, ruthenarsenite, by As-rich fluids with other trace metals. Dissolution and a simultaneous precipitation may be responsible for the phase change. (2) All Mo and most of the Tc were released from the epsilon phase. Galena precipitated surrounding the 4d-metal phases. (3) Once the uraninite matrix has dissolved, the epsilon nanoparticles were released and ''captured'' within alteration phases that are immediately adjacent to the uraninite

  14. THE FATE OF THE EPSILON PHASE IN UO2 OF THE OKLO NATURAL FISSON REACTORS

    Energy Technology Data Exchange (ETDEWEB)

    S. Utsunomiya; R.C. Ewing

    2005-09-08

    In spent nuclear fuel (SNF), the micron- to nano-sized epsilon phase (Mo-Ru-Pd-Tc-Rh) is an important host of {sup 99}Tc which has a long half life (2.13 x 10{sup 5} years) and can be an important contributor to dose in safety assessments of nuclear waste repositories. In order to examine the occurrence and the fate of the epsilon phase during the corrosion of SNF over long time periods, samples of uraninite from the Oklo natural reactors ({approx}2.0 Ga) have been investigated using transmission electron microscopy (TEM). Because essentially all of the {sup 99}Tc has decayed to {sup 99}Ru, this study focuses on 4d-elements of the epsilon phase. Samples were obtained from the research collection at University of Michigan representing reactor zone (RZ) 10 (836, 819,687) and from RZ 13 (864,910). Several phases with 4d-metals have been identified within UO{sub 2} matrix at the scale of 50-700 nm; fioodite, PdBi{sub 2}, with trace amounts of As, Fe, and Te, and palladodymite or rhodarsenide, (Pd,Rh){sub 2}As. The most abundant 4d-metal phase is ruthenarsinite, (Ru,Ni)As, which has a representative composition: As, 59.9; Coy 2.5; Ni, 5.2; Ru, 18.6; Rh, 8.4; Pd, 3.1; Sb, 2.4 in atomic%. Ruthenarsenite nanoparticles are typically surrounded by Pb-rich domains, galena in most cases; whereas, some particles reveal a complexly zoned composition within the grain, such as a Pb-rich domain at the core and enrichment of Ni, Co, and As at the rim. Some ruthenarsenites and Rh-Bi-particles are embedded in surrounding alteration products, e.g., chlorite, adjacent to uraninite (no further than {approx}5 {micro}m). A few of those particles are still coated by a Pb-rich layer. Based on these results, the history that epsilon phases have experienced can be described as follows: (1) The original epsilon phase was changed to, in most cases, ruthenarsenite, by As-rich fluids with other trace metals. Dissolution and a simultaneous precipitation may be responsible for the phase change. (2) All Mo and most of the Tc were released from the epsilon phase. Galena precipitated surrounding the 4d-metal phases. (3) Once the uraninite matrix has dissolved, the epsilon nanoparticles were released and ''captured'' within alteration phases that are immediately adjacent to the uraninite.

  15. Radioactive wastes in Oklo

    International Nuclear Information System (INIS)

    The acceptance of the Nuclear Energy as electric power supply implies to give answer to the population on the two main challenges to conquer in the public opinion: the nuclear accidents and the radioactive wastes. Several of the questions that are made on the radioactive wastes, its are the mobility migration of them, the geologic stability of the place where its are deposited and the possible migration toward the aquifer mantels. Since the half lives of the radioactive waste of a Nuclear Reactor are of several hundred of thousands of years, the technical explanations to the previous questions little convince to the public in general. In this work summary the results of the radioactive waste generated in a natural reactor, denominated Oklo effect that took place in Gabon, Africa, it makes several thousands of millions of years, a lot before the man appeared in the Earth. The identification of at least 17 reactors in Oklo it was carried out thanks to the difference in the concentrations of Uranium 235 and 238 prospective, and to the analysis of the non-mobility of the radioactive waste in the site. It was able by this way to determine that the reactors with sizes of hardly some decimeter and powers of around 100 kilowatts were operating in intermittent and spontaneous form for space of 150,000 years, with operation cycles of around 30 minutes. Recent studies have contributed information valuable on the natural confinement of the radioactive waste of the Oklo reactors in matrixes of minerals of aluminum phosphate that caught and immobilized them for thousands of millions of years. This extracted information from the nature contributes guides and it allows 'to verify' the validity of the current proposals on the immobilization of radioactive wastes of a nuclear reactor. This work presents in clear and accessible form to the public in general on the secure 'design', operation, 'decommissioning' and 'storage' of the radioactive waste of the reactors that the nature put into operation in Oklo before the man appeared in the Earth. (Author)

  16. Gas, benefits and question marks. The Oklo reactors: 100 % natural. The Kyoto protocol: use it or lose it?. Small hydro power: a great leap forward. The energy mix of South Korea

    International Nuclear Information System (INIS)

    This issue of Alternatives newsletter contains a main press-kit about natural gas economics worldwide and 4 articles dealing with the Oklo natural reactor, the Kyoto protocol, the small hydro-power in China, and the energy mix of South Korea: 1 - 'Gas benefits and question marks': The world's most widely distributed fossil fuel, natural gas is also the fastest-growing energy source of the past thirty years. Its position as the fuel of choice in the global energy mix is due in large part to its many domestic and industrial applications. 2 - 'The Oklo reactors: 100% natural': Another look at this extraordinary 2 billion year-old phenomenon in words and pictures: the nuclear fission reaction that created the natural reactors of Gabon. 3 - 'The Kyoto Protocol: use it or lose it?': Nearly eight years after its signature, the Kyoto Protocol is still hotly debated. Two experts give us their views: Spencer Abraham, former U.S. Secretary for Energy, and Jean-Charles Hourcade of CIRED, the international center for research on the environment and development. 4 - 'Small hydro power: a great leap forward': The Chinese government has responded to the need for rural electrification with an aid program for the country's poorest cantons. Enter the small hydro plant in northern Guangxi province. 5 - 'The energy mix of South Korea': Faced with continuing strong economic growth and energy demand, South Korea has multiplied its projects, from hydropower to tidal power to nuclear and evenropower to tidal power to nuclear and even hydrogen in the longer term

  17. Oklo stable isotopes

    International Nuclear Information System (INIS)

    It is generally accepted that the fission reactions at Oklo resulted in convective circulation of the water heated up in the reactor zones. These convective currents were likely the main cause for the redistribution of some of the uranium of the reactor zones and most of the migration of the fission products possibly occurred at this stage. In order to derive generic conclusions applicable to the problems of nuclear waste disposal one has to identify the pattern of circulation of the convective currents and relate the observed distribution of elements around the reactor zones to the patterns left behind by the paleohydrogeological regime. The objective of this project is to discern and delineate the pathways of elemental migration by determining the deuterium and oxygen signature in the rocks confining the reactor zones. Furthermore the stable isotope analysis provides insights regarding water-rock interaction. In pursuit of this objective the Toronto team is concentrating on measurements of deuterium while F. Gauthier-Lafaye of Strasbourg is responsible for the analysis of the oxygen isotopes. In the final synthesis of the results beyond the main objective we intend to evaluate the differences in migration between the various members of the decay chains by means of a semi-analytical 3 dimensional model. (author). 8 refs., 1 fig., 1 tab., 2 appendices

  18. Behavior of radionuclides around Oklo reactor

    International Nuclear Information System (INIS)

    Re-examination of a vast amount of data on the Oklo reactors which have been accumulated in the past reveals that radionuclides which have been retained and preserved at the site of nuclear reactions during the past 1.7 billion years have high melting and boiling points. Gaseous elements and elements with melting points lower than that of tellurium (452degC) appear to have mostly migrated out of the reactor. About one percent of fissiogenic xenon isotopes have been retained, however, and the isotopic compositions of small amounts of xenon released from the natural reactors were found to be abnormal in that the relative abundances of 131Xe and 132Xe are markedly enhanced. It seems that the origin of this anomalous xenon can be attributed to the nonlinear oscillatory mode of operation of the reactors at temperatures of about 400degC, periodically being turned on and off in a manner similar to the present-day geysers or intermittent hot springs. The time period during which the reactor was turned off was calculated to be about 3 hours from the observed ratios of 132Xe, 134Xe and 136Xe in the anomalous xenon. The knowledge gained from the study of the Oklo phenomenon has recently played a key role in solving some of the most difficult problems in the field of geochemistry and cosmochemistry: for example, the so-called 'puzzle of the xenon isotopes', which have remained unsolved for a period of a quarter-century since the 1960's. Results of latest calculations indicate that the carbonaceous chondrites and lunar fines contain amounts of 244Pu fission xenon which are much greater than hitherto believed and they appear to have started to retain their xenon 4800 to 4900 million years ago. (author)

  19. Radioactive wastes in Oklo; Desechos radiactivos en Oklo

    Energy Technology Data Exchange (ETDEWEB)

    Balcazar, M.; Flores R, J.H.; Pena, P.; Lopez, A. [ININ, 52045 Ocoyoacac, Estado de Mexico (Mexico)

    2006-07-01

    The acceptance of the Nuclear Energy as electric power supply implies to give answer to the population on the two main challenges to conquer in the public opinion: the nuclear accidents and the radioactive wastes. Several of the questions that are made on the radioactive wastes, its are the mobility migration of them, the geologic stability of the place where its are deposited and the possible migration toward the aquifer mantels. Since the half lives of the radioactive waste of a Nuclear Reactor are of several hundred of thousands of years, the technical explanations to the previous questions little convince to the public in general. In this work summary the results of the radioactive waste generated in a natural reactor, denominated Oklo effect that took place in Gabon, Africa, it makes several thousands of millions of years, a lot before the man appeared in the Earth. The identification of at least 17 reactors in Oklo it was carried out thanks to the difference in the concentrations of Uranium 235 and 238 prospective, and to the analysis of the non-mobility of the radioactive waste in the site. It was able by this way to determine that the reactors with sizes of hardly some decimeter and powers of around 100 kilowatts were operating in intermittent and spontaneous form for space of 150,000 years, with operation cycles of around 30 minutes. Recent studies have contributed information valuable on the natural confinement of the radioactive waste of the Oklo reactors in matrixes of minerals of aluminum phosphate that caught and immobilized them for thousands of millions of years. This extracted information from the nature contributes guides and it allows 'to verify' the validity of the current proposals on the immobilization of radioactive wastes of a nuclear reactor. This work presents in clear and accessible form to the public in general on the secure 'design', operation, 'decommissioning' and 'storage' of the radioactive waste of the reactors that the nature put into operation in Oklo before the man appeared in the Earth. (Author)

  20. Mineralogical and petrographic investigations at Strasbourg on the Oklo natural reactors

    International Nuclear Information System (INIS)

    Petrographic and mineralogical investigations have revealed the presence around the reaction zones of aureoles characterized by the nature of the phyllitic minerals which they enclose. Running from the outside towards the core, these are: illite 1Md and ferriferous chlorite (normal sediment), illite 2M1, magnesium chlorite and kaolinite, illite 1M and vermiculite chlorite. Detritic quartz dissolution figures are observed which disappear in the illite 2M aureole or in the magnesium chlorite aureole, depending on the degree of sandiness of the country rock. This zonal stucture could be attributable to the combined effect of neutron bombardment and hydrothermal alteration due to the action of a thermal syphon triggered off by the nuclear reactions. (author)

  1. Oklo - A nuclear reactor 1800 million years ago

    International Nuclear Information System (INIS)

    A scientific conference about the so-called OKLO-phenomenon will take place in Gabon in West Africa from 23?27 June this year. The conference is arranged jointly by the International Atomic Energy Agency, the Gabonese authorities and the French Atomic Energy Commission (CEA). As the OKLO phenomenon, named after a uranium mine in Gabon, does not seem to be known outside specialist circles, it may be of interest to report on a few details about this discovery and the interesting conclusions that have been drawn about what happened during a short period of 100?500 000 years, in the earth's development 1 800 million years ago. Natural uranium contains 0.7202% of uranium-235, the fissionable isotope contained in nuclear fuel. Until June 1972 this concentration had been found to be the same for all uranium that had been discovered until that time, regardless of the place of discovery, and the same concentration was encountered in the uranium of which traces have been found on the moon. In the French gaseous diffusion plant for enrichment of the isotope-235 at Pierrelatte, regular measurements are carried out on the concentration of uranium-235 in the uranium with which the plant is supplied. This is done primarily to ensure that the contained uranium really is of natural origin and does not come from a plant where some fraction of the uranium-235 has already been used. In the course of one such isotopic analysis it was found that the uranium-235 concentration was slightly le uranium-235 concentration was slightly less than what one would expect from natural uranium, namely 0.7171% instead of the value just mentioned. If the scientists at Pierrelatte had not made a point of being so careful they might have overlooked this result. However, they carried out a series of checks and discovered that it was not a question of measurement error, but that they were dealing with uranium which had a composition differing from that of 'normal' uranium, with additional variations between different samples. It was soon established that the uranium had come from Gabon ? or more precisely from a mine, OKLO, in the vicinity of Franceville in south-east Gabon

  2. Search for other natural fission reactors

    International Nuclear Information System (INIS)

    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 than 0.6 b.a. old and if they contained sufficient water but lacked neutron-absorbing impurities. While uranium deposits of northern Canada and northern Australia have received most attention, ore samples have been obtained from the following worldwide locations: the Shinkolobwe and Katanga regions of Zaire; Southwest Africa; Rio Grande do Norte, Brazil; the Jabiluka, Nabarlek, Koongarra, Ranger, and El Sharana ore bodies of the Northern Territory, Australia; the Beaverlodge, Maurice Bay, Key Lake, Cluff Lake, and Rabbit Lake ore bodies and the Great Bear Lake region, Canada. The ore samples were tested for isotopic variations in uranium, neodymium, samarium, and ruthenium which would indicate natural fission. Isotopic anomalies were not detected. Criticality was not achieved in these deposits because they did not have sufficient 235U content (a function of age and total uranium content) and/or because they had significant impurities and insufficient moderation. A uranium mill monitoring technique has been considered where the ''yellowcake'' output from appropriate mills would be monitored for isotopic alterations indicative of the exhumation and processing of a natural reactor

  3. Search for other natural fission reactors

    International Nuclear Information System (INIS)

    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 >1m3 and concentrations approximately >20% uranium are likely places for a fossil reactor if they are approximately >0.6x109 years old and if they contained sufficient water but lacked neutron-absorbing impurities. While uranium deposits of northern Canada and northern Australia have received most attention, ore samples have been obtained from the following world-wide locations: the Shinkolobwe and Katanga regions of Zaire; southwest Africa; Rio Grande do Norte, Brazil; the Jabiluka, Nabarlek, Koongarra, Ranger, and El Sharana ore bodies of the Northern Territory, Australia; the Beaverlodge, Maurice Bay, Key Lake, Cluff Lake, and Rabbit Lake ore bodies and the Great Bear Lake region, Canada. The ore samples were tested for isotopic variations in uranium, neodymium, samarium, and ruthenium which would indicate natural fission. Isotopic anomalies were not detected. Criticality was not achieved in these deposits because they did not have sufficient 235U content (a function of age and total uranium content) and/or because they had significant impurities and insufficient moderation. A uranium mill monitoring technique has been considered where the ''yellowcake'' output from appropriat the ''yellowcake'' output from appropriate mills would be monitored for isotopic alterations indicative of the exhumation and processing of a natural reactor. (author)

  4. Geochemistry of neo-formed minerals at Oklo (Gabon), geologic history of the Oklo basin: a contribution for the studies of geologic disposals of radioactive wastes

    International Nuclear Information System (INIS)

    Oklo uranium ore deposit (Francevillian basin, Gabon) is the unique place in the world where 2000 Ma old fossil nuclear reactors were described. The geological and thermal history of this basin, since 2000 Ma was retraced. Tholeiitic intrusion was 755 ± 83 Ma with Sm-Nd isochron on whole rock and plagioclase and 746 ± 16 Ma old with U-Pb dating on zircons. This event was linked to a pre-Pan-African rifting stage. A green schist facies metamorphism was detected on the granitic rocks of the substratum and seemed to affect the tholeiitic intrusion. Apatite fission tracks dating performed on granitic basement revealed a thermal event between Permian and middle-Jurassic time, linked to the Atlantic ocean opening. Fission track ages distribution suggest a brittle tectonics (T < 60 deg. C) occurred after middle Jurassic times. Geochemical and isotopic studies on apatites and zircons which crystallized on natural nuclear reactors let compare the confinement of these two crystalline structures. These minerals were affected by self-irradiation due to actinide incorporation. U, Pu and fission products (REE, Rb, Sr) were trapped by apatites. Zircons contain fissiogenic REE and radiogenic Ba. Apatites crystallized during the nuclear reactions, zircons at the end of this phenomenon. Isotopic study of tholeiitic intrusion minerals point out fissiogenic Nd and Sm incorporation in clinopyroxenes. This result implies a fissiogenic products remobilization during the tholeiitic intrusibilization during the tholeiitic intrusion event. (author)

  5. Determinations by irradiation in the Triton reactor of neutron capture cross-sections for isotopes involved in the Oklo phenomenon

    International Nuclear Information System (INIS)

    Experimental irradiations of separate elements and isotopes were carried out in a swimming-pool reactor (Triton) in order to obtain better information on the capture cross-sections of uranium fission products involved in the Oklo phenomenon. The irradiation conditions, sample analysis techniques, and calculation methods used to interpret the results are described. The elements irradiated were the following: uranium 93% and 20% enriched in 235U, 240Pu, sup(143+145)Nd, 147Sm, 99Tc, natural dysprosium, mixture of natural europium + natural gadolinium, natural krypton and natural xenon. The uranium and plutonium were used to determine the fluence and spectrum received by the other samples. The irradiations were carried out in two different locations of the Triton reactor to permit work with different spectra; the spectral indices, r, were 0.03 and 0.15. In this way accurate determinations were made of the effective capture cross-sections of a large number of isotopes as a function of the spectrum. In some cases the results differ considerably from those published in the literature. These findings contribute information which is of interest in interpreting the Oklo phenomenon. More particularly, they confirm the values for neutron fluence, and hence the age of the nuclear reaction determined from the fission neodymium balances. They afford a more accurate knowledge of the water/uranium ratios at the time of the nuclear reactions tios at the time of the nuclear reactions (through measurement of the spectral indices). They also explain the discrepancy observed earlier between the value for the duration of the reaction calculated on the basis of the participation of plutonium in the fissions and that deduced from the pair 99Tc-99Ru. (author)

  6. Time-variability of alpha from realistic models of Oklo reactors

    CERN Document Server

    Gould, C R; Lamoreaux, S K

    2006-01-01

    We reanalyze Oklo $^{149}$Sm data using realistic models of the natural nuclear reactors. Disagreements among recent Oklo determinations of the time evolution of $\\alpha$, the electromagnetic fine structure constant, are shown to be due to different reactor models, which led to different neutron spectra used in the calculations. We use known Oklo reactor epithermal spectral indices as criteria for selecting realistic reactor models. Two Oklo reactors, RZ2 and RZ10, were modeled with MCNP. The resulting neutron spectra were used to calculate the change in the $^{149}$Sm effective neutron capture cross section as a function of a possible shift in the energy of the 97.3-meV resonance. We independently deduce ancient $^{149}$Sm effective cross sections, and use these values to set limits on the time-variation of $\\alpha$. Our study resolves a contradictory situation with previous Oklo $\\alpha$-results. Our suggested $2 \\sigma$ bound on a possible time variation of $\\alpha$ over two billion years is stringent: $ -...

  7. Modification of apparent fission yields by Chemical Fractionation following Fission (CFF)

    Science.gov (United States)

    Hohenberg, Charles; Meshik, Alex

    2008-04-01

    Grain-by-grain studies of the 2 billion year old Oklo natural reactor, using laser micro-extraction^1,2, yield detailed information about Oklo, a water-moderated pulsed reactor, cycle times, total neutron fluence and duration, but it also demonstrates Chemical Fractionation following Fission. In the CFF process, members of an isobaric yield chain with long half-lives are subject to migration before decay can occur. Of particular interest is the 129 isobar where 17 million ^129I can migrate out of the host grain before decay, and iodine compounds are water soluble. This is amply demonstated by the variation of Xe spectra between micron-sized uranium-bearing minerals and adjacent uranium-free minerals. Fission 129 yields for the spontaneous fission of ^238U generally come from measured ^129Xe in pitchblend^2, ores emplaced by aqueous activity, and are incorrect due to the CFF process. ^238U yields for the 131 and 129 chains, reported in Hyde^3, as 0.455 +- .02 and < 0.012, respectively, the latter being anomalously low. ^1A Meshik, C Hohenberg and O Pravdivtesva, PRL 93, 182302 (2004); A Meshik Sci. Am. Nov (2005), 55; ^2E K Hyde, Nucl Prop of Heavy Elements III (1964).

  8. The Oklo reactors: five years of exploration of the site

    International Nuclear Information System (INIS)

    The main phases of the exploration of the Oklo site since the discovery of the ''reactor'' phenomenon are outlined briefly. Over 180 sampling holes were drilled during the interruption of the mining activities in the sector concerned. Several new zones have been found. Mining was resumed in the second half of 1975, providing an opportunity for highly fruitful geological follow-up work: more precise knowledge was gained of the morphology of the reactors, and very many additional samples were taken. Plant treatment of the ore and the systematic analysis of batches have made it possible to establish a balance of missing uranium-235. A small portion containing sites of intense reaction has been preserved by being anchored to the quarry wall. Mining in this sector has now finished, but new indications of fission have been found, especially in the Okelobondo sector. (author)

  9. The Oklo fossil reactor. Determinations of neutron capture cross sections of isotopes occurring in the Oklo phenomenon by irradiation in the reactor Triton

    International Nuclear Information System (INIS)

    An experimental irradiation of isotopes was carried out in a pool type reactor (Triton reactor) to better the knowledge of capture cross sections of uranium fission products arising in the Oklo phenomenon. Irradiation conditions analysis techniques of samples and methods of calculation to interpret results are described. Capture cross sections of 143Nd, 145Nd, 147Sm, 99Tc, 82Kr, 83Kr, 129Xe, 131Xe were determined will precision and were estimated for dysprosium isotopes and europium isotopes. Found values confirm known data for neodymium and xenon isotopes, but are smaller for 147Sm, 82Kr and 99Tc. These results bring interesting informations in the Oklo phenomenon interpretation. In particular neutron fluence values are confirmed, dating nuclear reactions with the fission neodymium. They give more accurately the ratios water/uranium at the time of nuclear reactions by measurement of spectrum indexes. They explain also the variation, found out before, between reaction duration calculated from plutonium taking part in fissions and the one deduced from the pair 99Tc-99Ru

  10. Geochemistry of actinides and fission products in natural aquifer systems

    International Nuclear Information System (INIS)

    The progress in the research area of the community project MIRAGE: 'Geochemistry of actinides and fission products in natural aquatic systems' has been reviewed. This programme belongs to a specific research and technical development programme for the European Atomic Energy Community in the field of management and storage of radioactive waste. The review summarizes research progresses in subject areas: complexation with organics, colloid generation in groundwater and basic retention mechanisms in the framework of the migration of radionuclides in the geosphere. The subject areas are being investigated by 23 laboratories under interlaboratory collaborations or independent studies. (orig.)

  11. Technical Application of Nuclear Fission

    Science.gov (United States)

    Denschlag, J. O.

    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.

  12. Uranium deposits of Gabon and Oklo reactors. Metallogenic model for rich deposits of the lower proterozoic

    International Nuclear Information System (INIS)

    The geology of the Franceville basin (Gabon) is examined: stratigraphy, tectonics and geodynamics. The mobile zone of the Ogooue is specially studied: lithology, metamorphism and tectonics, isotopic geochronologic data are given. The different uranium deposits are described. A whole chapter is devoted to the study of Oklo natural nuclear reactor. A metallogenic model is proposed evidencing conditions required for deposit genesis. Tectonics, microstructures sedimentology, organic matter, diagenesis and uraniferous mineralizations are examined

  13. Dating by fission track method: study of neutron dosimetry with natural uranium thin films

    International Nuclear Information System (INIS)

    Fission track dating is described, focalizing the problem of the decay constant for spontaneous fission of 238 U and the use of neutron dosimetry in fission track analysis. Experimental procedures using thin films of natural uranium as neutron dosimeters and its results are presented. The author shows a intercomparison between different thin films and between the dosimetry with thin film and other dosimetries. (M.V.M.). 52 refs, 12 figs, 9 tabs

  14. Contribution to a summary of the results obtained in the field of geology on the Oklo natural reactors and their environment

    International Nuclear Information System (INIS)

    The very special characteristics of the ore in the reaction zones may be attributed to the effects of the nuclear reactions themselves: de-structuration of the gangue by neutronic effects and hydrothermal leaching due to the generation of a true thermal syphon by the nuclear reactions. This mechanism contributes to the propagation of reactions from a number of initial reaction sites. The latter were initiated in certain parts of the deposit, enriched as a result of a tectonic episode, by oxidizing currents in the shear troughs. These enriched zones occur as anomalies within a pre-existent deposit, the formation of which still poses many questions of a metallogenic nature. (author)

  15. The nature of singlet exciton fission in carotenoid aggregates.

    Science.gov (United States)

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

    2015-04-22

    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 1B(u) 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

  16. The Nature of Singlet Exciton Fission in Carotenoid Aggregates

    Science.gov (United States)

    2015-01-01

    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

  17. Investigation of the fundamental constants stability based on the reactor Oklo burn-up analysis

    CERN Document Server

    Onegin, M S

    2014-01-01

    New severe constraints on the variation of the fine structure constant have been obtained from reactor Oklo analysis in our previous work. We investigate here how these constraints confine the parameter of BSBM model of varying $\\alpha$. Integrating the coupled system of equations from the Big Bang up to the present time and taking into account the Oklo limits we have obtained the following margin on the combination of the parameters of BSBM model: $$ |\\zeta_m (\\frac{l}{l_{pl}})^2|<6\\cdot 10^{-7}, $$ where $l_{pl}=(\\frac{G\\hbar}{c^3})^{\\frac{1}{2}} \\approx 1.6 \\cdot 10^{-33}$ cm is a Plank length and $l$ is the characteristic length of the BSBM model. The natural value of the parameter $\\zeta_m$ - the fraction of electromagnetic energy in matter - is about $10^{-4}$. As a result it is followed from our analysis that the characteristic length $l$ of BSBM theory should be considerably smaller than the Plank length to fulfill the Oklo constraints on $\\alpha$ variation.

  18. A study of radon retention and fission track annealing with temperature in natural apatites

    International Nuclear Information System (INIS)

    The release and the retention of radon-222, from sedimentary phosphate in which it is formed, are carried out. The heat treatment may be regarded as having two effects: an immediate effect (radon release) and a long term effect (retention of radon). In order to understand this behavior of radon to elevated temperatures, some analysis is carried out. One of them is the analysis of radiation damage (fission tracks) in natural apatite grains (Apatite Fission Track Analysis). Those tracks are produced continuously through geological time, as a result of spontaneous fission of 238U atoms and can be annealed at a rate that depends on temperature. In this work, we have examined this effect. The result is that in a single sample, the fission track density in individual apatite grains decreases with the increasing of the temperature. We study the hypothesis of the control of radon emanation by the fission track annealing process. (author)

  19. The discovery of the Oklo reactors

    International Nuclear Information System (INIS)

    Among the most important knowledge brought by the recent studies on Oklo phenomenon, we can give: models and data that could be used to quantify the interactions between uranium and lanthanides with an clayey material; information on the confinement of radioactive elements in the compounds such manganese and iron oxides, the clays, the phosphates; understanding of oxido-reduction phenomena in a clayey environment for very different burying conditions ( from the surface to 400 meters deep). These knowledge could be used for future storage sites if vitrified waste would be buried at several hundred meters deep and surrounded by clayey barriers in the aim to delay the water brought to waste contact and to confine the elements that could get out glasses including radioactive waste. (N.C.)

  20. Nature of the fission barrier heights of trans-uranium

    International Nuclear Information System (INIS)

    The theories of nuclear fission are guided by the extensive calculations of the potential energy surfaces (PES) in the multi-dimensional deformation space defining the shape of a deforming nucleus on the way to fission. Many approaches have been used for this. A well established technique is the microscopic-macroscopic (mic-mac) approach in which the macroscopic part is given by the liquid drop energy and the microscopic part is given in terms of Strutinsky shell correction. We have used the mic-mac approach to calculate the PES by using the Cassini ovaloid shape parameterization for nuclear potential. This formalism is due to Garcia et al. In this formalism, the single particle energies as a function of deformation parameters are calculated from an axially deformed Woods-Saxon potential. This single particle level scheme is used to calculate the shell and pairing corrections to the liquid drop energy (smooth macroscopic part) in Strutinsky approach

  1. Descriptive evaluation of the Oklo reactors

    International Nuclear Information System (INIS)

    The Oklo reactors are a terrain phenomenon: they cannot be explained without a previous description of their location, and particular samples cannot be studied without reference to their specific contexts. The authors have reviewed the information accumulated during the five years of exploration of the site and have singled out the main features. The paper successively describes each of the four large reaction zones, and gives the main topographic, sedimentological and structural data and information concerning the uranium distribution and the reaction rates. The area is described sector by sector; an attempt is made to bring out the features peculiar to each; any problems raised by the connections between the sectors are examined, and the most interesting locations are identified. In addition, an account of the sampling is given. The number of samples (over 5000 have been recorded, excluding the many uncut probes) made it impossible to publish a complete catalogue. The authors have aimed at describing the essential characteristics, giving useful information and linking the samples with the locations described. (author)

  2. Excitation function of 4He-ion-induced fission of Dy (natural)

    International Nuclear Information System (INIS)

    As part of a long-range programme of work on the measurement of fission excitation functions of low Z (Z 4He-ions in the energy range 35-50 MeV were measured using the sensitive ''fission track'' technique using lexan polycarbonate plastic as detectors. Targets of (spec. pure grade) high purity Dy2O3, further purified by a series of anion exchange technique, deposited on high purity (99.9999%) silver foils were irradiated with 4He-ions of different energies from the Variable Energy Cyclotron at Calcutta. The heavy elements contents of both the dysprosium oxide and the silver foils were estimated to be not more than 1-3 ppb. The experimental 4He-ion-induced fission cross sections of natural Dysprosium (162.5Dy) are presented. 7 refs, 1 tab

  3. Delayed neutron measurements with a natural uranium fission product source in Fast Breeder Test Reactor

    International Nuclear Information System (INIS)

    Highlights: • Delayed neutron measurements performed with a Fission Product Source (FPS) FBTR. • FPS provided by natural U–Ni pins with perforated clad. • Measurements have helped in quantification of sensitivity of DND system in FBTR. - Abstract: An assessment of the sensitivity and localization capabilities of clad failure detection by Delayed Neutron Detection (DND) system in Fast Breeder Test Reactor at Kalpakkam has been done, by a series of delayed neutron measurements. Experimental simulation of failed fuel pin is done by considering a natural uranium fission product source in the form of special subassembly containing natural uranium pins, each having a large exposed area in the form of small holes. The measurements and analysis of delayed neutron signals with special subassembly in several selected locations are presented

  4. Double sequential fission events produced in the interaction of 1539 MeV 208Pb ions with natural lead

    International Nuclear Information System (INIS)

    The 2?-geometry arrangement of mica track detectors has been employed for the study of multiprong fission events produced in the interaction of 1539 MeV 208Pb ions with natural lead. Particular attention was given to the analysis of four-pronged events. There is an indication of double sequential fission in the interactions. (orig.)

  5. New systematic analyses of the uranium in the Oklo ores

    International Nuclear Information System (INIS)

    The systematic analytical work on the uranium of the reactor sector described in papers IAEA-SM-204/21 and 204/23 at the symposium on the Oklo Phenomenon at Libreville, Gabon in 1975, has been continued: it has included radiometric measurements of concentration in core samples, measurements of concentration in powder, and isotopic analyses - about 300 additional isotopic analyses have been carried out at Pierrelatte since the Libreville symposium. The results are presented in tables with comments on the most interesting ones. This research has made an essential contribution to the description of the ''natural reactor'' phenomenon. In particular, the new reaction zones discovered at the end of 1974 and explored while the deposit was being mined have been extensively studied. It is very remarkable that reactions are found almost all over the site, over considerable stretches, even where rich bands are temporarily narrow or jagged-edged. Thus, very varied situations have been found, including large areas where the reaction rates are very low. The systematic analyses are important for the selection of appropriate samples for most other studies and for the proper definition of their environment. It has been shown, moreover, that the detailed study of reaction rate distributions is a rich source of information because the uranium has largely preserved its configuration: some particularly interesting ''situations'' have been studied. The possibility of remobilization of the The possibility of remobilization of the uranium near the edge of the reaction zones has also been examined more closely, and phenomena of contamination have been investigated by means of analyses carried out near to or further from the reactors. (author)

  6. Isotopic anomalies of xenon ad krypton in natural nuclear reactor and epicenter of nuclear explosion

    International Nuclear Information System (INIS)

    Samples from epicenter of the first nuclear explosion in Alamogordo (New Mexico, USA), of the natural uranium reactor (Oklo uranium deposit, Gabon), as well as 130 million year old pitchblende and uranium blacks were investigated. Xe and Kr isotope ration during stepwise annealing was studied. General properties of isotopic abnomalies in these samples were revealed. Abnomaly value correlates with half-lifes of ?-active Xe and Kr precursors in isobar chains of 235U fission fragments, the degree of Xe and Kr confinement by crystal structure of corresponding mineral phases of samples. The decisive effect of migration of intermediate members of isobar chains on occurrence of observed isotopic abnomalies was concluded

  7. Study on natural deposition of fission product aerosol in severe accidents

    International Nuclear Information System (INIS)

    Aerosol natural deposition model of gravitational sedimentation, diffusionphoresis, inertial impaction and thermophoresis are established based on integrated safety analysis model for 600 MW pressurized water reactor. Typical severe accidents are chosen, and natural deposition phenomenon of fission product aerosol is analyzed. Additionally, gravitational sedimentation model of MELCOR is coupled into integrated safety analysis model, and fraction of gravitational sedimentation is compared. The results show that gravitational sedimentation is the most important deposition mechanism, and deposition effect of gravitational sedimentation model in this paper is stronger than MELCOR. (authors)

  8. Migration of U-series radionuclides around the Bangombe natural fission reactor (Gabon)

    International Nuclear Information System (INIS)

    The Bangombe natural fission reactors has undergone extensive weathering phenomena and continues to be affected by the penetration of meteoric waters. Hence this system provides a model for studying the stability of spent fuel uraninite and the influence of various rock matrices on the mobilization/retardation of various actinides and fission products. The Bangombe uranium deposit has been investigated by drilling on a grid. Radiochemical analysis by alpha- and gamma-spectroscopy of the obtained rocks show significant disequilibria of the 234U/238U, 230Th/234U, and 226Ra/230Th parent-daughter pairs. In this paper, a conceptual model for spatio/temporal evolution of the Bangombe system is proposed. (J.P.N.)

  9. Summary of the mineralogical and petrographic studies of the Oklo ores, their gangues and the country rock

    International Nuclear Information System (INIS)

    Observations on the spot and mineralogical studies (reflection and transmission microscopy, X-ray examination, thermal analyses) have shown that the ore in the reaction zones differs from ''normal'' Oklo ore as regards both the nature of the mineralization and the gangue and the country rock. The relationship between the two ore types on one hand and between them and the country rock on the other is studied. Theories concerning the creation of the uraniferous deposit and the effects of subsequent changes due to diagenesis and recent weathering are discussed

  10. Fission xenon in trinities from the first nuclear test

    Science.gov (United States)

    Meshik, Alexander; Pravdivtseva, Olga; Hohenberg, Charles

    2008-04-01

    Trinitites, greenish glassy remnants found in the crater of the first nuclear test, refer to the molten material of the desert where the Trinity test was conducted. Recently the Los Alamos Lab^1 suggested that the sand was first vaporized by the fireball and then precipitated onto a cooler desert surface forming trinitites. We measured the Xe mass-spectra during stepped pyrolysis of two trinitites and found an unusual Xe isotopic structure, dominated by ^132Xe and ^131Xe compared to the nominal fission yield spectra, which cannot be due to n-capture or any other nuclear processes. This structure is caused by the chemical separation of the immediate neutron-rich fission products, a process similar to CFF observed in the Oklo natural reactor^2. When quantitatively applied to our observations it suggests that 17 min after the test one of the samples had a temperature of 1390^oC, while 5 min after the test the other was at 1320^oC. These results contribute to a reconstruction of the cooling history of the trinities and a demonstration of which formation scenario is the more likely. ^1V. Montoya et al, Denver X-ray Conf. (2007), ^2A. Meshik, C. Hohenberg and O. Pravdivtseva, PRL 93, 182302 (2004).

  11. Immobilization of fission iodine by reaction with insoluble natural organic matter

    International Nuclear Information System (INIS)

    Iodine-129 is a fission product and highly mobile in the environment. Along with other stable isotopes of iodine, 129I is released during reprocessing of nuclear fuel and must be trapped to prevent the release of radioactivity to the environment. Past studies have provided evidence that iodine can become associated with natural organic matter (NOM). This research explores the use of NOM (sphagnum peat and humic acid) to sequester iodine from the vapor and aqueous phases. NOM-associated iodine may be stable for geological storage. NOM-sequestered iodine can be recovered by pyrolysis to prepare target materials for transmutation. The nature of the NOM-iodine association has been explored. (author)

  12. Problems posed by the development of the Oklo phenomenon: tentative global interpretation

    International Nuclear Information System (INIS)

    This paper discusses the basic problems posed by the development of the Oklo phenomenon: the conditions in which the reactions are triggered and propagated and how they have been controlled. The reactions were maintained by the destruction of neutron poisons in the ore and were controlled by temperature. Oklo is made up of a large number of contiguous reactors. Geological problems of the origin of the clays, desilification, and uranium concentration are discussed. Oklo is shown to be a very complex phenomenon which developed in space and time. Besides the thermal, neutron, and geochemical coupling, there is also a tectonic coupling

  13. Neutron Dose Estimation Using a Natural Uranium Fission Fragment Track Personnel Dosimeter

    International Nuclear Information System (INIS)

    The idea of using a natural uranium fission fragment track dosimeter, in the neutron field of thermal, intermediate and fast neutrons in air, has recently been introduced. The system can be used for thermal neutron dose estimation as well as intermediate plus fast neutron dose estimation if the spectrum and the percentage contribution of each neutron group is known. This paper investigates feasibility of the use of such dosimeters when they are worn by radiation workers. Detailed study of the system shows the possibility of differentiating between doses received from fast, intermediate and thermal neutrons if one takes into account reflection from the body of thermal, intermediate and fast neutrons as consisting only of thermal neutrons. (author)

  14. La138/139 Isotopic Data and Neutron Fluences for Oklo RZ10 Reactor

    OpenAIRE

    Gould, C.R.; Sharapov, E.I.

    2012-01-01

    Recent years have seen a renewed interest in the Oklo phenomenon, particularly in relation to the study of time variation of the fine structure constant. The neutron fluence is one of the crucial parameters for Oklo reactors. Several approaches to its determination were elaborated in the past. We consider whether it possible to use the present isotopic La138/139 data for RZ10 as an additional indicator of neutron fluences in the active cores of the reactors. We calculate the...

  15. A fission-fusion hybrid reactor in steady-state L-mode tokamak configuration with natural uranium

    Science.gov (United States)

    Reed, Mark; Parker, Ronald R.; Forget, Benoit

    2012-06-01

    This work develops a conceptual design for a fusion-fission hybrid reactor operating in steady-state L-mode tokamak configuration with a subcritical natural or depleted uranium pebble bed blanket. A liquid lithium-lead alloy breeds enough tritium to replenish that consumed by the D-T fusion reaction. The fission blanket augments the fusion power such that the fusion core itself need not have a high power gain, thus allowing for fully non-inductive (steady-state) low confinement mode (L-mode) operation at relatively small physical dimensions. A neutron transport Monte Carlo code models the natural uranium fission blanket. Maximizing the fission power gain while breeding sufficient tritium allows for the selection of an optimal set of blanket parameters, which yields a maximum prudent fission power gain of approximately 7. A 0-D tokamak model suffices to analyze approximate tokamak operating conditions. This fission blanket would allow the fusion component of a hybrid reactor with the same dimensions as ITER to operate in steady-state L-mode very comfortably with a fusion power gain of 6.7 and a thermal fusion power of 2.1 GW. Taking this further can determine the approximate minimum scale for a steady-state L-mode tokamak hybrid reactor, which is a major radius of 5.2 m and an aspect ratio of 2.8. This minimum scale device operates barely within the steady-state L-mode realm with a thermal fusion power of 1.7 GW. Basic thermal hydraulic analysis demonstrates that pressurized helium could cool the pebble bed fission blanket with a flow rate below 10 m/s. The Brayton cycle thermal efficiency is 41%. This reactor, dubbed the Steady-state L-mode non-Enriched Uranium Tokamak Hybrid (SLEUTH), with its very fast neutron spectrum, could be superior to pure fission reactors in terms of breeding fissile fuel and transmuting deleterious fission products. It would likely function best as a prolific plutonium breeder, and the plutonium it produces could actually be more proliferation-resistant than that bred by conventional fast reactors. Furthermore, it can maintain constant total hybrid power output as burnup proceeds by varying the neutron source strength.

  16. Naturally etched tracks in apatites and the correction of fission track dating

    CERN Document Server

    Tien, J L

    1999-01-01

    Naturally etched tracks have been found in apatites from the rapid cooled, high-level Kunon pluton in the Zhangzhou Igneous Complex, SE China. This is manifested by the fact that the apatite fission track (FT) age derived from conventional counting of spontaneous and induced tracks yields a result of 140.6+-6.5 Ma, which is much older than the ages determined using other methods on different minerals from the same rock. When tracks are observed after etching the polished inner sections of the apatite grains, the naturally etched tracks characterized by having hazy boundaries can be distinguished from the normal tracks with sharp boundaries. The age obtained by omitting these fading-resistant hazy tracks, 76.5+-4.0 Ma, indicates the time of the Kunon pluton cooling down to approx 100 deg. C. The corrected peak age (73.8 Ma) is consistent with the other apatite FT peak ages (79.2 to 70.2 Ma) of the nearly contemporaneous plutons in the same igneous complex.

  17. High-energy Neutron-induced Fission Cross Sections of Natural Lead and Bismuth-209

    CERN Document Server

    Tarrio, D; Carrapico, C; Eleftheriadis, C; Leeb, H; Calvino, F; Herrera-Martinez, A; Savvidis, I; Vlachoudis, V; Haas, B; Koehler, P; Vannini, G; Oshima, M; Le Naour, C; Gramegna, F; Wiescher, M; Pigni, M T; Audouin, L; Mengoni, A; Quesada, J; Becvar, F; Plag, R; Cennini, P; Mosconi, M; Rauscher, T; Couture, A; Capote, R; Sarchiapone, L; Vlastou, R; Domingo-Pardo, C; Dillmann, I; Pavlopoulos, P; Karamanis, D; Krticka, M; Jericha, E; Ferrari, A; Martinez, T; Trubert, D; Oberhummer, H; Karadimos, D; Plompen, A; Isaev, S; Terlizzi, R; Cortes, G; Cox, J; Cano-Ott, D; Pretel, C; Colonna, N; Berthoumieux, E; Vaz, P; Heil, M; Lopes, I; Lampoudis, C; Walter, S; Calviani, M; Gonzalez-Romero, E; Embid-Segura, M; Stephan, C; Igashira, M; Papachristodoulou, C; Aerts, G; Tavora, L; Berthier, B; Rudolf, G; Andrzejewski, J; Villamarin, D; Ferreira-Marques, R; Tain, J L; O'Brien, S; Reifarth, R; Kadi, Y; Neves, F; Poch, A; Kerveno, M; Rubbia, C; Lazano, M; Dahlfors, M; Wisshak, K; Salgado, J; Dridi, W; Ventura, A; Andriamonje, S; Assimakopoulos, P; Santos, C; Voss, F; Ferrant, L; Patronis, N; Chiaveri, E; Guerrero, C; Perrot, L; Vicente, M C; Lindote, A; Praena, J; Baumann, P; Kappeler, F; Rullhusen, P; Furman, W; David, S; Marrone, S; Tassan-Got, L; Gunsig, F; Alvarez-Velarde, F; Massimi, C; Mastinu, P; Pancin, J; Papadopoulos, C; Tagliente, G; Haight, R; Chepel, V; Kossionides, E; Badurek, G; Marganiec, J; Lukic, S; Pavlik, A; Goncalves, I; Duran, I; Alvarez, H; Abbondanno, U; Fujii, K; Milazzo, P M; Moreau, C

    2011-01-01

    The CERN Neutron Time-Of-Flight (n\\_TOF) facility is well suited to measure small neutron-induced fission cross sections, as those of subactinides. The cross section ratios of (nat)Pb and (209)Bi relative to (235)U and (238)U were measured using PPAC detectors. The fragment coincidence method allows to unambiguously identify the fission events. The present experiment provides the first results for neutron-induced fission up to 1 GeV for (nat)Pb and (209)Bi. A good agreement with previous experimental data below 200 MeV is shown. The comparison with proton-induced fission indicates that the limiting regime where neutron-induced and proton-induced fission reach equal cross section is close to 1 GeV.

  18. Reactor AQUILON. The hardening of neutron spectrum in natural uranium rods, with a computation of epithermal fissions (1961)

    International Nuclear Information System (INIS)

    - Microscopic flux measurements in reactor Aquilon have allowed to investigate the thermal and epithermal flux distribution in natural uranium rods, then to obtain the neutron spectrum variations in uranium, Wescott '?' term of the average spectrum in the rod, and the ratio of epithermal to therma fissions. A new definition for the infinite multiplication factor is proposed in annex, which takes into account epithermal parameters. (authors)

  19. Split-Doa10: A Naturally Split Polytopic Eukaryotic Membrane Protein Generated by Fission of a Nuclear Gene

    OpenAIRE

    Stuerner, Elisabeth; Kuraku, Shigehiro; Hochstrasser, Mark; Kreft, Stefan G

    2012-01-01

    Large polytopic membrane proteins often derive from duplication and fusion of genes for smaller proteins. The reverse process, splitting of a membrane protein by gene fission, is rare and has been studied mainly with artificially split proteins. Fragments of a split membrane protein may associate and reconstitute the function of the larger protein. Most examples of naturally split membrane proteins are from bacteria or eukaryotic organelles, and their exact history is usually poorly understoo...

  20. Back to nature

    International Nuclear Information System (INIS)

    This article popularizes a study of the Cigar Lake orebody in Northern Saskatchewan as a natural analog for geologic disposal of fuel waste. It is argued that the clay sealing round a repository will act like the natural clay zone at Cigar Lake to keep radioactivity out of any circulating groundwater. A separate section is entitled 'Oklo - natural reactions'

  1. Apparatus used at Oklo for determining the isotopic composition of the uranium

    International Nuclear Information System (INIS)

    The ''Oklometer'', developed soon after the discovery of the Oklo fossil reactor, is used for measuring the degree of 235U enrichment of the uranium in the deposit at a laboratory near the mine without recourse to expensive or delicate techniques. The uranium to be measured must be in the form of a uranyl nitrate solution without chemical impurities or radioactive daughter products of uranium. This is achieved by grinding ore which contains about 5 g of uranium, treating the powder with a H2SO4-HNO3 mixture and then carrying out purification in an ion-exchange column. The solution is transferred to a cell with a scintillator. The area (s5) on the pulse spectrum of the 186-keV peak of the 235U is measured. A 60-keV gamma beam (241Am source) is then allowed to pass through the cell. The area of the transmitted peak is s1. While s5 depends both on the degree of enrichment and on the concentration of the solution, s1 depends only on the concentration. With s5 and s1, and a calibration curve plotted with a gradually diluted solution of natural uranium, it is easy to deduce the degree of enrichment of a sample. The stability of the apparatus is checked periodically, using a standard. Two ''Oklometers'' are in use - one at Mounana and the other at Saclay. The results agree to within +-1.5% with those obtained by mass spectrometryained by mass spectrometry

  2. Fine gamma spectrometry, before and after activation, on ore samples from Oklo

    International Nuclear Information System (INIS)

    Gamma spectrometry of uraniferous material, before or after activation, is a complex operation. The authors used techniques developed at the Orsay Laboratory in the study of samples from Oklo. Firstly, they wished to examine the secular equilibrium of the non-activated material, determining the various daughter nuclides of 235U and 238U. To ascertain the part played by each nuclide in the spectrum it was necessary beforehand to study a sample of isotopically pure 235U and one of natural uranium without its radon. Secondly, with the same material after irradiation, the authors tried to determine the stable elements in the ore in their different isotopic forms. The abundances were determined in an unusual context in activation and the following points must be borne in mind: the nuclides on the basis of which the measurements rest may be produced simultaneously in (n, f) and (n, ?) reactions; the 235U isotopic abundance varies from one sample to another (between 0.4 and 0.7%); the uranium concentration in the ore also varies (between 500 ppm and 50%)

  3. Enhanced effect of quark mass variation in 229Th and limits from Oklo data

    CERN Document Server

    Flambaum, V V

    2008-01-01

    The effects of the variation of the dimensionless strong interaction parameter Xq=mq/Lambda{QCD} (mq is the quark mass, Lambda{QCD} is the QCD scale) are enhanced about 1.5 x 10**5 times in the 7.6 eV "nuclear clock" transition between the ground and first excited states in the 229Th nucleus and about 1 x 10**8 times in the relative shift of the 0.1 eV compound resonance in 150Sm.The best terrestrial limit on the temporal variation of the fundamental constants, |delta(Xq)/Xq| < 4 x 10**-9 at 1.8 billion years ago (|d(Xq/Xq)/dt| < 2.2 x 10**-18 y**-1), is obtained from the shift of this Sm resonance derived from the Oklo natural nuclear reactor data. The results for 229Th and 150Sm are obtained by extrapolation from light nuclei where the many-body calculations can be performed more accurately. The errors produced by such extrapolation may be smaller than the errors of direct calculations in heavy nuclei. The extrapolation results are compared with the "direct" estimates obtained using the Walecka model....

  4. Dating by fission track method: study of neutron dosimetry with natural uranium thin films; Datacao com o metodo dos tracos de fissao: estudo da dosimetria de neutrons com filmes finos de uranio natural

    Energy Technology Data Exchange (ETDEWEB)

    Iunes, P.J.

    1990-06-01

    Fission track dating is described, focalizing the problem of the decay constant for spontaneous fission of {sup 238} U and the use of neutron dosimetry in fission track analysis. Experimental procedures using thin films of natural uranium as neutron dosimeters and its results are presented. The author shows a intercomparison between different thin films and between the dosimetry with thin film and other dosimetries. (M.V.M.). 52 refs, 12 figs, 9 tabs.

  5. Fission, total and neutron capture cross section measurements at ORELA for 233U, 27Al and natural chlorine

    International Nuclear Information System (INIS)

    The authors have made use of the Oak Ridge Electron Linear Accelerator (ORELA) to measure the fission cross section of 233U in the neutron energy range of 0.36 eV to ? 700 keV. This paper reports integral data and average cross sections. In addition they measured the total neutron cross section of 27Al and natural chlorine, as well as the capture cross section of Al over an energy range from 100 eV up to about 400 keV

  6. Oklo: The fossil nuclear reactors. Physics study - Translation of chapters 6, 13 and conclusions

    International Nuclear Information System (INIS)

    Three parts of the 1991 book 'Oklo: reacteurs nucleaires fossiles. Etude physique' have been translated in this report. The chapters bear the titles 'Study of criticality'(45 p.), 'Some problems with the overall functioning of the reactor zones'(45 p.) and 'Conclusions' (15 p.), respectively

  7. Statistical nature of neutron activity in the fission of heavy nuclei

    International Nuclear Information System (INIS)

    It is shown that some characteristics of the neutron emission can be explained in the framework of statistical theory, which studies the stability of the ensemble of nuclear fragments and fission neutrons. The theory able to reproduce the known experimental sawtooth-curve of the neutron multiplicity n(A) and allows one to set the total neutron multiplicity as a function of (A, Z) and the excitation energy of the initial nucleus

  8. Petrographic analysis of samples from the uranium deposit at Oklo, Republic of Gabon

    International Nuclear Information System (INIS)

    This study is preliminary to detailed X-ray diffraction analysis and additional electron microprobe analyses. Twenty samples were examined; seven from reactor zone 9 (RZ-9), ten from RZ-10, two from RZ-13 and one from RZ-16. This suite of samples includes examples from reactor cores and their associated hydrothermal alteration haloes. The most striking characteristic of the Oklo samples is their heterogeneity. In particular, the samples vary with respect to texture, mineralogy, uranium mineral content, and evidence for deformation. Deformation features provide evidence for both shear and extensional stresses and include brecciation and a variety of mineralized fractures. Opaque phases include orgainc matter, uraninite, coffinite, and sulfides. In many cases, the opaque assemblage is concentrated along fractures. Considerable textural evidence, viz., embayed grain margins and fractures with nonparallel margins, suggests partial dissolution of uraninite in the Oklo ores. Uraninite with embayed margins is commonly accompanied by organic matter. Oklo uraninites are, in many cases, altered to produce coffinite (USiO4.nH2O) and are associated with varying quantities of galena at grain boundaries, within fractures, and within individual grains at intracrystalline locations. Textural evidence suggests multiple periods of uraninite formation. Electron microprobe data are presented for uraninites from RZ-13. Analytical data are discussed for Oklo reactor zical data are discussed for Oklo reactor zones 2, 9, 10, 13, and 16 and for the reactor at Bangombe. Uraninites are compositionally similar with respect to Pb for RZ-2, RZ-9, RZ-13, RZ-16 and for the Bangombe reactor (average content of PbO is 5.92 weight %). Lead contents for uraninites from RZ-10 are generally higher and more variable than for the other reactor zones (e.g., PbO content for RZ-10 uraninites ranges from approximately 12 to 18 weight %). (orig.)

  9. Fast fission phenomena

    International Nuclear Information System (INIS)

    Experimental studies of fast fission phenomena are presented. The paper is divided into three parts. In the first part, problems associated with fast fission processes are examined in terms of interaction potentials and a dynamic model is presented in which highly elastic collisions, the formation of compound nuclei and fast fission appear naturally. In the second part, a description is given of the experimental methods employed, the observations made and the preliminary interpretation of measurements suggesting the occurence of fast fission processes. In the third part, our dynamic model is incorporated in a general theory of the dissipative processes studied. This theory enables fluctuations associated with collective variables to be calculated. It is applied to highly inelastic collisions, to fast fission and to the fission dynamics of compound nuclei (for which a schematic representation is given). It is with these calculations that the main results of the second part can be interpreted

  10. Uranium transport around the reactor zone at Okelobondo (Oklo). Data evaluation with M3 and HYTEC

    International Nuclear Information System (INIS)

    The Swedish Nuclear Fuel and Waste Management Company (SKB) is conducting and participating in Natural Analogue activities as part of various studies regarding the final disposal of high level nuclear waste (HLW). The aim of this study is to use the hydrogeological and hydrochemical data from Okelobondo (Oklo Natural Analogue) to compare the outcome of two independent modelling approaches (HYTEC and M3). The modelling helps to evaluate the processes associated with nuclear natural reactors such as redox, adsorption/desorption and dissolution/precipitation of the uranium and to develop more realistic codes which can be used for site investigations and data evaluation. HYTEC (1D and 2D) represents a deterministic, transport and multi-solutes reactive coupled code developed at Ecole des Mines de Paris. M3 (Multivariate Mixing and Mass balance calculations) is a mathematical-statistical concept code developed for SKB. M3 can relatively easily be used to calculate mixing portions and to identify sinks or sources of element concentrations that may exist in a geochemical system. M3 helped to address the reactions in the coupled code HYTEC. Thus, the major flow-paths and reaction paths were identified and used for transport evaluation. The reactive transport results (one-dimensional and two-dimensional simulations) are in good agreement with the statistical approach using the M3 model. M3 and HYTEC show a dissolution of the uranium layer in contact with upwardly oxidising waters. M3 and HYTEC show a gain of manganese rich minerals downstream the reactor. A comparison of the U and Mn plots for M3 deviation and HYTEC results showed an almost mirror behaviour. The U transport stops when the Mn gain increases. Thus, HYTEC and M3 modelling predict that a possible reason for not having U transport up to the surface in Okelobondo is due to an inorganic trap which may hinder the uranium transport. The two independent modelling approaches can be used to complement each other and to better understand the processes that can take place in nature. This provides the opportunity to assess the necessary tools for site investigations, data evaluation and helps to trace the reactions and to identify the hydro-geo-chemical system. Thus, we can build reliable tools which can be used to assess the performance of possible waste repository sites

  11. Indications of uranium transport around the reactor zone at Bagombe (Oklo)

    International Nuclear Information System (INIS)

    The aim of this study is to use the hydrogeological and hydrochemical data from Oklo Natural Analogue to compare the outcome of two independent modelling approaches (HYTEC-2D and M3) which can be used to model natural conditions surrounding the reactor. HYTEC-2D represents a 2D, deterministic, transport and multi-solutes reactive coupled code developed at Ecole des Mines de Paris. M3 (named Multivariate Mixing and Mass balance) is a mathematical-statistical concept code developed for SKB. The M3 results are visualised using the Voxel Analyst code and the outcome of the uranium transport predictions are made from a performance assessment point of view. This exercise was in the beginning intended to represent a validation for M3, by comparing this statistic approach with the standard hydrodynamic - geochemical coupled code HYTEC-2D. It was realized that the codes complete each other and a better understanding of the geochemical studied system is obtained. Thus, M3 can relatively easily be used to calculate mixing portions and to identify sinks or sources of element concentrations that may exist in a geochemical system. This can help to address the reactions in the coupled code such as HYTEC-2D, to identify the hydrodynamic and hydrochemical system and to reduce the computation time. M3 shows the existence of the buffer around the reactor. No transport of uranium was indicated downstream the reactor. HYTEC-2D gives the same result in the case when we consider the existence of the redox buffer in the model. M3 shows an increase of the alkalinity in the reactor zone. The increase of the alkalinity was indicated by the M3 modelling to be associated with microbial decomposition of organic material which added reducing capacity to the system. The modelling result was supported by new results from the last field campaign, which included in-situ Eh measurements and microbial sampling and identification. The effects from the same process was indicated also by the HYTEC-2D predictions which show an increase of the pH in the reactor zone, due to the existence of the buffer. The two modelling approaches can be used to complete each other and to better understand the processes that can take place in nature. Thus, we can build confident tools which can be used to support performance assessment

  12. Speciation of actinides and fission products at smectite rich natural clay-water interface

    International Nuclear Information System (INIS)

    Speciation of actinides (Am(lll), Pu(lV), Np(V)) and long lived fission products, (Cs(l), Sr(II), Tc(VII)) at the interface between smectite rich clay and water has been studied by batch sorption experiments under different experimental conditions of pH, ionic strength and metal ion concentration. Modeling of the sorption data have been used to delineate the mechanism of the sorption of the metal ions on the clay. The study revealed different mechanisms (surface complexation, ion exchange) operating under different pH conditions and for different metal ions. Studies have been extended to diffusion of these radionuclides in the compacted clay to obtain the diffusion coefficient in saturated clay

  13. Anomalous Xenon in the Precambrian Nuclear Reactor in Okelobondo (Gabon): A Possible Connection to the Fission Component in the Terrestrial Atmosphere

    Science.gov (United States)

    Meshik, A. P.; Kehm, K.; Hohenberg, C. M.

    1999-01-01

    Some CFF-Xe (Chemically Fractionated Fission Xenon), whose isotopic composition is established by simultaneous decay and migration of radioactive fission products, is probably present in the Earth's lithosphere, a conclusion based on available Xe data from various crustal and mantle rocks . Our recent isotopic analysis of Xe in alumophosphate from zone 13 of Okelobondo (southern extension of Oklo), along with the independent estimation of the isotopic composition of atmospheric fission Xe , supports the hypothesis that CFF-Xe was produced on a planetary scale. Additional information is contained in the original extended abstract.

  14. Fission measurements

    International Nuclear Information System (INIS)

    Fission was discovered by radiochemistry but confirmed soon afterwards by a physical method. Rapidly the military applications of fission resulted in a blackout of fission work for a long time. This work was again carried out in the open at national and international levels, especially to meet the needs of important nuclear energy programs. This paper presents a brief history of this period, a review of the requested fission data for these programs and of the fission measurements to meet these needs and also to obtain a better understanding of the fission process

  15. Coulomb fission

    International Nuclear Information System (INIS)

    A semiquantal theory of Coulomb fission is presented. It is shown that Coulomb fission is a two-step process, involving multiple Coulomb excitation of an actinide target nuclear by a heavy projectile :Zp >approx. 50) followed by radioactive decay. The historical background; dynamical formalism of the theory; phenomenological models of the theory; Coulomb fission experiments; comparison of theory and experiment; and prompt Coulomb fission theory; are all discussed. (U.K.)

  16. Coulomb fission

    Energy Technology Data Exchange (ETDEWEB)

    Oberacker, V.E.; Pinkston, W.T. (Vanderbilt Univ., Nashville, TN (USA). Dept. of Physics and Astronomy); Kruse, H.G.W. (Michigan State Univ., East Lansing (USA). Dept. of Physics)

    1985-03-01

    A semiquantal theory of Coulomb fission is presented. It is shown that Coulomb fission is a two-step process, involving multiple Coulomb excitation of an actinide target nuclear by a heavy projectile :Zp > approx. 50) followed by radioactive decay. The historical background; dynamical formalism of the theory; phenomenological models of the theory; Coulomb fission experiments; comparison of theory and experiment; and prompt Coulomb fission theory; are all discussed.

  17. Natural genetic variation impacts expression levels of coding, non-coding, and antisense transcripts in fission yeast.

    DEFF Research Database (Denmark)

    Clément-Ziza, Mathieu; Marsellach, Francesc X.

    2014-01-01

    Our current understanding of how natural genetic variation affects gene expression beyond well-annotated coding genes is still limited. The use of deep sequencing technologies for the study of expression quantitative trait loci (eQTLs) has the potential to close this gap. Here, we generated the first recombinant strain library for fission yeast and conducted an RNA-seq-based QTL study of the coding, non-coding, and antisense transcriptomes. We show that the frequency of distal effects (trans-eQTLs) greatly exceeds the number of local effects (cis-eQTLs) and that non-coding RNAs are as likely to be affected by eQTLs as protein-coding RNAs. We identified a genetic variation of swc5 that modifies the levels of 871 RNAs, with effects on both sense and antisense transcription, and show that this effect most likely goes through a compromised deposition of the histone variant H2A.Z. The strains, methods, and datasets generated here provide a rich resource for future studies.

  18. Chemistry and migration behaviour of the actinides and fission products in natural aquatic systems

    International Nuclear Information System (INIS)

    The 66th PTB seminar was held on April 24th and 25th, 1986, at the Munich Technical University (TUM) in Garching in cooperation with the Institute for Radiochemistry of the Munich Technical University, the 'Nuclear Chemistry' special group of the Society of German Chemists, and UB/SN responsible for the BMFT project. The seminar was organized by the TUM's Institute for Radiochemistry. The seminar dealt with the following main topics: primary geochemical reactions and colloid formation; sorption mechamisms and migration behaviour in Konrad/Gorleben aquifer systems; sampling and experimental investigations; evaluation and interpretation of the data obtained by experiments. The seminar was to achieve the following objectives: information and exchange of experience with regard to the work carried out up to the present; if necessary, formulation of new issues to be discussed; improvement of the interdisciplinary cooperation (chemistry, geosciences, modelling). The following topics and individual aspects were of particular interest and were given special attention: complementary basic research in order to interpret, support and model the results obtained by experiments (sorption mechanisms and thermodynamic data for natural systems); comparability of batch, column and diffusion tests; transferability of laboratory data to natural systems (e.g. Gorleben, Konrad); redox transitions for Np, Tc at Eh values of the natural systems; dependence of the sorption/desorption data on different influencing factors, importance of the influencing factors and selection of data for model calculations. Subject analyses of the individual contributions have been made for the Energy data base. (orig./RB)

  19. Syngenetic model for some early Proterozoic uranium deposits. Evidence from Oklo

    International Nuclear Information System (INIS)

    Massive, vein-like accumulations of uranium in Early Proterozoic metamorphic rocks have conventionally been explained by hydrothermal processes, metamorphism of original syngenetic or early epigenetic sedimentary deposits, mechanical accumulations, supergene processes, or some combination of these processes. Many of these deposits are located at unconformities and may be controlled by basement fault systems, but the unconformities are not necessarily the primary control for ore formation. Exploration of Proterozoic sedimentary basins is, for economic factors, usually restricted to the basin edges where distance to the unconformities is minimal. The 2.0+-0.1 billion year old Oklo uranium deposit, Republic of Gabon, is unique in that very high grade ore has apparently been derived from low grade ore in unmetamorphosed sedimentary rocks. The low grade ore is similar to Phanerozoic syngenetic or early epigenetic sandstone type deposits; the assemblage pitchblende-illite (1 Md polytype)-chlorite-organic carbon-dolomite is common. Uranium was mobilized from the low grade ore zones and concentrated as high grade ore in fractures. Pitchblende-illite (2M1 polytype)-chlorite-hematite-pyrite in the virtual absence of quartz and carbon is common in the high grade ore. Crystallization temperatures near 2000C at P=0.5-2 kb and Eh conditions favouring formation of either pyrite or hematite, in the pH range of 6-8 were likely. The reductant for the mobilized uraikely. The reductant for the mobilized uranium was apparently carbon which was oxidized as fractures opened, thus also accounting for the absence of quartz. The high grade ore, concentrated in shale-rich material down-filled into broken sandstone layers, was then severely folded and fractured. In cross sections, then, much of the Oklo ore resembles cross sections of high grade uranium ore in metamorphic rocks. It is proposed that Oklo may either be a hybrid type of deposit or a precursor to typical deposits in metamorphic rocks noted in Canada and elsewhere. It is considered significant that the Oklo deposit is located within the sedimentary sequence and not at the unconformity between this sequence and the basement granitic massif

  20. Nuclear fission

    International Nuclear Information System (INIS)

    A set of fission barriers and the corresponding nuclear level densities have been generated for various applications. Accurate level densities are prescribed within GSM for reactor physics studies. Since fission level densities and barrier parameters are strongly interdependent, the corresponding set of parameters for both the inner and outer fission barriers has also been provided. Some specific applications, such as accelerator-driven systems and stellar nucleosynthesis, require a knowledge of large numbers of fission barriers and level densities to estimate spontaneous as well as neutron-induced or ?-delayed fission probabilities. Hence, the present compilation includes fission barriers for some 2301 nuclei with 78 ? Z ? 120 derived by means of the ETFSI method, and the corresponding level densities at both saddle-point deformations predicted by the microscopic model based on HFBCS single-particle properties. (author)

  1. The topography of the nuclear fission barrier

    International Nuclear Information System (INIS)

    Fission theory first developed within the framework of the liquid drop model. Shell model concepts were introduced into fission theory much later than they were in nuclear structure theory but then with spectacular success in explaining striking experimental results then emerging in actinide fission. In the last two decades the complex topography of the fission barrier that is the result of shell model theory has been a major theme in the expanding knowledge of fission, most experimental data finding a natural explanation within this theme. The development of the concept of shell model structure in the fission barrier is outlined in this review. (author). 140 refs., 35 figs

  2. On the use of thin natural uranium film dosimetry in mineral dating by the fission track method

    International Nuclear Information System (INIS)

    Three obsidian samples were irradiated in a neutron facility and their age was measured by the fission track method; using a thin uranium film dosemeter. The results were compared to others made previously on the same type of rock using conventional neutron dosimetry. The use of thin uranium film for age determination is discussed. (F.E.). 20 refs, 4 tabs

  3. Current topics in nuclear fission research

    International Nuclear Information System (INIS)

    This year is the 50th anniversary of the discovery of nuclear fission by Otto Hahn and Fritz Strassmann. From the point of view of the fundamental physics research, nuclear fission was one of the oldest motivation of the nuclear physics. In this 50 years, many aspects of nuclear fission phenomena have been investigated. Owing to the nature that the nuclear fission involves a dynamical treatment of finite-many-body systems, there have been always some challenging new topics in nuclear fission research in these 50 years. By solving these problems one by one, we have come closer to the understanding of the nuclear fission dynamics. As examples of current topics in nuclear fission research, I will choose and discuss the following three: 1) Cold fission phenomena. 2) Heavy-particle radioactivity phenomena. 3) Transient effect phenomena. (author)

  4. Fission barriers

    International Nuclear Information System (INIS)

    Immediately after the discovery of fission in 1939 by Hahn and Strassmann and Meitner and Frisch, the latter authors gave a qualitative explanation of the process using the picture of a charged liquid drop. Still in the same year, Bohr and Wheeler developed this picture into their classical theory, which remained the basis for the description of nuclear fission for many years to come. Today it is known that many of the finer details of the fission process cannot be understood without reference to the shell structure of the nucleus. It is the merit of V. M. Strutinsky to have shown a practical way to combine the knowledge about shell structure with the liquid drop model in his open-quotes macroscopic-microscopicclose quotes method and to point to the important effect of shell structure on what we call the open-quotes fission barrierclose quotes. This chapter will thus describe the fission barrier first within the liquid drop model (Section II) and then discuss shell corrections according to the Strutinsky procedure (Section III). Section IV will deal with the transmission through the fission barrier, including the most immediate effects of its double-humped shape. Some of the more detailed consequences of this structure, namely the existence of different classes of compound nuclear states, will be briefly addressed in Section V; however, more detailed discussion of their effect will be postponed to Chapter 4. Finally, Section VI will describe some basic methods of obtaI will describe some basic methods of obtaining experimental information on the shape of the fission barrier. 61 refs., 11 figs., 1 tab

  5. Spontaneous fission

    International Nuclear Information System (INIS)

    The spontaneous fission (SF) of the heaviest actinides and the transactinides is of particular interest because of the dramatic changes in properties observed in the region of the heavy fermion isotopes and for still heavier elements. The existing experimental information on SF properties including half-life systematics, fragment kinetic-energy and mass-yield distributions, prompt neutron emission, and gamma emission will be reviewed. Possibility for extending studies of SF properties to other regions are considered and the potential for obtaining additional information about low-energy fission properties is discussed

  6. Benchmarking nuclear fission theory

    Science.gov (United States)

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

    2015-07-01

    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.

  7. Benchmarking Nuclear Fission Theory

    CERN Document Server

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

    2015-01-01

    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.

  8. Bimodal fission

    International Nuclear Information System (INIS)

    In recent years, the author has measured the mass and kinetic-energy distributions from the spontaneous fission of 258Fm, 259Md, 260Md, 258No, 262No, and 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. He concludes 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. He also concludes the low-energy but mass-symmetrical model 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 132Sn

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

    CERN Document Server

    Goddard, P M; Rios, A

    2015-01-01

    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 ...

  10. Dissolution studies of natural analogues spent fuel and U(VI)-Silicon phases of and oxidative alteration process

    International Nuclear Information System (INIS)

    In order to understand the long-term behavior of the nuclear spent fuel in geological repository conditions, we have performed dissolution studies with natural analogues to UO2 as well as with solid phases representatives of the oxidative alteration pathway of uranium dioxide, as observed in both natural environment and laboratory studies. In all cases, we have studied the influence of the bicarbonate concentration in the dissolution process, as a first approximation to the groundwater composition of a granitic environment, where carbonate is one of the most important complexing agents. As a natural analogue to the nuclear spent fuel some uraninite samples from the Oklo are deposit in Gabon, where chain fission reactions took place 2000 millions years ago, as well as a pitchblende sample from the mine Fe ore deposit, in Salamanca (spain) have been studied. The studies have been performed at 25 and 60 deg C and 60 deg C, and they have focussed on the determination of both the thermodynamic and the kinetic properties of the different samples studied, using batch and continuous experimental methodologies, respectively. (Author)

  11. Fission isomers

    International Nuclear Information System (INIS)

    The single particle (shell) effects giving rise to spontaneously fissioning shape isomeric states are outlined. Empirical data on static properties such as excitation energies and barrier heights are reviewed and compared with potential energy surface calculations. Half-life and branching ratio information are related to barrier penetration. Spectroscopic information on moments of inertia, quadrupole moments, spins and g-factors are reviewed. Recent developments on shape isomerism in other regions of the Chart of the Nuclides are presented

  12. Fission isomers

    International Nuclear Information System (INIS)

    The single particle (shell) effects giving rise to spontaneously fissioning shape isomeric states are outlined. Empirical data on static properties such as excitation energies and barrier heights are reviewed and compared with potential energy surface calculations. Half-life and branching ratio information are related to barrier penetration. Spectroscopic information on moments of inertia, quadrupole moments, spins and g-factors are reviewed. Recent developments on shape isomerism in other regions of the Chart of the Nuclides are presented. 22 refs., 5 figs

  13. Investigation of spatial distribution of fission-rate of natural uranium nuclei in the blanket of electronuclear setup 'Energy plus Transmutation' at Dubna Nuclotron proton beam at energy 1.5 GeV

    International Nuclear Information System (INIS)

    The 'Energy plus Transmutation' experimental setup of the Veksler and Baldin Laboratory of High Energy Physics within the Joint Institute for Nuclear Research (JINR) in Dubna, Russia, is a lead target (with a diameter of 8.4 cm and length of 45.6 cm) surrounded by a uranium blanket (weight 206.4 kg of natural uranium). A polyethylene plus cadmium shield is placed around the target-blanket assembly to modify the spallation and fission neutron spectra in the system. The setup was irradiated by a proton beam of energy 1.5 GeV using the Nuclotron accelerator. The spatial distribution of natural uranium fission-rate in the assembly and fission-rate in the blanket was determined experimentally and compared with Monte Carlo predictions using the MCNPX 2.6C code. Besides neutron-induced fission the calculations include the NatU(p,f), NatU(?,f) as well as NatU(?,f) reactions. Good agreement between the experimental and calculation results was obtained. The possible sources of errors in the experiment and calculations are discussed in detail

  14. Fission energy

    International Nuclear Information System (INIS)

    Fission energy research and development in the Division during this report period has spanned two primary programs. In one of these programs, some unique and important dissolution and solvent extraction work with fast reactor spent fuels was completed. Most of this work was done for the Consolidated Fuel Reprocessing Program (CFRP); a smaller project was completed under contract for Rockwell International Corp., Hanford, Washington. Specific studies on solvent cleanup were conducted under contract for Westinghouse Idaho Nuclear Company, Inc. Other work done by Chem Tech for CFRP included completing the preparation of 12 kg of uranium-plutonium mixed-oxide microspheres for fuel fabrication and irradiation tests. Detailed results from these studies are not included here, because of regulations governing the distribution of applied technology information. Results of this work are published in CFRP topical quarterly progress reports. The second area of Chem Tech's fission energy development has been in support work for the High-Temperature Gas-Cooled Reactor (HTGR) program. The applied technology information is not reported here in compliance with DOE regulations. Most of this work has been reported in internal documents and annual progress reports

  15. Bacteria, colloids and organic carbon in groundwater at the Bangombe site in the Oklo area

    International Nuclear Information System (INIS)

    This report describes how microorganisms, colloids and organic matter were sampled from groundwater from six boreholes at the Bangombe site in the Oklo region and subsequently analyzed. For analysis of microorganisms, DNA was extracted from groundwater, amplified and cloned and information available in the ribosomal 16S rRNA gene was used for mapping diversity and distribution of bacteria. Each borehole was dominated by species that did not dominate in any of the other boreholes, a result that probably reflects documented differences in the geochemical environment. Analyses of sampled colloids included SEM and ICP-MS analysis of colloids on membrane and single particle analysis of samples in bottles. The colloid concentration was rather low in these Na-Mg-Ca-HCO3 type waters. Trace element results show that transition metals and some heavy metals are associated with the colloid phase. Distribution coefficients of trace elements between the water and colloid phases were estimated. For example for uranium, an average of 200 pg/ml was detected in the water, and 40 pg/ml was detected in the colloid phase. A Kp value of 2* 106 ml/g was calculated, considering (colloid) = 100 ng/ml. Groundwater samples were collected for analysis of the concentration of organic carbon (TOC), humic substances and metals associated with the humic substances. TOC varied in the range 4-14 mg/l in three boreholes, one borehole had a TOC<1.5 mg/l. The metal speciation study indicated that a large fraction, 8-67% of uranium was bound to the humic matter compared to the fractions of Ca and Fe (<0.4% and 0.02-10%, resp.). 60 refs, 8 figs, 16 tabs

  16. An evaluation of the dissolution process of natural uranium ore as an analogue of nuclear fuel

    International Nuclear Information System (INIS)

    The assumption of congruent dissolution of uraninite as a mechanism for the dissolution behaviour of spent fuel was critically examined with regard to the fate of toxic radionuclides. The fission and daughter products of uranium are typically present in spent unreprocessed fuel rods in trace abundances. The principles of trace element geochemistry were applied in assessing the behaviour of these radionuclides during fluid/solid interactions. It is shown that the behaviour of radionuclides in trace abundances that reside in the crystal structure can be better predicted from the ionic properties of these nuclides rather than from assuming that they are controlled by the dissolution of uraninite. Geochemical evidence from natural uranium ore deposits (Athabasca Basin, Northern Territories of Australia, Oklo) suggests that in most cases the toxic radionuclides are released from uraninite in amounts that are independent of the solution behaviour of uranium oxide. Only those elements that have ionic and thus chemical properties similar to U4+, such as plutonium, americium, cadmium, neptunium and thorium can be satisfactorily modelled by the solution properties of uranium dioxide and then only if the environment is reducing. (84 refs., 7 tabs.)

  17. Fission theory and actinide fission data

    International Nuclear Information System (INIS)

    The understanding of the fission process has made great progress recently, as a result of the calculation of fission barriers, using the Strutinsky prescription. Double-humped shapes were obtained for nuclei in the actinide region. Such shapes could explain, in a coherent manner, many different phenomena: fission isomers, structure in near-threshold fission cross sections, intermediate structure in subthreshold fission cross sections and anisotropy in the emission of the fission fragments. A brief review of fission barrier calculations and relevant experimental data is presented. Calculations of fission cross sections, using double-humped barrier shapes and fission channel properties, as obtained from the data discussed previously, are given for some U and Pu isotopes. The fission channel theory of A. Bohr has greatly influenced the study of low-energy fission. However, recent investigation of the yields of prompt neutrons and ? rays emitted in the resonances of 235U and 239Pu, together with the spin determination for many resonances of these two nuclei cannot be explained purely in terms of the Bohr theory. Variation in the prompt neutron and ?-ray yields from resonance to resonance does not seem to be due to such fission channels, as was thought previously, but to the effect of the (n, ?, f) reaction. The number of prompt fission neutrons and the kinetic energy of the fission fragments are affected by the energy balance and damping or viscoshe energy balance and damping or viscosity effects in the last stage of the fission process, from saddle point to scission. These effects are discussed for some nuclei, especially for 240Pu. 17 figures, 56 ref

  18. Fine structure in the fission fragment yields

    International Nuclear Information System (INIS)

    Discussed are the most interesting experiments on the fine structure of fission product yields of U, Pu, Th, Cf, Es, Cm, Fr, Np isotopes. Modern comprehension of the fine structure nature in connection with other problems of fission dynamics is considered. It is noted, that the fine structure results from pairing correlations in a nucleus. The conclusion is drawn, that the available set of experimental data is not sufficient to elucidate the fine structure nature

  19. Seminar on Fission VI

    Science.gov (United States)

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

    2008-04-01

    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.

  20. Energy released in fission

    International Nuclear Information System (INIS)

    The effective energy released in and following the fission of U-235, Pu-239 and Pu-241 by thermal neutrons, and of U-238 by fission spectrum neutrons, is discussed. The recommended values are: U-235 ... 192.9 ± 0.5 MeV/fission; U-238 ... 193.9 ± 0.8 MeV/fission; Pu-239 ... 198.5 ± 0.8 MeV/fission; Pu-241 ... 200.3 ± 0.8 MeV/fission. These values include all contributions except from antineutrinos and very long-lived fission products. The detailed contributions are discussed, and inconsistencies in the experimental data are pointed out. In Appendix A, the contribution to the total useful energy release in a reactor from reactions other than fission are discussed briefly, and in Appendix B there is a discussion of the variations in effective energy from fission with incident neutron energy. (author)

  1. Prompt fission neutron spectra of n+235U above the (n,nf) fission threshold

    Science.gov (United States)

    Shu, Neng-Chuan; Jia, Min; Chen, Yong-Jing; Liu, Ting-Jin

    2015-05-01

    Calculations of prompt fission neutron spectra (PFNS) from the 235U(n, f) reaction were performed with a semi-empirical method for En = 7.0 and 14.7 MeV neutron energies. The total PFNS were obtained as a superposition of (n,xnf) pre-fission neutron spectra and post-fission spectra of neutrons which were evaporated from fission fragments, and these two kinds of spectra were taken as an expression of the evaporation spectrum. The contributions of (n,xnf) fission neutron spectra on the calculated PFNS were discussed. The results show that emission of one or two neutrons in the (n,nf) or (n,2nf) reactions influences the PFNS shape, and the neutron spectra of the (n,xnf) fission-channel are soft compared with the neutron spectra of the (n,f) fission channel. In addition, analysis of the multiple-chance fission component showed that second-chance fission dominates the PFNS with an incident neutron energy of 14.7 MeV whereas first-chance fission dominates the 7 MeV case. Supported by National Natural Science Foundation of China (11205246, 91126010, U1230127, 91226102), IAEA CRP (15905), and Defense Industrial Technology Development Program (B0120110034)

  2. Recent Results from Investigation of Prompt Fission Neutron Emission in Spontaneous Fission of 252CF

    International Nuclear Information System (INIS)

    The main motivation of the present work was investigation of the nature of anomalous (from the point of view of modern theory) dependence of the average prompt fission neutron number on the total kinetic energy of the fission fragments using modern digital signal processing approach. A twin Frisch-grid ionization chamber was used for fission fragment mass and kinetic energy spectroscopy. A fast neutron detector with NE213 (or analog) scintillation liquid was used for prompt fission neutron time of flight measurement. About 107 fission events, coinciding with prompt fission neutron detection was acquired in the experiment. Correlated fission fragment kinetic energies, their masses, an angle between fission axis and the prompt fission neutron, the prompt fission neutron velocity were measured with help of eight channel set-up of synchronized waveform digitizers, having 100 MHz sampling frequency and 12-bit pulse height resolution. Analysis of the acquired data revealed effects causing distortion of measured angular distribution of prompt fission neutron and the dependence of their average number on total kinetic energy of the fission fragment. Special modification of the experiment and respective modifications in the data analysis procedure brought to reasonable agreement between experimental results and theoretical calculations. In the first time the linear dependence of the average number of prompt fission neutron on total kinetic energy in the range of (14n total kinetic energy in the range of (140 - 220) MeV was demonstrated. The long time existing contradiction between experiment and theory was resolved and, a new measurement procedure allowing avoidance of above mentioned systematic errors in experiments with actinide targets like 235U, 239Pu, etc. was proposed. (author)

  3. Fifty years of nuclear fission: Nuclear data and measurements series

    International Nuclear Information System (INIS)

    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

  4. Fifty years of nuclear fission: Nuclear data and measurements series

    Energy Technology Data Exchange (ETDEWEB)

    Lynn, J.E.

    1989-06-01

    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.

  5. Fragment angular distributions in fission and fission like reactions

    International Nuclear Information System (INIS)

    Fragment angular distributions in fission is one of the oldest and well understood aspects of fission theory. However, recent heavy ion-induced fission and fission-like reactions have added a new dimension to this problem. The present understanding of the fragment angular distribution theory in fission and fission-like reactions is reviewed. (author). 23 refs., 7 figs

  6. Synthesis report on the relevant diffusion coefficients of fission products and helium in spent nuclear fuels

    International Nuclear Information System (INIS)

    This document corresponds to the deliverable D2 of the Work Package 1 of the 'Spent Fuel Stability under repository conditions' (SFS) European project. It constitutes a synthesis report on relevant diffusion coefficients of fission products and helium in spent nuclear fuels at high and low temperatures. Coefficients corresponding to thermally activated diffusion were reviewed from literature data for O, U (self-diffusion coefficients), fission gases and other fission products. Data showed that thermal diffusion was irrelevant at temperatures expected in repository conditions. The occurrence of diffusion enhanced by alpha self-irradiation was studied through different theoretical approaches. A 'best estimate' value of the alpha self-irradiation diffusion coefficient, D (m2.s-1), is proposed. It is extrapolated from enhanced diffusion under irradiation observed in reactor and would be proportional to the volume alpha activity in the spent nuclear fuel, Av (Bq.m-3) as: D/Av ? 2.10-41 (m5)The migration of stable Pb in Oklo's uraninites was studied in order to validate the proposed diffusion coefficient. The obtained value is one order of magnitude higher than the theoretical proposed value. As for He behaviour in spent nuclear fuel, a few data are today available in open literature. The document will be completed as soon as new experimental results are available. (authors)

  7. Geometry of membrane fission.

    Science.gov (United States)

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

    2015-01-01

    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

  8. Physics and chemistry of fission

    International Nuclear Information System (INIS)

    Full text: In the pleasant and hospitable atmosphere of the Kernforschungsanlage Juelich in the Federal Republic of Germany, the IAEA symposium on the Physics and Chemistry of Fission took place. Almost 200 scientists attended, 154 abstracts were submitted, and 57 papers presented, but more important than the numbers was the quality of the contributions and the progress reported at the symposium. The neutron was discovered almost 50 years ago; 40 years ago the idea of nuclear fission was born. Since then, a number of laboratories have worked hard to explain the phenomenon of fission One would expect that by now scientists would know exactly what happens in a nucleus before and during the process of fission, particularly as there are hundreds of power and research reactors in operation, and fission of uranium isotopes is the basis of their functioning. At first glance, fission seems a simple process: a neutron hits and penetrates the uranium nucleus which becomes excited, i.e. has a surplus of energy. One way to get rid of this energy is for the nucleus to split into two parts; additional products of this process are energy and more neutrons. Nature, however, seems to dislike such straightforward explanations. In the case of fission, scientists have observed a number of phenomena which disagree with a simple model. Sometimes, a nucleus will split into two parts without being 'attacked' by a neutron; this spontaneous fission opens up a new line of fission research and sns up a new line of fission research and several contributions at the symposium reported on sophisticated experiments designed to unravel some of its specific details. Sometimes, a fissioning nucleus will emit another particle: ternary fission has become a powerful tool for studying the properties of nuclei during the fission process. For the scientist, it is fascinating to observe how the nucleus behaves during fission. They invent models which are supposed to reproduce the most probable course of events leading to fission. In one of these models, the nucleus is imagined to be a very small drop of liquid; the theorist then devises many schemes that lead to its splitting into two smaller drops. It is surprising how many detailed features theorists can predict, based on such simple models, and how well these predictions have been confirmed by experiments. The symposium summarized the progress in this field, and indicated how many intricate details can be introduced into a simple liquid drop model to give better agreement with experimental results. Step by step, a picture is emerging and being continuously improved, coming closer and closer to the truth. However, the liquid drop model has several competitors of which the most prominent is the shell model. This model assumes that the constituents of the nucleus are sorted into well defined energy levels, or shells; the distribution of protons and neutrons in these shells, and their movements from one shell to another, can provide an explanation for many experimentally observed facts New theoretical results drawn from these models were reported at the symposium, together with some efforts to combine different theoretical concepts, thereby trying to create a unified picture of nuclear fission. The nucleus is too small for the scientist to be able to observe directly what is happening inside it. There is really only one way for an experimenter to study a process in a nucleus, he must measure the energies of the particles coming out of it. In the case of fission, these 'messengers' can be the fission fragments, i.e. nuclei of elements that are being created from the splitting atom, but they can also be the neutrons or gamma rays which emerge during and after the fission process. Several sessions in the symposium were devoted to reports of such studies. With the help of sophisticated electronics systems, or complicated radiochemical methods, experimenters have measured the energies of fission fragments, neutrons, gamma and X-rays, and other particles emerging from fissioning nuclei, with great accuracy. By putting t

  9. Dissolution studies of natural analogues spent fuel and U(VI)-Silicon phases of and oxidative alteration process; Estudios de disolucion de analogos naturales de combustible nuclear irradiado y de fases de U(VI)-Silicio representativas de un proceso de alteracion oxidativa

    Energy Technology Data Exchange (ETDEWEB)

    Perez Morales, I.

    2000-07-01

    In order to understand the long-term behavior of the nuclear spent fuel in geological repository conditions, we have performed dissolution studies with natural analogues to UO{sub 2} as well as with solid phases representatives of the oxidative alteration pathway of uranium dioxide, as observed in both natural environment and laboratory studies. In all cases, we have studied the influence of the bicarbonate concentration in the dissolution process, as a first approximation to the groundwater composition of a granitic environment, where carbonate is one of the most important complexing agents. As a natural analogue to the nuclear spent fuel some uraninite samples from the Oklo are deposit in Gabon, where chain fission reactions took place 2000 millions years ago, as well as a pitchblende sample from the mine Fe ore deposit, in Salamanca (spain) have been studied. The studies have been performed at 25 and 60 degree centigree and 60 degree centigree, and they have focussed on the determination of both the thermodynamic and the kinetic properties of the different samples studied, using batch and continuous experimental methodologies, respectively. (Author)

  10. Fission Mass Yield Studies

    International Nuclear Information System (INIS)

    Mass yields from fission induced by a span of neutron energies up to 18 MeV have been measured for Th232, U235 and U238 target nuclei. Particular attention has been given to the dependence of symmetric fission yields on energy. To study the effect of angular momentum, fission yields from the U236 compound nucleus formed by alpha-particle irradiations of Th232 were also studied over the same span of excitation energies. A standard set of Pd109, Ag111, Pd112 and Ag113 symmetric fission yields was generally measured for all irradiations. In addition, yields of Eu156, Cs136 and 2.3-d Cd115 were measured for some selected combinations of projectile, energy and target nucleus. Assays for Zr97 and sometimes also Ba139 served as fission monitors. Altogether 150 fission yields were measured for these combinations of target nucleus, projectile and incident energy. About one-third of these were checked by replicated irradiations. At highest energies for the U236 compound nucleus the symmetric fission yield from alpha-particle-induced fission is about 13% higher than for neutron-induced fission. Dips in symmetric fission yield were observed at the energy onset of third-chance fission for each target and projectile. Some indication of a small central peak in the mass distribution was observed in the yields from U236 compound nucleus fission, but not from the Th233 compound nucleus fission. Detailed mathematical methods have been developed to separate the effects of fissions preceding and following neutron emission. These methods were used to remove the effects of second- and third-chance fissions from the measured symmetric fission yields. These calculated yields for first-chance fission show no dips with energy. The calculations also show that perhaps half the difference between symmetric yields for alpha- particle-induced fission of Th232 and neutron-induced fission of U235 is attributable to angular momentum effects. Both calculated first-chance yields and measured yields (resulting from first-, second- and third-chance fissions) for the U236 compound nucleus are compared with the two-mode-of-fission hypothesis. Similar analyses are made for yields from neutron-induced fission of Th232 and U238. (author)

  11. Neutrons and fission

    International Nuclear Information System (INIS)

    The contribution that neutrons have made in the last decade to a better understanding of fission is reviewed with stressing the most recent aspects of this contribution which have been quite important. Special emphasis is put on the double-humped fission barrier situation, the macroscopic-microscopic approach to the calculation of fission barriers is presented together with the general consequences of double-humped barrier shapes; a comparison is also made between calculated and measured fission barrier parameters. More specific properties of neutron-induced fission relevant to the barrier shape are discussed. Fission induced by resonance neutrons is examined with special attention given to properties connected to the Bohr theory of fission exit channels and to intermediate structure effects. The existence and interpretation of other structure effects, in the near-threshold fission cross sections, are discussed. Some results on fission dynamics are presented: for the spontaneous fission half-lives of even-even nuclei, taking account of more accurate calculations of mass inertia parameter, and for damping effects in the low energy fission of 240Pu. Emphasis is put mainly on the fission mechanism for actinide nuclei and how it varies with the nucleus, its excitation energy and the quantum numbers J, ?, and K of the fissioning state. In contrast, very little attention is paid to a detailed description of the fission properties of a given nuclear state: for this reason, fission induced by thermal neutrons is ignored here, and the subject of neutrons emitted in fission is not treated as such

  12. Dynamics of Coulomb fission

    OpenAIRE

    Kruse, Hans; Pinkston, W. T.; Greiner, Walter; Oberacker, Volker

    2006-01-01

    A general formalism is described for the treatment of Coulomb fission, within the framework of the semiquantal theory. We develop a model for the fission probabilities of levels excited in Coulomb excitation. This model contains penetration of the double-humped fission barrier, competition from gamma and neutron emission, and the spreading of the collective states into noncollective compound states. For 74184W + 92238U, the fission probability at ?c.m.=180° is increased by a factor of 3...

  13. Fission yields measured with target materials in contact with solid state track detectors

    International Nuclear Information System (INIS)

    The configuration of the contact of fissionable target materials with dielectric track detectors is reviewed to obtain fission yields corrected for fragment self-absorption in fission sources of different thicknesses and for optical magnification for the observation of etched fission tracks. Total detection efficiency and effective thickness of the target sample are obtained in the case of formation of cone-shaped tracks by etching. A number of useful formulae for evaluation of fission yields in both induced and spontaneous fission experiments is reported. The method can be extended and applied also to fission-related problems, natural and induced emission of nuclear fragments, and nuclear reaction studies as well. (author)

  14. Numerical Simulations of Fission

    Science.gov (United States)

    Durisen, Richard H.; Gingold, Robert A.

    1987-01-01

    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.

  15. Fission neutron statistical emission

    International Nuclear Information System (INIS)

    The statistical model approach FINESSE (FIssion NEutronS' Statistical Emission) for the description of fission neutron multiplicities, energy spectra and angular distributions is described. Based on an extended Weisskopf ansatz and on a realistic temperature distribution it provides a fragment mass number dependent description of fission neutron data. Model parameters (optical potential, n/? competition) were fixed on the basis of the 252Cf(sf) (nuclear data standard). Combined with a phenomenological fission model for predicting relevant fragment data as function of asymmetry. FINESSE can be applied to any fission reaction of actinides in the Th-Cf region without further parameter adjustment. Results are presented for 252Cf(sf) and neutron induced fission of 235U, 239Pu, 232Th. Effects of multiple-chance fission are discussed for 232Th(n,xnf) reacation. (author). 46 refs, 11 figs

  16. Status of geological studies undertaken in France on the Oklo deposit since the Libreville Symposium

    International Nuclear Information System (INIS)

    The questions posed since the Libreville symposium can be grouped under four headings: origin of the deposits and the over-concentrations; degree of burial reached by the series; temperatures attained during the reactions, and effects of the reactions; perturbations subsequent to the reactions. These questions have been the subject of multidisciplinary investigations, including conventional petrographic and mineralogical investigations (Cogema, Fontenay-aux-Roses and the Centre for Sedimentology and Geochemistry of the Surface, Strasbourg), a study of fluid inclusions (Centre for Petrographic and Geochemical Research, Nancy), studies of organic material (French Institute of Petroleum, Rueil, and Cerchar, Verneuil-en-Halatte) and a study of fission traces (Rene Barnas Laboratory, Orsay). (author)

  17. Determination of the fission products yields, lanthanide and yttrium, in the fission of 238U with neutrons of fission spectra

    International Nuclear Information System (INIS)

    A radiochemical investigation is performed to measure the cumulative fission product yields of several lantanides and yttrium nuclides in the 238U by fission neutron spectra. Natural and depleted uranium are irradiated under the same experimental conditions in order to find a way to subtract the contribution of the 235U fission. 235U percentage in the natural uranium was 3.5 times higher than in the depleted uranium. Uranium oxides samples are irradiated inside the core of the Argonaut Reactor, at the Instituto de Engenharia Nuclear, and the lantanides and yttrium are chemically separated. The fission products gamma activities were detected, counted and analysed in a system constituted by a high resolution Ge(Li) detector, 4096 multichannel analyser and a PDP-11 computer. Cumulative yields for fission products with half-lives between 1 to 33 hours are measured: 93Y, 141La, 142La, 143Ce and 149Nd. The chain total yields are calculated. The cumulative fission yields measured for 93Y, 141La, 142La, 143Ce and 149Nd are 4,49%, 4,54%, 4,95%, 4,16% and 1,37% respectively and they are in good agreement with the values found in the literature. (Author)

  18. Solvent extraction of some fission products using tetracycline as a complexing agent : dependence on the ph of the aqueous phase and on the nature of some inorganic anions

    International Nuclear Information System (INIS)

    The behavior of tetracycline as a complexing agent in solvent extraction studies is presented. The extraction curves for the fission products 90Sr, 140Ba, 99Mo, sup(99m)Tc, 95Zr, 95Nb, 103Ru and also for U have been determined for the extraction system tetracycline-benzyl alcohol. The extraction dependence on the pH of the aqueous phase as well as on the kind of electrolyte present was examined. As a practical application, the possiblity of using the tetracycline-benzyl alcohol system for separation of the fission products present in a mixture of them, as well as for the separation of uranium from those elements, was tested. (Author)

  19. Is channeling of fission tracks taking place?

    CERN Document Server

    Yada, K

    1999-01-01

    A single crystal of natural zircon which is sliced to have (010) basal plane and thinned by ion thinning is electron microscopically observed after slow neutron irradiation to ascertain whether channeling of the nuclear fission fragments is taking place or not. A fairly large number of the induced fission tracks are recognized at low magnification images where a considerable number of them are parallel to low-index lattice planes such as 100, 001, 101, 301, 103 though their directions changed some time up to several degrees. High resolution images of fission tracks often show a variety of zigzag passing of the tracks along low-index lattice planes in atomistic level. The rate of the tracks which are parallel to these low-index lattice planes is fairly high as about 45%, which strongly suggests that channeling of the fission tracks is taking place.

  20. Intermediate energy nuclear fission

    International Nuclear Information System (INIS)

    Nuclear fission has been investigated with the double-kinetic-energy method using silicon surface barrier detectors. Fragment energy correlation measurements have been made for U, Th and Bi with bremsstrahlung of 600 MeV maximum energy. Distributions of kinetic energy as a function of fragment mass are presented. The results are compared with earlier photofission data and in the case of bismuth, with calculations based on the liquid drop model. The binary fission process in U, Yb, Tb, Ce, La, Sb, Ag and Y induced by 600 MeV protons has been investigated yielding fission cross sections, fragment kinetic energies, angular correlations and mass distributions. Fission-spallation competition calculations are used to deduce values of macroscopic fission barrier heights and nuclear level density parameter values at deformations corresponding to the saddle point shapes. We find macroscopic fission barriers lower than those predicted by macroscopic theories. No indication is found of the Businaro Gallone limit expected to occur somewhere in the mass range A = 100 to A = 140. For Ce and La asymmetric mass distributions similar to those in the actinide region are found. A method is described for the analysis of angular correlations between complementary fission products. The description is mainly concerned with fission induced by medium-energy protons but is applicable also to other projectiles and energies. It is shown that the momentum and excitation energy distributions of cascade residuals leading to fission can be extracted. (Author)

  1. Conclusions drawn from the study of the migration of the fission products

    International Nuclear Information System (INIS)

    The Oklo fossil reactor offers an opportunity for studying migrations of uranium fission products after an exceptionally long cooling and storage period (1800 million years). The samples studied lie along a core sample traversing a reaction zone. Panoramic analysis by spark mass spectrometry enables one to reconstruct qualitatively the curve of the fission yields of the different isotopes and to observe anomalies associated with the loss of some of them: alkalines, iodine, molybdenum, alkaline earths. Light has been thrown on the behaviour of certain elements through chemical and isotopic analyses. It is shown that the thorium resulting from 240Pu and 236U decay remained bound to the uranium; the same applies to neodymium, samarium and gadolinium. Most of the bismuth resulting from 241Pu and 237U decay is also found. Most of the ruthenium has remained in place; a deficit of about 30% is observed in certain samples, part of it being attributed to the migration of 99Tc. On the other hand, analysis of the krypton and xenon shows that the greater part of these gases has disappeared and that this disappearance began during the nuclear reaction

  2. The nuclear fission process

    International Nuclear Information System (INIS)

    Fifty years after its discovery, the nuclear fission phenomenon is of recurring interest. When its fundamental physics aspects are considered, fission is viewed in a very positive way, which is reflected in the great interest generated by the meetings and large conferences organized for the 50th anniversary of its discovery. From a purely scientific and practical point of view, a new book devoted to the (low energy) nuclear fission phenomenon was highly desirable considering the tremendous amount of new results obtained since the publication of the book Nuclear Fission by Vandenbosch and Huizenga in 1973 (Academic Press). These new results could be obtained thanks to the growth of technology, which enabled the construction of powerful new neutron sources, particle and heavy ion accelerators, and very performant data-acquisition and computer systems. The re-invention of the ionization chamber, the development of large fission fragment spectrometers and sophisticated multiparameter devices, and the production of exotic isotopes also contributed significantly to an improved understanding of nuclear fission. This book is written at a level to introduce graduate students to the exciting subject of nuclear fission. The very complete list of references following each chapter also makes the book very useful for scientists, especially nuclear physicists. The book has 12 chapters covering the fission barrier and the various processes leading to fission as well as the characteriading to fission as well as the characteristics of the various fission reaction products. In order to guarantee adequate treatment of the very specialized research fields covered, several distinguished scientists actively involved in some of these fields were invited to contribute their expertise as authors or co-authors of the different chapters

  3. Muon-induced fission

    International Nuclear Information System (INIS)

    A review of recent experimental results on negative-muon-induced fission, both of 238U and 232Th, is given. Some conclusions drawn by the author are concerned with muonic atoms of fission fragments and muonic atoms of the shape isomer of 238U. (author)

  4. Fission 2009 4. International Workshop on Nuclear Fission and Fission Product Spectroscopy - Compilation of slides

    International Nuclear Information System (INIS)

    This conference is dedicated to the last achievements in experimental and theoretical aspects of the nuclear fission process. The topics include: mass, charge and energy distribution, dynamical aspect of the fission process, nuclear data evaluation, quasi-fission and fission lifetime in super heavy elements, fission fragment spectroscopy, cross-section and fission barrier, and neutron and gamma emission. This document gathers the program of the conference and the slides of the presentations

  5. Study of hypernuclei fission

    International Nuclear Information System (INIS)

    This work is about PS177 experience made on LEAR machine at CERN in 1988. The annihilation reaction of anti protons on a target of Bismuth or Uranium is studied. Lambda particles are produced by this reaction, in the nucleus in 2% of cases 7.1 10-3 hypernuclei by stopped antiproton in the target are produced. The prompt hypernucleus fission probability of uranium is 75% and that of Bismuth 10%. The mass distribution of fission fragments is symmetrical ((? the excitation energy of the nucleus is very high). If the nucleus hasn't fissioned, the non-mesonic lambda decay, gives it an energy of 100 MeV, what allows to fission later. This fission is delayed because the hypernucleus lifetime is 1.3+0.25-0.21 10-10 sec for Bismuth

  6. Biomodal spontaneous fission

    Energy Technology Data Exchange (ETDEWEB)

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

    1989-09-26

    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.

  7. Xenon and krypton isotopic anomalies in a natural nuclear reactor and at the epicenter of a nuclear explosion

    Energy Technology Data Exchange (ETDEWEB)

    Shukolyukov, Yu.A.; Meshik, A.P.; Pravdivtseva, O.V.; Verkhovskii, A.B.

    1988-06-01

    The purpose of this work was to investigate the possibility of the appearance of Xe and Kr isotopic anomalies in a natural reactor owing to migration processes. Four objects of study were used. The first was a soil sample from the crater formed by the first atomic bomb in Alamagordo, New Mexico, in 1945. The second sample consisted of standard uranium resin circa 130 million years old. The third object consisted of samples of uranium black and the fourth object consisted of samples of uranium resins Nos. 1470 and 1348 from the natural reactor in large ore lenses of the Oklo uranium deposit. Isotope ratios from stepwise and thermal annealing, unirradiated as well as irradiated with neutrons, and subjected to strong heating or melting in rock, were determined. The migratory mechanism was found to operate in the natural nuclear reactor in the Oklo uranium deposit.

  8. Xenon and krypton isotopic anomalies in a natural nuclear reactor and at the epicenter of a nuclear explosion

    International Nuclear Information System (INIS)

    The purpose of this work was to investigate the possibility of the appearance of Xe and Kr isotopic anomalies in a natural reactor owing to migration processes. Four objects of study were used. The first was a soil sample from the crater formed by the first atomic bomb in Alamagordo, New Mexico, in 1945. The second sample consisted of standard uranium resin circa 130 million years old. The third object consisted of samples of uranium black and the fourth object consisted of samples of uranium resins Nos. 1470 and 1348 from the natural reactor in large ore lenses of the Oklo uranium deposit. Isotope ratios from stepwise and thermal annealing, unirradiated as well as irradiated with neutrons, and subjected to strong heating or melting in rock, were determined. The migratory mechanism was found to operate in the natural nuclear reactor in the Oklo uranium deposit

  9. Nucleon-induced fission at intermediate energies

    International Nuclear Information System (INIS)

    The absence of a satisfactory theoretical description to predict isotope yields as well as the need for experimental fragment mass and charge distributions at intermediate-energies form the motivation of this work. Like the objects under study, the research presented in this thesis consists two main parts. Part 1 concerns an activation experiment that has been performed at the 'Kernfysisch Versneller Instituut' (Nuclear Physics Accelerator Institute) in Groningen, Netherlands, using the AGOR cyclotron. Fission product yields have been measured resulting from 190 MeV proton-induced fission of natW, 197Au, natPb, 208Pb and 232Th. In Chapter 2 the experimental set up is discussed, followed in Chapter 3 by a description of the data analysis. The results on the reconstructed mass yields and the total fission cross sections are presented in Chapter 4. Part 2 is of a theoretical nature. The objective is to compute fission product mass yields from intermediate-energy nucleon-induced reactions. In the approach presented here, two stages can be distinguished. In the first stage the fission cross section is determined for the various fissioning isotopes as a function of their excitation energy in competition with other processes like pre-equilibrium decay and particle evaporation. ALICE-91 is a nuclear reaction code that takes care of this first stage. The second stage consists of constructing the total fission-fragment mass and charge distributions from thment mass and charge distributions from the different contributions of all the equilibrated fissioning systems. Hence, a model is needed that gives a prediction for the fission-product mass yields in a large range of mass, charge, and excitation energy of the fissioning nucleus. For this purpose, the multi-modal random neck-rupture model by Brosa is extended with temperature-dependent shell and pairing corrections and a temperature-dependent LDM. The combination of ALICE-91 and the modified Brosa approach is used for the analysis of the experiments given in the first part of this thesis as well as other available experimental results. Chapter 5 is dedicated to the extension of the Brosa model. The multi-chance fission treatment in ALICE-91 is discussed in Chapter 6. Chapter 7 contains the coupling between ALICE-91 and the revised Brosa model as well as the results obtained in this manner. Finally, a summary and outlook can be found in Chapter 8. Appendix A contains a list explaining all the abbreviations used in this manuscript. Parts of this work have already been published in journals and conference proceedings. refs

  10. Bimodal fission of Hs*

    Science.gov (United States)

    Itkis, I. M.; Itkis, M. G.; Knyazheva, G. N.; Kozulin, E. M.; Loktev, T. A.; Novikov, K. V.; Hanappe, F.; Vardaci, E.

    2014-05-01

    Mass and energy distributions of fission fragments obtained in the reactions 22Ne + 249Cf, 26Mg + 248Cm, and 22Ne + 238U have been measured. A special attention will be paid on the properties of mass-energy distribution of fission fragments obtained in the reaction 26Mg + 248Cm at an excitation energy of 35 MeV. At this energy shell effects should become more effective in fission, the TKE distribution of symmetric fragments obtained in the reaction 26Mg + 248Cm differs strongly from a Gaussian shape. Besides a low-energy component, a high-energy component, not foreseen in the LDM, arises. This is attributed to the fact that both fission fragments are close to the spherical neutron shell N = 82. It means that for the compound nucleus 274Hs*, formed in the reaction 26Mg + 248Cm, the phenomenon of bimodal fission was observed for the first time. For the compound nucleus 260No* formed in the reaction 22Ne + 238U at the initial excitation energy of 41 MeV the bimodal fission as well as superasymmetric fission were observed.

  11. Fiftieth anniversary of nuclear fission

    International Nuclear Information System (INIS)

    Few discoveries have influenced mankind and few discoveries have had such an intricate history as that of nuclear fission. Thus it is natural that it is remembered and commemorated in many places on its fiftieth anniversary. The author participated in the early phases in Rome and later in the USA and he knew well most of the principals, except Fritz Strassmann. He gives a short outline; a detailed history would require many hours and would be laborious to follow in detail. He begins the story with the first neutron bombardment of uranium

  12. The influence of fission dose on fission gas atom trapping

    International Nuclear Information System (INIS)

    The trapping of fission gas atoms in uranium dioxide irradiated to low doses was examined. It was possible to interpret the experimentally deduced trapping in terms of fission gas atoms being immobilised at very small vacancy clusters produced by fission fragment damage. Using this model experimental evidence for the thermal solubility of fission gas was investigated and was shown to be in good accord with the SINGAR fission gas release model and its representation of thermal solubility. (author)

  13. Fission-fragment mass distributions

    International Nuclear Information System (INIS)

    Available experimental data are analyzed to determine certain features of fission fragment mass distributions. The dependence of fission fragment yields on nuclear composition and excitation energy fissioning nuclei is considered. The fine structure of fragment mass distribution is discussed. Various ideas proposed to explain the experimental facts are analyzed. The inability of theoretical calculations to describe quantitatively fission fragment distributions is noted

  14. Potential Operating Orbits for Fission Electric Propulsion Systems Driven by the SAFE-400

    Science.gov (United States)

    Houts, Mike; Kos, Larry; Poston, David; Rodgers, Stephen L. (Technical Monitor)

    2002-01-01

    Safety must be ensured during all phases of space fission system design, development, fabrication, launch, operation, and shutdown. One potential space fission system application is fission electric propulsion (FEP), in which fission energy is converted into electricity and used to power high efficiency (Isp greater than 3000s) electric thrusters. For these types of systems it is important to determine which operational scenarios ensure safety while allowing maximum mission performance and flexibility. Space fission systems are essentially nonradioactive at launch, prior to extended operation at high power. Once high power operation begins, system radiological inventory steadily increases as fission products build up. For a given fission product isotope, the maximum radiological inventory is typically achieved once the system has operated for a length of time equivalent to several half-lives. After that time, the isotope decays at the same rate it is produced, and no further inventory builds in. For an FEP mission beginning in Earth orbit, altitude and orbital lifetime increase as the propulsion system operates. Two simultaneous effects of fission propulsion system operation are thus (1) increasing fission product inventory and (2) increasing orbital lifetime. Phrased differently, as fission products build up, more time is required for the fission products to naturally convert back into non-radioactive isotopes. Simultaneously, as fission products build up, orbital lifetime increases, providing more time for the fission products to naturally convert back into non-radioactive isotopes. Operational constraints required to ensure safety can thus be quantified.

  15. Characteristics of Coulomb fission

    OpenAIRE

    Oberacker, Volker; Greiner, Walter; Kruse, Hans; Pinkston, William T.

    2006-01-01

    Within an extended semiquantal theory we perform large-sized coupled-channel calculations involving 260 collective levels for Coulomb fission of 238U. Differential Coulomb fission cross sections are studied as a function of bombarding energy and impact parameter for several projectiles. In the Xe + U case, total cross sections are also given. We find a strong dependence on projectile charge number, PCF(180°)?(Zp)6 in the region 50?Zp?92 for a fixed ratio E/ECoul, which migh...

  16. Review of Fission Theory

    International Nuclear Information System (INIS)

    A survey of the present state of fission theory is attempted. The basic requirements of a theory of a physical process are outlined and against this background the state of fission theory is summarized, with special emphasis on developments in the past few years. An attempt is made to bring out the most important outstanding problems to be settled by future experiments and theory. (author)

  17. Fission product detection

    International Nuclear Information System (INIS)

    The response of photovoltaic cells to heavy ions and fission products have been tested on beam. Their main advantages are their extremely low price, their low sensitivity to energetic light ions with respect to fission products, and the possibility to cut and fit them together to any shape without dead zone. The time output signals of a charge sensitive preamplifier connected to these cells allows fast coincidences. A resolution of 12ns (F.W.H.M.) have been measured between two cells

  18. Fission-to-spallation ratio and fission dynamics manifestation

    International Nuclear Information System (INIS)

    Fission of highly excited nuclei is affected by the viscous character of the system motion in deformation coordinates for very heavy nuclei with Z ? 90. The long-time scale fission was proved for such systems formed in heavy-ion induced reactions. The overdamped diabatic motion may influence also fission of the spallation-residue products in reactions with protons at intermediate energy. The experimental results on fission-to-spallation ratio are analyzed and the evidences for the long-time scale fission are found in the fission excitation functions for medium-mass targets with Z=70-75

  19. Feasibility of Producing Molybdenum-99 on a Small Scale Using Fission of Low Enriched Uranium or Neutron Activation of Natural Molybdenum. Companion CD-ROM

    International Nuclear Information System (INIS)

    This publication documents the work performed within the IAEA coordinated research project (CRP) on developing techniques for small scale indigenous molybdenum-99 production using low enriched uranium (LEU) fission or neutron activation. The CRP enabled participating institutions to gain the knowledge necessary for indigenous molybdenum-99 production. The outcome serves to capture the steps participants undertook in examining the feasibility of becoming small scale 99Mo producers. Most participants carried out work related to the entire production process, from target assembly through irradiation, planning for target disassembly in hot cells, chemical processing of targets, quality control practices, and managing waste streams. Some participants focused on one particular area, for example, testing new methods for production of LEU foil for targets and the production of gel generators from 99Mo solution. The publication aggregates all of the work undertaken as part of the CRP in order to present the results as a whole. The accomplishments of participating institutions are detailed in individual country reports on this CD-ROM

  20. Feasibility of Producing Molybdenum-99 on a Small Scale Using Fission of Low Enriched Uranium or Neutron Activation of Natural Molybdenum

    International Nuclear Information System (INIS)

    This publication documents the work performed within the IAEA coordinated research project (CRP) on Developing Techniques for Small Scale Indigenous Molybdenum-99 Production Using LEU Fission or Neutron Activation. The project allowed participating institutions to receive training and information on aspects necessary for starting production of molybdenum-99 (99Mo) on a small scale, that is, to become national level producers of this medical isotope. Stable production of 99Mo is one of the most pressing issues facing the nuclear community at present, because the medical isotope technetium-99m (99mTc), which decays from 99Mo, is one of the most widely used radionuclides in diagnostic imaging and treatment around the world. In the past five years, there have been widespread shortages of 99Mo owing to the limited number of producers, many of which use ageing facilities. To assist in stabilizing the production of 99Mo, and to promote the use of production methods that do not rely on the use of highly enriched uranium (HEU), the IAEA initiated the abovementioned CRP on small scale 99Mo production using low enriched uranium (LEU) fission or neutron activation methods. The intention was to enable participating institutions to gain the knowledge necessary to become national level producers of 99Mo in the event of further global shortages. Some of the institutions that participated in the CRP have continued their work on 99Mo production, and are enlisting the assistance of other CRP members and the IAEA’s technical cooperation programme to set up a small scale production capability. In total, the CRP was active for six years, and concluded in December 2011. During the CRP, fourteen IAEA Member States took part; four research coordination meetings were held, and four workshops were held on operational aspects of 99Mo production, LEU target fabrication and waste management. Most participants carried out work related to the entire production process, from target assembly to irradiation (most only performed the thermal and hydraulic calculations necessary for irradiation), to planning for target disassembly in hot cells, chemical processing of targets, quality control practices and managing waste streams. However, some participants focused on one particular area, for example, testing new methods for production of LEU foil for targets or the production of gel generators from 99Mo solution. This publication aggregates all of the work undertaken as part of the CRP in order to present the results as a whole; the accomplishments of participating institutions are detailed in individual country reports on the attached CD-ROM. In addition to presenting the work performed within the CRP, this publication is intended to serve a wide readership that includes nuclear authorities, regulators and any institution that may have an interest in becoming a small scale producer of 99Mo using non-HEU production methods. The details presented here could serve as a template for a feasibility study to be carried out by an institution or State wishing to produce 99Mo; special care has been taken to note areas that were particularly challenging for participants and therefore may not be feasible for other small scale producers without significant investment in human resources or infrastructure

  1. How good are the laws of physics

    International Nuclear Information System (INIS)

    The nature of the stringent constraints on the temporal variation of the basic interactions of physics which has been demonstrated in studies of the relative abundances of naturally occurring and fission fragment produced isotopes at the natural reactor site at Oklo, are considered. (U.K.)

  2. From fission to multifragmentation

    International Nuclear Information System (INIS)

    Heavy ion collisions are known to have different reaction mechanisms depending on the beam energy. While binary fission is the most likely outcome at energies about 1-2 MeV/A, at intermediate energies (say above 5 MeV/A) several medium size fragments are usually produced. Here the authors report on a study on how this change of mechanisms takes place. They use the Bohr-Wheeler transition state method of binary fission generalized to higher breakup modes. They also contrast the kinematical observables obtained under a sequential production of fragments with those of a simultaneous multifragmentation with the hope of identifying the breakup mechanism

  3. Low energy nuclear fission

    International Nuclear Information System (INIS)

    In these lectures we present the liquid drop model of fission and compare some of its prediction with experiment. The liquid drop analogy allows to define in a rather simple and intuitive way a number of useful concepts and possible observables. We then discuss, using the example of the oscillator model, the generality of shell effects. We show how a synthesis of the liquid drop model and of the shell model can be made using the Strutinsky shell averaging procedure. Some experimental data related to the existence of shape isomers are presented and discussed. We conclude by discussing some aspects, both experimental and theoretical, of fission dynamics

  4. Uncertainties in nuclear fission data

    International Nuclear Information System (INIS)

    We review the current status of our knowledge of nuclear fission data, and quantify uncertainties related to each fission observable whenever possible. We also discuss the roles that theory and experiment play in reducing those uncertainties, contributing to the improvement of our fundamental understanding of the nuclear fission process as well as of evaluated nuclear data libraries used in nuclear applications. (paper)

  5. Discovery and confirmation of fission

    International Nuclear Information System (INIS)

    An outline of the history of fission is presented beginning 1934, when fission products were first produced by neutron-irradiation of uranium but were attributed to transuranium elements, till December 1938, when fission was discovered with radiochemical techniques and confirmed in the following weeks with physical methods. (orig.)

  6. Microscopic Description of Induced Fission

    OpenAIRE

    Schunck, N.

    2013-01-01

    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.

  7. Fission fragment transport effects on heat transfer in fissioning gases

    International Nuclear Information System (INIS)

    This paper discusses direct energy transfer by fission fragments near the wall of a cavity containing fissioning gas studied in plane and cylindrical geometries. Analytical formulas are derived for the fission fragment energy flux. Heat transfer equations are solved for optically thick fissioning gases by taking into account the fission fragment energy transport effect. The results are applied to a heat transfer analysis of the fuel assemblies of a heterogeneous gas core reactor. The energy transfer mechanism in the fissioning gas is essentially nonlinear. Thus, the cooling effect due to direct fission fragment energy loss to the container walls does not become significant until the stopping range considerably exceeds the characteristic dimensions of the container

  8. Fission yields in the thermal neutron fission of plutonium-239

    International Nuclear Information System (INIS)

    Fission yields for 27 mass numbers were determined in the thermal neutron fission of 239Pu using high resolution gamma ray spectrometry and radiochemical method. The results obtained using gamma ray spectrometry and from the investigations on the fission yield of 99Mo using radiochemical method were reported earlier. These data along with fission yields for 19 mass numbers determined using radiochemical method formed a part of Ph.D. thesis. The data given here are a compilation of all the results and are presented considering the neutron temperature correction to 239Pu fission cross-section which is used for calculating the total number of fissions in these studies. A comparison is made of the resulting fission yield values with the latest experimentally determined values and those given in two recent compilations. (author)

  9. Natural occurring radioactive substances. Vol. 1

    International Nuclear Information System (INIS)

    Naturally occurring radioactive substances produced by cosmic rays of those of terrestrial origin are surveyed. The different radioactive decay series are discussed. Special emphasis is given to the element radium as regards its properties and distribution in different environmental samples. The properties of naturally occurring k-40 and its distribution in different natural media are also outlined. Induced radionuclides which are formed as a result of the interaction of cosmic rays with the constituents of the atmosphere are mentioned. In this respect the intensity of natural background radiation and the dose at different locations and levels is surveyed. Some regions of exceptionally high radioactivity which result in high exposure rates are mentioned. Monazite deposits and water springs are mentioned in some detail. The Oklo phenomenon as a natural reactor is also discussed. 8 tabs

  10. Fission yield evaluation

    International Nuclear Information System (INIS)

    The report presents the topics discussed at the Specialists' Meeting on Fission Yield Evaluation organized by the IAEA at Studsvik, Sweden, between 11 and 15 September 1987, the conclusions and the recommendations drafted in order to establish a closer cooperation between evaluators, improve the communication with measurers and to define further experimental and evaluation work needed

  11. Fission product data library

    International Nuclear Information System (INIS)

    A library is described of data for 584 isotopes of fission products, including decay constants, branching ratios (both burn-up and decay), the type of emitted radiation, relative and absolute yields, capture cross sections for thermal neutrons, and resonance integrals. When a detailed decay scheme is not known, the mean energies of beta particles and neutrino and gamma radiations are given. In the ZVJE SKODA system the library is named BIBFP and is stored on film No 49 of the NE 803 B computer. It is used in calculating the inventory of fission products in fuel elements (and also determining absorption cross sections for burn-up calculations, gamma ray sources, heat generation) and in solving radioactivity transport problems in the primary circuit. It may also be used in the spectrometric method for burn-up determination of fuel elements. The library comprises the latest literary data available. It serves as the basis for library BIBGRFP storing group constants of fission products with independent yields of isotopes from fission. This, in turn, forms the basis for the BIBDN library collecting data on the precursors of delayed neutron emitters. (author)

  12. Fission then and now

    International Nuclear Information System (INIS)

    To recall briefly a few events of a scientific character out of each enterprise may give a little impression of what happened in the field of fission physics from January 1939 and December 1942, and between December 1942 and now. (author)

  13. Empirical description of ? -delayed fission partial half-lives

    Science.gov (United States)

    Ghys, L.; Andreyev, A. N.; Antalic, S.; Huyse, M.; Van Duppen, P.

    2015-04-01

    Background: The process of ? -delayed fission (? DF ) provides a versatile tool to study low-energy fission in nuclei far away from the ? -stability line, especially for nuclei which do not fission spontaneously. Purpose: The aim of this paper is to investigate systematic trends in ? DF partial half-lives. Method: A semi-phenomenological framework was developed to systematically account for the behavior of ? DF partial half-lives. Results: The ? DF partial half-life appears to exponentially depend on the difference between the Q value for ? decay of the parent nucleus and the fission-barrier energy of the daughter (after ? decay) product. Such dependence was found to arise naturally from some simple theoretical considerations. Conclusions: This systematic trend was confirmed for experimental ? DF partial half-lives spanning over seven orders of magnitude when using fission barriers calculated from either the Thomas-Fermi or the liquid-drop fission model. The same dependence was also observed, although less pronounced, when comparing to fission barriers from the finite-range liquid-drop model or the Thomas-Fermi plus Strutinsky integral method.

  14. Isotopic yields of fission fragments from transfer-induced fission

    International Nuclear Information System (INIS)

    It is proposed to use transfer-induced fission in inverse kinematics coupled to the large acceptance spectrometer VAMOS to identify in atomic and mass number the complete distribution of the fission fragments. The measure of the kinetic properties of the transfer partner allows for determining precisely the excitation of the fissioning system. For the first time, the isotopic yields of the heavy and light fragments may be measured as a function of the excitation energy in neutron-rich actinides. (authors)

  15. Fission track dating

    International Nuclear Information System (INIS)

    A review is made of the basic priciples of the Fission Track (FT) method and the available informations on fission track stability in minerals. The latter implies that the FT ages calculated with the usual age equation is an 'apparent' age often geochronologically meaningless due to the partial geological fading of the spontaneous 238U fission tracks. Significant ages can however be obtained, which take into account partial fossil track retentivity, either (i) by applying a 'correction procedure' to the apparent FT age, using an experimentally determined, relationship between the mean etchable track lenght and the etchable track density with increasing track annealing conditions, or (ii) by thermally treating the samples before FT measurements, as in the model age methods developed by the author's group. Three kinds of FT model ages are described:the Isochronal Plateau Age (ICPA), Isothermal Plateau Age (ITPA) and Isochrone type of model ages. These model ages present the advantages over previous procedures of FT dating of a better precision and a control of the geological closing temperatures and track identification. (Author)

  16. Coulomb fission and transfer fission at heavy ion collisions

    International Nuclear Information System (INIS)

    In the present thesis the first direct evidence of nuclear fission after inelastic scattering of heavy ions (sup(183,184)W, 152Sm ? 238U; 184W ? 232Th; 184W, 232Th ? 248Cm) is reported. Experiments which were performed at the UNILAC of the Gesellschaft fuer Schwerionenforschung in Darmstadt show the observed heavy ion induced fission possesses significant properties of the Coulomb fission. The observed dependence of the fission probability for inelastic scattering on the projectile charge proves that the nuclear fission is mediated by the electromagnetic interaction between heavy ions. This result suggests moreover a multiple Coulomb-excitation preceding the fission. Model calculations give a first indication, that the Coulomb fission proceeds mainly from the higher ? phonons. In the irradiation with 184W the fission probability of 232Th is for all incident energies about 40% smaller that at 238U. The target dependence of the Coulomb fission however doesn't allow, to give quantitative statements about the position and B(E2)-values of higher lying ? phonons. (orig./HSI)

  17. Disintegration constant of uranium-238 by spontaneous fission redetermined by glass track method

    International Nuclear Information System (INIS)

    The disintegration constant of U238 by spontaneous fission using glass as fission fragment detector was redetermined. A film of natural uranium (UO3) prepared by chemical methods on the glass lamina was used in a long time experience of exposure (about 16 years). The good conditions of sample preparation and storage allow to observe, after chemical etching, fission fragment tracks. (M.C.K.)

  18. Calculation of the fast fission factor from basic nuclear data

    International Nuclear Information System (INIS)

    Using a two group model the ratio of U238 fissions to U235 fissions, and hence the fast fission factor, ?, is calculated from basic nuclear data in near natural uranium fuelled lattices. Proper account is taken of reflection of fast neutrons from the moderator and of interaction between rods in separate channels. Both these effects are shown to he significant. The calculated fission ratios are compared with the results of a number of experiments in graphite lattices. Agreement is excellent with some 20 metal rod experiments carried out at Harwell and at Brookhaven, the calculated values being within the experimental error for all except the largest rods. Although agreement is not uniformly good with four oxide cluster experiments carried out at Winfrith, the greatest discrepancy amounts to less than 0.3% in ?. (author)

  19. Statistics for fission track analysis

    CERN Document Server

    Galbraith, Rex F

    2005-01-01

    Statistical analyses of the numbers, lengths, and orientations of fission tracks etched in minerals yield dating and thermal history information valuable in geological and geoscience applications, particularly in oil exploration. Fission tracks can be represented mathematically by a stochastic process of randomly oriented line segments in three dimensions, and this "line segment" model can describe and explain the essential statistical features of the data, providing a rigorous foundation for quantitative modelling and simulation studies.Statistics for Fission Track Analysis explores the line segment model and its consequences for the analysis and interpretation of data. The author derives the equations for fission track data and the theoretical probability distributions for the number, orientation, and length measurements of the tracks. He sets out the theory of fission track dating and through numerical examples, presents methods for analyzing and interpreting fission track counts. Later chapters address st...

  20. Fission barriers of light nuclei

    International Nuclear Information System (INIS)

    Experimental fission excitation functions for compound nuclei /sup 52/Fe, /sup 49/Cr, /sup 46/V, and /sup 44/Ti formed in heavy-ion reactions are analyzed in the Hauser-Feshbach/Bohr-Wheeler formalism using fission barriers based on the rotating liquid drop model of Cohen et al. and on the rotating finite range model of Sierk. We conclude that the rotating finite range approach gives better reproduction of experimental fission yields, consistent with results found for heavier systems

  1. Neutron emission prior to fission

    International Nuclear Information System (INIS)

    Neutron emission in coincidence with fission fragments has been measured in the reaction 16O+142Nd?158Er at 207 MeV. The neutron multiplicity preceding fission is interpreted by including the effects of transients and saddle-to-scission time on neutron emission prior to fission, and determines the limit ??5x1021 s-1 for the reduced nuclear dissipation coefficient ?. (orig.)

  2. Hidden systematics of fission channels

    International Nuclear Information System (INIS)

    It is a common procedure to describe the fission-fragment mass distributions of fissioning systems in the actinide region by a sum of at least 5 Gaussian curves, one for the symmetric component and a few additional ones, together with their complementary parts, for the asymmetric components. These components have been attributed to the influence of fragment shells, e.g. in the statistical scission-point model of Wilkins, Steinberg and Chasman. They have also been associated with valleys in the potential-energy landscape between the outer saddle and the scission configuration in the multi-channel fission model of Brosa. When the relative yields, the widths and the mean mass-asymmetry values of these components are fitted to experimental data, the mass distributions can be very well reproduced. Moreover, these fission channels are characterised by specific values of charge polarisation, total kinetic energy and prompt-neutron yields. The present contribution investigates the systematic variation of the characteristic fission-channel properties as a function of the composition and the excitation energy of the fissioning system. The mean position of the asymmetric fission channels in the heavy fragment is almost constant in atomic number. The deformation of the nascent fragments at scission, which is the main source of excitation energy of the separated fission fragments ending up in prompt-neutron emission, is found to be a unique function of Z for the light and the heavy fragment of the asymmetric fission channels. A variation of the initial excitation energy of the fissioning system above the fission saddle is only seen in the neutron yield of the heavy fragment. The charge polarisation in the two most important asymmetric fission channels is found to be constant and to appreciably exceed the macroscopic value. The variation of the relative yields and of the positions of the fission channels as a function of the composition and excitation energy of the fissioning system obey a hidden systematics that can be explained by the number of states in the vicinity of the outer fission barrier as a function of mass asymmetry, if the potential is constructed as the sum of the macroscopic contribution of the compound nucleus and empirically determined fragment shells. This hidden systematics also explains the transition from asymmetric to symmetric fission around 226Th and around 258Fm. (authors)

  3. Fission modes of mercury isotopes

    OpenAIRE

    Warda, M.; Staszczak, A.; Nazarewicz, W.

    2012-01-01

    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 nu...

  4. Hidden systematics of fission channels

    Directory of Open Access Journals (Sweden)

    Schmidt Karl-Heinz

    2013-12-01

    Full Text Available It is a common procedure to describe the fission-fragment mass distributions of fissioning systems in the actinide region by a sum of at least 5 Gaussian curves, one for the symmetric component and a few additional ones, together with their complementary parts, for the asymmetric components. These components have been attributed to the influence of fragment shells, e.g. in the statistical scission-point model of Wilkins, Steinberg and Chasman. They have also been associated with valleys in the potential-energy landscape between the outer saddle and the scission configuration in the multi-channel fission model of Brosa. When the relative yields, the widths and the mean mass-asymmetry values of these components are fitted to experimental data, the mass distributions can be very well reproduced. Moreover, these fission channels are characterised by specific values of charge polarisation, total kinetic energy and prompt-neutron yields. The present contribution investigates the systematic variation of the characteristic fission-channel properties as a function of the composition and the excitation energy of the fissioning system. The mean position of the asymmetric fission channels in the heavy fragment is almost constant in atomic number. The deformation of the nascent fragments at scission, which is the main source of excitation energy of the separated fission fragments ending up in prompt-neutron emission, is found to be a unique function of Z for the light and the heavy fragment of the asymmetric fission channels. A variation of the initial excitation energy of the fissioning system above the fission saddle is only seen in the neutron yield of the heavy fragment. The charge polarisation in the two most important asymmetric fission channels is found to be constant and to appreciably exceed the macroscopic value. The variation of the relative yields and of the positions of the fission channels as a function of the composition and excitation energy of the fissioning system obey a hidden systematics that can be explained by the number of states in the vicinity of the outer fission barrier as a function of mass asymmetry, if the potential is constructed as the sum of the macroscopic contribution of the compound nucleus and empirically determined fragment shells. This hidden systematics also explains the transition from asymmetric to symmetric fission around 226Th and around 258Fm.

  5. Fission barrier of 210Po

    International Nuclear Information System (INIS)

    Statistical model analysis of fission and evaporation residue cross-sections along with pre-fission neutron multiplicities (?pre) data for 12C+198Pt system yielded fission barriers much smaller (?13 MeV) than those (?21 MeV) obtained for same compound nuclei from the analysis of light ion induced reactions. In the present study, the fission excitation functions for p+209Bi, ?+206Pb, 12C+198Pt and 18O+192Os systems leading to the same compound nucleus has been investigated

  6. Fusion-fission type collisions

    International Nuclear Information System (INIS)

    Three examples of fusion-fission type collisions on medium-mass nuclei are investigated whether the fragment properties are consistent with fission from equilibrated compound nuclei. Only in a very narrow band of angular momenta the data fulfill the necessary criteria for this process. Continuous evolutions of this mechanism into fusion fission and into a deep-inelastic process and particle emission prior to fusion have been observed. Based on the widths of the fragment-mass distributions of a great variety of data, a further criterion for the compound-nucleus-fission process is tentatively proposed

  7. Mechanism of nuclear fission (Part I)

    International Nuclear Information System (INIS)

    The authors' 1941 paper on fission is translated. Bohr-Wheeler theory is used. After a general discussion of fission fragments and energy balance concepts, the neutron induced fission of uranium is considered

  8. Fission: The first 50 years

    International Nuclear Information System (INIS)

    The possibility of fission had been largely unanticipated prior to its discovery in 1938. This process, with its dramatically large energy release and its formation of previously unknown nuclides, immediately captured the imagination of the scientific community. Both theoretical and experimental developments occurred at a rapid pace. I will begin my discussion of fission with the far-reaching paper of Bohr and Wheeler, who in little more than half a year laid out a framework for understanding many features of the fission process. I will then turn to our current understanding of a number of aspects of fission. One of these is the pronounced tendency of many nuclear species to fission asymmetrically. In fact, the discovery of fission was based on the identification of barium isotopes produced in asymmetric fission. The dramatic changes in the preferred mass division and kinetic energy release with the addition of only a few neutrons to the spontaneously fissioning Fermium isotopes will be emphasized. The problem of the dynamics of saddle to scission will be discussed---this is one aspect of fission for which we do not have all the answers. Another dynamical effect to be discussed is the apparent failure of transition state theory at high excitation energies. The role of single particle (shell) effects in enriching the structure if the potential energy surface will be explored. Spontaneously fissioning isomers and intermediate structure resonances will be discussed. The recognition that short-lived fission isomers are superdeformed shape isomers has been followed by the recent observation of superdeformed shape isomers in the rare earth region. 18 refs., 3 figs

  9. Study of fission dynamics in fusion–fission reactions

    International Nuclear Information System (INIS)

    Highlights: ? A modified wall and window dissipation was used in Langevin equations. ? Prefission multiplicities of particles were calculated for 200Pb. ? Fission probabilities were calculated for 200Pb and compared with the experimental data. -- Abstract: One-dimensional Langevin equations were applied to study the fission dynamics of compound nucleus 200Pb formed in heavy ion-induced fusion reactions in an intermediate range of excitation energies. A modified wall and window dissipation with a reduction coefficient, ks, has been used in the Langevin equations. The average pre-fission multiplicities of neutrons, light charged particles and fission probabilities were calculated for 200Pb and results compared with the experimental data. It was shown that the results of the calculations are in good agreement with the experimental data of neutron and charged particles (p and alphas) multiplicities and fission probabilities by using values of ks in the range 0.27 ? ks ? 0.48.

  10. Post-scission fission theory: neutron emission in fission

    International Nuclear Information System (INIS)

    A survey of theoretical representations of two of the observables in neutron emission in fission is given, namely, the prompt fission neutron spectrum N(E) and the average prompt neutron multiplicity ?-barp. Early representations of the two observables are presented and their deficiencies are discussed. This is followed by summaries and examples of recent theoretical models for the calculation of these quantities. Emphasis is placed upon the predictability and accuracy of the recent models. In particular, the dependencies of N(E) and ?-barp upon the fissioning nucleus and its excitation energy are treated. Recent work in the calculation of the prompt fission neutron spectrum matrix N(E, En), where En is the energy of the neutron inducing fission, is then discussed. Concluding remarks address the current status of our ability to calculate these observables with confidence, the direction of future theoretical efforts, and limitations to current (and future) approaches. (author)

  11. Post-scission fission theory: Neutron emission in fission

    Energy Technology Data Exchange (ETDEWEB)

    Madland, D.G.

    1997-11-01

    A survey of theoretical representations of two of the observables in neutron emission in fission is given, namely, the prompt fission neutron spectrum N (E) and the average prompt neutron multiplicity {bar {nu}}{sub p}. Early representations of the two observables are presented and their deficiencies are discussed. This is followed by summaries and examples of recent theoretical models for the calculation of these quantities. Emphasis is placed upon the predictability and accuracy of the recent models. In particular, the dependencies of N (E) and {bar {nu}}{sub p} upon the fissioning nucleus and its excitation energy are treated. Recent work in the calculation of the prompt fission neutron spectrum matrix N (E, E{sub n}), where E{sub n} is the energy of the neutron inducing fission, is then discussed. Concluding remarks address the current status of our ability to calculate these observables with confidence, the direction of future theoretical efforts, and limitations to current (and future) approaches.

  12. Fission and Fusion Game

    Science.gov (United States)

    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.

  13. Baby fission chambers

    International Nuclear Information System (INIS)

    The present report is intended, on the one band, as a study of the main types of fission chambers produced to date, and on the other, to deal more generally with this type of detector. Originally, it was with a view to the charting of neutron scatter in 'Proserpine' that the authors undertook the study of these chambers. During the course of the task, it was considered worth tbe trouble of developing its scope to include a more general application: neutron scatter measurement of various energy neutrons within a reduced volume with slight local disturbance. (author)

  14. Progress in fission product nuclear data

    International Nuclear Information System (INIS)

    This is the tenth issue of a report series on Fission Product Data, which informs us about all the activities in this field, which are planned, ongoing, or have recently been completed. The types of activities included are measurements, compilations and evaluations of: fission product yields (neutron induced and spontaneous fission), neutron reaction cross sections of fission products, data related to the radioactive decay of fission products, delayed neutron data of fission products, lumped fission product data (decay heat, absorption, etc.). There is also a section with recent references relative to fission product nuclear data

  15. The fission-track analysis: An alternative technique for provenance studies of prehistoric obsidian artefacts

    CERN Document Server

    Bellot-Gurlet, L; Dorighel, O; Oddone, M; Poupeau, G; Yegingil, Z

    1999-01-01

    Comparison of fission-track parameters - age and track densities - is an alternative tool for correlating obsidian artefacts with their potential natural sources. This method was applied by different fission-track groups in various regions and results were compared with those obtained using the more popular provenance identification techniques based on chemical composition studies. Hundreds of analyses prove that fission-track dating is a complementary technique which turns out to be very useful, specially when the chemical composition does not fully discriminate different sources. Archaeologically significant results were obtained applying the fission-track analysis in various regions of earth.

  16. The fundamental role of fission during r-process nucleosynthesis in neutron star mergers

    Energy Technology Data Exchange (ETDEWEB)

    Goriely, S. [Universite Libre de Bruxelles, Institut d' Astronomie et d' Astrophysique, CP-226, Brussels (Belgium)

    2015-02-01

    The rapid neutron-capture process, or r-process, is known to be of fundamental importance for explaining the origin of approximately half of the A > 60 stable nuclei observed in nature. Despite important efforts, the astrophysical site of the r-process remains unidentified. Here we study r-process nucleosynthesis in a material that is dynamically ejected by tidal and pressure forces during the merging of binary neutron stars. r-process nucleosynthesis during the decompression is known to be largely insensitive to the detailed astrophysical conditions because of efficient fission recycling, producing a composition that closely follows the solar r-abundance distribution for nuclei with mass numbers A > 140. Due to the important role played by fission in such a scenario, the impact of fission is carefully analyzed. We consider different state-of-the-art global models for the determination of the fission paths, nuclear level densities at the fission saddle points and fission fragment distributions. Based on such models, the sensitivity of the calculated r-process abundance distribution is studied. The fission path is found to strongly affect the region of heavy nuclei responsible for the fission recycling, while the fission fragment distribution of nuclei along the A ? 278 isobars defines the abundance pattern of nuclei produced in the 110 fission neutrons is also shown to affect the abundance distribution, and in particular the shape of the third r-process peak around A ? 195. (orig.)

  17. Optical spectroscopy of fission isomers

    International Nuclear Information System (INIS)

    An experiment is prepared at the EN-Tandem accelerator to measure spins, hyperfine constants and the isomer shifts of the odd-odd fission isomers sup(242,244m)Am and the odd-even isomer sup(243m)Am. The signal will be the fission fragment anisotropy after laser induced nuclear orientation (optical pumping with polarized light). (orig.)

  18. Fission channels in 258Fm

    International Nuclear Information System (INIS)

    Quantum effects generate ''channels'' which guide a nucleus from ground state to scission. We present here the channels of 258Fm and relate them to the measured kinetic energies of the fission products, to the mass asymmetry and to the relative abundance of the various fission components. The microscopic reason is discussed. (orig.)

  19. Fission fragment driven neutron source

    International Nuclear Information System (INIS)

    Fissionable uranium formed into a foil is bombarded with thermal neutrons in the presence of deuterium-tritium gas. The resulting fission fragments impart energy to accelerate deuterium and tritium particles which in turn provide approximately 14 MeV neutrons by the reactions t(d,n)4He and d(t,n)4He

  20. Diffusion process of nuclear fission

    International Nuclear Information System (INIS)

    A fission diffusion model was proposed to explain the experimental data for high energy ion collisions. This model takes the fission process as a diffusion process, which can be described by Smoluchowski equation. It has been applied to explain the enhancement of neutron emission in heavy ion collisions forming the composite nucleus 158Er. The experimental data are well reproduced by the model calculations

  1. Fission throughout the periodic table

    Energy Technology Data Exchange (ETDEWEB)

    Moretto, L.G.; Wozniak, G.J.

    1989-04-01

    The dualistic view of fission and evaporation as two distinct compound nucleus processes is substituted with a unified view in which fission, complex fragment emission, and light particle evaporation are seen as different aspects of a single process. 47 refs., 22 figs.

  2. New fission valley for 258Fm and nuclei beyond

    International Nuclear Information System (INIS)

    The advent of the macroscopic-microscopic Strutinsky shell-correction method about 20 years ago made possible detailed theoretical studies of the fission processes. With this method the potential energy of a nucleus can be calculated for arbitrary shapes, within given shape parametrization. Coupled with a wealth of new experimental results this has led to a better understanding of the stability of elements at the end of the periodic system. The model to the 264Fm regin is applied, for which new and somewhat unexpected experimental data are available. The first observation of the onset of symmetric fission in the region at the end of the periodic system was the study of 257Fm fission . Subsequently, more observations of symmteric fission have been made in this region. Later, more extensive measurements on 258Fm and other neighbouring elements have shown that there often are two components in the kinetic-energy distribution. The aim of this paper is to understand the nature of the fission process for the nuclei for which these new data are available and then to make predictions of properties of other nuclei in the vicinity of 264Fm and of fission half-lives for a heavier even nuclei

  3. Industrial use of fission products

    International Nuclear Information System (INIS)

    Perhaps the most disappointing and surprising development in the fifty year history of nuclear fission is the small role fission products play in modern technology. As a large and potentially inexpensive source of ionizing radiation, fission products were expected to offer major practical benefits. The attractive opportunities stimulated imaginative efforts to realize their fulfillment, but their direct impact has been minor. Fission products have not fared well, not only in somewhat indirect competition with nonradioactive alternatives, but also in direct competition with other radiation sources, especially electron accelerators and 60Co. There is one major triumph for fission product technology: the application of 99Mo and its daughter 99mTc as an almost universal tracer system in nuclear medicine

  4. Spontaneous fission of heavy nuclei

    International Nuclear Information System (INIS)

    The fundamental investigations of heavy nucleus spontaneous fission are placed into a historical perspective since as early as 1939. The investigations have been conducted in two basic directions. The first one is connected with spontaneous fission mechanism. The second relates to clarifying the role of spontaneous fission in the problem of heavy nicleus stability. It is concluded from the data available on heavy nucleus half-lives that the droplet model reflects but the rude average picture, and that the nuclear structure plays a significant part. The fundamentals of the isomeric nucleus fission theory are considered which provides a tool to calculate nucleus energy under large deformations conditions and, therefore, the shape and height of fission barriers. The experimental results of searching for superheavy nuclei in meteorites and by an artificial synthesis are discussed. It is noted that a qualitative break-through in synthesizing artificially transuranium elements can be attained only by heavy ion nuclear reactions

  5. Pulsed fission/fusion hybrid engines

    International Nuclear Information System (INIS)

    Research into high-thrust, high-specific impulse rocket engines using energy from nuclear reactions which has been conducted at this organization will be discussed. The engines are all conceptual in nature, yet are within the realization of conventional or near-term technology. The engine concepts under study at Foundation, Inc. are designed to obviate or minimize these negative effects of the ORION scheme. By using non-chemical triggers to initiate a non-breakeven fusion reaction at the core of a target composed of both fission and fusion fuel, it should be possible to employ the fusion neutrons thus produced to begin a fission reaction in U-235 or Pu-239. Since the density of the target can be increased by as much as a factor of 250 through compression of the pellet, the amount of fission material necessary to produce a critical mass can be greatly reduced. (This also means that the amount of fission products produced for a giventhrust level is also reduced from the ORION levels.) Coupling this eeffect to the large number of 14 MeV fusion neutrons produced early in the compression process and subsequently to the heating of some additional fusion fuel surrounding the critical mass leads to the very efficient burnup of the target. This insures both high yield from the target as well as low cost per MJ energy released. Finally, the use of such small pellets allows the scale of the energy released to be tailored to a level usable in rocket engines of a few tens of tons thrust level. (orig.)

  6. Activity decay of fission products produced by fast fissions

    International Nuclear Information System (INIS)

    After an introduction presenting the calculation of the gamma activity in fission products either after the pile shutdown or after a certain cooling time, the authors report the determination of the gamma activity of each radioactive nuclide formed during fission. They present the calculation method which uses the most recent data for each nuclide (decay period, fission efficiency, gamma ray energy emitted by each disintegration, emission percentage). Results are presented under the form of activity decay curves for each group and for each nuclide after a 30-day or infinite irradiation

  7. Dynamical features of nuclear fission

    International Nuclear Information System (INIS)

    It is now well established that the transition-state theory of nuclear fission due to N. Bohr and J.A. Wheeler underestimates several observables in heavy-ion induced fusion-fission reactions. Dissipative dynamical models employing either the Langevin equation or the Fokker-Planck equation following the work of Kramers have been developed for fission of heavy nuclei at high excitations (T ? 1MeV or higher). The dissipation strength, an ingredient in the above theories, is usually treated as an adjustable parameter to reproduce experimental data. In the present talk, the physical picture underlying the dissipative fission dynamics is presented. The work mainly concentrates upon the Kramers' prescription for including dissipation in fission dynamics. The results of a statistical model analysis of the pre-scission neutron multiplicity data from the reactions 19F+ 194,196,198Pt using Kramers' fission width are discussed in some detail. Various aspects of Kramers' approach with numerical simulations using Langevin equation in the context of nuclear fission are compared

  8. Fifty years with nuclear fission

    International Nuclear Information System (INIS)

    The news of the discovery of nucler 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 fiftieth anniversary of its discovery by holding a topical meeting entitled, ''Fifty years with nuclear fission,'' in the United States during the year 1989. The objective of the meeting was to bring together pioneers of the nuclear industry and other scientists and engineers to report on reminiscences of the past and on the more recent developments in fission science and technology. The conference highlighted the early pioneers of the nuclear industry by dedicating a full day (April 26), consisting of two plenary sessions, at the National Academy of Sciences (NAS) in Washington, DC. More recent developments in fission science and technology in addition to historical reflections were topics for two full days of sessions (April 27 and 28) at the main sites of the NIST in Gaithersburg, Maryland. The wide range of topics covered by Volume 2 of this topical meeting included plenary invited, and contributed sessions entitled, Nuclear fission -- a prospective; reactors II; fission science II; medical and industrial applications by by-products; reactors and safeguards; general research, instrumentation, and by-products; and fission data, astrophysics, and space applications. The astrophysics, and space applications. The individual papers have been cataloged separately

  9. How fission was discovered

    International Nuclear Information System (INIS)

    After the great survey of neutron induced radioactivity by Fermi and co-workers, the laboratories in Paris and Berlin-Dahlen tried to disentangle the complex results found in uranium. At that time neutron sources were small, activities low, and equipment very simple. Chemistry beyond uranium still was unknown. Hahn and Meitner believed to have observed three transuranic isomeric chains, a doubtful result even then. Early in 1938, Curie and Savic in Paris found an activity interpreted to be actinium, and Hahn and Meitner another to be radium. Both interpretations seemed impossible from energy considerations. Hahn and Strassmann, therefore, continued this work and succeeded to separate the new activity from radium. There remained no doubt that a barium isotope had been produced, the uranium nucleus splitting in the yet-unknown process we now call fission

  10. Fission data by surrogate reactions

    Science.gov (United States)

    Hirose, Kentaro

    2014-09-01

    A project of the fission data measurement for actinides (fragment mass distribution, cross sections and neutron multiplicities) using multi-nucleon transfer reactions is running at Japan Atomic Energy Agency (JAEA). Actinide targets such as 238U and 232Th were irradiated with 18O beam and fission induced by a nucleon transfer was observed. The experiment was performed at the tandem accelerator facility of Japan Atomic Energy Agency. A target of 232Th (~ 150 ? g/cm2) and 238U (~ 80 ? g/cm2) deposited on a 100- ?g/cm2 thick nickel foil was bombarded with 157.7 MeV 18O beam. The scattered projectile-like nuclei were detected by a segmented ?E-E silicon telescope located at the forward angle with respect to the beam. The thicknesses of ?E and E detector are 75 ?m and 300 ?m, respectively. From the scattered particle, the compound nucleus was identified. Fission fragments by multi-nucleon transfer fission were detected in coincidence using four multi-wire proportional counters (MWPCs) located at 45 and 135 degree with a distance of 224 mm from the target. Around the reaction chamber, 12 liquid scintillators were placed to detect the fission neutrons. Mass split of each fission event was determined using the mass and momentum conservation. We obtained the mass distributions for 239,240U, 239-242Np and 241-243Pu using the 238U target and for 232-234Th, 233-236Pa and 237U using the 232Th target. As well as the fission fragment mass distribution, fission cross sections by the surrogate ratio method and the fission neutron multiplicities will also be shown in the conference.

  11. Correlations between preequilibrium particles and fission fragments?

    International Nuclear Information System (INIS)

    By combining an exciton-model description of preequilibrium particle emission out of a fissioning system with a diffusion model for the fission dynamics it is conjectured that in induced fission there might be dynamical correlations of preequilibrium particles and fission fragments. (orig.)

  12. Performance simulation of fusion-fission hybrid blanket concepts in existing fission test facilities

    International Nuclear Information System (INIS)

    This paper examines the usefulness of testing hybrid fusion-fission blanket components in fission reactors, and reports the results of calculations indicating that blanket heating profiles, tritium breeding rates, fertile breeding rates, and fast-fission rates can be accurately duplicated in a fission reactor test. These results indicate that fission testing can play a major part in the hybrid blanket development program

  13. The spectroscopy of fission fragments

    Energy Technology Data Exchange (ETDEWEB)

    Phillips, W.R. [Department of Physics and Astronomy, University of Manchester, Manchester, M13 9PL (United Kingdom); Collaboration: La Direction des Sciences de la Matiere du CEA (FR); Le Fonds National de la Recherche Scientifique de Belgique (BE)

    1998-12-31

    High-resolution measurements on {gamma} rays from fission fragments have provided a rich source of information, unobtainable at the moment in any other way, on the spectroscopy of neutron-rich nuclei. In recent years important data have been obtained on the yrast- and near yrast-structure of neutron-rich fission fragments. We discuss the scope of measurements which can be made on prompt gamma rays from secondary fission fragments, the techniques used in the experiments and some results recently obtained. (author) 24 refs., 8 figs., 1 tab.

  14. Fission modes of 24Mg

    International Nuclear Information System (INIS)

    Coincidence measurements of electrodisintegration products have been used to simultaneously study the 12C+12C, 160+8Be, and 20Ne+? decay channels of 24Mg. Asymmetric fission into 160+8Be, is concentrated between 18 and 28 MeV in 24Mg and exhibits resonances with cross sections ten times those of symmetric fission. There is little correlation among resonances in the three decay channels. The fission yields are not consistent with statisfical decays from giant resonances, and suggest highly clustered states in 24Mg

  15. The spectroscopy of fission fragments

    International Nuclear Information System (INIS)

    High-resolution measurements on ? rays from fission fragments have provided a rich source of information, unobtainable at the moment in any other way, on the spectroscopy of neutron-rich nuclei. In recent years important data have been obtained on the yrast- and near yrast-structure of neutron-rich fission fragments. We discuss the scope of measurements which can be made on prompt gamma rays from secondary fission fragments, the techniques used in the experiments and some results recently obtained. (author)

  16. Spontaneous fission and nuclear dissipation

    Energy Technology Data Exchange (ETDEWEB)

    Dagdeviren, N.R.; Weidenmueller, H.A.

    1987-03-12

    We investigate the effect on the spontaneous fission lifetime of dissipative coupling of the fission degree of freedom. The Gamow factor is modified substantially if the strength of this coupling is inferred from induced fission and heavy-ion reactions. Since experimental lifetimes and those calculated without dissipation agree reasonably well, we use our result to establish an upper bound on the reduced nuclear dissipation coefficient ..beta.. at low excitation energies. This bound ..beta.. < or approx. 3x10/sup 20/ s/sup -1/, is consistent with ideas developed in the context of mean-field theories.

  17. Nuclear shell structure and fission

    International Nuclear Information System (INIS)

    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 theory can be formed consistently combining both the macroscopic and microscopic features. The shell structure varies in the fissioning nucleus on its way to scission leading to a double-humped shape of a fission barrier. This is due to modifications of classical periodic paths responsible for the quantal nonuniformity of particle phase space. Briefly results of the combined theory of the fission process are outlined

  18. Gamma Radiation from Fission Fragments

    International Nuclear Information System (INIS)

    The gamma radiation from the fragments of the thermal neutron fission of 235U has been investigated, and the preliminary data are presented here with suggestions for further lines of research and some possible interpretations of the data. The data have direct bearing on the fission process and the mode of fragment de-excitation. The parameters measured are the radiation decay curve for the time interval (1 - 7) x 10-10 sec after fission, the photon yield, the total gamma ray energy yield, and the average photon energy. The last three quantities are measured as a function of the fragment mass

  19. Energy partition in nuclear fission

    International Nuclear Information System (INIS)

    A scission point model (two spheroid model TSM) including semi-empirical temperature-dependent shell correction energies for deformed fragments at scission is presented. It has been used to describe the mass-asymmetry-dependent partition of the total energy release on both fragments from spontaneous and induced fission. Characteristic trends of experimental fragment energy and neutron multiplicity data as function of incidence energy in the Th-Cf region of fissioning nuclei are well reproduced. Based on model applications, information on the energy dissipated during the descent from second saddle of fission barrier to scission point have been deduced. (author). 39 refs, 13 figs

  20. Spontaneous fission and nuclear dissipation

    International Nuclear Information System (INIS)

    We investigate the effect on the spontaneous fission lifetime of dissipative coupling of the fission degree of freedom. The Gamow factor is modified substantially if the strength of this coupling is inferred from induced fission and heavy-ion reactions. Since experimental lifetimes and those calculated without dissipation agree reasonably well, we use our result to establish an upper bound on the reduced nuclear dissipation coefficient ? at low excitation energies. This bound ? 20 s-1, is consistent with ideas developed in the context of mean-field theories. (orig.)

  1. Fission and deep spallation characteristics in relativistic nuclear collisions

    International Nuclear Information System (INIS)

    Numbers of emitted fast charged particles associated with heavier nuclear fragments are employed as a graphic means of differentiating fission and spallation contributions to target fragment emission in relativistic nuclear collisions. The violent nature of the deep spallation mechanism is observed directly

  2. Fission nuclide identification using the photoneutrons and the fission neutrons

    International Nuclear Information System (INIS)

    Using the microtron M-30 at the electron energy of 8 MeV, the kinetic functions of 232Th, 235,238U, 237Np, 239Pu and those of the mixtures 232Th+238U, where the amount of the delayed neutrons is normalized to the summary photoneutron and prompt fission neutron yield, are determined. The kinetic functions are characterized by the discrimination relations ? 2 and that permits to identify the fission nuclides with error of ±0.1

  3. Natural repository analogue program. Progress report, January 1-March 30, 1982

    International Nuclear Information System (INIS)

    Lead and uranium isotopic abundances in rocks from the Oklo mine show large deficiencies of radiogenic lead in the mineralized regions and enormous excesses of this element outside the uraniferous zones. A fracture lined with secondary minerals and its host rock from distances as far as approx. 13 meters away contain lead that was deposited contemporaneously. The isotopic composition of lead in these samples varies systematically as a function of distance from the fracture. This regularity may reflect the nature of the processes that transported lead from the ores and deposited it in the surrounding rocks

  4. Microscopic Description of Nuclear Fission Dynamics

    OpenAIRE

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

    2010-01-01

    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 towards this goal. In particular, we provide preliminary calculations for studying fission fo...

  5. Theory of nuclear fission: a review

    International Nuclear Information System (INIS)

    General properties of nuclear fission are reviewed and related to our present knowledge of fission theory. For this purpose the basic reasons for the shape of the fission barriers are discussed and their consequences compared with experimental results on barrier shapes and structures. Special emphasis is put on the asymmetry of the fission barriers and mass-distributions and its relation to the shells of the nascent fragment shells. Finally the problem of calculating fission cross sections is discussed

  6. Event-by-event study of neutron observables in spontaneous and thermal fission

    Energy Technology Data Exchange (ETDEWEB)

    Vogt, R; Randrup, J

    2011-09-14

    The event-by-event fission model FREYA is extended to spontaneous fission of actinides and a variety of neutron observables are studied for spontaneous fission and fission induced by thermal neutrons with a view towards possible applications for SNM detection. We have shown that event-by-event models of fission, such as FREYA, provide a powerful tool for studying fission neutron correlations. Our results demonstrate that these correlations are significant and exhibit a dependence on the fissioning nucleus. Since our method is phenomenological in nature, good input data are especially important. Some of the measurements employed in FREYA are rather old and statistics limited. It would be useful to repeat some of these studies with modern detector techniques. In addition, most experiments made to date have not made simultaneous measurements of the fission products and the prompt observables, such as neutron and photons. Such data, while obviously more challenging to obtain, would be valuable for achieving a more complete understanding of the fission process.

  7. Background radiation from fission pulses

    International Nuclear Information System (INIS)

    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: 235U, 238U, 232Th, and 239Pu; these bracket the range of the delayed spectra. Results at several cooling (decay) times are presented. For ?- and ? spectra, only 235U and 239Pu 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 ?- and ? decay energies are included. 27 refs., 47 figs., 9 tabs

  8. Background radiation from fission pulses

    Energy Technology Data Exchange (ETDEWEB)

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

    1988-05-01

    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.

  9. Fission barriers of exotic nuclei

    International Nuclear Information System (INIS)

    Using available experimental data on fission barriers and ground-state masses a detailed study on the predictions of different models concerning the isospin dependence of saddle-point masses is performed. (authors)

  10. An analytical procedure for calculating the fast fission factor

    International Nuclear Information System (INIS)

    Processes occurring in fast reactors or in thermal reactors due to fast neutrons are treated by multigroup method. This is needed because of the complexity of operator representing the inelastic scattering on heavy nuclei. This paper shows and analytical procedure for solving the slowing-down equation in the fuel. This procedure is applied to calculate the fast fission spectrum and number of reactions in the natural uranium fuel element. The method for calculating the fast fission factor in the isolated fuel element is shown as well

  11. Fission-track stability in zircons under geological conditions

    International Nuclear Information System (INIS)

    The stability behavior of fission tracks in zircon under natural annealing conditions has been studied. The samples have been obtained from the drill core of basement rocks (1664 to 3330 m depth) of Urach (Southwest Germany). Using the external detector method, Zircon fission-track ages between 158 and 327 Myr were found. The ages decrease steadily downhole. For a cooling rate of 1degC/1 Myr the closure temperature for zircon has been estimated to 210 +- 20degC. A geometry factor of 1.47 +- 4.7% (4?-zircon/2?-muscovite) has been determined relevant to the dating procedure used in this work. (author)

  12. Composition of fission product mixtures

    International Nuclear Information System (INIS)

    The report gives a compilation of the isotopic composition and specific activity of fission products produced by thermal neutron fission of U-235 and Pu-239. The composition was computed using an electronic computer ES 1040. The presentation comprises data of 27 elements at the end of a neutron irradiation of 3 years and after a time interval of 1, 4 and 10 years after the end of irradiation. (author)

  13. International handling of fissionable material

    International Nuclear Information System (INIS)

    The opinion of the ministry for foreign affairs on international handling of fissionable materials is given. As an introduction a survey is given of the possibilities to produce nuclear weapons from materials used in or produced by power reactors. Principles for international control of fissionable materials are given. International agreements against proliferation of nuclear weapons are surveyed and methods to improve them are proposed. (K.K.)

  14. The microscopic theory of fission

    OpenAIRE

    Younes, W.; Gogny, D.

    2009-01-01

    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 multipliciti...

  15. The Microscopic Theory of Fission

    Energy Technology Data Exchange (ETDEWEB)

    Younes, W; Gogny, D

    2009-06-09

    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.

  16. Terracentric Nuclear Fission Reactor: Background, Basis, Feasibility, Structure, Evidence, and Geophysical Implications

    OpenAIRE

    Herndon, J. Marvin

    2013-01-01

    The background, basis, feasibility, structure, evidence, and geophysical implications of a naturally occurring Terracentric nuclear fission georeactor are reviewed. For a nuclear fission reactor to exist at the center of the Earth, all of the following conditions must be met: (1) There must originally have been a substantial quantity of uranium within Earth's core; (2) There must be a natural mechanism for concentrating the uranium; (3) The isotopic composition of the uraniu...

  17. A stochastic approach to fission

    International Nuclear Information System (INIS)

    A microscopically derived Langevin equation is applied to thermally induced nuclear fission. An important memory effect is pointed out. A strong friction coefficient, calculated from microscopic quantities, tends to decrease the stationary limit of the fission rate and to increase the transient time. Fission was described as a diffusion over a barrier of a collective variable, and a Langevin Equation (LE) was used to study the phenomenon. A study of the stationary flow over the saddle point with a Fokker-Planck Equation (FPE), equivalent to the LE was used to give formula for the stationary fission rate (or reaction rate for the chemistry applications). More recently, a complete study of the fission process was performed numerically with both FPE and LE. A long transient time, that could allow more pre-scission neutrons to evaporate, was pointed out. The derivation of this new LE is recalled, followed by the description of the memory dependence and by the effect of a large friction coefficient on the fission rate. (author) 6 refs., 3 figs

  18. Modelling isothermal fission gas release

    International Nuclear Information System (INIS)

    The present paper presents a new fission gas release model consisting of two coupled modules. The first module treats the behaviour of the fission gas atoms in spherical grains with a distribution of grain sizes. This module considers single atom diffusion, trapping and fission induced re-solution of gas atoms associated with intragranular bubbles, and re-solution from the grain boundary into a few layers adjacent to the grain face. The second module considers the transport of the fission gas atoms along the grain boundaries. Four mechanisms are incorporated: diffusion controlled precipitation of gas atoms into bubbles, grain boundary bubble sweeping, re-solution of gas atoms into the adjacent grains and gas flow through open porosity when grain boundary bubbles are interconnected. The interconnection of the intergranular bubbles is affected both by the fraction of the grain face occupied by the cavities and by the balance between the bubble internal pressure and the hydrostatic pressure surrounding the bubbles. The model is under validation. In a first step, some numerical routines have been tested by means of analytic solutions. In a second step, the fission gas release model has been coupled with the FTEMP2 code of the Halden Reactor Project for the temperature distribution in the pellets. A parametric study of some steady-state irradiations and one power ramp have been simulated successfully. In particular, the Halden threshold for fission gas release and two simplified FUMEX cases have been computed and are summarised. (author)

  19. Fission fragment angular distributions and fission cross section validation

    International Nuclear Information System (INIS)

    The present knowledge of angular distributions of neutron-induced fission is limited to a maximal energy of 15 MeV, with large discrepancies around 14 MeV. Only 238U and 232Th have been investigated up to 100 MeV in a single experiment. The n-TOF Collaboration performed the fission cross section measurement of several actinides (232Th, 235U, 238U, 234U, 237Np) at the n-TOF facility using an experimental set-up made of Parallel Plate Avalanche Counters (PPAC), extending the energy domain of the incident neutron above hundreds of MeV. The method based on the detection of the 2 fragments in coincidence allowed to clearly disentangle the fission reactions among other types of reactions occurring in the spallation domain. I will show the methods we used to reconstruct the full angular resolution by the tracking of fission fragments. Below 10 MeV our results are consistent with existing data. For example in the case of 232Th, below 10 MeV the results show clearly the variation occurring at the first (1 MeV) and second (7 MeV) chance fission, corresponding to transition states of given J and K (total spin and its projection on the fission axis), and a much more accurate energy dependence at the 3. chance threshold (14 MeV) has been obtained. In the spallation domain, above 30 MeV we confirm the high anisotropy revealed in 232Th by the single existing data set. I'll discuss the implications of this finding, related to the low anisotropy exhibited in proton-induced fission. I also explore the critical experiments which is valuable checks of nuclear data. The 237Np neutron-induced fission cross section has recently been measured in a large energy range (from eV to GeV) at the n-TOF facility at CERN. When compared to previous measurements, the n-TOF fission cross section appears to be higher by 5-7 % beyond the fission threshold. To check the relevance of n-TOF data, we simulate a criticality experiment performed at Los Alamos with a 6 kg sphere of 237Np. This sphere was surrounded by enriched uranium 235U so as to approach criticality with fast neutrons. The simulation predicts a multiplication factor keff in better agreement with the experiment (the deviation of 750 pcm is reduced to 250 pcm) when we replace the ENDF/B- VII.0 evaluation of the 237Np fission cross section by the n-TOF data. We also explore the hypothesis of deficiencies of the inelastic cross section in 235U which has been invoked by some authors to explain the deviation of 750 pcm. The large distortion that should be applied to the inelastic cross sections in order to reconcile the critical experiment with its simulation is incompatible with existing measurements. Also we show that the ?-bar of 237Np can hardly be incriminated because of the high accuracy of the existing data. Fission rate ratios or averaged fission cross sections measured in several fast neutron fields seem to give contradictory results on the validation of the 237Np cross section but at least one of the benchmark experiments, where the active deposits have been well calibrated for the number of atoms, favors the n-TOF data set. These outcomes support the hypothesis of a higher fission cross section of 237Np. (author)

  20. Fusion fission studies at the University of Texas at Austin

    International Nuclear Information System (INIS)

    Fusion-fission studies at The University of Texas at Austin are divided into two distinct phases. These are (1) neutronic and photonic analyses of fast fission blankets and (2) economic feasibility investigations of fusion based energy storage systems. The fast fission blanket studies included both thorium and natural uranium fuels. Detailed results for liquid lithium cooled blankets are presented. The economic feasibility studies have only recently begun. The system currently being considered runs only in off-peak periods and accomplishes energy storage by producing hydrogen from a thermochemical water-splitting process. Utility system operation is simulated using the ORSIM program to determine the optimum capacity factor for the hybrid system. Income is derived by sale of both hydrogen and fissile fuel

  1. Reference Reactor Module for the Affordable Fission Surface Power System

    International Nuclear Information System (INIS)

    Surface fission power systems on the Moon and Mars may provide the first US application of fission reactor technology in space since 1965. The requirements of many surface power applications allow the consideration of systems with much less development risk than most other space reactor applications, because of modest power (10s of kWe) and no driving need for minimal mass (allowing temperatures 2-fueled, liquid metal-cooled fission reactor coupled to free-piston Stirling converters. The reactor shielding approach utilizes both in-situ and launched shielding to keep the dose to astronauts much lower than the natural background radiation on the lunar surface. One of the important 'affordability' attributes is that the concept has been designed to minimize both the technical and programmatic safety risk

  2. Measurements of the effective range of fission fragments in UO2 and the disintegration constant for spontaneous fission of 238U

    International Nuclear Information System (INIS)

    The results of measuments of the disintegration constant for spontaneous fission in 238U are presented, with a discussion on the method used for the detection of fission tracks in muscovite mica. Samples of muscovite mica sandwiched between two natural uranium dioxide cylinders were irradiated with fragments of spontaneous fission and the etched tracks counted with projetion optical microscope. The effective thickness of the UO2 layer which contributed to the observed tracks was measured through irradiation of mica samples, in contact with the UO2 cylinder with 14,0 MeV neutrons from a (d,t) reaction. (Author)

  3. Quasi-fission and fusion-fission competition in 32S + 184W reaction

    International Nuclear Information System (INIS)

    The angular distribution of fission fragments for the 32S+184W reaction at center-of-mass energies of 118.8, 123.1, 127.3, 131.5, 135.8, 141.1 and 144.4 MeV were measured. The experimental fission excitation function is obtained. The fragment angular anisotropy is found by extrapolating the fission angular distributions. The measured fission cross sections are decomposed into fusion-fission, quasi-fission and fast-fission contributions by the dinuclear system model. The total evaporation residue and fusion-fission excitation functions are calculated in the framework of the advanced statistical model. (authors)

  4. Reference reactor module for NASA's lunar surface fission power system

    International Nuclear Information System (INIS)

    Surface fission power systems on the Moon and Mars may provide the first US application of fission reactor technology in space since 1965. The Affordable Fission Surface Power System (AFSPS) study was completed by NASA/DOE to determine the cost of a modest performance, low-technical risk surface power system. The AFSPS concept is now being further developed within the Fission Surface Power (FSP) Project, which is a near-term technology program to demonstrate system-level TRL-6 by 2013. This paper describes the reference FSP reactor module concept, which is designed to provide a net power of 40 kWe for 8 years on the lunar surface; note, the system has been designed with technologies that are fully compatible with a Martian surface application. The reactor concept uses stainless-steel based. UO2-fueled, pumped-NaK fission reactor coupled to free-piston Stirling converters. The reactor shielding approach utilizes both in-situ and launched shielding to keep the dose to astronauts much lower than the natural background radiation on the lunar surface. The ultimate goal of this work is to provide a 'workhorse' power system that NASA can utilize in near-term and future Lunar and Martian mission architectures, with the eventual capability to evolve to very high power, low mass systems, for either surface, deep space, and/or orbital missions.

  5. Prompt Emission in Fission Induced with Fast Neutrons

    Science.gov (United States)

    Wilson, J. N.; Lebois, M.; Halipré, P.; Oberstedt, S.; Oberstedt, A.

    Prompt gamma-ray and neutron emission data in fission integrates a large amount of information on the fission process and can shed light on the partition of energy. Measured emission spectra, average energies and multiplicities also provide important information for energy applications. While current reactors mostly use thermal neutron spectra, the future reactors of Generation IV will use fast neutron spectra for which little experimental prompt emission data exist. Initial investigations on prompt emission in fast neutron induced fission have recently been carried out at the LICORNE facility at the IPN Orsay, which exploits inverse reactions to produce naturally collimated, intense beams of neutrons. We report on first results with LICORNE to measure prompt fission gamma-ray spectra, average energies and multiplicities for 235U and 238U. Current improvements and upgrades being carried out on the LICORNE facility will also be described, including the development of a H2 gas target to reduce parasitic backgrounds and increase intensities, and the deployment of 11B beams to extend the effective LICORNE neutron energy range up to 12 MeV. Prospects for future experimental studies of prompt gamma-ray and neutron emission in fast neutron induced fission will be presented.

  6. Contribution to the study of nuclear fission

    International Nuclear Information System (INIS)

    The author proposes an overview of his research activity during the past fifteen years and more particularly that dealing with nuclear fission. The first part reports works on nucleus physics at the scission via the investigation of ternary fission (experimental procedure, influence of fission modes, influence of resonance spin, influence of excitation energy of the fissioning nucleus, emission probabilities, energy spectra of ternary alphas and tritons, emission mechanism). The second part reports measurements and assessments of neutron-induced fission cross sections. The third part reports the investigation of some properties of fission products (efficiencies, branching ratios of the main delayed neutron precursors)

  7. The latest progress of fission track analysis

    International Nuclear Information System (INIS)

    Fission track analysis as a new nuclear track technique is based on fission track annealing in mineral and is used for oil and gas exploration successfully. The west part of China is the main exploration for oil and gas. The oil and gas basins there experienced much more complicated thermal history and higher paleotemperature. In order to apply fission track analysis to these basins, following work was be carried out: 1. The decomposition of grain age distribution of zircon fission tracks. 2. Study on thermal history of Ordos basin using zircon fission track analysis. 3. The fission track study on the Qiang Tang basin in tibet

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

    International Nuclear Information System (INIS)

    Full text: A concept for detecting the presence of special nuclear material (235U or 239Pu) concealed in inter modal cargo containers is described. It is based on interrogation with a pulsed beam of 6-8 MeV neutrons and fission events are identified between beam pulses by their ?-delayed neutron emission or ? -delayed high-energy ?-radiation. The high-energy ?-ray signature is being employed for the first time. Fission product ?-rays above 3 MeV are distinct from natural radioactivity and from nearly all of the induced activity in a normal cargo. High-energy ?-radiation is nearly 10X more abundant than the delayed neutrons and penetrates even thick cargo's readily. The concept employs two large (8x20 ft) arrays of liquid scintillation detectors that have high efficiency for the detection of both delayed neutrons and delayed ?-radiation. Detector backgrounds and potential interferences with the fission signature radiation have been identified and quantified. This information, together with predicted signature strength, has been applied to the estimation of detection probability for the nuclear material and estimation of false alarm rates. This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48

  9. Compact fission counter for DANCE

    International Nuclear Information System (INIS)

    The Detector for Advanced Neutron Capture Experiments (DANCE) consists of 160 BF2 crystals with equal solid-angle coverage. DANCE is a 4? ?-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 ?-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 ? 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 ? particles, which is important for experiments with ?-emitting actinides. Therefore, a PPAC is an ideal detector for experiments requiring a fast and clean trigger foequiring 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 ?'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 ?'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.

  10. Change over from compound nuclear fission to quasi-fission

    International Nuclear Information System (INIS)

    Fission fragment mass distribution has been measured in two reactions to populate compound nucleus 246Bk. Both the target nuclei were deformed. However, entrance channel mass asymmetry of the two systems was on the either side of the Businaro Gallone mass asymmetry parameter. Near the Coulomb barrier, at similar excitation energies, the width of the fission fragment mass distribution was found to be significantly different for the 14N+232Th reaction compared to the 11B+235U reaction. The entrance channel mass asymmetry was found to play a significant role in deciding the fusion process. (authors)

  11. Fission fragment angular distribution and fission cross section validation

    OpenAIRE

    Leong, Lou Sai

    2013-01-01

    The present knowledge of angular distributions of neutron-induced fission is limited to a maximal energy of 15 MeV, with large discrepancies around 14 MeV. Only 238U and 232Th have been investigated up to 100 MeV in a single experiment. The n_TOF Collaboration performed the fission cross section measurement of several actinides (232Th, 235U, 238U, 234U, 237Np) at the n_TOF facility using an experimental set-up made of Parallel Plate Avalanche Counters (PPAC), extending the energy domain of th...

  12. Analysis of emission fission of lead isotopes

    International Nuclear Information System (INIS)

    The experimental excitation functions of the fission of lead isotopes with Z = 199-204 are used to find cross sections of the preemission fission and the fission of the daughter nuclei produced during the evaporation cascade process. The values of experimental cross sections for the emission fission indicate that while analysing the main characteristics of the fission of comparatively slightly fissioning nuclei one should not restrict oneself to the consideration of the fission of only the initial compound nucleus, as the role of the emission fission increases with excitation energy. The experimental information on cross sections for the emission fission of lead isotopes has been analysed in terms of the statistical fission model and under certain assumptions concerning the fission barrier structure and the energy dependence of the level density parameters. Satisfactory agreement has been observed between theoretical and experimental cross sections. This indicates that the chosen model, which takes into account the influence of the shell effects on the fission barriers and level density parameters, is suitable for describing the fission cross sections

  13. Fission matrix capability for MCNP Monte Carlo

    International Nuclear Information System (INIS)

    The element Fij of the fission matrix is equal to the number of fission neutrons born in region i due to one average fission neutron starting in region j. The fission matrix is a spatially discretized Green's function for the next generation fission neutron source. We describe recent experience and results from implementing a fission matrix capability into the MCNP Monte Carlo code. The fission matrix can be used to provide estimates of the fundamental mode fission distribution, the dominance ratio, the eigenvalue spectrum, and higher mode forward and adjoint eigenfunctions of the fission neutron source distribution. It can also be used to accelerate the convergence of the power method iterations and to provide basis functions for higher-order perturbation theory. The higher-mode fission sources can be used in MCNP to determine higher-mode forward fluxes and tallies, and work is underway to provide higher-mode adjoint-weighted fluxes and tallies. Past difficulties and limitations of the fission matrix approach are overcome with a new sparse representation of the matrix, permitting much larger and more accurate fission matrix representations. The new fission matrix capabilities provide a significant advance in the state-of-the-art for Monte Carlo criticality calculations

  14. Report of fission study meeting

    International Nuclear Information System (INIS)

    This book is the report of fission Study Meeting held from September 19 to 21, 1985 in the Research Center for Nuclear Physics, Osaka University. The objective of this study meeting was to stimulate the research on nuclear physics in Japan, which began to show new development accompanying the advance of the research on heavy ion nuclear reaction, and to make this a new starting point. More than 50 participants from physical, chemical and engineering fields, who have interest in the theory and experiment related to nuclear fission, gathered, and the meeting was a success beyond expectation. The contents covered a wide range including nuclear smashing reaction as well as nuclear fission in a narrow sense. In this book, the gists of 28 papers are collected. (Kako, I.)

  15. Fission distribution measurements of Atucha's fuel pellets with solid state track detectors

    International Nuclear Information System (INIS)

    Distribution of fissions in a UO2 rod has been measured by means of solid state detectors. Mica muscovite and Makrofol-N detectors were used in the experiment. The merits of mica muscovite relative to the Makrofol-N for the detection of fission fragments have been verified. However both fission track detectors closely agree (0,5%) in the final fission distribution of the UO2 rod. Sensitivity of the detectors shows to be linear in the range between 50.000and 360.000 fission tracks per square centimeter. Due to the high spatial resolution this method is better than any other technique. Determination were made in UO2 pellets similar to the fuel element of the Atucha reactor. The average fission rate in the rod has been measured within 0,8% error, and provides an accurate determination for the distribution of fissions in the rod wich is needed for the determination of energy liberated per fission in the natural uranium rod.(author)

  16. Fission transient time with quantum master equation

    International Nuclear Information System (INIS)

    Using a quantum master equation for the reduced density matrix, the influence of microscopical diffusion coefficients on the fission transient time and the probability of the first-chance fission are studied. (authors)

  17. Fission Matrix Capability for MCNP Monte Carlo

    Science.gov (United States)

    Brown, Forrest; Carney, Sean; Kiedrowski, Brian; Martin, William

    2014-06-01

    We describe recent experience and results from implementing a fission matrix capability into the MCNP Monte Carlo code. The fission matrix can be used to provide estimates of the fundamental mode fission distribution, the dominance ratio, the eigenvalue spectrum, and higher mode forward and adjoint eigenfunctions of the fission neutron source distribution. It can also be used to accelerate the convergence of the power method iterations and to provide basis functions for higher-order perturbation theory. The higher-mode fission sources can be used in MCNP to determine higher-mode forward fluxes and tallies, and work is underway to provide higher-mode adjoint-weighted fluxes and tallies. Past difficulties and limitations of the fission matrix approach are overcome with a new sparse representation of the matrix, permitting much larger and more accurate fission matrix representations. The new fission matrix capabilities provide a significant advance in the state-of-the-art for Monte Carlo criticality calculations.

  18. Progress in fission product nuclear data

    International Nuclear Information System (INIS)

    This is the 12th issue of a report series on Fission Product Nuclear Data (FPND) which is published by the Nuclear Data Section (NDS) of the IAEA. The purpose of this series is to inform scientists working on FPND, or using such data, about all activities in this field which are planned, ongoing, or have recently been completed. The type of activities included are: measurements, compilations and evaluations of fission product yields (neutron induced and spontaneous fission), neutron reaction cross sections of fission products, data related to the radioactive decay of fission products, delayed neutron data of fission products and lumped fission product data (decay heat, absorption etc.). The first part of the report consists of unaltered original contributions which the authors have sent to IAEA/NDS. The second part contains recent references relative to fission product nuclear data, which were not covered by the contributions submitted, and selected papers from conferences

  19. Fission properties of the heaviest elements

    International Nuclear Information System (INIS)

    The authors discuss fission properties of the heaviest elements. In particular they focus on stability with respect to spontaneous fission and on the prospects of extending the region of known nuclei beyond the peninsula of currently known nuclides

  20. Fission properties of the heaviest elements

    International Nuclear Information System (INIS)

    We discuss fission properties of the heaviest elements. In particular we focus on stability with respect to spontaneous fission and on the prospects of extending the region of known nuclei beyond the peninsula of currently known nuclides. (author)

  1. Characterization of Samples with Spontaneously Fissioning Isotopes

    International Science & Technology Center (ISTC)

    Development of the Method for Characterization of the Samples, Containing Spontaneously Fissioning Radionuclides, by Measuring Fission Products Gamma-Radiation (for the System of NM Control and Accountability of the Federal State Unitarian Enterprise "PA"Mayak")

  2. Ceramic Hosts for Fission Products Immobilization

    Energy Technology Data Exchange (ETDEWEB)

    Peter C Kong

    2010-07-01

    Natural spinel, perovskite and zirconolite rank among the most leach resistant of mineral forms. They also have a strong affinity for a large number of other elements and including actinides. Specimens of natural perovskite and zirconolite were radioisotope dated and found to have survived at least 2 billion years of natural process while still remain their loading of uranium and thorium . Developers of the Synroc waste form recognized and exploited the capability of these minerals to securely immobilize TRU elements in high-level waste . However, the Synroc process requires a relatively uniform input and hot pressing equipment to produce the waste form. It is desirable to develop alternative approaches to fabricate these durable waste forms to immobilize the radioactive elements. One approach is using a high temperature process to synthesize these mineral host phases to incorporate the fission products in their crystalline structures. These mineral assemblages with immobilized fission products are then isolated in a durable high temperature glass for periods measured on a geologic time scale. This is a long term research concept and will begin with the laboratory synthesis of the pure spinel (MgAl2O4), perovskite (CaTiO3) and zirconolite (CaZrTi2O7) from their constituent oxides. High temperature furnace and/or thermal plasma will be used for the synthesis of these ceramic host phases. Nonradioactive strontium oxide will be doped into these ceramic phases to investigate the development of substitutional phases such as Mg1-xSrxAl2O4, Ca1-xSrxTiO3 and Ca1-xSrxZrTi2O7. X-ray diffraction will be used to establish the crystalline structures of the pure ceramic hosts and the substitution phases. Scanning electron microscopy and energy dispersive X-ray analysis (SEM-EDX) will be performed for product morphology and fission product surrogates distribution in the crystalline hosts. The range of strontium doping is planned to reach the full substitution of the divalent metal ions, Mg and Ca, in the ceramic host phases. The immobilization of rear earth (lanthanide series) fission products in these ceramic host phases will also be studied this year. Cerium oxide is chosen to represent the rear earth fission product for substitution studies in spinel, perovskite and zirconolite ceramic hosts. Cerium has +3 and +4 oxidation states and it can replace some of the trivalent or tetravalent host ions to produce the substitution ceramics such as MgAl2-xCexO4, CaTi1-xCexO3, CaZr1-xCexTi2O7 and CaZrTi2-xCexO7. X-ray diffraction analysis will be used to compare the crystalline structures of the pure ceramic hosts and the substitution phases. SEM-EDX analysis will be used to study the Ce distribution in the ceramic host phases. The range of cerium doping is planned to reach the full substitution of the trivalent or tetravalent ions, Al, Ti and Zr, in the ceramic host phases.

  3. Ceramic Hosts for Fission Products Immobilization

    International Nuclear Information System (INIS)

    Natural spinel, perovskite and zirconolite rank among the most leach resistant of mineral forms. They also have a strong affinity for a large number of other elements and including actinides. Specimens of natural perovskite and zirconolite were radioisotope dated and found to have survived at least 2 billion years of natural process while still remain their loading of uranium and thorium . Developers of the Synroc waste form recognized and exploited the capability of these minerals to securely immobilize TRU elements in high-level waste . However, the Synroc process requires a relatively uniform input and hot pressing equipment to produce the waste form. It is desirable to develop alternative approaches to fabricate these durable waste forms to immobilize the radioactive elements. One approach is using a high temperature process to synthesize these mineral host phases to incorporate the fission products in their crystalline structures. These mineral assemblages with immobilized fission products are then isolated in a durable high temperature glass for periods measured on a geologic time scale. This is a long term research concept and will begin with the laboratory synthesis of the pure spinel (MgAl2O4), perovskite (CaTiO3) and zirconolite (CaZrTi2O7) from their constituent oxides. High temperature furnace and/or thermal plasma will be used for the synthesis of these ceramic host phases. Nonradioactive strontium oxide will be doped into these ceramic phases to investigoped into these ceramic phases to investigate the development of substitutional phases such as Mg1-xSrxAl2O4, Ca1-xSrxTiO3 and Ca1-xSrxZrTi2O7. X-ray diffraction will be used to establish the crystalline structures of the pure ceramic hosts and the substitution phases. Scanning electron microscopy and energy dispersive X-ray analysis (SEM-EDX) will be performed for product morphology and fission product surrogates distribution in the crystalline hosts. The range of strontium doping is planned to reach the full substitution of the divalent metal ions, Mg and Ca, in the ceramic host phases. The immobilization of rear earth (lanthanide series) fission products in these ceramic host phases will also be studied this year. Cerium oxide is chosen to represent the rear earth fission product for substitution studies in spinel, perovskite and zirconolite ceramic hosts. Cerium has +3 and +4 oxidation states and it can replace some of the trivalent or tetravalent host ions to produce the substitution ceramics such as MgAl2-xCexO4, CaTi1-xCexO3, CaZr1-xCexTi2O7 and CaZrTi2-xCexO7. X-ray diffraction analysis will be used to compare the crystalline structures of the pure ceramic hosts and the substitution phases. SEM-EDX analysis will be used to study the Ce distribution in the ceramic host phases. The range of cerium doping is planned to reach the full substitution of the trivalent or tetravalent ions, Al, Ti and Zr, in the ceramic host phases.

  4. The VERDI fission fragment spectrometer

    OpenAIRE

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

    2013-01-01

    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 conf...

  5. NEACRP thermal fission product benchmark

    International Nuclear Information System (INIS)

    The objective of the thermal fission product benchmark was to compare the range of fission product data in use at the present time. A simple homogeneous problem was set with 200 atoms H/1 atom U235, to be burnt up to 1000 days and then decay for 1000 days. The problem was repeated with 200 atoms H/1 atom Pu239, 20 atoms H/1 atom U235 and 20 atoms H/1 atom Pu239. There were ten participants and the submissions received are detailed in this report. (author)

  6. Determination of fission yields in the fast neutron induced fission of 238U, 237Np and 243Am using fission track etch-cum gamma spectrometry

    International Nuclear Information System (INIS)

    The absolute fission yields of 39 fission products in pure 238U(99,9997 atom percent), 36 fission products in 237Np and 30 fission products in 243Am (99.998 atom percent) were determined in the fast neutron induced fission, employing fission track etch-cum gamma spectrometry. The fissions were induced by a well defined reactor neutron spectrum which was measured by using threshold detectors. 5 refs, 3 tabs

  7. Multiple-Coincidence Interrogation of Fissionables

    International Nuclear Information System (INIS)

    The multiple coincidence technique uses 14.1 MeV neutrons to produce (n, multiple-?) coincidences to detect fissile and fissionable materials. Measurements of n-?-? coincidences with targets of depleted uranium (DU), W, and Pb, show that the counting rate for the DU is substantially above that for the non-fissionables. Also, the data involving prompt neutrons and delayed gammas in the DU time spectra provide a signature for fissionables that is distinct from that of non-fissionables

  8. Multiple-coincidence interrogation of fissionables

    Science.gov (United States)

    Hurley, J. P.; Keegan, R. P.; Tinsley, J. R.; Trainham, R.

    2009-05-01

    The multiple coincidence technique uses 14.1 MeV neutrons to produce (n, multiple-?) coincidences to detect fissile and fissionable materials. Measurements of n-?-? coincidences with targets of depleted uranium (DU), W, and Pb, show that the counting rate for the DU is substantially above that for the non-fissionables. Also, the data involving prompt neutrons and delayed gammas in the DU time spectra provide a signature for fissionables that is distinct from that of non-fissionables.

  9. Nuclear fission in covariant density functional theory

    OpenAIRE

    Afanasjev A.V.; Abusara H.; Ring P.

    2013-01-01

    The current status of the application of covariant density functional theory to microscopic description of nuclear fission with main emphasis on superheavy nuclei (SHN) is reviewed. The softness of SHN in the triaxial plane leads to an emergence of several competing fission pathes in the region of the inner fission barrier in some of these nuclei. The outer fission barriers of SHN are considerably affected both by triaxiality and octupole deformation.

  10. Nuclear fission in covariant density functional theory

    International Nuclear Information System (INIS)

    The current status of the application of covariant density functional theory to microscopic description of nuclear fission with main emphasis on superheavy nuclei (SHN) is reviewed. The softness of SHN in the triaxial plane leads to an emergence of several competing fission paths in the region of the inner fission barrier in some of these nuclei. The outer fission barriers of SHN are considerably affected both by triaxiality and octupole deformation. (authors)

  11. Investigation of exotic fission modes

    International Nuclear Information System (INIS)

    Fission approach to the cluster radioactivities and ?-decay has been systematically developed during the last two decades. A more complex process, the ternary fission, was observed since 1946 both in neutron-induced and spontaneous fission. We obtained interesting results concerning the binary fission saddle-point reflection asymmetric nuclear shapes, and we can explain how a possible nuclear quasimolecular state is formed during the 10 Be accompanied cold fission of 252 Cf. The equilibrium nuclear shapes in fission theory are usually determined by minimizing the deformation energy for a given surface equation. We developed a method allowing to obtain a very general saddle-point shape as a solution of a differential equation without an a priori introduction of a shape parametrization. In the approach based on a liquid drop model (LDM), saddle-point shapes are always reflection symmetric: the deformation energy increases with the mass-asymmetry parameter ? = (A1 - A2)/(A1 + A2). By adding the shell corrections to the LDM deformation energy, we obtained minima at a finite mass asymmetry for parent nuclei 238 U, 232,228 Th in agreement with experiments. This correction was calculated phenomenologically. A technique based on the fragment identification by using triple ? coincidences in the large arrays of Ge-detectors, like GAMMASPHERE, was employed at Vanderbilt University to discoloyed at Vanderbilt University to discover new characteristics of the fission process, and new decay modes. The possibility of a whole family of new decay modes, the multicluster accompanied fission, was envisaged. Besides the fission into two or three fragments, a heavy or superheavy nucleus spontaneously breaks into four, five or six nuclei of which two are asymmetric or symmetric heavy fragments and the others are light clusters, e.g. ?-particles, 10 Be, 14 C, or combinations of them. Examples were presented for the two-, three- and four cluster accompanied cold fission of 252 Cf and 262 Rf, in which the emitted clusters are: 2?, ? + 6 He, ? + 10 Be, 3?, etc. The strong shell effect corresponding to the doubly magic heavy fragment 132 Sn was emphasized. We concluded that the most favorable mechanism of such decay modes should be the cluster emission from an elongated neck formed between the two heavy fragments. A formation mechanism of the touching configuration, based on a three-center phenomenological model is suggested. It is derived from the liquid drop model under the assumption that the aligned configuration, with the emitted particle between the light and heavy fragment is obtained by increasing continuously the separation distance, while the radii of the heavy fragment and of the light particle are kept constant. During the first stage of the deformation one has a two-center evolution until the neck radius becomes equal to the radius of the emitted particle. Then the three center starts developing by decreasing with the same amount the two tip distances. In such a way a new minimum, typical for a cluster molecule, appears in the deformation energy. A single-particle three center shell model just developed by us will be used in the future. It represents an extension of the advanced two center shell model which takes into account 5 deformation coordinates. The existence of this minimum proves the quasimolecular character of the aligned configuration of three fragments in touch. It explains why the 3.368 MeV ?-ray, by which decays the first excited state of 10 Be accompanying cold fission of 252 Cf, is not Doppler-broadened as it should be if this ?-ray would be emitted in flight. (authors)

  12. Origin of empirical threshold for dissipative fission

    Science.gov (United States)

    Vandenbosch, Robert

    1994-11-01

    The recent observation that the empirical threshold for fission hindrance correlates with the ratio of the threshold temperature to the temperature dependent fission barrier height is interpreted in terms of Bohr-Wheeler theory. A total fission delay of (2-4) times 10 sup -2- s is deduced from the empirical value of this ratio.

  13. Origin of empirical threshold for dissipative fission

    International Nuclear Information System (INIS)

    The recent observation that the empirical threshold for fission hindrance correlates with the ratio of the threshold temperature to the temperature dependent fission barrier height is interpreted in terms of Bohr-Wheeler theory. A total fission delay of (2--4) times 10 sup -2--- s is deduced from the empirical value of this ratio

  14. Hybrid nuclear cycles for nuclear fission sustainability

    International Nuclear Information System (INIS)

    Nuclear fission can play and must play an important role in paving the road to Energy Sustainability. Nuclear Fission does not produce CO2 emissions, and it is already exploited at commercial level with the current NPP (Nuclear Power Plants). Most of them are based on LWR reactors, which have a very good safety record. It must be noted, however, that all LWR (including the advanced or evolutionary ones) have some drawbacks, particularly their very poor efficiency in exploiting the natural resources of nuclear fuels. In this paper, an analysis is presented on how to maximize the energy actually generated from the potential contents of fission natural resources. The role of fertile-to-fissile breeding is highlighted, as well as the need of attaining a very high safety performance in the reactors and other installations of the fuel cycle. The proposal presented in this paper is to use advanced and evolutionary LWR as energy producing reactors, and to use subcritical fast assemblies as breeders. The main result would be to increase by two orders of magnitude the percentage of energy effectively exploited from fission natural resources, while keeping a very high level of safety standards in the full fuel cycle. Breeders would not be intended for energy production, so that safety standards could rely on very low values of the thermal magnitudes, so allowing for very large safety margins for emergency cooling. Similarly, subcriticality would offer a very large margin for not to reach prompt criticality in any event. The main drawback of this proposal is that a sizeable fraction of the energy generated in the cycle (about 1/3, maybe a little more) would not be useful for the thermodynamic cycle to produce electricity. Besides that, a fraction of the generated electricity, between 5 and 10 %, would have to be recirculated to feed the accelerator activating the neutron source. Even so, the overall result would be very positive, because more than 50 % of the natural resources could be exploited with such a cycle, using very safe reactors. This percentage is much higher than the actual value for the once-through cycle (0.5 %) and the value for multiple Pu recycling in the MOX scheme (1 %). Moreover, thorium could also be exploited through fertile conversion into U-233 in the subcritical breeders. The separation between energy production (to be done in LWR) and nuclear breeding (to be done in subcritical hybrids) presents a scenario with very appealing safety features and a high potential for an efficient utilization of all natural resources of uranium and thorium, that account for 1024 J, i.e., 25 Gtoe, which is 35,000 times as large as the annual production of Nuclear Energy nowadays, and about 2,500 times as large as the total annual energy consumption all over the globe

  15. Fission fragment angular distributions for neutron fission of 232Th and their interpretation with a triple-humped fission barrier

    International Nuclear Information System (INIS)

    The fission fragment angular distributions have been measured for the neutron fission of 232Th at a number of energies near the neutron threshold. An exhaustive search has been made for a set of transition states and barrier parameters that would simultaneously fit the angular distributions and reproduce quantitatively the structure seen in the neutron fission cross section. No satisfactory fit to both types of data could be obtained with a double-humped fission barrier. However, use of a triple-humped fission barrier does provide a reasonable fit to all the experimental data. (Auth.)

  16. Calculation of fission fragment yields at low and intermediate energy fission

    International Nuclear Information System (INIS)

    The model for fission fragment mass distributions and results of calculations for low energy fission and fission induced by intermediate energy nucleons is presented. Formation of mass distributions is considered as a result of oscillations on mass asymmetry degree of freedom in the potential well calculated in the macroscopic-microscopic approach. For intermediate energy fission the distribution of fissioning nuclei is taken into account with detailed reaction calculations including direct, preequilibrium and statistical reaction stages. (authors)

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

    OpenAIRE

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

    2015-01-01

    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 $^{240}$P...

  18. Sustainable and safe nuclear fission energy technology and safety of fast and thermal nuclear reactors

    CERN Document Server

    Kessler, Günter

    2012-01-01

    Unlike existing books of nuclear reactor physics, nuclear engineering and nuclear chemical engineering this book covers a complete description and evaluation of nuclear fission power generation. It covers the whole nuclear fuel cycle, from the extraction of natural uranium from ore mines, uranium conversion and enrichment up to the fabrication of fuel elements for the cores of various types of fission reactors. This is followed by the description of the different fuel cycle options and the final storage in nuclear waste repositories. In addition the release of radioactivity under normal and possible accidental conditions is given for all parts of the nuclear fuel cycle and especially for the different fission reactor types.

  19. Search for singlet fission chromophores.

    Czech Academy of Sciences Publication Activity Database

    Havlas, Zden?k; Akdag, Akin; Smith, M. B.; Dron, P.; Johnson, J. C.; Nozik, A. J.; Michl, Josef

    Philadelphia : American Chemical Society, 2012. 31PHYS. ISSN 0065-7727. [National Fall Meeting of the American Chemical Society /244./. 19.08.2012-23.08.2012, Philadelphia] Institutional support: RVO:61388963 Keywords : singlet fission * chromophores Subject RIV: CF - Physical ; Theoretical Chemistry

  20. Nuclear fission in reactor instrumentation

    International Nuclear Information System (INIS)

    The limitation in designing a high neutron sensitive fission counter comes from the alpha induced pulse pile-up with increase in coated quantity of 235U. The thicker coating reduces the number of fission fragments reaching the active volume and increase in coated surface area gives rise to higher capacitance resulting in severe alpha pile-up reducing the effective neutron sensitivity. The short resolving time (small capacitance) and small charge collection time (smaller electrode spacing) are the required features to overcome the problems associated with alpha pulse pile-up for achieving higher sensitivities. One such detector configuration using large number of electrodes connected in series as transmission line will achieve both the features. The adjacent signal electrodes are connected to each other through inductive elements thus each electrode constitutes a lumped-element transmission-line. The processing of pulses from each end of the transmission line to a time coincidence gate can improve discrimination. This configuration of fission detector can achieve sensitivity of about 6 cps/nv for detector of length 1 m and diameter 70 mm. The talk gives an overview of the fission detectors in reactor application and the recent developments

  1. Brownian shape dynamics in fission

    Directory of Open Access Journals (Sweden)

    Randrup Jørgen

    2013-12-01

    Full Text Available It was recently shown that remarkably accurate fission-fragment mass distributions are obtained by treating the nuclear shape evolution as a Brownian walk on previously calculated five-dimensional potentialenergy surfaces; the current status of this novel method is described here.

  2. How spontaneous fission was discovered

    International Nuclear Information System (INIS)

    The 70th anniversary of the discovery of spontaneous fission by the young Russian physicists Konstantin A. Petrzhak and Georgii N. Flerov is commemorated. The situation in the 1940s is described and the activities of the 2 scientists, including their involvement in the development of the A-bomb, is outlined. (P.A.)

  3. Nuclear data for fission reactors

    International Nuclear Information System (INIS)

    Nuclear reactions induced by neutrons play an important role in fission reactors and relevant cross-sections need to be known with great accuracy. After a brief history and a general presentation, the nuclear data situation is discussed for Pressurized-Water and Liquid-Metal Fast Breeder Reactors

  4. Deep-Earth reactor: Nuclear fission, helium, and the geomagnetic field

    OpenAIRE

    Hollenbach, D. F.; Herndon, J. M.

    2001-01-01

    Geomagnetic field reversals and changes in intensity are understandable from an energy standpoint as natural consequences of intermittent and/or variable nuclear fission chain reactions deep within the Earth. Moreover, deep-Earth production of helium, having 3He/4He ratios within the range observed from deep-mantle sources, is demonstrated to be a consequence of nuclear fission. Numerical simulations of a planetary-scale geo-reactor were made by using the SCALE seq...

  5. Brownian motion model of the fission process

    International Nuclear Information System (INIS)

    Fission process is considered as a multi-dimensional Brownian motion. The Fokker-Planck equation is solved and the fission probability in the steady state approximation is calculated. The results are compared with Bohr--Wheeler theory. A numerical calculation for the fission of 236U shows the capability of the model in taking the effect of viscosity into account. From the available estimate of the fission viscosity, it is estimated that such effects can reduce the fission probability by 20% to 40%

  6. Process chemistry in fission product solidification

    International Nuclear Information System (INIS)

    Chemical processes play an important role in all stages of the FIPS process (= Fission Product Solidification). Process and product control require special methods of chemical analysis. An IR spectrometer is used to find out the gas species in a denitration unit (reaction products: NO and CO2). Other gases are analyzed quantitatively and qualitatively by the same method in various measuring points. The main problem is the volatilisation of dried products during vitrification. By means of a coupled system of thermoanalyzer - mass spectromrter, losses of weight and the nature of the evaporating species can be detected simultaneously. In addition, changes of phase during melting can be observed which are a further important problem in process chemistry. In this context, also the influence of Al2O3 - and CaO-additives on phase separation in the end product was investigated. (RB)

  7. Fission dynamics at low excitation energy

    CERN Document Server

    Aritomo, Y

    2013-01-01

    The origin of mass asymmetry in the fission of uranium at a low excitation energy is clarified by a trajectory analysis of the Langevin equation. The positions of the peaks in the mass distribution of fission fragments are mainly determined by fission saddle points originating from the shell correction energy. The widths of the peaks, on the other hand, result from a shape fluctuation around the scission point caused by the random force in the Langevin equation. We found that a random vibration in the oblate direction of fissioning fragments is essential for the fission process. According to this picture, fission does not occur with continuous stretching in the prolate direction, similarly to that observed in starch syrup. This is expected to lead to a new viewpoint of fission dynamics and the splitting mechanism.

  8. Theory of nuclear fission. A textbook

    International Nuclear Information System (INIS)

    This book brings together various aspects of the nuclear fission phenomenon discovered by Hahn, Strassmann and Meitner almost 70 years ago. Beginning with an historical introduction the authors present various models to describe the fission process of hot nuclei as well as the spontaneous fission of cold nuclei and their isomers. The role of transport coefficients, like inertia and friction in fission dynamics is discussed. The effect of the nuclear shell structure on the fission probability and the mass and kinetic energy distributions of the fission fragments is presented. The fusion-fission process leading to the synthesis of new isotopes including super-heavy elements is described. The book will thus be useful for theoretical and experimental physicists, as well as for graduate and PhD students. (orig.)

  9. Progress in fission product nuclear data

    International Nuclear Information System (INIS)

    This is the eleventh issue of a report series on Fission Product Nuclear Data (FPND) which is published by the Nuclear Data Section (NDS) of the International Atomic Energy Agency (IAEA). The purpose of this series is to inform scientists working on FPND, or using such data, about all activities in this field which are planned, ongoing, or have recently been completed. The types of activities being included in this report are measurements, compilations and evaluations of: Fission product yields (neutron induced and spontaneous fission); Neutron reaction cross sections of fission products; Data related to the radioactive decay of fission products; Delayed neutron data of fission products; and lumped fission product data (decay heat, absorption etc.). The main part of this report consists of unaltered original contributions which the authors have sent to IAEA/NDS

  10. Fission, fusion and the energy crisis. 2. ed.

    International Nuclear Information System (INIS)

    The subject is covered in chapters, entitled: living on capital (energy reserves and consumption forecasts); the atom and its nucleus, mass and energy; fission and the bomb; the natural uranium reactor; enriched reactors; control and safety; long-term economics (the breeder reactions and nuclear fuel reserves); short-term economics (cost per kilowatt hour); national nuclear power programmes; nuclear power and the environment (including reprocessing, radioactive waste management, public relations); renewable energy sources; the fusion programme; summary and comment. (U.K.)

  11. A brief history of the ''Delayed'' discovery of nuclear fission

    International Nuclear Information System (INIS)

    This year marks the Fiftieth Anniversary of the discovery of Nuclear Fission. In the early 1930's, the neutron was discovered, followed by the discovery of artificial radioactivity and then the use of the neutron to produce artificial radioactivity. The first experiments resulting in the fission of uranium took place in 1934. A paper which speculated on fission as an explanation was almost immediately published, yet no one took it seriously not even the author herself. Why did it take an additional five years before anyone realized what had occurred? This is an abnormally long time in a period when discoveries, particularly in nuclear physics, seemed to be almost a daily occurrence. The events which led up to the discovery are recounted, with an attempt made to put them into their historical perspective. The role played by Mendeleev's Periodic Table, the role of the natural radioactive decay chain of uranium, the discovery of protactinium, the apparent discovery of masurium (technetium) and a speculation on the reason why Irene Curie may have missed the discovery of nuclear fission will all be discussed. 43 refs

  12. Monte Carlo based toy model for fission process

    International Nuclear Information System (INIS)

    There are many models and calculation techniques to obtain visible image of fission yield process. In particular, fission yield can be calculated by using two calculations approach, namely macroscopic approach and microscopic approach. This work proposes another calculation approach in which the nucleus is treated as a toy model. Hence, the fission process does not represent real fission process in nature completely. The toy model is formed by Gaussian distribution of random number that randomizes distance like the distance between particle and central point. The scission process is started by smashing compound nucleus central point into two parts that are left central and right central points. These three points have different Gaussian distribution parameters such as mean (?CN, ?L, ?R), and standard deviation (?CN, ?L, ?R). By overlaying of three distributions, the number of particles (NL, NR) that are trapped by central points can be obtained. This process is iterated until (NL, NR) become constant numbers. Smashing process is repeated by changing ?L and ?R, randomly

  13. Monte Carlo based toy model for fission process

    Energy Technology Data Exchange (ETDEWEB)

    Kurniadi, R., E-mail: rijalk@fi.itb.ac.id; Waris, A., E-mail: rijalk@fi.itb.ac.id; Viridi, S., E-mail: rijalk@fi.itb.ac.id [Department of Physics, Nuclear Physics and Biophysics Research Division, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung (Indonesia)

    2014-09-30

    There are many models and calculation techniques to obtain visible image of fission yield process. In particular, fission yield can be calculated by using two calculations approach, namely macroscopic approach and microscopic approach. This work proposes another calculation approach in which the nucleus is treated as a toy model. Hence, the fission process does not represent real fission process in nature completely. The toy model is formed by Gaussian distribution of random number that randomizes distance like the distance between particle and central point. The scission process is started by smashing compound nucleus central point into two parts that are left central and right central points. These three points have different Gaussian distribution parameters such as mean (?{sub CN}, ?{sub L}, ?{sub R}), and standard deviation (?{sub CN}, ?{sub L}, ?{sub R}). By overlaying of three distributions, the number of particles (N{sub L}, N{sub R}) that are trapped by central points can be obtained. This process is iterated until (N{sub L}, N{sub R}) become constant numbers. Smashing process is repeated by changing ?{sub L} and ?{sub R}, randomly.

  14. The influence of fission products on UO2 matrix microstructure

    International Nuclear Information System (INIS)

    The presence of the fission products, regardless of their chemical or physical state, drastically affects the fuel properties. With increasing burnup, defects in the pellet microstructure appear, their mobility enhances, the rate of fission gas release enlarges, and the central hole creates, leading to the impairing of fuel quality. The study of processes occurring in the nuclear fuel at high burnups is made on the simulated fuel type SIMFUEL in order to avoid the problems which appear because of the special safety conditions imposed to the irradiated fuel work (the working in hot cell). The SIMFUEL consists in a natural UO2 matrix in which chemical compounds (fission products) were introduced, without radioactivity and having the microstructure compatible to the burnup level. The paper presents the experimental results on the sintered SIMFUEL pellets and the influence of oxidic compounds that appear as fission products on UO2 matrix. The sintered SIMFUEL pellets were characterized by density, mean grain size, porosity, and the presence of oxides' agglomerates by destructive methods and ultra-acoustic microscopy. The experimental data concerning the manufacturing of sintered simulated fuel are presented in tables, diagrams and images of their microstructural characteristics. (authors)

  15. Mass distribution in the fission of /sup 232/Th by degraded-fission-spectrum neutrons

    International Nuclear Information System (INIS)

    The mass-yield distribution of fission products following degraded-fission-spectrum neutron-induced fission of /sup 232/Th was measured by gamma spectrometry for 25 mass chains including mass 138 for the first time for fast fission. Cumulative yields for /sup 83g/Se and /sup 130g/Sb were observed, the latter also for the first time for fast fission. In general, the yields for degraded-fission-spectrum neutron-induced fission of /sup 232/Th were slightly higher in the inner portions of both the heavy and light mass wings than for those from reactor-neutron-induced fission of /sup 232/Th. This was expected, since the average energy of degraded-fission-spectrum neutrons is slightly above that of reactor neutrons

  16. Fission yield covariance generation and uncertainty propagation through fission pulse decay heat calculation

    International Nuclear Information System (INIS)

    Highlights: • Fission yield data and uncertainty comparison between major nuclear data libraries. • Fission yield covariance generation through Bayesian technique. • Study of the effect of fission yield correlations on decay heat calculations. • Covariance information contribute to reduce fission pulse decay heat uncertainty. - Abstract: Fission product yields are fundamental parameters in burnup/activation calculations and the impact of their uncertainties was widely studied in the past. Evaluations of these uncertainties were released, still without covariance data. Therefore, the nuclear community expressed the need of full fission yield covariance matrices to be able to produce inventory calculation results that take into account the complete uncertainty data. State-of-the-art fission yield data and methodologies for fission yield covariance generation were researched in this work. Covariance matrices were generated and compared to the original data stored in the library. Then, we focused on the effect of fission yield covariance information on fission pulse decay heat results for thermal fission of 235U. Calculations were carried out using different libraries and codes (ACAB and ALEPH-2) after introducing the new covariance values. Results were compared with those obtained with the uncertainty data currently provided by the libraries. The uncertainty quantification was performed first with Monte Carlo sampling and then compared with linear perturbation. Indeed, correlations between fission yields strongly affect the uncertainty of decay heat. Eventually, a sensitivity analysis of fission product yields to fission pulse decay heat was performed in order to provide a full set of the most sensitive nuclides for such a calculation

  17. Unifying fission, quasi-fission and the extra push

    Directory of Open Access Journals (Sweden)

    Rowley Neil

    2013-12-01

    Full Text Available Using the above-barrier fusion probabilities of Berriman and the appropriate extra-push energies, we re-investigate the quasi-fission dynamics of reactions leading to the compound nucleus 220Th. A consistent description is obtained in terms of the entrance-channel barriers that are known to determine the initial capture process. The different dynamical deformations that give rise to these barriers significantly influence the potential-energy landscapes onto which the captured system is injected.

  18. Cluster fission from the standpoint of nuclear fission

    International Nuclear Information System (INIS)

    Atomic nucleus belongs to a quantal finite many body system. Nucleus shows great resemblance to cluster, above all metal cluster, although the strength of interaction is different. The works of Brechignac group, Saunder, Martin and P. Froeblich are explained by the critical size Nc as the central term. The differences between cluster and nucleus are investigated and a future view of cluster fission is explained. (S.Y.)

  19. Terracentric Nuclear Fission Reactor: Background, Basis, Feasibility, Structure, Evidence, and Geophysical Implications

    CERN Document Server

    Herndon, J Marvin

    2013-01-01

    The background, basis, feasibility, structure, evidence, and geophysical implications of a naturally occurring Terracentric nuclear fission georeactor are reviewed. For a nuclear fission reactor to exist at the center of the Earth, all of the following conditions must be met: (1) There must originally have been a substantial quantity of uranium within Earth's core; (2) There must be a natural mechanism for concentrating the uranium; (3) The isotopic composition of the uranium at the onset of fission must be appropriate to sustain a nuclear fission chain reaction; (4) The reactor must be able to breed a sufficient quantity of fissile nuclides to permit operation over the lifetime of Earth to the present; (5) There must be a natural mechanism for the removal of fission products; (6) There must be a natural mechanism for removing heat from the reactor; (7) There must be a natural mechanism to regulate reactor power level, and; (8) The location of the reactor or must be such as to provide containment and prevent ...

  20. Sensitivity of Makrofol fission track detectors

    International Nuclear Information System (INIS)

    Neutron fluence can be determined by means of fission track detectors consisting of fission foils in contact with suitable dielectrics (Makrofol E plastic was used in this case). Fission fragments emitted from the fissionable material into the plastic sheet generate permanent damage trails which can be made visible by an etching process. These tracks are then counted by means of an optical microscope or other methods and the number of tracks is proportional to the neutron fluence. The efficiency is defined as the ration of the number of tracks counted to the number of fissions in the fissionable layer. It is calculated from the mean range of the fission products in the fissionable material and in the plastic. The loss of very flat tracks with a small penetration angle caused by etching a certain bulk layer from the plastic foil is also taken into account. The formulas for the efficiency are deduced for thin fission layers and for thick fission foils. These calculations are made on the basis of the experimentally confirmed assumption that the ratio V of the track etching rate to the bulk etching rate is at least equal to 200. These high values for this ratio V are valid if an adequate period (several days) of oxygen influence to the damage trails is guaranteed. The calculated values of the efficiency are compared with experimental values and the uncertainty is discussed. (orig./HP)

  1. The Non-Adiabatic dynamics of Singlet Fission in Polyacenes

    Science.gov (United States)

    Bradforth, Stephen

    2015-03-01

    Singlet fission involves the splitting of a single excitation into two coupled triplet excitations and is manifested in an increasing range of aromatic crystals and amorphous thin films. If the energy of the lowest triplet state is one half (or less) of the first singlet excited state, as it is for tetracene or pentacene and their derivatives, singlet fission may occur between two adjacent chromophores. Since there is no change in the overall spin state of the system, singlet fission can be exceptionally fast, occuring on the fs - ps range. If the triplets can diffuse away from the fission site they are available for harvesting as a dissociated carriers with up to two charge carrier pairs per absorbed photon. The possibility of recovering excess energy above the material band gap (in this case determined by the triplet energy) when a higher energy photon is absorbed has led to great recent interest in exploiting this process for increased efficiency solar energy harvesting. The nature of the electronic couplings between the chromophores, intermediate electronic configurations, and the role of entropy in the spin-allowed primary fission event have all come under great scrutiny. Results from a series of femtosecond spectroscopy experiments on a variety of amorphous thin films, nanoparticles and isolated acene dimer compounds will be presented that shed light on the electronic intermediate states key to the efficiency and speed of this process. Singlet fission involves the splitting of a single excitation into two coupled triplet excitations and is manifested in an increasing range of aromatic crystals and amorphous thin films. If the energy of the lowest triplet state is one half (or less) of the first singlet excited state, as it is for tetracene or pentacene and their derivatives, singlet fission may occur between two adjacent chromophores. Since there is no change in the overall spin state of the system, singlet fission can be exceptionally fast, occuring on the fs - ps range. If the triplets can diffuse away from the fission site they are available for harvesting as a dissociated carriers with up to two charge carrier pairs per absorbed photon. The possibility of recovering excess energy above the material band gap (in this case determined by the triplet energy) when a higher energy photon is absorbed has led to great recent interest in exploiting this process for increased efficiency solar energy harvesting. The nature of the electronic couplings between the chromophores, intermediate electronic configurations, and the role of entropy in the spin-allowed primary fission event have all come under great scrutiny. Results from a series of femtosecond spectroscopy experiments on a variety of amorphous thin films, nanoparticles and isolated acene dimer compounds will be presented that shed light on the electronic intermediate states key to the efficiency and speed of this process. Work supported as part of the Center for Energy Nanoscience, an Energy Frontier Research Center funded by the U.S. Department of Energy (DE-SC0001013).

  2. Assembly for fission product transmutation

    International Nuclear Information System (INIS)

    99Tc rods, as fission products, are loaded into fuel cans at the outermost circumference, and 99rods or zirconium hydride (ZrH1.6) as a compound containing hydrogen atoms are loaded into fuel cans at the central portion. Fast neutrons generated in the core of the FBR type reactor are moderated and transmuted into slow neutrons. 99Tc causes capturing reaction by the slow neutrons and is transmuted into 100Tc. Then, 100Tc is transmuted into 100Ru immediately. 100Ru is a stable element. Then, 99Tc can effectively be annihilated. The similar effect can be obtained by using 93Zr or 129I as fission products. Further, the same effect can be obtained by using yttrium hydride or calcium hydride as the compounds containing hydrogen atoms for moderating neutrons. (I.N.)

  3. Fission hindrance and nuclear viscosity

    International Nuclear Information System (INIS)

    Measurements of GDR gamma-rays in coincidence with fission fragments from medium heavy to very heavy systems are drawn. These measurements have shown excess yield of GDR gamma-rays from the fissioning compound nucleus than what is expected from simple transition state model. The excess yield of GDR gamma-rays is explained by incorporating dissipative mechanism through the Kramers formalism in the statistical model calculations. It will be shown, through a systematic analysis of different systems, namely, 16O+208Pb, and 32S+208Pb, over a wide range of excitation energy that the Kramers' viscosity parameter has ? no apparent temperature dependence. Instead, it may have some dependence on the angular momentum. The role of various parameters in the modified statistical model analysis, their importance and limitations, will be discussed

  4. Shaping Fission Yeast with Microtubules

    OpenAIRE

    Chang, Fred; Martin, Sophie G.

    2009-01-01

    For cell morphogenesis, the cell must establish distinct spatial domains at specified locations at the cell surface. Here, we review the molecular mechanisms of cell polarity in the fission yeast Schizosaccharomyces pombe. These are simple rod-shaped cells that form cortical domains at cell tips for cell growth and at the cell middle for cytokinesis. In both cases, microtubule-based systems help to shape the cell by breaking symmetry, providing endogenous spatial cues to position these sites....

  5. Sexual differentiation in fission yeast

    DEFF Research Database (Denmark)

    Egel, R; Nielsen, O

    1990-01-01

    The regulation of sexual reproduction in yeast constitutes the highest level of differentiation observed in these unicellular organisms. The various ramifications of this system involve DNA rearrangement, transcriptional control, post-translational modification (such as protein phosphorylation) and receptor/signal processing. A few basic similarities are common to both fission and budding yeasts. The wiring of the regulatory circuitry, however, varies considerably between these divergent yeast groups.

  6. Fission tracks dating for obsidian

    International Nuclear Information System (INIS)

    Obsidian from South America are dated by fission tracks methods. Samples are irradiated in a nuclear reactor with a flux of 1015 n/cm2. Results, corrected by 'Plateau' methods, are the following: obsidian from Bolivia: 4.14 x 106 yr., Ecuador: 8.79 x 105 yr., Colombia: 3.52 x 106 yr., Peru: 6.55 x 106 yr., Chile: 1.13 x 106 yr. (MMZ). 5 refs., 3 tabs

  7. The VERDI fission fragment spectrometer

    Directory of Open Access Journals (Sweden)

    Frégeau M.O.

    2013-12-01

    Full Text Available 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.

  8. Weathering processes at the natural nuclear reactor of Bangombe (Gabon). Identification and geochemical modeling of the retention and migration mechanisms of uranium and rare earth elements

    International Nuclear Information System (INIS)

    The natural nuclear fission reactor of Bangombe (Gabon) was discovered in 1985. It is located 30 km SE of the uranium Oklo ore deposit which is well-known for its reactors discovered in 1972. In contrast to the latter ones, the reaction zone of Bangombe is situated close to the surface and therefore has been affected by supergene weathering processes. The purpose of this study was to characterize the main effects related to these alteration processes on the rocks surrounding the Bangombe reactor zone as well as to determine the major mechanisms, influencing the migration and retention of U and REE in this geological system. The different approaches considered in this study comprise mineralogical and geochemical investigations, mass balance calculations, sequential extraction experiments as well as thermodynamic simulations. It could be shown that the present rock and mineral assemblages result from a complex and multi-stage history during which the rocks were affected by diagenetic, hydrothermal, tectonic and recent alteration processes. Multiple transformations led to the setting of different horizons characterized by very specific physico-chemical conditions and mineral associations. It has been shown that in the various units of the weathering sequence, the mechanisms and mineral phases determining the U and REE migration/retention behaviour are quite different and highly dependent on the physico-chemical conditions prevailing in the ambient environment. Apart froming in the ambient environment. Apart from residual and neo-formed clays, especially amorphous and crystalline Fe- and Mn oxides and oxy-hydroxides, phosphates as well as minor phases such as carbonates and heavy minerals were identified to play an important role in REE and U mobility. The acquisition of hydrodynamic data enabled to simulate water-rock interaction and mass-transfer processes which have been produced during the alteration of the Bangombe reactor zone. Thermodynamic simulations showed that elevated U-concentrations downstream the reactor zone at present-days may be simply explained by local re-equilibration of the aquifer forming pelites (containing primary and secondary U-minerals) with the ambient weathering solution. (authors)

  9. Status of fission yield evaluations

    International Nuclear Information System (INIS)

    Very few yield compilations are also evaluations, and very few contain an extensive global library of measured data and extensive models for unmeasured data. The earlier U.K. evaluations and US evaluations were comparable up to the retirements of the primary evaluators. Only the effort in the US has been continued and expanded. The previous U.K. evaluations have been published. In this paper we summarize the current status of the US evaluation, philosophy, and various integral yield tests for 34 fissioning nuclides at one or more neutron incident energies and/or for spontaneous fission. Currently there are 50 yield sets and for each we have independent and cumulative yields and uncertainties for approximately 1100 fission products. When finalized, the recommended data will become part of the next version of the US Evaluated Nuclear Data File (ENDF/B-VI). The complete set of data, including the basic input of measured yields, will be issued as a sequel to the General Electric evaluation reports (better known by the authors' names: Rider - or earlier - Meek and Rider). 16 references

  10. Asymmetric fission of preactinide nuclei

    International Nuclear Information System (INIS)

    The paper reports on experimental study of asymmetric fission of pre actinide nuclei from 213At to 205Bi in (?, f) and (p, f) reactions on the sup(204, 206, 208)Pb and 197Au nuclei. Information obtained in the experiment makes possible to describe the bulk propetrties of that new phenomenon. The average masess of a heavy fission fragment weakly varies in a wide range of mass numbers, A, from the average mass values of the heavy fragment M=136-137 amu for 205Bi to M=142 amu for 252Gf, while the mass of a light fragment is considerably shofted towards the mass of a heavy fragment with the A growth. The width of the fission asymmetric component at the half-height of the mass yield curve maximum varies rather smoothly with the A growth. The asymmetric component contribution to the total yield with the A decrease monotonously drowps and sharply and sharply breaks at 205Bi amu-atomic mass unit

  11. Multigroup antiproton transport and fission

    International Nuclear Information System (INIS)

    Antiprotons are negatively charged protons that continuously slow down in matter until they are stopped and captured on the surface of a nucleus by a proton; in which case, both proton and antiproton annihilate into gammas, pions, and other short-lived particles. When an antiproton annihilates at rest on the surface of an actinide nucleus, such as uranium, many fragments and neutrons are also produced, following direct reaction, nuclear evaporation, and fission processes, along with production of high-energy gammas and pions. Collectively, these processes have been termed antiproton fission, for simplicity, because many neutrons are produced as the end result of all reactions. Recent experiments at CERN suggest that as many as 15 to 20 neutrons ar emitted following antiproton annihilation on 238U, that their distribution is peaked near 5 MeV in energy, and that a sizeable fraction (45 to 75%) of the annihilation energy (1.88 GeV per annihilation) is deposited locally in the 238U. A fit to the experimental neutron spectrum of Angelopoulos et al. is presented, and the systematics of transporting and annihilating antiprotons in a multigroup representation are investigated for the first time. Applications of antiproton transport and fission in small spherical assemblies are discussed and contrasted, mainly systematics of local and nonlocal antiproton annihilation, criticality, and disassembly

  12. Fission characteristics of individual deformation paths in heavy elements

    International Nuclear Information System (INIS)

    The deformation properties of heavy nuclei undergoing the individual fission paths are studied. To understand the nuclear mass division process at low energy, fission events for the symmetric and asymmetric fission paths are analyzed from the overall fission events. The fragment mass-yield distributions for the symmetric and asymmetric fission paths in the fission processes of 210Po, 227Ac, 233Pa, 249Bk, and 259Md are systematically studied. Fission characteristics including the deformation of the fissioning nucleus at the scission configuration, the fragment mass-yield distributions, and the total kinetic energy release for individual fission paths are presented. (author)

  13. International conference on fifty years research in nuclear fission

    International Nuclear Information System (INIS)

    These proceedings contain extended abstracts of the papers presented at the named conference. They deal with static properties of fission, instrumentation for fission studies, fission in compound-nucleus reactions, fission dynamics, fission-like heavy ion reactions, and fusion reactions. See hints under the relevant topics. (HSI)

  14. Sustainable and safe nuclear fission energy. Technology and safety of fast and thermal nuclear reactors

    International Nuclear Information System (INIS)

    Written by one of the world-leading specialists in reactor physics and safety Most comprehensive book on nuclear fission technology, new safety concepts and waste disposal Complete description and evaluation of nuclear fission power generation Covers the whole nuclear fuel cycle, from the extraction of natural uranium, uranium conversion and enrichment up to the fabrication of fuel elements Description of the different fuel cycle options Presents viable solutions for safe and long-term storage of nuclear waste Recently developed new safety concepts for fission reactors Unlike existing books of nuclear reactor physics, nuclear engineering and nuclear chemical engineering this book covers a complete description and evaluation of nuclear fission power generation. It covers the whole nuclear fuel cycle, from the extraction of natural uranium from ore mines, uranium conversion and enrichment up to the fabrication of fuel elements for the cores of various types of fission reactors. This is followed by the description of the different fuel cycle options and the final storage in nuclear waste repositories. In addition the release of radioactivity under normal and possible accidental conditions is given for all parts of the nuclear fuel cycle and especially for the different fission reactor types.

  15. The importance of pools, sprays and ice beds in fission product retention in containment

    International Nuclear Information System (INIS)

    The retention of fission products, which may become airborne during a postulated severe accident, is an important consideration in risk assessment of nuclear plants. Both natural processes and engineered safety features are characterized by mechanisms which remove and retain fission products. Theoretical and empirical formulations have been developed which shot substantial fission product retention by pressure suppression pools, containment sprays, and ice bed condensers. Ice bed data is minimal, and more experiments are necessary for retention model verification. Theoretical trends for pool and spray retention have been verified by available data, but a more extensive data base over a broader range of geometric and thermodynamic parameters would improve model evaluation and verification, and help to minimize conservatisms. This paper provides a summary of the technological state of the art of fission product retention by pools, sprays and ice beds

  16. MODELING AND FISSION CROSS SECTIONS FOR AMERICIUM.

    Energy Technology Data Exchange (ETDEWEB)

    ROCHMAN, D.; HERMAN, M.; OBLOZINSKY, P.

    2005-05-01

    This is the final report of the work performed under the LANL contract on the modeling and fission cross section for americium isotopes (May 2004-June 2005). The purpose of the contract was to provide fission cross sections for americium isotopes with the nuclear reaction model code EMPIRE 2.19. The following work was performed: (1) Fission calculations capability suitable for americium was implemented to the EMPIRE-2.19 code. (2) Calculations of neutron-induced fission cross sections for {sup 239}Am to {sup 244g}Am were performed with EMPIRE-2.19 for energies up to 20 MeV. For the neutron-induced reaction of {sup 240}Am, fission cross sections were predicted and uncertainties were assessed. (3) Set of fission barrier heights for each americium isotopes was chosen so that the new calculations fit the experimental data and follow the systematics found in the literature.

  17. Collective spectra along the fission barrier

    Directory of Open Access Journals (Sweden)

    Pigni M. T.

    2012-12-01

    Full Text Available Discrete and continuous spectra of fissioning nuclei at the humps of fission barriers (Bohr transition states and in the intermediate wells (superdeformed and hyperdeformed states play a key role in the calculation of fission cross sections. A theoretical evaluation of the collective parts of the spectra is possible within the framework of the dinuclear system model, which treats the wave function of the fissioning nucleus as a superposition of a mononucleus configuration and two–cluster configurations in a dynamical way, permitting exchange of upper–shell nucleons between clusters. The impact of theoretical spectra on neutron–induced fission cross sections and, in combination with an improved version of the scission–point model, on angular distribution of fission fragments is evaluated for plutonium isotopes of interest to nuclear energy applications.

  18. The resonance neutron fission on heavy nuclei

    International Nuclear Information System (INIS)

    A new approach to the description of the fission, similar to the well-known reaction theory and based on the helicity representation for the exit fission channels, is briefly summarized. This approach allows one to connect the multimodal fission representation with A. Bohr's concept of the fission transition states and to obtain formulae for the partial and differential fission cross sections. The formulae are used for analysis of the angular anisotropy of fragments in the neutron resonance induced fission of aligned 235U nuclei and of the P-even angular forward-backward and right-left correlations of fragments oe the P-odd correlations caused by the interference of s- and p-wave neutron resonances

  19. Fission dynamics for three decay modes

    International Nuclear Information System (INIS)

    Available as short communication only. An investigation of the optimum fission trajectories in a tri-dimensional configuration space with respect to elongation, necking-in and mass-asymmetry is carried out. The paths are obtained by solving the two associated Euler-Lagrange equations. Calculations for alpha-decay, 28 Mg -radioactivity and cold fission with the light fragment 100 Zr of 234 U are performed. The optimal fission asymmetry kept nearly constant during the decay process. A different situation appears in the case of Mg -radioactivity and cold fission were in the first stage the decay goes through diamond-like shapes. For cold fission the neck radius decreases in the vicinity of the scission point. A general increase of the radius of the larger fragment before reaching the final value is characteristics for cluster emission while in cold fission a small decrease is observed. (Author)

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

    Science.gov (United States)

    Clement, J. D.

    1973-01-01

    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.

  1. Measurements of Fission Cross Sections of Actinides

    CERN Multimedia

    Wiescher, M; Cox, J; Dahlfors, M

    2002-01-01

    A measurement of the neutron induced fission cross sections of $^{237}$Np, $^{241},{243}$Am and of $^{245}$Cm is proposed for the n_TOF neutron beam. Two sets of fission detectors will be used: one based on PPAC counters and another based on a fast ionization chamber (FIC). A total of 5x10$^{18}$ protons are requested for the entire fission measurement campaign.

  2. Benchmarking the LAHET trademark fission models

    International Nuclear Information System (INIS)

    There has been considerable interest in improving the fission models in the LAHET Monte Carlo code for the transport and interaction of nucleons, pions, muons, light ions, and antinucleons. Although subactinide fission contributes little to neutron production in lead or tungsten targets, it can be significant for simulation of target activation and fission product contamination. The availability of new data permits new comparisons to be made between experiment and calculation

  3. Channel theory of fission with diffusive dynamics

    International Nuclear Information System (INIS)

    The channel theory of fission with diffusive dynamics is proposed based on Bohr channel theory of fission and Fokker-Planck equation. The main features of the theory proposed are illustrated both in analytical and numerical way. n + 238U as an example to calculate ?f by using the channel theory of fission with diffusive dynamics in the range of incident neutron energy from 1 to 9 MeV is presented. (2 figs.)

  4. Dissipative dynamics in quasi-fission

    OpenAIRE

    Oberacker, V. E.; Umar, A. S; Simenel, C.

    2014-01-01

    Quasi-fission is the primary reaction mechanism that prevents the formation of superheavy elements in heavy-ion fusion experiments. Employing the time-dependent density functional theory approach we study quasi-fission in the systems $^{40,48}$Ca+$^{238}$U. Results show that for $^{48}$Ca projectiles the quasi-fission is substantially reduced in comparison to the $^{40}$Ca case. This partly explains the success of superheavy element formation with $^{48}$Ca beams. For the fi...

  5. Superfluid dynamics of 258Fm fission

    OpenAIRE

    Scamps, Guillaume; Simenel, Cédric; Lacroix, Denis

    2015-01-01

    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 ...

  6. Fission barriers and half-lives

    Energy Technology Data Exchange (ETDEWEB)

    Moeller, P.; Nix, J.R.; Swiatecki, W.J.

    1989-01-01

    We briefly review the development of theoretical models for the calculation of fission barriers and half-lives. We focus on how results of actual calculations in a unified macroscopic-microscopic approach provide an interpretation of the mechanisms behind some of the large number of phenomena observed in fission. As instructive examples we choose studies of the rapidly varying fission properties of elements at the end of the periodic system. 31 refs., 10 figs.

  7. Fission of nuclei far from stability

    International Nuclear Information System (INIS)

    The secondary-beam facility of GSI provided the technical equipment for a new kind of fission experiment. Fission properties of short-lived neutron-deficient nuclei have been investigated in inverse kinematics. The measured element distributions reveal new kinds of systematics on shell structure and even-odd effects and lead to an improved understanding of structure effects in nuclear fission. Prospects for further experimental studies are discussed. (orig.)

  8. Dynamics of incomplete fusion-fission reactions

    OpenAIRE

    Crouzen, Paulus Caorlus Nicolaas

    1988-01-01

    Fifty years after its first observation, nuclear fission is still a lively field of research. The contemporary interest in this well established phenomenon is mainly related to heavy-ion physics, where fission provides a valuable means for the study of reaction mechanisms. Until recently, most of the experiments on heavy-ion induced fission reactions were inclusive and often could not distinguish between complete and incomplete fusion. The present thesis work, however, was specifically focuss...

  9. Future Scenarios for Fission Based Reactors

    Science.gov (United States)

    David, S.

    2005-04-01

    The coming century will see the exhaustion of standard fossil fuels, coal, gas and oil, which today represent 75% of the world energy production. Moreover, their use will have caused large-scale emission of greenhouse gases (GEG), and induced global climate change. This problem is exacerbated by a growing world energy demand. In this context, nuclear power is the only GEG-free energy source available today capable of responding significantly to this demand. Some scenarios consider a nuclear energy production of around 5 Gtoe in 2050, wich would represent a 20% share of the world energy supply. Present reactors generate energy from the fission of U-235 and require around 200 tons of natural Uranium to produce 1GWe.y of energy, equivalent to the fission of one ton of fissile material. In a scenario of a significant increase in nuclear energy generation, these standard reactors will consume the whole of the world's estimated Uranium reserves in a few decades. However, natural Uranium or Thorium ore, wich are not themselves fissile, can produce a fissile material after a neutron capture ( 239Pu and 233U respectively). In a breeder reactor, the mass of fissile material remains constant, and the fertile ore is the only material to be consumed. In this case, only 1 ton of natural ore is needed to produce 1GWe.y. Thus, the breeding concept allows optimal use of fertile ore and development of sustainable nuclear energy production for several thousand years into the future. Different sustainable nuclear reactor concepts are studied in the international forum "generation IV". Different types of coolant (Na, Pb and He) are studied for fast breeder reactors based on the Uranium cycle. The thermal Thorium cycle requires the use of a liquid fuel, which can be reprocessed online in order to extract the neutron poisons. This paper presents these different sustainable reactors, based on the Uranium or Thorium fuel cycles and will compare the different options in term of fissile inventory, capacity to be deployed, induced radiotoxicities, and R&D efforts.

  10. Fission cross section measurement of 248Cm

    International Nuclear Information System (INIS)

    The even isotopes of curium have large spontaneous fission decay rates, requiring a large neutron intensity to measure the fission cross section in the presence of a strong spontaneous fission background. The RINS (Rensselaer Intense Neutron Spectrometer) system, consisting of a 75-ton lead slowing-down spectrometer coupled to the RPI Gaerttner Laboratory electron linac, produces a very intense neutron flux of broad resolution in the 1 to 100,000 eV energy range, and this system has been used to measure the fission cross section of 248Cm

  11. Theoretical Description of the Fission Process

    Energy Technology Data Exchange (ETDEWEB)

    Witold Nazarewicz

    2003-07-01

    The main goals of the project can be summarized as follows: Development of effective energy functionals that are appropriate for the description of heavy nuclei. Our goal is to improve the existing energy density (Skyrme) functionals to develop a force that will be used in calculations of fission dynamics. Systematic self-consistent calculations of binding energies and fission barriers of actinide and trans-actinide nuclei using modern density functionals. This will be followed by calculations of spontaneous fission lifetimes and mass and charge divisions using dynamic adiabatic approaches based on the WKB approximation. Investigate novel microscopic (non-adiabatic) methods to study the fission process.

  12. Theoretical Description of the Fission Process

    International Nuclear Information System (INIS)

    The main goals of the project can be summarized as follows: Development of effective energy functionals that are appropriate for the description of heavy nuclei. Our goal is to improve the existing energy density (Skyrme) functionals to develop a force that will be used in calculations of fission dynamics. Systematic self-consistent calculations of binding energies and fission barriers of actinide and trans-actinide nuclei using modern density functionals. This will be followed by calculations of spontaneous fission lifetimes and mass and charge divisions using dynamic adiabatic approaches based on the WKB approximation. Investigate novel microscopic (non-adiabatic) methods to study the fission process

  13. Status of fission product yield data

    International Nuclear Information System (INIS)

    The topics covered in this paper are: (a) cumulative yields in thermal neutron fission and in fast fission up to 14 MeV incident neutron energy, (b) dependence of the yields on incident neutron energy and spectrum, (c) independent yields, (d) charge dispersion and distribution, and (e) yields of light particles from ternary fission. The paper reviews information on these subjects for fission of actinides from 232Th upwards with special emphasis on data published since the 1973 Bologna FPND Panel, compares data sets, and discusses the gaps still to be found in them. (author)

  14. Some Fission Problems Circa 1950 and 2008

    Science.gov (United States)

    ?wiatecki, W. J.

    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.

  15. Cold valleys in fusion and fission

    International Nuclear Information System (INIS)

    The cold fission configuration after the preformation of the fragments resembles a short-lived dinuclear or quasi-molecular system. The most conceivable scission configuration is given by two fission fragments in touching with the symmetry axes aligned (pole-pole orientation). This conclusion was based on the simple argument that this configuration offers the optimal tunneling time, i.e. the difference between the Coulomb barrier and the decay energy Q is minimal. Other orientations are apparently precluded in cold spontaneous fission and should be regarded as quasi-fission doorways in the synthesis of superheavy elements by cold fusion. (orig.)

  16. Fusion and fission of heavy nuclei

    International Nuclear Information System (INIS)

    The theories used to calculate the potential energy surface and the mass parameters are reviewed. For nuclear fission the theoretical data can be quantitatively compared with experimental data, but of heavy ion interactions a quantitative theory is still missing. Damping of collective motion by the concept of nuclear viscosity is discussed and its consequences for fission and fusion described. The structure of compound nuclei at high excitation energies as they are being formed in a heavy ion reaction is discussed. The close relationship between fission and heavy ion processes is stressed by using formalisms for the description of the latter that originated in fission theory. (Auth.)

  17. Attachment of gaseous fission products to aerosols

    International Nuclear Information System (INIS)

    Accidents may occur in which the integrity of fuel cladding is breached and volatile fission products are released to the containment atmosphere. In order to assess the magnitude of the subsequent radiological hazard it is necessary to know the transport behaviour of such fission products. It is frequently assumed that the fission products remain in the gaseous phase. There is a possibility, however, that they may attach themselves to particles and hence substantially modify their transport properties. This paper provides a theoretical assessment of the conditions under which gaseous fission products may be attached to aerosol particles. Specific topics discussed are: the mass transfer of a gaseous fission product to an isolated aerosol particle in an infinite medium; the rate at which the concentration of fission products in the gas phase diminishes within a container as a result of deposition on a population of particles; and the distribution of deposited fission product between different particle sizes in a log-normal distribution. It is shown that, for a given mass, small particles are more efficient for fission product attachment, and that only small concentrations of such particles may be necessary to achieve rapid attachment. Conditions under which gaseous fission products are not attached to particles are also considered, viz, the competing processes of deposition onto the containment walls and onto aerosol particles, and the possibility of the removal of aerosols from the containment by various deposition processes, or agglomeration, before attachment takes place. (author)

  18. Fission - track age of the Marjalahti Pallasite

    International Nuclear Information System (INIS)

    Full text: Investigation of fossil charged-particle tracks in various mineral phases of extraterrestrial samples is a powerful method for research the early stages of the solar system. Over geological time, meteorites crystals have accumulated a record of tracks produced by heavily charged energetic particles from both internal (spontaneous fission of 238U and some other extinct isotopes) and external sources (galactic cosmic rays with Z>20). The fortunate fact that meteorite grains can accumulate latent and very long-lived tracks since soon after the end of nucleosynthesis in the solar nebula enables one to decode their radiation history and to detect any thermal events in the meteorite cosmic history by revealing these tracks through suitable etching procedures. Only a few minerals in meteorites (mainly phosphates) contain small amount of uranium; the fact that 238U undergoes fission with fission-decay constant ?f?8.2x10-17 yr-1 allows one to use this isotope as a chronometer. By measuring the U concentration in the crystals (by reactor irradiation) and the density of the spontaneous-fission tracks it is relatively easy to calculate the 'fission-track age' if 238U is the main source of fission tracks. However the fission-track dating of extraterrestrial samples compared with the terrestrial ones has some peculiar features due to presence of a number of other potential track sources except the spontaneous fission of 238U, such as the spontaneous fission of presently extinct 244Pu, heavy nuclei of cosmic rays and induced fission by cosmic ray primaries. Only tracks from the spontaneous fission of U and Pu are suitable for fission-track dating. The competing effects of these fissioning elements, whose half-lives differ by a factor of ?50, form a basis for a fission-track chronology for samples older than ? 4.0 Gyr. Over small intervals in time (? few x108 yr ) the track density from spontaneous fission of 238U is nearly constant. However, the contribution from 244Pu doubles every 82 Myr providing a very sensitive measure of the age of a studied sample. The results of the determination of the fission-track age of the Marjalahti pallasite (stony-iron meteorite) are presented. Thorough examination of fossil tracks in the phosphate (whitlockite) crystals coupled with U content determination in whitlockites allowed us to estimate the contributions of all possible track sources to the total track density and to calculate a value of the model fission-track age. It was found out that whitlockite crystals of the Marjalahti pallasite contain fossil tracks due to galactic cosmic rays (VH, VVH nuclei); induced fission of U and Th by cosmic rays; spontaneous fission of 238U; spontaneous fission of extinct short-lived 244Pu nuclei presented in significant quantities in the early solar system. The initial ratio (244Pu/238U)0 at the time of the pallasite parent body formation (taken as 4.6x109 yr) was estimated as 0.015. A great track density attributed to the extinct 244Pu testified to the high value of the fission-track age. The model fission-track ages of (4.37± 0.02)x109 yr for the Marjalahti pallasite was calculated. The comparison of the represented data with petrographic analyses allowed us to interpret a value of the fission-track age as the time of the last intensive shock/thermal event in the cosmic history of the pallasite. (author)

  19. The evaluation of some reference fission yield data from 235U fission

    International Nuclear Information System (INIS)

    Based on available experimental data up to now and processed by using average data with weight code Average and Simultaneous evaluation code Zott, the 38 cumulative fission yield for 18 product nuclides were evaluated. The evaluated reference fission yield date from 235U fission are presented. The comparison of present evaluated data with JENDL-3 and ENDF/B-6 are shown out

  20. Shell Effects in Nuclear Fission

    International Nuclear Information System (INIS)

    The important part played by shell effects in nuclear fission has been reliably established experimentally and forms the basis of the theory of asymmetry of fission and other properties of fission fragments. However, from the theoretical point of view there are certain difficulties in understanding these effects, since at the moment of scission the fragments axe considerably deformed. When the shell effects are calculated in succession, the energy of the fissioning nucleus before scission may be presented in the form of the sum of the energies of the spherical fragments taking shell effects into account, the Coulomb interaction energy of the fragments and their deformation energy. The deformation energy of the fragments should be calculated not using the elasticity values of the fragments according to the drop model, but, for very low deformations, the single particle elasticity values taking into account the magic effects, with a gradual transition to the drop values for deformations at which the levels of neighbouring shells intersect. The single-particle elasticity values can be obtained from the experimental data on the Coulomb excitation of the nuclei. In Vandenbosch's calculations of fragment deformation, the elasticity of the fragments was based on the condition of coincidence between the deformation energy of the fragments and the experimental values for their excitation energy. However, in this case the elasticity was assumed to be constant at all deformations, and for this reason, although the elasticity values found in Vandenbosch do show magic'effects, they differ considerably in magnitude from the experimental elasticity values (see above).. The calculations of Vandenbosch also failed to take into account the magic effects for non-deformed fragments that lead to a reduction in the energy of the magic nucleus. Therefore, according to these calculations fission should be symmetrical, since the elasticity and consequently also the deformation energy (at the same deformation) are greater for magic than for non-magic nuclei. In fact, since the energy gain for magic spherical fragments is greater than the loss resulting from the increase in elasticity, the formation of magic and near-magic fragments, i.e. asymmetrical fission, is energetically advantageous. This energy gain is essentially connected with the fact that because of the high elasticity value at low deformations the magic fragments are so little deformed that the deformation energy does not compensate for the difference in mass of magic and non-magic fragments. Apart from the deformation energy, the kinetic energy of the separating degrees of freedom at the moment of scission should be taken into account when calculating the excitation energy of fragments. For the shell effects of the fragments to play an important part in fission, the process of deformation of the nucleus on descending from the saddle point (in the case of threshold fission) must be, as in fact it is, fairly slow with respect to the nucleonic degrees of freedom, i.e. ?def >> ?nucleon (?def is the descent time, ?nucleon ? n/?Enucleon, and ?Enucleon is the distance between the nucleon levels). In this case nucleonic shells are formed before scission. At the same time ?def rot, i.e. the process of descent is fast with respect to the rotational degrees of freedom (?rot h/?Erot) - In the case of fission of an excited nucleus with fairly high excitation energy at the saddle point, ?Enucleon may be so low that not only ?def rot but also ?def nucleon, i.e. the process of descent is accelerated with respect to all the degrees of freedom. In this case the density matrix of the nucleus does not change on moving from the saddle point. This would seem to explain the fact that the theoretical angular distribution of fragments at fission of an excited nucleus agrees with the experimental value only when the parameters determining the rotational state of the nucleus (moment of inertia) at the saddle point and not at the scission point are used. (author). (author)

  1. Reference fission yield data evaluation of 79Se etc.17 fission product nuclides from 235U fission

    International Nuclear Information System (INIS)

    The reference fission yield data of 79Se etc. 17 product nuclides from 235U fission were evaluated based on available experimental data up to now. The data were processed with average code AVERAG and simultaneous evaluation code ZOTT. The evaluated data were compared with ENDF/B-6, JEF-2, JENDL-3 and CENDL/FY. The data were updated and improved

  2. Microscopic theory of fission dynamics

    International Nuclear Information System (INIS)

    A microscopic theory of fission is presented in which a Feynman path integral is used to understand tunneling. The idea of an instanton in the case of a Boson field theory is generalized to many Fermions and used to determine the dynamical path self-consistently. The essential roles of Fermion nodal surfaces and symmetry breaking are emphasized. The theory is applied to a solvable pedagogical model, which demonstrates its quantitative accuracy and the importance of solving for the optimal collective path. Similar features are observed in a more realistic calculation of a 32-Fermion system in three dimensions. (orig.)

  3. Ignored priorities: first fission fragment (1925) and first mention of fission (1934)

    International Nuclear Information System (INIS)

    This year is being hailed as the 50th anniversary of the discovery of fission. But what has been ignored is that the first fission fragment was found in 1925 and the process of fission first postulated in 1934. During her scientific career the German chemist Ida Noddack-Tacke twice touched upon aspects of fission: in 1925 together with Walter Noddack and Otto Berg she first observed a fission product and in 1934 she suggested that neutron-irradiated uranium could break up into lighter elements. 18 refs., 1 tab

  4. Cumulative fission yield of Ce-148 produced by thermal-neutron fission of U-235

    International Nuclear Information System (INIS)

    Cumulative fission yield of 148 cesium isotopes and some other fission products produced by thermal-neutron fission of 235 uranium is determined by Germanium/Lithium spectroscopic methods. The measuremets were done at Tsing-Hua open pool reactor using 3 to 4 mg of 93.15% enriched 235 uranium samples. Gamma rays are assigned to the responsible fission products by matching gamma rays energies and half lives. Fission rate is calculated by fission track method. Cumulative fission yields of 148 cesium, 90 krypton, 130 iodine, 144 lanthanum, 89 krypton, 136 xenon, 137 xenon and 140 cesium are calculated. This values are compared with previously predicted values and showed good agreement. 21 Ref

  5. A Computer Code For Calculation Of Fission Product Concentrations For Time Following Fission Burst

    International Nuclear Information System (INIS)

    Precise information of the variation of fission product concentration for time after a fission burst is necessary for safety designs and operations of nuclear power reactors, fuel storage, transport flasks, and for spent fuel management and processing. In this study, a computer code has been developed for exact analysis of the buildup and decay of fission products for time following a fission burst. In which, a new numerical measure to solve the linear and nonlinear decay chains was introduced. The analytical data of fission product concentration, obtained by using the present code, was applied to calculate aggregate fission product decay heat from neutron fission of 235U, 238U, 233U, 239Pu, 241Pu and 232Th. (author)

  6. Nuclear Power from Fission Reactors. An Introduction.

    Science.gov (United States)

    Department of Energy, Washington, DC. Technical 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…

  7. Fission stability diagram of 240Pu

    OpenAIRE

    Garcias, Francisca; Barranco Go?mez, Manuel; Wio, Horacio S.; Ngo?, Christian; Nemeth, J.

    1989-01-01

    We have used an axially symmetric deformed Thomas-Fermi model to evaluate the fission barrier of 240Pu as a function of the quadrupole moment Q2 for different values of the angular momentum L and temperature T. The fission stability diagram of this nucleus is investigated.

  8. Progress in fission product nuclear data

    International Nuclear Information System (INIS)

    This is the seventh issue of a report series on Fission Product Nuclear Data (FPND) which is published by the Nuclear Data Section (NDS) of the International Atomic Energy Agency (IAEA). The purpose of this series is to inform scientists working on FPND, or using such data, about all activities in this field which are planned, ongoing, or have recently been completed. The present issue contains also a section with some recent references relative to fission product nuclear data, which were not covered by the contributions submitted. The types of activities being included in this report are measurements, compilations and evaluations of: fission product yields (neutron induced and spontaneous fission); neutron reaction cross sections of fission products; data related to the radioactive decay of fission products; delayed neutron data of fission products; and lumped fission product data (decay heat, absorption etc.). The sixth issue of this series has been published in June 1980 as INDC(NDS)-113/G+P. The present issue includes contributions which were received by NDS between 1 August 1980 and 25 May 1981

  9. Qualitative specific features of nuclear fission dynamics

    International Nuclear Information System (INIS)

    Influence of the attainment of a statistical equilibrium on compound nucleus decay by means of fission or neutron emission was investigated. Analitic expressions for the probabilities of distribution in time and for the pre-equilibrium fission fragments spectra were obtained. They were determined by character of initial state, excitation energy and shell structure of compound nucleus

  10. Spontaneous fission properties and lifetime systematics

    International Nuclear Information System (INIS)

    Half-lives for spontaneous fission of nuclides with even and odd numbers of particles are compared with recent theoretical calculations. A summary of odd particle hindrance factors is given. The most recent measurements of kinetic-energy and mass distributions and neutron emission for spontaneous fission of the heaviest nuclides are summarized and discussed. 51 refs., 9 figs

  11. Consistent dynamical and statistical description of fission

    International Nuclear Information System (INIS)

    The research survey of consistent dynamical and statistical description of fission is briefly introduced. The Channel theory of fission with diffusive dynamics based on Bohr channel theory and Fokker-Planck equation, and Kramers-Modified Bohr-Wheeler expression according to Strutinsky method given by P. Frobrich et al. are compared and analyzed

  12. Dissipation and friction in nuclear fission

    International Nuclear Information System (INIS)

    We give a short review on experimental evidence for dissipation in nuclear fission as well as on the development of theories of nuclear dissipation and friction applied to the fission process. Theories span from two-body viscosity and one-body dissipation via the time dependent Schroedinger equation to linear response theory and the Fokker-Planck equation. (orig.)

  13. Fission ?-ray data measurements - a challenging endeavour

    International Nuclear Information System (INIS)

    The OECD has published in its high priority data request list a demand for new data on prompt fission ?-ray emission for the standard actinide isotopes 235U and 239Pu in view of their importance for the development of future nuclear fission applications and a responsible handling of nuclear waste with respect to heat production and toxicity. Prompt fission ?-rays can be used to study the configurations of fission fragments very close to the scission point and to better understand how the total excitation energy available in the fissioning system gets transferred to intrinsic excitation in the fragments. They should preferably be known as a function of fission-fragment mass and excitation energy. Existing experimental data, however, were obtained in the 1970s for the above mentioned isotopes. In order to arrive at new and precise correlated ?-ray emission data the problem of efficient neutron/?-ray separation has to be solved. This is usually achieved by means of time-of-flight and the pulse-shape discrimination technique and requires excellent timing resolution of the measurement system. Additionally, high detection efficiency is required. The talk discusses present activities on fission ?-ray measurements with a particular emphasis on state-of-the art fission-fragment and ?-ray detectors.

  14. Methods for determination of fission gases

    International Nuclear Information System (INIS)

    This paper describes procedures for determination of fission gases by measuring the quantity of released and remaining gases in the fuel after irradiation. Experiments are described for determining the quantity of fission gases release from fuel during irradiation in the reactor as well as the pressure of gases in fuel cladding. Principles of gamma scintillation spectroscopy, mass spectrometry and gas chromatography are included

  15. Calculation code of the fission products activity

    International Nuclear Information System (INIS)

    The document describes the two codes for the calculation of the fission products activity. The ''Pepin le bref'' code gives the exact value of the beta and gamma activities of completely known fission products. The code ''Plus Pepin'' introduces the beta and gamma activities whose properties are partially known. (A.L.B.)

  16. Correlation measurements of fission-fragment properties

    Directory of Open Access Journals (Sweden)

    Oberstedt A.

    2010-10-01

    Full Text Available For the development of future nuclear fission applications and for a responsible handling of nuclear waste the a-priori assessment of the fission-fragments’ heat production and toxicity is a fundamental necessity. The success of an indispensable modelling of the fission process strongly depends on a good understanding of the particular mechanism of scission, the mass fragmentation and partition of excitation energy. Experimental observables are fission-fragment properties like mass- and energy-distributions, and the prompt neutron as well as ?-ray multiplicities and emission spectra. The latter quantities should preferably be known as a function of fragment mass and excitation energy. Those data are highly demanded as published by the OECD-NEA in its high priority data request list. With the construction of the double (v, E spectrometer VERDI we aim at measuring pre- and post-neutron masses directly and simultaneously to avoid prompt neutron corrections. From the simultaneous measurement of pre- and post-neutron fission-fragment data the prompt neutron multiplicity may then be inferred fully correlated with fragment mass yield and total kinetic energy. Using an ultra-fast fission event trigger spectral prompt fission ?-ray measurements may be performed. For that purpose recently developed lanthanum-halide detectors, with excellent timing characteristics, were coupled to the VERDI spectrometer allowing for a very good discrimination of fission ?-rays and prompt neutrons due to their different time-of-flight.

  17. Neutronics of Laser Fission-Fusion Systems

    International Nuclear Information System (INIS)

    Neutronics of Fission-Fusion microsystems inertially confined by Lasers are analysed by transport calculation, both stationary (DTF, TIHOC) and time dependent (TDA, TIHEX), discussing the results obtained for the basic parameters of the fission process (multiplication factor, neutron generation time and Rossi-?). (Author) 14 refs

  18. Progress in fission product nuclear data

    International Nuclear Information System (INIS)

    This is the eighth issue of a report series on Fission Product Nuclear Data (FPND) which is published by the Nuclear Data Section (NDS) of the International Atomic Energy Agency (IAEA). The purpose of this series is to inform scientists working on FPND, or using such data, about all activities in this field which are planned, ongoing, or have recently been completed. The main part of this report consists of unaltered original contributions which the authors have sent to IAEA/NDS. Therefore, the IAEA cannot be held responsible for the information contained nor for any consequences resulting from the use of this information. The present issue contains also a section with some recent references relative to fission product nuclear data, which were not covered by the contributions submitted. The types of activities being included in this report are measurements, compilations and evaluations of: Fission product yields (neutron induced and spontaneous fission); Neutron reaction cross sections of fission products; Data related to the radioactive decay of fission products; Delayed neutron data of fission products; and lumped fission product data (decay heat, absorption etc.). The seventh issue of this series has been published in July 1981 as INDC(NDS)-116. The present issue includes contributions which were received by NDS between 1 August 1981 and 15 June 1982

  19. Progress in fission product nuclear data

    International Nuclear Information System (INIS)

    This is the ninth issue of a report series on Fission Product Nuclear Data (FPND) which is published by the Nuclear Data Section (NDS) of the International Atomic Energy Agency (IAEA). The purpose of this series is to inform scientists working on FPND, or using such data, about all activities in this field which are planned, ongoing, or have recently been completed. The main part of this report consists of unaltered original contributions which the authors have sent to IAEA/NDS. The present issue contains also a section with some recent references relative to fission product nuclear data, which were not covered by the contributions submitted. The types of activities being included in this report are measurements, compilations and evaluations of: Fission product yields (neutron induced and spontaneous fission); Neutron reaction cross sections of fission products; Data related to the radioactive decay of fission products; Delayed neutron data of fission products; and lumped fission product data (decay heat, absorption etc.). The eighth issue of this series has been published in July 1982 as INDC(NDS)-130. The present issue includes contributions which were received by NDS between 1 August 1982 and 25 June 1983

  20. Fission cross section calculations for Pa isotopes

    International Nuclear Information System (INIS)

    Based on the recently measured cross-section values for the neutron-induced fission of 231Pa and our experience gained with other isotopes, new self consistent neutron cross section calculations for n+231Pa have been performed up to 30 MeV. The results are quite different to the existing evaluations, especially above the first chance fission threshold. (authors)

  1. Theoretical Description of the Fission Process

    International Nuclear Information System (INIS)

    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.

  2. Theoretical Description of the Fission Process

    Energy Technology Data Exchange (ETDEWEB)

    Witold Nazarewicz

    2009-10-25

    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.

  3. Adsorption and excess fission xenon

    Science.gov (United States)

    Podosek, F. A.; Bernatowicz, T. J.; Kramer, F. E.

    The adsorption of Xe and Kr on lunar soil 10084 was measured by a method that employs only very low fractions of monolayer coverage. Results are presented as parameters for calculation of the Henry constant for adsorption as a function of temperature. The adsorption potentials are about 3 kcal/mole for Kr and 5 kcal/mole for Xe; heating the sample in vacuum increased the Xe potential to nearly 7 kcal/mole. Henry constants at the characteristic lunar temperature are about 0.3 cu cm STP/g-atm. These data were applied to consider whether adsorption is important in producing the excess fission Xe effect characteristic of highland breccias. Sorption equilibrium with a transient lunar atmosphere vented fission Xe produces concentrations seven orders of magnitude lower than observed concentrations. Higher concentrations result because of the resistance of the regolith to upward diffusion of Xe. A diffusion coefficient of 0.26 sq cm/sec is estimated for this process.

  4. Downstream behavior of fission products

    International Nuclear Information System (INIS)

    The downstream behavior of fission products (Cs, I, and Te) has been studied by injection into a stream of super-heated steam and analyzing the deposits formed on the wall of a reaction duct on which a temperature gradient (1,000-200 degree C) had been imposed. Deposits were formed by vapor and aerosol deposition. Studies of mixtures of CsI and CsOH indicated that the formation of a complex, CsI · CsOH, in the gas phase influenced the vapor deposition. Studies of mixtures of CsOH, CsI, Te, and TeO2 indicated the existence of gas phase reactions between Te, TeO2, and CsOH which effected the deposition. The revaporization of fission product deposits, as would occur due to radioactive decay heating, has been studied by the rapid heating of a section of the reaction duct, on which a deposit had been formed, in a stream of steam

  5. Empirical description of beta-delayed fission partial half-lives

    CERN Document Server

    Ghys, L; Antalic, S; Huyse, M; Van Duppen, P

    2015-01-01

    Background: The process of beta-delayed fission (bDF) provides a versatile tool to study low-energy fission in nuclei far away from the beta-stability line, especially for nuclei which do not fission spontaneously. Purpose: The aim of this paper is to investigate systematic trends in bDF partial half-lives. Method: A semi-phenomenological framework was developed to systematically account for the behavior of bDF partial half-lives. Results: The bDF partial half-life appears to exponentially depend on the difference between the Q value for beta decay of the parent nucleus and the fission-barrier energy of the daughter (after beta decay) product. Such dependence was found to arise naturally from some simple theoretical considerations. Conclusions: This systematic trend was confirmed for experimental bDF partial half-lives spanning over 7 orders of magnitudes when using fission barriers calculated from either the Thomas-Fermi or the liquid-drop fission model. The same dependence was also observed, although less p...

  6. Theory of neutron emission in fission

    International Nuclear Information System (INIS)

    Neutron emission in fission is usually described in terms of two observables: the energy spectrum of emitted neutrons N(E) and the average number of neutrons emitted per fission, or average neutron multiplicity, /bar v/p. These observables are measured before the residual fission fragments decay toward the valley of ? stability and are therefore referred to as the prompt neutron spectrum N(E) and the average prompt neutron multiplicity /bar v/p. They are of fundamental importance to the design of macroscopic systems that are driven by the fission reaction, such as thermal or fast reactors. It is the purpose of this paper to describe existing theoretical models for these two observables. Other observables for neutron emission in fission will not be described here due to space limitations. 12 refs., 2 figs

  7. Systematics of Fission-Product Yields

    International Nuclear Information System (INIS)

    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 ZF = 90 thru 98, mass number AF = 230 thru 252, and precursor excitation energy (projectile kinetic plus binding energies) PE = 0 thru ?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 ? 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 (? fission spectrum) induced fission reactions

  8. Calculated medium energy fission cross sections

    International Nuclear Information System (INIS)

    An analysis has been made of medium-energy nucleon induced fission of 238U and 237Np using detailed models of fission, based upon the Bohr-Wheeler formalism. Two principal motivations were associated with these calculations. The first was determination of barrier parameters for proton-rich uranium and neptunium isotopes normally not accessible in lower energy reactions. The second was examination of the consistency between (p,f) experimental data versus new (n,f) data that has recently become available. Additionally, preliminary investigations were also made concerning the effect of fission dynamics on calculated fission cross sections at higher energies where neutron emission times may be significantly less than those associated with fission

  9. Fission dynamics at low excitation energy. 2

    CERN Document Server

    Aritomo, Y; Ivanyuk, F A

    2014-01-01

    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.

  10. Fission fragment pumping of a neon plasma

    International Nuclear Information System (INIS)

    A method for calculating excitation and ionization rates in a plasma generated by the slowing of fission fragments in a gaseous medium (neon) is presented. The energy distribution of the fission fragments as they slow down, and the excitation and ionization of neon due to collisions with the fission fragments, are discussed. Effective W values for ionization and excitation of neon directly by the fission fragments of uranium (71.6 and 110 eV) are derived. The source function for electrons produced by direct ionization by the fission fragments is discussed and compared to that produced by an e beam. The source function of electrons produced by heavy ions has the lower average energy

  11. Theory of neutron emission in fission

    International Nuclear Information System (INIS)

    Following a summary of the observables in neutron emission in fission, a brief history is given of theoretical representations of the prompt fission neutron spectrum N(E) and average prompt neutron multiplicity bar ?p. This is followed by descriptions, together with examples, of modern approaches to the calculation of these quantities including recent advancements. Emphasis will be placed upon the predictability and accuracy of the modern approaches. In particular, the dependence of N(E) and bar ?p on the fissioning nucleus and its excitation energy will be discussed, as will the effects of and competition between first-, second- and third-chance fission in circumstances of high excitation energy. Finally, properties of neutron-rich (fission-fragment) nuclei are discussed that must be better known to calculate N(E) and bar ?p with higher accuracy than is currently possible

  12. Physics of neutron emission in fission

    International Nuclear Information System (INIS)

    The document contains the proceedings of the IAEA Consultants' Meeting on the Physics of Neutron Emission in Fission, Mito City (Japan), 24-27 May 1988. Included are the conclusions and recommendations reached at the meeting and the papers presented by the meeting participants. These papers cover the following topics: Energy dependence of the number of fission neutrons ?-bar (3 papers), multiplicity distribution of fission neutrons (3 papers), competition between neutron and ?-ray emission (4 papers), the fission neutron yield in resonances (2 papers) and the energy spectrum of fission neutrons in experiment (9 papers), theory (4 papers) and evaluation (1 paper). A separate abstract was prepared for each of these papers. Refs, figs and tabs

  13. Experimental studies of fission barrier properties

    International Nuclear Information System (INIS)

    A review is presented of the experimental techniques for the determination of fission barrier properties including fission isomer and fission probability measurements. Microscopic statistical models for the extraction of barrier parameter estimates from the experimental data are described. The importance of nuclear symmetry effects on the calculation of fission widths is demonstrated. Evidence is presented for the fragmentation of the mass asymmetric second barrier in the thorium region and the axial asymmetric first barrier in the californium region. Detailed analyses of experimental data suggest the presence of two parallel second barriers; the normal mass asymmetric, axial symmetric barrier and a slightly higher mass symmetric, axial asymmetric barrier. Experimental barrier parameters are determined systematically and compared to calculations from various theoretical models. Techniques for expanding fission probability measurements to higher energies are discussed. (author)

  14. Superfluid dynamics of 258Fm fission

    CERN Document Server

    Scamps, Guillaume; Lacroix, Denis

    2015-01-01

    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.

  15. Fission

    International Nuclear Information System (INIS)

    Progress is reported in the areas of radiation physics; radiation dosimetry and radiation biophysics; microdosimetry of internal sources; dosimetry of internal emitters; real-time measurement of Pu in air at below-MPC levels; analytical techniques for measurement of 99Tc in environmental samples; and radiation instrumentation--radiological chemistry

  16. Automatic fission track counting using the Quantimet 720

    International Nuclear Information System (INIS)

    Several sets of Makrofol SSTR were irradiated on the natural uranium shell of the NISUS assembly at the University of London Reactor CONSORT. In each set pairs of films were placed one on the outer surface of the shell and the other on the inner surface. The ratio of the fission rates in the two positions were calculated by ANISN transport code and found to be 10.86. The etched films were counted by the Quantimet 720 and by eye using an optical microscope. The results showed that for the six pairs satisfactorily counted by eye the mean fission ratio was 10.31 with standard deviation of 1.4%. The mean fission ratio for the same pairs satisfactorily counted by the Quantimet was 10.53 with standard deviation of 2.3%. The relative efficiency of the Quantimet to eye was found to be 0.975 +- 0.005 (random). This value is subject to a systematic error of +-2% attributable to the calibration of the fields of view. (Auth.)

  17. Radiation Specifications for Fission Power Conversion Component Materials

    Science.gov (United States)

    Bowman, Cheryl L.; Shin, E. Eugene; Mireles, Omar R.; Radel, Ross F.; Qualls, A. Louis

    2011-01-01

    NASA has been supporting design studies and technology development that could provide power to an outpost on the moon, Mars, or an asteroid. One power-generation system that is independent of sunlight or power-storage limitations is a fission-based power plant. There is a wealth of terrestrial system heritage that can be transferred to the design and fabrication of a fission power system for space missions, but there are certain design aspects that require qualification. The radiation tolerance of the power conversion system requires scrutiny because the compact nature of a space power plant restricts the dose reduction methodologies compared to those used in terrestrial systems. An integrated research program has been conducted to establish the radiation tolerance of power conversion system-component materials. The radiation limit specifications proposed for a Fission Power System power convertor is 10 Mrad ionizing dose and 5 x 10(exp 14) neutron per square centimeter fluence for a convertor operating at 150 C. Specific component materials and their radiation tolerances are discussed. This assessment is for the power convertor hardware; electronic components are not covered here.

  18. Uncertainties and credibility building of safety analyses. Natural analogues

    International Nuclear Information System (INIS)

    The substance of natural analogues and their studies is defined as a complementary method to laboratory and in-situ experiments and modelling. The role of natural analogues in the processes of development of repositories is defined, mainly in performance assessment of repository system and communication with public. The criteria for identification of natural analogues which should be evaluated in the phase of initiation of new studies are specified. Review part of this report is divided to study of natural analogues and study of anthropogenic and industrial analogues. The main natural analogue studies performed in various countries, in different geological setting, with various aims are characterized. New results acquired in recently finished studies are included: Palmottu (2nd phase of project financed by European Commission), Oklo (results of research financed also by European Commission), Maqarin (3rd phase) and other information obtained from last meetings and workshops of NAWG. In view of the fact that programmes of development of deep repositories in Czech and Slovak Republics are interconnected, the natural analogues studies carried out in the Czech republic are incorporated in separate chapter - study of uranium accumulation in Tertiary clays at Ruprechtov site and study of degradation of natural glasses. In final part the areas of natural analogue studies as an integral part of development of deep geological repository are proposed along with characterizationy are proposed along with characterization of broader context and aspects of realization of these studies (international cooperation, preparation and evaluation of procedures, communication with public). (author)

  19. Fission-suppressed fusion breeder on the thorium cycle and nonproliferation

    Energy Technology Data Exchange (ETDEWEB)

    Moir, R. W. [Vallecitos Molten Salt Research, 607 E. Vallecitos Rd., Livermore, CA 94550 925-447-8804 (United States)

    2012-06-19

    Fusion reactors could be designed to breed fissile material while suppressing fissioning thereby enhancing safety. The produced fuel could be used to startup and makeup fuel for fission reactors. Each fusion reaction can produce typically 0.6 fissile atoms and release about 1.6 times the 14 MeV neutron's energy in the blanket in the fission-suppressed design. This production rate is 2660 kg/1000 MW of fusion power for a year. The revenues would be doubled from such a plant by selling fuel at a price of 60/g and electricity at $0.05/kWh for Q=P{sub fusion}/P{sub input}=4. Fusion reactors could be designed to destroy fission wastes by transmutation and fissioning but this is not a natural use of fusion whereas it is a designed use of fission reactors. Fusion could supply makeup fuel to fission reactors that were dedicated to fissioning wastes with some of their neutrons. The design for safety and heat removal and other items is already accomplished with fission reactors. Whereas fusion reactors have geometry that compromises safety with a complex and thin wall separating the fusion zone from the blanket zone where wastes could be destroyed. Nonproliferation can be enhanced by mixing {sup 233}U with {sup 238}U. Also nonproliferation is enhanced in typical fission-suppressed designs by generating up to 0.05 {sup 232}U atoms for each {sup 233}U atom produced from thorium, about twice the IAEA standards of 'reduced protection' or 'self protection.' With 2.4%{sup 232}U, high explosive material is predicted to degrade owing to ionizing radiation after a little over 1/2 year and the heat rate is 77 W just after separation and climbs to over 600 W ten years later. The fissile material can be used to fuel most any fission reactor but is especially appropriate for molten salt reactors (MSR) also called liquid fluoride thorium reactors (LFTR) because of the molten fuel does not need hands on fabrication and handling.

  20. Fission-suppressed fusion breeder on the thorium cycle and nonproliferation

    Science.gov (United States)

    Moir, R. W.

    2012-06-01

    Fusion reactors could be designed to breed fissile material while suppressing fissioning thereby enhancing safety. The produced fuel could be used to startup and makeup fuel for fission reactors. Each fusion reaction can produce typically 0.6 fissile atoms and release about 1.6 times the 14 MeV neutron's energy in the blanket in the fission-suppressed design. This production rate is 2660 kg/1000 MW of fusion power for a year. The revenues would be doubled from such a plant by selling fuel at a price of 60/g and electricity at 0.05/kWh for Q=Pfusion/Pinput=4. Fusion reactors could be designed to destroy fission wastes by transmutation and fissioning but this is not a natural use of fusion whereas it is a designed use of fission reactors. Fusion could supply makeup fuel to fission reactors that were dedicated to fissioning wastes with some of their neutrons. The design for safety and heat removal and other items is already accomplished with fission reactors. Whereas fusion reactors have geometry that compromises safety with a complex and thin wall separating the fusion zone from the blanket zone where wastes could be destroyed. Nonproliferation can be enhanced by mixing 233U with 238U. Also nonproliferation is enhanced in typical fission-suppressed designs by generating up to 0.05 232U atoms for each 233U atom produced from thorium, about twice the IAEA standards of "reduced protection" or "self protection." With 2.4% 232U, high explosive material is predicted to degrade owing to ionizing radiation after a little over 1/2 year and the heat rate is 77 W just after separation and climbs to over 600 W ten years later. The fissile material can be used to fuel most any fission reactor but is especially appropriate for molten salt reactors (MSR) also called liquid fluoride thorium reactors (LFTR) because of the molten fuel does not need hands on fabrication and handling.

  1. Fission-Fusion Neutron Source

    International Nuclear Information System (INIS)

    Full text of publication follows: In order to meet the requirement of fusion reactor developing and nuclear waste treatment, a concept of fission-fusion neutron source has been proposed with LiD cylinder in heavy water region of China Advanced Research Reactor (CARR) by slow neutrons to transfer to fusion neutron. The principal is the reaction of 6Li(n,?) to produce energetic tritium ion with 2.739 MeV in LiD by slow neutron, which will be bombarding the deuteron of LiD to induce fusion reaction to produce 14 MeV neutron. The fusion reaction rate will increase with the accumulation of tritium in LiD by the reaction between tritium and deuteron recoils produced by 14 MeV neutrons. When the concentration of tritium in LiD reaches O.5 x 1022 T/cm3 and the fraction of fusion reaction induced by deuteron recoils with tritium approaches to 1, the 14 MeV neutron flux will be doubled and redoubled increasing to approach saturation in which the produced tritium at time t is exhausted by fusion reaction to keep the constant of tritium concentration in LiD. At this case the 14 MeV neutron production rate is too high, it has to decrease the slow neutron flux with decreasing CARR reactor power progressively when the fusion neutron flux approaches to presetting value, for example 3.5 x 1014 n/cm2 sec and will approach to saturation at the low level of neutron flux. This paper describes the principle of fission-fusion neutron sthe principle of fission-fusion neutron source, including the production rate of fusion neutron, the accumulation rate and concentration of tritium, the fusion reaction rate induced by deuteron recoils with tritium, the 14 MeV neutron flux of inner surface of LiD cylinder in the heavy water region of CARR reactor without neutron depression and the influence factors. To consider the neutron depression an assembly of LiD rods in 20 x 20 cm with a centre hole in CARR reactor must be designed to optimize the fusion neutron flux in centre hole. (author)

  2. Progress in fission product nuclear data

    International Nuclear Information System (INIS)

    This is the fifth issue of a report series on Fission Product Nuclear Data (FPND) which is published by the Nuclear Data Section (NDS) of the International Atomic Energy Agency (IAEA). The purpose of this series is to inform scientists working on FPND, or using such data, about all activities in this field which are planned, ongoing, or have recently been completed. The types of activities being included in this report are measurements, compilations and evaluations of: Fission product yields (neutron induced and spontaneous fission); neutron reaction cross sections of fission products; data related to the radioactive decay of fission products; delayed neutron data of fission products; and lumped fission product data (decay heat, absorption etc.). The fourth issue of this series has been published in July 1978 as INDC(NDS)-95/G+P. The present issue includes contributions which were received by NDS between 1 August 1978 and 15 May 1979. The next issue of this report series is envisaged to be published in June 1980

  3. On the mechanism of fission neutron emission

    International Nuclear Information System (INIS)

    This review represents the present knowledge of the mechanism of prompt fission neutron emission. Starting with a brief fission process characterization related with neutron emission, possible emission mechanisms are discussed. It is emphasized that the experimental study of special mechanisms, i.e. scission neutron emission processes, requires a sufficiently correct description of emission probabilities on the base of the main mechanism, i.e. the evaporation from fully accelerated fragments. Adequate statistical-model approaches have to account for the complexity of nuclear fission reflected by an intricate fragment distribution. The present picture of scission neutron emission is not clarified neither experimentally nor theoretically. Deduced data are contradictory and depend on the used analysis procedures often involving rough discriptions of evaporated-neutron distributions. The contribution of two secondary mechanisms of fission neutron emission, i.e. the neutron evaporation during fragment acceleration and neutron emission due to the decay of 5He after ternary fission, is estimated. We summarize the recent progress of the theoretical description of fission neutron spectra in the framework of statistical models considering the standard spectrum of 252Cf(sf) neutrons especially. The main experimental basis for the study of fission neutron emission is the accurate measurement of emission probabilities as a function of emission energy and angle (at least) as well as fragment parameters (mass number ratio and kinetic energy). The present status is evaluated. (author)

  4. Prompt fission neutron multiplicity and spectrum evaluation

    International Nuclear Information System (INIS)

    The prompt fission neutron multiplicity and spectrum for spontaneous fission and neutron induced reactions in the energy range of the first chance fission threshold are evaluated using the 'point by point' approach that takes into account all possible fragmentations of the fissioning nucleus, the multi-modal concept of fission and the most probable fragmentation approach. At higher incident energy when only the most probable fragmentation approach can be used, for the first time the model was extended to take into account the fission of the secondary compound nucleus chains formed by charged particle emission. The model parameters and their dependencies on the incident energy are determined by the study of the reactions where the respective nuclei are the main compounds. The linear dependence of the prompt gamma-ray energy on prompt multiplicity is parameterized as function of the mass and charge numbers of the fissioning nucleus. The above models were successfully applied for many neutron induced reactions on actinides, giving also good results in integral benchmarks. (authors)

  5. Aerosols and fission product transport

    International Nuclear Information System (INIS)

    A survey is presented of current knowledge of the possible role of aerosols in the consequences of in- and out-of-core LOCAs and of end fitting failures in CANDU reactors. An extensive literature search has been made of research on the behaviour of aerosols in possible accidents in water moderated and cooled reactors and the results of various studies compared. It is recommended that further work should be undertaken on the formation of aerosols during these possible accidents and to study their subsequent behaviour. It is also recommended that the fission products behaviour computer code FISSCON II should be re-examined to determine whether it reflects the advances incorporated in other codes developed for light water reactors which have been extensively compared. 47 refs

  6. Nuclear fission industry in Japan

    International Nuclear Information System (INIS)

    The status of the nuclear fission industry in Japan is described. Japanese nuclear policy, vision, goals, and supporting organizational structures are reviewed. The facilities of the Japanese Atomic Energy Research Institute (JAERI), Power Reactor and Nuclear Fuel development Corporation (PNC), and the Japan Atomic Power Company (JAPCO) are illustrated and described. Nuclear power statistics and power generation costs by power source are shown for Japan. Photographic details and technical descriptions are presented for Japan's: nuclear fuel cycle (NFC), light water reactor (LWR), advanced thermal reactor (ATR), fast breeder reactor (FBR), gas centrifuge uranium enrichment, LWR spent fuel reprocessing, ATR and FBR spent fuel uranium/plutonium mixed oxide fuel (MOX) co-conversion process, high level nuclear waste management (NWM) policy, reactor operation safety, newly developed decommissioning and dismantling policy for obsolete nuclear facilities, and new future technology

  7. Downstream behavior of fission products

    International Nuclear Information System (INIS)

    The downstream behavior of fission products has been investigated by injecting mixtures of CsOH, CsI, and Te into a flowing steam/hydrogen stream and determining the physical and chemical changes that took place as the gaseous mixture flowed down a reaction duct on which a temperature gradient (10000 to 2000C) had been imposed. Deposition on the wall of the duct occurred by vapor condensation in the higher temperature regions and by aerosol deposition in the remainder of the duct. Reactions in the gas stream between CsOH and CsI and between CsOH and Te had an effect on the vapor condensation. The aerosol was characterized by the use of impingement tabs placed in the gas stream

  8. Asymmetric fission from egg shape deformation

    International Nuclear Information System (INIS)

    Asymmetric mass distributions have proved to be one of the most persistent puzzles in the fission process. The asymmetric fission of heavy nucleus is considered to occur because of the shell effects. In the fissioning process however, at some point of deformation the nucleus has to assume an asymmetrical shape in the fissioning direction. Simplest asymmetrical shape is like an egg. This egg shape is obtained basically from two hemi-ellipsoids of revolution (about the major axis, b and c with equal minor axis, a), by joining the equal circular faces. With the increase of b and c values the value of a decreases so as to conserve the total volume. The fission occurs when the joint is snapped as a result of the total surface energy increasing beyond the total surface energy of the spherical fragments. It is important that the fission process or the cleavage starts in this proceedings of elongation at a point where the surface curvature is least and it is at the joint of the two hemi-ellipsoids. For the first time the Coulomb energy of this egg shaped 235U92 nucleus has been evaluated. Most importantly the Coulomb energy for various fragment combinations is seen to decreases from that of the symmetric fission. This behaviour will lead to lower Coulomb barriers and shapes varying around the saddle point. So far this aspect of P3(cos?) deformation has not been investigated and present work indicates smaller amount of shell corrections (due to smaller fission barriers) to be applicable in the asymmetric fission

  9. Towards a microscopic description of the fission process

    CERN Document Server

    Goutte, H; Berger, J F

    2010-01-01

    One major issue in nuclear physics is to develop a consistent model able to describe on the same footing the different aspects of the fission process, i.e. properties of the fissioning system, fission dynamics and fragment distributions. Microscopic fission studies based on the mean-field approximation are here presented.

  10. Future challenges for nuclear data research in fission (u)

    Energy Technology Data Exchange (ETDEWEB)

    Chadwick, Mark B [Los Alamos National Laboratory

    2010-01-01

    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.

  11. Calibration of fission track dating parameters

    International Nuclear Information System (INIS)

    A comparison of fission track and K-Ar ages for a set of mineral age standards has been used to evaluate the 238U spontaneous fission decay constant, 238lambdasub(f). Neutron doses were monitored with two fission-track glasses calibrated against a series of Co wire neutron flux monitors in an irradiated facility with a uniform flux distribution in the Herald reactor. An interlaboratory comparison shows that these calibrations compare closely with standard dose measurements made at the U.S. National Bureau of Standards. A value of (7.00 +- 0.28) x 10-17 yr-1 was obtained for 238lambdasub(f). (author)

  12. Nuclear fission induced by high energy protons

    International Nuclear Information System (INIS)

    The fission of 203Pb, 232Th, 238U, 239Pu, 209Br nuclei in the energy region T approximately equal to 0.1-2 GeV is considered on the basis of intranuclear cascade model. The competition between fission and evaporation of excited nuclei remaining after the cascade phase of the interaction is taken into account. Fong's model is used to calculate the fission process. The multiplicity of produced particles (d, t, 3He, ?), the energy spectra of neutrons, the distributions of residual nuclei are discussed. The calculated results are compared with the experiment and with the known theoretical data

  13. Nuclear fission as resonance-mediated conductance

    OpenAIRE

    Bertsch, G. F.

    2014-01-01

    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 li...

  14. The chemistry of the fission products

    International Nuclear Information System (INIS)

    This is a review of chemistry of some chemical elements in fission products. The elements mentioned are krypton, xenon, rubidium, caesium, silver, strontium, barium, cadmium, rare earth elements, zirconium, niobium, antimony, molybdenum, tellurium, technetium, bromine, iodine, ruthenium, rhodium and palladium. The chemistry of elements and their oxides is briefly given together with the chemical species in aqueous solution. The report also contains tables of the physical properties of the elements and their oxides, of fission products nuclides with their half-life and fission yields and of the permissible concentrations. (author)

  15. Low energy fission: dynamics and scission configurations

    International Nuclear Information System (INIS)

    In the first part of this paper we recall a recent study concerning low energy fission dynamics. Propagation is made by use of the Time Dependent Generator Coordinate Method, where the basis states are taken from self-consistent Hartree-Fock-Bogoliubov calculations with the Gogny force. Theoretical fragment mass distributions are presented and compared with the evaluation made by Wahl. In the second part of this paper, new results concerning scission configurations are shown. Deviations of the fission fragment proton numbers from the Unchanged Charge Distribution prescription and fission fragment deformations are discussed. (authors)

  16. Effects of fissioning nuclei distributions on fragment mass distributions for high energy fission

    Directory of Open Access Journals (Sweden)

    Rossi P C R

    2012-02-01

    Full Text Available We study the effects of fissioning nuclei mass- and energy-distributions on the formation of fragments for fission induced by high energy probes. A Monte Carlo code called CRISP was used for obtaining mass distributions and spectra of the fissioning nuclei for reactions induced by 660 MeV protons on 241Am and on 239Np, by 500 MeV protons on 208Pb, and by Bremsstrahlung photons with end-point energies at 50 MeV and 3500 MeV on 238U. The results show that even at high excitation energies, asymmetric fission may still contribute significantly to the fission cross section of actinide nuclei, while it is the dominante mode in the case of lead. However, more precise data for high energy fission on actinide are necessary in order to allow definite conclusions.

  17. Active inspection fission signatures for the detection, quantification and identification of fissionable materials

    International Nuclear Information System (INIS)

    Recently there has been heightened interest in active inspection techniques that can nondestructively detect, identify and quantify fissionable materials for security, nonproliferation and nuclear forensics applications. These active techniques use a source of neutrons or high energy photons to stimulate nuclear reactions in the inspection object and then monitor the emitted secondary radiation for unique fissionable material signatures. These signatures are based on detecting emissions from fission reactions (e.g., prompt and delayed neutrons) and/or non fission reactions (e.g., nuclear resonance fluorescence). In this presentation, the authors will present recent experimental results using prompt neutrons, delayed neutrons and delayed ? rays as fissionable material signatures. The research first focused on how to detect these emissions in an intense radiation environment and the algorithms required to produce unique fissionable material signatures. The sensitivity, accuracy, speed and isotope specificity of each signature was then explored. Current work is focusing on how to effectively combine multiple signatures. (author)

  18. Neutron-induced fission cross section on actinides using microscopic fission energy surfaces

    International Nuclear Information System (INIS)

    Microscopic Hartree-Fock-Bogolyubov (HFB) calculations are now available and can provide all the nuclear ingredients required to describe the fission path from the equilibrium deformation up to the nuclear scission point. The aim of this paper is to apply the basic features of the optical model for fission, using the full microscopic information obtained from HFB models to calculate neutron-induced fission cross sections on selected actinide nuclei. This approach includes not only the details of the energy surface along the fission path, but also the estimate of the nuclear level density derived within the combinatorial approach on the basis of the same HFB single-particle properties, in particular at the fission saddle points. The sensitivity of the calculated fission transmission coefficients to different model approximations is studied and the predictive power of such a microscopic approach tested. (authors)

  19. Investigation of short-living fission products from the spontaneous fission of Cf-252

    International Nuclear Information System (INIS)

    In this paper, a method of separating and measuring fission products of Cf-252 is presented. The measurement was achieved by means of ?-spectrometry and thus provides a quantitative analysis with a good separation of the fission products with respect to both atomic number Z and mass number A. The separation of the fission products from the fission source was achieved by means of solid traps. An automatic changing apparatus made it possible to keep irradiation and measuring times short, so even very short-lived fission products could be registered. The quantitative evaluation of primary fission products was made possible by correction according to Bateman equations. With that, the yields of single nuclides and the dispersion of charge can be determined. (orig./WL)

  20. Influence of fission fragment excitation energy on prompt fission neutron observables

    International Nuclear Information System (INIS)

    We have implemented a Monte-Carlo simulation of the statistical decay of fission fragments by sequential neutron emission. In this presentation, we report on some numerical results obtained for the spontaneous fission of 252Cf and neutron-induced fission of 235U at 0.53 MeV neutron energy, and compare them to the results of the Los Alamos model for the calculation of the average number of prompt fission neutrons ?-bar and the prompt fission neutrons spectrum N(E). Within this approach, we also calculate neutron multiplicity distributions P(?) as well as neutron-neutron correlations such as the full matrix ?-bar (A,TKE). Two assumptions for partitioning the total available excitation energy among the light and heavy fragments are considered. The influence of the fission fragments excitation energy for low total kinetic energies on prompt neutron energy spectrum, multiplicity distributions and ?-bar (A,TKE) is discussed. (authors)

  1. Fission Matrix Capability for MCNP Monte Carlo

    International Nuclear Information System (INIS)

    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, keff). 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 methodstion 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 N2 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 pressur

  2. Fission product induced swelling of U-Mo alloy fuel

    Science.gov (United States)

    Kim, Yeon Soo; Hofman, G. L.

    2011-12-01

    Fuel swelling of U-Mo alloy was modeled using the measured data from samples irradiated up to a fission density of ˜7 × 10 27 fissions/m 3 at temperatures below ˜250 °C. The overall fuel swelling was measured from U-Mo foils with as-fabricated thickness of 250 ?m. Volume fractions occupied by fission gas bubbles were measured and fuel swelling caused by the fission gas bubbles was quantified. The portion of fuel swelling by solid fission products including solid and liquid fission products as well as fission gas atoms not enclosed in the fission gas bubbles is estimated by subtracting the portion of fuel swelling by gas bubbles from the overall fuel swelling. Empirical correlations for overall fuel swelling, swelling by gas bubbles, and swelling by solid fission products were obtained in terms of fission density.

  3. Neutron emission as a probe of fusion-fission and quasi-fission dynamics

    International Nuclear Information System (INIS)

    Pre- and post scission neutron yeilds have been measured as a function of projectile mass, compound nucleus fissility, and fission mass-split and total kinetic energy (TKE) for 27 fusion-fission and quasi-fission reactions induced by beams of 16,18O, 40Ar and 64Ni. A new method of interpretation of experimental pre-scission neutron multiplicities ?-pre and mean kinetic energies ?? allows the extraction of fission time scales with much less uncertainty than previously, all fusion-fission results being consistent with a dynamical time scale of (35±15) x 10-21s for symmetric fission. All reactions show that ?-pre falls quite rapidly with increasing mass-asymmetry; evidence is presented that for fusion-fission reactions this is partly due to a reduction of the dynamical fission time scale with mass-asymmetry. For quasi-fission, the data indicate that the pre-scission multiplicity and mean neutron kinetic energy are very sensitive to the final mass-asymmetry, but that the time scale is virtually independent of mass-asymmetry. It is concluded that for fusion-fission there is no dependence of ?-pre on TKE, whilst for 64Ni-induced quasi-fission reactions, a strong increase of ?-pre with decreasing TKE is observed, probably largely caused by neutron emission during the acceleration time of the fission fragments in these fast reactions. Interpretation of post-scission multiplicities in terms of fragment excitation energies leads to deduced time scales consistent with those determined from the pre-scission data. 54 refs., 17 tabs., 25 figs

  4. Description of peculiarities of prompt fission neutron spectrum in spontaneous fission of 252Cr

    International Nuclear Information System (INIS)

    Full text : 252Cf is the model object in theoretical and experimental studying of prompt fission neutron spectrum in the both spontaneous and induced fission of heavy nuclei. However, the form of spectrum observed has not been clearly understood especially in the region of lower and higher energies. The last compiled data are frequently used as a standart for the test of theoretical prescriptions of the neutron spectrum in spontaneous fission of 252Cf

  5. Measurement of prompt fission gamma-ray spectra in fast neutron-induced fission

    International Nuclear Information System (INIS)

    Knowledge of prompt fission gamma-ray emission has been of major interest in reactor physics for a few years. Since very few experimental spectra were ever published until now, new measurements would be also valuable to improve our understanding of the fission process. An experimental method is currently being developed to measure the prompt fission gamma-ray spectrum from some tens keV up to 10 MeV at least. The mean multiplicity and total energy could be deduced. In this method, the gamma-rays are measured with a bismuth germanate (BGO) detector which has the advantage to present a high P/T ratio and a high efficiency compared to other gamma-ray detectors. The prompt fission neutrons are rejected by the time of flight technique between the BGO detector and a fission trigger given by a fission chamber or a scintillating active target. Energy and efficiency calibration of the BGO detector were carried out up to 10.76 MeV by means of the Al-27(p, gamma) reaction. First prompt fission gamma-ray spectrum measurements performed for the spontaneous fission of Cf-252 and for 1.7 and 15.6 MeV neutron-induced fission of U-238 at the CEA, DAM, DIF Van de Graaff accelerator, will be presented. (authors)

  6. Integral experiments for fission-product yield data

    International Nuclear Information System (INIS)

    The amount of the decay heat of fission products is known very sensitive to the basic fission yield data. Therefore, experiment of measuring the decay heat is one of good integral experiments to evaluate the fission yield data. From this viewpoint, the ?-decay heat of 235U, 238U and 232Th following 14 MeV neutron fissions have been measured, and these data were compared with decay heat data for fast-neutron fissions and summation calculations. (author)

  7. Geometrical and statistical factors in fission of small metal clusters

    OpenAIRE

    Obolensky, O. I.; Lyalin, A. G.; Solov'yov, A V; Greiner, W

    2005-01-01

    Fission of metastable charged univalent metal clusters has been studied on example of Na_{10}^{2+} and Na_{18}^{2+} clusters by means of density functional theory methods. Energetics of the process, i.e. dissociation energies and fission barriers, as well as its dynamics, i.e. fission pathways, have been analyzed. The dissociation energies and fission barriers have been calculated for the full range of fission channels for the Na_{10}^{2+} cluster. The impact of cluster stru...

  8. Advanced modeling of prompt fission neutrons

    Energy Technology Data Exchange (ETDEWEB)

    Talou, Patrick [Los Alamos National Laboratory

    2009-01-01

    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.

  9. Electron spectra from decay of fission products

    International Nuclear Information System (INIS)

    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

  10. A new neutron counter for fission research

    International Nuclear Information System (INIS)

    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

  11. Channel theory of fission with diffusive dynamics

    International Nuclear Information System (INIS)

    The channel theory of fission with diffusive dynamics is proposed based on Bohr channel theory of fission and Fokker-Planck equation. The influence of the details from deformed ground state to saddle point is taken into account in the fission width calculations. The main features of the theory is illustrated both in analytical and numerical ways. Since the model is physically clear and consistent with Bohr-Wheeler formula when the friction coefficient of the system goes to zero, and also is rather easy to work with in a statistical model, it can be used in the analysis of fission process and other related calculations of many other nuclear science and technology applications

  12. Nuclear fission as resonance-mediated conductance

    CERN Document Server

    Bertsch, G F

    2014-01-01

    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.

  13. Charge transfer-mediated singlet fission.

    Science.gov (United States)

    Monahan, N; Zhu, X-Y

    2015-04-01

    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

  14. Fission-product release during accidents

    International Nuclear Information System (INIS)

    One of the aims when managing a reactor accident is to minimize the release of radioactive fission products. Release is dependent not only on the temperature, but also on the partial pressure of oxygen. Strongly oxidizing atmospheres, such as those that occurred during the Chernobyl accident, released semi-volatile elements like ruthenium, which has volatile oxides. At low temperatures, UO2 oxidization to U3O8 can result in extensive breakup of the fuel, resulting in the release of non-volatile fission products as aerosols. Under less oxidizing conditions, when hydrogen accumulates from the zirconium-water reaction, the resulting low oxygen partial pressure can significantly reduce these reactions. At TMI-2, only the noble gases and volatile fission products were released in significant quantities. A knowledge of the effect of atmosphere as well as temperature on the release of fission products from damaged reactor cores is therefore a useful, if not necessary, component of information required for accident management

  15. The Fission Time Projection Chamber Project

    Science.gov (United States)

    Hill, Tony

    2009-10-01

    New high-precision fission experiments have become a priority within the low-energy nuclear community. Modern sensitivity calculations have revealed unacceptable liabilities in some of the underlying fundamental nuclear data and have provided target accuracies for new measurements that are well beyond what can be delivered using current experimental technologies. A potential breakthrough in the precision barrier for these measurements is the deployment of a Time Projection Chamber (TPC). TPC detector systems were originally developed within the particle physics community and have played a central role in that field for nearly 25 years. A group of 6 universities and 3 national laboratories have undertaken the task of building the first TPC designed specifically for the purpose of measuring fission cross sections. In this talk, I will present the motivation for the fission TPC concept, a few details of the device and why we think an improvement on 50 years of fission experiments can be accomplished.

  16. Uranium deposits obtention for fission chambers

    International Nuclear Information System (INIS)

    The obtention of uranium deposits of the required quality for small cylindrical fission chambers presents some difficulties. With the method of electroplating here described the uniformity, reproducibility and adherence of the obtained deposits were satisfactory. (Author) 6 refs

  17. Cold fragmentation and high-energy fission

    International Nuclear Information System (INIS)

    Cold fragmentation and hot fission processes are analyzed from the viewpoint of the maximum entropy principle (MEP), which is seen to provide a good description of the main features that characterize these phenomena. (orig.)

  18. What can we learn from fission times?

    International Nuclear Information System (INIS)

    Fission times have been measured by the blocking technique in single crystal for uranium nuclei and for super-heavy elements with Z = 120. The fission times measured for uranium nuclei can be reproduced by statistical calculations following the Bohr and Wheeler approach only if a friction coefficient increasing with temperature is considered. In the super-heavy element domain, a discrimination between the fast quasi-fission process and the slow fusion-fission one has been achieved from reaction time measurements. A minimum cross-section ? = 22 mb for formation of Z 120 compound nuclei in 238U+Ni reactions at 6.62 MeV/A has been inferred. (authors)

  19. Charge Transfer-Mediated Singlet Fission

    Science.gov (United States)

    Monahan, N.; Zhu, X.-Y.

    2015-04-01

    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.

  20. Neutron and ?-emission from fission fragments

    International Nuclear Information System (INIS)

    The statistical model of nuclear reactions is applied to describe the fission fragment neutron and gamma emission characteristics for spontaneous fission of 252Cf and fission of 235U by thermal neutrons. Averaged excitation energies of fission fragments were obtained from experimental neutron multiplicities. The observable characteristics of an emission are reproduced in a wide range of complementary fragments' total kinetic energies and fragment masses. Observed averaged spins are also reproduced. The fractional independent isomeric yield calculation method, based on the gamma-cascade model, is used to describe experimental data for the 235U(nth,f) and 238U(?,f) reactions. The influence on the calculated isomeric yields of two opposing assumptions regarding the nuclear population spin distributions - one based on the rotational degrees of freedom and one on the internal degrees of freedom of completely accelerated fragments - is investigated. (author)

  1. Development of fission Mo-99 production technology

    Energy Technology Data Exchange (ETDEWEB)

    Park, Jin Ho; Choung, W. M.; Lee, K. I. and others

    2000-05-01

    Fission Mo-99 is the only parent nuclide of Tc-99m, an extremely useful tool for mdeical diagnosis, with an estimated usage of greater than 80% of nuclear medicine applicatons. HEU and LEU targets to optimize in HANARO irradiation condition suggested and designed for domestic production of fission Mo-99. The optimum process conditions are established in each unit process to meet quality requirements of fission Mo-99 products, and the results of performance test in combined process show Mo separation and purification yield of the above 97%. The concept of Tc generator production process is established, and the result of performance test show Tc production yield of 98.4% in Tc generator procuction process. The drafts is prepared for cooperation of technical cooperation and business investment with foreign country. Evaluation on economic feasibility is accompanied for fission Mo-99 and Tc-99m generator production.

  2. "UCx fission targets oxidation test stand"

    CERN Document Server

    Lacroix, Rachel

    2014-01-01

    "Set up a rig dedicated to the oxidation of UCx and define a procedure for repeatable, reliable and safe method for converting UC2 fission targets into an acceptable uranium carbide oxide waste for subsequent disposal by the Swiss Authorities."

  3. Fast neutron fission of 241Am

    International Nuclear Information System (INIS)

    For the fission of 241Am induced by fast neutrons from a 239Pu critical assembly, we have determined the mass-yield distribution and measured independent fission yields and one isomer ratio. The mass-yield distribution curve was constructed from the results for 29 total chain yields which were derived from measurements of fission products ranging from 91Y to 161Tb. Absolute fission yields were obtained with an accuracy of 4% by the requirement of unit total yield in each half of the mass-yield distribution curve and by use of the 235U(n,f) and 238U(n,f) monitor reactions. The peak-to-valley ratio is about 60. Several independent fractional chain yields were measured. Values of Z/sub p/, the most probable charge for a given mass number, inferred from these measurements are in good agreement with those estimated from independent-yield systematics

  4. Neutron energy spectra of spontaneous fission sources

    International Nuclear Information System (INIS)

    Some characteristics of energy distributions of neutrons from spontaneous fission sources are presented. The data on neutron energy spectrum of 252Cf are considered in detail. Main properties of neutron source on the basis of 252Cf are discussed. (author)

  5. Feasibility study on fission moly target development

    International Nuclear Information System (INIS)

    A multi-purpose research reactor, HANARO has been operated on the beginning of 1995 and can be utilized for production of various radioisotopes. And a R and D program for fission Mo production was established, and the technical and economical feasibility study has been performed for fission Mo production in Korea. In this study the process for fission Mo production was recommended as follows; 1. Target : UO2 of annulus type. 2. Separation and purification : Nitric acid dissolution ? Alumina adsorption ? Benzoin oxime precipitation ? Alumina adsorption. And more desirable plan for steady supply of fission Mo were suggested in following viewpoints; 1. Technical collaboration with foreign company. 2. Backup supply system. 3. Marketing arrangement. (Author)

  6. Development of fission Mo-99 production technology

    International Nuclear Information System (INIS)

    Fission Mo-99 is the only parent nuclide of Tc-99m, an extremely useful tool for mdeical diagnosis, with an estimated usage of greater than 80% of nuclear medicine applicatons. HEU and LEU targets to optimize in HANARO irradiation condition suggested and designed for domestic production of fission Mo-99. The optimum process conditions are established in each unit process to meet quality requirements of fission Mo-99 products, and the results of performance test in combined process show Mo separation and purification yield of the above 97%. The concept of Tc generator production process is established, and the result of performance test show Tc production yield of 98.4% in Tc generator procuction process. The drafts is prepared for cooperation of technical cooperation and business investment with foreign country. Evaluation on economic feasibility is accompanied for fission Mo-99 and Tc-99m generator production

  7. Present status of fission yield data

    International Nuclear Information System (INIS)

    Fission yield data of minor actinides are needed for transmutation of nuclear waste by an ADS system. The yield data, however, are not enough for the application. The present status of the yield data is presented in this report. (author)

  8. Bimodality in macroscopic dynamics of nuclear fission

    International Nuclear Information System (INIS)

    The elastodynamic collective model of nuclear fission is outlined whose underlying idea is that the stiff structure of nuclear shells imparts to nucleus properties typical of a small piece of an elastic solid. Emphasis is placed on the macroscopic dynamics of nuclear deformations resulting in fission by two energetically different modes. The low-energy S-mode is the fission due to disruption of elongated quadrupole spheroidal shape. The characteristic features of the high-energy T-mode of division by means of torsional shear deformations is the compact scission configuration. Analytic and numerical estimates for the macroscopic fission-barrier heights are presented, followed by discussion of fingerprints of the above dynamical bimodality in the available data

  9. Fission of 209Bi, natPb and 197Au in the particle field of a fast accelerator driven system

    International Nuclear Information System (INIS)

    Highlights: ? Fission rates of Bi, Pb and Au were measured in a particle field similar to that of fast ADS. ? The experimental results on fission rates are in agreement with MCNPX calculations. ? The most up to date fission cross-sections and related parameterizations were used. ? New parameterizations were produced from the published cross-section data. - Abstract: Accelerator driven systems (ADS) are expected to have particle spectra of significantly greater energy range than that of current power reactors. The Energy plus Transmutation (EpT) set-up of the Joint Institute for Nuclear Research, Dubna, Russia, is designed to emulate the neutron spectrum in a fast ADS through the use of a spallation target surrounded by a blanket of natural uranium. The spectrum is further modified by a reflective layer of polyethylene and an internal absorbing layer of cadmium. The spallation target of EpT was irradiated with a beam of 4 GeV deuterons, and the fission rates of bismuth, lead and gold samples, placed in the target-blanket region were recorded using a fission track detector technique. The fission rates were also calculated using the MCNPX Monte Carlo code with the INCL4 cascade model and cross sections for nucleon induced fission obtained from literature. Agreement between the measured and calculated results indicates the model’s ability to predict the particle spectra and spatial distribution

  10. Measurements of the U-235 fission atomic percentage by thermoionic mass spectroscopy

    International Nuclear Information System (INIS)

    The most widely used methods in precise measurements of uranium isotopic abundance and uranium-235 percent fission for the purpose of burnup determination, are based on thermoionic mass spectrometry. Employing a surface ionization mass spectrometer coupled with a data processing system, uranium ratios have been obtained from irradiated and non-irradiated dilute solutions of natural uranium oxide sinterized pellets. The fission products separation and uranium chemical purification have been carried out by anion exchange. Detailed description of irradiation, dissolution, chemical separation and purification, deposition, data collecting and processing procedures is given. (Author)

  11. Experimental Determination of the Antineutrino Spectrum of the Fission Products of $^{238}$U

    CERN Document Server

    Haag, N; Hofmann, M; Oberauer, L; Potzel, W; Schreckenbach, K; Wagner, F M

    2013-01-01

    An experiment was performed at the scientific neutron source FRM II in Garching to determine the cumulative antineutrino spectrum of the fission products of $^{238}$U. This was achieved by irradiating target foils of natural uranium with a thermal and a fast neutron beam and recording the emitted $\\beta$-spectra with a gamma-suppressing electron-telescope. The obtained $\\beta$-spectrum of the fission products of $^{235}$U was normalized to the data of the magnetic spectrometer BILL of $^{235}$U. This method strongly reduces systematic errors in the $^{238}$U measurement. The $\\beta$-spectrum of $^{238}$U was converted into the corresponding antineutrino spectrum. The final $\\bar\

  12. Progress on the conceptual design of a mirror hybrid fusion--fission reactor

    International Nuclear Information System (INIS)

    A conceptual design study was made of a fusion-fission reactor for the purpose of producing fissile material and electricity. The fusion component is a D-T plasma confined by a pair of magnetic mirror coils in a Yin-Yang configuration and is sustained by neutral beam injection. The neutrons from the fusion plasma drive the fission assembly which is composed of natural uranium carbide fuel rods clad with stainless steel and helium cooled. It was shown conceptually how the reactor might be built using essentially present-day technology and how the uranium-bearing blanket modules can be routinely changed to allow separation of the bred fissile fuel

  13. An ER clamp for endosome fission.

    Science.gov (United States)

    Raiborg, Camilla; Stenmark, Harald

    2015-01-13

    Endosomes are known to undergo budding and fission reactions that separate regions destined for lysosomal degradation from carriers to be recycled to the plasma membrane. A recent paper (Rowland et al, 2014) shows that contact sites between endosomes and the endoplasmic reticulum (ER) define the position and timing for fission. This uncovers an unanticipated role for the ER in controlling endosomal sorting and maturation. PMID:25502456

  14. Energy partition in low energy fission

    OpenAIRE

    Mirea, M.

    2011-01-01

    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 obtain...

  15. Modeling Fission Product Sorption in Graphite Structures

    International Nuclear Information System (INIS)

    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)

  16. MCNP6 Fission Multiplicity with FMULT Card

    International Nuclear Information System (INIS)

    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 data sets for thermal neutron induced fission on U-235.

  17. Fission Barriers of Compound Superheavy Nuclei

    OpenAIRE

    Pei, J.C.; Nazarewicz, W.; Sheikh, J. A.; Kerman, A. K.

    2008-01-01

    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 fission barriers by means of the self-consistent nuclear density functional theory. The relationship between isothermal and isentropic descriptions is demonstrated. Calculations have been carried out for [superscript 264]Fm, [superscript 272]Ds, [superscript 278]112, [sup...

  18. Anatomy of neck configuration in fission decay

    OpenAIRE

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

    2010-01-01

    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...

  19. Prompt fission neutron emission: Problems and challenges

    OpenAIRE

    Hambsch F.-J.; Bry? T.; Gamboni T.; Geerts W; Göök A.; Matei C.; Oberstedt S.; Vidali M.

    2013-01-01

    This paper presents some of the challenges ahead of us even after 75 years of the discovery of the fission process and large progress made since then. The focus is on application orientation, which requires improved measurements on fission cross-sections and neutron and ?-ray multiplicities. Experimental possibilities have vastly improved the past decade leading to developments of highly sophisticated detector systems and the use of digital data acquisition and signal processing. The develop...

  20. A revised calculational model for fission

    Energy Technology Data Exchange (ETDEWEB)

    Atchison, F.

    1998-09-01

    A semi-empirical parametrization has been developed to calculate the fission contribution to evaporative de-excitation of nuclei with a very wide range of charge, mass and excitation-energy and also the nuclear states of the scission products. The calculational model reproduces measured values (cross-sections, mass distributions, etc.) for a wide range of fissioning systems: Nuclei from Ta to Cf, interactions involving nucleons up to medium energy and light ions. (author)

  1. A revised calculational model for fission

    International Nuclear Information System (INIS)

    A semi-empirical parametrization has been developed to calculate the fission contribution to evaporative de-excitation of nuclei with a very wide range of charge, mass and excitation-energy and also the nuclear states of the scission products. The calculational model reproduces measured values (cross-sections, mass distributions, etc.) for a wide range of fissioning systems: Nuclei from Ta to Cf, interactions involving nucleons up to medium energy and light ions. (author)

  2. Fission-fragment excitation of metal electrons

    International Nuclear Information System (INIS)

    The authors mathematically formulate the formation and relaxation of excited-electron regions along the paths of fission fragments under conditions of first wall sputtering and ionization and fission fragment transport into the wall. Their model incorporates all collisional and absorptional aspects of energy transfer between fragments and electrons and includes thermal diffusion and heat transfer between electrons and the metal lattice. Interactions with quasi particles in the solid-state regime are also given consideration

  3. Competition between multifragmentation and fusion-fission

    International Nuclear Information System (INIS)

    With the recently completed Michigan State Univ. 4? logarithmic detection system, the authors studied the competition between intermediate mass fragment (IMF) and fission fragment (FF) production from highly excited systems produced in intermediate energy heavy ion collisions. To discriminate between multifragmentation and fusion-fission they studied two systems, Ar+Th and Ar+Sc, from 15 to 115 MeV/nucleon. Results will be discussed

  4. Modeling Fission Product Sorption in Graphite Structures

    Energy Technology Data Exchange (ETDEWEB)

    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

    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).

  5. Microscopic description of fission in odd nuclei

    International Nuclear Information System (INIS)

    We present preliminary results for the fission properties of odd mass nuclei obtained in the framework of the mean field approximation with the equal filling approximation to handle the unpaired odd nucleon. In the calculations the Gogny force with the D1S parameterization has been used. The results for the nucleus 235U are discussed and the hindrance factor for the spontaneous fission half life is partially attributed to the reduction of pairing correlations. (authors)

  6. The Risoe Fission Gas Project

    International Nuclear Information System (INIS)

    The RISOE Fission Gas Project has provided experimental data on fission gas release (FGR) from high-burnup water reactor fuel. The data are well-characterized with respect to pre-irradiation measurement, irradiation and post-irradiation examination, thus enabling their use in fuel performance code validation. The experimental data were obtained with 12 Zircaloy-clad UO2 pellet fuel pins, irradiated to burnups in the range 27,000-36,000 MWD/tU (pin average, peak pellet 43,700 MWD/tU). Most of the fuel pins were subjected to short-term reirradiations at increased power levels (''bump testing''), in order to simulate postulated power increases late in life. The 11 bump tests covered a range of bump terminal levels (BTL) of 301-434 W/cm (peak pellet), with hold time of 24 h except for one test at 72 h. The axial power shape during the bump testing differed from the base irradiation, thus each bump test was in fact a whole series of experiments with a range of BTLs. The integral pin FGR resulting from the bump testing was in the range 0-16%, increasing with BTL above 375 W/cm (peak pellet). Owing to the form of the axial power distributions, local release data were emphasized in the project, some of the observations being: (a) FG and Cs-137 releases seemed to correlate with local BTL as well as axial and radial position, and to do so in a similar manner; at the highest local BTL investigated (414 W/cm), local FGR had apparently saturated at 40% within 24 h; (b) the local releases increased with local BTL above 350 W/cm; (c) bump testing to about 414 W/cm virtually emptied the central region of the fuel for FG and Cs-137; (d) the release measurements and the ceramographic observations for the bump test with 72 h hold time suggest that this longer time may have given more local release for the lower local BTLs. (author)

  7. Shapes of nuclei in nuclear fission

    International Nuclear Information System (INIS)

    The study of nuclear fission is the only means of obtaining information on highly deformed nuclear shapes. The shape is macroscopically described in terms of deformation parameters or nuclear moments. In low-energy nuclear physics, one is primarily interested in static deformation of the ground or excited states of stable nuclei. On the other hand in fission one encounters the dynamic behaviour of the deformation during the passage of the nucleus from saddle point to scission point. Macroscopic information about the deformation of the nucleus at the transition state, which is several times larger than ground state deformation, can be obtained from a study of fragment angular distributions. The angular distribution of the fragments depends on the fraction of the total angular momentum converted into the relative orbital angular momentum between the fragments and on a factor Ksub(0)sup(2) which characterizes the effective moment of inertia. The factor Ksub(0)sup(2) is therefore a measure of deformation. Theoretical studies of the potential energy as a function of deformation have shown that actinide nuclei exhibit a double humped fission barrier. The occurence of spontaneously fissioning isomers is now well understood as resulting from the spontaneous fission of nuclei in the second well. A study of the spectroscopy of the states in the second well provides information about the shape of nuclei in the second well. These aspects pertaining to highly elongated shapes encopertaining to highly elongated shapes encountered in nuclear fission have been discussed. (auth.)

  8. Modelisation of the fission cross section

    International Nuclear Information System (INIS)

    The neutron cross sections of four nuclear systems (n+235U, n+233U, n+241Am and n+237Np) are studied in the present document. The target nuclei of the first case, like 235U and 239Pu, have a large fission cross section after the absorption of thermal neutrons. These nuclei are called 'fissile' nuclei. The other type of nuclei, like 237Np and 241Am, fission mostly with fast neutrons, which exceed the fission threshold energy. These types of nuclei are called 'fertile'. The compound nuclei of the fertile nuclei have a binding energy higher than the fission barrier, while for the fissile nuclei the binding energy is lower than the fission barrier. In this work, the neutron induced cross sections for both types of nuclei are evaluated in the fast energy range. The total, reaction and shape-elastic cross sections are calculated by the coupled channel method of the optical model code ECIS, while the compound nucleus mechanism are treated by the statistical models implemented in the codes STATIS, GNASH and TALYS. The STATIS code includes a refined model of the fission process. Results from the theoretical calculations are compared with data retrieved from the experimental data base EXFOR. (author)

  9. Theoretical descriptions of neutron emission in fission

    International Nuclear Information System (INIS)

    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 ?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 ?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 ?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

  10. Statistical model investigation of nuclear fission

    International Nuclear Information System (INIS)

    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 and calculated yields. The parameter is interpreted as the spacing between the tips of the fragments at the instant of scission or as the length of a neck in the fissioning nucleus immediately prior to scission. With this spacing parameter semi-quantitative agreement is obtained between calculated and measured mass chain yields for six cases investigated, 233U(n/sub th/, f), 235U(n/sub th, f), 239Pu(n/sub th/, f), 235U(n+14, f), 238U(n+14, f), and 252Cf(sf). An indication of the source of mass asymmetry in fission is presented. The model developed predicts a mass and energy dependence of some of the parameters of models currently in use in data generation. A procedure for the estimation of the fission product yields for an arbitrary fissioning system is proposed. 63 references

  11. Correlation of recent fission product release data

    International Nuclear Information System (INIS)

    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. FASTGRASS contains mechanistic models for such phenomena as: diffusive transfer of species within grains to internal bubbles and to grain boundaries; diffusive transfer of bubbles to grain boundaries; diffusion of fission product species along grain boundaries and through interlinked cracks; growth of the grain size with irradiation and with time at temperature, and the effects of such grain growth on the transport. 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. This paper discusses one of the most widely used such correlation, called CORSOR-M which is the present fission product/aerosol release model used in the NRC source term code package

  12. Dynamics in heavy ion fusion and fission

    International Nuclear Information System (INIS)

    Dynamical aspects of heavy ion fussion and fission, mainly the aspect of damping which is meant as the dissipation of kinetic energy and the aspect of the effective mass of the fission motion, are discussed. Two categories of evidence of damping effects are given. One relates to the damping of the fission motion for the ground state shape and for the isomeric more elongated shape. The other relates to the damping of the fission motion from the last barrier to the scission point. The dependence of the effective mass associated with the fission motion on the deormation of nucleus is shown. As the elongation of the nucleus increases the effective mass of the fission motion varies strongly from being about forty times greater than the reduced mass in the beta-vibrational state of the ground state shape to being equal to the reduced mass in the moment of scission. Damping effects are expected to be propartional to the difference between the effective mass and the reduced mass. It is concluded that the damping in fussion reactions is relatively weak for lighter products and quite strong for superheavy products like 236U or 252Cf. (S.B.)

  13. Spontaneous fission of /sup 259/Md

    Energy Technology Data Exchange (ETDEWEB)

    Hulet, E.K.; Wild, J.F.; Lougheed, R.W.; Baisden, P.A.; Landrum, J.H.; Dougan, R.J.; Mustafa, M.; Ghiorso, A.; Nitschke, J.M.

    1979-05-04

    The mass and kinetic energy distributions of fission fragments from the spontaneous fission of th newly discovered nuclide /sup 259/Md were obtained. /sup 259/Md was identified as the E. C. daughter of /sup 259/No, and was found to decay entirely (> 95%) by spontaneous fission with a 95-min half-life. From the kinetic energies measured for 397 pairs of coincident fragments, a mass distribution was derived that is symmetric with sigma = 13 amu. /sup 259/Md, together with /sup 258/Fm and /sup 259/Fm, form a select group of three nuclides whose mass division in spontaneous fission is highly symmetric. Unlike the total-kinetic-energy (TKE) distributions of /sup 258/Fm and /sup 259/Fm, which peak at approx. = to 240 MeV, this distribution for /sup 259/Md is broad and is 50 MeV lower in energy. Analysis of the mass and energy distributions shows that events near mass symmetry also exhibit a broad TKE distribution, with one-third of the symmetric events having TKEs less than 200 MeV. The associated of low TKEs with symmetric mass division in the fission of very heavy actinides is anomalous and inconsistent with theories based upon the emergence of fragment shells near the scission point. Either three-body fragmentation or peculiar fragment shapes are assumed as the cause for the large consumption of Coulomb energy observed for a significant fraction of symmetric fissions in /sup 259/Md. 6 figures.

  14. DIRECT ENERGY CONVERSION (DEC) FISSION REACTORS - A U.S. NERI PROJECT

    Energy Technology Data Exchange (ETDEWEB)

    D. BELLER; G. POLANSKY; ET AL

    2000-11-01

    The direct conversion of the electrical energy of charged fission fragments was examined early in the nuclear reactor era, and the first theoretical treatment appeared in the literature in 1957. Most of the experiments conducted during the next ten years to investigate fission fragment direct energy conversion (DEC) were for understanding the nature and control of the charged particles. These experiments verified fundamental physics and identified a number of specific problem areas, but also demonstrated a number of technical challenges that limited DEC performance. Because DEC was insufficient for practical applications, by the late 1960s most R&D ceased in the US. Sporadic interest in the concept appears in the literature until this day, but there have been no recent programs to develop the technology. This has changed with the Nuclear Energy Research Initiative that was funded by the U.S. Congress in 1999. Most of the previous concepts were based on a fission electric cell known as a triode, where a central cathode is coated with a thin layer of nuclear fuel. A fission fragment that leaves the cathode with high kinetic energy and a large positive charge is decelerated as it approaches the anode by a charge differential of several million volts, it then deposits its charge in the anode after its kinetic energy is exhausted. Large numbers of low energy electrons leave the cathode with each fission fragment; they are suppressed by negatively biased on grid wires or by magnetic fields. Other concepts include magnetic collimators and quasi-direct magnetohydrodynamic generation (steady flow or pulsed). We present the basic principles of DEC fission reactors, review the previous research, discuss problem areas in detail and identify technological developments of the last 30 years relevant to overcoming these obstacles. A prognosis for future development of direct energy conversion fission reactors will be presented.

  15. DIRECT ENERGY CONVERSION (DEC) FISSION REACTORS - A U.S. NERI PROJECT

    International Nuclear Information System (INIS)

    The direct conversion of the electrical energy of charged fission fragments was examined early in the nuclear reactor era, and the first theoretical treatment appeared in the literature in 1957. Most of the experiments conducted during the next ten years to investigate fission fragment direct energy conversion (DEC) were for understanding the nature and control of the charged particles. These experiments verified fundamental physics and identified a number of specific problem areas, but also demonstrated a number of technical challenges that limited DEC performance. Because DEC was insufficient for practical applications, by the late 1960s most R and D ceased in the US. Sporadic interest in the concept appears in the literature until this day, but there have been no recent programs to develop the technology. This has changed with the Nuclear Energy Research Initiative that was funded by the U.S. Congress in 1999. Most of the previous concepts were based on a fission electric cell known as a triode, where a central cathode is coated with a thin layer of nuclear fuel. A fission fragment that leaves the cathode with high kinetic energy and a large positive charge is decelerated as it approaches the anode by a charge differential of several million volts, it then deposits its charge in the anode after its kinetic energy is exhausted. Large numbers of low energy electrons leave the cathode with each fission fragment; they are suppressed by negatively biased on grid wires or by magnetic fields. Other concepts include magnetic collimators and quasi-direct magnetohydrodynamic generation (steady flow or pulsed). We present the basic principles of DEC fission reactors, review the previous research, discuss problem areas in detail and identify technological developments of the last 30 years relevant to overcoming these obstacles. A prognosis for future development of direct energy conversion fission reactors will be presented

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

    Science.gov (United States)

    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

    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.

  17. Determination of the fission coefficients in thermal nuclear reactors for antineutrino detection

    Energy Technology Data Exchange (ETDEWEB)

    Araujo, Lenilson M. [Coordenacao dos Programas de Pos-Graduacao de Engenharia (PEN/COPPE/UFRJ), Rio de Janeiro, RJ (Brazil). Programa de Engenharia Nuclear; Cabral, Ronaldo G., E-mail: rgcabral@ime.eb.b [Instituto Militar de Engenharia (IME), Rio de Janeiro, RJ (Brazil); Anjos, Joao C.C. dos, E-mail: janjos@cbpf.b [Centro Brasileiro de Pesquisas Fisicas (CBPF), Rio de Janeiro, RJ (Brazil). Dept. GLN - G

    2011-07-01

    The nuclear reactors in operation periodically need to change their fuel. It is during this process that these reactors are more vulnerable to occurring of several situations of fuel diversion, thus the monitoring of the nuclear installations is indispensable to avoid events of this nature. Considering this fact, the most promissory technique to be used for the nuclear safeguard for the nonproliferation of nuclear weapons, it is based on the detection and spectroscopy of antineutrino from fissions that occur in the nuclear reactors. The detection and spectroscopy of antineutrino, they both depend on the single contribution for the total number of fission of each actinide in the core reactor, these contributions receive the name of fission coefficients. The goal of this research is to show the computational and mathematical modeling used to determinate these coefficients for PWR reactors. (author)

  18. Fission track geochrobiology of India

    International Nuclear Information System (INIS)

    Fission track technique has been applied for dating muscovite, biotite, vermiculite, apatite, sphene zircon, hornblended and garnet samples collected from different geological regions of India. Geological annealing of tracks in each of these samples was ascertained and observed ages were corrected wherever necessary. The corrected age data ranging between 5 m.y., to 1,500 m.y., though deficient in older age measurements due to inherent limitations of the method, make a significant contribution towards throwing additional light on various metamorphic and thermal episodes in the sub-continent. Age measurements are peaked at 30 m.y., 500 m.y., and 875 m.y., corresponding to the Himalayan Orogeny, Indian Ocean Orogeny and Satpura Orogeny respectively. The data have been compared wherever possible, with the measurements made by other radiometric methods. From the knowledge of annealing characteristics of the minerals, the age data of cogenetic/coexisting minerals have been utilized to delineate the thermal history of different regions of India. (author)

  19. Biological effectiveness of fission neutrons

    International Nuclear Information System (INIS)

    Human peripheral blood lymphocytes were exposed to the uranium fission neutrons with different energy spectra, and the effects of changing pattern of energy spectrum on the relative biological effectiveness (RBE) were studied by analyzing dose-response relationship of chromosome aberrations. When the contribution of contaminated gamma-rays was subtracted, the efficiency of chromosomal response to the neutron dose was found to be refractory to the difference in the energy spectrum while the mean energy ranged from 2 MeV to 27 keV. This chromosomal refractoriness to energy spectrum may be explained by the similarity of energy spectrum for kerma contribution; most of the doses being given by neutrons with energy above 50 keV. Small doses given by short tracks may be less efficient. A comparison of these observations with chromosome aberration frequencies in lymphocytes of A-bomb survivors leads to somewhat higher estimate of neutron dose in Hiroshima than the estimate by the recently revised dosimetry system, DS86. (author)

  20. Fusion-fission hybrid reactors

    International Nuclear Information System (INIS)

    This chapter discusses the range of characteristics attainable from hybrid reactor blankets; blanket design considerations; hybrid reactor designs; alternative fuel hybrid reactors; multi-purpose hybrid reactors; and hybrid reactors and the energy economy. Hybrid reactors are driven by a fusion neutron source and include fertile and/or fissile material. The fusion component provides a copious source of fusion neutrons which interact with a subcritical fission component located adjacent to the plasma or pellet chamber. Fissile fuel and/or energy are the main products of hybrid reactors. Topics include high F/M blankets, the fissile (and tritium) breeding ratio, effects of composition on blanket properties, geometrical considerations, power density and first wall loading, variations of blanket properties with irradiation, thermal-hydraulic and mechanical design considerations, safety considerations, tokamak hybrid reactors, tandem-mirror hybrid reactors, inertial confinement hybrid reactors, fusion neutron sources, fissile-fuel and energy production ability, simultaneous production of combustible and fissile fuels, fusion reactors for waste transmutation and fissile breeding, nuclear pumped laser hybrid reactors, Hybrid Fuel Factories (HFFs), and scenarios for hybrid contribution. The appendix offers hybrid reactor fundamentals. Numerous references are provided

  1. Natural nuclear reactors

    International Nuclear Information System (INIS)

    By the analysis of Xenon, formatted by fission, the author and two colleagues could prove recently, that one of this reactor was active half an hour and between the activities took a break for two hours and a half. This discovery from a primeval time offers the fantastic chance to investigate the long-term behaviour of nuclear wastes as possible change of Natural Constants. Further investigations of Xenon in minerals shall perhaps prove natural reactors in other regions of the earth. (GL)

  2. Fission-track ages of four meteorites

    International Nuclear Information System (INIS)

    A method for selective annealing of cosmic-ray tracks has been developed, permitting determination of fission-track ages in the presence of a large background of cosmic-ray tracks. The mesosiderite Bondoc contains 41 fission tracks/cm2, of which about 75% are due to neutron-induced fission of U235 during cosmic-ray exposure. Its net fission-track age is 140 +- 40 Myr, nearly identical to its cosmic-ray exposure age of 150 Myr. The mesosiderite Mincy has a fission-track age of 1500 +- 400 Myr. Nakhla (nakhlite) contains an excess of apparent fission tracks, which may be either genuine fission tracks from Pu244 or etch pits mimicking fission tracks in length, thermal stability, random orientation, and other characteristics. On the assumption that they are fission tracks, the Pu244/U238 ratio at the onset of track retention in Nakhla was (3.1 +- 1.3) x 10-3, nearly an order of magnitude lower than the initial solar system ratio. This may reflect a chemical fractionation of Pu and U, or a late impact or magmatic event. Different minerals of the Washougal howardite have different Pu244/U238 ratios, from (24 +- 7) x 10-3 to (2.3 +- 0.7) x 10-3. This may imply a succession of impacts over a period of time. Additionally, Pu and U may have been chemically fractionated from each other in this meteorite. Shocked meteorites show no consistent pattern in the retentivity ofo consistent pattern in the retentivity of fission tracks and of fissiogenic or radiogenic noble gases. Some meteorites, e.g. Bondoc, Serra de Mage, and Mincy, retain gases more completely than tracks; others e.g. Nakhla and Allende, retain them less completely. Uranium was determined in feldspar and/or pyroxene from 19 Ca-rich achondrites and mesosiderites. For most, only upper limits of 0.01 to 0.03 ppb were obtained. Apparently the uranium in these meteorites resides almost exclusively in minor phases, as in terrestrial and lunar rocks. (author)

  3. Reference reactor module for NASA's lunar surface fission power system

    Energy Technology Data Exchange (ETDEWEB)

    Poston, David I [Los Alamos National Laboratory; Kapernick, Richard J [Los Alamos National Laboratory; Dixon, David D [Los Alamos National Laboratory; Werner, James [INL; Qualls, Louis [ORNL; Radel, Ross [SNL

    2009-01-01

    Surface fission power systems on the Moon and Mars may provide the first US application of fission reactor technology in space since 1965. The Affordable Fission Surface Power System (AFSPS) study was completed by NASA/DOE to determine the cost of a modest performance, low-technical risk surface power system. The AFSPS concept is now being further developed within the Fission Surface Power (FSP) Project, which is a near-term technology program to demonstrate system-level TRL-6 by 2013. This paper describes the reference FSP reactor module concept, which is designed to provide a net power of 40 kWe for 8 years on the lunar surface; note, the system has been designed with technologies that are fully compatible with a Martian surface application. The reactor concept uses stainless-steel based. UO{sub 2}-fueled, pumped-NaK fission reactor coupled to free-piston Stirling converters. The reactor shielding approach utilizes both in-situ and launched shielding to keep the dose to astronauts much lower than the natural background radiation on the lunar surface. The ultimate goal of this work is to provide a 'workhorse' power system that NASA can utilize in near-term and future Lunar and Martian mission architectures, with the eventual capability to evolve to very high power, low mass systems, for either surface, deep space, and/or orbital missions.

  4. Determination of Exposure Rate of the Fission Products in the UO2 Irradiated Sample

    International Nuclear Information System (INIS)

    The system HERBE contains the fast core loaded with the natural uranium fuel elements. It is surrounded by a neutron filter and a neutron converter. Thermal core is composed of the 80 % enriched UO2 in the 12 cm square lattice cell, moderated and reflected by heavy water. A vertical channel, in which the UO2 sample is irradiated, is placed in the thermal core, at 30 cm distance from the centre of the HERBE system. In order to determine the fission rate in the coupled fast-thermal system HERBE the UO2 sample is irradiated in a vertical channel. Absolute fission rate density is determined by gamma-ray activity measurement of 140La nuclide from UO2 irradiated sample. Calculation of exposure rates of the fission products are made taking into account the handling of the irradiated sample. The developed gamma spectroscopy method using coaxial Ge detector is used for nondestructive analysis of the irradiated sample and determination of the exposure rate of the fission products. The results show that for a relatively short measurement time a satisfactory information about creation of the fission products and theirs activities and exposure dose rates, are obtained. The applied method is achieved by a simple and fast evaluation of the measured gamma spectrum by using the APOGEE computer code as well as calculation of the average efficiency of the detected gamma rays with given energies, for the real geometry of the sample-detector disposition, by the EFI computer code

  5. Evidence for the occurrence of new shoulders in low-energy-fission mass distribution

    International Nuclear Information System (INIS)

    The results of investigations aimed at defining the nature of the low-yield wing portions of the mass yield curve in the reactor-neutron-induced highly asymmetric binary fission of 238U are reported. Fission yields for mass chains 66, 67, 72, 73, 77, 161, 167, 171, 172, 173, 175, and 177, together with the upper limits for the yields of mass chains 179, 183 and 199, were determined relative to 99Mo by using stringent radiochemical techniques and have been used to obtain the complete mass yield curve. The yields of these mass numbers are in the range of 10-3 - 10-6%. The yields of mass chains 66-67 on the lighter mass side and 171-177 on the heavier mass side were found to be about three orders of magnitude higher than the normally expected trend. This observation, coupled with the upper limits for mass chains 179, 183 and 199, unambiguously shows the presence of 'shoulders' in the very asymmetric mass region which the authors attribute to the possible influence of the 28-proton shell in low-energy fission. Some interesting new features concerning low-energy highly asymmetric fission seem to emerge from these studies. Various plausible explanations for the occurrence of the new shoulders in low-energy-fission mass distribution are discussed in the light of recently available experimental and theoretical data from other laboratories. (author)

  6. Prompt gamma-ray coincidences from U-235 induced fission

    Science.gov (United States)

    Jewell, J. Keith; Cole, Jerald; Drigert, Mark; Reber, Edward; Aryaeinejad, Rahmat

    1999-10-01

    An experiment to measure gamma-ray emission from the prompt fission fragments of U-235 was recently performed at the Intense Pulsed Neutron Source facility at Argonne National Laboratory. Ten HPGE detectors were used to observe coincident gamma-rays from the fission fragments. Unlike previous fission studies which focused on the fission fragments populated by beta decay, we have measured the prompt fission yields by inducing fission in the U-235 target. Coincidence information between light and heavy fission fragments permits the assignment of observed gamma-rays to a particular isotope. Preliminary analysis indicates new spectroscopic information for dozens of nuclei, as well as the observation of isotopes for which gamma-ray decays were previously unreported. We will report on the prompt fission yields of the major fission fragments, as well as the new spectroscopic information for select nuclei.

  7. Asymmetry in ternary fission induced by polarized neutrons and fission mechanism

    International Nuclear Information System (INIS)

    The results of measuring the P-odd, P-even (right-left) and T-odd asymmetries of the charged particles emission in the double and ternary fission, induced by the polarized neutrons, are considered. It is shown, what kind of information on the mechanism of the ternary nuclear fission may be obtained from the theoretical analysis of these data

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

    OpenAIRE

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

    2013-01-01

    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.

  9. Model Calculation of Fission Product Yields Data using GEF Code

    International Nuclear Information System (INIS)

    Fission yields data are classified with spontaneous fission data and neutron induced fission data. The fission product yields data at several energy points for the limited actinides are included in nuclear data libraries such as ENDF/B, JEFF and JENDL because production of those is based mainly on experimental results and it is very difficult to conduct experiments for all actinides and continuous energies. Therefore, in order to obtain fission yields data without experimental data, a theoretical fission model should be introduced to produce the yields data. GEneral Fission model (GEF) is developed to predict the properties for fissioning systems that have not been measured and that are not accessible to experiment. In this study, the fission yields data generated from GEF code are compared with the measured data and the recently available nuclear data libraries. The GEF code is very powerful tool to generate fission yields without measurements. Also, it can produce the distribution of fission product yields for continuous neutron energy while measured data are given only at several energies. The fission yields data of 235U have been tentatively generated with GEF code in this work. Comparing GEF results with measurements and recently released evaluated fission yields data, it is confirmed that GEF code can successfully predict the fission yields data. With its sophisticated model, GEF code is playing a significant role in nuclear industry

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

    CERN Document Server

    Farget, F; 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; Caceres, L; Casarejos, E; Chibihi, A; Fernandez-Dominguez, B; Gaudefroy, L; Golabek, C; Grevy, 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

    2012-01-01

    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 fragmen...

  11. Particle evaporation-fission competition in nuclear fission considered as a diffusion process

    International Nuclear Information System (INIS)

    Nuclear fission is treated as a diffusion process in phase space corresponding to the essential collective variable of fission. The solution of the two-dimensional Fokker-Planck equation is used to obtain an escape rate over the collective potential barrier. This escape rate over the barrier presents a transient regime, the asymptotic value of which is identified to the fission width given by the usual statistical model. This time dependent fission width is included in a schematic formalism for the deexcitation of the compound nucleus to calculate the multiplicities of pre-fission neutrons. A sensitive dependence of the multiplicities on the friction and an enhancement of the multiplicities with respect to the standard statistical model at high energy are obtained

  12. A simple method for detection of fission product fallout

    International Nuclear Information System (INIS)

    An outdoor gamma-ray detector with a 76mm x 76mm NaI(T1) crystal and 1 256 channel analyzor measures the ambient gamma-ray background due to natural radioactivity. The data are transmitted to a computer that continuously updates the background count rates of 10 windows for reference purposes. The influence of washout of atmospheric radon-daughters during precipitation is eliminated by a stripping technique. Automatic investigations of the corrected gamma-ray spectrum each 12 minutes unveil whether fission product fallout or other artificial radioactive nuclides are present. Depending on circumstances the level of detection varies form 0.3 to 0.8 microroentgen per hour. The exposure rate due to natural radioactivity at the locality varies from app. 7 to 9 microroentgen per hour on an annual basis with peaks up to 14 microroentgen per hour caused by radon-daughter washout during heavy rain. (author) 11 refs

  13. Consistent dynamical and statistical description of fission and comparison

    International Nuclear Information System (INIS)

    In order to understand the fission cross section behaviors at the energy range above 20 MeV by neutron induced reactions on actinides, the channel theory of fission with diffusive dynamics is proposed based on Bohr channel theory of fission and Fokker-Planck equation in the way of dynamical and statistical consistent description of fission for excited nuclei. The influence of the details of fission process for nucleus deforming from its ground state to saddle point is properly taking into account in fission width calculation

  14. Light charged particle emission in the fission process

    International Nuclear Information System (INIS)

    Light charged particle (LCP) accompanied fission provides a source of information on the configuration near the acission point. The emission probabilities per fission of alpha particles, tritons and protons have been measured in keV neutron induced fission. Angular distribution of alpha particles emitted in fission was also extracted from measurements with particle telescope. The variations of the yields of these particles with neutron energy have been studied for both equatorial LCP's which are emitted perpendicular to the fission axis and the polar LCP's emitted close to the fission axis. 11 refs.; 1 fig

  15. Nuclear fission induced by heavy ions

    International Nuclear Information System (INIS)

    Because the accelerators of the 50's and 60's mostly provided beams of light ions, well suited for studying individual quantum states of low angular momentum or reactions involving the transfer of one or two nucleons, the study of fission, being an example of large-scale collective motion, has until recently been outside of the mainstream of nuclear research. This situation has changed in recent years, due to the new generation of accelerators capable of producing beams of heavy ions with energies high enough to overcome the Coulomb barriers of all stable nuclei. These have made possible the study of new examples of large-scale collective motions, involving major rearrangements of nuclear matter, such as deep-inelastic collisions and heavy-ion fusion. Perhaps the most exciting development in the past few years is the discovery that dissipative effects (nuclear viscosity) play an important role in fission induced by heavy ions, contrary to earlier assumptions that the viscosity involved in fission was very weak and played only a minor role. This review will be mainly concerned with developments in heavy-ion induced fission during the last few years and have an emphasis on the very recent results on dissipative effects. Since heavy-ion bombardment usually results in compound systems with high excitation energies and angular momenta, shell effects might be expected to be small, and the subject of low energy fission, where they are important, will not be addressed. 285 refs., 58 figs

  16. Physicochemical processes in track of fission recoil

    International Nuclear Information System (INIS)

    An attempt is made to consider in succession the processes involving free electrons in a nuclear fission fragment track. First the dynamic stage of the electron divergence from the primary ionization region is investigated, and the energy carried away by delta-electrons and ''lKcked'' in the vicinity of the track is calculated. Then the interaction between the ''locked'' electrons and ions is considered as well as the mechanism of structural defect formation in solid dielectrics. And, finally, the process is studied of water vapor and carbon dioxide radiolysis in a fission fragment track taking into account ionization, and electronic and oscillatory excitation of molecules by delta-electrons. Analysing the dynamic stage of the electron divergence from the fission fragment track has shown that the energy of ''locked'' electrons increases logarithmically with the density of matter. For the density of a solid it makes up about half of all the fission fragment losses. This energy is sufficient for displacing the lattice ions and for formation of structural defects in solid dielectrics. At lower densities of matter (n0 22 cm-3) the main part of the fission fragment energy is transferred to delta-electrons and spent primarily for ionization, and electronic and oscillatory excitation of the matter molecules. A possibility of using the processes of water vapor- and CO2 radiolysis for production of synthetical fuel and hydrogen is shown to be promising

  17. Further experimental evidence for fast fission

    International Nuclear Information System (INIS)

    Fusion-fission products have been studied for three reactions: Ar+Au, Ar+Bi and Ar+U (5.25-7.5 MeV/u). By measuring symmetric fragmentation components (fission-like events), cross sections for fusion were deduced and compared with the predictions of static and dynamic models. With increasing projectile energy, the width of the mass distributions strongly increases for the two lighter systems. By contrast, for Ar+U it remains essentially constant at a very large value. These results clearly demonstrate that the large increase of the width of the mass distribution cannot be attributed simply to large values of the angular momentum. However, they can be explained by the occurence of a different dissipative process, fast fission, which can be expected if there is no barrier to fission. For the reaction Ar+Au, the total kinetic-energy distributions were also studied in detail. In this case fast fission occurs only at high incident energy. The average total kinetic energy (TKE) was found to be constant with increasing energy whereas the widths of the TKE distribution increase. (orig.)

  18. Fission product decay heat for thermal reactors

    International Nuclear Information System (INIS)

    In the past five years there have been new experimental programs to measure decay heat (i.e., time dependent beta- plus gamma-ray energy release rates from the decay of fission products) following thermal-neutron fission of 235U, 239Pu, and 241Pu for times after fission between 1 and approx. 105 sec. Experimental results from the ORNL program stress the very short times following fission, particularly in the first few hundred sec. Complementing the experimental effort, computer codes have been developed for the computation of decay heat by summation of calculated individual energies released by each one of the fission products. By suitably combining the results of the summation calculations with the recent experimental results, a new Decay Heat Standard has been developed for application to safety analysis of operations of light water reactors. The new standard indicates somewhat smaller energy release rates than those being used at present, and the overall uncertainties assigned to the new standard are much smaller than those being used at present

  19. AMS measurements of fission products at CIAE

    International Nuclear Information System (INIS)

    Fission products are present in special nuclear materials as contaminants remaining from isotope separation or reprocessing, or through ingrowth due to spontaneous and neutron induced fission. The long half-lived fission products (LLFPs) are among the most dangerous radionuclides to the environment. Ultra-high-sensitivity measurement of LLFPs in rocks or soil samples from the fission environment would provide very important information for nuclear safety inspection. The Beijing HI-13-AMS facility with a high terminal voltage of 13 MV is suitable for measuring LLFPs, especially for heavy fission products such as 79Se, 93Zr, 99Tc, 107Pd, 121mSn, 126Sn, 129I and 151Sm. In this paper some new methods developed for AMS measurement of 79Se, 93Zr, 99Tc, 121mSn, 126Sn, 129I and 151Sm are presented. Major features of these methods will be introduced, including the preparation of samples, the selection of target material and the molecular ions extracted from the material in the ion source, as well as the identification and detection of the nuclides to be determined.

  20. Correlation of recent fission product release data

    International Nuclear Information System (INIS)

    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

  1. Some aspects of the nuclear fission process

    International Nuclear Information System (INIS)

    In the following report one can find first a short general view on the present situation of our knowledge concerning the nuclear fission process, namely on the nucleus going through the saddle-point. Then there are some aspects connected with the excitation energy of the fissioning nucleus. The measurements made at Saclay on the fast neutron fission cross-section of U233, U235, Pu239, U238 are described at the beginning of this work. It appears that for U233 there is some characteristic shape modulation of the cross-section curve, in relation with the collective excited state of the deformed nucleus at the saddle-point. Good evidence of this is also given by the study of the relative fission rate with emission of long-range particles; it appears also that this ternary fission rate does not change substantially for neutron between thermal energy and 2 MeV, but that is very lower for the compound nucleus U239 than for even-even compound nuclei. At the end there are some experiments on the strong 4,5 MeV gamma-ray originated by slow neutron absorption in U235. Time-of-flight device is used to establish that this 4,5 MeV gamma-ray seems mostly connected with radiative capture. (author)

  2. Fission fragment escape from bare fission foils: Measurement and comparison with calculations based on the use of the LSS-theory for fission fragment range determination

    International Nuclear Information System (INIS)

    The fission fragment escape fraction from bare 235U, 10% 239Pu/Al and 10% 237Np/Al foils were measured for four selected fission products, relevant for reactor neutron dosimetry, using the absolute radiometric technique. The escape fraction for the foils studied amounts up to 4% for the light fission fragments measured, a non-negligible correction in neutron dosimetry. Attempts for prediction of the fission fragment escape fraction, based on fission fragment range calculations using the LSS-theory accounting for Z2-oscillations, were performed and compared to the measurements. Agreement ranging from 2 to 16% could be achieved. Furthermore, the experimental fission fragment escape fraction measurements were interpreted in terms of fission fragment range determination. (orig.)

  3. Phase Transition Induced Fission in Lipid Vesicles

    CERN Document Server

    Leirer, C; Myles, V M; Schneider, M F

    2010-01-01

    In this work we demonstrate how the first order phase transition in giant unilamellar vesicles (GUVs) can function as a trigger for membrane fission. When driven through their gel-fluid phase transition GUVs exhibit budding or pearl formation. These buds remain connected to the mother vesicle presumably by a small neck. Cooling these vesicles from the fluid phase (T>Tm) through the phase transition into the gel state (Tfission of the neck, while the mother vesicle remains intact. Pearling tubes which formed upon heating break-up and decay into multiple individual vesicles which then diffuse freely. Finally we demonstrate that mimicking the intracellular bulk viscosity by increasing the bulk viscosity to 40cP does not affect the overall fission process, but leads to a significant decrease in size of the released vesicles.

  4. Process for fine purification of fission molybdenum

    International Nuclear Information System (INIS)

    The invention deals with a method for the fine purification of fission molybdenum, dissolved in anionic form together with the anions of the fission products of J, Sn, Ce, Ru, and Zr in an aqueous mineral acid solution; in this process the fission molybdenum is a) fixed on a metal oxide in a sorption step and b) released again in a desorption step. By the invention, a method shall be created, which is, under less favourable working conditions, almost insusceptible to failure and can be safely carried out with low expenditure of operation time, working equipment and handling technique and which delivers a highly pure Mo-99 product with a decreased volume of radioactive waste at the same time. (orig./RB)

  5. Fuel morphology effects on fission product release

    International Nuclear Information System (INIS)

    Results are presented of fission product release behavior observed during four severe fuel damage tests on bundles of UO2 fuel rods. Transient temperatures up to fuel melting were obtained in the tests that included both rapid and slow cooldown, low and high (36 GWd/t) burnup fuel and the addition of Ag-In-Cd control rods. Release fractions of major fission product species and release rates of noble gas species are reported. Significant differences in release behavior are discussed between heatup and cooldown periods, low and high burnup fuel and long- and short-lived fission products. Explanations for the observed differences are offered that relate fuel morphology changes to the releases

  6. Fission Barriers of Compound Superheavy Nuclei

    International Nuclear Information System (INIS)

    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 fission barriers by means of the self-consistent nuclear density functional theory. The relationship between isothermal and isentropic descriptions is demonstrated. Calculations have been carried out for 264Fm, 272Ds, 278112, 292114, and 312124. For nuclei around 278112 produced in 'cold-fusion' reactions, we predict a more rapid decrease of fission barriers with excitation energy as compared to the nuclei around 292114 synthesized in 'hot-fusion' experiments. This is explained in terms of the difference between the ground-state and saddle-point temperatures. The effect of the particle gas is found to be negligible in the range of temperatures studied.

  7. NUCLEAR FISSION PRODUCTS BEHAVIOR IN THE ENVIRONMENT

    Directory of Open Access Journals (Sweden)

    HUSSAM AL-RABAI’AH

    2008-08-01

    Full Text Available The movement of radionuclides from its source, inside reactor containment, and in the environment has been studied with the principal objective of tracing the routes by which they accumulate in the food chain and become available for human consumption. A large number of studies and models were established to explain the fission products behavior within terrestrial and water ecosystems, but a number of behaviors were non understandable, which always attributed to unknown reasons. Deep Atomic Binding (DAB hypothesis suggested that almost all fission products behaviors in terrestrial and water ecosystems could be interpreted in wide coincidence. The gap between former models predictions and field behavior of fission products after accidents like Chernobyl has been explained. DAB represents a tool to reduce radio-phobia as well as radiation protection expenses.

  8. Transport efficiency of fission products in IGISOL

    Science.gov (United States)

    Kudo, H.; Maruyama, M.; Tanikawa, M.; Fujita, M.; Shinozuka, T.; Fujioka, M.

    Two types of double-room target chambers were constructed for effective stopping of fission fragments in ion-guide isotope separator on-line (IGISOL). It was found that the efficiencies for the double-room chambers are about three and four times larger than that for the standard one. The yield/?C decreases with an increase of the beam intensity. The decreasing trends for both chambers quite resemble each other. This fact suggests that the plasma effect remains even in the double-room chambers. Using the charge distribution of fission products obtained by IGISOL, the yield of RI beam was estimated for the proton-induced fission of 238U.

  9. Fission and geosynchronous release of the moon

    Science.gov (United States)

    Grjebine, T.; Marchal, C.

    1980-05-01

    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.

  10. Preparation for storage of fission products

    International Nuclear Information System (INIS)

    A method of preparing waste fission products for storage comprises combining graphite powder and a carbonaceous binder into one component, mixing this component with alpha-silicon carbide, and sprinkling this mixture on to waste fission product particles as the particles are tumbled in the presence of a solvent to form a tacky ''overcoating'' around the particles. The ''overcoated'' particles are warm pressed to form a ''green'' body, then the temperature is raised to carbonize the binder. The body is then heated at an elevated temperature in contact with silicon so as to melt the silicon and impregnate the body, to form a matrix of beta-silicon carbide enclosing the waste fission product particles by reaction-sintering. 6 claims

  11. Antiproton Induced Fission and Fragmentation of Nuclei

    CERN Multimedia

    2002-01-01

    The annihilation of slow antiprotons with nuclei results in a large highly localized energy deposition primarily on the nuclear surface. \\\\ \\\\ The study of antiproton induced fission and fragmentation processes is expected to yield new information on special nuclear matter states, unexplored fission modes, multifragmentation of nuclei, and intranuclear cascades.\\\\ \\\\ In order to investigate the antiproton-nucleus interaction and the processes following the antiproton annihilation at the nucleus, we propose the following experiments: \\item A)~Measurement of several fragments from fission and from multifragmentation in coincidence with particle spectra, especially neutrons and kaons. \\item B)~Precise spectra of $\\pi$, K, n, p, d and t with time-of-flight techniques. \\item C)~Installation of the Berlin 4$\\pi$ neutron detector with a 4$\\pi$ Si detector placed inside for fragments and charged particles. This yields neutron multiplicity distributions and consequently distributions of thermal excitation energies and...

  12. Lunar surface fission power supplies: Radiation issues

    International Nuclear Information System (INIS)

    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 those seen in free space. For a well designed shield, the additional mass required to be brought from earth should be less than 1,000 kg. Detailed radiation transport calculations confirm the feasibility of such a shield

  13. Lunar surface fission power supplies: Radiation issues

    International Nuclear Information System (INIS)

    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

  14. Dissipative dynamics in quasi-fission

    CERN Document Server

    Oberacker, V E; Simenel, C

    2014-01-01

    Quasi-fission is the primary reaction mechanism that prevents the formation of superheavy elements in heavy-ion fusion experiments. Employing the time-dependent density functional theory approach we study quasi-fission in the systems $^{40,48}$Ca+$^{238}$U. Results show that for $^{48}$Ca projectiles the quasi-fission is substantially reduced in comparison to the $^{40}$Ca case. This partly explains the success of superheavy element formation with $^{48}$Ca beams. For the first time, we also calculate the repartition of excitation energies of the two fragments in a dynamic microscopic theory. The system is found in quasi-thermal equilibrium only for reactions with $^{40}$Ca. The differences between both systems are interpreted in terms of initial neutron to proton asymmetry of the colliding partners.

  15. Fission-fragment energy deposition in argon

    International Nuclear Information System (INIS)

    The gas-dynamic response of argon to fission-fragment energy deposition is simulated, for the first time explicitly including the coupling between the gas density, which is spatially and temporally varying, and the power density. In simulations of three experiments with different initial fill pressures of argon, good agreement was found between calculated and observed pressure rises, after the experimental pressure rise data from one case were used as a calibration. However, in each case, the calculated thermal energy deposition corresponding to the experimental pressure data was about half the fission-fragment kinetic energy release into the gas predicted by neutron and fission-fragment transport calculations. Also, the experimental pressure data exhibited a decay not seen in the simulations, which did not incorporate an energy-loss mechanism

  16. Fission product measurement methods. Present state of knowledge

    International Nuclear Information System (INIS)

    Latest state of development of nuclear charge and mass distributions in fission products is presented. A global view (still incomplete) is given using distribution variations in function of number of mass, atomic number and excitation energy of the fissioning nucleus

  17. Fundamental Fission Research with the NIFFTE Time Projection Chamber

    Science.gov (United States)

    Kleinrath, Verena; Niffte Collaboration

    2013-10-01

    The Neutron Induced Fission Fragment Tracking Experiment (NIFFTE) has developed a novel instrument for fission research - a Time Projection Chamber (TPC), which enables detailed tracking of charged particles emitted in neutron-induced fission. While the primary goal of the project is to measure fission cross sections with unprecedented precision, the TPC can also facilitate more fundamental fission studies. The detector's high efficiency (4-pi acceptance) and precise tracking capabilities (including energy deposition) provide a large amount of valuable information. Recent data collected during engineering runs using a U238/U235 target will be used to generate fission fragment angular distributions and yields as a function of incident neutron energy. These experimental results can lend insight into the evolution of nuclear shapes with respect to energy on the path to scission and therefore immediately drive fission theory development. Preliminary angular distributions and yields using the NIFFTE TPC will be presented. Neutron Induced Fission Fragment Tracking Experiment.

  18. New experimental insights into the nuclear fission reaction

    International Nuclear Information System (INIS)

    Experimental results on cold-deformed fragmentation, spontaneous nuclear tripartition, alpha particle associated nuclear fission and on fission fragment kinetic energy fluctuations in resolved neutron resonances are presented and discussed. (orig.)

  19. Cyclin C mediates stress-induced mitochondrial fission and apoptosis

    OpenAIRE

    Wang, Kun; Yan, Ruilan; Cooper, Katrina F.; Strich, Randy

    2015-01-01

    Mitochondria are dynamic organelles that undergo constant fission and fusion cycles. In response to cellular damage, this balance is shifted dramatically toward fission and apoptosis. This work describes the role of the transcription factor cyclin C in mediating both responses.

  20. A device for trapping fission products

    International Nuclear Information System (INIS)

    Description is given of a device for trapping the solid fission products carried by the coolant of a high temperature nuclear reactor, driven through the core, then through the reactor reflector through channels. This device is characterized in that it comprises stacks of balls or cylinders of an adsorbent substances, mounted in housings provided in the reflector. This device can adsorb 99% of the fission products carried by the coolant, without running the risk of re-cycling these products should be a depressurization occur