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Evaluation of prompt neutron spectra for minor actinide nuclei
1997-03-01
Measurement data on fission prompt neutron spectra of minor actinide (MA) is much little, and its accuracy is also unsufficient. Therefore, conventional evaluation value of fission spectra of MA was assumed for its nuclear temperature by using a method of determining from its systemicity owing to assumption of the Maxwell type distribution, but it can be said that this method consider fully to features of MA isotopes. In this paper, some evaluation calculation results are shown by adopting an evaluation method developed by authors and based on modified Madland Nix model and are conducted by concept of physical properties on target nuclei. As a result, by adopting the level density parameter of fission fragments, the inverse process cross section, the fission product yield distribution and the total release energy, effect of inverse process cross section, mass distribution of fission product, calculation results of Cm isotope and systemicity of fission spectra of actinide isotope were investigated. (G.K.)
2010-01-01
ABSTRACT The Donbas Foldbelt (DF) is the compressionally deformed segment of a large Late Palaeozoic rift cross-cutting the southern part of the East European Craton and is traditionally described as a classic example of an inverted intracratonic rift basin. Proposed formational models are often controversial and numerous issues are still a matter of speculation, primarily due to the lack of absolute time constraints and insufficient knowledge of the thermal evolution. We investigate the low-temperature thermal history of the DF by means of zircon fission track and apatite fission track (AFT) thermochronology applied to Upper Carboniferous sediments. In all samples, the AFT chronometer was reset shortly after deposition in the Early Permian (275 Ma). Samples contained kinetically variable ...
Measurement of MA fission cross sections at YAYOI
1998-03-01
Fission cross section ratios of minor actinide nuclides (Am-241, Am-243) relative to U-235 in the fast neutron energy region have been measured using a back-to-back (BTB) fission chamber at YAYOI fast neutron source reactor. A small BTB fission chamber was developed to measure the fission cross section ratios in the center of the core at YAYOI reactor. Dependence of the fission cross section ratios on neutron spectra was investigated by changing the position of the detector in the reactor core. The measurement results were compared with the fission cross sections in the JENDL-3.2, ENDF/B-VI and JEF-2.2 libraries. It was found that calculated values of Am-241 using the JENDL-3.2, ENDF/B-VI and JEF-2.2 data are lower by about 15% than the measured value in the center of the core (the neutron average energy is 1.44E+6(eV)). And, good agreement can be seen the measured value and calculated value of Am-243 using the JENDL-3.2 data in the center of the core (the neutron average energy is 1.44E+6)(eV), but calculated values of Am-243 using the ENDF/B-VI and JEF-2.2 data are lower by 11% and 13% than the measured value. (author)
Use of the linear accelerator for incinerating the fission products of /sup 137/Cs and /sup 90/Sr
1980-07-01
Transmutation of fission products /sup 137/Cs and /sup 90/Sr using the neutron produced by high energy proton collision with heavy nuclei were investigated. Because of the small thermal neutron cross section for (n,..gamma..) reaction of /sup 137/Cs (0.1 barn), a high neutron flux of 10/sup 17/ n/cm/sup 2/ sec is required to transmute /sup 137/Cs at a rate ten times faster than the natural decay. This range of high flux is attainable in the spallation reaction of high energy proton beam interact with liquid Pb target. The neutronic calculation by using NMTC, HIST3D, EPR, TAPEMAKER and ANISN codes indicates that the spallation neutron can transmute 222 kg /sup 137/Cs and 155 kg /sup 90/Sr fission products per year (at a rate of 10 and 30 times faster than their natural decay rate) by running a 300 mA, 1.5 GeV proton beam. Thus, if we transmute these fission products, just after a burning cycle, this accelerator can transmute these fission products produced in five or six 1000 MWe power plants.
In the past several years there has been a renewed interest in sodium fast reactor (SFR) technology for the purpose of destroying transuranic waste (TRU) produced by light water reactors (LWR). The utility of SFRs as waste burners is due to the fact that higher neutron energies allow all of the actinides, including the minor actinides (MA), to contribute to fission. It is well understood that many of the design issues of LWR spent nuclear fuel (SNF) disposal in a geologic repository are linked to MAs. Because the probability of fission for essentially all the "non-fissile" MAs is nearly zero at low neutron energies, these isotopes act as a neutron capture sink in most thermal reactor systems. Furthermore, because most of the isotopes produced by these capture reactions are also non-fissile, they too are neutron sinks in most thermal reactor systems. Conversely, with high neutron energies, the MAs can produce neutrons by fast fission. Additionally, capture reactions transmute the MAs into mostly plutonium isotopes, which can fission more readily at any energy. The transmutation of non-fissile into fissile atoms is the premise of the plutonium breeder reactor. In a breeder reactor, not only does the non-fissile "fertile" U-238 atom contribute fast fission neutrons, but also transmutes into fissile Pu-239. The fissile value of the plutonium produced by MA transmutation can only be realized in fast neutron spectra. This is due to the fact that the predominate isotope produced by MA transmutation, Pu-238, is itself not fissile. However, the Pu-238 fission cross section is significantly larger than the original transmutation parent, predominately: Np-237 and Am-241, in the fast energy range. Also, Pu-238's fission cross section and fission-to-capture ratio is almost as high as that of fissile Pu-239 in the fast neutron spectrum. It is also important to note that a neutron absorption in Pu-238, that does not cause fission, will instead produce fissile Pu-239. Given this fast fissile quality and also the fact that Pu-238 is transmuted from Np-237 and Am-241, these MAs are regarded as fertile material in the SFR design proposed by this dissertation. This dissertation demonstrates a SFR design which is dedicated to plutonium breeding by targeting Am-241 transmutation. This SFR design uses a moderated axial transmutation target that functions primarily as a pseudo-blanket fuel, which is reprocessed with the active driver fuel in an integrated recycling strategy. This work demonstrates the cost and feasibility advantages of plutonium breeding via MA transmutation by adopting reactor, reprocessing and fuel technologies previously demonstrated for traditional breeder reactors. The fuel cycle proposed seeks to find a harmony between the waste management advantages of transuranic burning SFRs and the resource sustainability of traditional plutonium breeder SFRs. As a result, the enhanced plutonium conversion from MAs decreases the burner SFR's fuel costs, by extracting more fissile value from the initial TRU purchased through SNF reprocessing.
Analysis of americium isotope fission cross sections. Analiz sechenij deleniya izotopov ameritsiya
1988-01-01
Consistency of americium isotope fission factors in a wide range od excitation energy and observed cross sections of fission by neutrons with energies up to 20 MeV are analyzed. The behaviour of the first chance fission cross sections is determined according to the results obtained in coordinated analysis of cross section of (n, f) and (n, xn) reactions for 238U and 235U. The contradictions in the fissionability of 242Am compound nuclei at E
1992-01-01
Apatite fission-track ages have been determined for 29 samples from two transects in the southern Appalachians. The northern transect extends from the VA Piedmont northwest through the Valley and Ridge Province, Cumberland Plateau, and into the Appalachian foreland of southeastern OH. An additional transect was collected from the Pine Mountain thrust in southeastern KY extending northwest to the Cincinnati Arch. Precambrian gneisses and granites from the VA Piedmont yield reset apatite fission-track ages ranging from 103 [+-] 6 to 138 [+-] 11 Ma. Ordovician through Mississippian sedimentary rocks from the Valley and Ridge Province of VA-WV also yield reset apatite fission-track ages ranging from 120 [+-] 8 to 144 [+-] 20 Ma. The cooling histories for the Piedmont and Valley and Ridge rocks of VA and WV thus appear similar, having cooled rapidly between about 103 and 144 Ma. Pennsylvanian samples from the Cumberland Plateau of WV yield rest apatite fission-track ages of 112 [+-] 7 to 169 [+-] 13 MA in the southeast which grade into partially reset (mixed ages) northwest of Charlestown (133 [+-] 13 to 156 [+-] 10 Ma). The Permian Dunkard Formation from the OH-WV border yielded a mixed age of 197 [+-] 13 Ma, suggesting that the Permian has not been subjected to temperatures > 100 C for times greater than 1 Ma, since it was deposited. Mississippian--Pennsylvanian samples from eastern KY yield reset apatite fission-track ages which decrease from the Pine Mt. Thrust (186 [+-] 16 Ma) to Mozelle, KY (136 [+-] 12 Ma), then increase toward the Cincinnati Arch (166 [+-] 18 [minus] 186 [+-] 21 Ma). This is consistent with older apatite fission-track ages (200 Ma) from Ordovician K-bentonites in the vicinity of the Cincinnati Arch.
1994-12-31
An experimental facility for measurements of fission cross sections of heavy nuclei by particles of intermediate energies is presented. Thin film breakdown counters are used to detect the fission fragments. The results of tests and measurements at the neutron beam are presented.
2009-01-01
The mineralization ages reported in the past in the Altai Mountains, northern Xinjiang, China, not only are different, but also fall into the Hercynian epoch. This study has achieved 17 zircon fission track analysis results from different ore deposits. The zircon fission track ages range from 134 +- 9 Ma to 339 +- 49 Ma. We consider that the zircon fission track age could reveal the mineralization age based on an annealing zone temperature of 140-300 deg. C and a retention temperature of approx250 deg. C for zircon fission tracks, and a metallogenetic temperature of 150-260 deg. C in various ore districts. The mineralization age agrees with the regional tectonics. A total of four mineralization epochs have been identified, i.e., 339-312 Ma, 255-234 Ma, 218-174 Ma and 158-126 Ma, and these indicate occurrence of the mineralizations in the ...
2008-01-01
We present zircon fission track (FT) ages from the lower parts of the Higher Himalayan crystalline (HHC) ranging from 3.9 to 4.3 Ma and apatite FT age as 1.9+-0.4Ma. Combined with previous radiometric dates, these ages provide the low temperature data for the area and enable us to draw temperature-time plot which shows significant increase in cooling rates from 25 deg. C/Ma in Oligocene and 40C/Ma in Miocene to about 64 deg. C/Ma during Pliocene. For the Mandi granite, the zircon FT ages range from 3.9 to 4.9 Ma while apatite FT obtained is 2.8+-0.5Ma. The rapid Pliocene exhumation is characterized by a rapid increase in cooling rates from approx3.4 deg. C/Ma in Miocene to approx77 deg. C/Ma after 5.0 Ma. Our results confirm the rapid Pliocene to Pleistocene cooling of rocks of Kulu-Beas valley similar to that of the ...
Innovative Fission Measurements with a Time Projection Chamber
This study explores a pioneering idea to utilize a Time Projection Chamber (TPC) to measure fission cross sections and other fission quantities. The TPC is inherently capable of measuring fragments from fission events, decay alphas, and beam-material scatters. This document explores whether the TPC can improve the precision of the {sup 239}Pu(n,f) cross section and measure other new and significant fission quantities simultaneously. This work shows that the TPC can in fact deliver sub-1% cross section measurements and should provide breakthroughs in both the quality and quantity of information available from neutron-induced fission experiments.
Innovative Fission Measurements with a Time Projection Chamber
2005-11-16
This study explores a pioneering idea to utilize a Time Projection Chamber (TPC) to measure fission cross sections and other fission quantities. The TPC is inherently capable of measuring fragments from fission events, decay alphas, and beam-material scatters. This document explores whether the TPC can improve the precision of the {sup 239}Pu(n,f) cross section and measure other new and significant fission quantities simultaneously. This work shows that the TPC can in fact deliver sub-1% cross section measurements and should provide breakthroughs in both the quality and quantity of information available from neutron-induced fission experiments.
1998-01-01
Fission and total level densities modelling approach was developed. Neutron-induced fission cross section data for incident energies from 10 keV up to emissive fission threshold were employed to extract level density and fission barrier parameters. In particular, fission barrier parameters (inner barrier height, outer barrier height, curvatures) were extracted for altogether 49 isotopes of Th, Pa, U, Np, Pu, Am, Cm, Bk, and Cf. The adopted level density modelling approach and fission barrier parametrization was supported by calculations of fission cross section data above the emissive fission threshold, up to 20 MeV neutron incident energy. (author)
1985-09-01
On the basis of an analysis of experimental data on fission cross sections in the framework of the statistical model we have obtained the fission-barrier parameters and the statistical characteristics of transition states of the isotopes of U and Pu. We have shown that the energy dependence of the fission cross sections in the region of the first plateau can be described by taking into account shell, superfluid, and collective effects in the nuclear level density in equilibrium and highly deformed states.
243Cm neutron fission cross section
2009-01-01
The neutron fission cross section of 243Cm for neutron energies 0.03 eV 20 keV is measured with a neutron spectrometer at the Institute for Nuclear Research of the Russian Academy of Sciences on the basis of the moderation time in lead (SVZ-100). The values of the resonance fission integral and the Westcott factor g(T) are obtained. A comparison is made with existing data and recommended values. A new evaluation of the fission cross section for thermal neutrons is made.
The Fission of Thorium with Alpha Particles
The fission distribution of fission of thorium with alpha particle of average energy 37.5 Mev has been measured by the chemical method. The distribution found shows that the characteristic dip in the fission yield mass spectrum has been raised to within a factor of two of the peaks compared to a factor of 600 in slow neutron fission of U{sup 235}. The raise in the deip has caused a corresponding lowering in fission yield of these elements at the peaks. The cross section for fission of thorium with 37.5 Mev alphas was found to be about 0.6 barn, and the threshold for fission was found to be 23 to 24 Mev.
The Fission of Thorium with Alpha Particles
The fission distribution of fission of thorium with alpha particle of average energy 37.5 Mev has been measured by the chemical method. The distribution found shows that the characteristic dip in the fission yield mass spectrum has been raised to within a factor of two of the peaks compared to a factor of 600 in slow neutron fission of U{sup 235}. The raise in the deip has caused a corresponding lowering in fission yield of these elements at the peaks. The cross section for fission of thorium with 37.5 Mev alphas was found to be about 0.6 barn, and the threshold for fission was found to be 23 to 24 Mev.
The Fission of Thorium with Alpha Particles
1948-04-15
The fission distribution of fission of thorium with alpha particle of average energy 37.5 Mev has been measured by the chemical method. The distribution found shows that the characteristic dip in the fission yield mass spectrum has been raised to within a factor of two of the peaks compared to a factor of 600 in slow neutron fission of U{sup 235}. The raise in the deip has caused a corresponding lowering in fission yield of these elements at the peaks. The cross section for fission of thorium with 37.5 Mev alphas was found to be about 0.6 barn, and the threshold for fission was found to be 23 to 24 Mev.
2001-01-01
Based on basalt K-Ar and zircon fission track dating, Barrington shield volcano was active for 55 million years. Activity in the northeast, at 59 Ma, preceded more substantial activity between 55 and 51 Ma and more limited activity on western and southern flanks after 45 Ma. Eruptions brought up megacrystic gemstones (ruby, sapphire and zircon) throughout the volcanism, particularly during quieter eruptive periods. Zircon fission track dating (thermal reset ages) indicates gem-bearing eruptions at 57, 43, 38, 28 and 4-5 Ma, while U-Pb isotope SHRIMP dating suggests two main periods of zircon crystallisation between 60 and 50 Ma and 46-45 Ma. Zircons show growth and sector twinning typical of magmatic crystallisation and include low-U, moderate-U and high-U types. The 46 Ma high-U zircons exhibit trace and rare-earth element patterns that approach those of zircon ...
Properties of Fission-Product decay heat from Minor-Actinide fissioning systems
2000-03-01
The aggregate Fission-Product (FP) decay heat after a pulse fission is examined for Minor Actinide (MA) fissiles {sup 237}Np, {sup 241}Am, {sup 243}Am, {sup 242}Cm and {sup 244}Cm. We find that the MA decay heat is comparable but smaller than that of {sup 235}U except for cooling times at about 10{sup 8} s (approx. = 3 y). At these cooling times, either the {beta} or {gamma} component of the FP decay heat for these MA's is substantially larger than the one for {sup 235}U. This difference is found to originate from the cumulative fission yield of {sup 106}Ru (T{sub 1/2} = 3.2x10{sup 7} s). This nuclide is the parent of {sup 106}Rh (T{sub 1/2} = 29.8 s) which is the dominant source of the decay heat at 10{sup 8} s (approx. = 3 y). The fission yield is nearly an increasing function of the fissile mass number so that the FP decay heat is the largest for {sup 244}Cm among the MA's at the cooling time. (author)
1992-01-01
The 235U fission spectrum-averaged cross sections for 13 threshold reactions were measured with the fission plate (27 cm in diameter and 1.1 cm thick) at the heavy water thermal neutron facility of the Kyoto University Reactor. The Monte Carlo code MCNP was applied to check the deviation from the 235U fission neutron spectrum due to the room-scattered neutrons, and it was found that the resultant spectrum was close to that of 235U fission neutrons. Supplementally, the relations to derive the absorbed dose rates with the fission plate were also given using the calculated neutron spectra and the neutron Kerma factors. Finally, the present values of the fission spectrum-averaged cross sections were employed to adjust the 235U fission neutron spectrum with the NEUPAC code. The adjusted spectrum showed a good agreement with the ...
2000-03-01
A new type of safe fast reactor with lead coolant was proposed in Russia. The use of coolants with low moderating properties is one of the ways to get a hard neutron spectrum and an increase in the burning of Np-237, Am-243 and other miner actinides(MA) fissionable preferentially in the fast reactor. The stable lead isotope, Pb-208, is proposed as the one of such coolants. The neutron inelastic scattering cross-section of Pb-208 is 3.0-3.5 times less than the one of other lead isotopes. Calculation of the MA transmutation rates in the standard BN-type fast reactor with different coolants is performed by Monte-Carlo method using Code MMKFK. Six various models are simulated for the fast reactor blanket with different kinds of fuel and coolant. The fast reactor with natural-lead coolant practically does not differ from the reactor with sodium coolant relative to MA incineration. The use of Pb-208 as a coolant in the fast reactor results in increasing incineration of MA from 18 to 26% in comparison with a usual fast reactor. Calculation of induced radioactivity was performed using the FISPACT-3 inventory code, also. The results include total induced radioactivity and dose rate for initial material composition and selected long-lived radionuclides. The calculations show that the coolant consisting of lead isotope, Pb-206, or Pb-207, can be considered as the low-activation one because it does not practically contain long-lived toxic radionuclides. (M. Suetake)
Above-threshold structure in {sup 244}Cm neutron-induced fission cross section
1997-03-01
The quasi-resonance structure appearing above the fission threshold in neutron-induced fission cross section of {sup 244}Cm(n,f) is interpreted. It is shown to be due to excitation of few-quasiparticle states in fissioning {sup 245}Cm and residual {sup 244}Cm nuclides. The estimate of quasiparticle excitation thresholds in fissioning nuclide {sup 245}Cm is consistent with pairing gap and fission barrier parameters. (author)
1994-12-31
Available experimental data are considered on fission cross sections of nuclei in the Th-Am region by protons of 20-100 MeV. Fission probabilities in this region are obtained using inelastic cross sections calculated on the basis of known systematics. An analysis of published results on the fission cross sections and the probabilities of fission induced by neutrons and {gamma}-quanta in the same target mass and projectile energy region is performed also. It is found that in all the cases the total fission probability increases with projectile energy increasing and reaching a saturation at a definite energy. The value of this energy as well as the value of the fission probability in the saturation region is found to be a function of the parameter Z{sup 2}/{lambda}.
Fission cross section measurement of 248Cm
1981-01-01
The even isotopes of curium have large spontaneous fission decay rates, requiring a large neutron intensity to measure the fission cross section in the presence of a strong spontaneous fission background. The RINS (Rensselaer Intense Neutron Spectrometer) system, consisting of a 75-ton lead slowing-down spectrometer coupled to the RPI Gaerttner Laboratory electron linac, produces a very intense neutron flux of broad resolution in the 1 to 100,000 eV energy range, and this system has been used to measure the fission cross section of 248Cm
Fission cross section measurement of /sup 248/Cm
1981-01-01
The even isotopes of curium have large spontaneous fission decay rates, requiring a large neutron intensity to measure the fission cross section in the presence of a strong spontaneous fission background. The RINS (Rensselaer Intense Neutron Spectrometer) system, consisting of a 75-ton lead slowing-down spectrometer coupled to the RPI Gaerttner Laboratory electron linac, produces a very intense neutron flux of broad resolution in the 1 to 100,000 eV energy range, and this system has been used to measure the fission cross section of /sup 248/Cm.
1998-08-01
In order to investigate the applicability of the Cascade-Exciton model (CEM) of nuclear reactions to fission cross sections and hoping to learn more about intermediate-energy fission, the authors use an extended version of the CEM, as realized in the code CEM95 to perform a detailed analysis of proton- and neutron-induced fission cross sections of {sup 209}Bi and {sup 208}Pb nuclei and of the linear momentum transfer to the fissioning nuclei in the 45--500 meV energy range.
2009-01-01
To establish the tectonic evolution of the eastern Sichuan basin, apatite fission track dating and time-temperature thermal history modeling were carried to analyze on 11 samples collected from Jurassic sandstones. The results indicate that the cooling and exhumation process of the eastern Sichuan basin can be divided into three stages since Cretaceous, (1) a rapid cooling phase between approx100 and approx70 Ma, (2) following by a period of relative thermal stability phase between approx70 and approx15 Ma, (3) and then a new rapid cooling stage after approx15 Ma. Two rapid cooling events imply that the eastern Sichuan basin once underwent two tectonic movements since Cretaceous. The first rapid cooling is associated with Mesozoic tectonic reactivation beginning at 100 Ma, which result in folds and faults of ...
Nucleon-induced fission cross-sections at transitive energy region 20-200 MeV
2001-03-01
The new approach to the calculation of nucleon induced fission cross sections at energies 20-200 MeV is presented. The cross sections of multiconfiguration fission is calculated as a sum of fission cross-sections for nuclei formed in process of fast (direct) and precompound stage of fission reaction. The intranuclear cascade model is used for description of direct stage and precompound-statistical model for calculation of fission and de-excitation cross sections. Calculated with new optical model parameters sets fission cross sections are compared with experimental data for neutron-induced fission of {sup 237}Np, {sup 239}Pu, {sup 235,238}U and proton-induced fission of {sup 235,238}U. Brief information about new code system is also presented. (author)
Neutron-induced fission cross section on actinides using microscopic fission energy surfaces
2008-01-01
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 ...
A measurement of the /sup 238/U fission cross section between 5 eV and 3.5 MeV was performed. Included is the identification of 85 resonances or clusters of resonances below 200 keV. Also the fission widths for the 27 resolved class I levels were computed from their fission areas, and a neutron width of 0.005 MeV was estimated for the quasi-class II level in the 721 eV fission cluster. The fission level spacing and cross sections are discussed. 9 references. (JFP)
1978-01-01
A measurement of the /sup 238/U fission cross section between 5 eV and 3.5 MeV was performed. Included is the identification of 85 resonances or clusters of resonances below 200 keV. Also the fission widths for the 27 resolved class I levels were computed from their fission areas, and a neutron width of 0.005 MeV was estimated for the quasi-class II level in the 721 eV fission cluster. The fission level spacing and cross sections are discussed. 9 references. (JFP)
/sup 238/U subthreshold neutron induced fission cross section. [600 eV to 2 MeV]
High resolution measurements of the /sup 238/U neutron induced fission cross section are reported for neutron energies between 600 eV and 2 MeV. The average subthreshold fission cross section between 10 and 100 keV was found to be 44 +- 6 ..mu..b. (SDF)
/sup 238/U subthreshold neutron induced fission cross section. [600 eV to 2 MeV]
1976-01-01
High resolution measurements of the /sup 238/U neutron induced fission cross section are reported for neutron energies between 600 eV and 2 MeV. The average subthreshold fission cross section between 10 and 100 keV was found to be 44 +- 6 ..mu..b. (SDF)
Some remarks on the fissile isotopes
2010-01-01
Data on the fission cross-section of actinides, obtained from the cross-section libraries, support the Fissile Rule. Some observations on the fissile properties of odd and even isotopes are also presented.
Apatite fission track dating and thermal history of Qing-He region in Altay Mountains
2005-01-01
Fission track ages (FTA) and track lengths of apatite from Qing-He diorite intrusion in Altay Mountains are measured. Apatite fission track ages of three diorite samples is range from (78+-5) Ma to (95 +- 5) Ma, and the lengths of horizontal confined spontaneous fission tracks are (13.2 +- 1.2)-(13.5 +-1.3) mum. The distribution of the track length is narrow and symmetrical with a mean length of approximately 13.3 mum and a standard deviation of around 0.1 mum. The inverse modeling results show that thermal history of this region has four stages, two rapid uplift of this region still existed magmatic intrusion and tectonic movements in Yanshanian. (authors)
2010-01-01
Fission fragment mass distributions in the reaction of 30Si+238U were measured at the energies around the Coulomb barrier. At the above-barrier energies, the mass distribution showed Gaussian shape. At the sub-barrier energies, triple-humped distribution was observed, which consists of symmetric fission and asymmetric fission peaked at AL/AHapprox =90/178. The asymmetric fission should be attributed to quasifission from the results of the measured evaporation residue (ER) cross-sections produced by 30Si+238U. The cross-section for 263Sg at the above-barrier energy agree with the statistical model calculation which assumes that the measured fission cross-sections are equal to the fusion cross-sections, whereas the one for 264Sg measured at the ...
Coulomb fission of 24 AMeV {sup 238}U in the field of a {sup 197}Au nucleus
1996-09-01
Coulomb fission (CF) is a fission induced by the time-varying field of another nucleus passing by, outside the range of the strong nuclear force. The main difficulty in investigating this process stems from the presence of nuclear fission (NF) which can be easily confused with electromagnetic induced fission. At relativistic energies and due to the strong excitation of the Giant Resonance modes, CF represents a large fraction of the total fission cross section when induced by very heavy partner nuclei. Fission fragment Z distributions for Coulomb fission and nuclear fission are presented. (K.A.). 4 refs.
Improved fission product model for fast reactor analysis. [LMFBR]
1980-01-01
A new and highly effective procedure for generating fission product cross sections for LMFBR studies has been developed. The resultant simplified cross sections agree with more detailed treatments to within a few percent, and thus, are particularly valuable for fuel cycle and other studies. The proposed model consists of a two-lump fission product set, one based on the odd-A fission products and the other based on the even-A fission products with transmutation between the odd and even-A isotopes through capture. To examine the behavior of the proposed odd-even model, a detailed burnup analysis of 181 fission product elements in 84 chains was performed using the fission product code EPRI-CINDER. A 154-group fission product cross-section library generated from the ENDFB/4 library was used as the basic cross-section library. These cross sections were collapsed to a four-group set suitable for use in CINDER using two spectra, one representative of the soft spectrum zones and the other representative of the hard spectrum zones of the FMSR. The analysis was performed for Pu-239, U-235 and U-238 fission in both spectra.
Dependence of heavy metal burnup on nuclear data libraries for fast reactors
Japan Nuclear Cycle Development Institute (JNC) is considering the highly burnt fuel as well as the recycling of minor actinide (MA) in the development of commercialized fast reactor cycle systems. Higher accuracy in burnup calculation is going to be required for higher mass plutonium isotopes ( sup 2 sup 4 sup 0 Pu, etc.) and MA nuclides. In the framework of research and development aiming at the validation and necessary improvements of fast reactor burnup calculation, we investigated the differences among the burnup calculation results with the major nuclear data libraries: JEF-2.2, ENDF/B-VI Release 5, JENDL-3.2, and JENDL-3.3. We focused on the heavy metal nuclides such as plutonium and MA in the central core region of a conventional sodium-cooled fast reactor. For main heavy metal nuclides ( sup 2 sup 3 sup 5 U, sup 2 sup 3 sup 8 U, sup 2 sup 3 sup 9 Pu, sup 2 sup 4 sup 0 Pu, and sup 2 sup 4 sup 1 Pu), number densities after 1-cycle burnup did not change over one or two percent. Library dependence was relatively large for MA nuclides. Number densities after 1-cycle burnup showed remarkable changes over 5% through 50%, especially for sup 2 sup 3 sup 6 U, sup 2 sup 3 sup 7 Np, sup 2 sup 4 sup 2 sup m Am, sup 2 sup 4 sup 3 Am, and curium isotopes. A burnup sensitivity analytical system based on the generalized perturbation theory enabled us to find out quantitatively the causative nuclide, reaction, and energy region. Taking sup 2 sup 4 sup 2 Cm (an important nuclide as a source of heat and neutron emission) as an example, discrepancy of its number density after burnup was composed of following three parts: the capture cross-section of sup 2 sup 4 sup 1 Am (energy range: 1 keV to 1 MeV), the isomeric ratio of sup 2 sup 4 sup 1 Am capture, and the fission cross-section of sup 2 sup 4 sup 2 Cm (around 500 keV). These three parts brought the differences of about 7%, about 12%, and about 4% in sup 2 sup 4 sup 2 Cm number density after 1-cycle burnup, respectively.
Accelerator driven subcritical reactors
2001-01-01
ADS concepts have been proposed in the last decade for a variety of applications. However, there is a convergence of interest of several countries and laboratories on the application of ADS to transmutation. This applies to plutonium, and/or minor actinides (MA) and long-lived fission products (LLFP). As far as the so-called partitioning and transmutation (PIT) strategies, it was indicated that they can be clarified according to the option taken with respect to Pu and MA, i.e., a) keep Pu and MA together, b) separate Pu from MA. At present several programs are going on ADS: in Japan, USA Europe, where activities in 9 countries are coordinated by a European Technical Working Group (ETWG), and in Russia. As far as the implications for the definition of nuclear data needs, dedicated subcritical cores should have new type of fuels (Pu+MA in different proportions). Proposals are being ...
Systematics of fission cross sections at the intermediate energy region
1997-03-01
The systematics was obtained with fitting experimental data for proton induced fission cross sections of Ag, {sup 181}Ta, {sup 197}Au, {sup 206,207,208}Pb, {sup 209}Bi, {sup 232}Th, {sup 233,235,238}U, {sup 237}Np and {sup 239}Pu above 20 MeV. The low energy cross section of actinoid nuclei is omitted from systematics study, since the cross section has a complicated shape and strongly depends on characteristic of nucleus. The fission cross sections calculated by the systematics are in good agreement with experimental data. (author)
1979-03-01
In response to an action by the Standards Subcommittee of the Cross Section Evaluation Working Group, a workshop was convened to determine the status of available information on prompt fission neutron spectra. The experimental data were reviewed and theoretical models were developed. The current ENDF/B fission neutron spectra files were summarized. Further work is currently under way, especially to provide a better theoretical tool to represent energy-dependent fission spectra. 5 references.
Neutron induced fission cross section measurements aimed at nuclear technology development
Neutron induced fission cross sections of 233U, 238U, 241Am, 243Am and 245Cm in the energy range between 500 keV and 20 MeV obtained at the n_TOF Neutron Time of Flight facility at CERN (Genve) are presented. Fission fragments had been detected by a gas counter with good discrimination between nuclear fission products and background events. A comparison between the extracted cross sections, previous experimental results and evaluated libraries is reported.
Cross section for the subbarrier fission of 244Cm
2010-01-01
The cross section for 244Cm fission induced by neutrons of energy in the range between 0.07 eV and 20 keV was measured by using the lead slowing-down spectrometer (LSDS-100) of the Institute for Nuclear Research (Russian Academy of Sciences, Moscow). The parameters of the resonance areas were determined for the lowest eight s-wave neutron resonances, and the respective fission widths were evaluated. Also, the parameters of the intermediate structure in the cross section for the subbarrier fission of 244Cm nuclei were evaluated. The results were compared with available data and recommendations based on evaluations.
Preliminary calculations of medium-energy fission cross sections and spectra
Nucleon-induced fission cross sections determined from a statistical preequilibrium model are used in conjunction with a new scission-point model of fission fragment mass, charge and excitation energy distributions to produce evaporation model calculations of particle and gamma spectra and multiplicities from fission. Comparisons are made to experiment for the 14.5-MeV neutron-induced fission of /sup 238/U. In addition, calculated particle and gamma spectra will be compared with the ENDF/B library for 2- and 5-MeV neutron-induced fission of /sup 235/U and /sup 238/U, respectively. Initial predictions for these same quantities for proton-induced fission reactions at energies up to 100 MeV will be presented and discussed. 6 refs., 3 figs.
Preliminary calculations of medium-energy fission cross sections and spectra
1988-01-01
Nucleon-induced fission cross sections determined from a statistical preequilibrium model are used in conjunction with a new scission-point model of fission fragment mass, charge and excitation energy distributions to produce evaporation model calculations of particle and gamma spectra and multiplicities from fission. Comparisons are made to experiment for the 14.5-MeV neutron-induced fission of /sup 238/U. In addition, calculated particle and gamma spectra will be compared with the ENDF/B library for 2- and 5-MeV neutron-induced fission of /sup 235/U and /sup 238/U, respectively. Initial predictions for these same quantities for proton-induced fission reactions at energies up to 100 MeV will be presented and discussed. 6 refs., 3 figs.
2010-01-01
We constrain the timing and kinematics of the Serifos detachment in the southwestern Cyclades, Greece, using low-temperature thermochronometry. Fission-track dating shows that the Serifos detachment was active between ~13 and 6Ma and that the Serifos granodiorite in its footwall intruded at or before ~1211Ma into the extensional shear zone and initially cooled very rapidly at rates
2007-01-01
Calculations of 239Pu(n, F) prompt fission neutron spectra have been performed for neutron energy up to 20 MeV. The exclusive spectra of pre-fission neutron reactions (n, xnf) were calculated on the basis of the Hauser-Feshbach model simultaneously with the cross sections of (n, F) and (n, 2n) reactions. The spectra of neutrons emitted by fission fragments were approximated by a sum of two Watt distributions. The components of the prompt fission neutron spectra due to pre-fission neutrons are manifested in the prompt fission neutron spectra and the average neutron energy. A correlation is established between this effect in the contribution of emissive fission (n, xnf) in the fission cross-section of 239Pu(n, F) and 235U(n, F). It is shown that the 239Pu(n, F) prompt fission neutron spectra used in applied calculations do not ...
Fission studies with 140 MeV alpha particles
2009-01-01
Binary fission induced by 140 MeV alpha particles has been measured for natAg, 139La, 165Ho, and 197Au targets. The measured quantities are the total kinetic energies, fragment masses, and fission cross sections. The results are compared with other data and systematics. A minimum of the fission probability in the vicinity Z2/A=24 is observed
Fission studies with 140 MeV $\\bm{\\alpha}$-Particles
2009-07-24
Binary fission induced by 140 MeV $\\alpha$-particles has been measured for $^{\\rm nat}$Ag, $^{139}$La, $^{165}$Ho and $^{197}$Au targets. The measured quantities are the total kinetic energies, fragment masses, and fission cross sections. The results are compared with other data and systematics. A minimum of the fission probability in the vicinity $Z^2/A=24$ is observed.
1958-01-01
a) Measurements of neutron induced fission cross-sections in the low energy region. The variation of the fission cross sections of several fissile isotopes has been measured and analysed, for neutron energies below 0,025 eV. The monochromator was a crystal spectrometer used in conjunction with a mechanical velocity selector removing higher order Bragg reflections. The fissile material was laid down on the plates of a fission chamber by painting technic. An ionization chamber, having its plates coated with thin 10B layers, was used as the neutron flux monitor. b) Measurement of the fission cross section of 235U. We intend to measure the variation of the neutron induced fission cross section of 235U over the neutron energy range from 1 keV by the time of flight method. The neutron source is the uranium target of a pulsed 28 MeV electron linear ...
sup 1 sup 9 sup 7 Au(800 A MeV)-on-proton collisions are used to investigate the fission dynamics at high excitation energy. The kinematic properties together with the isotopic identification of the fission fragments allow to determine the mass, charge and excitation energy of the fissioning nucleus at saddle. The comparison of these observables and the measured total fission cross section with model calculations evidences a clear hindrance of fission at high excitation energy that can be explained in terms of nuclear dissipation. Assuming a statistical evaporation for other de-excitation channels than fission, an estimated value of the transient time of fission of (3+-1)x10 sup - sup 2 sup 1 s is obtained.
Fifty years of nuclear fission: Nuclear data and measurements series
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.
Fifty years of nuclear fission: Nuclear data and measurements series
1989-06-01
This report is the written version of a colloquium first presented at Argonne National Laboratory in January 1989. The paper begins with an historical preamble about the events leading to the discovery of nuclear fission. This leads naturally to an account of early results and understanding of the fission phenomena. Some of the key concepts in the development of fission theory are then discussed. The main theme of this discussion is the topography of the fission barrier, in which the interplay of the liquid-drop model and nucleon shell effects lead to a wide range of fascinating phenomena encompassing metastable isomers, intermediate-structure effects in fission cross-sections, and large changes in fission product properties. It is shown how study of these changing effects and theoretical calculations of the potential energy of the deformed nucleus have led to broad qualitative understanding of the nature of the fission process. 54 refs., 35 figs.
1976-01-01
The evaluation of the /sup 235/U fission cross section from 100 eV to 20 MeV for ENDF/B-V is described. The evaluated average cross sections from 100 eV to 200 keV are given, and it is proposed to include structure in the cross section in this energy region. Above 200 keV, the cross section is given as a smooth curve, and is recommended as a standard. Preliminary error estimates in the cross section are also given.
Measurement of reaction cross sections of fission products induced by DT neutrons
1998-03-01
With the view of future application of fusion reactor to incineration of fission products, we have measured the {sup 129}I(n,2n){sup 128}I reaction cross section by DT neutrons with the activation method. The measured cross section was compared with the evaluated nuclear data of JENDL-3.2. From the result, it was confirmed that the evaluation overestimated the cross section by about 20-40%. (author)
Neutron induced fission cross section measurements on Actinides at n-TOF
2009-01-01
A series of measurements of neutron induced fission cross section of various transuranic elements have been performed at the CERN n-TOF spallation neutron facility, in the energy range from thermal to nearly 250 Me V. The experimental apparatus consists in a fast ionization chamber (FIC), used as a fission fragment detector with a high efficiency. Good discrimination between alpha particles and fission fragments can be obtained with a simple amplitude threshold. In order to allow the monitoring of the neutron beam and to extract the n-TOF neutron flux, the well known cross section of the 235 U(n,j) reaction, considered as a fission standard, has been used. Preliminary results for the cross section are shown for some selected isotopes such as 235 U, 233U and 245Cm in the energy range from ...
Instrumentation for fission cross section measurements on actinides
The paper describes three developments in instrumentation for actinide fission cross section measurements at ORNL. Two of these are related to the problem of detecting a few fission events in the presence of an extremely large alpha background. Time-of-flight measurements of neutron fission cross sections on highly alpha active actinide samples at electron linear accelerators have been hindered by pileup of alpha pulses in the amplifier, a noise contribution which is normally overwhelming. In the past, such measurements could only be made using underground nuclear explosions; indeed, much of the present knowledge of the fission cross sections of highly alpha-active nuclides comes from such measurements. The third development is an improved neutron beam monitor for time-of-flight measurements.
Instrumentation for fission cross section measurements on actinides
1978-01-01
The paper describes three developments in instrumentation for actinide fission cross section measurements at ORNL. Two of these are related to the problem of detecting a few fission events in the presence of an extremely large alpha background. Time-of-flight measurements of neutron fission cross sections on highly alpha active actinide samples at electron linear accelerators have been hindered by pileup of alpha pulses in the amplifier, a noise contribution which is normally overwhelming. In the past, such measurements could only be made using underground nuclear explosions; indeed, much of the present knowledge of the fission cross sections of highly alpha-active nuclides comes from such measurements. The third development is an improved neutron beam monitor for time-of-flight measurements.
Instrumentation for fission cross section measurements on actinides
1978-01-01
The paper describes three developments in instrumentation for actinide fission cross section measurements at ORNL. Two of these are related to the problem of detecting a few fission events in the presence of an extremely large alpha background. Time-of-flight measurements of neutron fission cross sections on highly alpha active actinide samples at electron linear accelerators have been hindered by pileup of alpha pulses in the amplifier, a noise contribution which is normally overwhelming. In the past, such measurements could only be made using underground nuclear explosions. Indeed, much of the present knowledge of the fission cross sections of highly alpha-active nuclides comes from such measurements. The third development is an improved neutron beam monitor for time-of-flight measurements
Fission cross sections in the intermediate energy region
1991-01-01
Until recently there has been very little cross section data for neutron-induced fission in the intermediate energy region, primarily because no suitable neutron source has existed. At Los Alamos, the WNR target-4 facility provides a high-intensity source of neutrons nearly ideal for fission measurements extending from a fraction of a MeV to several hundred MeV. This paper summarizes the status of fission cross section data in the intermediate energy range (En > 30 MeV) and presents our fission cross section data for {sup 235}U and {sup 238}U compared to intranuclear cascade and statistical model predictions.
Effects of nuclear orientation on fusion and fission process for reactions using 238U target nucleus
2010-01-01
Fission fragment mass distributions in the reaction of 30Si+238U were measured at the energies around the Coulomb barrier. At the above-barrier energies, the mass distribution showed Gaussian shape. At the sub-barrier energies, asymmetric fission mode peaked at AL/AHapprox =90/178 was observed. The asymmetric fission should be attributed to quasifission from the results of the measured evaporation residue (ER) cross-sections produced by 30Si+238U. The cross-section for 263Sg at the above-barrier energy agree with the statistical model calculation which assumes that the measured fission cross-sections are equal to the fusion cross-sections, whereas the one for 264Sg measured at the sub-barrier energy is smaller than the calculation, indicating the ...
On epidote fission track dating
2005-01-01
The use of epidote in fission track dating was abandoned since the beginning of the 1980s due to difficulties like absence of a standard etching procedure, obtainment of different closure temperatures and the percentage of the datable samples. The results become much more reproducible when restricting fission track analysis to a peculiar kind of track. We are also studying confined track length, what makes possible to obtain information about fossil track annealing. Fission tracks in epidote were successfully etched with 48% HF at 35 deg. C for 12.5min. Dating samples by the external detector method was not possible due to problems in measuring the efficiency factor held between the number of fossil fission tracks and tracks induced in mica. Dating a sample from Brejui, RN, Brazil with the population method gave a corrected age of 510+-69Ma, in agreement with ...
Neutron capture and fission reaction cross sections are usually measured relative to a standard basis. The most common absolute cross sections which are used in the thermal neutron energy region are /sup 197/Au and /sup 59/Co for capture reactions and /sup 235/U and /sup 239/Pu for fission reactions. Values for these four cross sections have been compiled and evaluated for the purpose of recommending standard values. 24 refs., 5 tabs. (WRF)
1985-01-01
Neutron capture and fission reaction cross sections are usually measured relative to a standard basis. The most common absolute cross sections which are used in the thermal neutron energy region are /sup 197/Au and /sup 59/Co for capture reactions and /sup 235/U and /sup 239/Pu for fission reactions. Values for these four cross sections have been compiled and evaluated for the purpose of recommending standard values. 24 refs., 5 tabs. (WRF)
1992-11-01
The [sup 235]U fission spectrum-averaged cross sections for 13 threshold reactions were measured with the fission plate (27 cm in diameter and 1.1 cm thick) at the heavy water thermal neutron facility of the Kyoto University Reactor. The Monte Carlo code MCNP was applied to check the deviation from the [sup 235]U fission neutron spectrum due to the room-scattered neutrons, and it was found that the resultant spectrum was close to that of [sup 235]U fission neutrons. Supplementally, the relations to derive the absorbed dose rates with the fission plate were also given using the calculated neutron spectra and the neutron Kerma factors. Finally, the present values of the fission spectrum-averaged cross sections were employed to adjust the [sup 235]U fission neutron spectrum with the NEUPAC code. The adjusted spectrum showed a good agreement with the Watt-type fission neutron spectrum. (author).
2007-01-01
Apatite fission-track (FT) and single grain (UTh)/He ages from four vertical profiles in central Dronning Maud Land (East Antarctica) range from 31220Ma to 13511Ma and 30428Ma to 1048Ma, respectively. The combined age data allows to discriminate between undisturbed cooled (due to exhumation) and thermally overprinted crustal blocks. Profiles at the Zwieselhhe and the Conradgebirge revealed unusual apatite FT vs. elevation relationships and (UTh)/He ages older than the corresponding central apatite FT ages, possibly providing evidence for a Jurassic thermal overprint. Most probably Jurassic magmatism and associated advective heating led to total annealing of the apatite fission-tracks but helium only partially diffused. The model developed in this paper suggests that...
2010-01-01
The clinical implications of microalbuminuria (MA) in nondiabetic persons with the metabolic syndrome (MS) are largely unknown. The present post hoc analysis of the Multiethnic Study of Atherosclerosis (MESA) included 5,809 nondiabetic persons with no history of cardiovascular disease aged 45 to 84 years. The study population was divided according to the presence or absence of MS and MA into 4 study groups: no MS and no MA, MA only, MS only, and MS plus MA. The measurements included markers of systemic inflammation, subclinical atherosclerosis, left ventricular mass index, composite and individual cardiovascular end points, and all-cause mortality. Prospective and cross-sectional analyses were performed to ascertain the association of study groups with these covariates. The MS plus MA grou...
2008-08-15
We present zircon fission track (FT) ages from the lower parts of the Higher Himalayan crystalline (HHC) ranging from 3.9 to 4.3 Ma and apatite FT age as 1.9{+-}0.4Ma. Combined with previous radiometric dates, these ages provide the low temperature data for the area and enable us to draw temperature-time plot which shows significant increase in cooling rates from 25 deg. C/Ma in Oligocene and 4{sup 0}C/Ma in Miocene to about 64 deg. C/Ma during Pliocene. For the Mandi granite, the zircon FT ages range from 3.9 to 4.9 Ma while apatite FT obtained is 2.8{+-}0.5Ma. The rapid Pliocene exhumation is characterized by a rapid increase in cooling rates from {approx}3.4 deg. C/Ma in Miocene to {approx}77 deg. C/Ma after 5.0 Ma. Our results confirm the rapid Pliocene to Pleistocene cooling of rocks of Kulu-Beas valley similar to that of the neighboring units from the frontal parts of HHC.
Silicic tephras in Pleistocene shallow-marine sediments of Wanganui Basin, New Zealand
2005-01-01
Vitric-rich volcaniclastic horizons are important for correlation of glacio-eustatic sedimentary cycles, both within the well known shallow-marine record of Wanganui Basin, and other New Zealand terrestrial and deep marine records. They also record distal major rhyolitic eruptions from the Taupo (TVZ) and Coromandel (CVZ) Volcanic Zones that are lacking in proximal source areas. Twenty-eight volcaniclastic horizons are recognised in the Castlecliffian and late Nukumaruan strata of Wanganui Basin from glass shard major element geochemistry and stratigraphic position, and are dated using magnetostratigraphy, orbitally tuned cyclostratigraphy and isothermal plateau fission track (ITPFT) ages. The major named volcaniclastic horizons (with ITPFT and/or astronomical ages, respectively) are: Onepuhi (0.57 Ma), Kupe (0.63 ± 0.08 Ma; 0.65 Ma), Kaukatea (0.86 ± 0.08 Ma; 0.90 Ma), Potaka (1.00 ± 0.03 Ma; 0.99 Ma), Rewa (1.20 ± 0.14 Ma; 1.19 Ma), Mangapipi (1.51 ± 0.16 Ma, 1.54 Ma), Ridge (1.56 Ma), Pakihikura (1.58 ± 0.08 Ma; 1.58 Ma), Birdgrove (1.60 Ma), Mangahou (1.63 Ma), Maranoa (1.63 Ma), Ototoka (1.72 ± 0.32 Ma; 1.64 Ma), Table Flat (1.71 ± 0.12 Ma; 1.65 Ma), Vinegar Hill (1.75 ± 0.20 Ma; 1.75 Ma), and Waipuru (1.79 ± 0.15 Ma; 1.83 Ma). The ITPFT ages are consistent with the astronomically tuned Geomagnetic Polarity Timescale. Volcaniclastic horizons in Wanganui Basin have been emplaced through a variety of primary and secondary processes, including direct tephra-fall as well as transitional water supported mass flow through to hyperconcentrated flow. No gas supported flow deposits have yet been recognised. Only some horizons from Wanganui Basin can be chemically and chronologically linked to known TVZ eruptions, while others remain uncorrelated owing to proximal source area erosion and/or burial as well as vapour phase alteration and devitrification within near-source welded ignimbrites. Nevertheless, many volcaniclastic deposits in Wanganui Basin can be reliably correlated to distal sedimentary successions in Auckland Region, Hawke’s Bay and in Ocean Drilling Program (ODP) cores 1123 and 1124, to the east of New Zealand. The orbitally tuned chronology for ODP cores, which is calibrated by numeric ages on tephras and magnetostratigraphy, enhances inter-regional correlation, providing an important framework for future palaeoenvironmental reconstructions. Publisher: ePublications@SCU Format: application/pdf Source: Humanities and Creative Arts Research Outputs
Measurement of the integral capture and fission cross sections for /sup 232/Th in the CFRMF
1979-01-01
The recent evaluation of the cross-section data bases for /sup 232/Th capture and fission emphasized significant normalization discrepancies between the available differential data. To help resolve the normalization discrepancies, the capture and fission integral cross sections were measured for /sup 232/Th in the fast neutron zone of the Coupled Fast Reactivity Measurements Facility (CFRMF). The cross sections are derived from the radiometric determination of the saturation reaction rates for fission and capture based on the Ge(Li) spectrometric measurement of the absolute gamma emission rates of the 537-keV and 1596-keV lines in the /sup 140/Ba - /sup 140/La decay and the 311.9-keV line in the /sup 233/Pa decay. For capture and fission, respectively, the measured integral cross sections are 291 mb +- 3% and 19.6 mb +- 5%. The ratios of the integral cross sections computed with ENDF/B-IV thorium cross sections and the CFRMF neutron spectrum to the above values are 0.99 for capture and 0.90 for fission. 19 references.
Evaluation of Cross-Section Sensitivities in Computing Burnup Credit Fission Product Concentrations
U.S. Nuclear Regulatory Commission Interim Staff Guidance 8 (ISG-8) for burnup credit covers actinides only, a position based primarily on the lack of definitive critical experiments and adequate radiochemical assay data that can be used to quantify the uncertainty associated with fission product credit. The accuracy of fission product neutron cross sections is paramount to the accuracy of criticality analyses that credit fission products in two respects: (1) the microscopic cross sections determine the reactivity worth of the fission products in spent fuel and (2) the cross sections determine the reaction rates during irradiation and thus influence the accuracy of predicted final concentrations of the fission products in the spent fuel. This report evaluates and quantifies the importance of the fission product cross sections in predicting concentrations of fission products proposed for use in burnup credit. The study includes an assessment of the major fission products in burnup credit and their production precursors. Finally, the cross-section importances, or sensitivities, are combined with the importance of each major fission product to the system eigenvalue (k{sub eff}) to determine the net importance of cross sections to k{sub eff}. The importances established the following fission products, listed in descending order of priority, that are most likely to benefit burnup credit when their cross-section uncertainties are reduced: {sup 151}Sm, {sup 103}Rh, {sup 155}Eu, {sup 150}Sm, {sup 152}Sm, {sup 153}Eu, {sup 154}Eu, and {sup 143}Nd.
Evaluation of Cross-Section Sensitivities in Computing Burnup Credit Fission Product Concentrations
2005-08-12
U.S. Nuclear Regulatory Commission Interim Staff Guidance 8 (ISG-8) for burnup credit covers actinides only, a position based primarily on the lack of definitive critical experiments and adequate radiochemical assay data that can be used to quantify the uncertainty associated with fission product credit. The accuracy of fission product neutron cross sections is paramount to the accuracy of criticality analyses that credit fission products in two respects: (1) the microscopic cross sections determine the reactivity worth of the fission products in spent fuel and (2) the cross sections determine the reaction rates during irradiation and thus influence the accuracy of predicted final concentrations of the fission products in the spent fuel. This report evaluates and quantifies the importance of the fission product cross sections in predicting concentrations of fission products proposed for use in burnup credit. The study includes an assessment of the major fission products in burnup credit and their production precursors. Finally, the cross-section importances, or sensitivities, are combined with the importance of each major fission product to the system eigenvalue (k{sub eff}) to determine the net importance of cross sections to k{sub eff}. The importances established the following fission products, listed in descending order of priority, that are most likely to benefit burnup credit when their cross-section uncertainties are reduced: {sup 151}Sm, {sup 103}Rh, {sup 155}Eu, {sup 150}Sm, {sup 152}Sm, {sup 153}Eu, {sup 154}Eu, and {sup 143}Nd.
What happens to the fission process above the 2nd- and 3rd-chance fission thresholds
1976-01-01
Although the multiple fission process is important at high neutron energies, most of the evaluations available today do not include these individual fission cross sections or their associated fission spectra. The representations used in the Los Alamos and Livermore libraries are described and calculations compared with 14-MeV integral experiments available on /sup 235/U, /sup 238/U, and /sup 239/Pu. Further work is needed to clearly delineate the specific problems in order to propose unique solutions.
Fusion-fission of heavy and superheavy nuclei
2003-01-01
Fusion-fission process of heavy and superheavy elements with Z = 82-122, formed in reactions with 48Ca and 58Fe ions at energies close to and below the Coulomb barrier, is studied. The experiments were conducted in the U-400 accelerator of the Flerov Laboratory of Nuclear Reactions (JINR) and in Legnaro Laboratory (LNL) using the time-of-flight spectrometer of fission fragments CORSET and neutron multi-detector DEMON. Mass and energy distributions of fission fragments, quasi-fission and cross sections of evaporating residues, multiplicities of neutrons and gamma-quanta and their dependences on the mechanism of formation and decay of compound systems were studied
Fission cross section measurements for minor actinides
1997-03-01
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)
Recent fission cross section standards measurements
The /sup 235/U(n,f) reaction is the standard by which most neutron induced fission cross sections are determined. Most of these cross sections are derived from relatively easy ratio measurements to /sup 235/U. However, the more difficult /sup 235/U(n,f) cross section measurements require the use of advanced neutron detectors for the determination of the incident neutron fluence. Examples of recent standard cross section measurements are discussed, various neutron detectors are described, and the status of the /sup 235/U(n,f) cross section standard is assessed. 23 refs., 8 figs., 4 tabs.
Curves and tables of neutron cross sections in JENDL-3.3
2002-11-01
Neutron cross sections of 337 nuclides in JENDL-3.3 are presented in figures and tables. In the tables, shown are cross sections at 0.0253 eV and 14 MeV, Maxwellian average cross sections (kT = 0.0253 eV), resonance integrals and fission spectrum average cross sections. The average cross sections calculated with typical reactor spectra are also tabulated. The numbers of delayed and total neutrons per fission are given in figures. (author)
MODELING AND FISSION CROSS SECTIONS FOR AMERICIUM.
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.
MODELING AND FISSION CROSS SECTIONS FOR AMERICIUM.
2005-05-01
This is the final report of the work performed under the LANL contract on the modeling and fission cross section for americium isotopes (May 2004-June 2005). The purpose of the contract was to provide fission cross sections for americium isotopes with the nuclear reaction model code EMPIRE 2.19. The following work was performed: (1) Fission calculations capability suitable for americium was implemented to the EMPIRE-2.19 code. (2) Calculations of neutron-induced fission cross sections for {sup 239}Am to {sup 244g}Am were performed with EMPIRE-2.19 for energies up to 20 MeV. For the neutron-induced reaction of {sup 240}Am, fission cross sections were predicted and uncertainties were assessed. (3) Set of fission barrier heights for each americium isotopes was chosen so that the new calculations fit the experimental data and follow the systematics found in the literature.
Comparison of {sup 235}U fission cross sections in JENDL-3.3 and ENDF/B-VI
2002-01-01
Comparisons of evaluated fission cross sections for {sup 235}U in JENDL-3.3 and ENDF/B-VI are carried out. The comparisons are made for both the differential and integral data. The fission cross sections as well as the fission ratios are compared with the experimental data in detail. Spectrum averaged cross sections are calculated and compared with the measurements. The employed spectra are the {sup 235}U prompt fission neutron spectrum, the {sup 252}Cf spontaneous fission neutron spectrum, and the neutron spectrum produced by a {sup 9}Be(d, xn) reaction. For {sup 235}U prompt fission neutron spectrum, the ENDF/B-VI evaluation reproduces experimental averaged cross sections. For {sup 252}Cf and {sup 9}Be(d, xn) neutron spectra, the JENDL-3.3 evaluation gives better results than ENDF/B-VI. (author)
Mass distribution in [sup 16]O-induced fission of [sup 232]Th
1993-01-01
The recoil catcher technique and gamma spectrometry of fission products were used to determine the cumulative/independent cross-sections of 18 fission products in 92 and 105 MeV [sup 16]O-induced fission of [sup 232]Th. The charge distribution parameters were obtained from the best fit of the mass distribution. At both energies the mass distributions are single peaked Gaussian. The fission cross-sections at 92 and 105 MeV are 386[+-]35 and 595[+-]48 mb and the total number of neutrons emitted per fission 8.4[+-]1.4 and 10.2[+-]1.6 respectively. (orig.)
Application of dynamic pseudo fission products and actinides for accurate burnup calculations
1996-09-01
The introduction of pseudo fission products for accurate fine-group spectrum calculations during burnup is discussed. The calculation of the density of the pseudo nuclides is done before each spectrum calculation from the actual densities and their cross sections of all nuclides to be lumped into a pseudo fission product. As there are also many actinides formed in the fuel during its life cycle, a pseudo actinide with fission cross section is also introduced. From a realistic burnup calculation it is demonstrated that only a few fission products and actinides need to be included explicitly in a spectrum calculation. All other fission products and actinides can be accurately represented in the pseudo nuclides. (author)
Energy dependence of fission probabilities induced by negative pions in Sn, Au and Bi
2007-01-15
Fission probabilities induced by negative pions in Sn, Au and Bi at different energies using variety of nuclear track detectors have been studied. The target-detector assemblies in 4{pi}-geometric configuration were irradiated at the AGS facility of Brookhaven National Laboratory, USA. After etching the exposed detectors at appropriate etching conditions the detectors have been scanned for the tracks of fission fragments produced as a result of interaction of pions with the target nuclei. Based on the track counts, the values of fission cross sections have been measured and fission probabilities have been calculated using the reaction cross-section calculated with the help of the cascade-exciton model code CEM95. The values of fission probability based on experimental fission cross-sections have been compared with the theoretically calculated values of fission probabilities obtained using the CEM95 code. Theoretical values of fission probability have been computed for incident pion energy up to 2500 MeV in Sn, Au and Bi for comparison to fission data for high energy negative pions at 500, 672, 1068, 1665 MeV and 2300 MeV energies for the same targets. The values of fission probability based on the experimental fission cross section and theoretically calculated values of fission probability have been compared. Reasonable agreement has been observed among the experimentally measured and theoretically computed values of fission probabilities. A saturation of probabilities has been observed for Au and Bi at higher energies, but for Sn an increase of probability with the increase of pion beam momentum up to 1665 MeV has been observed.
2008-01-01
Mass-energy distributions (MEDs) and capture-fission cross sections have been measured in the reaction 48Ca + 208Pb 256No at the energies Formula Not Shown using a double-arm time-of-flight spectrometer CORSET. It has been observed that MED of the fragments consists of two parts, namely, the classical fusion-fission process corresponding to the symmetric fission of 256No and quasi-fission "shoulders" corresponding to the light fragment masses Formula Not Shown and complimentary heavy fragment masses. The quasi-fission "shoulders" have a higher total kinetic energy (TKE) as compared with that expected for the classical fission. A mathematical formalism was employed for the MEDs fragment decomposition into fusion-fission and quasi-fission components. In the fusion-fission process a high-ener...
Very heavy fission fragments produced in the spallation reaction 238U+p at Formula Not Shown
2006-01-01
Fission fragments from Formula Not Shown GeV 238U ions impinging a hydrogen target are investigated by using the fragment separator FRS for magnetic selection of reaction products including ray-tracing, and DE-ToF techniques. On the basis of the kinematics of the fragments, binary fission can be assigned as production process up to very heavy fragments. Fission fragments are separated and identified as far as 184Re for the first time. Cross sections are measured and found in the range of 500 mb to 5 mb. Isobaric cross sections decrease smoothly with increasing masses. Beyond tungsten, fission fragments are hidden in the more abundant spallation evaporation residues. 283 isotopes of elements gadolinium to rhenium in the mass range 147 to 184 are observed and cross sections measured. All the...
The relationship between integral experimental data and nuclear fission parameters
1989-01-01
High sensitivities of critical assembly and reactor design parameters to the fission cross sections, prompt and delayed neutron yields, and fission spectra parameters have resulted in an important role of experimental integral data for the testing and verification of differential data and computational methods. The higher accuracy of the experimental integral data compared with the uncertainties of reactor parameters which result from the uncertainties of the differential data has led to their utilization in data adjustment procedures. Improvements of up to a factor of ten are obtained for reactor parameters, however, the uncertainties of the basic data are reduced by smaller amounts. Other integral data like the fission spectra averaged cross sections are used for the evaluation of cross sections and fission spectra. 33 refs., 4 figs., 4 tabs.
Neutron-induced fission cross-sections of actinides have been recently measured at the neutron time of flight facility n_TOF at CERN in the frame of a research project involving isotopes relevant for nuclear astrophysics and nuclear technologies. Fission fragments are detected by a gas counter with good discrimination between nuclear fission products and background events. Neutron-induced fission cross-sections of 233U and 243Am were determined relative to 235U. The present paper reports the results obtained at neutron energies between 0.5 and 20 MeV.
Recent improvements in the calculation of prompt fission neutron spectra: Preliminary results
1988-01-01
Three tropics have been considered in the refinement and improvement of our original calculations of prompt fission neutron spectra. These are an improved calculation of the prompt fission neutron spectrum N(E) from the spontaneous fission of /sup 252/Cf, a complete calculation of the prompt fission neutron spectrum matrix N(E,E/sub n/) from the neutron-induced fission of /sup 235/U, at incident neutron energies ranging from 0 to 15 MeV, and an assessment of the scission neutron component of the prompt fission neutron spectrum. Preliminary results will be presented and compared with experimental measurements and an evaluation. A suggestion has been made for new integral cross-section measurements.
Systematics of neutron-induced--fission cross sections in the MeV range
1977-07-11
Evidence of systematic behavior in neutron-induced--fussion cross sections has been observed in the actinide elements. Recently measured fission cross-section ratios show this behavior over the incident-neutron-energy range from 3 to 5 MeV.
Symmetric uranium neutron-induced fission
The symmetric SL-mode fission cross sections of sup 2 sup 3 sup 5 U(n, f) and sup 2 sup 3 sup 8 U(n, f) are analyzed up to the emissive fission threshold within a Hauser-Feshbach statistical model. A separate outer fission barrier is assumed for the SL-mode, while the inner one is assumed to be the same for the symmetric SL- and the asymmetric S1- and S2-modes. Axial asymmetry and mass-symmetry is assumed for the outer saddle of the SL-mode, as distinct from the S1- and S2-modes, which are axially symmetric and mass-asymmetric. The observed fission cross section behaviour is modelled using the interplay of few-quasiparticle excitations in the level density of the fissioning and residual nuclei. The SL-mode fission cross section seems to be controlled by a rather high outer fission barrier with significant transparency.
Production and validation of ORIGEN-S libraries from JEF2.2 and EAF3 data
1995-12-01
The data libraries for light elements, actinides and fission products of the ORIGEN-S code for depletion and transmutation calculations in the SCALE4.1 computer code system have been updated with respect to cross-section data, radioactive-decay data and fission-product yield data using JEF2.2 as the basic data source and EAF3 as an additional source. This required the fission-product library to be extended with 201 new fission-product nuclides or isomeric states. The effect of the update of different quantities involved is evaluated with a burnup benchmark. When ORIGEN-S is used as a stand-alone code, i.e without regular update of cross sections of the major nuclides due to changes in the neutron spectrum during burnup, the results show appreciable differences in actinide and fission-product densities due to the cross-section update. The effects of decay data and fission-product yield updates are generally small, but with noticeable exceptions. The update of fission and capture reaction energies gives a small but systematic change in actinide and fission-product concentration. (orig.).
Neutron cross sections for uranium-235 (ENDF/B-IV Release 3)
1996-09-01
The resonance parameters in ENDF6 (Release 2) U235 were adjusted to make the average capture and fission cross sections below 900 eV agree with selected differential capture and fission measurements. The measurements chosen were the higher of the credible capture measurements and the lower of the fission results, yielding a higher epithermal alpha. In addition, the 2200 m/s cross sections were adjusted to obtain agreement with the integral value of K1. As a result, criticality calculations for thermal benchmarks, and agreement with a variety of integral parameters, are improved.
Neutron characteristics of salt blanket micromodels containing eutectic mixtures of sodium, zirconium and uranium sulphides were measured on FKBN-2M, BIGR and MAKET installations. The effective fission cross sections of neptunium, plutonium, americium and curium isotopes were measured on the neutron spectra formed by micromodels. KEYWORDS: transmutation, minor actinides, fluoride salts, micromodel, critical assembly, neutron spectrum, multiplication coefficient, fission, effective cross section, nuclear track detector, nuclear data library
Neutron characteristics of salt blanket micromodels containing eutectic mixtures of sodium, zirconium and uranium sulphides were measured on FKBN-2M, BIGR and MAKET installations. The effective fission cross sections of neptunium, plutonium, americium and curium isotopes were measured on the neutron spectra formed by micromodels. KEYWORDS: transmutation, minor actinides, fluoride salts, micromodel, critical assembly, neutron spectrum, multiplication coefficient, fission, effective cross section, nuclear track detector, nuclear data library
2001-01-01
Neutron characteristics of salt blanket micromodels containing eutectic mixtures of sodium, zirconium and uranium sulphides were measured on FKBN-2M, BIGR and MAKET installations. The effective fission cross sections of neptunium, plutonium, americium and curium isotopes were measured on the neutron spectra formed by micromodels. KEYWORDS: transmutation, minor actinides, fluoride salts, micromodel, critical assembly, neutron spectrum, multiplication coefficient, fission, effective cross section, nuclear track detector, nuclear data library
2006-07-24
Fission cross sections and fission probabilities have been calculated for positive and negative pion induced fission of {sup 208}Pb, {sup 209}Bi, {sup 232}Th and {sup 238}U in small steps across the (3,3) resonance using the cascade-exciton model code CEM95. The values of these quantities computed using CEM95 code exhibited reasonable agreement with those of experimental values found in literature. In this selected energy interval, fission cross sections of {sup 232}Th and {sup 238}U depicted an increase with an increase in the energy of incident pion, reaching a maximum value and then decreasing, however fission probabilities remained unchanged. For {sup 208}Pb and {sup 209}Bi, both fission cross sections and probabilities indicated an increasing trend. Cross sections for actinides are found to be less dependent on the ratio of the level density parameters as compared to preactinidies. No significant change in the reaction mechanism was observed in the selected energy range.
2008-08-15
The study of pion-induced nuclear reactions are important because pion not only plays the role of a projectile, but also serves as intermediate step particle as in the case of interaction of other projectiles like photon and antiproton. The studies of pion-induced nuclear reaction have important applications, such as in accelerator-driven system (ADS) and in basic nuclear research to probe the nuclear structure. The studies of pion-induced reaction, particularly fission, are as important as the studies of nucleon-induced nuclear reactions, because inter-nuclear cascades in spallation targets are partly propagated by pions. The pion-induced fission has not been as much studied as fission induced by nucleons. The reason is that there is a limited number of facilities available for production of pions, and beam time is scant. Previously, pion-induced fission has been studied using dielectric track-detectors; at present the work has not been carried out using this technique due to non-availability of exposure facilities. So there is a need of computer codes to study cross-section of pion-induced fission, and the proper documentation of existing experimental data. In the present work, fission cross-sections induced by positive pions, for targets {sup 209}Bi, {sup 231}Pa, {sup 232}Th, {sup 238}U and {sup 239}Pu are computed using the cascade-exciton model code CEM95 upto 2500 MeV energy. Also a systematics of positive pion-induced fission is performed on the basis of that performed cross-sections of proton-induced fission. The computed cross-sections of fission using CEM95 have been compared with the available experimental data and with the fission cross-sections obtained using the systematics analysis. A reasonable agreement has been observed.
Theory in evaluation of actinide fission and capture cross sections
2004-01-01
The authors discuss the possibilities and limitations of the use of theory as a tool in the evaluation of actinide fission and capture cross-sections. They consider especially the target 235U as an example. They emphasize the roles of intermediate structure in the fission cross-section and of level width fluctuations in both intermediate structure and fine structure, noting that these lead to a breakdown of Hauser-Feshbach theory at sub-barrier and near barrier energies. At higher energies (where fluctuation-averaged Hauser-Feshbach theory is applicable) semi-quantitative and intuitive representations of transition state spectra and barrier level density functions have to be tested against experimental data wherever these are available. Adjustment of the fission cross-section against inelastic scattering to the much better known levels of the ...
Study of fission cross sections induced by nucleons and pions using the cascade-exciton model CEM95
2010-01-01
Nucleon and pion-induced fission cross sections at intermediate and at higher energies are important in current nuclear applications, such as accelerator driven systems (ADS), in medicine and for effects on electronics. In the present work, microscopic fission cross sections induced by nucleons and pions are calculated on a few important targets using the cascade-exciton model code CEM95 at various energies. A change of the ratio of the level density parameter in fission to neutron emission channels is taken into account with the change in the incident energy of the projectile. The computed cross sections indicate a good agreement when are compared with the experimental values found in the literature
Isotopic dependence of the cross section for the induced fission of heavy nuclei
2009-01-01
The cross sections for the induced fission of 211223Ra, 203211Rn, and 221231Th nuclei undergoing peripheral collisions with 208Pb nuclei are calculated on the basis of the statistical model. The role of the N = 126 neutron shell is studied. The level density in excited nuclei is determined within the Fermi gas model and a model that takes into account the collective enhancement of the level density. The inclusion of a particlehole excitation in addition to a collective Coulomb excitation makes it possible to obtain a satisfactory description of experimental cross sections for the fission of radium isotopes. The calculated ratios of the cross sections for the induced fission of 236U (237U) and 238U (239U) nuclei agree with experimental data.
2000-02-01
A simultaneous evaluation code SOK (Simultaneous evaluation on KALMAN) has been developed, which is a least-squares fitting program to absolute and relative measurements. The SOK code was employed to evaluate the fission cross sections of {sup 233}U, {sup 235}U, {sup 238}U, {sup 239}Pu, {sup 240}Pu, and {sup 241}Pu for the evaluated nuclear data library JENDL-3.3. Procedures of the simultaneous evaluation and the experimental database of the fission cross sections are described. The fission cross sections obtained were compared with evaluated values given in JENDL-3.2 and ENDF/B-VI. (author)
Astroneutron: Theoretical and Experimental Investigations into Neutron Cross-Sections of Neutron-Enriched Nuclei Capture and Fission, Creation of a Data Bank and Simulation of Natural Nucleosynthesis Processes.
NuMA after 30 years: the matrix revisited
2010-01-01
The large nuclear mitotic apparatus (NuMA) protein is an abundant component of interphase nuclei and an essential player in mitotic spindle assembly and maintenance. With its partner, cytoplasmic dynein, NuMA uses its cross-linking properties to tether microtubules to spindle poles. NuMA and its invertebrate homologs play a similar tethering role at the cell cortex, thereby mediating essential asymmetric divisions during development. Despite its maintenance as a nuclear component for decades after the final mitosis of many cell types (including neurons), an interphase role for NuMA remains to be established, although its structural properties implicate it as a component of a nuclear scaffold, perhaps as a central constituent of the proposed nuclear matrix.
2010-01-01
Hyperbranched poly(ester amide) polymer (Hybrane S1200, Mn 1200gmol-1) was functionalized with maleic anhydride (MA) and propylene sulfide, to obtain multifunctional cross-linkers with fumaric and thiol end groups, S1200MA and S1200SH, respectively. The degree of substitution (DS) of maleic acid groups was controlled by varying the molar ratio of MA to S1200 in the reaction mixture. Hydrogels were obtained by UV cross-linking of functionalized S1200 and poly(ethylene glycol) diacrylate in aqueous solutions. Compressive modulus increased with decreasing S1200/PEG ratio and also depended on the DS of the multifunctional cross-linker (S1200). Also, heparin-based macromonomers together with functionalized hyperbranched polymers were used to construct novel functional hydrogels. The multivalent...
2010-01-01
ABSTRACT We present the first fission-track (FT) thermochronology results for the NW Zagros Belt (SW Iran) in order to identify denudation episodes that occurred during the protracted Zagros orogeny. Samples were collected from the two main detrital successions of the NW Zagros foreland basin: the Palaeocene-early Eocene Amiran-Kashkan succession and the Miocene Agha Jari and Bakhtyari Formations. In situ bedrock samples were furthermore collected in the Sanandaj-Sirjan Zone. Only apatite fission-track (AFT) data have been successfully obtained, including 26 ages and 11 track-length distributions. Five families of AFT ages have been documented from analyses of in situ bedrock and detrital samples: pre-middle Jurassic at 171 and 225 Ma, early-late Cretaceous at 91 Ma, Maastrichtian at 66 Ma...
2009-01-01
Abstract Apatite fission track dating of five samples from Cenozoic volcanic strata in the Nimu District in the southern Gangdese Terrane exhibits single population grain ages with a single mean age and associated central ages ranging from 6.8 +- 0.6 Ma to 9.7 +- 1.2 Ma. Mean track lengths are between 12.9 +- 1.7 m and 14.2 +- 2.3 m with a single peak characteristic of a single thermal event. The newly documented ages coincide well with the age of high sedimentation rates in the North Tibet Basin that resulted from a 9-5 Ma compressional event. Track length modeling allows three stages to be identified in the sample cooling. The first stage (12-8 Ma) records a period of relative stability with little, if any, cooling at temperatures of 120-110degreeC suggesting this region had low relief. ...
2000-07-01
In the present work the performance of several processes used for advanced reprocessing of commercial LWR fuels as well as transmutation targets is compared. As a first step uranium and plutonium were recovered by PUREX type reprocessing. The raffinate, containing fission products, lanthanides and the minor actinides (MA) were used as feed for the second step in which minor actinides and lanthanides were separated from the bulk of the fission products. The five different processes tested use CMPO, DIDPA, TRPO, Diamide and CYANEX 923 as extractant. In the third step MA are separated from lanthanides. Here three processes were tested, i.e. using CYANEX 301, the synergistic mixture of di-chloro substituted CYANEX 301 and TOPO, and BTP solvents. Column-, batch- and continuous counter-current extraction techniques were used for the tests. The different processes will be described and discussed in terms of performances and efficiencies for Am and Cm. Efficient separation of MA from different genuine fuel solutions could be demonstrated and thereby also the possibility of closing a future transmutation fuel cycle. The combination, Diamide and BTP was found to be the best among extractants tested to achieve an efficient MA recovery from spent fuel. (authors)
Recent experimental data on sub-barrier fission of light actinides
1986-01-01
Neutron induced fission cross-section and fission fragment angular distribution data for the light actinide elements are reviewed and examined to see how well some of the data can be explained in terms of the properties of the fission potential barrier. Our understanding is at a stage where the 'thorium anomaly' which arises when certain cross-sections are interpreted in terms of a double-hump fission potential barrier, has been removed by interpreting the data in terms of a shallow third minimum. The data for /sup 230/Th provide a sensitive test for this model and their interpretation is examined in detail. The data available for the target nuclei /sup 227/Ac, /sup 228/Th, /sup 232/Th, /sup 231/Pa and the sub-actinide /sup 226/Ra are also noted.
Properties of the reaction 238U Formula Not Shown at the vibrational resonances
2009-01-01
Recent fission cross-section calculations for the reaction 238U Formula Not Shown , based on an extended statistical model, predict a significant change of fission fragment properties, such as the mean mass by Formula Not Shown and a notable increase in total kinetic energy in the region of the vibrational resonance at an incident neutron energy Formula Not Shown . This model includes individual fission cross-sections by the asymmetric standard 1 (S1) and standard 2 (S2) as well as the symmetric super-long (SL) mode. In order to verify the model predictions, a dedicated experiment on 238U has been carried out to measure fission-fragment mass yield distributions for incident neutron energies from Formula Not Shown down to 0.9 MeV, where the fission characteristics at the vibrational resonan...
Nuclide Cross-Sections Of Fission Fragments In The Reaction 208Pb+p At 500 A MeV
The isotopic distributions and recoil velocities of the fission fragments produced in the spallation reaction 208Pb+p at 500 A MeV have been measured using the inverse kinematics technique. The shapes of the different distributions are found in good agreement with previously published data while the deduced total fission cross-section is higher than expected. From the experimental data, the characteristics of the average fissioning system can be reconstructed in charge, mass and excitation energy and the number of post-fission neutrons can be inferred. The results are also compared to different models describing the spallation reaction.
Methodology and application of the WIMS-D4M fission product data
1995-02-01
The WIMS-D4 code has been modified (WIMS-D4m) to generate burn-up dependent microscopic cross sections for use in full core depletion calculations. The calculation of neutron absorption by fission products can be obtained from a reduced fission-product-chain model that includes the {sup 135}Xe and {sup 149}Sm chains, and a lumped fission product to account for the absorption by fission products not explicitly treated. Burn-up calculations were performed for the ANS MEU core using WIMS and EPRI-CELL cross sections. The calculated eigenvalues and material loadings are in good agreements.
1967-01-01
The comparison of measured and calculated central fission ratios provides a useful method for checking the accuracy of calculated spectra and fission cross-section data. A set of parallel plate fission chambers was specially made for Zebra. The design was based on that of Kirn's chambers used by the ZPR-III group at ANL, Idaho, and incorporated a number of improvements. In particular, the wall thickness was reduced to reduce the degradation of the spectrum. The fissile coatings in the earlier chambers were prepared by a painting technique and those in the later chambers by an electrodeposition method. The mass deposited was determined by low geometry or assay. The construction of the chambers and the method of calibration and use are described. Central fission ratios in six Zebra cores measured to an accuracy of 1-3% are compared with values computed using the FD2 data set and the ...
2003-09-29
The capture-fission cross-sections in an energy range of 206-242 MeV of 48Ca-projectiles and mass-energy distributions (MEDs) of reaction products in an energy range of 211-242 MeV have been measured in the 48Ca+208Pb reaction using the double-arm time-of-flight spectrometer CORSET. The MEDs of fragments for heated fission were shown to consist of two components. One component, which is due to classical fusion-fission, is associated with the symmetric fission of the 256No compound nucleus. The other component, which appears as ''shoulders'', is associated with the quasi-fission process and can be named ''quasi-fission shoulders''. Those quasi-fission shoulders enclose light fragments whose masses are 60-90 a.m.u. The total kinetic energy (TKE) of the fragments that belong to the shoulders is higher than the value expected for a classical fusion-fission process. We have come to the conclusion that in quasi-fission, spherical shells with Z=28 and N=50 play a great role. It has also been demonstrated that the properties of the MEDs of fragments formally agree with a well-known hypothesis of two independent fission modes; in this case the modes are normal fusion-fission and quasi-fission processes. A high-energetic Super-Short mode of classical fission has been found at low excitation energies in the mass range of heavy fragments M = 130-135 and TKE = 233 MeV; however the yield associated with this mode is small.
Prompt fission neutron spectra of {sup 235}U above emissive fission threshold
2005-10-17
Statistical model calculations of prompt fission neutron spectra (PFNS) from {sup 235}U(n,F) reaction were performed for incident neutron energies up to E{sub n}{approx}20 MeV. Exclusive spectra of the pre-fission (pre-saddle) (n,xnf) reaction neutrons, were calculated with Hauser-Feshbach statistical model, fission and (n,xn) reaction cross section data being described consistently. Spectra of neutrons, evaporated from the fission fragments, were approximated as a sum of two Watt distributions. The reduced neutron velocity in the center-of-mass system due to the neutron emission during fragment acceleration was assumed. PFNS component due to pre-saddle neutrons is evidenced in the shape of the measured PFNS data. We show it to be strongly correlated with the emissive fission contributions to the observed fission cross sections.
Prompt fission neutron spectra of 235U above emissive fission threshold
2005-01-01
Statistical model calculations of prompt fission neutron spectra (PFNS) from 235U(n,F) reaction were performed for incident neutron energies up to Enapprox20 MeV. Exclusive spectra of the pre-fission (pre-saddle) (n,xnf) reaction neutrons, were calculated with Hauser-Feshbach statistical model, fission and (n,xn) reaction cross section data being described consistently. Spectra of neutrons, evaporated from the fission fragments, were approximated as a sum of two Watt distributions. The reduced neutron velocity in the center-of-mass system due to the neutron emission during fragment acceleration was assumed. PFNS component due to pre-saddle neutrons is evidenced in the shape of the measured PFNS data. We show it to be strongly correlated with the emissive fission contributions to the observed fission cross sections
Prompt fission neutron spectra and average prompt neutron multiplicities
1983-01-01
We present a new method for calculating the prompt fission neutron spectrum N(E) and average prompt neutron multiplicity anti nu/sub p/ as functions of the fissioning nucleus and its excitation energy. The method is based on standard nuclear evaporation theory and takes into account (1) the motion of the fission fragments, (2) the distribution of fission-fragment residual nuclear temperature, (3) the energy dependence of the cross section sigma/sub c/ for the inverse process of compound-nucleus formation, and (4) the possibility of multiple-chance fission. We use a triangular distribution in residual nuclear temperature based on the Fermi-gas model. This leads to closed expressions for N(E) and anti nu/sub p/ when sigma/sub c/ is assumed constant and readily computed quadratures when the energy dependence of sigma/sub c/ is determined from an optical model. Neutron spectra and average multiplicities calculated with an energy-dependent cross section agree well with experimental data for the neutron-induced fission of /sup 235/U and the spontaneous fission of /sup 252/Cf. For the latter case, there are some significant inconsistencies between the experimental spectra that need to be resolved. 29 references.
1988-01-01
An improved calculation is presented for the prompt fission neutron spectrum N(E) from the spontaneous fission of /sup 252/Cf. In this calculation the fission-spectrum model of Madland and Nix is used, but with several improvements leading to a physically more accurate representation of the spectrum. Specifically, the contributions to N(E) from the entire fission-fragment mass and charge distributions will be calculated instead of calculating on the basis of a seven-point approximation to the peaks of these distributions as has been done in the past. Therefore, values of the energy release in fission, fission-fragment kinetic energy, nuclear level density, and compound nucleus cross section for the inverse process will be considered on a point-by-point basis over the fragment yield distributions instead of considering averages of these quantities over the peaks of the distributions. Particular attention will be given to the energy-dependent compound nucleus cross sections and to the nuclear level density model. Other refinements to the calculation of N(E) will also be discussed. Results will be presented and compared with earlier calculations of the spectrum and with recent experimental measurements of the spectrum. 9 figs.
Fission studies in the reaction of 19F with 209Bi at 99.2 MeV
2009-01-01
Fission product yield studies in the reaction of 99.2 MeV 19F with 209Bi have been carried out for the first time using gamma-ray spectrometry. The cross sections for the production of fission products have been determined. The yield distribution of fission products was found to be symmetric and broad with FWHM around 22 mass units and peak near mass 111. The average number of neutrons emitted per fission has been found to be around 6.7. The comparison of the fission products yield distribution of 209Bi using projectiles like 4He, 12C, 16O, and 19F have shown that the mass of symmetric peak increases as the mass of the compound nucleus increases. The high fission yield around mass 112 has been attributed to the presence of deformed neutron shells. The total fission cross section and width ...
Statistical and dynamical aspects of nuclear fission
1995-12-31
In the analysis of pre-fission neutron multiplicity, long life time fission component and fission probability, the behaviours of essential parameters characterizing fission dynamics, i.e., the friction parameter {gamma}/2{omega}{sub 0}, the critical temperature for healing of shell and pairing correction T{sub c}, the transient time parameter t{sub c} and the level density parameter a{sub f}/a{sub n} are discussed in the frame of a modified statistical model. It is found that the critical temperature T{sub c} affects significantly the experimental observables and is crucial especially for the estimation of evaporation residue cross section in competition with fission process, i.e., sensitive for the synthesis of super heavy elements. (authors). 33 refs., 9 figs.
Medium energy proton induced fission in Tb, La and Ag
1979-01-01
Coincidence studies with silicon surface barrier detectors have been used to determine fragment kinetic energies, angular correlations and fission cross sections in the fission of Ag, 139La, 159Tb and U nuclei induced by 600 MeV protons. Symmetric mass distributions are deduced for Ag and Tb, whereas La shows an indication of a stable asymmetric mass distribution. We find no indication of the Businaro-Gallone point. Fission-spallation competition calculations are used to deduce values of macroscopic fission barrier heights and nuclear level density parameter values at deformation corresponding to the saddle point shapes. We find macroscopic fission barriers lower than those predicted by macroscopic theories. The total kinetic energies at symmetric mass divisions follow closely the Viola prediction. (orig.)
2010-01-01
Yield-weighted average cross sections of neutron radiative capture, (n,2n), and (n,3n) reactions over prompt fission products (FPs) from 235U and 239Pu are calculated. The prompt fission production yields are taken from the ENDF/B-VII.0 library. The FPs for each fissile material exist over a range of approximately 1000 neutron-rich nuclides. Several nuclear reaction codes are utilized for calculating the cross sections on each individual fission product - EMPIRE-2.19, TALYS-1.0, GNASH, and CoH. The influence of the FP isomers on the average cross sections is examined with TALYS. We investigate the dependence of the average cross sections on the number of FPs taken for averaging. It is shown that the average capture cross section is much more sensitive to the number of FPs included, compared with the (n,2n) and (n,3n) reactions. An intercomparison ...
Graphs of all neutron cross sections and photon production cross sections on the Recommended Monte Carlo Cross Section (RMCCS) library have been plotted along with local neutron heating numbers. Values for anti ..nu.., the average number of neutrons per fission, are also given.
Graphs of all neutron cross sections and photon production cross sections on the Recommended Monte Carlo Cross Section (RMCCS) library have been plotted along with local neutron heating numbers. Values for anti ..nu.., the average number of neutrons per fission, are also given.
1980-05-01
Graphs of all neutron cross sections and photon production cross sections on the Recommended Monte Carlo Cross Section (RMCCS) library have been plotted along with local neutron heating numbers. Values for anti ..nu.., the average number of neutrons per fission, are also given.
1980-06-01
Graphs of all neutron cross sections and photon production cross sections on the Alternate Monte Carlo Cross Section (AMCCS) library have been plotted along with local neutron heating numbers. The values of ..nu..-bar, the average number of neutrons per fission, are also plotted for appropriate isotopes.
1990-01-01
Flurite mineralization occuring along two major faults in coastal areas of inner Trondheimsfjord has been dated by the fission-track method. Fluorite from the Ystad Fault near Hylla gave ages of 57.4 +- 31.6 and 64.8 +- 22.6 Ma, while a sample from the Slipra Fault near Mosvik gave a date of 76.1 +- 41.2 Ma. Although caution must be exercised in view of the large error margins, the dating provides a minimum age of Late Cretaceous/Early Tertiary for this hydrothermal activity. It is suggested that the fluorite mineralization developed in Late Cretaceous time shortly before a phase of rapid crustal uplift recorded in the Early Tertiary. 23 refs., 1 tab
Determination of absolute fission cross section ratios using the method of threshold cross sections
Fission cross section measurements for a collection of uranium and plutoninm isotopes are presertly being made at LLL by using the 100-MeV electron linear accelerator as a pulsed source for neutrons. The cross sections are measured as a function of neutron energy from 15 MeV down to thermal energy by using the time-of-flight technique. For neutron energies above 1 MeV, a new method for determining absolute fission cross section ratios is used. This method, called the method of threshold cross sections, gives absolute fission cross section ratios without the need for determing the absolute masses of flssionable material within flssion chambers. An explanation of the threshold cross section method is given, and an example is cited for the absolute ratio sigma /sub f/(238): sigma /sub f/ (235) above 1 MeV. (auth)
Principles of nuclear science and engineering
1987-01-01
The book begins with a discussion and analysis of the fundamental connection between matter and energy. Selected nuclear phenomena are then introduced, relevant to nuclear engineering. The individual chapters cover specific themes: nuclear structure and properties, nuclear decay, radiation assessment, neutron-nucleus interactions, fission dynamics, fission reactors, nuclear energy conversion, fission phenomena and fission energetics. An understanding of the main areas of physical science and mathematics at undergraduate level is assumed, although formulae are derived from first principles. Selected data, physical constants, specialized topics (particle accounting and cross sections), recommended demonstration experiments and a reading list are given in appendices. A chart of the nuclides is also included.
Fusion barrier distributions and fission anisotropies
1995-01-01
Fusion excitation functions for 16,17O+144Sm have been measured to high precision. The extracted fusion barrier distributions show a double-peaked structure interpreted in terms of coupling to inelastic collective excitations of the target. The effect of the positive Q-value neutron stripping channel is evident in the reaction with 17O. Fission and evaporation residue cross-sections and excitation functions have been measured for the reaction of 16O+208Pb and the fusion barrier distribution and fission anisotropies determined. It is found that the moments of the fusion l-distribution determined from the fusion and fission measurements are in good agreement. ((orig.))
Fission product inventory calculation by a CASMO/ORIGEN coupling program
1997-12-31
A CASMO/ORIGEN coupling utility program was developed to predict the composition of all the fission products in spent PWR fuels. The coupling program reads the CASMO output file, modifies the ORIGEN cross section library and reconstructs the ORIGEN input file at each depletion step. In ORIGEN, the burnup equation is solved for actinides and fission products based on the fission reaction rates and depletion flux of CASMO. A sample calculation has been performed using a 14 x 14 PWR fuel assembly and the results are given in this paper. 3 refs., 1 fig., 1 tab. (Author)
Fission product inventory calculation by a CASMO/ORIGEN coupling program
1997-10-01
A CASMO/ORIGEN coupling utility program was developed to predict the composition of all the fission products in spent PWR fuels. The coupling program reads the CASMO output file, modifies the ORIGEN cross section library and reconstructs the ORIGEN input file at each depletion step. In ORIGEN, the burnup equation is solved for actinides and fission products based on the fission reaction rates and depletion flux of CASMO. A sample calculation has been performed using a 14 x 14 PWR fuel assembly and the results are given in this paper.
Energy and mass distributions of induced-fission of 197Au nucleus by 29 MeV protons
2007-01-01
A thin target of 197Au is bombarded with 29 MeV protons from the cyclotron at Department of Nuclear Research Centre for Agriculture and Medicine. Correlated energies of fission-fragment pairs are measured with silicon surface-barrier detectors and their time of flights is made using a spectrometry pair. The fission cross section, fragment mass distribution, and total kinetic energy distribution of the fission fragments are measured in our experiment. The results are also compared with the previous works and good agreements are found. (authors)
Fission fragments of 1 GeV/nucleon U238 nuclei interacting with a deuterium target have been investigated with the Fragment Separator at GSI (Darmstadt) by measuring the isotopic production cross sections and fragment velocities. The combination of these two observables enabled to disentangle the high- and low-energy fission modes. Specific properties of these two modes were analyzed; in particular, the charge distribution of the fissioning projectile-like prefragments could be determined for the first time.
Photonuclear reactions of actinides in the giant dipole resonance region
2010-01-01
Photonuclear reactions at energies covering the giant dipole resonance (GDR) region are analyzed with an approach based on nuclear photoabsorption followed by the process of competition between light-particle evaporation and fission for the excited nucleus. The photoabsorption cross-section at energies covering the GDR region is contributed by both the Lorentz-type GDR cross-section and the quasi-deuteron cross-section. The evaporation-fission process of the compound nucleus is simulated in a Monte Carlo framework. Photofission reaction cross-sections are analyzed in a systematic manner in the energy range of propor to 10-20 MeV for the actinides 232Th, 238U and 237Np. Photonuclear cross-sections for the medium-mass nuclei 63Cu and 64Zn, for which there are no fission events, are also ...
Photonuclear reactions of actinides in the giant dipole resonance region
2009-11-03
Photonuclear reactions at energies covering the giant dipole resonance (GDR) region are analyzed with an approach based on nuclear photoabsorption followed by the process of competition between light particle evaporation and fission for the excited nucleus. The photoabsorption cross section at energies covering the GDR region is contributed by both the Lorentz type GDR cross section and the quasideuteron cross section. The evaporation-fission process of the compound nucleus is simulated in a Monte-Carlo framework. Photofission reaction cross sections are analyzed in a systematic manner in the energy range of $\\sim$ 10-20 MeV for the actinides $^{232}$Th, $^{238}$U and $^{237}$Np. For medium mass nuclei such as $^{64}$Zn, there are no fission events at these energies. The study reproduces satisfactorily the available experimental data of photofission cross sections at GDR energy region and the increasing trend of nuclear fissility with the fissility parameter $Z^2/A$ for the actinides.
2010-01-01
Abstract The Yanji area, located at the border of China, Russia, and Korea, where the Phanerozoic granitoids have been widely exposed, was considered part of the orogenic collage between the North China Block in the south and the Jiamusi-Khanka Massifs in the northeast. In this study, the cooling and inferred uplift and denudation history since the late Mesozoic are intensively studied by carrying out apatite and zircon fission-track analyses, together with electron microprobe analyses (EMPA) of chemical compositions of apatite from the granitoid samples in the Yanji area. The results show that: (i) zircon and apatite fission-track ages range 91.7-99.6 Ma and 76.5-85.4 Ma, respectively; (ii) all apatite fission-track length distributions are unimodal and yield mean lengths of 12-13.2 m, an...
Multi-layered parallel plate ionization chamber for cross-section measurements of minor actinides
A multi-layered parallel plate ionization chamber (MLPPIC) has been developed for the measurement of neutron-induced fission cross-sections using the lead slowing-down neutron spectrometer at the Research Reactor Institute, Kyoto University. The MLPPIC consists of two sets of multi-layered electrodes to detect fission fragments from two samples located back-to-back between them. The performance of the MLPPIC was tested with a spontaneous fission of 248Cm. The cross-section for the neutron-induced fission of 241Am was successfully obtained using that of 235U as a reference.
JEF-1 and JEF-2 fission product cross-section files
1992-01-01
The paper contains a short description of the JEF-1 and JEF-2 fission product cross-section file. JEF-1 contains a selection of European and Japanese cross-section evaluations, supplemented with ENDF/B-V data for less important fission products. In JEF-2 revisions and updates have been made, mainly in the thermal and resolved-resonance range. The JEF-1 fission product file has been extensively benchmarked for fast reactor applications. Since most of the revisions in JEF-2 apply to the low energy range, these results are still valid. Further benchmarking is in progress.
FISSION OF Ag AND Br IN NUCLEAR EMULSION BY 1.0-3.0 Bev PROTONS
ABS>A study is made of the fission stars produced in a lowsensitivity nuclear emulsions by protons at 1 to 3 Bev. These events are characterized by two densely ionizlng tracks in approximately opposite directions. The fractions of the inelastic cross section of Ag and Br leading to fission at 1.0, 2.0, and 3.0 Bev are 0.03, 0.06, and O.1l, respectively. Symmetric fission is most probable: in 4I% of the events the ratio of track lengths is 1.Oto 1.5; in 27% the ratio is 1.5 to 2.0. The fission fragment velocity distribution (mean of 0.044c) is derived from the range distribution (mean of 9 mu ). The average angle between the fission fragments deviates from pi by 42 deg , indicating that the center-of-mass system is moving at a mean velocity of 0.016c approximately along the line bisecting the angle between the fragments. From a study of the energy spectrum of the alpha particles and of their angular distribution with respect to the-fission fragments it appears that about 75% of the alphas are emitted prior to fission and about 25% simultaneously with fission. (auth)
Competition between fusion-fission and quasifission processes in $^{32}$+$^{184}$W reaction
2009-06-05
The angular distribution of fission fragments for the $^{32}$S + $^{184}$W reaction at center-of-mass energies of 118.8, 123.1, 127.3, 131.5, 135.8, 141.1 and 144.4 MeV were measured. The experimental fission excitation function is obtained. The fragment angular anisotropy is found by extrapolating the fission angular distributions. The measured fission cross sections are decomposed into fusion-fission, quasifission and fast fission contributions by the dinuclear system model. The total evaporation residue and fusion-fission excitation functions are calculated in the framework of the advanced statistical model. The hindrance to complete fusion at small collision energies increases due to the increase of quasifission events and it is explained by the elongated shape of the dinuclear system which is formed in collisions with small orientation angles to the beam direction. An increase of the hindrance to complete fusion at large beam energies is explained by the dependence of the quasifission and intrinsic fusion barriers of dinuclear system on its angular momentum: at large angular momentum the quasifission barrier decreases and the intrinsic fusion barrier increases. In this reaction the contributions of fusion-fission and quasifission fragments are comparable.
Decay heat calculation for minor actinides in the hybrid method
1999-03-01
For evaluation of decay heat from the fission of minor actinides (MAs) we are currently forced to rely only on summation calculations since there has been no direct measurement for these nuclides. In this paper, we use an alternative approach (named `hybrid` method) to evaluate the MA decay heat power using the measured decay heat powers for major actinides at YAYOI. Results for the fast fissions of {sup 237}Np, {sup 241}Am, {sup 243}Am, {sup 242}Cm and {sup 244}Cm are in support of the summation calculations for {beta} decay heat, but suggest notable uncertainties in {gamma} decay-heat summation calculations. (author)
Spallation-Fission Competition in Heaviest Elements; HeliumIon-Induced Reactions in Uranium Isotopes
1958-01-01
A radiochemical study of fission and spallation products produced by bombardment of U{sup 233}, U{sup 235}, and U{sup 238} with 18-46 Mev helium ions has been made. As in the case of similar studies using isotopes of plutonium as targets, most of the reaction cross section is taken up by fission. Also, the pronounced increase of the total cross section for ({alpha},xn) reactions with increasing mass number of the target that was observed for plutonium targets is observed for uranium targets.
Spallation-Fission Competition in Heaviest Elements; HeliumIon-Induced Reactions in Uranium Isotopes
1957-11-01
A radiochemical study of fission and spallation products produced by bombardment of U{sup 233}, U{sup 235}, and U{sup 238} with 18-46 Mev helium ions has been made. As in the case of similar studies using isotopes of plutonium as targets, most of the reaction cross section is taken up by fission. Also, the pronounced increase of the total cross section for ({alpha},xn) reactions with increasing mass number of the target that was observed for plutonium targets is observed for uranium targets.
This seminal article contains the first evidence of the fission of plutonium239 by slow neutrons. It reports that the cross section for fission of Pu239 is greater that that for U235. The researchers used two separate methods to prove that the fission was not due to the presence of uranium impurity: the chemical isolation and identification of plutonium and the measurements of the ratios of cross sections of slow neutrons to fast neutrons in Pu239 and natural uranium, which resulted in different values. The half life of Pu239 was estimated to be 30,000 years. The article was submitted in 1941, withheld from publication during World War II, and published in 1946 with some omissions of classified material.
Neutron data evaluation of 233U
2003-01-01
Consistent evaluation of 233U measured data base is performed. Hauser-Feshbach- Moldauer theory, coupled channel model and double-humped fission barrier model are employed. Total, differential scattering, fission and (n,xn) data are calculated using fission cross section data description as a major constraint. The direct excitation of ground state is calculated within rigid rotator model. Average resonance parameters are provided, which reproduce evaluated cross sections in the range of 0.6-40.5 keV. (author)
Fission and Quasifission in the 'Warm' Fusion Reactions
2010-01-01
Mass-energy distributions, as well as capture cross-section of fission-like fragments for the reactions of 48Ca, 58Fe and 64Ni ions with actinides leading to the formation of superheavy compound system with Z = 112-120 at energies near the Coulomb barrier have been measured. Fusion-fission cross sections were estimated from the analysis of mass and total kinetic energy distributions. It was found that the fusion probability is approximately the same for the reactions with 48Ca ions and drops three orders of magnitude at the transition to 64Ni ions
Distribution of Nuclides Produced in the Collision of 1 AGeV 238U-Ions on p
Production cross sections and kinematical properties of the complete set of fission fragment residues from the reaction 238U (1 A.GeV) + p have been obtained. Isotopic distributions are measured for all elements from O (Z = 8) to W (Z = 74). Fission velocities and production cross sections are shown as a function of Z, the charge and N, the number of neutrons of the fragments. The very asymmetric pairs of fragments can be attributed to excited fissioning parent nuclei of charge Z, 88< Z < 92.
Systematics of Proton-Induced Fission Cross Sections for Intermediate Energy Applications
The recent systematics of proton-induced fission cross sections is extended to a wider range of target nuclei and incident energies. Reasonable agreement with available experimental data is demonstrated. The extended systematics is employed to generate a data library for use in the CINDER'90 transmutation inventory code.
Resolved resonance parameters for sup 2 sup 3 sup 6 Np
Multilevel Breit-Wigner parameters were obtained for fission cross-section representation in the 0.01-33 eV energy region from evaluation of a sup 2 sup 3 sup 6 Np experimental fission cross-section in the resolved resonance region.
Neutron characteristics of salt blanket micromodels containing mixtures of sodium, zirconium and uranium sulphides were measured on FKBN-2M, BIGR and MAKET installations. The effective fission cross sections of neptunium, plutonium, americium and curium isotopes were measured on the neutron spectra formed by micromodels.
Zirconia inert matrix for plutonium utilisation and minor actinides disposition in reactors
2007-01-01
The radiotoxicity of the UO2 spent fuel is dominated by plutonium and minor actinides (MA): Np, Am and Cm, after decay of the short life fission products. Zirconia ceramics containing Pu and MA in the form of an inert matrix fuel (IMF) could be used to burn these actinides in light water reactors or in high temperature reactors. Optimisation of the fuel designs dictated by properties such as thermal, mechanical, chemical and physical must be performed with attention for their behaviour under irradiation. Zirconia must be stabilised by yttria to form a solid solution such as MAzYyPuxZr1-yO2-z where minor actinide oxides are also soluble. MA may act as a burnable poison reducing the reactivity at the beginning of life and yielding fertile nuclides improving the reactivity at the end of life....
Glaucony ages of Vindhyan sediments in Rajasthan
1990-01-01
This report deals with the fission track (F-T) dating and geological correlation of glauconitic sandstone beds of Vindhyan sediments in Rajasthan. The glaucony F-T ages of sandstone beds exposed at Bodwali in Chittorgarh district and at Astal village in Karauli area are reported. Except for the samples from Bodwali, which are dated to 1070 Ma, the ages of the other samples range from 600-700 Ma. On the basis of F-T age data, geological correlation of Vindhyan deposits in Rajasthan with those in eastern part at Son Valley and Chitrakut has been attempted. Apatite mineral age for the Bearch granite, the base rock of Vindhyan sediments at Chittogarh has been obtained as 1470 Ma. (author). 3 tabs., 11 refs
Fission track ages of fossil woods from Deorikhurd, Keria and Mohgaonkalan, Madhya Pradesh, India
1990-01-01
Sedimantary beds in between the successive Deccan lava flows contain fossil evidences of vegetational history of peninsular India. To use the evidence of plants fossils for reconstructing palaeofloras and palaeoenvironments it is necessary to ascertain the age of the fossil material as precisely as possible. This report deals with the F-T dating of the petrified woods collected from the Deccan Intertrappean beds near Deorikhurd in Mandla district and Keria and Mohgaonkalan in Chhindwara district., Madhya Pradesh (M.P.). The specimen from Deorikhurd is a dicotyledonous wood fragment and those from Keria and Mohgaonkalan are fossil palm woods usually described under the generic name Palmoxylon. F-T ages obtained are (48+-4) Ma for Deorikhurd, (51+-6) Ma for Kerla and (45+-5) Ma for Mohgaonkalan samples. The present results agree ...
1981-11-01
The /sup 235/U fission spectrum averaged cross section for the /sup 199/Hg(n, n')sup(199m)Hg reaction has been measured relative to that for the /sup 115/In(n, n')sup(115m)In reaction. Fast neutrons were obtained with a fission plate in a large heavy water thermal neutron facility of KUR. The present value of the /sup 235/U fission spectrum averaged cross section for the /sup 199/Hg(n, n')sup(199m)Hg reaction is 277 +- 15.4 mb, while the average cross section calculated with the recent energy dependent cross section and a Watt-type fission neutron spectrum is about 14% lower than this value. In the present uncertainty analysis, it is demonstrated how to generate and combine the experimental uncertainties in the form of a covariance matrix in order to obtain the best value from the experimental data.
Neutron cross section covariances in the resolved resonance region.
2008-04-01
We present a detailed analysis of the impact of resonance parameter uncertainties on covariances for neutron capture and fission cross sections in the resolved resonance region. Our analysis uses the uncertainties available in the recently published Atlas of Neutron Resonances employing the Multi-Level Breit-Wigner formalism. We consider uncertainties on resonance energies along with those on neutron-, radiative-, and fission-widths and examine their impact on cross section uncertainties and correlations. We also study the effect of the resonance parameter correlations deduced from capture and fission kernels and illustrate our approach on several practical examples. We show that uncertainties of neutron-, radiative- and fission-widths are important, while the uncertainties of resonance energies can be effectively neglected. We conclude that the correlations between neutron and radiative (fission) widths should be taken into account. The multi-group cross section uncertainties can be properly generated from both the resonance parameter covariance format MF32 and the cross section covariance format MF33, though the use of MF32 is more straightforward and hence preferable.
Measurement of fast neutron induced fission cross section of americium isotopes
1999-03-01
In a fuel cycle with recycled actinide, americium isotopes largely influence core characteristics for a fast reactor. Accurate nuclear data for americium isotopes such as fission cross section are required to estimate erect of those isotopes on a fast reactor core. Nevertheless, experimental data for those isotopes are not enough to evaluate them accurately at the present time. Under these circumstances, fast neutron induced fission cross sections of those isotopes have been measured using Dynamitron Accelerator of Tohoku University. In the present study, fission cross section ratios of Am241/Np237 and Am243/Np237 were measured at 4.0 MeV and 6.3 MeV using the improved tools and samples, which have previously developed in this study. The measured results for the fission cross sections of Am241 and Am243 at the two energy points did not agree with those in a nuclear data library, and different nuclear data libraries were supported by the present results dependent on energy and isotope. (author)
The Ma-Trudinger-Wang curvature for natural mechanical actions
2009-09-01
The Ma-Trudinger-Wang curvature -- or cross-curvature -- is an object arising in the regularity theory of optimal transportation. We study this quantity for costs defined by natural mechanical actions. We show the least action corresponding to a harmonic oscillator has zero cross-curvature, and in particular satisfies the necessary and sufficient condition (A3w) for the continuity of optimal maps. We also study gentle perturbations of the free action by a potential, and find conditions on the potential which guarantee either that the corresponding cost satisfies the more restrictive condition (A3s) of Ma, Trudinger and Wang, or in some cases has positive cross-curvature. In particular, the quartic potential of the anharmonic oscillator satisfies (A3s) in the perturbative regime.
Fast neutron nuclear data: Pu-239 revision and Am status
1992-01-01
Neutron cross sections for Pu-239 and Am-241, -242m, -243 have been analyzed with the aid of theoretical models. A deformed optical potential that fits total, elastic and inelastic differential cross section data and neutron strength functions for Pu-239 and Am-241 have been used. In case of Pu-239 the consistency of absolute fission data and (n, 2n) cross section is investigated. Because of the strong discrepancies in Am fission cross section data a consistent set of calculated cross section values for the chain of Am nuclei is proposed. The present state of knowledge concerning first chance fission cross section allows to analyze fission cross section data of Am-241, -242m, -243, up to 20 MeV. The results thus obtained are compared with ENDF/B-V and JENDL-3 libraries. (orig.)
Systematic features of mass yield curves in low-energy fission of actinides
1999-07-01
Characteristics of mass yield curves in fission of wide range of nuclides from pre-actinides through transactinides are reviewed and the following points are discussed. (1) Systematic trends of the mass yield distributions in low-energy proton-induced fission of actinides and in spontaneous fission of actinides are discussed in terms of weighted mean mass numbers of the light and heavy asymmetric mass yield peaks and widths of the heavy asymmetric mass yields. (2) Gross features of the two kinds of mass yield curves, symmetric and asymmetric ones, as a function of a fissioning nucleus. (3) Competition between the symmetric and asymmetric fission as a function of not only Z (proton number) but also N (neutron number) of a fissioning nucleus. (4) Experimental verification of the existence of two kinds of deformation paths in low energy fission of actinides; the first path is initiated at higher threshold energy and ends with elongated scission configuration, giving a final mass yield distribution centered around the symmetric mass division, 'symmetric fission path'. In the second path, a fissioning nucleus experiences lower threshold energy and results in more compact scission configuration, which gives a double humped mass distribution always centered around A=140 for the heavier fragment, 'asymmetric fission path'. (5) Interpretation of the 'bimodal fission' observed in the spontaneous fission of heavy actinides as the presence of the two fission paths of the ordinary asymmetric one and a strongly shell-affected symmetric path from the systematic analysis of scission configurations. (6) A dynamical fission process deduced from the analysis of the experimental mass yield curves and the correlation data of neutron multiplicity and fragment mass and total kinetic energy. (7) Prediction of the characteristics of gross properties of fission in superheavy nuclei around {sup 280}114. (8) Characteristics of highly asymmetric fission: formation cross section as a function of excitation energy and angular distribution. (9) Based on the systematic analysis of the heavy asymmetric mass yield curves in thermal neutron- and proton-induced fission of actinides, and spontaneous fission of medium and heavy actinides, the relation between the fragment shell structure and the shape of the mass yield curves which reflect the final mass division process is discussed. (author)
New signatures on dissipation from fission induced by relativistic heavy-ion collisions
2004-03-01
Fissile nuclei with small shape distortion relative to the ground-state deformation and with low angular momentum were produced in peripheral heavy-ion collisions. Under the conditions of small shape distortions and low angular momentum, the theoretical description of the fission process can be considerably simplified, and the relevant information on dissipation can be better extracted than in conventional experiments based on fusion-fission reactions. In addition, this experimental approach induces very high excitation energies, a condition necessary to observe transient effects. The experimental data were taken at GSI using a set-up especially conceived for fission studies in inverse kinematics. This set-up allowed determining three observables whose sensitivity to dissipation was investigated for the first time: the total fission cross sections of {sup 238}U at 1 A GeV as a function of the target mass, and, for the reaction of {sup 238}U at 1 A GeV on a (CH{sub 2}){sub n} target, the partial fission cross sections and the partial charge distributions of the fission fragments. The comparison of the new experimental data with a reaction code adapted to the conditions of the reactions investigated leads to clear conclusions on the strength of dissipation at small deformation where the existing results are rather contradictory. (orig.)
New signatures on dissipation from fission induced by relativistic heavy-ion collisions
Fissile nuclei with small shape distortion relative to the ground-state deformation and with low angular momentum were produced in peripheral heavy-ion collisions. Under the conditions of small shape distortions and low angular momentum, the theoretical description of the fission process can be considerably simplified, and the relevant information on dissipation can be better extracted than in conventional experiments based on fusion-fission reactions. In addition, this experimental approach induces very high excitation energies, a condition necessary to observe transient effects. The experimental data were taken at GSI using a set-up especially conceived for fission studies in inverse kinematics. This set-up allowed determining three observables whose sensitivity to dissipation was investigated for the first time: the total fission cross sections of 238U at 1 A GeV as a function of the target mass, and, for the reaction of 238U at 1 A GeV on a (CH2)n target, the partial fission cross sections and the partial charge distributions of the fission fragments. The comparison of the new experimental data with a reaction code adapted to the conditions of the reactions investigated leads to clear conclusions on the strength of dissipation at small deformation where the existing results are rather contradictory.
2010-01-01
A new method of measuring fission fragment mass and energy distributions as a function of incident neutron energy in the range from below 0.1 eV to 1 keV has been developed. The method involves placing a double-sided Frisch-gridded fission chamber in Rensselaer Polytechnic Institute's lead slowing-down spectrometer (LSDS). The high neutron flux of the LSDS allows for the measurement of the energy-dependent, neutron-induced fission cross sections simultaneously with the mass and kinetic energy of the fission fragments of various small samples. The samples may be isotopes that are not available in large quantities (submicrograms) or with small fission cross sections (microbarns). The fission chamber consists of two anodes shielded by Frisch grids on either side of a single cathode. The sample is located in the center of the cathode and is made by depositing small amounts of ...
FISSION OF GOLD BY CARBON IONS
1960-06-08
Angular distribution and kinetic-energy spectra of fragments, and cross sections for fission of gold with 68- to 124-Mev C{sup 12} ions have been obtained by observation of the fragments in two types of detectors, gas scintillation chambers and silicon p-n junctions. From the parameters used to fit the angular distributions to the theoretical curves of Halpern and Strutinski, we have obtained the average excitation energy of the fissioning nucleus at the time of fission. This quantity is approximately 25 Mev, which is nearly independent of bombarding energy, suggesting that fission is preceded by the emission of several particles from the compound nucleus. The fission cross section increases from a value of 100 mb at 68 Mev to 1.28 b. at 124 Mev. Over this range of bombarding energies, the total fragment kinetic-energy release rises from 142 {+-} 6 to 146 {+-} 6 Mev. At all bombarding energies, the variation of laboratory-system kinetic energy of the fragments with laboratory-system angle indicates full momentum transfer by the bombarding particle to the fissioning system.
Extension of the nuclear reaction model code Empire to actinides' nuclear data evaluation
2008-07-01
Recent extensions and improvements of the EMPIRE code system are outlined. They add new capabilities to the code, such as prompt fission neutron spectra calculations using Hauser-Feshbach plus pre-equilibrium pre-fission spectra, cross section covariance matrix calculations by Monte Carlo method, fitting of optical model parameters, extended set of optical model potentials including new dispersive coupled channel potentials, parity-dependent level densities and transmission through numerically defined fission barriers. These features, along with improved and validated Endf formatting, exclusive/inclusive spectra, and recoils make the current EMPIRE release a complete and well validated tool for the evaluation of nuclear data at incident energies above the resonance region. The current EMPIRE release has been used in the evaluations of neutron induced reaction files for {sup 232}Th and {sup 231,233}Pa nuclei in the fast neutron region at IAEA. Triple-humped fission barriers and exclusive pre-fission neutron spectra were considered for the fission data evaluation. Total, fission, capture and neutron emission cross section, average resonance parameters and angular distributions of neutron scattering are in excellent agreement with the available experimental data. (authors)
EXTENSION OF THE NUCLEAR REACTION MODEL CODE EMPIRE TO ACTINIDES NUCLEAR DATA EVALUATION.
Recent extensions and improvements of the EMPIRE code system are outlined. They add new capabilities to the code, such as prompt fission neutron spectra calculations using Hauser-Feshbach plus pre-equilibrium pre-fission spectra, cross section covariance matrix calculations by Monte Carlo method, fitting of optical model parameters, extended set of optical model potentials including new dispersive coupled channel potentials, parity-dependent level densities and transmission through numerically defined fission barriers. These features, along with improved and validated ENDF formatting, exclusive/inclusive spectra, and recoils make the current EMPIRE release a complete and well validated tool for evaluation of nuclear data at incident energies above the resonance region. The current EMPIRE release has been used in evaluations of neutron induced reaction files for {sup 232}Th and {sup 231,233}Pa nuclei in the fast neutron region at IAEA. Triple-humped fission barriers and exclusive pre-fission neutron spectra were considered for the fission data evaluation. Total, fission, capture and neutron emission cross section, average resonance parameters and angular distributions of neutron scattering are in excellent agreement with the available experimental data.
EXTENSION OF THE NUCLEAR REACTION MODEL CODE EMPIRE TO ACTINIDES NUCLEAR DATA EVALUATION.
2007-04-22
Recent extensions and improvements of the EMPIRE code system are outlined. They add new capabilities to the code, such as prompt fission neutron spectra calculations using Hauser-Feshbach plus pre-equilibrium pre-fission spectra, cross section covariance matrix calculations by Monte Carlo method, fitting of optical model parameters, extended set of optical model potentials including new dispersive coupled channel potentials, parity-dependent level densities and transmission through numerically defined fission barriers. These features, along with improved and validated ENDF formatting, exclusive/inclusive spectra, and recoils make the current EMPIRE release a complete and well validated tool for evaluation of nuclear data at incident energies above the resonance region. The current EMPIRE release has been used in evaluations of neutron induced reaction files for {sup 232}Th and {sup 231,233}Pa nuclei in the fast neutron region at IAEA. Triple-humped fission barriers and exclusive pre-fission neutron spectra were considered for the fission data evaluation. Total, fission, capture and neutron emission cross section, average resonance parameters and angular distributions of neutron scattering are in excellent agreement with the available experimental data.
Summary talk covering application-oriented sessions
1985-01-01
Some progress is mentioned in nuclear data, including: nonfuel actinide cross sections, fusion charged particle reactions, lithium-7 breakup reaction, neutrons per fission, decay heat from fission products, the form of the fission spectrum, and neutron scattering differential cross sections. Trends are then identified, particularly N(E,t) for delayed neutrons, internationally focussed efforts to resolve outstanding problems, dosimetry cross sections and techniques, fusion integral experiments, data adjustment, rigorous analysis of differential data, reconsideration of ''completed'' data areas, and particle emission cross sections for fusion systems. Challenges pertaining to data for applications are listed, including neutron kerma data for neutrons above 10 MeV, helium production from neutrons on boron-10, the resonance and thermal regions of fuel nuclides, and tightening of accuracies. (LEW)
Status of U-235 fission as a cross section standard. [10 keV to 20 MeV]
1976-06-25
A review is made of the current status of /sup 235/U fission cross section data from thermal to 20 MeV neutron energies. The accuracy achieved is compared with the 1 percent accuracy required of a reaction-cross-section standard throughout this range. The energy ranges from thermal to 10 keV, 10 keV to 0.8 MeV and 0.8 to 20 MeV are considered separately because of the different experimental techniques required in each. The goal of normalizing all fission cross sections to the thermal value and the current degree of success is discussed.
Very heavy fission fragments produced in the spallation reaction 238U+p at 1A GeV
Fission fragments from 1A GeV 238U ions impinging a hydrogen target are investigated by using the fragment separator FRS for magnetic selection of reaction products including ray-tracing, and ?E-ToF techniques. On the basis of the kinematics of the fragments, binary fission can be assigned as production process up to very heavy fragments. Fission fragments are separated and identified as far as 184Re for the first time. Cross sections are measured and found in the range of 500 ?b to 5 ?b. Isobaric cross sections decrease smoothly with increasing masses. Beyond tungsten, fission fragments are hidden in the more abundant spallation evaporation residues. 283 isotopes of elements gadolinium to rhenium in the mass range 147 to 184 are observed and cross sections measured. All the fragments are formed by fission of excited parent nuclei following emission of a cascade of secondary neutrons.
1967-06-15
The comparison of measured and calculated central fission ratios provides a useful method for checking the accuracy of calculated spectra and fission cross-section data. A set of parallel plate fission chambers was specially made for Zebra. The design was based on that of Kirn's chambers used by the ZPR-III group at ANL, Idaho, and incorporated a number of improvements. In particular, the wall thickness was reduced to reduce the degradation of the spectrum. The fissile coatings in the earlier chambers were prepared by a painting technique and those in the later chambers by an electrodeposition method. The mass deposited was determined by low geometry or assay. The construction of the chambers and the method of calibration and use are described. Central fission ratios in six Zebra cores measured to an accuracy of 1-3% are compared with values computed using the FD2 data set and the CRAM or SCRAMBLE multigroup diffusion theory programmes. This comparison suggests that the calculations give too few neutrons at high energies. There is also evidence that some of the fission cross-section data used in the FD2 set is in error. (author)
Fission product release in the first two PHEBUS tests FPT0 and FPT1
2005-01-01
The fission product (FP) behaviour in PHEBUS FPT0 (fresh fuel rods) and FPT1 (irradiated fuel) in-pile experiments is interpreted. The main experimental results in FPT0 and FPT1 are first summarized, and the FP release rates measured in both tests are reported and related to degradation events. The interpretation is performed in two steps. First, using general knowledge from the open literature and from previous interpretations of VERCORS analytical experiments, a qualitative description of the possible behaviour of fission gases, Cs, Mo and Ba is given by considering only intact fuel geometry. This interpretation is illustrated by calculations performed with the mechanistic MFPR code. Then, in a second step, possible effects of fuel dissolution, foaming and interactions with structural ma...
1988-01-01
An improved calculation is presented for the prompt fission neutron spectrum N(E) from the spontaneous fission of /sup 252/Cf. In this calculation the fission-spectrum model of Madland and Nix is used, but with several improvements leading to a physically more accurate representation of the spectrum. Specifically, the contributions to N(E) from the entire fission-fragment mass and charge distributions will be calculated instead of calculating on the basis of a seven- point approximation to the peaks of these distributions as has been done in the past. Therefore, values of the energy release in fission, fission-fragment kinetic energy, and compound nucleus cross section for the inverse process will be considered on a point-by-point basis over the fragment yield distributions instead of considering averages of these quantities over the peaks of the distributions. Preliminary results will be presented and compared with a measurement, an earlier calculation, and a recent evaluation of the spectrum. 14 refs., 4 figs.
Measurement of {sup 233}U fission spectrum-averaged cross sections for some threshold reactions
1994-12-31
The {sup 233}U fission spectrum-averaged cross sections for twelve threshold reactions were measured relative to the average cross section of 0.688 {+-} 0.040 mb for the {sup 27}Al(n,{alpha}){sup 24}Na reaction. The reference value was obtained by calculation using the energy dependent cross section in the Japanese Evaluated Nuclear Data Library (JENDL) Dosimetry File and the Watt-type fission spectrum in ENDF/B-VI. General agreement was seen between the measured and the calculated fission-spectrum averaged cross sections. However, there exist discrepancies of more than 10% between the measured and the calculated average cross sections for the {sup 24}Mg(n,p){sup 24}Na, {sup 47}Ti(n,p){sup 47}Sc, and {sup 64}Zn(n,p){sup 64}Cu reactions. The tendencies in the calculated-to-measured ratios are similar to those for {sup 235}U fission spectrum-averaged cross sections the authors previously measured. The measured average cross sections were also applied for the spectrum adjustment of the {sup 233}U fission neutrons using the Neutron Unfolding Package Code (NEUPAC). The adjusted spectrum is close to the Watt-type fission spectrum of {sup 233}U within the uncertainties of the obtained spectrum, although there exist some fluctuations in the ratio spectrum of the adjusted to the Watt-type.
Fission cross-section measurements of sup 247 Cm, sup 254 Es, and sup 250 Cf from 0. 1 eV to 80 keV
1991-12-01
This paper reports on the fission cross sections of {sup 247}Cm, {sup 254}Es, and {sup 250}Cf that are measured with the Rensselaer intense neutron spectrometer from 0.1 eV to 80 keV. The cross sections are normalized to the {sup 235}U ENDF/B-V broadened cross section. Fission areas and resonance widths are determined for low-energy resonances in {sup 247}Cm. The {sup 254}Es and {sup 250}Cf fission cross sections are the only reported measurements for these isotopes. The {sup 254}Es isotope is the heaviest odd- odd isotope ever measured over this energy range. The thermal fission cross sections for {sup 247}Cm, {sup 254}Es, and {sup 250}Cf are determined by extrapolation of the low-energy region of the cross section and are in good agreement with other reported measurements. Resonance integrals are reported for the energy range of 0.1 eV to 80 keV, and the areas for {sup 247}Cm and {sup 250}Cf resonances are also reported. The previously reported {sup 246}Cm fission cross section was corrected for fission in {sup 247}Cm.
Measurement of 233U fission spectrum-averaged cross sections for some threshold reactions
1994-01-01
The 233U fission spectrum-averaged cross sections for twelve threshold reactions were measured relative to the average cross section of 0.688 +- 0.040 mb for the 27Al(n,alpha)24Na reaction. The reference value was obtained by calculation using the energy dependent cross section in the Japanese Evaluated Nuclear Data Library (JENDL) Dosimetry File and the Watt-type fission spectrum in ENDF/B-VI. General agreement was seen between the measured and the calculated fission-spectrum averaged cross sections. However, there exist discrepancies of more than 10% between the measured and the calculated average cross sections for the 24Mg(n,p)24Na, 47Ti(n,p)47Sc, and 64Zn(n,p)64Cu reactions. The tendencies in the ...
Protactinium neutron-induced fission up to 200 MeV
The theoretical evaluation of 230-233Pa(n,F) cross sections is based on direct data, 230-234Pa fission probabilities and ratios of fission probabilities in first-chance and emissive fission domains, surrogate for neutroninduced fission. First chance fission cross sections trends of Pa are based on consistent description of 232Th(n,F), 232Th(n,2n) and 238U(n,F), 238U(n,xn) data, supported by the ratio surrogate data by Burke et al., 2006, for the 237U(n,F) reaction. Ratio surrogate data on fission probabilities of 232Th(6 Li,4 He)234Pa and 232 Th(6 Li,d)236U by Nayak et al., 2008, support the predicted 233Pa(n, F) cross section at En=11.5-16.5 MeV. The predicted trends of 230-232Pa(n, F) cross section up to En=20 MeV, are consistent with fissilities of Pa nuclides, extracted by 232Th(p,F) (Isaev et al., 2008) and 232Th(p,3n) (Morgenstern et al., 2008) data analysis. The excitation energy and nucleon composition dependence of the transition from asymmetric to symmetric scission for fission observables of Pa nuclei is defined by analysis of p-induced fission of 232Th at Ep=1-200 MeV. Predominantly symmetric fission in 232Th(p,F) at En( p)=200 MeV as revealed by experimental branching ratios (Dujvestijn et al., 1999) is reproduced. Steep transition from asymmetric to symmetric fission with increase of nucleon incident energy is due to fission of neutron-deficient Pa (A?229) nuclei. A structure of the potential energy surface (a drop of f f symmetric and asymmetric fission barriers difierence (EfSYM - EfASYM) from ~3.5 MeV to ~1 MeV) of N-deficient Pa nuclides (A?226) and available phase space at outer fission saddles, are shown to be responsible for the sharp increase with En( p) of the symmetric fission component contribution for 232Th(p,F) and 230-233 Pa(n, F) reactions. That is a strong evidence of emissive fission nature of moderately excited Pa nuclides, reliably quantified only up to En( p)~20(30) MeV. Predicted fission cross section of 232Pa(n,F) coincides 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.
Nuclear fuel cycle and actinide wastes: cross section needs and recent measurements
What happens to actinides in reactors. The growth and decay of these nuclides are controlled primarily by capture and fission cross sections and by the reactor flux, all of which are strong functions of neutron energy. A number of selected cross section measurements are still required to predict with confidence answers to two important future questions. These are (1) whether specific neutron shielding will be required during fuel transportation or reprocessing (i.e., the spontaneous fission yields expected) and (2) whether it is possible and desirable to recycle chemically separated heavy actinides in reactors and ''burn'' them to short-lived fission products. Recent progress in the understanding of these questions is reviewed. Several recent measurements at ORELA which are germane to these questions are described briefly. Among these are fission cross section measurements on small ultrapure samples which are intensely alpha-radioactive. An ionization chamber with hemispherical plates is used to reduce the alpha pulses counted by a factor greater than 10/sup 10/ while permitting greater than 95 percent fission counting efficiency. Preliminary results of measurements on /sup 245/Cm and /sup 243/Cm and results of an earlier measurement on /sup 249/Cf with solid state detectors are presented.
2006-02-06
Fission induced by energetic negative pions in gold and bismuth has been studied experimentally and theoretically. CR-39 dielectric track detectors in 4{pi}-geometry were used to determine experimental cross sections, and the computer code CEM95 has been used for theoretical calculations. Experimental fission cross sections for gold have been determined at energies of 500, 672, 1068 and 1665 MeV, and for bismuth at energies of 500, 672 and 1068 MeV. The targets and detectors were irradiated at the AGS of Brookhaven National Laboratory (USA). Theoretical fission cross sections were calculated from 50 MeV to 2500 MeV to compare with a wider range of measurements. Good agreement is observed among the measured and computed results. For validation of the code CEM95 and our methodology, we also benchmarked fission cross sections induced by protons and neutrons on targets of lead and bismuth, and for pions on gold and bismuth over a wide energy range.
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