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1

Geochemical properties and nuclear chemical characteristics of Oklo natural fission reactors

Energy Technology Data Exchange (ETDEWEB)

There are six uranium deposits in the Gabonese Republic in the cnetral Africa. `Fission reactor zone`, the fission chain reactions generated about 200 billion years ago, was existed in a part of them. CEA begun geochemical researches of Oklo deposits etc. in 1991. The geochemical and nuclear chemical properties of Oklo were reviewed from the results of researches. Oklo deposits is consisted of main five sedimentary faces such as sandstone (FA), Black Shale formation (FB), mudstone (FC), tuff (FD) and volcaniclastic sandstone (FE) from the bottom on the base rock of granite in the Precambrian era. Uranium is enriched in the upper part of FA layer and the under part of FB layer. {sup 235}U/{sup 238}U, U content, fission proportion, duration time, neutron fluence, temperature, restitution factor of {sup 235}U and epithermal index ({gamma}) were investigated and compared. The geochemical properties of Oklo are as followed: large enrich of uranium, the abundance ratio of {sup 235}U as same as that of enriched uranium, interaction of natural water and small rear earth elements. These factors made casually Oklo fission reactor. (S.Y.)

Hidaka, Hiroshi [Hiroshima Univ., Higashi-Hiroshima (Japan). Faculty of Science

1997-07-01

2

Oklo: natural fission reactor program. Progress report, July 1-September 30, 1979

International Nuclear Information System (INIS)

Nearly 200 samples were collected at the Oklo mine in Gabon this quarter for shipment to the United States to continue studies of lead, ruthenium, and technetium migration around natural fission reactors. The first analyses of samples collected near a rich uranium ore body in Canada show the presence of radiogenic lead in pyrite and sandstone materials. Analyses of additional samples are underway to permit the interpretation of the data in terms of transport paths. A technique was developed this quarter to eliminate the interference of organic materials during the mass spectrometric analyses of ruthenium in Oklo samples with high asphaltic contents. A proposal was drafted for a study of naturally occurring radionuclide migration at rich uranium ore bodies in Australia to be performed jointly by the US Department of Energy and the Australian Atomic Energy Commission

3

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

4

Migration of fission products into micro-minerals of the Oklo Natural Reactors

International Nuclear Information System (INIS)

Isotopic characterization of two kinds of unique micro inclusions, metallic aggregate and apatite, in reactor core samples at the Oklo uranium ore in Republic of Gabon was studied. In order to investigate the migration and retention mechanism of fission products, in-situ isotopic analyses by secondary ion mass spectrometry (SIMS), and precise isotopic measurements by thermal ionization mass spectrometry (TIMS) and inductively coupled plasma mass spectrometry (ICP-MS) were carried out. The results of isotopic analyses led to the following observations: (1) fissiogenic Ru, Pd and Te are enriched in the micrometallic inclusions, and (2) micro apatites contain fissiogenic alkaline, alkaline earth, and rare earth elements (REE). Moreover, the geochemical behaviour of long-lived radionuclides 99Tc and 137Cs could be estimated from the precise isotopic determination of fissiogenic Ru and Ba, respectively. Fissiogenic REE have fractionated chemically during the migration processes from the uraninite matrix inot an apatite structure. (orig.)

5

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

6

The Oklo reactors: natural analogues to nuclear waste repositories

International Nuclear Information System (INIS)

Natural reactors at Oklo offer a unique opportunity to study the geochemical stability of fission products. Despite high temperatures, large radiation doses and circulating fluids the Oklo minesite successfully contained large quantities of radioactive waste material for some two billion years. Despite the fact that some radioactive species migrated, the actinides remained in-situ. The relevance of the Oklo evidence to high-level waste disposal is stressed

7

Coupled processes at the Oklo Natural reactor

International Nuclear Information System (INIS)

This paper discusses how the Oklo Natural Reactor, Gabon, is an excellent site in which to study, asses, and evaluate coupled processes of interest to radionuclide migration in natural media. The uranium accumulations in which the fission reactions occured are dated at about two Gy (billions of years), and the nuclear reactions lasted for some 500,000 y (plus). Temperatures in the reactor zones were on the order of 300-450C, although local, higher temperatures may have been reached. This thermal regime aided in the diffusion of some fission products, and possibly actinides, from host pitch-blende. Post-reactor diagenesis events have masked some of the radionuclide mThis paper discusses how the Oklo Natural Reactor, Gabon, is an excellent site in which to study, asses, and evaluate coupled processes of interest to radionuclide migration in natural media. The uranium accumulations in which the fission reactions occurred are dated at about two Gy (billions of years), and the nuclear reactions lasted for some 500,000 y (±). Temperatures in the reactor zones were on the order of 300-450 degrees C, although local, higher temperatures may have been reached. This thermal regime aided in the diffusion of some fission products, and possibly actinides, from host pitch-blende. Post-reactor diagenesis events have masked some of the radionuclide migration paths, but most can still be studied.igration paths, but most can still be studied

8

Thermoluminescence and electron-spin resonance studies of the Oklo natural-fission reactor materials

International Nuclear Information System (INIS)

In a previous paper, the authors had concluded that the remarkable thermoluminescence (TL) properties of samples obtained from within the 'reaction zone 2', namely the total absence of natural TL in them and their inability to exhibit artificially induced TL, could be attributed to a high degree of radiation damage suffered by them in the reactor core. By contrast, samples from outside the reaction zone exhibited normal TL properties. In the present investigation, a 'second set' of samples (six in number) are examined, which had been collected from outside the reaction zone. Preliminary geological examination during their selection had indicated that one subset of three samples had a clay matrix very similar to that of the ore of the core, and the second subset of three samples consisted of rich ore but with a very low reaction rate. X-ray fluorescence (XRF), TL, and electron-spin resonance (ESR) studies of the 'second set' have been carried out with a view to ascertaining whether the differences in the TL properties of the in-core and off-core samples in the 'first set' could be attributed to compositional differences rather than to radiation damage. It is found that considerable compositional inhomogeneity exists within the 'second-set' samples. However, on comparing samples in the first and second sets that have broad compositional likeness, it is concluded that the original radiation-damage hypothesis is still tenable. The hypothesis is lent further support by an hypothesis is lent further support by an experiment in which material from two in-core samples of the 'first set' was heated at 10000C for three days and it was observed that the resulting recrystallization enabled these samples to exhibit normal TL. Also, a certain degree of correlation has been found between the ESR and TL properties of each set. (author)

9

?-ray fluxes in Oklo natural reactors

Background: Uncertainty in the operating temperatures of Oklo reactor zones impacts the precision of bounds derived for time variation of the fine structure constant ?. Improved 176Lu/175Lu thermometry has been discussed but its usefulness may be complicated by photoexcitation of the isomeric state 176mLu by 176Lu(?,?') fluorescence.Purpose: We calculate prompt, delayed, and equilibrium ?-ray fluxes due to fission of 235U in pulsed mode operation of Oklo zone RZ10.Methods: We use Monte Carlo modeling to calculate the prompt flux. We use improved data libraries to estimate delayed and equilibrium spectra and fluxes.Results: We find ?-ray fluxes as a function of energy and derive values for the coefficients ??,?' that describe burn-up of 176Lu through the isomeric 176mLu state.Conclusion: The contribution of the (?,?') channel to the 176Lu/175Lu isotopic ratio is negligible in comparison to the neutron burn-up channels. Lutetium thermometry is fully applicable to analyses of Oklo reactor data.

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

2012-11-01

10

The natural reactors of Oklo (Gabun)

International Nuclear Information System (INIS)

The Oklo uranium deposit lies in the precambrian sedimentary series of the Francevillien. It consists of a common, ore-bearing sandstone containing pitchblende and organic matter and of a higher-enriched phyllite largely free of silicium. The reaction zones are located in the latter type. They are located along a tectonic window where the tectonic processes have a noticeable influence. The deposition conditions of the uranium concentrate are presented, and the critical parameters and control mechanisms of the nuclear reactions are discussed. The dispersion aureolas of the depleted uranium and of the greater part of the fission products around the reaction zones are limited, indicating that the original configuration has been maintained. Hints are given on the duration of the chain reaction and the quantities of uranium that participated in it. (orig.)

11

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

12

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

13

Energy Technology Data Exchange (ETDEWEB)

The occurrence of more than 15 natural nuclear Reactor Zones (RZ) in a geological environment remains a mystery even 40 years after their discovery. The present work gives for the first time an explanation of the chemical and physical processes that caused the start-up of the fission reactions with two opposite processes, uranium enrichments and progressive impoverishment in {sup 235}U. Based on Monte-Carlo neutronics simulations, a solution space was defined taking into account realistic combinations of relevant parameters acting on geological conditions and neutron transport physics. This study explains criticality occurrence, operation, expansion and end of life conditions of Oklo natural nuclear reactors, from the smallest to the biggest ones. (authors)

Bentridi, Salah-Eddine [UMR 7517, laboratoire d' hydrologie et de geochimie de Strasbourg, CNRS/universite de Strasbourg, 1, rue Blessig, 67084 Strasbourg (France); Laboratoire de l' energie et des systemes intelligents, CUKM, route de Theniet, El-Hed 44225 (Algeria); Gall, Benoit [UMR 7178, institut pluridisciplinaire Hubert-Curien, CNRS-IN2P3/universite de Strasbourg, 23, rue du Loess, 67037 Strasbourg (France); Gauthier-Lafaye, Francois [UMR 7517, laboratoire d' hydrologie et de geochimie de Strasbourg, CNRS/universite de Strasbourg, 1, rue Blessig, 67084 Strasbourg (France); Seghour, Abdeslam [Centre de recherches nucleaires d' Alger - CRNA, 2, boulevard Frantz-Fanon, 16000 Alger (Algeria); Medjadi, Djamel-Eddine [Ecole normale superieure, Vieux-Kouba, 16050 Alger (Algeria)

2011-11-15

14

The role of mass spectrometry to study the Oklo-Bangombé natural reactors.

The discovery of the existence of chain reactions at the Oklo natural reactors in Gabon, Central Africa in 1972 was a triumph for the accuracy of mass spectrometric measurements, in that a 0.5% anomaly in the (235)U/(238)U ratio of certain U ore samples indicated a depletion in (235)U. Mass spectrometric techniques thereafter played a dominant role in determining the nuclear parameters of the reactor zones themselves, and in deciphering the geochemical characteristics of various elements in the U-rich ore and in the surrounding rock strata. The variations in the isotopic composition of a large number of elements, caused by a combination of nuclear fission, neutron capture and radioactive decay, provide a powerful tool for investigating this unique geological environment. Mass spectrometry can be used to measure the present-day elemental and isotopic abundances of numerous elements, so as to decipher the past history of the reactors and examine the retentivity/mobility of these elements. Many of the fission products have a radioactive decay history that have been used to date the age and duration of the reactor zones, and to provide insight into their nuclear and geochemical behavior as a function of time. The Oklo fission reactors and their near neighbor at Bangombé, some 30 km to the south-east of Oklo, are unique in that not only did they become critical some 2 x 10(9) years ago, but also the deposits have been preserved over this period of geological time. The long-term geochemical behavior of actinides and fission products have been extensively studied by a variety of mass spectrometric techniques over the past 30 years to provide us with significant information on the mobility/retentivity of this material in a natural geological repository. The Oklo-Bangombé natural reactors are therefore geological analogs that can be evaluated in terms of possible radioactive waste containment sites. As more reactor zones were discovered, it was realized that they could be classified into two groups according to their burial depth in the Oklo mine-site. Reactor Zones 10, 13, and 16 were buried more deeply, and were therefore less weathered than the other zones. The less-weathered zones are of great importance in mobility/retentivity studies and therefore to the question of radioactive waste containment. Isotopic studies of these natural reactors are also of value in physics to examine possible variations in fundamental constants over the past 2 billion years. PMID:17583569

De Laeter, J R; Hidaka, H

2007-01-01

15

Gamma-ray fluxes in Oklo natural reactors

Uncertainty in the operating temperatures of Oklo reactor zones impacts the precision of bounds derived for time variation of the fine structure constant $\\alpha$. Improved $^{176}$Lu/$^{175}$Lu thermometry has been discussed but its usefulness may be complicated by photo excitation of the isomeric state $^{176m}$Lu by $^{176}$Lu($\\gamma,\\gamma^\\prime $) fluorescence. We calculate prompt, delayed and equilibrium $\\gamma$-ray fluxes due to fission of $^{235}$U in pulsed mode operation of Oklo zone RZ10. We use Monte Carlo modeling to calculate the prompt flux. We use improved data libraries to estimate delayed and equilibrium spectra and fluxes. We find $\\gamma$-ray fluxes as a function of energy and derive values for the coefficients $\\lambda_{\\gamma,\\gamma^\\prime}$ that describe burn-up of $^{176}$Lu through the isomeric $^{176m}$Lu state. The contribution of the ($\\gamma,\\gamma^\\prime $) channel to the $^{176}$Lu/$^{175}$Lu isotopic ratio is negligible in comparison to the neutron burn-up channels. Lutetium...

Gould, C R; Sonzogni, A A; 10.1103/PhysRevC.86.054602

2012-01-01

16

International Nuclear Information System (INIS)

The natural fission reactors of Oklo consists of a core of uraninite (60%) with fission products, embedded in a pure clay matrix. Thus, the aim of geological, mineral, and geochemical studies of the Oklo Reactors is to assess the behaviour of fission products in an artificial waste depository. Previous studies have shown that Reactor Zone 10, located in the Oklo mine, represents an example for an exceptional confinement of fission products since 2 Ga. In reactor Zone 9, located in Oklo open pit, migrations are more important. Reactor ZOne 13 was influenced by a thermal event due to a doleritic intrusion, located some twenty meters far away, one Ga years after fission reaction operations. In this study,we characterized temperature and redox conditions of fluids by using stable isotopes of uraninites and clays. Moreover mineralogical and chemical characteristics were defined. (author)

17

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

18

International Nuclear Information System (INIS)

The purpose of the study of the Oklo Natural Analogue - Transport in the Reactor for field to identify and model current groundwater flow which may mobilize elements produced in the fossil fission reaction zones. The first important step is to understand the circulation patter, of the water involved in transporting the elements and then to describe the geochemical system by which it is governed. Hydrogeologic studies were carried out at two sites: a deep site at Okelobondo which offers an opportunity to study potential radionuclide migration from the reaction zone, over a distance of 400 m. Through very heterogeneous layers and a superficial site at Bangombe with a more homogeneous layering but situated in a area of meteoric alteration. The rationale and scope of performed field studies are presented together with results of hydrogeological characterization, conceptualizations (at different scales) and results of modelling of groundwater flow and transport. After an overview of the geology and hydrogeology which inspired our treatment of the flow in the near far fields of the reaction zones, the different mathematical models used are described. The Okelobondo site is discussed first. For this site we used a hydrodynamic model together with a model of the migration of natural environmental tracers. The results lead us to propose a flow pattern associated with transfer times between the reaction zone and the surface discharge zone. Then a similar approach is used for Bane. Then a similar approach is used for Bangombe. For this site, we added a geochemistry model describing the migration of uranium in the vicinity of the reaction zone using the METIS, CHIMERE and STELE software, developed in the MIRAGE programme. The isotopic ratio 235U/238U was used as a natural, original, tracer of the reactor zone. (author)

19

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

20

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)

21

Lutetium thermometry for Oklo natural reactors: a new look at old data

Lutetium thermometry has been used to analyze Oklo natural nuclear reactor zones but leads to widely varying and puzzling predictions for the temperatures $T_O$ which in turn impacts bounds on time variation of the fine structure constant $\\alpha$. We revisit results for reactor zone RZ10 in light of new measurements of the isomer branching ratio $B^g$ in $^{175}$Lu neutron capture at 5 and 25 keV. We recalculate predictions for $T_O$ as a function of $B^g$ using realistic m...

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

2012-01-01

22

Thermohydraulic and nuclear modeling of natural fission reactors

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.

Viggato, Jason Charles

23

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

24

Study of ores from the natural nuclear reactor ''OKLO'' by leaching

International Nuclear Information System (INIS)

Mass-spectral and radiochemical methods have been used to investigate ore samples of Oklo deposits upon leaching. Isotope shifts between U235 and U238 in the isotope mixture of uranium separated from the solution upon leaching are observed. This fact results from the 238U(n, 2#betta#)239Pu ? 235U reaction according to the Scillard Chambers effect. Mineralogical investigations of heavy sample fractions are conducted. For the first time visual tracks of natural nuclear reactor activity which consist in formation of isotropic X-ray amorphous mass (''slags'') at the interface of rockforming and uranium minerals are revealed. The quantity of this mass grows as the extent of U235 burnup increases

25

International Nuclear Information System (INIS)

The TSN 206SA Mass Spectrometer has been developed for both routine and research thermal isotopic analysis. Automatic data collection and processing control by a desk top calculator permit an increase of precision on isotopic ratios. A complete control is also available as standard for routine operation. An example of applications is illustrated by a summary of studies made on Oklo Natural Reactor by French Atomic Energy Center Laboratory in Saclay which is equipped with two TSN 206SA Mass Spectrometers. (auth.)

26

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...

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

2006-01-01

27

International Nuclear Information System (INIS)

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 -4x10-17??·/??3x10-17 yr-1. F>-17 yr-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

28

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.

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

2006-12-01

29

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

30

Fullerenes have been reported from diverse geologic environments since their discovery in shungite from Karelian Russia. Our investigation is prompted by the presence of onionskin-like structures in some carbonaceous substances associated with the fossil nuclear fission reactors of Oklo, Gabon. The same series of extractions and the same instrumental techniques, laser desorption ionization and high-resolution mass spectroscopy (electron-impact mass spectroscopy), were employed to test for fullerenes in samples from three different localities: two sites containing putative fullerenes (Sudbury Basin and Russian Karelia) and one new location (Oklo, Gabon). We confirm the presence of fullerenes (C60 and C70) in the Black Tuff of the Onaping Formation impact breccia in the Sudbury Basin, but we find no evidence of fullerenes in shungite samples from various locations in Russian Karelia. Analysis of carbonaceous substances associated with the natural nuclear fission reactors of Oklo yields no definitive signals for fullerenes. If fullerenes were produced during sustained nuclear fission at Oklo, then they are present below the detection limit (˜100 fmol), or they have destabilized since formation. Contrary to some expectations, geologic occurrences of fullerenes are not commonplace.

Mossman, David; Eigendorf, Guenter; Tokaryk, Dennis; Gauthier-Lafaye, François; Guckert, Kristal D.; Melezhik, Victor; Farrow, Catharine E. G.

2003-03-01

31

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)

32

Investigations of the natural fission reactor program. Progress report, October 1977--September 1978

International Nuclear Information System (INIS)

The U.S. study of the Oklo natural reactor began in 1973 with the principal objectives of understanding the processes that produced the reactor and that led to the retention of many of its products. Major facets of the program have been the chemical separation and mass spectrometric analysis of the reactor components and products, the petrological and mineralogical examination of samples taken from the reactor zones, and an interdisciplinary modeling of possible processes consistent with reactor physics, geophysics, and geochemistry. Most of the past work has been on samples taken within the reactor zones. Presently, these studies give greater emphasis to the measurement of mobile products in additional suites of samples collected peripherally and ''downstream'' from the reactor zones. This report summarizes the current status of research and the views of U.S. investigators, with particular reference to the extensive work of the French scientists, concerning the main features of the Oklo natural fission reactor. Also mentioned briefly is the U.S. search for natural fission reactors at other locations

33

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

34

International Nuclear Information System (INIS)

A research contract was agreed between the IAEA and the Centre de Recherches Petrographiques et Geochimiques of Nancy (France) to analyze some aspects of the fluid phases present during diagenesis of the Precambrian Francevillean sandstones of Gabon, which include the Oklo uranium deposit in which because of the geometry of the ore body, the high ore grade, etc., a natural uranium reactor was formed. The investigation was orientated to define some special characteristics of the fluid inclusions and two main methods were applied for this purpose: The Raman spectroscopy (MOLE microsonde) and microthermometric analysis. The main conclusions of the research are the following: 1. The Francevillean sandstones were buried up to a depth of 4-5 km where the corresponding geothermal temperature was of around 2400C but during the Oklo nuclear reaction, the fluid temperatures were higher than 4500C and in at least one case (Zone II) up to 6000C. 2. The tectonic fracturing has favoured the fluid circulation, which was possibly the responsible of the mineral re-concentration after the Oklo nuclear reaction. 3. The diagenetic fluids were essentially aqueous solutions and no sulphur components were identified. 4. The hydrogen presence in a quartz veinlet is surprising and possibly due to water decomposition by strong irradiation

35

Time-variability of alpha from realistic models of Oklo reactors

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 mode...

Gould, C. R.; Sharapov, E. I.; Lamoreaux, S. K.

2007-01-01

36

The Oklo bound on the time variation of the fine-structure constant revisited

It has been pointed out by Shlyakhter that data from the natural fission reactors which operated about two billion years ago at Oklo (Gabon) had the potential of providing an extremely tight bound on the variability of the fine-structure constant alpha. We revisit the derivation of such a bound by: (i) reanalyzing a large selection of published rare-earth data from Oklo, (ii) critically taking into account the very large uncertainty of the temperature at which the reactors operated, and (iii) connecting in a new way (using isotope shift measurements) the Oklo-derived constraint on a possible shift of thermal neutron-capture resonances with a bound on the time variation of alpha. Our final (95% C.L.) results are: -0.9 \\times 10^{-7} <(alpha^{Oklo} - alpha^{now})/alpha <1.2\\times 10^{-7} and -6.7 \\times 10^{-17} {yr}^{-1} < {\\dot alpha}^{averaged}/alpha <5.0\\times10^{-17} {yr}^{-1}.

Damour, Thibault Marie Alban Guillaume; Damour, Thibault; Dyson, Freeman

1996-01-01

37

International Nuclear Information System (INIS)

Until recently, scientists believed that the chemical elements were synthesized only in stars. The discovery of the Oklo phenomenon in the Republic of Gabon in 1972 has revealed, however, that a nuclear ''fire'' had existed on the earth and large-scale transmutations of the elements were occurring on our planet 1.7x109 years ago. The formation of natural (or Pre-Fermi) reactors is closely related to the appearance of life on our planet earth. The Pre-Fermi reactors were probably never formed until about 2x109 years ago, when oxygen was injected into the earth's atmosphere by a new generation of living organisms carrying out photosynthesis. (orig.)

38

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)

39

International Nuclear Information System (INIS)

Events leading up to the discovery during the summer of 1972 of the Oklo fossil reactor in Gabon and its subsequent exploration are reviewed. Results of studies are summarized; future investigations are outlined

40

Oklo reactors and implications for nuclear science

We summarize the nuclear physics interests in the Oklo natural nuclear reactors, focusing particularly on developments over the past two decades. Modeling of the reactors has become increasingly sophisticated, employing Monte Carlo simulations with realistic geometries and materials that can generate both the thermal and epithermal fractions. The water content and the temperatures of the reactors have been uncertain parameters. We discuss recent work pointing to lower temperatures than earlier assumed. Nuclear cross sections are input to all Oklo modeling and we discuss a parameter, the $^{175}$Lu ground state cross section for thermal neutron capture leading to the isomer $^{176\\mathrm{m}}$ Lu, that warrants further investigation. Studies of the time dependence of dimensionless fundamental constants have been a driver for much of the recent work on Oklo. We critically review neutron resonance energy shifts and their dependence on the fine structure constant $\\alpha$ and the ratio $X_q=m_q/\\Lambda$ (where $m_...

Davis, E D; Sharapov, E I

2014-01-01

41

Radioactive wastes in Oklo; Desechos radiactivos en Oklo

Energy Technology Data Exchange (ETDEWEB)

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)

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

2006-07-01

42

International Nuclear Information System (INIS)

Mineralogical and isotopic studies were carried out on the natural nuclear reaction zone 2 from the Oklo deposit to evaluate the mobility of several nuclear reaction products in response to the alteration of the reaction zone and to identify the mechanisms which could retard the transport of released radionuclides. To address these issues, in situ isotopic analyses by SHRIMP and a selective extraction procedure were performed to constrain the structural location of nuclear reaction products (exchangeable and non exchangeable) and their association with mineral phases. The distribution patterns of U, REE, Zr and Mo isotopes reveal that substantial amounts were released from the core and migrated through the hydrothermal alteration halo over metric distances, owing to uraninite dissolution and advective transport by hydrothermal solutions during and soon after criticality. The results emphasize the mobility of Zr at Oklo, this element being often considered as 'immobile' during water-rock interactions. The main output is the demonstration of the net effects of sorption and coprecipitation processes. Chlorite and to a lesser extent illite were found to have adsorbed significant amounts of U, REE, Zr (and probably Th) and less sorbing elements such as Mo. Coprecipitation of secondary UO2 and P-rich coffinite within the alteration halo is also an important means of retardation. The concentration of radionuclides released from the reactor were probably high and t from the reactor were probably high and they display solubility limited transport behaviour. No retention effect was found for Se in the immediate vicinity of the reactor and this element may have moved farther from its source of production. These results have interesting implications for the evaluation of long-term containment of radionuclides. They provide a simple illustration of the performance of a clay barrier in the uptake of radionuclides by sorption onto clays and reincorporation in secondary U-minerals. This study also demonstrates the robustness of these retention processes over extremely long periods of time

43

Oklo reactors and implications for nuclear science

We summarize the nuclear physics interests in the Oklo natural nuclear reactors, focusing particularly on developments over the past two decades. Modeling of the reactors has become increasingly sophisticated, employing Monte Carlo simulations with realistic geometries and materials that can generate both the thermal and epithermal fractions. The water content and the temperatures of the reactors have been uncertain parameters. We discuss recent work pointing to lower temper...

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

2014-01-01

44

International Nuclear Information System (INIS)

Natural nuclear fission reactors are only known in two uranium deposits in the world, the Oklo and Bangombe deposits of the Franceville basin: Gabon. Since 1982, five new reactor zones have been discovered in these deposits and studied since 1989 in a cooperative European program. New geological, mineralogical, and geochemical studies have been carried out in order to understand the behavior of the actinides and fission products which have been stored in a geological environment for more than 2.0 Ga years. The Franceville basin and the uranium deposits remained geologically stable over a long period of time. Therefore, the sites of Oklo and Bangombe are well preserved. For the reactors, two main periods of actinide and radionuclides migration have been observed: during the criticality, under P-T conditions of 300 bars and 400-500 degrees C, respectively, and during a distention event which affected the Franceville basin 800 to 900 Ma ago and which was responsible for the intrusion of dolerite dikes close to the reactors. New isotopic analyses on uranium dioxides, clays, and phosphates allow us to determine their respective importance for the retention of fission products. The UO2 matrix appears to be efficient at retaining most actinides and fission products such as REEs, Y, and Zr but not the volatile fission products (Cd, Cs, Xe, and Kr) nor Rb, Sr, and Ba. Some fissiogenic elements such as Mo, Tc, Ru, Rh, Pd, and Te could have formed metallic and oxide i Te could have formed metallic and oxide inclusion in the UO2 matrix which are similar to those observed in artificial spent fuel. Clays and phosphate minerals also appear to have played a role in the retention of fissiogenic REEs and also of Pu. 82 refs., 21 figs., 12 tabs

45

Ranges of 233U fission fragments in natural elements

International Nuclear Information System (INIS)

By using the theory of Lindhard et al (K. Danske Vidensk Selsk., Mat.-Fys. Meddr. 33:14 (1963)) together with experimental data, a complete set of average ranges of 233U fission fragments in all existing natural elements was evaluated. This set includes ranges for the median light fission fragment, the median heavy fission fragment and the overall median fission fragment for each stopping element. (author)

46

International Nuclear Information System (INIS)

We developed a method allowing the identification of ancient fluid circulations through trace-element patterns in hydrothermal minerals. Application of this technique to Oklo nuclear reactors as natural analogues involves apatite and lanthanides for early circulations, and sulfides and chalcophile elements for late events. At least four different fluid generations have been found, and are tentatively assigned to episodes of Oklo site history. (1) Zr- and U-rich fluids predate criticality near reaction zone 10. (2) Isotopic anomalies of lanthanides provide evidence for mobility of fission products during criticality. Up to now, anomalies are restricted to the near field (desilicified zone around reaction zones). (3) A first pyrite stage is focused around reaction zones, up to a few tens of meters. (4) The latest event is most probably of regional extent. Besides direct evidence of fission-product migration, the present study is expected to provide the geological background and geochemical constraints for modelling ancient fluid circulation and consequent element migration near reaction zones. (orig.)

47

Time-variability of alpha from realistic models of Oklo reactors

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: $ -...

Gould, C R; Lamoreaux, S K

2006-01-01

48

The nature of dynamics of the last stages of the fission process

International Nuclear Information System (INIS)

It is shown that the existing data for the different fissioning nuclei on the proton odd-even effect ?p, conditional charge variance (?Z2(Z:A)) and the light-charged-particle accompanied ternary fission-to-binary fission ratio T/B, can be treated in a coherent way to understand the nature of dynamics that comes into play during the last stages of the fission process through the rupture of the neck joining the nascent fission fragments. (author)

49

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)

50

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.)

51

Energy Technology Data Exchange (ETDEWEB)

The 'Energy plus Transmutation' experimental setup of the Joint Institute for Nuclear Research (JINR), Dubna, Russia, is a lead target surrounded by a natural uranium blanket. A polyethylene plus cadmium shield is placed around the target-blanket assembly to modify the spallation and fission neutron spectra in the system. In this work the spatial distribution of natural uranium fission rate in the assembly and fission rate in the blanket were determined experimentally and compared with Monte Carlo predictions using the MCNPX 2.6C code. Besides neutron-induced fission the calculations include the reactions {sup Nat}U(p, f), {sup Nat}U({pi}, f) and {sup Nat}U({gamma}, f). Good agreements between the experimental and calculations results were obtained. The possible sources of errors in the experiment and calculations are discussed in detail.

Hashemi-Nezhad, S.R. [School of Physics, University of Sydney, A28, NSW 2006 (Australia)], E-mail: reza@physics.usyd.edu.au; Zhuk, Igor; Kievets, M. [Joint Institute of Power and Nuclear Research-Sosny NASB, 220109 Minsk (Belarus); Krivopustov, M.I.; Sosnin, A.N. [Joint Institute for Nuclear Research, 141980 Dubna (Russian Federation); Westmeier, W.; Brandt, R. [Fachbereich Chemie, Philipps University, Marburg (Germany)

2008-07-01

52

The nature of dynamics of the last stages of the fission process

Energy Technology Data Exchange (ETDEWEB)

It is shown that the existing data for the different fissioning nuclei on the proton odd-even effect {delta}{sub p}, conditional charge variance ({sigma}{sub Z}{sup 2}(Z:A)) and the light-charged-particle accompanied ternary fission-to-binary fission ratio T/B, can be treated in a coherent way to understand the nature of dynamics that comes into play during the last stages of the fission process through the rupture of the neck joining the nascent fission fragments. (author)

Bouzid, B.; Djebara, M.; Medkour, M. [Institut de Physique, USTHB, BP El Alia, Bab Ezzouar (Algeria); Asghar, M. [Institut des Sciences Nucleaires, Universite Joseph Fourier, F-38026 Grenoble (France)

1998-05-01

53

Technical Application of Nuclear Fission

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

Denschlag, J. O.

54

Nature of fission-product deposits inside LWR fuel rods

International Nuclear Information System (INIS)

The deposits of fission products observed on the inner clad surfaces of the high fission gas release population of Maine Yankee Core 1 rods and of a low gas release rod from the H.B. Robinson reactor are discussed. Available thermodynamic data are used to provide the basis for a phenomenological model for the formation of the various observed fission product deposits. The relationship between the deposits and the inferred fuel rod chemistry is discussed. 22 refs

55

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

56

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

57

International Nuclear Information System (INIS)

Isotopic compositions of ruthenium from various terrestrial sources were compared between them and with ruthenium from a sample of the meteorite of Canyon Diablo. It was not possible to detect any isotopic anomalies, beyond precision of measurement, this result shows that less than 0.5% of the earth crust uranium participated in Oklo type nuclear reactions, in the hypothesis of a complete rehomogeneization of ruthenium in the earth crust. Chemical and isotopic analysis of fission ruthenium along the SC 36 boring of zone II show a noticeable differenciation between ruthenium and technetium at the time of nuclear reaction and a ruthenium distribution slightly narrower in comparison with that of fission neodymium

58

Implications of the Oklo Phenomenon in a Chiral Approach to Nuclear Matter

It has been customary to use data from the Oklo natural nuclear reactor to place bounds on the change that has occurred in the electromagnetic fine structure constant ? over the last 2 billion years. Alternatively, an analysis could be based on a recently proposed expression for shifts in resonance energies which relates them to changes in both ? and the average m q of the u and d current quark masses, and which makes explicit the dependence on mass number A and atomic number Z. (Recent model independent results on hadronic {?} -terms suggest sensitivity to the strange quark mass is negligible.) The most sophisticated analysis, to date, of the quark mass term invokes a calculation of the nuclear mean-field within the Walecka model of quantum hadrodynamics. We comment on this study and consider an alternative in which the link to low-energy quantum chromodynamics and its pattern of chiral symmetry-breaking is more readily discernible. Specifically, we investigate the sensitivity to changes in the pion mass {M_?} of a single nucleon potential determined by an in-medium chiral perturbation theory ({?} PT) calculation which includes virtual {{?}} -excitations. Subject to some reasonable assumptions about low-energy constants, we confirm that the m q -contribution to resonance shifts is enhanced by a factor of 10 or so relative to the {?} -term and deduce that the Oklo data for Sm imply that {|m_q(Oklo)- m_q(now)| ? 10^{-9}m_q(now)}.

Davis, Edward D.

2014-09-01

59

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

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.

Onegin, M S

2014-01-01

60

Microscopic study of uraniferous ores from Oklo

International Nuclear Information System (INIS)

Three categories of ore can be distinguished at Oklo: (A) Types with carbonaceous matter, observable in sandstone or in conglomeratic rocks with disseminations of pitchblende (colloform UO2) as very small globules in polymerized asphaltic material; (B) Types with uraninite (euhedral UO2) in a clay matrix (chiefly chlorite), the whole being reconstituted or scattered in a microbreccia of a galena almost entirely of radiogenic lead; (C) Intermediate types, containing uraninite and globular pitchblende together, the pitchblende globules being larger than in the case of category A and appearing to have been formed at the expense of the uraninite - the matrix contains phyllites and accessory quartz, sometimes with disseminated carbonaceous materials (asphaltic). Coffinite is often present in the case of categories A and C, but it may have derived from recent processes. Deficiencies in 235U have been observed only in the case of category B. No difference from a mineralogical point of view is observable between ''normal'' massive uraninite ores and those from Oklo, with modified isotopic spectra. In particular, no evidence of significant thermal or mechanical modification has been found

61

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)

62

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

63

A series of laboratory annealing experiments are designed to evaluate the thermal annealing characteristics of fission tracks for a large number of glasses of varying chemical compositions. A comparative study of thermal stability has been made by comparing the calculated value of activation energy (Ea) for each glass. The present investigations suggest that fission tracks in glass samples with a high silica content are more resistant to annealing than those with a low silica content. In addition, the influence of chemical composition on etching characteristics for both synthetic and natural glasses has also been investigated.

Singh-Sandhu, A; Preece, S J

1999-01-01

64

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

65

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

66

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.)

67

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)

68

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.)

69

Investigation of the Fundamental Constants Stability Based on the Reactor Oklo Burn-Up Analysis

The burn-up of few samples of the natural Oklo reactor zones 3, 5 was calculated using the modern Monte Carlo code. We reconstructed the neutron spectrum in the core by means of the isotope ratios: 147Sm/148Sm and 176Lu/175Lu. These ratios unambiguously determine the water content and core temperature. The isotope ratio of the 149Sm in the sample calculated using this spectrum was compared with experimental one. The disagreement between these two values allows one to limit a possible shift of the low lying resonance of 149Sm. Then, these limits were converted to the limits for the change of the fine structure constant ?. We have found out, that for the rate of ? change, the inequality ?rt? {? }/? ?rt<= 5× 10-18 is fulfilled, which is one order higher than our previous limit.

Onegin, M. S.; Yudkevich, M. S.; Gomin, E. A.

2012-12-01

70

Two billion years ago, the increase of oxygen in atmosphere and the high 235U/ 238U uranium ratio (>3%) made possible the occurrence of natural nuclear reactors on Earth. These reactors are considered to be a good natural analogue for nuclear waste disposal. Their preservation during such a long period of time is mainly due to the geological stability of the site, the occurrence of clays surrounding the reactors and acting as an impermeable shield, and the occurrence of organic matter that maintained the environment in reducing conditions, favourable for the stability of uraninite. Hydrogeochemical studies and modelling have shown the complexity of the geochemical system at Oklo and Bangombé (Gabon) and the lack of precise data about uranium and fission products retention and migration mechanisms in geological environments. To cite this article: F. Gauthier-Lafaye, C. R. Physique 3 (2002) 839-849.

Gauthier-Lafaye, François

2002-10-01

71

Natural radioactivity measurements in some Siwalik vertebrates using fission track technique

International Nuclear Information System (INIS)

Uranium, thorium and their daughter products are significant sources of natural radioactivity in the environment. They may constitute health hazard effects if their concentrations are considerably high enough. Uranium and thorium concentrations in the geological samples are helpful for study of environmental pollution, geochemical exploration and for establishing a correlation between uranium and elemental composition of vertebrates. The results of uranium content of some fossil bone samples collected from Siwalik Himalayas are reported in this paper. Uranium concentration of Siwalik vertebrates are estimated by the fission track technique, using solid state nuclear track detectors (SSNTDs). The uranium concentration in these samples has been found to be varying from 20-55 ppm, which is quite low as compared to uranium contents observed in the fossil bones from the uranium mineralised zones. (author)

72

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

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_{p...

Onegin, M. S.

2014-01-01

73

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

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.

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

2012-06-01

74

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

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.

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

75

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%)

76

Implications of the Oklo phenomenon in a chiral approach to nuclear matter

It has been customary to use data from the Oklo natural nuclear reactor to place bounds on the change that has occurred in the electromagnetic fine structure constant $\\alpha$ over the last 2 billion years. Alternatively, an analysis could be based on a recently proposed expression for shifts in resonance energies which relates them to changes in both $\\alpha$ and the average $m_q$ of the $u$ and $d$ current quark masses, and which makes explicit the dependence on mass number $A$ and atomic number $Z$. (Recent model independent results on hadronic $\\sigma$-terms suggest sensitivity to the strange quark mass is negligible.) The most sophisticated analysis, to date, of the quark mass term invokes a calculation of the nuclear mean-field within the Walecka model of quantum hadrodynamics. We comment on this study and consider an alternative in which the link to low-energy quantum chromodynamics (QCD) and its pattern of chiral symmetry-breaking is more readily discernible. Specifically, we investigate the sensitivi...

Davis, Edward D

2014-01-01

77

International Nuclear Information System (INIS)

Real and simulated ILW embedded in cement and bitumen has been subjected to leaching through various binary brines. The resulting solutions containing americium, plutonium, cesium, antimony, ruthenium, cobalt, and strontium have been led through columns packed with the natural Na3? salt rock from the Gorleben salt dome, in order to determine the mobility characteristics of these elements in the near-field range of a projected waste repository in the Gorleben salt dome, specifically for the case of water intrusion. Leaching data and experimental results are explained and discussed, special attention being given to the impact of the pH-value of the systems studied, and to the formation of carrier (or 'pseudo') colloids during radionuclide release. The paper also gives data obtained on the mobility of transuranium elements and fission products, together with information on differences in behaviour of the actinides and the fission products (ruthenium in particular). (orig.)

78

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

79

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

80

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

Energy Technology Data Exchange (ETDEWEB)

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.

Naudet, R. [CEA, Paris (France)

1996-09-01

81

Natural uranium impurities in fission track detectors and associated geocronological parameters

International Nuclear Information System (INIS)

A technique, based in counting neutron induced fission tracks, has been developed for the measurement of uranium impurities in mica. Uranium concentrations of 10-10 and 10-9 (U atom/mica atom) have been measured. As a part of the development of this technique, the mica geological age was also measured, by fossil and induced track detection. The agreement obtained by this method, T = (472+-52) x 106 years with that of (450+-15) x 106 years obtained by the Ar-K technique is satisfactory and is an indirect test of the fission track technique used. A careful analysis of the neutron field parameters and nuclear data used in the age determination was made. This analysis is useful for applications in geocronology. According to this analysis a value of lambdasub(f)=(7.1+-0.1) x 10-17 years-1 is recommended for the spontaneous fission of U238. However, in order to compare the results, the quoted age, T=(472+-52) x 106 years, was obtained with the generally accepted value of lambdasub(f)=(6.85-0.20) x 10-17 years-1 (Fleischer and Price 1964). (author)

82

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.)

83

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

84

Energy Technology Data Exchange (ETDEWEB)

Delayed fission is a nuclear decay process that couples {beta} decay and fission. In the delayed fission process, a parent nucleus undergoes {beta} decay and thereby populates excited states in the daughter. If these states are of energies comparable to or greater than the fission barrier of the daughter, then fission may compete with other decay modes of the excited states in the daughter. In this paper, mechanism and some experiments of the delayed fission will be discussed. (author)

Hatsukawa, Yuichi [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment

1997-07-01

85

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

86

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

87

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

Energy Technology Data Exchange (ETDEWEB)

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 16 refs, 16 figs

Gurban, I.; Laaksoharju, M. [INTERA KB, Sollentuna (Sweden); Ledoux, E.; Made, B.; Salignac, A.L. [Ecole des Mines, Paris (France)

1998-08-01

88

Natural repository analogue program. Progress report, October 1-December 31, 1981

International Nuclear Information System (INIS)

The final draft of a paper entitled The Oklo Reactors: Natural Analogs to Nuclear Waste Repositories has been submitted for publication. This paper discusses the chemical stability of the fossil reactors with respect to uranium, neodymium, ruthenium, and technetium, the transport of elements in the geologic environment at Oklo; and the geochemical conditions that may have influenced these processes. Measurements of barium isotopic ratios limit the abundance of fissiogenic barium to -7 g/g and -6 g/g in two samples peripheral of Oklo reactor zone 9. Samples from the Oklo mines have been sent to Australia for cooperative studies on the geochemistry of palladium, silver, cadmium, tin, and tellurium. Four samples representing a traverse to the east of reactor zone 9 are being analyzed to determine the isotopic composition of molybdenum and ruthenium

89

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.

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

1999-01-01

90

Neutron- and proton-induced fission cross-sections of separated isotopes of tungsten (182W, 183W, 184W, and 186W) and natural tungsten relative to 209Bi have been measured in the incident nucleon energy region 50-200 MeV using fission chambers based on thin-film breakdown counters (TFBC) at quasi-monoenergetic neutrons from the 7Li(p,n) reaction and at the proton beams of The Svedberg Laboratory (TSL), Uppsala University (Uppsala, Sweden). The preliminary experimental data a...

Eismont, V. P.; Filatov, N. P.; Smirnov, A. N.; Soloviev, S. M.; Blomgren, J.; Conde, H.; Prokofiev, A. V.; Mashnik, S. G.

2005-01-01

91

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

Rubchenya, V. A.

2001-10-01

92

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)

93

International Nuclear Information System (INIS)

The nuclear fission process is pedagogically reviewed from a macroscopic-microscopic point of view. The Droplet model is considered. The fission dynamics is discussed utilizing path integrals and semiclassical methods. (L.C.)

94

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.)

95

Energy Technology Data Exchange (ETDEWEB)

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.

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

96

International Nuclear Information System (INIS)

Basic concepts and definitions of the atomic nucleus, binding energy, forces between nucleons, neutron reactions, radioactive decay and nuclear fission are discussed. Fission reactor technology and the utilization of fission energy as a resource are also discussed. The problem of the environment and reactor safety are considered. (R.L.)

97

Natural analogue studies and geochemistry of long lived transuranic actinides and fission products

International Nuclear Information System (INIS)

The initial natural analogue studies at the Cigar Lake uranium deposit were reported at the first RCM in 1988 and additional work has been undertaken since 1989 in co-operation with the Swedish Nuclear Fuel and Waste Management Co. (SKB). Field and laboratory work was carried out on samples of ore, host rock and groundwater and cores from a new drillhole through the ore zone were examined in detail. Two new samples (CS-615 and CS-620) were analyzed by a number of methods including X-ray Photo-electron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), chemical and instrumental analysis. Analysis of plutonium-239, iodine-129 and technetium-99 were carried out at Los Alamos National Laboratory (LANL), as well as iodine-129 at the University of Toronto

98

International Nuclear Information System (INIS)

V.M. STRUTINSKY's semi-classical method is the most precise to determine the energy of the different states along the fission way. The double-humped fission barrier explains fission isomerism. V.M. STRUTINSKY's barrier explains the ''intermediate structure'' observed in the cross section under the threshold; it provides also the observed effect of ''vibrational resonances'' with an interpretation. Taking an asymmetry parameter in consideration, a triple-humped fission barrier seems to be essential now for the light actinides. There is still a microscopic fission barrier to be explained

99

Sorption of 239Np and 235U fission products by zeolite Y, Mexican natural erionite, and bentonite

International Nuclear Information System (INIS)

Zeolite Y, erionite, and bentonite have been used in this work to remove 239Np and 235U fission products from aqueous solutions at various pH values. It was found that the sorption of fission products by aluminosilicates takes place by different mechanisms, mainly ion exchange, precipitation, and electrostatic surface interaction. The radionuclides content was determined by ?-spectrometry, and X-ray diffraction was used to learn whether the solids maintained their crystallinity at different pH values

100

Nature and properties of the fission modes of the neutron deficient 220,224,226Th nuclides

International Nuclear Information System (INIS)

On the U-400 accelerator of FLNR and the Tandem (Catania) by means of a double arm DEMAS spectrometer were measured the mass-energy distributions of fission fragments, the emission of pre- and post-fission neutrons and ?-multiplicity of 220,224,226Th nuclei produced in the reactions 204,208Pb(16O,f) with energies E16O=75, 78, 85, 108 MeV and 208Pb(18O,f) with energies E18O=75, 78 MeV. The range of excitation energies at the saddle point for these nuclei was E*sp=16-40 MeV. The contribution of the asymmetric fission mode characterized by the total yields ratio Ya/Ys increases sharply for heavier isotopes of thorium. Such a behaviour of Ya/Ys is in qualitative agreement with theoretical calculations predicting predominantly symmetric fission for the lightest thorium isotopes and predominantly asymmetric - for heavy ones at low E*sp. The sorted out asymmetric fission mode Ya=Ytot - Ys for all studied isotopes has a complex structure characterized by two components Ya=Ya1 -Ya2 with average masses Ma1 132 and Ma2 139. The energy characteristics of fragments: kinetic energy Ek and its dispersion ?2E for the lowest E*sp also have certain irregularities which are characteristics of the multimodal fission of nuclei - increase of Ek and a peak in ?2E in the region where Ya manifests itself

101

Nuclear data in Oklo and time-variability of fundamental coupling constants

International Nuclear Information System (INIS)

We re-examined Shlyakhter's analysis of the Sm data in Oklo. With a special care of minimizing contamination due to the inflow of the isotope after the end of the reactor activity, we confirmed that his result on the time-variability of the fine-structure constant, |?/?|-17y-1, was basically correct. In addition to this upper bound, however, we obtained another result that indicates a different value of ? 2 billion years ago. We add comments on the recent result from QSO's. (author)

102

To study geochemical processes for migration and fixation of fissiogenic rare earth elements (REE) in association with uranium dissolution, in situ isotopic analyses using an ion microprobe were performed on U- and REE-bearing secondary minerals, such as coffinite, françoisite, uraniferous goethite, and uraninite found in a sandstone layer 30 to 110 cm beneath a natural fission reactor at Bangombé, Gabon. Phosphate minerals such as phosphatian coffinite and françoisite with depleted 235U ( 235U/ 238U = 0.00609 to 0.00638) contained large amount of fissiogenic light REE, while micro-sized uraninite grains in a solid bitumen aggregate have normal U isotopic values ( 235U/ 238U = 0.00725) and small amount of fissiogenic REE components. The proportions of fissiogenic and non-fissiogenic REE components in four samples from the core of BAX03 vary in depth ranging from 30 cm to 130 cm beneath the reactor, which suggests mixing between fissiogenic isotopes from the reactor and non-fissiogenic isotopes from original minerals in the sandstone. Significant chemical fractionation was observed between Ce and the other REE in the secondary minerals, which shows evidence of an oxidizing atmosphere during their formation. Pb-isotopic analyses of individual minerals do not directly provide chronological information because of the disturbance of U-Pb decay system due to recent geologic alteration. However, systematic Pb-isotopic results from all of the minerals reveal the mobilization of fissiogenic isotopes, Pb and U from the reactor in association with dolerite dyke intrusion ˜0.798 Ga ago and the formation of the secondary minerals by mixing event between 2.05 Ga-old original minerals and reactor materials due to recent alteration.

Hidaka, Hiroshi; Janeczek, Janusz; Skomurski, Frances N.; Ewing, Rodney C.; Gauthier-Lafaye, François

2005-02-01

103

International Nuclear Information System (INIS)

Recent experimental results for spontaneous fission half-lives and fission fragment mass and kinetic-energy distributions and other properties of the fragments are reviewed and compared with recent theoretical models. The experimental data lend support to the existence of the predicted deformed shells near Z = 108 and N = 162. Prospects for extending detailed studies of spontaneous fission properties to elements beyond hahnium (element 105) are considered. (orig.)

104

Energy Technology Data Exchange (ETDEWEB)

Zeolite Y, erionite, and bentonite have been used in this work to remove {sup 239}Np and {sup 235}U fission products from aqueous solutions at various pH values. It was found that the sorption of fission products by aluminosilicates takes place by different mechanisms, mainly ion exchange, precipitation, and electrostatic surface interaction. The radionuclides content was determined by {gamma}-spectrometry, and X-ray diffraction was used to learn whether the solids maintained their crystallinity at different pH values.

Olguin, M.T.; Solache, M.; Iturbe, J.L. [Instituto Nacional de Investigaciones Nucleares, C.P. (Mexico)]|[Universidad Autonoma Metropolitana, C.P. (Mexico)] [and others

1996-09-01

105

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

106

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

107

International Nuclear Information System (INIS)

In order to simulate the spallation source target, 3 cm diameter by 1 mm thick disks of natural lead and depleted uranium were irradiated at 1100 MeV proton energy. The targets were inbedded between 5 cm thick bricks of the respective material. Gamma-ray spectrometric methods of gamma-peak and halflife analysis were developed to deduce mass yield distributions of the radionuclides produced. Both for lead and uranium fission products have been observed. The mass yield distributions and axial distributions of some isotopes are given. For lead the total production rates of some isotopes with a 100 x 50 x 450 mm target block are given

108

International Nuclear Information System (INIS)

After a short historical account of superdeformed nuclei which are able to de-excite by spontaneous fission (hence their name of fission isomers) the principles of different experimental set-ups are described. These set-ups were used to study various properties: half-life, excitation energy, spin, gyromagnetic factor, moment of inertia and quadrupole moment. The most significant values are given. Finally, the question of the various types of excited states of fission isomers is tackled. (author) 20 refs.; 17 figs

109

International Nuclear Information System (INIS)

The report treats more fundamental and practical aspects of the fission process. By means of several examples of measurements already done or in execution it is demonstrated that all fission measurements on nuclei with a high thermal cross-section (e.g.235U with O = 587,6 b) are feasable at a typical BR2 neutron beam with a flux of about 107 neutrons/sec.cm2 and a cadmium ratio of about 30. Fission measurements on nuclei such as 231Pa and 237Np e.g. with a cross section of about 20 mb are hardly possible. (author)

110

International Nuclear Information System (INIS)

Fission approach to the cluster radioactivities and ?-decay has been systematically developed during the last two decades. One has to stress the quantum nature of these decay modes and of the fission process as well. The three groups of binary phenomena are taking place by tunneling through a potential barrier. A more complex phenomenon, the ternary fission, was observed since 1946 both in neutron-induced and spontaneous fission. Several such processes, in which the charged particle is a proton, deuteron, triton, 3-6,8 He, 6-11 Li, 7-14 Be, 10-17 B, 13-18 C, 15-20 N, 15-22 O, have been detected. A very powerful technique, based on the fragment identification by using triple ? coincidences in the large arrays of Ge-detectors, like GAMMASPHERE, was employed to discover new characteristics of the fission process, and new decay modes (emission of an alpha particle and of 10 Be, accompanying the cold fission of 252 Cf, the double fine structure, and the triple fine structure in binary and ternary fission, respectively). The possibility of a whole family of new decay modes, the multi-cluster accompanied fission, was recently envisaged. Besides fissioning 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, 20 O, 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, ? + 14 C, 3?, ? + 6 He + 10 Be, 2? + 6 He, 2? + 8 Be, 2? + 14 C, and 4?. The strong shell effect corresponding to the doubly magic heavy fragment 132 Sn was emphasized. From the analysis of different configurations of fragments in touch, we concluded that the most favorable mechanism of such a decay mode should be the cluster emission from an elongated neck formed between the two heavy fragments. The fact that the potential barrier height is lower, suggests that in a competition between aligned and compact configurations, the former should prevail. This idea is further exploited by suggesting a formation mechanism of the touching configuration, based on a three-center phenomenological model. able to explain the difference in the observed yield of a particle-accompanied fission and that of binary fission. It is derived from the Myers-Swiatecki's 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 second minimum, typical for a cluster molecule, appears in the deformation energy. An example is presented for 252 Cf parent nucleus emitting 10 Be and a heavy fragment 132 Sn. The corresponding deformation energy for the binary cold fission of the same nucleus is also shown. We would like to stress two striking features. Besides the first ground state minimum, there is a second minimum, proving the nuclear molecular character of the aligned configuration of three fragments in touch. On the second hand, by comparing the surface areas under the deformation energy curves of the binary and ternary processes, one can see the difference, which can qualitatively explain the difference in yield of the binary and ternary cold fission. (authors)

111

Ternary fission and cluster radioactivities

International Nuclear Information System (INIS)

Ternary fission yield for different kinds of light particle accompanied fission processes is compared to the Q-values for the corresponding cold phenomena, showing a striking correlation. The experimental evidence for the existence of a quasimolecular state in 10 Be accompanied fission of 252 Cf may be explained using a three-center phenomenological model which generates a third minimum in the deformation energy at a separation distance very close to the touching point. This model is a natural extension of the unified approach to three groups of binary decay modes (cold fission, cluster radioactivities and ? decay), illustrated by 234 U decay modes, and the ? valley on the potential energy surfaces of 106 Te. New measurements of cluster decay modes, confirming earlier predictions within analytical superasymmetric fission model, are included in a comprehensive half-life systematics. (authors)

112

International Nuclear Information System (INIS)

Experimental data on such studies as fission isomerism and structure in neutron-induced fission cross sections show how the double-hump fission barrier concept has returned fission to the mainstream of nuclear physics

113

Monte Carlo Based Toy Model for Fission Process

Fission yield has been calculated notoriously by two calculations approach, macroscopic approach and microscopic approach. This work will proposes another calculation approach which the nucleus is treated as a toy model. The toy model of fission yield is a preliminary method that use random number as a backbone of the calculation. Because of nucleus as a toy model hence the fission process does not represent real fission process in nature completely. Fission event is modeled...

Kurniadi, R.; Waris, A.; Viridi, S.

2014-01-01

114

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

115

International Nuclear Information System (INIS)

The measurement of the 176Lu/175Lu ratio in the Oklo uranium ore zones where nuclear reactions have been identified, can be related to the average equilibrium temperature of the neutrons at the time of the nuclear reactions; indeed, the effective neutron capture cross section of the isotope 176Lu is particularly sensitive to temperature. A simple model has been developed to calculate the temperature. The results obtained on seven samples from three reactor zones are presented. From six samples an average value of 280 +- 500C is obtained, corresponding integrated neutron flux tau varies from 0.06 x 1020 to 6 x 1020 n/cm2 and 176Lu/175Lu from 0.0254 to 0.0054. From one sample a very high temperature is obtained: T > 1000C, tau = 4.4 x 1020 n/cm2, 176Lu/175Lu = 0.0032. The validity of this result is sharply dependent on the relative stability of uranium and the rare earths during and after the nuclear reactions; so, it can be noticed that the two samples giving the highest temperatures present a surprisingly high enrichment in heavy rare earth elements. (orig.)

116

International Nuclear Information System (INIS)

The data from the QSO absorption lines indicating a nonzero time-variability of the fine-structure constant has been re-analyzed on the basis of a 'damped-oscillator' fit, as motivated by the same type of behavior of a scalar field, dilaton, which mimics a cosmological constant to understand the accelerating universe. We find nearly as good fit to the latest data as the simple weighted mean. In this way, we offer a way to fit the more stringent result from the Oklo phenomenon, as well

117

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

118

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.)

119

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

120

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

Energy Technology Data Exchange (ETDEWEB)

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-HCO{sub 3} 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 K{sub p} value of 2* 10{sup 6} 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.

Pedersen, K. [ed.

1996-02-01

121

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

122

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

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

2008-04-01

123

Thorium-uranium fission radiography

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

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

1976-01-01

124

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)

125

Energy Technology Data Exchange (ETDEWEB)

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)

Perez Morales, I.

2000-07-01

126

Fifty years of nuclear fission: Nuclear data and measurements series

Energy Technology Data Exchange (ETDEWEB)

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

Lynn, J.E.

1989-06-01

127

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

128

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)

129

Excitation-energy dependence of the nuclear fission characteristics

Energy Technology Data Exchange (ETDEWEB)

It is known that the width parameter of the fragment mass yield distribution follows a beautiful systematics with respect to the excitation energy. According to this systematics, the fission characteristics following the systematics should disappear when the excitation energy Ex goes down to 14 MeV. The present purpose is to elucidate if, where, how and why a transition takes place in the fission characteristics of the asymmetric fission of light actinide elements. Two types of experiments are performed, one is the double-energy measurement of the kinetic energies of complementary fragments in the thermal-neutron fission of {sup 235,233}U and proton-induced fission of {sup 238}U at 13.3- and 15.7-MeV excitations, and the other is the radiochemical study of proton-induced fission and photofission of {sup 238}U at various excitation energies. In conclusion, it has demonstrated that there are two distinctive fission mechanisms in the low-energy fission of light actinide elements and the transition between them takes place around 14-MeV excitation. The characteristics of proton fission and photofission in the energy range lower than the above transition point are the essentially the same as those of thermal-neutron fission and also spontaneous fission. The results of GDR fission indicates the fission in the high-energy side starts from the nuclear collective states, whereas the lower-energy fission is of non-collective nature. It is likely that thermal-neutron fission is rather of the barrier-penetrating type like spontaneous fission than the threshold fission. (S.Y.)

Baba, H.; Saito, T.; Takahashi, N. [Osaka City Univ. (Japan). Faculty of Science] [and others

1996-03-01

130

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

131

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

132

International Nuclear Information System (INIS)

The fission of sodium clusters is discussed using Nuclear Physics method. After presenting the Liquid Drop Model for spherical jelly clusters, we introduce shell corrections and compare the obtained energies with self-consistent quantal results. Fission is studied evaluating Q-values and fission barriers, with the shell correction method and the Two Center Shell Model. The threshold of stability with respect to fission is predicted within the Liquid Drop Model. (author)

133

Directory of Open Access Journals (Sweden)

Full Text Available Fission Research at JRC-IRMM has a longstanding tradition. The present paper is discussing recent investigations of fission fragment properties of 238 U(n,f, 234 U(n,f, prompt neutron emission in fission of 252 Cf(SF as well as the prompt fission neutron spectrum of 235 U(n,f and is presenting the most important results.

Al-Adili A.

2010-03-01

134

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...

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

2006-01-01

135

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

Joy Hakim

2007-08-17

136

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)

137

Model ages in fission-track dating

International Nuclear Information System (INIS)

Since it was realised that incomplete fossil track retention was the cause of anomalously young fission-track (FT) ages, much attention has been paid to the thermal stability of uranium fission tracks in natural minerals. This has led to the establishment of various methods of FT age 'correction' procedures. We report here and in a companion paper the results of a continuous investigation of the stepwise plateau heating methods. (author)

138

Numerical Simulations of Fission

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

Durisen, Richard H.; Gingold, Robert A.

1987-01-01

139

Measurements of alpha particle induced fission of actinide nuclei and fission of the composite system. Yb170 formed in C12 and Ne20 bombardments both show significantly greater neutron emission prior to fission than is consistent with current statistical models. Implications of these results are discussed in the context of possible extreme models: (1) the enhancement of fission at low excitation energies due to shell effects; (2) the inhibition of fission at high excitations due to a limiting of the fission width; and (3) the possibility of significant neutron emission during the descent from saddle to scission. In addition the apparent incompatibility between current models of incomplete fusion processes and the analysis of light heavy ion induced fission which ignore incomplete fusion is discussed.

Britt, H. C.; Gavron, A.

140

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

141

International Nuclear Information System (INIS)

This chapter examines the liquid drop model of fission and compares some of its predictions with experiment. Shows how a synthesis of the liquid drop model and of the shell model can be made using the Strutinsky shell averaging procedure. Presents experimental data related to the existence of shape isomers. Investigates some experimental and theoretical aspects of fission dynamics. Discusses mass distributions, fission barriers, structures in fission cross sections, even-odd effects on charge distributions, experimental consequences of the splitting of the fission barrier, the Thorium anomaly, the origin of shell effects in deformed nuclei, the anisotropic harmonic oscillator case, more general potentials, origin of the asymmetry of fragments mass distributions; the saddle point model; and the scissor point models. Finds that basic understanding of the statics of the fission process is satisfactory and interesting effects are still being found related to the potential energy surfaces. Concludes that the understanding of the fission dynamics is still rather poor

142

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)

143

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)

144

Heavy ions and nuclear fission

International Nuclear Information System (INIS)

This chapter reveals and analyzes various interrelations between fission physics and heavy-ion physics. Heavy ions as a tool to produce novel nuclei fissionable at low excitation energies and to excite novel nuclear states decaying via fission are discussed. Nuclear fission and nucleus-nucleus collisions as large-amplitude collective nuclear motions are considered. Spontaneous fission and the stability of very heavy nuclei are discussed. Experimental data are presented on beta-delayed fission, and some unusual fission properties of very heavy actinide nuclei are examined. The distinguishing features of fission, fast fission, and compound nucleus formation are presented

145

Is channeling of fission tracks taking place?

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.

Yada, K

1999-01-01

146

International Nuclear Information System (INIS)

Data are summed up necessary for determining the yields of individual fission products from different fissionable nuclides. Fractional independent yields, cumulative and isobaric yields are presented here for the thermal fission of 235U, 239Pu, 241Pu and for fast fission (approximately 1 MeV) of 235U, 238U, 239Pu, 241Pu; these values are included into the 5th version of the YIELDS library, supplementing the BIBFP library. A comparison is made of experimental data and possible improvements of calculational methods are suggested. (author)

147

Fission neutron multiplicity calculations

International Nuclear Information System (INIS)

A model for calculating neutron multiplicities in nuclear fission is presented. It is based on the solution of the energy partition problem as function of mass asymmetry within a phenomenological approach including temperature-dependent microscopic energies. Nuclear structure effects on fragment de-excitation, which influence neutron multiplicities, are discussed. Temperature effects on microscopic energy play an important role in induced fission reactions. Calculated results are presented for various fission reactions induced by neutrons. Data cover the incident energy range 0-20 MeV, i.e. multiple chance fission is considered. (author). 28 refs, 13 figs

148

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

149

Energy Technology Data Exchange (ETDEWEB)

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 (m{sup 2}.s{sup -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, A{sub v} (Bq.m{sup -3}) as: D/A{sub v} {approx_equal} 2.10{sup -41} (m{sup 5})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)

Lovera, P.; Ferry, C.; Poinssot, Ch. [CEA Saclay, Dept. de Physico-Chimie (DPC), 91 - Gif sur Yvette (France); Johnson, L. [Nagra, Baden (Switzerland)

2003-07-01

150

International Nuclear Information System (INIS)

A concept for detecting the presence of special nuclear material (235U or 239Pu) concealed in intermodal cargo containers is described. It is based on interrogation with a pulsed beam of 7 MeV neutrons that produce fission events and their ?-delayed neutron emission or ?-delayed high-energy ? radiation between beam pulses provide the detection signature. Fission product ?-delayed ?-rays above 3 MeV are nearly 10 times more abundant than ?-delayed neutrons and are distinct from natural radioactivity and from nearly all of the induced activity in a normal cargo. Detector backgrounds and potential interferences with the fission signature radiation have been identified and quantified

151

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

152

International Nuclear Information System (INIS)

Based on the Fermi gas model, the author suggests a simple model which can reproduce the two-bump structure of the distribution of mass of fission products and the ratio between the probabilities of the most probable and symmetric fission. 7 refs., 1 fig

153

International Nuclear Information System (INIS)

A remotely operable retained fission gas analyser has been designed, fabricated and tested to determine the fission gases Xe and Kr retained in the irradiated fuel. Using the calibration plot, amount of Xe, Kr and He present in a standard gas mixture could be estimated with sufficient accuracies

154

Uranium content of petroleum by fission track technique

International Nuclear Information System (INIS)

The feasibility of the fission track registration technique to investigate the natural uranium concentration in petroleum is examined. The application of this technique to petroleum is briefly described and discussed critically. The results obtained so far indicate uranium concentrations in samples of Brazilian petroleum which are over the detect ion limit of fission track technique. (Author)

155

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

156

Energy Technology Data Exchange (ETDEWEB)

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

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

1989-09-26

157

International Nuclear Information System (INIS)

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

158

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

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

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

2011-10-01

159

International Nuclear Information System (INIS)

A new evaluation of fission cross sections for the 232 Th(n,f) reaction in an extended energy range is proposed. The calculations are performed within the optical model for fission implemented in the code Empire-II. A better description of second and third chance fission is based on detailed analysis of 232 Th(gamma,f) and 230 Th(n,f) processes. The fission barrier of Thorium isotopes is described by a complex potential - the real part is represented by a triple-humped barrier parametrized by five smoothly joined parabolas, and the imaginary part simulates absorption in the isomeric well. The level densities at saddles points are calculated using EMPIRE-specific approach that accounts for collective enhancements and nuclear shape asymmetries. Fission coefficients are calculated in WKB approximation. A good description of the experimental data including the gross resonant structure due to the undamped vibrational states in the tertiary well is obtained. The agreement between the calculated fission cross sections and the measured data represents an indirect proof sustaining the hypothesis of the triple-humped fission barrier in light actinides. (authors)

160

International Nuclear Information System (INIS)

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

161

Fission products experimental programme

Energy Technology Data Exchange (ETDEWEB)

The 'Fission Products (FPs)' experimental programme was carried out from 1998 to 2004 in CEA/Valduc Apparatus B in the framework of the IRSN-AREVA NC Common Interest Program dealing with 'burnup credit' studies. It aims at compensating for the lack of critical experiments with FPs in the literature and validating a selection of 6 stable, non-volatile, fission products representing half of the irradiated fuel absorption of all fission products: {sup 103}Rh, {sup 133}Cs, {sup 143}Nd, {sup 149}Sm, {sup 152}Sm and {sup 155}Gd. This paper provides a more exhaustive approach of the k{sub eff} results, uncertainties and tendencies associated with the different steps of the 'Fission Products' programme. (authors)

Leclaire, N. [Institut de Radioprotection et de Surete Nucleaire IRSN, BP 17, 92262 Fontenay-aux-Roses Cedex (France); Anno, J. [Commissariat a l' Energie Atomique CEA, Institut de Protection et de Surete Nucleaire (CEA/IPSN) (France); Girault, E. [Commissariat a l' Energie Atomique CEA, Centre de Valduc, 21120 Is-Sur-Tille (France); Letang, E. [Institut de Radioprotection et de Surete Nucleaire IRSN, BP 17, 92262 Fontenay-aux-Roses Cedex (France)

2006-07-01

162

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

163

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)

164

Characteristics of Coulomb fission

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...

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

2006-01-01

165

Fission properties of transactinide elements

International Nuclear Information System (INIS)

Nuclear fission properties of transactinide elements were reviewed. Most important parameters describing fission properties are ascribed to masses and kinetic energies of fission fragments. Half-life of spontaneous nuclear fission, and multiplicities and kinetic energies of neutrons emitted from fission are also critical parameters for understanding mechanism of nuclear fission. Cross-sections for the production of transactinide elements are less than 1 nb, and the smallest cross-section is even as small as 1pb. Systematic changes for mass distributions of fission fragments and half-life of spontaneous fission were explored from experimental results accumulated up to now. In light actinide elements, mass distribution of heavy fission fragments peaked at A?140, which unchanged in spite of the change of masses of fertile nuclei, but the peak for light fission fragments depended on the masses of fertile nuclei. A quite different phenomenon was observed in elements with atomic number than Z=100 (Fermium; Fm). For elements with neutronnumbers less than N=156, asymmetric nuclear fission was observed likewise the fission of light actinide elements, but for isotopes with N=158(A=258) or above, symmetric fission became dominant. The correlation between half-life of spontaneous fission and neutron numbers was described in respect to experiments and theoretical predictions. Facilities, accelerators, and detectors used in experiments were summarized in Table for spontaneous nuclear fission of elements with Z>100. (Kazumata, Y.)

166

International Nuclear Information System (INIS)

Although the recently completed fission product yield evaluations constitute a considerable improvement over the older ones, they still do not satisfy all user requirements, mainly due to a lack of manpower. Therefore fission yield evaluators and other experts in this field have established a closer co-operation which resulted in an IAEA Co-ordinated Research Programme (CRP). Each CRP participant has taken up a specific task to contribute to the improvement of the current status of fission yield data. Some of the most important tasks are : further development of semi-empirical models for the prediction of unmeasured or unmeasurable fission yields; resolution of discrepancies among measured data; evaluation of fission yields as a function of incident neutron energy; introduction of correlations and covariances in the evaluation process. The paper includes discussions of the current status and deficiencies of fission yield data, and descriptions of the work of the CRP and the special evaluation tasks to be performed by the CRP participants

167

Induction of nuclear fission by high-voltage application

In nuclear power generation, fissile materials are mainly used. For example, $U^{235}$ is fissile and therefore quite essential for use of nuclear energy. However, the material $U^{235}$ has very small natural abundance less than 1 %. We should seek possibility of utilizing fissionable materials such as $U^{238}$ because natural abundance of such fissionable materials is generally much larger than fissile ones. In this paper, we show that thermal neutrons with vanishing kine...

Maruyama, Hirokazu

2007-01-01

168

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 together with data reported earlier. In the radiochemical method, the total number of fissions were calculated without considering the neutron temperature correction to the 239Pu fission cross-section. This paper presents the results taking into account the effect of neutron temperature on the fission cross-section and gives a comparison of the resulting fission yield values with the latest experimentally determined values and those given in two recent compilations. (orig.)

169

Nucleus-nucleus coherent Bremsstrahlung in 252Cf spontaneous fission

International Nuclear Information System (INIS)

The nature of high energy ?-ray spectra emitted in the spontaneous fission of 252Cf for energies above 10 MeV has been one of the fundamental problems of nuclear fission physics. The yield of the ?-ray in the energy range of 10 - 20 MeV is mainly associated with direct excitation of the giant dipole resonance from the daughter nuclei arising in the fission process. The calculations in different models differ by several orders of magnitude. The discrepancy in experimental and theoretical situations of coherent Bremsstrahlung from nuclear fission requires further investigation. For this reason, an extensive experiment was carried out using 252Cf source to investigate the photon emission accompanying the spontaneous fission at Variable Energy Cyclotron Centre (VECC), Kolkata

170

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

171

Current position on fission product behavior

International Nuclear Information System (INIS)

The following phenomena are treated and modeled: fission product release from fuel, both in-vessel and ex-vessel; fission product deposition in the primary system, fission product deposition in the containment, and fission product revolatization

172

Energy Technology Data Exchange (ETDEWEB)

A model based on energy conservation with a detailed simulation of the cascade neutron emission process from exited fragments was applied for prompt neutron emission calculations. The results for the prompt neutron multiplicity, {nu}(A), the neutron energy, {epsilon}(A), as a function of fission fragment mass A and total kinetic energy (TKE), {nu}(TKE) are compared with available experimental data for the spontaneous fission of {sup 252}Cf, {sup 244,248}Cm and thermal neutron induced fission of {sup 235}U. Several problems connected with the distribution of the available energy between exited fragments and the mechanisms of neutron emission in fission are discussed. The high TKE range >190 MeV is assumed as a possible region for scission neutron emission. In the framework of this assumption, an excellent agreement between experimental and calculated data for the TKE range from 150 MeV to 205 MeV (containing {approx}98% of all fission events) within 1-2% was found for all spontaneously fissioning isotopes mentioned above. An additional unfolding between the calculated results and the rather poor experimental energy resolution improved the agreement also in case of {sup 235}U(n{sub th}, at f). However, one may conclude that in spite of the good agreement between the results of three experimental investigations for {sup 235}U(n{sub th}, at f), they maybe all have similar systematic uncertainties which result in a common observation, namely a very low neutron multiplicity and a positive slope of d{nu}/dE in the low TKE range (<150 MeV)

Kornilov, N.V. [EC-JRC-Institute for Reference Materials and Measurements (IRMM), Retieseweg 111, 2440 Geel (Belgium); Hambsch, F.-J. [EC-JRC-Institute for Reference Materials and Measurements (IRMM), Retieseweg 111, 2440 Geel (Belgium)]. E-mail: franz-josef.hambsch@ec.europa.eu; Vorobyev, A.S. [St. Petersburg Nuclear Physics Institute (PNPI), 188350 Gatchina, Leningrad district (Russian Federation)

2007-06-01

173

International Nuclear Information System (INIS)

In these lectures the liquid drop model of fission is presented and some of its predictions compared with experiment. The liquid drop analogy allows to define in a rather simple and intuitive way a number of useful concepts and possible observables. It is shown 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

174

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

175

Fission gas measuring technology

Energy Technology Data Exchange (ETDEWEB)

Safety and economy of nuclear plant are greatly affected by the integrity of nuclear fuels during irradiation reactor core. A series of post-irradiation examination (PIE) including non-destructive and destructive test is to be conducted to evaluate and characterize the nuclear performance. In this report, a principle of the examination equipment to measure and analyse fission gases existing nuclear fuels were described and features of the component and device consisting the fission gas measuring equipment are investigated. (author). 4 refs., 2 tabs., 6 figs.

Lee, Hyung Kwon; Kim, Eun Ka; Hwang, Yong Hwa; Lee, Eun Pyo; Chun, Yong Bum; Seo, Ki Seog; Park, Dea Gyu; Chu, Yong Sun; Ahn, Sang Bok

1998-02-01

176

Status of fission yield measurements

International Nuclear Information System (INIS)

Fission yield measurement and yield compilation activities in the major laboratories of the world are reviewed. In addition to a general review of the effort of each laboratory, a brief summary of yield measurement activities by fissioning nuclide is presented. A new fast reactor fission yield measurement program being conducted in the US is described

177

Neutron emission at spontaneous fission

International Nuclear Information System (INIS)

Integral and differential characteristics of the emission of spontaneous fission neutrons are considered. There is a discussion of the theoretical aspects and of the experimental investigation of the probability of neutron emission at different stages of the nuclear fission. Data are presented on the energy distribution of californium-252 spontaneous fission neutrons. (author)

178

Microscopic Description of Induced Fission

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.

Schunck, N.

2013-01-01

179

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)

180

International Nuclear Information System (INIS)

The fission product filter for He consists of a winding body composed of two corrugated metal sheets simultaneously wound on a core laterally reversed. It is inserted into an enclosing tube and held at top and bottom by a star-shaped yoke. (orig./PW)

181

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)

182

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

183

Fission modes of mercury isotopes

Recent experiments on beta-delayed fission in the mercury-lead region and the discovery of asymmetric fission in $^{180}$Hg [1] have stimulated renewed interest in the mechanism of fission in heavy nuclei. Here we study fission modes and fusion valleys in $^{180}$Hg and $^{198}$Hg using the self-consistent nuclear density functional theory employing Skyrme and Gogny energy density functionals. We show that the observed transition from asymmetric fission in $^{180}$Hg towards more symmetric distribution of fission fragments in $^{198}$Hg can be explained in terms of competing fission modes of different geometries that are governed by shell effects in pre-scission configurations. The density distributions at scission configurations are studied and related to the experimentally observed mass splits.

Warda, M; Nazarewicz, W

2012-01-01

184

International Nuclear Information System (INIS)

This paper describes a method for measuring ?28, the ratios of fissions in U238 to fissions in U235. The method was developed as a part of the D2O lattice programme at the Massachusetts Institute of Technology (MIT) ; however, it can be used for measurements in any thermal reactor of natural or slightly enriched uranium. The fast fission factor in uranium cannot be measured directly. It is, however, related to ?28 which can be measured: ? =1 + C?28 , where C is a constant involving nuclear properties of U238 and U235: Previous methods of measuring ?28 utilize a comparison of fission-product gamma or beta activity in foils of differing U235 concentration irradiated within a fuel rod in the lattice. A double fission chamber is then used to relate the U238 and U235 fission product activity to the ratio of the corresponding fission rates. Most of the experimental uncertainty associated with the measurement of ?28 a is generally attributed to the fission chamber calibration. The method developed at MIT avoids the need for a fission chamber calibration and is accomplished directly with foils irradiated within a fuel rod in the lattice. Two foils of differing U235 concentration are irradiated and allowed to cool for at least a week. The relative activity of the 1.60 MeV gamma ray of the fission product La140140 is determined for the two foils. This ratio, the foil weights and atomic densities, and the ratio of fission yields ?25/?28 for La140 are then used to determine ?28. This value of ?28 is used to calibrate simpler measurements in which the relative gamma activity above 0.72 MeV is determined for sets of foils irradiated in fuel rods of the lattices of interest. The energy 0.72 MeV is a convenient discrimination level, as it is the maximum energy of Bremsstrahlung from 2.3-d Np239. This method appears to offer the advantages of direct measurement and increased accuracy (the major uncertainty being the ratio of ?25/?28 La140). In addition, the results can be improved as better fission product yield ratio data become available, and the method facilitates comparison of ?28 values obtained by different laboratories. (author). (author)

185

[Fission product yields of 60 fissioning reactions]. Final report

International Nuclear Information System (INIS)

In keeping with the statement of work, I have examined the fission product yields of 60 fissioning reactions. In co-authorship with the UTR (University Technical Representative) Talmadge R. England ''Evaluation and Compilation of Fission Product Yields 1993,'' LA-UR-94-3106(ENDF-349) October, (1994) was published. This is an evaluated set of fission product Yields for use in calculation of decay heat curves with improved accuracy has been prepared. These evaluated yields are based on all known experimental data through 1992. Unmeasured fission product yields are calculated from charge distribution, pairing effects, and isomeric state models developed at Los Alamos National Laboratory. The current evaluation has been distributed as the ENDF/B-VI fission product yield data set

186

Use of Prompt Fission Neutrons for Measuring the Fission Efficiency

The pressing need for high-precision data on neutron-induced reactions of interest for emerging nuclear technologies and nuclear astrophysics has triggered the development of new methods and experiments, especially on capture cross-section measurements of fissile nuclei. In these measurements, radiative capture ?-rays are hidden in a large background of fission ?-rays. The latter has then to be subtracted via a veto method, by detecting fission events with a very good efficiency. This efficiency is limited by the backscattering and the self-absorption of the fission fragments (FF) in the target, and by the alpha radioactivity of the sample. An accurate determination of the fission efficiency is rather difficult. It is often determined by using known fission cross sections if the neutron flux is given. However, in some cases, the fission cross section is not well known and the neutron flux cannot be measured with sufficient accuracy. Another method to determine the fission efficiency is based on the detection of prompt fission neutrons in coincidence or anti-coincidence with the fission detector. Different examples are presented and advantages and disadvantages of this method will be discussed.

Companis, I.; Mathieu, L.; Aïche, M.; Schillebeeckx, P.; Heyse, J.; Barreau, G.; Czajkowski, S.; Ducasse, Q.; Gunsing, F.; Jurado, B.; Kessedjian, G.; Matarranz, J.; Tsekhanovich, I.

187

252Cf fission revisited - new insights into the fission process

International Nuclear Information System (INIS)

?-ray energies and multiplicities and neutron multiplicities from Cf spontaneous fission were measured with NaI detectors in 4? at the Heidelberg-Darmstadt Crystal Ball together with the mass and kinetic energy of the fission fragments. The correlation of neutron multiplicity with fragment mass and kinetic energy is presented and discussed in the context of nascent fragment deformation. The ?-multiplicity unfolded for individual fragments is found to be rather independent of mass. A high-energy component in the ?-spectra is found in the vicinity of symmetric fission. The results are discussed in the framework of current fission models. (orig.)

188

Ternary fission of neutron induced uranium fissioning isomers

International Nuclear Information System (INIS)

Spontaneously fissioning isomers (SFI) of uranium were produced in 236,238U(n, n') reactions at 4.5 MeV mean neutron energy. A pulsed beam electrostatic accelerator was used and a time analysis of fission events was applied. Fission fragments were detected by a scintillation method, and long-range fission particles were detected by an ionization technique. Relative fission probabilities through the SFI state for both the nuclei were determined as (1.30±.01).10-4 in 236U and (1.48±.02).10-4 in 238U case. The SFI half-lives were determined as 121±2 ns and 267±13 ns respectively. As a result of uranium SFI ternary fission study it was observed that one ternary per 163±44 binary fissions of 236mfU and one ternary per 49±14 binary fissions of 238mfU took place. These figures seem to be rather high as compared with nonisomeric ternary fission probability data, and tentative effect of a particular nucleon configuration in the uranium SFI is supposed. (orig.)

189

Ternary fission of uranium fissioning isomers, excited by neutrons

International Nuclear Information System (INIS)

Spontaneously fissioning isomers (SFI) of uranium have been excited in the reactions 236,238U(n, n') at 4.5 MeV mean neutron energy. An electrostatic accelerator with pulsed beam and the time analysis of events have been used. The fission fragments were detected by the scintillation method. Detection of long-range particles was carried out by the ionization method. The relative probability of nuclear fission through the SFI states has been measured: (1.30±0.01)x10-4 (236U) and (1.48±0.02)x10-4 (238U). The decay half-lifes of the isomers have been determined: 121±2 ns (236U SFI) and 267±13 ns (238U SFI). Studying the ternary fission of the uranium SFI have been found that the probability of the process is one ternary per 163±44 binary fissions of 236U SFI and one ternary per 49±14 binary fissions of 238U SFI. Essential increase of the uranium SFI ternary fission probability as compared to the case of ternary fission of nuclei in nonisomeric states may be attributed to a specific nucleon configuration of uranium fissionable isotopes

190

New developments in nuclear fission

International Nuclear Information System (INIS)

A few recently observed new effects in nuclear fission are reviewed from the experimental side and theoretical explanations are indicated: (i) The structures in the mass yields and in the maximum fragment kinetic energies in cold fission are due to Coulomb effects; (ii) Mass-symmetric fission of even-even nuclei does not proceed by splitting the nucleus into two equal parts and the fragments are differently deformed; (iii) The dip in the total fragment kinetic energy at symmetry is due to a different symmetric fission barrier; (iv) In analogy to the cold compact fission events with highest kinetic energy, also those events of lowest kinetic energy but highest deformation are cold at the scission point; (v) Cold fission proceeds close to the saddle point. (orig.)

191

Statistics for fission track analysis

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...

Galbraith, Rex F

2005-01-01

192

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.)

193

Fission decay properties of ultra neutron-rich uranium isotopes

The fission decay of highly neutron-rich uranium isotopes is investigated which shows interesting new features in the barrier properties and neutron emission characteristics in the fission process. ^{233}U and ^{235}U are the nuclei in the actinide region in the beta stability valley which are thermally fissile and have been mainly used in reactors for power generation. The possibility of occurrence of thermally fissile members in the chain of neutron-rich uranium isotopes is examined here. The neutron number N=162 or 164 has been predicted to be magic in numerous theoretical studies carried out over the years. The series of uranium isotopes around it with N=154-172 are identified to be thermally fissile on the basis of the fission barrier and neutron separation energy systematics; a manifestation of the close shell nature of N=162 (or 164). We consider here the thermal neutron fission of a typical representative ^{249}U nucleus in the highly neutron-rich region. Semiempirical study of fission barrier height and width shows that ^{250}U nucleus is stable against spontaneous fission due to increase in barrier width arising out of excess neutrons. On the basis of the calculation of the probability of fragment mass yields and the microscopic study in relativistic mean field theory, this nucleus is shown to undergo exotic decay mode of thermal neutron fission (multi-fragmentation fission) whereby a number of prompt scission neutrons are expected to be simultaneously released along with the two heavy fission fragments. Such properties will have important implications in stellar evolution involving r-process nucleosynthesis.

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

2008-01-01

194

International Nuclear Information System (INIS)

Mass-energy distributions of fragments produced near the fission threshold of 213At have been measured. the experiment reveals a difference between the barrier heights for the asymmetryc and symmetric fission types, Efa-Efs ? 2.5 MeV. the results of the analysis of the experimental data explain an anomalous character of the energy dependence of their yield ratio and confirm the ''valley'' structure of the fission barrier for pre-actinide nuclei which is predicted by theoretical calculations

195

Fission of charged alanine dipeptides

In this work we have performed for the first time a systematic analysis of the dissociation and fission pathways of neutral, singly and doubly charged alanine dipeptide ions with the aim to identify the fission mechanism and the most probable fragmentation channels of these type of molecules. We demonstrate the importance of rearrangement of the molecule structure during the fission process. This rearrangement may include transition to another isomer or a quasi-molecular state before actual separation of the daughter fragments begins.

Yakubovitch, A V; Soloviov, A V; Greiner, W; Yakubovitch, Alexander V.; Solov'yov, Ilia A.; Solov'yov, Andrey V.; Greiner, Walter

2004-01-01

196

Fission in Rapidly Rotating Nuclei

We study the effect of rotation in fission of the atomic nucleus 256Fm using an independent-particle shell model with the mean field represented by a deformed Woods-Saxon potential and the shapes defined through the Cassinian oval parametrization. The variations of barrier height with increasing angular momentum, appearance of double hump in fission path are analysed. Our calculations explain the appearance of double hump in fission path of 256Fm nucleus. The second minimum vanishes with ...

Rhine Kumar, A. K.; Vinay Suram

2014-01-01

197

Fission Yield Predictions with TALYS

International Nuclear Information System (INIS)

The nuclear model code TALYS has been extended to enable the prediction of fission yields. The mass yield curves are extracted from temperature-dependent multi-modal random-neck rupture calculations. Charge yields of the fission fragment are determined using the scission-point model and subsequently folded with the mass yields. We present a comparison of several fission-fragment mass yields and isotopic yields with experimental data

198

Fission hindrance in hot nuclei

International Nuclear Information System (INIS)

The role of dynamics in fission has attracted much interest since the discovery of this process over fifty years ago. However, the study of the dynamical aspects of fission was for many years hampered by the lack of suitable experimental observables against which theoretical calculations could be tested. For example, it was found that the total kinetic energy release in fission can be described equally well by very different dissipation mechanisms, namely the wall formula, that is based on the collisions of the nucleons with the moving wall of the system, as well as a bulk viscosity of the nuclear matter. Although early theoretical work suggested that the fission process may be described as a diffusion process over the fission barrier, this was largely forgotten because of the success of a purely statistical model which instead of enumerating the ultimate final states of the process argues that the fission rate is determined at the open-quote transition state close-quote as the system traverses the fission saddle point. It was therefore significant when Gavron showed that the transition state model was unable to describe the number of neutrons emitted prior to scission at high excitation energy in reactions of 16O+142Nd. Subsequent experimental work using different methods to measure the fission dissipation/viscosity has confirmed these initial observations. It was therefore very surprising when Moretto in recent publications concluded that their analysis of fission excitation functions obtained with a and ? and 3He induced projectiles was perfectly in accord with the transition state model and left no room for fission viscosity. In this paper we'll show that Moretto's analysis is flawed by assuming first chance fission only (in direct contradiction to the experimental observation of pre-scission neutron emission in heavy-ion induced fission), and reveal why the systematics presented by Moretto looked so convincing despite these flaws

199

Hidden systematics of fission channels

Directory of Open Access Journals (Sweden)

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.

Schmidt Karl-Heinz

2013-12-01

200

Fission before K statistical equilibration

International Nuclear Information System (INIS)

For the reaction systems with ?BG, the fissioning nucleus goes through saddle-point to fission with some memories of the entrance-channel plane. In these cases, by taking the relaxation process of K degree of freedom into account, the variance of K distribution, ?K2 is obtained. It is shown that ?K2 exponentially depends on the square of the angular momentum, J2 for the reaction systems with ?BG. Therefore, we have put forward a new version of preequilibrium fission model, and shown the experimental evidence for this new fission mechanism

201

Some aspects of nuclear fission

International Nuclear Information System (INIS)

Fission is still actively studied both from the theoretical and experimental points of view in order to know better the statics and the dynamics of the process. A good knowledge of the fission barrier has been obtained by using the Strutinsky procedure. Good agreement is now reached between double-humped fission barrier heights and experiments, except for light actinides for which the calculated inner hump is too low to explain the fission data. Closer examination of the calculations together with the analysis of the best fission data for 230Th, 231Pa and 232Th neutron-induced fission lead to the conclusion that the fission barrier for 231Th is triple-humped whereas the data for 231Pa and 232Th, though consistent with a triple-humped barrier, do not provide indisputable evidence for its existence. The dynamics, in contrast to the statics, are poorly known. Detailed results have been obtained from the measurements of fragment properties for thermal-neutron induced fission of 235U. These results can be interpreted as moderate dissipation between saddle point and scission. Yet, other recent results obtained from ''cold fragmentation'' in thermal-neutron induced fission in 233U and 235U are not consistent with this hypothesis. Rather, according to recent microscopic calculations of the potential energy surface, cold fragmentation seems to stem from a new mechanism whereby the fissioning nucleus undergoes a sudden shape transition from the fission to the fusion valley. In this respect, cold fragmentation would be similar to the inverse process for heavy-ion fusion

202

International Nuclear Information System (INIS)

Cold fission is defined to be the limiting case of nuclear fission where virtually all of the available energy is converted into the total kinetic energy of the fragments. The fragments have, therefore, to be born in or at least close to their respective ground states. Starting from the viewpoint that cold fission corresponds to most compact scission configurations, energy constraints have been exploited to calculate minimum tip distances between the two nascent fragments in binary fission. Crucial input parameters to this tip model of cold fission are the ground-state deformations of fragment nuclei. It is shown that the minimum tip distances being compatible with energy conservation vary strongly with both the mass and charge fragmentation of the fission prone nucleus. The tip distances refer to nuclei with equivalent sharp surfaces. In keeping with the size of the surface width of leptodermous nuclei, only configurations where the tip distances are smaller than a few fm may be considered as valid scission configurations. From a comparison with experimental data on cold fission this critical tip distance appears to be 3.0 fm for the model parameters chosen. Whenever the model calculation yields tip distances being smaller than the critical value, a necessary condition for attaining cold fission is considered to be fulfilled. It is shown that this criterion allows to understand in fair agreement with experiment which mass fragmentations are susceptible to lead to colgmentations are susceptible to lead to cold fission and which fragment-charge divisions are the most favored in each isobaric mass chain. Being based merely on energy arguments, the model cannot aim at predicting fragment yields in cold fission. However, the tip model proposed appears well suited to delineate the phase space where cold fission phenomena may come into sight. (orig.)

203

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.

204

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 bar ?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 ?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, 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

205

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)

206

Post-scission fission theory: Neutron emission in fission

Energy Technology Data Exchange (ETDEWEB)

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.

Madland, D.G.

1997-11-01

207

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

208

Fission throughout the periodic table

International Nuclear Information System (INIS)

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

209

Fission throughout the periodic table

Energy Technology Data Exchange (ETDEWEB)

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.

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

1989-04-01

210

Shells in superasymmetric nuclear fission

International Nuclear Information System (INIS)

The multimodal approach to fission and the macroscopic-microscopic method for the calculations of charge distribution parameters for isobaric chains have been used to analyze fission product yields. In order to describe the peculiarities of fragment mass curve at very asymmetric mass split, the two narrow fission modes related to the magic numbers Z = 28 and N = 50 were introduced. The reliability of the models predicting power was demonstrated by the agreement between calculated and experimental data on the thermal-neutron-induced fission of actinides. It was found that weight of the fission modes related to the spherical doubly-magic clusters (132Sn or 78Ni) depends on the neutron-to-proton ratio of a compound system

211

Decay modes in spontaneous fission

Spontaneous fission (SF) is considered to be the choice reaction for studying the influence of shell and pairing effects in fission in general, and in particular their impact on the mass and energy distributions of fission fragments. For the time being some 35 SF reactions have been analysed in detail for elements ranging from Pu up to Rf. Going from the lighter to the heavier actinides both, the distributions of fragment mass (or charge) and of total kinetic energy undergo dramatic changes. It is observed in experiment, however, that these distributions may be well described as a superposition of a few fission modes, each with its own characteristic mass an energy pattern. The experimental modes are traced in theory to fine structures in the potential energy surface of a fissioning nucleus, provided shell and pairing corrections to the basic liquid drop model are accounted for.

Gönnenwein, F

1999-01-01

212

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

213

Fission of heavy and superheavy nuclei at low excitation energies

The talk presents the results of an investigation of the main characteristics (mass and energy distributions of fission fragments and multiplicity of neutrons) of the fission of the nuclei of sup 2 sup 2 sup 0 Ra, sup 2 sup 2 sup 6 Th, sup 2 sup 5 sup 6 No, sup 2 sup 7 sup 0 Sg, sup 2 sup 8 sup 6 112 produced in reactions with ions of sup 1 sup 8 O, sup 2 sup 2 Ne and sup 4 sup 8 Ca at energies close to and essentially below the Coulomb barrier. The data obtained show that the form of the mass and energy distributions of the fission fragments of sup 2 sup 2 sup 6 Th and sup 2 sup 7 sup 0 Sg is accounted for by the multimodal nature of the fission. In addition, for sup 2 sup 2 sup 6 Th, a new phenomenon was established: there is a significant difference between the numbers of prescission neutrons for symmetric and asymmetric fission modes. It was found that, for the low-energy fission of the nucleus of sup 2 sup 8 sup 6 112, the mass distribution of the fragments is of a clear-cut asymmetric form, contrary to ...

Itkis, M G; Hanappe, F; Itkis, Y M; Kelic, A; Kondratev, N A; Kozulin, E M; Oganessian, Yu T; Pokrovsky, I V; Prokhorova, E V; Rudolf, G; Rusanov, A Ya; Stuttgé, L

1999-01-01

214

The use of recoil for the separation of uranium fission products

International Nuclear Information System (INIS)

The recoil distance of fission fragments in U3O8 is about 8 microns. By using highly diluted suspensions of uranium oxide particles having dimension much smaller than this figure (mean diameter 0,5 micron), we were able to study the re-adsorption of fission products on uranium oxide. Separation results have been studied as a function of the nature of the irradiation medium (solid or liquid) and the separation medium, of particle size and of concentration of particles in the dispersing medium. Decay curves can be used to discriminate between 239Np and mixed fission products. Most of the 239Np is found in the U3O8 particles. The location of fission products in solid dispersing media has been determined, fission products being found always inside the dispersing medium particles. The results obtained can be applied to the rapid separation of short-lived fission products from a uranium-free starting material. (author)

215

From the ancient times to the present debates on nature and environment, the idea of Nature has been one of the main concepts which interested Geographers. This paper deals with the representations of this idea in the works of thinkers who played a major role in shaping modern Geography, with a special focus on the Mediterranean world. It aims to clarify how Nature was important in defining heuristic strategies of the geographical sciences and their explications of reality. In the first part ...

Ferretti, Federico; Schmidt Di Friedberg, Marcella

2012-01-01

216

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

217

Fission product yields in 238Np thermal fission

International Nuclear Information System (INIS)

Relative cumulative yields for 23 products in the range A=131-155 thermal fission of short-lived odd-odd 238Np nuclide are determined, using mass spectrometric method. The curve of mass yield in the region of heavy product peak is plotted, the absolute yields of the above-mentioned masses and the main parameters of the heavy product peak are evaluated. Irregularities in the curve of fission product mass distribution, observed in the ranges of mass yields A=134-136, A=137-140, A=144 and A=151-152, are explained in the framework of the Wilkins-Steinberg-Chasman statistical model of fission

218

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.)

219

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

220

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

221

International Nuclear Information System (INIS)

This presentation consists of a review of fission-product source terms for light water reactor (LWR) fuel. A source term is the quantity of fission products released under specified conditions that can be used to calculate the consequences of the release. The source term usually defines release from breached fuel-rod cladding but could also describe release from the primary coolant system, the reactor containment shell, or the site boundary. The source term would be different for each locality, and the chemical and physical forms of the fission products could also differ

222

The spectroscopy of fission fragments

Energy Technology Data Exchange (ETDEWEB)

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.

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

223

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

224

Transition from fission to multifragmentation

Energy Technology Data Exchange (ETDEWEB)

Fragment-fragment correlations have been studied in ..cap alpha..-induced reactions to incident enrgies from 70 to 800 MeV/u on Ag, Ho and Au targets. Even at the highest energy binary thermal fission is observed with excitation energies up to 800-900 MeV. In addition, events with mass number around 30 and relative velocities up to twice the values expected for thermal fission occur and are attributed to multifragmentation. The energy deposit rather than the projectile velocity seems to be the parameter governing the appearance of the multifragmentation process which competes strongly with fission for imparted energies beyond 800 MeV.

Klotz-Engmann, G.; Oeschler, H.; Kankeleit, E.; Cassagnou, Y.; Conjeaud, M.; Dayras, R.; Harar, S.; Mostefai, M.; Legrain, R.; Pollacco, E.C.

1987-03-26

225

Transition from fission to multifragmentation

International Nuclear Information System (INIS)

Fragment-fragment correlations have been studied in ?-induced reactions to incident enrgies from 70 to 800 MeV/u on Ag, Ho and Au targets. Even at the highest energy binary thermal fission is observed with excitation energies up to 800-900 MeV. In addition, events with mass number around 30 and relative velocities up to twice the values expected for thermal fission occur and are attributed to multifragmentation. The energy deposit rather than the projectile velocity seems to be the parameter governing the appearance of the multifragmentation process which competes strongly with fission for imparted energies beyond 800 MeV. (orig.)

226

Evaluation of fission product yields

International Nuclear Information System (INIS)

A preliminary fission product yield library has been set up. At present, it contains 10 fissioning systems: U235T, U235F, U235HE, U238F, U238HE, Pu239T, Pu239F, Pu241T, U233T and Th232F, each of them involves 1170 fission product nuclides. For every one of the nuclides, both independent and cumulative yields together with their uncertainties are given. The 10 sets of yield recommended values are compiled in two formats: one, ENDF/B-V; the other, legible form. This paper will summarize the evaluation procedure, and present some resultants compared with ENDF/B-VE yields

227

Experimental fission research at Lucas Heights

International Nuclear Information System (INIS)

An account is given of fission research at the AAEC which includes: 1) measurement of the average number of prompt neutrons per fission event for 252Cf; 2) studies of fission neutrons, fission fragments, kinetic energies and angular distribution which provide information on the properties of the compound nucleus as it proceeds from the saddle point through to scission and beyond. (R.L.)

228

Binary fission origin of the moon

International Nuclear Information System (INIS)

The major arguments for and against the binary fission model of lunar origin are reviewed. Unresolved problems include: (1) how the protoearth acquired sufficient angular velocity to fission, and (2) how the earth-moon system lost its excess angular momentum after fission. Despite these uncertainties, the compositional similarities between the earth's mantle and the bulk moon suggest that the fission model is worth considering. The proposed sequence of events in the formation of the moon by binary fission is given. 54 references

229

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

230

Dynamics of cold fission processes

International Nuclear Information System (INIS)

The neutron-rich 264 Fm should be the best cold-fissioning nucleus, owing to the strong shell effect of the doubly magic fragments 132 Sn. The optimum cold-fission path in the plane of the two independent shape coordinates, the separation distance R and of the radius of the light fragment R2, is determined. Werner-Wheeler inertia tensor and Yukawa-plus-exponential deformation energy are used to calculate the action integral. Microscopic shell and pairing correction ar based on the asymmetric two-center single-particle model. Different variation laws R2 = R2 (R), for the fission trajectory were tested: polynomials of 2nd, 3rd and 4th degree and an exponential function. The partial half-life for cold fission is estimated to be several orders of magnitude shorter than that of ?-decay. (authors)

231

Chemical Production using Fission Fragments

International Nuclear Information System (INIS)

Some reactor design considerations of the use of fission recoil fragment energy for the production of chemicals of industrial importance have been discussed previously in a paper given at the Second United Nations International Conference on the Peaceful Uses of Atomic Energy [A/Conf. 15/P.76]. The present paper summarizes more recent progress made on this topic at AERE, Harwell. The range-energy relationship for fission fragments is discussed in the context of the choice of fuel system for a chemical production reactor, and the experimental observation of a variation of chemical effect along the length of a fission fragment track is described for the irradiation of nitrogen-oxygen mixtures. Recent results are given on the effect of fission fragments on carbon monoxide-hydrogen gas mixtures and on water vapour. No system investigated to date shows any outstanding promise for large-scale chemical production. (author)

232

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

233

Background radiation from fission pulses

Energy Technology Data Exchange (ETDEWEB)

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

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

1988-05-01

234

Protactinium neutron-induced fission up to 200 MeV

Directory of Open Access Journals (Sweden)

Full Text Available The theoretical evaluation of 230-233Pa(n,F cross sections is based on direct data, 230-234Pa fission probabilities and ratios of fission probabilities in first-chance and emissive fission domains, surrogate for neutroninduced fission. First chance fission cross sections trends of Pa are based on consistent description of 232Th(n,F, 232Th(n,2n and 238U(n,F, 238U(n,xn data, supported by the ratio surrogate data by Burke et al., 2006, for the 237U(n,F reaction. Ratio surrogate data on fission probabilities of 232Th(6 Li,4 He234Pa and 232 Th(6 Li,d236U by Nayak et al., 2008, support the predicted 233Pa(n, F cross section at En=11.5-16.5 MeV. The predicted trends of 230-232Pa(n, F cross section up to En=20 MeV, are consistent with fissilities of Pa nuclides, extracted by 232Th(p,F (Isaev et al., 2008 and 232Th(p,3n (Morgenstern et al., 2008 data analysis. The excitation energy and nucleon composition dependence of the transition from asymmetric to symmetric scission for fission observables of Pa nuclei is defined by analysis of p-induced fission of 232Th at Ep=1-200 MeV. Predominantly symmetric fission in 232Th(p,F at En( p=200 MeV as revealed by experimental branching ratios (Dujvestijn et al., 1999 is reproduced. Steep transition from asymmetric to symmetric fission with increase of nucleon incident energy is due to fission of neutron-deficient Pa (A?229 nuclei. A structure of the potential energy surface (a drop of f f symmetric and asymmetric fission barriers difierence (EfSYM - EfASYM from ~3.5 MeV to ~1 MeV of N-deficient Pa nuclides (A?226 and available phase space at outer fission saddles, are shown to be responsible for the sharp increase with En( p of the symmetric fission component contribution for 232Th(p,F and 230-233 Pa(n, F reactions. That is a strong evidence of emissive fission nature of moderately excited Pa nuclides, reliably quantified only up to En( p~20(30 MeV. Predicted fission cross section of 232Pa(n,F coincides with that of 232Th(p,F at En(p?80 MeV, that means that entrance channel dependence of fission cross section with increase of nucleon incident energy diminishes.

Maslov V.

2010-03-01

235

The Microscopic Theory of Fission

Energy Technology Data Exchange (ETDEWEB)

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

Younes, W; Gogny, D

2009-06-09

236

Hidden systematics of fission channels

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 th...

Schmidt Karl-Heinz; Jurado Beatriz

2013-01-01

237

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)

238

Fission modes of mercury isotopes

Background: Recent experiments on ?-delayed fission in the mercury-lead region and the discovery of asymmetric fission in 180Hg [A. N. Andreyev , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.105.252502 105, 252502 (2010)] have stimulated theoretical interest in the mechanism of fission in heavy nuclei.Purpose: We study fission modes and fusion valleys in 180Hg and 198Hg to reveal the role of shell effects in the prescission region and explain the experimentally observed fragment mass asymmetry and its variation with A.Methods: We use the self-consistent nuclear density functional theory employing Skyrme and Gogny energy density functionals.Results: The potential energy surfaces in multidimensional space of collective coordinates, including elongation, triaxiality, reflection-asymmetry, and necking, are calculated for 180Hg and 198Hg. The asymmetric fission valleys—well separated from fusion valleys associated with nearly spherical fragments—are found in both cases. The density distributions at scission configurations are studied and related to the experimentally observed mass splits.Conclusions: The energy density functionals SkM* and D1S give a very consistent description of the fission process in 180Hg and 198Hg. We predict a transition from asymmetric fission in 180Hg toward a more symmetric distribution of fission fragments in 198Hg. For 180Hg, both models yield 100Ru/80Kr as the most probable split. For 198Hg, the most likely split is 108Ru/90Kr in HFB-D1S and 110Ru/88Kr in HFB-SkM*.

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

2012-08-01

239

The microscopic theory of fission

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...

Younes, W.; Gogny, D.

2009-01-01

240

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

Energy Technology Data Exchange (ETDEWEB)

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.

Vogt, R; Randrup, J

2011-09-14

241

Directory of Open Access Journals (Sweden)

Full Text Available Concepción y Valdivia representan dos tipos -aparentemente- opuestos de relación entre el medio urbano y natural. El estudio comparativo de estas ciudades, permite explorar posibles factores de la ocupación urbana, desde la época fundacional hasta fines del siglo XX. Los resultados señalan la persistencia de la traza en la manera en que ambas ciudades se relacionan con su entorno natural. En Concepción el modelo colonial habría inhibido -hasta fines del siglo XX- la valorización del paisaje. En el extremo opuesto, en Valdivia el modelo colonial 'costero' habría favorecido la valorización de los ríos y sus riberas. Por otra parte -en ambas ciudades- la visión utilitaria del paisaje habría sido determinante en la ocupación de zonas de riesgo y modificación del entorno natural. Así, cualidades consideradas 'útiles' para los objetivos urbanos, fueron valorizadas. Y las que representaban un freno para estos objetivos, fueron alteradas por la expansión de la ciudad.

Mar\\u00EDa Isabel L\\u00F3pez Meza

2003-01-01

242

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

243

Measurement of fission gas release from irradiated nuclear fuel elements

International Nuclear Information System (INIS)

A fission gas measurement system for the analysis of released gases from MOX and PHWR fuels has been designed, fabricated and commissioned in the hot cells of Post Irradiation Examination Division of Bhabha Atomic Research Centre, Mumbai. The system was used for the measurement of fission gases released from natural UO2 fuels and ThO2 fuels from PHWRs. The burnups of these fuels ranged from 2 GWD/TeU to 15 GWD/TeU. Some of the results from PHWR fuel elements from Kakrapar Atomic Power Station are presented in the paper, to highlight the utility of the system. (author)

244

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)

245

Chemical reactions of fission products with ethylene using the gas jet technique

International Nuclear Information System (INIS)

An understanding of the nature of the chemical reactions taking place between fission products and their carrier gases, and the designing of a fast separation procedure were the purposes of this investigation. Chemical reactions of short-lived (less than one minute half-life) fission products with carrier gases lead to various chemical species which can be separated in the gas phase. The Gas Jet Facility at the Ford Nuclear Reactor was used to study the yields of volatile selenium and bromine fission products of 235U using a semi-automatic batch solvent extraction technique. Heptane and water were used as organic and inorganic solvents. A carrier gas mixture of ethylene to pre-purified nitrogen (1 : 3) was used to sweep the fission products from the target to the chemistry area for analysis. The results indicated that the volatile selenium products generated by the interaction of selenium fission fragments with ethylene were predominantly organic in nature (84%), possibly organoselenides. The selenium values were used to resolve the fractions of the bromine nuclides, which come from two major sources, viz., directly from fission and from the beta-decay of selenium. The data showed that the fractions of independent bromine fission products in the organic phase were much lower compared to selenium; the bromine values range from 10 to 22% and varied with mass number. Results indicated that the bromine products were inorganic in nature, as possibly hydrogen chlrganic in nature, as possibly hydrogen chloride. ((orig.))

246

International Nuclear Information System (INIS)

The fission product gamma spectra of 233U, 235U, and 239Pu were measured at 12 cooling times following 20,000-s irradiations in the thermal column of the Omega West Reactor. The mean cooling times ranged from 29 s to 146,500 s. The total gamma energies were obtained by integrating over the energy spectra, and both the spectra and the total energies are compared with calculations using the CINDER-10 code and ENDF/B-IV data base. The measured and calculated gamma spectra are compared in a series of figures. The measured total gamma energies are approx. 14% larger than the calculated energies during the earliest counting period (4 s to 54 s cooling time). For 235U, the measured and calculated total gamma energies are nearly the same after 1200 s cooling time, and the measurements are 2% to 6% lower at longer cooling times. For 239Pu, the measured and calculated total gamma energies are nearly the same at cooling times longer than 4,000 s, and for 233U this condition prevails at cooling times longer than 10,000 s. 39 figures, 4 tables

247

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)

248

Separation of fission molybdenum for the production of technetium generators

International Nuclear Information System (INIS)

There are two basically different methods for Mo-99 production: Activation of Mo-98 contained at about 24% in natural isotopic mixtures. Mo-98 enriched targets are irradiated in high-flux reactors in order to achieve the highest possible specific acitivity of the product. Isolation of fission molybdenum from irradiated nuclear fuel targets which have undergone short-term cooling. Maximum fission yields can be attained by irradiation of uranium-235 with the highest possible enrichment. On account of its approximately 1000 times higher specific activity, fission molybdenum has almost replaced worldwide the product fabricated by activation. However, fission molybdenum-99 production has as its prerequisite a suitably advanced technology by which the production process taking place under high activity conditions can be controlled. An integral part of the process consists in the retention of the fission gases the recycling of non-consumed nuclear fuel, and the treatment of the waste streams arising. Ths publication will deal with the individual steps in the process. (orig.)

249

Separation of fission Molybdenum for production of technetium generator

International Nuclear Information System (INIS)

There are two basically different methods for Mo-99 productions: Activation of Mo-99 contained at about 24% in natural isotopic mixtures. Mo-98 enriched targets are irradiated in high-flux reactors in order to achieve the highest possible specific activity of the product. Idolisation of fission molybdenum from irradiated nuclear fuel targets which have undergone short-term cooling. Maximum fission yield can be attained by irradiation of uranium-235 with the highest possible enrichment. On account of its approximately 1000 times higher specific activity. Fission molybdenum has almost replaced worldwide the product fabricated by activation. However, fission molybdenum-99 production has as its prerequisite a suitably advanced technology by which the production process taking place under high activity conditions can be controlled. An integral part of the process consist in the retention of the fission gases the recycling of non-consumed fuel and the treatment of the waste streams arising. This publication will deal with the individual steps in the process

250

The risks of the nuclear fission fuel cycle

International Nuclear Information System (INIS)

An overview is given of the title subject in comparison with other electric power generating techniques. This overview is based on reports from several foreign institutes (UNSCEAR, EPRI, US-DOE, EC, and ORNL) and Dutch institutes (VROM, COVRA, URENCO, and ECN). It appears that the Dutch nuclear power plants (Dodewaard and Borssele) and other installations of the nuclear fission fuel cycle in the Netherlands show a lower individual risk than the risk values estimated by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). The risks, outlined by UNSCEAR, is mainly determined by ore exploration and processing, the reactor operation and the breeder conversion. The total global risk of the nuclear fission fuel cycle (with 200 GWej and 100% recycling) is a factor 10,000 lower than the risk, caused by natural radiation. The main cause of risks of the cycle by accidents are nuclear power plant accidents (varying in the literature from circa 95% to more than 99%). For normal operational conditions nuclear fission, natural gas, wind and thermal solar energy are more favourable than coal, oil and photovoltaic solar cells. It is expected that the use of hydro power (dam collapse and floods) and coal (mine disasters) on average per GWje will cause the largest amount of immediate victims. A separate abstract has been prepared for the appendices in which descriptions are given of all the processes of the nuclear fission fuel cycle: mining and extractear fission fuel cycle: mining and extraction, refining and conversion, enrichment, fission fuel elements fabrication, reactor operation, reprocessing, aboveground storage facilities, ultimate storage, and transport. 4 figs., 14 refs., 2 appendices, 17 refs

251

Neutron dosimetry in fission-track analysis

International Nuclear Information System (INIS)

This paper reports a series of irradiation experiments performed to illustrate the effects of neutron energy on fission-track age determinations. These experiments reveal that errors of several percent can be introduced into an age determination when fluence monitors which contain U in non-natural isotopic ratios and (or) contain Th are used in the irradiations, or when age standards and samples of unknown age are irradiated at different conditions (i.e. with neutrons having different energy spectra). To avoid errors in age determinations it is recommended that all irradiations be performed at identical conditions, preferably with a highly thermalized neutron flux, or that fluence monitors which do not contain Th and which contain U in natural abundances be used in the age-determination process. (author)

252

Fission product solvent extraction

International Nuclear Information System (INIS)

Two main objectives concerning removal of fission products from high-level tank wastes will be accomplished in this project. The first objective entails the development of an acid-side Cs solvent-extraction (SX) process applicable to remediation of the sodium-bearing waste (SBW) and dissolved calcine waste (DCW) at INEEL. The second objective is to develop alkaline-side SX processes for the combined removal of Tc, Cs, and possibly Sr and for individual separation of Tc (alone or together with Sr) and Cs. These alkaline-side processes apply to tank wastes stored at Hanford, Savannah River, and Oak Ridge. This work exploits the useful properties of crown ethers and calixarenes and has shown that such compounds may be economically adapted to practical processing conditions. Potential benefits for both acid- and alkaline-side processing include order-of-magnitude concentration factors, high rejection of bulk sodium and potassium salts, and stripping with dilute (typically 10 mM) nitric acid. These benefits minimize the subsequent burden on the very expensive vitrification and storage of the high-activity waste. In the case of the SRTALK process for Tc extraction as pertechnetate anion from alkaline waste, such benefits have now been proven at the scale of a 12-stage flowsheet tested in 2-cm centrifugal contactors with a Hanford supernatant waste simulant. SRTALK employs a crown ether in a TBP-modified aliphatic kerosene diluent, is economically competitive with other applicable separation processes being considered, and has been successfully tested in batch extraction of actual Hanford double-shell slurry feed (DSSF)

253

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)

254

Assessment of fissionable material behaviour in fission chambers

A comprehensive study is performed in order to assess the pertinence of fission chambers coated with different fissile materials for high neutron flux detection. Three neutron scenarios are proposed to study the fast component of a high neutron flux: (i) high neutron flux with a significant thermal contribution such as BR2, (ii) DEMO magnetic fusion reactor, and (iii) IFMIF high flux test module. In this study, the inventory code ACAB is used to analyze the following questions: (i) impact of different deposits in fission chambers; (ii) effect of the irradiation time/burn-up on the concentration; (iii) impact of activation cross-section uncertainties on the composition of the deposit for all the range of burn-up/irradiation neutron fluences of interest. The complete set of nuclear data (decay, fission yield, activation cross-sections, and uncertainties) provided in the EAF2007 data library are used for this evaluation.

Cabellos, O.; Fernández, P.; Rapisarda, D.; García-Herranz, N.

2010-06-01

255

The measurement of ruthenium in uranium ores and 238U spontaneous fission yields

International Nuclear Information System (INIS)

In the process of evaluating the potential use of ruthenium as a monitor for natural fission reactors, 25 selected samples from known rich uranium ore deposits were analysed for ruthenium. All of the samples gave an isotopic composition which could not be solely attributed to natural ruthenium or from 235U thermal fission. After correction for natural ruthenium, it was concluded that the residual ruthenium was a mixture of ruthenium produced from 238U spontaneous fission and induced 235U thermal fission. For the present, it is assumed that the ruthenium isotopic values which show the greatest divergence from that for 235U thermal fission most closely approximate the ruthenium isotopic distribution for 238U spontaneous fission. The 238U spontaneous fission yields for ruthenium were calculated by normalizing the isotopic abundance of 99Ru to 6.0%. The analysis procedure consists of separating ruthenium from the dissolved ore sample by distillation of the tetraoxide, and measurement using thermal ionization mass spectrometry. As little as a few nanograms of ruthenium can be measured using this technique. For concentration measurements, 96Ru is used as the spike isotope. Details of the chemical separations and mass spectrometry procedure are given. (author)

256

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.

257

International Nuclear Information System (INIS)

Thin films of natural uranium and thorium deposited on muscovite were used as sources of neutron-induced fission fragments. Fragment energy loss in thin-source geometry is negligible. In this way, the observed fragment range results from the interaction of the fragment with the detector material. This characteristic enables the investigation of asymmetric fission and etching, through measurements of projected track length distributions in muscovite micas coupled with thin films. The means and standard deviations of the etchable length distributions of the heavy and light fission-fragment tracks were estimated by fitting a theoretical equation to the experimental data. The light fission-fragment accounts for ?54% and the heavy fission-fragment for ?46% of the etchable length of a full fission track. This average partition is the same for tracks from thermal-neutron-induced fission of 235U and fast-neutron-induced fission of 232Th. The mean etchable length of uranium fission tracks is ?2.5% longer than that of thorium fission tracks. This difference is at the resolution limit of these measurements but correlates with the difference in the mean combined initial kinetic energies of the fission fragments. The mean etchable length of uranium fission tracks in muscovite is ?5% shorter than their calculated latent track length, supporting earlier estimates of a length deficit of this magnitude. The length deficit and the standard deviation of the and the standard deviation of the etchable length distribution of the light fission-fragment tracks are twice the equivalent values for the heavy fission-fragment tracks. This is interpreted in terms of a vt-profile (track etch rate) that depends on the mass of the track-forming particle

258

Fission products measurements in the SLOWPOKE 2 reactor at the University of Toronto

International Nuclear Information System (INIS)

During 1995 and 1996 new measurements on fission and activation products in the water and air of the SLOWPOKE 2 nuclear reactor at the University of Toronto were performed. Due to the age of the fuel, small quantities of fission products are released during normal operation of the reactor. Low concentrations of fission and activation products can be measured in the water and air of the reactor. Studying the behaviour of fission and activation products in their natural conditions inside the reactor is very useful, both for improving the understanding of their real chemical and physical properties and for the development and evaluation of analytical methodologies. Adsorption and desorption of noble gases on charcoal can play an important role during any release of fission and activation products from containment to the atmosphere following a reactor accident. Experiments conducted at the SLOWPOKE 2 Reactor permitted the study of these phenomena

259

Isotopic search for spontaneous fission-produced ruthenium, silver and tellurium in uraninite

Energy Technology Data Exchange (ETDEWEB)

Isotopic compositions of Ru, Te and Ag in several types of uraninite sample were determined by thermal ionization mass spectrometry in order to elucidate the spontaneous fission phenomenon of uranium. Ru and Te in a few samples show clear isotopic anomalies for [sup 99]Ru, [sup 101]Ru, [sup 102]Ru, [sup 104]Ru, [sup 128]Te and [sup 130]Te because of probable addition of spontaneous fission fragments to natural isotopes, while no significant evidence of fissiogenic Ag could be obtained from the isotopic measurements of Ag because of its low fission yield. The fission pattern of Ru obtained from one uraninite, Morogoro (Tanzania), indicates the possibility that this uraninite had reached a critical condition for neutron-induced fission of [sup 235]U.

Hidaka, Hiroshi (Department of Chemistry, Tokyo Metropolitan University, Hachioji, Tokyo (Japan)); Masuda, Akimasa (Department of Chemistry, University of Electro-communications, Chofu, Tokyo (Japan))

1993-05-05

260

Change over from compound nuclear fission to quasi-fission

Directory of Open Access Journals (Sweden)

Full Text Available 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.

Bhattacharya P.

2010-03-01

261

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)

262

Fission fragment angular distribution and fission cross section validation

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...

Leong, Lou Sai

2013-01-01

263

Experimental approach to fission process of actinides

Energy Technology Data Exchange (ETDEWEB)

From experimental views, it seems likely that the mechanism of nuclear fission process remains unsolved even after the Bohr and Weeler`s study in 1939. Especially, it is marked in respect of mass distribution in unsymmetric nuclear fission. The energy dependency of mass distribution can be explained with an assumption of 2-mode nuclear fission. Further, it was demonstrated that the symmetrical fission components and the unsymmetrical ones have different saddle and fission points. Thus, the presence of the 2-mode fission mechanism was confirmed. Here, transition in the nuclear fission mechanism and its cause were investigated here. As the cause of such transition, plausible four causes; a contribution of multiple-chance fission, disappearance of shell effects, beginning of fission following collective excitation due to GDR and nuclear phase transition were examined in the condition of excitation energy of 14.0 MeV. And it was suggested that the transition in the nuclear fission concerned might be related to phase transition. In addition, the mechanism of nuclear fission at a low energy and multi-mode hypothesis were examined by determination of the energy for thermal neutron fission ({sup 233,235}U and {sup 239}Pu) and spontaneous nuclear fission ({sup 252}Cf). (M.N.)

Baba, Hiroshi [Osaka Univ., Toyonaka (Japan). Faculty of Science

1997-07-01

264

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

265

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.)

266

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")

267

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

268

Fission yields: measurement techniques and data status

International Nuclear Information System (INIS)

Techniques for the measurement of absolute and relative fission yields are reviewed. The preferred techniques are isotope dilution mass spectrometric measurement of the individual fission products and the heavy-element mass difference or the fission product summation method to establish the number of fissions. The accuracy of most thermal fission yields appears adequate, and the status of the various yield compilations is reviewed. For fast fission yields, the data are not nearly so well established. For many heavy nuclides, fast-fission yield data are nearly nonexistent. Because fast-fission yields change with neutron energy, it is imperative that fast yield data be evaluated as a function of neutron energy to generate the most complete and accurate compilation. 4 figures, 1 table

269

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

270

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)

271

Absolute calibration technique for spontaneous fission sources

International Nuclear Information System (INIS)

An absolute calibration technique for a spontaneously fissioning nuclide (which involves no arbitrary parameters) allows unique determination of the detector efficiency for that nuclide, hence of the fission source strength

272

Non-equilibrium processes in Heavy-ion induced Fission Reactions

Heavy ion induced reactions offer a wide range of possibilities in exploring the collective behavior of nuclei and nuclear processes. Recent years have seen a spurt in the experimental and theoretical studies to understand the mechanism of the fission process in heavy target projectile systems, arising from the interest to produce elements in the superheavy region. A number of new features are observed experimentally with respect to the kinetic energy, mass and angular distributions of fission fragments and their correlations, implying prevalence of non-equilibrium phenomena in the fission process in many target projectile systems. There are many theoretical attempts both in terms of static potential energy considerations and dynamics to understand the important degrees of freedom that govern the evolution of the nuclear system from initial interaction to the final fission stages. Depending on the degree and nature of equilibration, various processes such as fast-fission, quasi-fission and pre-equilibrium fission have been invoked that can compete with the fully equilibrated compound nuclear fission process. In what we call a C-T Fissility plot, we show the remarkable dependence of the onset of these non-equilibrium processes on the entrance channel parameters.

Choudhury, R. K.; Thomas, R. G.

2011-02-01

273

The VERDI fission fragment spectrometer

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...

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

2013-01-01

274

Heavy-element fission barriers

International Nuclear Information System (INIS)

We present calculations of fission properties for heavy elements. The calculations are based on the macroscopic-microscopic finite-range liquid-drop model with a 2002 parameter set. For each nucleus we have calculated the potential energy in three different shape parametrizations: (1) for 5 009 325 different shapes in a five-dimensional deformation space given by the three-quadratic-surface parametrization, (2) for 10 850 different shapes in a three-dimensional deformation space spanned by ?2, ?4, and ? in the Nilsson perturbed-spheroid parametrization, supplemented by a densely spaced grid in ?2, ?3, ?4, and ?6 for axially symmetric deformations in the neighborhood of the ground state, and (3) an axially symmetric multipole expansion of the shape of the nuclear surface using ?2, ?3, ?4, and ?6 for intermediate deformations. For a fissioning system, it is always possible to define uniquely one saddle or fission threshold on the optimum trajectory between the ground state and separated fission fragments. We present such calculated barrier heights for 1585 nuclei from Z=78 to Z=125. Traditionally, actinide barriers have been characterized in terms of a ''double-humped'' structure. Following this custom we present calculated energies of the first peak, second minimum, and second peak in the barrier for 135 actinide nuclei from Th to Es. However, for so from Th to Es. However, for some of these nuclei which exhibit a more complex barrier structure, there is no unique way to extract a double-humped structure from the calculations. We give examples of such more complex structures, in particular the structure of the outer barrier region near 232Th and the occurrence of multiple fission modes. Because our complete results are too extensive to present in a paper of this type, our aim here is limited: (1) to fully present our model and the methods for determining the structure of the potential-energy surface, (2) to present fission thresholds for a large number of heavy elements, (3) to compare our results with the two-humped barrier structure deduced from experiment for actinide nuclei, and (4) to compare to additional fission-related data and other fission models.

275

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)

276

Ballistic piston fissioning plasma experiment.

The production of fissioning uranium plasma samples such that the fission fragment stopping distance is less than the dimensions of the plasma is approached by using a ballistic piston device for the compression of uranium hexafluoride. The experimental apparatus is described. At room temperature the gun can be loaded up to 100 torr UF6 partial pressure, but at compression a thousand fold increase of pressure can be obtained at a particle density on the order of 10 to the 19th power per cu cm. Limited spectral studies of UF6 were performed while obtaining the pressure-volume data. The results obtained and their implications are discussed.

Miller, B. E.; Schneider, R. T.; Thom, K.; Lalos, G. T.

1971-01-01

277

Search for Singlet Fission Chromophores

Energy Technology Data Exchange (ETDEWEB)

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

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

2012-01-01

278

International Nuclear Information System (INIS)

In this paper the author presents the problems of the radioactive wastes generated by the nuclear fission. The first part devoted to the fission phenomenon explains the incident neutron energy and the target nuclei role. The second part devoted to the nuclear wastes sources presents the production of wastes upstream of the reactors, in the reactors and why these wastes are dangerous. The third part discusses the radioactive wastes management in France (classification, laws). The last part details the associated research programs: the radionuclides separation, the disposal, the underground storage, the transmutation and the thorium cycle. (A.L.B.)

279

Ternary fission of uranium induced by 414 MeV Ar-ions as studied with a hole detector

International Nuclear Information System (INIS)

The ratio of ternary fission to binary fission is determined to be (2.4 +- 1.0%) in the interaction of uranium with 414 MeV Ar-ions. The results are obtained by applying a new experimental technique: the hole detector in mica as suggested by Starke. This new technique is tested with binary fission of natural uranium, induced with thermal neutrons. Furthermore, some angular distributions of fission fragments are measured and some recent theoretical developments are discussed in a qualitative manner. (orig.)

280

International Nuclear Information System (INIS)

Measurements and regression analysis of mass-energy distributions of fragments from 213At, 210Po, and 205Bi fission have been made. The results have proved three-component structure of fragment kinetic energy spectra. The nature of the phenomenon and its similarity to recently observed bimodal spontaneous fission of nuclei in the vicinity of Fm are discussed

281

Production techniques of fission 99Mo

International Nuclear Information System (INIS)

Generally two different techniques are available for molybdenum-99 production for use in medical technetium-99 generation. The first one is based on neutron irradiation of molybdenum targets of natural isotopic composition or enriched in molybdenum-98. In these cases the Mo-99 is generated via the nuclear reaction 98Mo (n,?) 99Mo. Although this process can be carried out at low expenditure it gives a product of low specific activity and, hence, restricted applicability. In a second process Mo-99 is obtained as a result of the neutron induced fission of U-235 according to 235U (n,f) 99Mo. This technique provides a product with a specific activity several orders of magnitude higher than that obtained from the 98Mo (n,?) 99Mo nuclear reaction and perhaps even more important up to several thousands curies of Mo-99 per production run. In this paper a modern production procedure of Mo-99 via the fission reaction, which was developed at the Institute of Radiochemistry of the Nuclear Research Centre Karlsruhe will be described. The targeting, irradiation of U-235, the separation and purification steps involved as well as the recycling of the non-converted U-235, which should be a major consideration in any production technique, will be discussed. (author). 24 refs, 14 figs, 1 tab

282

Fission-fusion dynamics: New research frameworks

Renewed interest in fission-fusion dynamics is due to the recognition that such dynamics may create unique challenges for social interaction and distinctive selective pressures acting on underlying communicative and cognitive abilities. New frameworks for integrating current knowledge on fission-fusion dynamics emerge from a fundamental rethinking of the term "fission- fusion" away from its current general use as a label for a particular modal type of social system (i.e., "fission-fusion soci...

Aureli, F.; Schaffner, Cm; Boesch, C.; Bearder, Sk; Call, J.; Chapman, Ca; Connor, R.; Di Fiore, A.; Dunbar, Rim; Henzi, Sp; Holekamp, K.; Korstjens, Ah; Layton, R.; Lee, P.; Lehmann, J.

2008-01-01

283

Fission properties of the BCPM functional

We explore the properties of the Barcelona Catania Paris Madrid (BCPM) energy density functional concerning fission dynamics. Potential energy surfaces as well as collective inertias relevant in the fission process are computed for several nuclei where experimental data exists. Inner and outer barrier heights as well as fission isomer excitation energies are reproduced quite well in all the cases. The spontaneous fission half lives $t_{\\textrm{\\textrm{SF}}}$ are also compute...

Giuliani, Samuel A.; Robledo, Luis M.

2013-01-01

284

Nuclear fission in covariant density functional theory

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.

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

2013-01-01

285

Fission through quasi-molecular shapes and fragmentation. Chapter 15

International Nuclear Information System (INIS)

The decay path which leads an initial spherical nucleus through compact and creviced shapes with almost spherical ends and to two or more spherical tangent fragments which later go away has been investigated within a generalized liquid drop model taking into account both the proximity energy, an accurate sharp radius, the decay asymmetry and the temperature effects. The original value of the surface coefficient has been maintained. Within this approach of the nuclear deformation energy, this exit channel through quasi-molecular shapes is compatible with most of the experimental data : symmetric fission barrier heights in the whole mass range, asymmetric fission barrier heights of In, Tb and Mo, Businaro-Gallone point, double-humped barriers of actinides, fragment kinetic energies, partial half-lives of radioactive nuclei emitting heavy clusters and critical momenta for light and medium nuclei. The rotational hyperdeformed states recently observed might also come up and survive in this fusion-like fission valley. The rotation as well as the thermal excitation favour the symmetric splitting. In this peculiar decay path, the fission barrier is a scission barrier hindering the rupture of the neck between the nascent fragments. The nature of the saddle-point is unusual, it corresponds to separated fragments maintained in metastable equilibrium by the balance between the attractive proximity forces and the repulsive Coulomb forces. Analytical formulas given the fission barrAnalytical formulas given the fission barrier characteristics in this deformation path will be provided in a close future. The fragmentation barriers for emission in a plane or in the whole space as well the deformation energies of toroids and bubbles have been determined. For very heavy systems, minima lying below the barriers of plane fragmentation exist in the toroidal deformation valley allowing some stability and relaxation of the excited toroidal system before its decay in several fragments emitted in a plane due to the surface tension and proximity forces

286

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)

287

Post-scission dynamics in fission

Energy Technology Data Exchange (ETDEWEB)

A dynamical model for fission from the classical turning point to scission and beyond is presented. We consider the fissioning nucleus as well as the fission fragments as incompressible irrotational deformable charged liquid drops. We focus on the post-scission time evolution of the neck, stretching of the fragments, kinetic energy and excitation energy.

Samanta, B.C.; Sperber, D.; Zielinska-Pfabe, M. (Rensselaer Polytechnic Inst., Troy, NY (USA). Dept. of Physics); Samaddar, S.K. (Darjeeling Government Coll. (India). Dept. of Physics)

1982-01-14

288

Post-scission dynamics in fission

International Nuclear Information System (INIS)

A dynamical model for fission from the classical turning point to scission and beyond is presented. We consider the fissioning nucleus as well as the fission fragments as incompressible irrotational deformable charged liquid drops. We focus on the post-scission time evolution of the neck, stretching of the fragments, kinetic energy and excitation energy. (orig.)

289

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

290

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.)

291

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.

Kessler, Günter

2012-01-01

292

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

293

Chemical effects of fission recoils

International Nuclear Information System (INIS)

The temperature in the track of a 235U fission recoil is probed by utilizing the difference in the heats of formation of the isopropyl and normal propyl radicals (3.6 kcal/mol). End products of the reactions of the isomeric propyl radicals are analyzed in the radiolysis of gaseous propane and a mixture of methane, ammonia and propane with #betta# rays or fission recoils at the same density. The product distribution is independent of density in the #betta# radiolysis while it varies in the fission recoil radiolysis in a manner suggesting an increase in temperature with density. Kinetic analysis leads to an 'effective' temperature, which is a time average of a localized temperature from the time of particle passage until end product formation. The 'effective temperature' varies approximately linearly with density from ambient at 5 g/L to 40 deg C above ambient at 100 g/L. This is much lower than the rise calculated by assuming that the track region is heated adiabatically by the entire energy lost by the fission recoil. This is ascribed to diffusive migration of the initially produced species during the physico-chemical stage for a finite relaxation interval. This model suggests a relaxation interval of 2 x 10-10 sec. (author)

294

Multimodal fission and neutron evaporation

International Nuclear Information System (INIS)

The average multiplicities nu-bar(A) of prompt neutrons emitted in the spontaneous fission of /sup 252/Cf and /sup 258/Fm are derived. Two new features are predicted: A simple sawtooth for /sup 258/Fm and a triple one for /sup 252/Cf. Experiments to check these predictions should be feasible now

295

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

296

Energetics of the fission process

International Nuclear Information System (INIS)

The mass asymmetry of fragments from nuclear fission of heavy nuclei is reviewed. While mass asymmetry is a common and well-known phenomenon for low-energy fission of the lighter actinides, more recent experiments have demonstrated that, for the heaviest actinides, the mass distribution switches to a symmetric one. On the other hand, it has been discovered that, though for fissioning nuclei with mass numbers A< or ?225 the mass distribution is basically symmetric, an asymmetric component is clearly to be identified for nuclei down to the Pb-region. In the absence of a generally accepted dynamical theory of fission, the above experimental findings are discussed in terms of static energy considerations. Triggered from the outset by the structure of the potential energy surface at the saddlepoint, the energy balance at the scission point between the available energy (Q-value) of the reaction and the Coulomb and deformation energy of the nascent fragments is shown to steer the characteristics of the fragment mass distributions. (orig.)

297

Brownian shape dynamics in fission

Directory of Open Access Journals (Sweden)

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.

Randrup Jørgen

2013-12-01

298

Spontaneous fission of rutherfordium isotopes

International Nuclear Information System (INIS)

We have found several new spontaneous fission (SF) activities and suggested assignments for some of them to rutherfordium (element 104) isotopes. Their half-lives and production cross sections have been measured by collecting recoils on a moving nickel or steel tape and transporting them past stationary mica track detectors at known velocities. The following tentative assignments are based on several cross bombardments and comparisons between experimental and calculated production cross sections: 256Rf(9 +- 2 ms), 257Rf(3.8 +- 0.8 s, 14 +- 9% SF), 258Rf(13 +- 3 ms), 259Rf(3.4 +- 1.7 s, 9 +- 3% SF), 260Rf(21 +- 1 ms), and 262Rf(47 +- 5 ms). Presently we are unable to assign several other new spontaneous fission activities with half-lives of approx.15 ms, approx.22 ms, approx.100 ms (Z260Rf, in reactions in which we expected to produce this isotope. Our measurements support a shift in the spontaneous fission half-life systematics at element 104, first proposed by Flerov and Oganessian et al. and later predicted by Randrup et al. and Baran et al. and attributed to the disappearance of the second hump of the double-humped fission barrier and a weakening of the 152-ission barrier and a weakening of the 152-neutron subshell

299

International Nuclear Information System (INIS)

The fission fragment angular distribution have been measured for neutron induced fission of 232Th at a number of energies near the neutron threshold between 1.35 and 1.95 MeV. The fission fragments have been detected at average angles of 5, 26, 37, 55, 73 and 90 degrees with respect to the incident neutron beam direction. A 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. The fission fragment angular distribution has been fitted with even-degree Legendre fourth power polynomials by the least square method. No satisfactory fit could be obtained with a double-humped fission barrier. Use of a triple-humped fission barrier provides a reasonable fit to all the experimental data

300

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)

301

The decay and fission of uranium

Energy Technology Data Exchange (ETDEWEB)

According to the Bernai liquid drop alpha particle model, the nuclear structure of uranium contains a core of 38 alpha particles comprised of 5 concentric layers. The innermost core of 4 alpha particles corresponding to the oxygen 16 nuclide is enclosed by 4 more alpha particles giving the structure of the sulphur 32 nuclide. The third layer of 6 alpha particles completes the 14 alpha particle model of nickel 56. The fourth and fifth layers each contain 12 alpha particles. It will be shown that the fifth layer forms a barrier to the natural radioactive decay of uranium isotopes. Furthermore, it appears that whist the fourth layer sets a limit on the minimum size of the larger daughter fragment of the thermal neutron induced fission of a uranium isotope, the third layer sets a limit on the minimum size of the smaller fragment. 4 refs., 3 tabs., 6 figs.

Norman, P.D. [Monash Univ., Clayton, VIC (Australia). Dept. of Physics

1997-12-31

302

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

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 spectromet...

Haag, N.; Gu?tlein, A.; Hofmann, M.; Oberauer, L.; Potzel, W.; Schreckenbach, K.; Wagner, F. M.

2013-01-01

303

Charge distribution, neutron evaporation, and energy distribution in higher energy binary fission

International Nuclear Information System (INIS)

A computational procedure based on the order-disorder model for predicting independent yields of fission products in higher energy fission is described. A scheme for the distribution of extra excitation between the fragments has been evolved. The extra excitation energy is shown to be shared between the two impending fragments in proportion to the number of neutrons out of the balance number (as per the order-disorder model) going to either of the fragments. The calculational procedure essentially consists of making use of the scheme and obtaining the excitation energy of the fragments for higher energy fission from those for spontaneous fission. Data on neutrons evaporated nu-bar (Z/sub i/,N/sub j/) individual fragments for the higher energy fission are calculated from the excitation energy using the cascade evaporation scheme. The product isotopic distributions are calculated from nu-bar data. The product isotopic distributions thus calculated along with experimental product mass yield data give the independent yields of the products. The results obtained for fission of 235U by fission spectrum neutrons (fast) and 14.7 MeV (high energy) neutrons are discussed. A comparison of the predicted independent yields with experimental values shows good agreement. The total isotopic yield versus Z distribution for fast and high energy neutron fission show a decrease in peak to valley ratio with increasing excitation energy of the compound nucleus. Less pronounced sof the compound nucleus. Less pronounced shell effects at N=50 and 82 appear than in the case of thermal fission. The isotopic isobaric and isotonic averages of nu-bar retain the sawtooth nature. The study confirms the experimental observation that Z/subp/ for higher energy fission lies between the values predicted by the unchanged charge density and excited charge density hypotheses

304

Fission dynamics at low excitation energy

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.

Aritomo, Y

2013-01-01

305

Fission product behaviour in severe accidents

International Nuclear Information System (INIS)

The understanding of fission product (FP) behaviour in severe accidents is important for source term assessment and accident mitigation measures. For example in accident management the operator needs to know the effect of different actions on the behaviour and release of fission products. At VTT fission product behaviour have been studied in different national and international projects. In this presentation the results of projects in EU funded 4th framework programme Nuclear Fission Safety 1994-1998 are reported. The projects are: fission product vapour/aerosol chemistry in the primary circuit (FI4SCT960020), aerosol physics in containment (FI4SCT950016), revaporisation of test samples from Phebus fission products (FI4SCT960019) and assessment of models for fission product revaporisation (FI4SCT960044). Also results from the national project 'aerosol experiments in the Victoria facility' funded by IVO PE and VTT Energy are reported

306

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

307

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

308

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

309

Cluster fission from the standpoint of nuclear fission

Energy Technology Data Exchange (ETDEWEB)

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.)

Lee, Sangmoo [Tsukuba Univ., Ibaraki (Japan). Inst. of Physics

1996-03-01

310

A fission fragment detector for correlated fission output studies

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

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

2014-09-01

311

Material synergism fusion-fission

Energy Technology Data Exchange (ETDEWEB)

In fission and fusion reactors the common features such as operating temperatures and neutron exposures will have the greatest impact on materials performance and component lifetimes. Developing fast neutron irradiation resisting materials is a common issue for both fission and fusion reactors. The high neutron flux levels in both these systems lead to unique materials problems like void swelling, irradiation creep and helium embitterment. Both fission and fusion rely on ferritic-martensitic steels based on 9%Cr compositions for achieving the highest swelling resistance but their creep strength sharply decreases above {proportional_to} 823K. The use of oxide dispersion strengthened (ODS) alloys is envisaged to increase the operating temperature of blanket systems in the fusion reactors and fuel clad tubes in fast breeder reactors. In view of high operating temperatures, cyclic and steady load conditions and the long service life, properties like creep, low cycle fatigue,fracture toughness and creepfatigue interaction are major considerations in the selection of structural materials and design of components for fission and fusion reactors. Currently, materials selection for fusion systems has to be based upon incomplete experimental database on mechanical properties. The usage of fairly well developed databases, in fission programmes on similar materials, is of great help in the initial design of fusion reactor components. Significant opportunities exist for sharing information on technology of irradiation testing, specimen miniaturization, advanced methods of property measurement, safe windows for metal forming, and development of common materials property data base system. Both fusion and fission programs are being directed to development of clean steels with very low trace and tramp elements, characterization of microstructure and phase stability under irradiation, assessment of irradiation creep and swelling behaviour, studies on compatibility with helium and developing fabrication and joining technologies for ferritic steels. There is also synergy in codifying mechanical design rules for high temperature structural materials. The rapid development of fusion requires a fundamental understanding and a robust predictive capability of radiation damage in materials located in high flux regions. A joint approach for solving material problems would bring significant benefits, including the acceleration of development of both areas. (orig.)

Sankara Rao, K.B.; Raj, B. [Indira Gandhi Centre for Atomic Research, Kalpakkam (India); Cook, I. [D3 Culham Science Centre, Abingdon, Oxfordshire (United Kingdom); Kohyama, A. [Kyoto Univ. (Japan); Dudarev, S. [UKAEA (United Kingdom)

2007-07-01

312

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

Energy Technology Data Exchange (ETDEWEB)

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

Boeckstiegel, C.; Steinhaeuser, S. [Institut fuer Kernphysik, Technische Universitaet Darmstadt, Schlossgartenstrasse 9, 64289 Darmstadt (Germany); Schmidt, K.-H. [Gesellschaft fuer Schwerionenforschung m.b.H., Planckstrasse 1, 64291 Darmstadt (Germany)], E-mail: k.h.schmidt@gsi.de; Clerc, H.-G.; Grewe, A.; Heinz, A.; Jong, M. de [Institut fuer Kernphysik, Technische Universitaet Darmstadt, Schlossgartenstrasse 9, 64289 Darmstadt (Germany); Junghans, A.R. [Gesellschaft fuer Schwerionenforschung m.b.H., Planckstrasse 1, 64291 Darmstadt (Germany); Mueller, J. [Institut fuer Kernphysik, Technische Universitaet Darmstadt, Schlossgartenstrasse 9, 64289 Darmstadt (Germany); Voss, B. [Gesellschaft fuer Schwerionenforschung m.b.H., Planckstrasse 1, 64291 Darmstadt (Germany)

2008-04-01

313

Nuclear Dissipation from Fission Time

Energy Technology Data Exchange (ETDEWEB)

Fission times, pre-scission neutron multiplicities and GDR pre-scission {gamma}-ray multiplicities measured for uranium or thorium nuclei formed with temperatures T {approx} 1.8 MeV have been compared with calculations performed with CDSM2, a two-dimensional dynamical model combined with a statistical one. Among the three experimental approaches considered, fission times give access to the most precise pieces of information on nuclear dissipation at high excitation energy. For the temperature range under consideration, an agreement between the model and data is achieved if one-body dissipation is used with a strength factor k{sub red} {approx} 0.45 {+-} 0.10 applied to the wall term for the mononuclear configuration. (authors)

Gontchar, I.; Morjean, M.; Basnary, S. [GANIL DSM/CEA, IN2P3/CNRS, BP 5027, 14076 Caen Cedex 5 (France)

2000-04-21

314

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

315

Nuclear fission and spatial chaos

International Nuclear Information System (INIS)

Nuclear fission is the most fundamental reaction between neutrons and atomic nuclei of nuclear fuel in a reactor. In this paper, according to the nonlinear dynamical behavior of the neutron transport system in space (or the distribution behavior of neutrons in the reactor) which reveals this essential reaction, we investigate the relation between nuclear fission and spatial chaos, neutron multiplication theory, as well as the relation between spatial periodic bifurcation, concentration rate of uranium and neutron effective gain coefficient. In addition, from the chaotic behavior of spatial nonlinear dynamical system, we obtain that the absolutely stable area of nuclear reactor is neutron effective multiplication factor 0 < k < 3/4, which is markedly different from the formerly mentioned k < 1

316

Applicability of a technique for fission-track dating in opaque and other SSNTDs

International Nuclear Information System (INIS)

The fission-track dating technique has often been used for age determination in various samples of archaeological and geological interest. It is, however, not always possible to acquire hand specimens in which the natural-fission track density per unit area, from the spontaneous-fission decay of heavy elements over a long timescale, and the subsequent thermal-neutron-induced fission track density, can be easily measured. The obstacle to fission-track dating (FTD) in these materials is due to the absence of clear SSNTDs. Hand specimens of a few minerals studied by the authors, having thicknesses of 1 mm or more, are quite opaque to permit the transmission-mode optical-microscopic analysis of tracks. The procedure described in the paper uses the replication technique and the subsequent viewing of fission tracks by Scanning Electron Microscope (SEM) or Optical Microscope (OM). Simulation experiments utilizing fission fragments from a 252Cf source have been carried out in several SSNTDs and described in detail in order to optimize the technique. The implications of the application of the technique in FTD, and in acquiring other information of track parameters, are also described in detail in the paper. (author)

317

Thermal Performance of Deep-Burn Fusion-Fission Hybrid Waste in a Repository

International Nuclear Information System (INIS)

The Laser Inertial Confinement Fusion Fission Energy (LIFE) Engine (1) combines a neutron-rich but energy-poor inertial fusion system with an energy-rich but neutron-poor subcritical fission blanket. Because approximately 80% of the LIFE Engine energy is produced from fission, the requirements for laser efficiency and fusion target performance are relaxed, compared to a pure-fusion system, and hence a LIFE Engine prototype can be based on target performance in the first few years of operation of the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL). Similarly, because of the copious fusion neutrons, the fission blanket can be run in a subcritical, driven, mode, without the need for control rods or other sophisticated reactivity control systems. Further, because the fission blanket is inherently subcritical, fission fuels that can be used in LIFE Engine designs include thorium, depleted uranium, natural uranium, spent light water reactor fuel, highly enriched uranium, and plutonium. Neither enrichment nor reprocessing is required for the LIFE Engine fuel cycle, and burnups to 99% fraction of initial metal atoms (FIMA) being fissioned are envisioned. This paper discusses initial calculations of the thermal behavior of spent LIFE fuel following completion of operation in the LIFE Engine (2). The three time periods of interest for thermal calculations are during interim storage (probably at the LIFE Engine site), during the preclosure opera Engine site), during the preclosure operational period of a geologic repository, and after closure of the repository

318

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)

319

FY04&05 LDRD Final Report Fission Fragment Sputtering

Energy Technology Data Exchange (ETDEWEB)

Fission fragments born within the first 7 {micro}m of the surface of U metal can eject a thousand or more atoms per fission event. Existing data in the literature show that the sputtering yield ranges from 10 to 10,000 atoms per fission event near the surface, but nothing definitive is known about the energy of the sputtered clusters. Experimental packages were constructed allowing the neutron irradiation of natural uranium foils to investigate the amount of material removed per fission event and the kinetic energy distribution of the sputtered atoms. Samples were irradiated but were never analyzed after irradiation. Similar experiments were attempted in a non-radioactive environment using accelerator driven ions in place of fission induced fragments. These experiments showed that tracks produced parallel to the surface (and not perpendicular to the surface) are the primary source of the resulting particulate ejecta. Modeling studies were conducted in parallel with the experimental work. Because the reactor irradiation experiments were not analyzed, data on the energy of the resulting particulate ejecta was not obtained. However, some data was found in the literature on self sputtering of {sup 252}Cf that was used to estimate the velocity and hence the energy of the ejected particulates. Modeling of the data in the literature showed that the energy of the ejecta was much lower than had been anticipated. A mechanism to understand the nature of the ejecta was pursued. Initially it was proposed that the fission fragment imparts its momenta on the electrons which then impart their momenta on the nuclei. Once the nuclei are in motion, the particulate ejecta would result. This initial model was wrong. The error was in the assumption that the secondary electrons impart their momenta directly on the nuclei. Modeling and theoretical considerations showed that the secondary electrons scatter many times before imparting all their momenta. As a result, their energy transfer is more isotropic than directional. It was therefore concluded that the nuclei are set in motion not by direct collisions with the secondary electrons, but by repulsive forces cased by the temporary net positive local charge of the nuclei. This is cased by ejected electrons and by the reduced bonding nature of the nuclei cased by many of the local electrons being in excited and in nonbonding states.

Ebbinghaus, B; Trelenberg, T; Meier, T; Felter, T; Sturgeon, J; Kuboda, A; Wolfer, B

2006-02-22

320

The VERDI fission fragment spectrometer

Directory of Open Access Journals (Sweden)

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.

Frégeau M.O.

2013-12-01

321

The VERDI fission fragment spectrometer

International Nuclear Information System (INIS)

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. (authors)

322

Sexual differentiation in fission yeast

DEFF Research Database (Denmark)

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.

Egel, R; Nielsen, O

1990-01-01

323

The VERDI fission fragment spectrometer

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

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

2013-12-01

324

Fission Data and Nuclear Technology

International Nuclear Information System (INIS)

Accurate nuclear data for fissile nuclei are required not only by reactor designers, but also by reactor physicists for the interpretation of integral experiments, e.g. studies of the change of reactivity with irradiation. Some of the requests that have been made for such fission data, and the reasons behind them, are discussed, along with the progress that has been made towards their fulfilment. An attempt is made to outline those areas where better data are required. (author)

325

Fission product holdup in graphite

International Nuclear Information System (INIS)

Multicomponent time-dependent concentration diffusion and radioactive decay of isotopic species is an important aspect of fission product migration and release from fuel particles and fuel elements in a High Temperature Gas-Cooled Reactor (HTGR). After fission products escape from a fuel particle in an HTGR, it is still necessary for them to diffuse across the graphite web of a fuel block to a coolant hole before they can be entrained in the primary coolant. The time required for a given fission product species to diffuse across the graphite web has a direct influence on the time-dependent release associated with a significant increase in the power/flow ratio. The main purpose of the paper is to present the results of a study of the holdup time in graphite of Sr as a function of the diffusion constants. The study employs a newly-developed multicomponent time-dependent diffusion and decay code called DASH. Analysis methods for solving the type of problem discussed are well known, and some applications to fission product decay and diffusion in HTGRs have appeared in the literature. However, the methods employed are often subject to time step limitations, and the effects of decay are not adequately handled. The DASH code uses a one dimensional spatial discretization for the diffusion operator and an analytic matrix operator method to remove the time dependence. Comparisons of the solutions given by DASH with a number of analytic solutions have been made, and in all instances considered the agreement with analytical solutions is excellent and limited only by the inaccuracy inherent in the spatial discretization

326

International Nuclear Information System (INIS)

The Thomas-Fermi model of average nuclear properties described in Parts 1 and 2 is applied to the calculation of fission barriers and charge distributions. Comparison with experimental data reveals a barriers vs. size discrepancy. The suggestion is made that an extension of the Thomas-Fermi method is called for in order to describe the presence in nuclei of the ''quantal halo,'' i.e. of the classically forbidden region around the nuclear surface where matter exists at negative kinetic energy

327

Status of fission yield evaluations

Energy Technology Data Exchange (ETDEWEB)

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.

England, T.R.; Rider, B.F.

1983-01-01

328

The discovery of uranium fission

International Nuclear Information System (INIS)

Uranium was discovered 200 years ago. Its radioactive character was first demonstrated in 1896 and two years later radium was extracted from uranium minerals. In 1911 studies with alpha rays from radioactive decay led to the unexpected discovery of the atomic nucleus. Exposure of beryllium to alpha rays yielded neutrons, first detected in 1932. Starting in 1934, neutron irradiation of uranium produced radioactive substances erroneously attributed to transuranium elements but with confusing properties. Painstaking experiments by chemists left no doubt on 17 December 1938 that barium was produced by these irradiations: the neutrons had split some uranium nuclei. The physics of the fission process was understood two weeks later; after a few months, neutron multiplication was found to be probable. This review deals with the eminent scientists involved, their successes, errors and disappointments, and the unexpected insights which occurred on the paths and detours of scientific research. It is, therefore, instructive also to discuss how fission was not discovered. The momentous discovery must be considered inevitable; the great tragedy was that Germany started World War II just at the time when the possibility of nuclear chain reactions and bombs became known. The consequences and anxieties that remain after 50 years of nuclear fission demand that mankind act with reason and conscience to maintain peace. (author)

329

Fission fusion hybrids- recent progress

Fission-fusion hybrids enjoy unique advantages for addressing long standing societal acceptability issues of nuclear fission power, and can do this at a much lower level of technical development than a competitive fusion power plant- so it could be a nearer term application. For waste incineration, hybrids can burn intransigent transuranic residues (with the long lived biohazard) from light water reactors (LWRs) with far fewer hybrid reactors than a comparable system within the realm of fission alone. For fuel production, hybrids can produce fuel for ˜4 times as many LWRs with NO fuel reprocessing. For both waste incineration or fuel production, the most severe kind of nuclear accident- runaway criticality- can be excluded, unlike either fast reactors or typical accelerator based reactors. The proliferation risks for hybrid fuel production are, we strongly believe, far less than any other fuel production method, including today's gas centrifuges. US Thorium reserves could supply the entire US electricity supply for centuries. The centerpiece of the fuel cycle is a high power density Compact Fusion Neutron Source (major+minor radius ˜ 2.5-3.5 m), which is made feasible by the super-X divertor.

Kotschenreuther, M.; Valanju, P.; Mahajan, S.; Covele, B.

2012-03-01

330

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 UK 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 UK evaluations have been published. In this paper 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 are summarized. Currently there are 50 yield sets and for each there are 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

331

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

332

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)

333

Fission product and core material behavior

International Nuclear Information System (INIS)

Knowledge of the location and inventory of fission products are essential to plant cleanup and are measurable quantities. This paper continues the discussion of fission products and emphasizes the mechanisms of fission-product transport and the pathways through which the fission products were moved from their initial locations in the core to their final locations in the plant systems. Detailed results of the fission-product inventory analyses are also discussed to demonstrate how data from the damaged core can be used to enhance the authors knowledge of the accident phenomenology and aid in resolution of SFD accident source-term issues. Understanding of the transport mechanisms and behavior of the fission products and other core materials in the TMI-2 plant systems can contribute to resolving technical issues that are of importance to source-term research

334

Collective spectra along the fission barrier

Directory of Open Access Journals (Sweden)

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.

Pigni M. T.

2012-12-01

335

MODELING AND FISSION CROSS SECTIONS FOR AMERICIUM.

Energy Technology Data Exchange (ETDEWEB)

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.

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

2005-05-01

336

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

Clement, J. D.

1973-01-01

337

Bimodal fission in binary and ternary spontaneous fission of 252Cf

International Nuclear Information System (INIS)

The hot bimodal fission of 252Cf is reexamined with new high-statistics data. We constructed a ?-?-? coincidence cube for binary fission and LCP-gated ?-? matrix for ternary fission. By identifying the secondary fission fragments from their ?-ray transitions, we measured the yields for various fission splits. The normal neutron yield distribution is found to be Gaussian for Xe-Ru. However, the binary fission split of Ba-Mo is found to exhibit a bimodal neutron distribution with the 'hot mode' corresponding to ?3.1% of the total yield. In ? ternary fission, the first measurements of yields for specific fission splits are presented. The Te-?-Ru and Xe-?-Mo neutron yields fit well with a single mode, but the Ba-?-Zr split shows evidence for an enhanced hot mode with an intensity of ?13.8% of the normal mode

338

International Nuclear Information System (INIS)

The subject is discussed under the headings: introduction describing atoms, nuclei, isotopes, binding energy of particles in nuclei; nuclear fission (with special reference to U235 and Pu239); nuclear reactors (basic principles and brief descriptions of different types); the breeder reactor; reactor safety (brief descriptions of four reactor accidents); radioactive waste (fission products, problems of disposal); other applications of nuclear energy; Nature got there first (description of the natural fission reactor at Oklo, Gabon); nuclear fusion (principles, types of thermonuclear devices, outlook for success); radiological effects (associated with fusion reactors). (U.K.)

339

Dissipative phenomena: fusion, fast fission and quasifission

International Nuclear Information System (INIS)

The last theoretical developments concerning the fusion process are reviewed. They concern the appearance of new dissipative mechanisms: fast fission, when the fission barrier of the compound nucleus vanishes due to angular momentum, and quasifission which takes place for heavy systems. The conditions under which these processes, as well as fusion, occur are discussed in details using the fast fission and the extra push models

340

Nuclear Fission Products: From Source to Environment

After a peer review of data about nuclear fission products, we can see easily that, no clear chemical species, chemical compounds, or chemical processes were available after actual releases of nuclear Fission Products (FP) during planned releases, accidents, or in nuclear detonations. The models based on these ordinary reactions and species could not interpret the behaviors of the fission products or expect their effects in the environment or on the living creatures. To interpret the chemical...

Ajlouni, A. W.; Almasa Efah, Y. S.; Abdelsalam, M.

2010-01-01

341

Statistical Analysis of Fission Chamber Signal

International Nuclear Information System (INIS)

Fission Chamber (FC) is widely used at power range of commercial power reactors to measure neutron flux due to its longer life time than other detectors. However, detecting neutron counts from fission chamber during fuel loading is normally very low counting number. Fission chamber sensitivity is determined by experimental test to validate sensitivity on design specifications and linearity of neutron counts have been verified at fine range from 0.03 to 0.1 cps

342

Fission product retention in HTGR fuels

International Nuclear Information System (INIS)

Retention data for gaseous and metallic fission products are presented for both Triso-coated and Biso-coated HTGR fuel particles. Performance trends are established that relate fission product retention to operating parameters, such as temperature, burnup, and neutron exposure. It is concluded that Biso-coated particles are not adequately retentive of fission gas or metallic cesium, and Triso-coated particles which retain cesium still lose silver. Design implications related to these performance trends are identified and discussed

343

Fission-product retention in HTGR fuels

Energy Technology Data Exchange (ETDEWEB)

Retention data for gaseous and metallic fission products are presented for both Triso-coated and Biso-coated HTGR fuel particles. Performance trends are established that relate fission product retention to operating parameters, such as temperature, burnup, and neutron exposure. It is concluded that Biso-coated particles are not adequately retentive of fission gas or metallic cesium, and Triso-coated particles which retain cesium still lose silver. Design implications related to these performance trends are identified and discussed.

Homan, F.J.; Kania, M.J.; Tiegs, T.N.

1982-01-01

344

Fission-product retention in HTGR fuels

International Nuclear Information System (INIS)

Retention data for gaseous and metallic fission products are presented for both Triso-coated and Biso-coated HTGR fuel particles. Performance trends are established that relate fission product retention to operating parameters, such as temperature, burnup, and neutron exposure. It is concluded that Biso-coated particles are not adequately retentive of fission gas or metallic cesium, and Triso-coated particles which retain cesium still lose silver. Design implications related to these performance trends are identified and discussed

345

Fission barriers and half-lives

International Nuclear Information System (INIS)

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

346

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.)

347

Fission barriers and half-lives

Energy Technology Data Exchange (ETDEWEB)

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.

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

1989-01-01

348

Attachment of gaseous fission products to aerosols

International Nuclear Information System (INIS)

The circumstances under which gaseous fission products may be attached to aerosols are examined. A simple model is assumed for the interaction between the fission product molecules and the aerosol, in which the probability of attachment of a molecule on any encounter is given by a constant ?, the sticking probability. It is concluded that when gaseous fission products are released in the presence of a population of particles, particularly small particles, there is a strong possibility that they will attach rapidly to those particles. In such circumstances gaseous fission product transport would be governed by the transport properties of the particles. (author)

349

Experimental Fission Studies at Intermediate Energies

A series of nuclear fission experiments have been performed in the intermediate energy range. The dynamics of the fission process have been studied by means of detection of neutrons emitted from compound nuclei formed by ion beams of protons, ?-particles, and 12C-ions, all at a beam energy of 100 MeV. The neutron emission data have been interpreted using a statistical model analysis, and the fission time scale has been found to vary between 6.4 and 170?10-21 s. Neutron-induced fission cros...

Elmgren, Klas

2002-01-01

350

Correlated prompt fission ?-ray data measurements

International Nuclear Information System (INIS)

The OECD-NEA has published in its recent high priority data request list a demand for new and precise 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 for a responsible handling of nuclear waste during an a-priori assessment of the fission-fragments' heat production and toxicity. Prompt fission ?-rays, together with prompt neutrons, represent very powerful probes of the nuclear fission process near the scission point. They provide information to better understand how the total excitation energy available in the fissioning system gets transferred to intrinsic excitation in the fragments. Prompt fission ?-rays should preferably be known as a function of fission-fragment mass and excitation energy, but existing experimental data date back to the early 1970s for the above mentioned isotopes. We have performed a detailed feasibility study on novel lanthanum-halide and cerium-bromide detectors with a particular focus on their corresponding time and energy resolution, essential parameters to arrive at a set-up with high detection efficiency in conjunction with a high neutron/?-ray separation power. New prompt fission ?-ray spectra from the reactions 252Cf(SF) and 235U(nth, f) are presented.

351

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)

352

Radiochemical studies on nuclear fission at Trombay

International Nuclear Information System (INIS)

Kinetic energy distribution in neutron induced fission of 232Th, 232-233U, 237Np, 239-241Pu and 234Cm were measured from recoil range distribution. Consistent with literature, kinetic energy for symmetric mass division was found to be lower than asymmetric mass division, clearly showing the spherical fragment shell effect at 132 (Z=50, N=82) mass region on the kinetic energy of the fission fragment. Work on angular momentum and mass resolved angular distribution of fission fragment in neutron, alpha and heavy ion induced fission were also carried out. A glimpse of the work carried out is presented

353

Facility for neutron multiplicity measurements in fission

International Nuclear Information System (INIS)

The description of an experimental set-up for neutron multiplicity measurements and its specific data processing procedures are presented together with some results for 252Cf(sf). With this experimental set-up the light and heavy fission fragment kinetic energies for every fission event can be registered simultaneously with the number of prompt neutrons emitted by each of the complementary fission fragments. The proposed data processing makes it possible to perform the reconstruction of pre-neutron fission fragment masses and kinetic energies as well as the initial neutron multiplicity distribution

354

Facility for neutron multiplicity measurements in fission

Energy Technology Data Exchange (ETDEWEB)

The description of an experimental set-up for neutron multiplicity measurements and its specific data processing procedures are presented together with some results for {sup 252}Cf(sf). With this experimental set-up the light and heavy fission fragment kinetic energies for every fission event can be registered simultaneously with the number of prompt neutrons emitted by each of the complementary fission fragments. The proposed data processing makes it possible to perform the reconstruction of pre-neutron fission fragment masses and kinetic energies as well as the initial neutron multiplicity distribution.

Dushin, V.N.; Hambsch, F.-J.; Jakovlev, V.A.; Kalinin, V.A.; Kraev, I.S.; Laptev, A.B.; Nikolaev, D.V.; Petrov, B.F.; Petrov, G.A.; Petrova, V.I.; Pleva, Y.S.; Shcherbakov, O.A.; Shpakov, V.I.; Sokolov, V.E.; Vorobyev, A.S. E-mail: alexander.vorobyev@pnpi.spb.ru; Zavarukhina, T.A

2004-01-11

355

Absolute thermal fission yields for 239Pu

International Nuclear Information System (INIS)

Absolute 239Pu thermal fission yields are given for the stable and long-lived isotopes of krypton, rubidium, strontium, zirconium, xenon, cesium, barium, cerium, neodymium, and samarium. The principal measurement technique for the fission product isotopes was isotope dilution mass spectrometry. The number of fissions was established by summing the number of fission product atoms in the heavy mass peak. The propagated standard deviations associated with the bulk of the measured yields range from 1 to 2%, relative. Significant differences between the current data and that previously reported from this laboratory are identified. 14 references

356

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.)

357

Some Fission Problems Circa 1950 and 2008

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

?wiatecki, W. J.

358

Spin distributions of fission fragments in the spontaneous fission of 252Cf

International Nuclear Information System (INIS)

Spin distributions of fission fragments in the spontaneous fission of 252Cf were deduced from ?-? coincidence measurements and from ?-ray multiplicity measurements. The obtained ?-ray multiplicity distribution clearly shows that the two fragments have almost same spin after the fission. (author)

359

International Nuclear Information System (INIS)

Fractional cumulative yields (FCY) of various fission products in the light mass region have been determined in the thermal neutron induced fission of 229Th, 241Pu and 245Cm as well as in the spontaneous fission of 252Cf using the direct gamma spectrometric technique. These data and similar data from the literature were used to deduce the charge distribution parameters such as the width parameter (?z), the most probable charge (Zp) and the charge polarization (?Z=Zp-ZUCD) as a function of the fragment mass for these four fissioning systems. Results of the present work along with our earlier work for heavy mass chains show smaller value of ?z for Np=50 (A=84-90) and Zp=50, Np=82 (A=128-136) indicating an effect of shell closure proximity where as the oscillating nature of ?z and ?Z in the interval of five mass units indicates a proton pairing effect. Besides the oscillating nature, the ?Z values decrease systematically with the approach of symmetric split which is characteristic of low energy fission. (orig.)

360

Energy Technology Data Exchange (ETDEWEB)

Fission fragment angular distributions have been measured for {sup 16}O + {sup 194}Pt reaction forming the compound system {sup 210}Rn, in the laboratory energy range from 79 to 90 MeV. The measured fission fragment anisotropies as a function of E{sub c.m.}/V{sub B} are compared with the predictions of standard saddle point statistical model (SSPM). Anisotropies calculated using the average excitation energy and angular momentum values could not reasonably fit the experimental data. Statistical model calculations were performed using the PACE with modified fission barrier and level density parameters. Fission probability, evaporation residue cross section and neutron multiplicity were simultaneously used to fix the statistical parameters. Model calculations incorporating the chance nature of fission decay and scaled values of the rotating finite range model (RFRM) moment of inertia could reasonably fit the fragment angular anisotropies.

Prasad, E., E-mail: prasad.e.nair@gmail.com [Department of Physics, School of Mathematical and Physical Sciences, Central University of Kerala, Nileshwar, 671328 (India); Department of Physics, University of Calicut, Calicut, 673635 (India); Varier, K.M. [Department of Physics, University of Calicut, Calicut, 673635 (India); Thomas, R.G. [Nuclear Physics Division, Bhabha Atomic Research Centre, Mumbai, 400085 (India); Vinodkumar, A.M. [Department of Physics, University of Calicut, Calicut, 673635 (India); Mahata, K. [Nuclear Physics Division, Bhabha Atomic Research Centre, Mumbai, 400085 (India); Appannababu, S. [Department of Physics, Faculty of Science, The M. S. University of Baroda, Vadodara, 390002 (India); Sugathan, P.; Golda, K.S. [Inter University Accelerator Centre, Aruna Asaf Ali Marg, Post Box 10502, New Delhi, 110067 (India); Babu, B.R.S. [Department of Physics, University of Calicut, Calicut, 673635 (India); Department of Physics, Sultan Qaboos University, Muscat (Oman); Saxena, A.; John, B.V.; Kailas, S. [Nuclear Physics Division, Bhabha Atomic Research Centre, Mumbai, 400085 (India)

2012-05-15

361

International Nuclear Information System (INIS)

In the framework of the C.E.C. research project ECP-5 entitled ''The behaviour of radionuclides in natural and semi-natural ecosystems'' our institute carried out investigations on selected sites of forest ecosystems in the 30-km-zone of Chernobyl in cooperation with research instituts of the C.I.S. states Russia and Ukraine. Our research is concentrated on the transfer of radionuclides from soil to plants of the understorey, especially species of farns and berries, as this plants take up their nutrients mainly from the upper organic horizons. (orig.)

362

Least squares analysis of fission neutron standard fields

International Nuclear Information System (INIS)

A least squares analysis of fission neutron standard fields has been performed using the latest dosimetry cross sections. Discrepant nuclear data are identified and adjusted spectra for 252Cf spontaneous fission and 235U thermal fission fields are presented

363

Effect of inertia parameters on static fission path

International Nuclear Information System (INIS)

Properties of static (minimum potential) fission path in the formalism of Hofmann are investigated. It is pointed out that the inertial parameters greatly affect the fission path and hence the penetrability. The difficulty of determining fission path is discussed

364

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

365

Neutron emission prior to fission

International Nuclear Information System (INIS)

Neutron emission in the 158Er composite system is studied in order to investigate particle emission with energy spectrum and angular distribution in excess of statistical model predictions. Data are analyzed using a modified statistical model which incorporates effects due to nuclear dissipation, and also calculates neutron emission during the descent from the saddle to the scission point. Calculations consider the Kramers effect and the Transient effect. It is concluded that a detailed interpretation of enhanced neutron emission preceding fission in compound nucleus reactions is possible, and that an upper limit may be set on the reduced nuclear dissipation coefficient. 5 refs., 2 figs

366

Systematics of mass distribution in low energy fission

International Nuclear Information System (INIS)

We have systematically studied the mass distribution in fission of wide range of nuclides from pre-actinides through trans-actinides . The problems connected to fragment properties, asymmetric and symmetric fission modes, and mode structure of fission fragment mass distribution have been investigated. The particular attention is paid to the experimental evidence for the relations of fission fragment properties to the multimodal nuclear fission. This work has given its contribution to the present understanding of fission process

367

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

368

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

369

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

370

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

371

The fission track dating of obsidian

International Nuclear Information System (INIS)

Recent work has been done using fission track detection to date obsidian artefact source material. The limitations of the method and realistic errors of dates produced are discussed. The long half-life of 238U spontaneous fission and the low levels of uranium present in most artefacts of archaeological interest will always limit the technique to a minor role in archaeometry

372

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

373

Fission stability diagram of 240Pu

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.

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

1989-01-01

374

Detector instrumentation for nuclear fission studies

International Nuclear Information System (INIS)

New kind of detector telescopes have been developed for energy measurement and nuclear charge identification of particles in transfer and fission experiments. An experimental program using the General Purpose Scattering Chamber (GPSC) and National Array of Neutron Detector (NAND) for performing fission experiments with Tandem-LINAC accelerator system at IUAC is underway from last few years. New developments in detector instrumentation has been carried out. Multi-wire Proportional counter based (MWPC) time of flight (TOF) spectrometers have been developed for investigating fission mass distribution and Neutron Multiplicity experiments. For generating absolute timing, experiments with TOF system based on start-stop detector has also been developed. To extract fission cross-section, a detection system based on hybrid telescopes has been developed for extracting fission angular distribution. To investigate pre and post-scission charged particle multiplicity in fission process, a charged particle array, based on CsI(TI) scintillators coupled to photodiode, has been developed for detecting light charged particles (protons and alphas) in coincidence with fission fragments. Recent developments in detector development and its nuclear instrumentation for carrying out fission experiments will be discussed

375

Collective and relative motion of fission fragments

International Nuclear Information System (INIS)

A classical dynamical calculation has been performed to study the time evolution of deformation, kinetic energy, and internal excitation in post-scission motion of the fission fragments. The model has been applied to the spontaneous fission of 252Cf and results compare favourably with experiment. (author)

376

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.)

377

Chaos controlled dissipative dynamics in nuclear fission

International Nuclear Information System (INIS)

Dissipative forces operates in the dynamics of a fissioning nucleus as descends from the saddle point to scission. In the present work an ideal gas in a cavity subjected to a fission-like quadrupole deformation is considered. The energy transferred to the gas particles from its surface motion have been calculated

378

Correlation measurements of fission-fragment properties

Directory of Open Access Journals (Sweden)

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.

Oberstedt A.

2010-10-01

379

Nuclear Power from Fission Reactors. An Introduction.

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

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

380

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

381

Determination of uranium fission rate in an arbitrary neutron field using fission track detectors

Energy Technology Data Exchange (ETDEWEB)

In accelerator driven systems, particularly near the spallation target, the neutron spectrum covers a very wide range of energies and has a complex angular distribution. It is possible to determine the fission rate of fissionable nuclei in such neutron fields using fission track technique. We use the mean density of fission tracks in the two track detectors in contact with two faces of a fission foil (radiator). A calibration factor, w, relating the number of fission events to the track density is needed and was determined in a very well-known neutron field. It was used to estimate the fission rate in a uranium-lead assembly when the lead target was irradiated with protons of energy 1 GeV. Experimental results are compared with Monte Carlo predictions using MCNPX code.

Hashemi-Nezhad, S.R. [School of Physics, A28, University of Sydney, NSW 2006 (Australia)], E-mail: reza@physics.usyd.edu.au; Zhuk, I.V.; Potapenko, A.S. [Joint Institute of Power and Nuclear Research-Sosny NASB, 220109 Minsk (Belarus); Krivopustov, M.I. [Joint Institute for Nuclear Research, 141980 Dubna (Russian Federation); Westmeier, W.; Brandt, R. [Fachbereich Chemie, Philipps University, Marburg (Germany)

2008-08-15

382

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

383

A study of some fission characteristics in the ?-particle-induced fission of transuranium nuclei

International Nuclear Information System (INIS)

Aiming at studying the dependence of the symmetric and asymmetric types of fission on excitation energy there have been measured the mass distributions if fission fragments produced in the ?-particle-induced fission of 237Np, 238U, 242Pu, and 243Am in the energy range of 24-36 MeV. Data on the mass dependence of the fission fragment total kinetic energies are presented. It has become clear that as the excitation energy of the compound nucleus increases the contribution from symmetric fission grows faster than the asymmetric one. The shell effects play an important role in the production of the mass distribution structures at excitation energies E* up to approximately 30 MeV. The observed increase of symmetric fission yields at E*>19 MeV in the case of the 247 Bk compond nucleus is interpreted as being due to an anhanced probability of symmetric fission as one approaches nuclei with Z=100

384

Fission wire plane chambers (WPC)

International Nuclear Information System (INIS)

Wire Plane Chamber (WPC) with multiple grid planes was found to be useful for detection of alpha particles with argon fill gas. Using this concept, studies have been carried out using wire plane chamber for neutron detection using 235U as the neutron converter material. The experimental studies have been done using 252Cf source mounted on the cathode plate inside the WPC. WPC is found to be operated at low working voltages and with better pulse shape features: faster and narrower pulse shapes better suited for high count rate applications. Present grid configuration is found to be superior to conventional ionization chamber of similar dimensions in performance. This is achieved as the average distance traveled by the charge particle cloud from the ionization track to reach the nearest electrode has been reduced as compared to two electrode ionization chamber of similar size. The capacitance of the WPC is considerably reduced with presently used multi anode wire plane electrodes so that large area fission chambers in parallel plate or cylindrical geometry can be realized. The results obtained with this novel fission WPC are described for the first time. (author)

385

International Nuclear Information System (INIS)

The aim of this work is to gain more insight into the physics of hadrons and to develop a theoretical framework for the treatment of hadronic fission. The description of hadronic matter in terms of quantum chromodynamics, which is generally accepted as the fundamental theory of strong interactions, is intimately connected with the concept of colour confinement. Since this phenomenon is a property of the vacuum state, much effort has been invested into trying to understand it in analogy with the occurence of the condensed ground state in the theory of superconductivity. In Chapter II, we therefore go back to non-relativistic physics, discuss the methods used there, and report in Chapter III on various attempts to apply these methods in quantum field theories, in particular in connection with the so-called 'dynamical symmetry breaking'. Although the fundamental problem of the 'true' vacuum state has not yet been solved, its solution has been anticipated in the so-called bag models which are discussed in great detail in Chapter IV. In Chapter V, we finally seek to understand the microscopic process of fission of hadrons. (orig./HSI)

386

Actinide transmutation in fission reactors

International Nuclear Information System (INIS)

This study evaluates the long-term performance of fission reactors to transmute actinides (Np, Am, Cm) recovered from irradiated fuel. The evaluation is based on a criterion of overall reduction factor of actinide content by transmuting Np, Am, Cm in a liquid-metal fast breeder reactor (LMFBR). It is shown that recycling and transmuting Np, Am, Cm can ultimately reduce the mass and water-dilution volume of these radionclides by two orders of magnitude, depending mainly upon the fraction of the actinides lost to the wastes. However, transmutation in reactors is slow, the Np, Am, Cm must be exposed through several successive irradiation cycles, and for a long time the total amount of these radionuclides continues to build-up in the reactor and fuel cycle. To obtain appreciably reduction in total Np, Am, Cm inventory, the inventory in the core and fuel cycle of a decommissioned reactor must be transferred to the next replacement reactor, and so on to subsequent replacement reactors as long as fission reactors exist. Therefore, for a realistic evaluation of the benefits from partitioning and transmutation, we calculate a time-dependent overall reduction factor defined as the ratio of the amount of Np, Am, Cm accumulated in wastes without recycling to the total inventory of these actinides in the reactor, fuel cycle and wastes with recycling

387

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.

388

Theoretical Description of the Fission Process

Energy Technology Data Exchange (ETDEWEB)

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

Witold Nazarewicz

2009-10-25

389

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

390

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

391

Standards for the fission yields measurements

International Nuclear Information System (INIS)

Two main methods are now used for the determination of fission yields. The gamma spectrometry, without or with radiochemical separations and the mass spectrometry using isotopic dilution. Fission yields are needed in burn up determination, dosimetry, safeguards and also in basic science (study of the fission mechanism). The 235U thermal neutron induced fission yields have been extensively studied. Complete and up to date evaluations for this system are available. The development of the most important of these fission yields, as standards, could be a good solution. They are easily measured and they allow the fulfilment of all the applications. A short review of all data available will be given. Only the gamma spectrometry method will be described. Some recommended decay data will be discussed. The experimental method will be also shortly described

392

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 /nu///sub 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 /nu///sub 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 /nu///sub p/ with higher accuracy than is currently possible. 17 refs., 11 figs

393

Superfluid dynamics of 258Fm fission

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

Scamps, Guillaume; Lacroix, Denis

2015-01-01

394

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

395

Criticality calculations with fission spectrum matrix

International Nuclear Information System (INIS)

In the present study, the author implemented a procedure to treat a fission spectrum matrix into neutron transport solvers of a code system CBG, and quantified errors of usual procedures utilizing a fission spectrum vector. Numerical results showed that the errors of the usual procedures are negligible if the fission spectrum vector is generated from the fission spectrum matrix with weight functions obtained by cell calculations. On the other hand, when a library built-in function is used as a weight function for the fission spectrum vector generation, the errors become large if there is a large difference between the library built-in function and the neutron energy spectrum of the target system. (author)

396

Progress in fission product nuclear data

International Nuclear Information System (INIS)

This is the first issue of a report series on Fission Product Nuclear Data (FPND), published every six months by the Nuclear Data Section (NDS) of the International Atomic Energy Agency (IAEA). Its purpose 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 cross-section data of fission products; data related to ?-, ?-decay of fission products; delayed neutron data; and fission product decay-heat. The present issue includes contributions which were received by NDS before 1 November 1975

397

Fission dynamics at low excitation energy. 2

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.

Aritomo, Y; Ivanyuk, F A

2014-01-01

398

Fission dynamics at low excitation energy

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

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

2014-11-01

399

Theoretical study of fission dynamics with muons

International Nuclear Information System (INIS)

Following muon capture by actinide atoms, some of the inner shell muonic transitions proceed by inverse internal conversion, i.e. the excitation energy of the muonic atom is transferred to the nucleus. In particular, the muonic E2:(3d?1s) transition energy is close to the peak of the isoscalar giant quadrupole resonance in actinide nuclei which exhibits a large fission width. Prompt fission in the presence of a bound muon allows us to study the dynamics of large-amplitude collective motion. We solve the time-dependent Dirac equation for the muonic spinor wave function in the Coulomb field of the fissioning nucleus on a 3-dimensional lattice and demonstrate that the muon attachment probability to the light fission fragment is a measure of the nuclear energy dissipation between the outer fission barrier and the scission point

400

Event-by-Event Fission with FREYA

Energy Technology Data Exchange (ETDEWEB)

The recently developed code FREYA (Fission Reaction Event Yield Algorithm) generates large samples of complete fission events, consisting of two receding product nuclei as well as a number of neutrons and photons, all with complete kinematic information. Thus it is possible to calculate arbitrary correlation observables whose behavior may provide unique insight into the fission process. The presentation first discusses the present status of FREYA, which has now been extended up to energies where pre-equilibrium emission becomes significant and one or more neutrons may be emitted prior to fission. Concentrating on {sup 239}Pu(n,f), we discuss the neutron multiplicity correlations, the dependence of the neutron energy spectrum on the neutron multiplicity, and the relationship between the fragment kinetic energy and the number of neutrons and their energies. We also briefly suggest novel fission observables that could be measured with modern detectors.

Randrup, J; Vogt, R

2010-11-09

401

Systematics of Fission-Product Yields

Energy Technology Data Exchange (ETDEWEB)

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

A.C. Wahl

2002-05-01

402

Spontaneous fission with ? -parameterized quasimolecular shape

In the framework of a generalized liquid drop model (GLDM), a quasimolecular mechanism is introduced to describe the deformation of a nucleus in the procedure of nuclear fission or fusion. In order to more appropriately evaluate the shell correction on the fission or fusion path, the quasimolecular shape is described in terms of deformation parameters ? (i.e., so-called ? parameterized) by a transformation. For symmetric fission it is done analytically, whereas for asymmetric fission it is performed in a pure numerical way. Thereafter, for each quasimolecular shape, the shell correction can be calculated by the Strutinsky method where the single-particle energies are derived from a shell model in an axially deformed Woods-Saxon potential with the ? -parameterized quasimolecular shape. We then use this recipe to predict the half-lives of several spontaneous fission channels for some heavy nuclei, and the results are in agreement with the experimental data.

Zhang, Haifei; Zhang, Hongfei; Li, Junqing; Bao, Xiaojun; Ma, Nana

2014-11-01

403

Los Alamos National Laboratory Fission Basis

Energy Technology Data Exchange (ETDEWEB)

This report is an overview of two main publications that provide a comprehensive review of the Los Alamos National Laboratory (LANL) Fission Basis. The first is the experimental paper, {sup F}ission Product Data Measured at Los Alamos for Fission Spectrum and Thermal Neutrons on {sup 239}Pu, {sup 235}U, {sup 238}U, [Selby, H. D., et al., Nucl. Data Sheets, Vol. 111 2010, pp. 2891-2922] and the second is the theoretical paper, Fission Product Yields from Fission Spectrum n+ {sup 239}Pu for ENDF/B-VII.1, [Chadwick, M. B., et al., Nucl. Data Sheets, Vol. 111, 2010, pp. 2923-2964]. One important note is that none of this work would have been possible without the great documentation of the experimental details and results by G.W. Knobeloch, G. Butler, C.I. Browne, B. Erdal, B. Bayhurst, R. Prestwood, V. Armijo, J. Hasty and many others. (authors)

Keksis, A.L.; Chadwick, M.B.; Selby, H.D.; Mac Innes, M.R.; Barr, D.W.; Meade, R.A.; Burns, C.J.; Wallstrom, T.C. [Los Alamos National Laboratory, NM 87545 (United States)

2011-07-01

404

Los Alamos National Laboratory Fission Basis

International Nuclear Information System (INIS)

This report is an overview of two main publications that provide a comprehensive review of the Los Alamos National Laboratory (LANL) Fission Basis. The first is the experimental paper, Fission Product Data Measured at Los Alamos for Fission Spectrum and Thermal Neutrons on 239Pu, 235U, 238U, [Selby, H. D., et al., Nucl. Data Sheets, Vol. 111 2010, pp. 2891-2922] and the second is the theoretical paper, Fission Product Yields from Fission Spectrum n+ 239Pu for ENDF/B-VII.1, [Chadwick, M. B., et al., Nucl. Data Sheets, Vol. 111, 2010, pp. 2923-2964]. One important note is that none of this work would have been possible without the great documentation of the experimental details and results by G.W. Knobeloch, G. Butler, C.I. Browne, B. Erdal, B. Bayhurst, R. Prestwood, V. Armijo, J. Hasty and many others. (authors)

405

Improved Calculation of Thermal Fission Energy

Thermal fission energy is one of the basic parameters needed in the calculation of antineutrino flux for reactor neutrino experiments. It is useful to improve the precision of the thermal fission energy calculation for current and future reactor neutrino experiments, which are aimed at more precise determination of neutrino oscillation parameters. In this article, we give new values for thermal fission energies of some common thermal reactor fuel iso-topes, with improvements on two aspects. One is more recent input data acquired from updated nuclear databases. The other, which is unprecedented, is a consideration of the production yields of fission fragments from both thermal and fast incident neutrons for each of the four main fuel isotopes. The change in calculated antineutrino flux due to the new values of thermal fission energy is about 0.33%, and the uncertainties of the new values are about 30% smaller.

Ma, X B; Wang, L Z; Chen, Y X; Cao, J

2013-01-01

406

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

407

This research resolves two problems that have long been of important concern in experimental fission physics: (1) determination of pulse height distribution response of ionization chambers in fission fragment detection measurements, and (2) correction of "thick-foil effect" systematic errors in standard values of the fundamental parameters of fission physics--the average number of prompt neutrons per fission (=nu), absolute fission activity and true fission rate of samples (TFR), and isotopic fission cross sections (sigma _{f}). Results are obtained by a comprehensive digital simulation of the electrostatics and pulse height distribution response of the parallel-plate, ungridded, electron-pulse ionization fission chamber together with prompt neutron -fragment multiplicity and angular distribution correlations, neutron-fragment coincidence detection and related variations in the 4pi^here around the chamber for a wide range of the relevant factors--foil thickness, alpha particle interference bias level, fission detector configuration characteristics, fissile isotopes (^{252}Cf, ^{235}U, etc.) and other experimental parameters. Isotope-specific double-energy (E_1,E_2) natural variations in fragment spectrum, in fragment-specific range-energy (dE/dx) relations and in prompt neutron-fragment multiplicity (nu) and nuclear temperature dependent angular distribution correlations are simulated in detail. Detailed results are obtained for double-energy, fragment-specific count loss fractions resulting from in -foil fragment absorption and from alpha -interference discrimination as well as for chamber detection efficiency, fragment spectrum distortion and prompt neutron -fragment coincidence detection distribution variations. Decay alpha pulse pileup statistics are discussed, and the behavior of and factors affecting the fragment pulse height distribution tail are analyzed in detail. Fragment pairs and prompt neutrons issued from them are tracked in the 4pi^ace around the chamber. Light-to-heavy fragment detection ratio variations in neutron-gated coincidence measurements are also obtained in 4pi space. Effects of these systematics on absolute, relative and ratio measurements of fundamental fission parameters are discussed. Magnitudes and mechanisms of production of thick-foil errors are identified and analyzed in detail, and methods for correcting these errors and for improving measurement setup design are given.

Cohensedgh, Farhad

408

Long-range particles in fission

International Nuclear Information System (INIS)

The authors determined the relative probabilities of 14-MeV neutron-induced fission of 232Th, 233U, 238U and 237Np involving the emission of long-range particles ('long-range particle' fission) and of 'long-range particle' fission of 235U induced by slow neutrons. The ratios are, respectively, 0.3 ± 0.2, 1.2 ± 0.1, 0.64 ± 0.06 and 1.3 ± 0.1. Then they measured proton and triton yields in the 14-MeV neutron-induced fission of the above-mentioned nuclei (other than 232Th) and in the fission of 233U and 235U by slow neutrons and the spontaneous fission of 244Cm. The alpha-particle and triton spectra were measured in all cases (except for 232Th) and the proton spectra were also measured for the fission of 235U by slow neutrons and the spontaneous fission of 244Cm. Coincidences between the fragment and the long-range particle were recorded experimentally, fragments being recorded by a small ionization chamber and long-range particles by a CsI(Tl) crystal. The mass distribution of the particles was determined by analysing the duration of fluorescence in the crystal when particles were recorded. The data obtained show that: (1) The probability of 'long-range particle' fission increases as Z2/A increases; (2) Proton and triton yields per 100 alpha particles are between 2 and 4% and 7 and 10%, respectively, and are independent of thespectively, and are independent of the excitation energy; (3) The alpha particle energy distribution peaks are at 16 ± 1 MeV for all nuclei, the corresponding value for protons and tritons being between 8 and 9 MeV. The authors discuss the possible reasons for the variation in the probability of 'long-range particle' fission with changes in Z2/A and the excitation energy. (author)

409

Mass, Energy and Charge Distribution in Fission

International Nuclear Information System (INIS)

Potentialities and limitations of modem techniques used for studies of mass and charge distribution in fission are discussed. Recent experimental developments and new findings concerning the distribution of mass, charge, and of energy - as far as the latter bear on these distributions - are reviewed and commented. This concerns results from thermal-, low-, medium and high-energy-particle-induced fission and is limited to heavy nuclei in a brief phenomenological way. Initial and final mass distributions as determined by pure instrumental methods are discussed, and the final distributions are compared with radiochemical results. The asymmetry and fine structure in these distributions are commented. The results from high-energy-induced fission are presented in view of the fragment shell theory and the two-fission-mode hypothesis. It is shown that asymmetric fission persists to high bombarding energies. Recent results from range studies in high-energy-induced fission are discussed, and the importance of the observation that the scission distance increases with increasing excitation energy of the fissioning nucleus is stressed. In connection with charge distribution and dispersion, emphasis is laid on the problem of correction of measured masses due to neutron emission which ought to be known for single fragments and not for groups of fragments as at present. The implication of this on the charge dispersion is stressed. Experimental studies of charge dispersion widths (Gaussian) in thermal-neutron-induced fission are discussed as well as shell and odd-even effects on these distributions. The equal-charge displacement hypothesis in the pre-neutron emission and closed-shell representation still gives the best fit to the experimental Zp dependence on the initial mass. The review includes also charge division in charged-particle-induced fission in the medium energy range and in high-energy fission. In the latter the observation of the trend of Np/Zp with the fragment mass is presented and correlated with the symmetric peak of the mass distribution. (author)

410

Fission-energy release for 16 fissioning nuclides. Final report

Energy Technology Data Exchange (ETDEWEB)

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

Sher, R.

1981-03-01

411

Thermal stability of fission tracks in apatite and sphene: using confined-track-length measurements

International Nuclear Information System (INIS)

Confined track lengths have been used to monitor the annealing behaviour of fission tracks in Durango apatite and in two natural sphene samples subjected to laboratory annealing treatment. The residual track length and residual track density in apatite are found not to follow a linear one-to-one relationship. Comparison of the spontaneous and induced fission track lengths in sphene samples shows no evidence for the natural fading as is observed in apatite. No significant difference is found between the stability of neutron-induced and spontaneous fission track lengths in sphene over the temperature and time combinations employed. The behaviour of confined track lengths in sphene is found to follow Arrhenius law over the experimental domain investigated. On the basis of the Arrhenius law, our results indicate that, corresponding to a time-period of 106 yr, the closure temperature would be 123 +- 10 C for Durango apatite and 423 +- 27 C for the sphene sample investigated. (author)

412

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)

413

Fission-suppressed fusion breeder on the thorium cycle and nonproliferation

Energy Technology Data Exchange (ETDEWEB)

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.

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

2012-06-19

414

Fission-suppressed fusion breeder on the thorium cycle and nonproliferation

International Nuclear Information System (INIS)

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 pr 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.

415

Fission-suppressed fusion breeder on the thorium cycle and nonproliferation

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.

Moir, R. W.

2012-06-01

416

International Nuclear Information System (INIS)

Most people would agree that fission is the most probable way to form binary systems, especially the close systems. The angular momentum must be the deciding factor as to whether a gas cloud becomes a single star or a binary system. In the case of critical angular momentum it may become a contact system. There has been a debate as to whether zero age contact systems exist, and this is particularly true for massive systems with a common radiative envelope and a mass ratio different from unity. Convincing evidence for two such massive zero-age systems seems to have been found by studies of the light curves of V701 Sco and V1010 OpH with the aid of the Wilson-Devinney (1971) binary model. Parameters are derived for these two massive, unevolved, contact binaries. (Auth.)

417

Laser driven fusion fission hybrids

International Nuclear Information System (INIS)

The role of the fusion-fission hybrid reactor (FFHR) as a fissile fuel and/or power producer is discussed. As long range options to supply the world energy needs, hybrid-fueled thermal-burner reactors are compared to liquid metal fast breeder reactors (LMFBR). A discussion of different fuel cycles (thorium, depleted uranium, and spent fuel) is presented in order to compare the energy multiplication, the production of fissile fuel, the laser efficiency and pellet gain requirements of the hybrid reactor. Lawrence Livermore Laboratory (LLL) has collaborated with Bechtel Corporation and with Westinghouse in two engineering design studies of laser fusion driven hybrid power plants. The hybrid designs which have resulted from these two studies are briefly described and analyzed by considering operational parameters, such as energy multiplication, power density, burn-up and plutonium production as a function time

418

Fission time measurement by crystal blocking method

International Nuclear Information System (INIS)

The nucleus evolution to the scission point is slowed down by nuclear dissipation in highly excited nuclei. This phenomena leads to longer fission times than expected by the Bohr and Wheeler's statistical model. A dynamical description of the nucleus has to be taken into account. Measuring fission times is then a real 'probe' of nuclear dissipation effects. We made a reverse kinematic experiment at GANIL in the 4 ? neutron detector ORION, using a lead beam accelerated at 29 MeV/u on a single crystal silicon target mounted on a goniometer. We measured fission times of the projectile-like nuclei with the crystal blocking method, as a function of initial excitation energy. This method, which consists in measuring directly the recoil distance to a row of atoms where the fission occurs in the crystal, gives access to long fission times (> 10-19 s) in the fission times distribution. Blocking dips of the axis and (001) and (110) planes has been analysed with Monte-Carlo simulation code. For the first time in such simulation the particle evaporation of the fission fragments has been calculated in a precise way. (author)

419

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)

420

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

421

Sub-threshold fission in the actinides

International Nuclear Information System (INIS)

Two experiments, which have been performed on the Harwell Synchrocyclotron using fast neutrons, are described and the results discussed. In one experiment the neutron-induced fission cross-section of the isotope 231Pa was measured by detection of the fission fragments in a gas scintillation detector. In the other, sub-threshold fission of the isotope 232Th was investigated by the detection of the neutrons emitted during the fission process. The results are interpreted in the light of the double-humped fission barriers, which are a consequence of the Strutinsky model which combines the effects of the liquid drop and shell models of the nucleus. A new method is presented for calculating the penetrability of such barriers, and comparison is made with the measured fission cross-sections of two isotopes, 230Th and 232Th. The low energy fission cross-section of 231Pa is found to be consistent with the concept of a series of rotational bands based upon vibrational levels. (U.K.)

422

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)

423

Prompt fission neutron multiplicity and spectrum evaluation

Energy Technology Data Exchange (ETDEWEB)

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)

Tudora, Anabella; Vladuca, G. [Department of Physics, University of Bucharest, PO Box MG-11, RO-077125 Bucharest-Magurele (Romania); Morillon, B. [Commissariat a l' Energie Atomique, DAM Ile-de-France, BP 12, 91680 Bruyeres-le-Chatel (France); Hambsch, F.J.; Oberstedt, S. [EC-JRC-Institute of reference Materials and Measurements, Retieseweg 111, B-2440 Geel (Belgium)

2005-07-01

424

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

425

Nuclear fission reactors from thousand of million years

International Nuclear Information System (INIS)

This book is about nuclear reactors, not only of the industrial ones that work to provide electric power, neither of those experimental ones as the first one that worked in Chicago in the first half of the XX Century but, mainly, of those that worked in the Earth thousands of millions of years ago. The book examines what happened in last geologic times, when the natural uranium had a different constitution to the current one. We will give you information on the nuclear fission reactors that worked in Gabon, Africa. A discussion of the radioactive isotopes formed during the operation of those reactors and its behavior until our days is presented. (Author)

426

Pulsed neutron uranium borehole logging with prompt fission neutrons

International Nuclear Information System (INIS)

The gross count natural gamma log normally used for uranium borehole logging is seriously affected by disequilibrium. Methods for the direct measurement of uranium, such as neutron logging, which are not affected by disequilibrium have been the object of considerable effort in recent years. This paper describes a logging system for uranium which uses a small accelerator to generate pulses of 14 MeV neutrons to detect and assay uranium by the measurement of prompt fission neutrons in the epithermal energy range. After an initial feasibility study, a prototype logging probe was built for field evaluation which began in January 1976. Physical and operational characteristics of the prototype probe, the neutron tube-transformer assembly, and the neutron tube are described. In logging operations, only the epithermal prompt fission neutrons detected between 250 microseconds to 2500 microseconds following the excitation neutron pulse are counted. Comparison of corrected neutron logs with the conventional gross count natural gamma logs and the chemical assays of cores from boreholes are shown. The results obtained with this neutron probe clearly demonstrate its advantages over the gross count natural gamma log, although at this time the accuracy of the neutron log assay is not satisfactory under some conditions. The necessary correction factors for various borehole and formation parameters are being determined and, when applied, should improve the assay accuracy

427

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)

428

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)

429

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

430

Neutron distribution at the nuclear spontaneous fission

International Nuclear Information System (INIS)

The results of experiments on neutron distribution at the spontaneous fission of 288U and 252Cf are analysed. It is shown that these distributions are described by the superposition of binomial distributions for neutrons emitted from fission fragments. It is shown that the value of average neutron number for unknown spontaneous emitter is within 3 252Cf. It is shown that modelling of neutron distributions over multiplicity by means of binomial or superposition of these two distributions gives more unambiguous results as compared to the statistical regularization method applied earlier for spontaneous fission of fermium isotopes

431

Fission induced by nucleons at intermediate energies

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

Meo, Sergio Lo; Massimi, Cristian; Vannini, Gianni; Ventura, Alberto

2014-01-01

432

A third minimum in the fission barrier

International Nuclear Information System (INIS)

The latest refinements of the fission barrier pinpointed the occurrence of a third minimum. This paper reviews the search for such a minimum through high energy resolution fission probability measurements. After successful experiments with neutrons, deuteron beams were used. Higher J spin members of a pair of rotational bands with opposite parities were found, in the (d,pf) experimental results, as expected. The experimental fission barrier parameters are compared to the theoretical calculations obtained from the macroscopic-microscopic model and the purely microscopic one. The properties of nuclei at the third minimum deformation are also discussed

433

Fission cross section measurements for minor actinides

Energy Technology Data Exchange (ETDEWEB)

The main task of this work is the measurement of fast neutron induced fission cross section for minor actinides of {sup 238}Pu, {sup 242m}Am, {sup 243,244,245,246,247,248}Cm. The task of the work is to increase the accuracy of data in MeV energy region. Basic experimental method, fissile samples, fission detectors and electronics, track detectors, alpha counting, neutron generation, fission rate measurement, corrections to the data and error analysis are presented in this paper. (author)

Fursov, B. [IPPE, Obninsk (Russian Federation)

1997-03-01

434

Nuclear fission as resonance-mediated conductance

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...

Bertsch, G. F.

2014-01-01

435

Analysis of fission with selective channel scission model

International Nuclear Information System (INIS)

The mass distributions of fission product yields for neutron-induced fissions of 232Th, 235U, 239Pu and 241Pu were calculated by the selective channel scission model with simple assumptions. Although the present calculation is a rough estimation, it is applicable to the wide range of fissionable nuclei without the adjustable parameters for each fission channel. (author)

436

Recovery and use of fission product noble metals

Energy Technology Data Exchange (ETDEWEB)

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

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

1980-06-01

437

Future challenges for nuclear data research in fission (u)

Energy Technology Data Exchange (ETDEWEB)

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

Chadwick, Mark B [Los Alamos National Laboratory

2010-01-01

438

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)

439

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

440

Fission Matrix Capability for MCNP Monte Carlo

Energy Technology Data Exchange (ETDEWEB)

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

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

2012-09-05

441

Measurement of fission yields from 235U fission induced by 24.4 KeV neutrons

International Nuclear Information System (INIS)

The fission yields of 99Mo, 132Te and 140Ba from 235U fission induced by 24.4 KeV neutrons are measured radiochemically. The neutron source is an iron filter neutron beam from a swimming pool reactor. The fission number is recorded by polycarbonate film as a fission track recorder, which is immersed in liquid uranium standard targets

442

Measurement of Prompt Fission ?-ray Spectra in Fast Neutron-induced Fission

Knowledge of prompt fission ?-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 ?-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 ?-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 ?-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 27Al(p,?) reaction. First prompt fission ?-ray spectrum measurements performed for the spontaneous fission of 252Cf and for 1.7 and 15.6 MeV neutron-induced fission of 238U at the CEA, DAM, DIF Van de Graaff accelerator, will be presented.

Laborie, J.-M.; Belier, G.; Taieb, J.

443

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)