EXFOR-based simultaneous evaluation for fast neutron-induced fission cross section of thorium-232

The $^{232}$Th neutron-induced fission cross section was evaluated from 500 keV to 200 MeV. The experimental $^{232}$Th fission cross sections and their ratios to the $^{235,238}$U fission cross sections in the EXFOR library were reviewed and analysed by the least-squares method. The newly published $^{232}$Th/$^{235}$U fission cross section ratios from the time-of-flight measurements at the CERN n_TOF and CSNS Back-n facilities were compiled in EXFOR. Additional simultaneous evaluation was performed by including the experimental $^{233,238}$U and $^{239,240,241}$Pu fission cross sections and their ratios. The new evaluation provides the $^{232}$Th fission cross section systematically lower than the JENDL-5 cross section. The reduction is 4% in the plateau region between 2 and 6 MeV and more significant in the subthreshold fission region. The present evaluation reduces the $^{232}$Th fission cross section averaged over the $^{252}$Cf spontaneous fission neutron spectrum from the JENDL-5 evaluation by 4%, which is closer to the other general purpose libraries but underestimates Grundl et al's measurement by 11%.Comment: Submitted to Journal of Nuclear Science and Technolog

EXFOR-based simultaneous evaluation for neutron-induced fission cross section of plutonium-242

The $^{242}$Pu neutron-induced fission cross section was evaluated from 100 keV to 200 MeV. The experimental $^{242}$Pu and $^{235}$U fission cross sections and their ratios in the EXFOR library were reviewed and analysed by the least-squares method. Additional simultaneous evaluation was performed by including the experimental database of the $^{233,238}$U and $^{239,240,241}$Pu fission cross sections and their ratios developed for JENDL-5 evaluation. The $^{242}$Pu fission cross sections from our evaluation and JENDL-5 evaluation are close to each other below 1 MeV while systematically differ from each other above 10 MeV. The cross section from our evaluation is systematically lower than the JENDL-4.0 cross section in the prompt fission neutron spectrum peak region ($\sim$5% lower around 1 MeV). The newly evaluated $^{242}$Pu fission cross section was verified against the cross section measured in the $^{252}$Cf spontaneous fission neutron field and criticalities of small-sized LANL fast systems, and demonstrated better performance than the JENDL-4.0 cross section on the same level with the JENDL-5 cross section.Comment: Submitted to Journal of Nuclear Science and Technolog

EXFOR – a global experimental nuclear reaction data repository: Status and new developments

Members of the International Network of Nuclear Reaction Data Centres (NRDC) have collaborated since the 1960s on the worldwide collection, compilation and dissemination of experimental nuclear reaction data. New publications are systematically complied, and all agreed data assembled and incorporated within the EXFOR database. Recent upgrades to achieve greater completeness of the contents are described, along with reviews and adjustments of the compilation rules for specific types of data

Experiments in the EXFOR library for evaluation of thermal neutron constants

E.J. Axton’s experimental database adopted in evaluation of thermal neutron constants by himself and also by a recent project to update the IAEA Neutron Standard was checked against the experimental literature and EXFOR library. We discovered that many data are found neither in the EXFOR library nor in the articles quoted by Axton due to various reasons. This paper summarizes the status of the experimental data cited by Axton in the experimental literature as well as in the EXFOR library

Sideward Peak of Intermediate Mass Fragments in High Energy Proton Induced Reactions

Intermediate mass fragment (IMF) formation in the 12 GeV proton induced reaction on Au target is analyzed by using a combined framework of a transport model (JAM/MF) and a newly developed non-equilibrium percolation (NEP) model. In this model, we can well reproduce the mass distribution of fragments. In addition, the sideward peaked angular distribution would emerge under the condition that the fragment formation time is very short, around 20 fm/c. Within this short time period, the un-heated part of the residual nucleus is kept to have doughnut shape, then the Coulomb repulsion from this shape strengthens the sideward peak of IMF.Comment: 22 pages, Latex, 6 embedded PS figure

EXFOR-based simultaneous evaluation of neutron-induced uranium and plutonium fission cross sections for JENDL-5

The neutron-induced fission cross sections were simultaneously evaluated for the JENDL-5 library for $^{233,235}$U and $^{239,241}$Pu from 10 keV to 200 MeV and for $^{238}$U and $^{240}$Pu from 100 keV to 200 MeV. Evaluation was performed by least-squares fitting of Schmittroth's roof function to the logarithms of the experimental cross sections and cross section ratios in the EXFOR library. A simultaneous evaluation code SOK was used with its extension to data in arbitrary unit. The outputs of the code were adopted as the evaluated cross sections without any further corrections. The newly obtained evaluated cross sections were compared with the evaluated cross sections in the JENDL-4.0 library and the IAEA Neutron Data Standards 2017. The evaluated cross sections were also validated against the californium-252 spontaneous fission neutron spectrum averaged cross sections, $\Sigma\Sigma$ (coupled thermal/fast uranium and boron carbide spherical assembly) neutron spectrum averaged cross sections, and small-sized LANL fast system criticalities. The changes in the obtained evaluated cross sections from those in the JENDL-4.0 library are within 4% ($^{241}$Pu), 3% ($^{233}$U, $^{240}$Pu), or 2% ($^{235}$U, $^{239}$Pu). The newly evaluated $^{235}$U, $^{238}$U and $^{239}$Pu cross sections agree with the IAEA Neutron Data Standards 2017 within 2% with some exceptions.Comment: Published online in Journal of Nuclear Science and Technology (open access

Simultaneous evaluation of uranium and plutonium fast neutron fission cross sections up to 200 MeV for JENDL-5 and its updates

Simultaneous evaluation of 233,235,238U and 239,240,241Pu fission cross sections for fast neutrons up to 200 MeV was performed for the JENDL-5 library. Experimental covariances were estimated for each experimental dataset of cross sections or cross section ratios extracted from the EXFOR library, and they were stored in an experimental database dedicated to the new evaluation. The cross sections were expressed by Schmittroth’s roof functions, and the values on defined incident energy grids were adjusted by the least-squares method to reproduce the experimental cross sections and their ratios. The newly evaluated cross sections were validated using the spectrum averaged cross sections measured in the 252Cf spontaneous fission neutron standard field. The evaluation adopted by the JENDL-5 library was further updated by addition of two datasets and deletion of one dataset

Covariance analysis on the thermal neutron capture cross sections using an Am-Be neutron source

We measured the thermal cross sections of 71Ga(n, γ)72Ga using an Am-Be neutron source having strength of 4 × 107 neutrons/sec using the two monitor reactions 197Au(n, γ)198Au and 55Mn(n, γ)56Mn, and obtained 4.07±0.27 b and 3.97±0.31 b as the values measured relative to Au and Mn neutron captures, respectively. We constructed their covariance matrix by taking into account the correlation of parameters which are not independent in derivation of these two thermal cross sections (e.g., Ga sample weight, decay data of 72Ga, detector efficiency of γ -ray emitted from 72Ga). The off-diagonal weighted mean of the two cross sections 4.04±0.27 b was derived from the two thermal cross sections and their covariance matrix

Completeness of experimental fission product yields in EXFOR database

The Nuclear Reaction Data Centres (NRDC) collaborate on worldwide compilation and dissemination of experimental nuclear reaction data by developing and maintaining the EXFOR database. With the growing interests in the fission product yields of various projectiles and a wide range of energies, several evaluation activities are ongoing. In line with these activities, the IAEA conducted completeness check of fission product yield data in EXFOR against two experimental datasets developed by the ENDF and UKFY library evaluators. The present status and statistics of these datasets as well as the result of the EXFOR completeness review are presented

Covariance analysis on the thermal neutron capture cross sections using an Am-Be neutron source

We measured the thermal cross sections of 71Ga(n, γ)72Ga using an Am-Be neutron source having strength of 4 × 107 neutrons/sec using the two monitor reactions 197Au(n, γ)198Au and 55Mn(n, γ)56Mn, and obtained 4.07±0.27 b and 3.97±0.31 b as the values measured relative to Au and Mn neutron captures, respectively. We constructed their covariance matrix by taking into account the correlation of parameters which are not independent in derivation of these two thermal cross sections (e.g., Ga sample weight, decay data of 72Ga, detector efficiency of γ -ray emitted from 72Ga). The off-diagonal weighted mean of the two cross sections 4.04±0.27 b was derived from the two thermal cross sections and their covariance matrix