Keiichi Shibata

JENDL-4.0 : A New Library for Nuclear Science and Engineering

The fourth version of the Japanese Evaluated Nuclear Data Library has been produced in cooperation with the Japanese Nuclear Data Committee. In the new library, much emphasis is placed on the improvements of fission product and minor actinoid data. Two nuclear model codes were developed in order to evaluate the cross sections of fission products and minor actinoids. Coupled-channel optical model parameters, which can be applied to wide mass and energy regions, were obtained for nuclear model calculations. Thermal cross sections of actinoids were carefully examined by considering experimental data or by the systematics of neighboring nuclei. Most of the fission cross sections were derived from experimental data. A simultaneous evaluation was performed for the fission cross sections of important uranium and plutonium isotopes above 10 keV. New evaluations were performed for the thirty fissionproduct nuclides that had not been contained in the previous library JENDL-3.3. The data for light elements and structural materials were partly reevaluated. Moreover, covariances were estimated mainly for actinoids. The new library was released as JENDL-4.0, and the data can be retrieved from the Web site of the JAEA Nuclear Data Center.

Coupled-channels optical model analyses of nucleon-induced reactions for medium and heavy nuclei in the energy region from 1 keV to 200 MeV

Optical model analyses were carried out using the coupled-channels method over various medium and heavy nuclei for incident neutrons and protons in the energy region from 1 keV to 200 MeV. Global systematics were consequently obtained for the optical potential parameters with simple functional forms. It was confirmed that coupled-channels analyses were indispensable to achieving a global description of experimental data for wide ranges of energies and mass numbers (50 ≤ A ≥ 240). It was also found that the parameter set obtained would be useful for nuclear data evaluations of fission-product nuclei for which available experimental data are scarce.

JENDL-3.2 Covariance File

Covariances of neutron nuclear data have been estimated for 16 nuclides contained in JENDL-3.2. The physical quantities for which covariances are deduced are cross sections, resolved and unresolved resonance parameters, the first order Legendre-polynomial coefficients for the angular distribution of elastically scattered neutrons, and fission neutron spectra. As for 233,235,238U and 239,241Pu, covariances were obtained also for the average number of neutrons emitted in fission. Least-squares methods were applied to obtain the covariances of those cross sections which were based on experimental data. A simultaneous evaluation method yielded uncertainties in the fission cross sections of 235U, 238U, 239Pu, 240Pu and 241Pu. Covariances of nuclear model calculations were determined from uncertainties in model parameters. The covariance file thus obtained is processed by a system which has been developed, and used for the adjustment of group cross sections.

Simultaneous Evaluation of Fission Cross Sections of Uranium and Plutonium Isotopes for JENDL-3.3

A simultaneous evaluation of the fission cross sections of 233U, 235U, 238U, 239Pu, 240Pu and 241Pu was carried out for the evaluated nuclear data library JENDL-3.3. A least-squares method was applied to selected absolute and relative measurements on the fission cross sections. Covariance matrices of the experimental data were constructed from the uncertainty information reported in the references. The fission cross sections obtained were compared with the JENDL-3.2 and ENDF/B-VI evaluations. It was found from the comparison that the present results are not so different from those in JENDL-3.2, except for the fission cross sections of 233U and the cross sections above 15MeV, and give smaller X2 value than the JENDL-3.2 cross sections. The averaged fission cross sections of 233U, 238U, and 239Pu relative to that of 235U were calculated for a neutron spectrum produced by 9Be (d,xn) reaction. It was confirmed that the calculated cross-section ratios are in good agreement with the experimental data.

Uncertainty analyses of neutron cross sections for nitrogen-15, lead-206,207,208, bismuth-209, plutonium-238, americium-242m, and curium-244 in JENDL-3.3

Covariances of neutron cross sections for 15N, 206,207,208Pb, 209Bi, 238Pu, 242m Am and 244Cm contained in JENDL-3.3 have been evaluated for the design of accelerator-driven transmutation systems. The covariances were obtained from the experimental data and model calculations on which the JENDL-3.3 data were based. The physical quantities for which covariances were deduced are the elastic scattering cross section of 15N, the inelastic scattering cross sections of 206,207,208Pb and 209Bi, and the fission and capture cross sections of 238Pu, 242m Am and 244Cm. Uncertainties in the resolved resonance parameters were estimated for 238Pu, 242m Am and 244Cm. The results were compiled in the ENDF-6 format and merged with the JENDL-3.3 data.

JENDL Fusion File 99

The double-differential cross sections (DDXs) of secondary neutrons have been evaluated for 79 isotopes and 13 natural elements ranging from H to Bi to improve the accuracy of predictions for the neutronics calculations in the D-T thermonuclear fusion applications. The data given in JENDL-3.1, which was the newest version of JENDL general purpose file when this project was initiated, was combined with new calculations based on the optical model, DWBA, pre-equilibrium and multi-step statistical models, and the DDX data were generated based on various kinds of systematics for medium-mass nuclei. Different methods were employed for light nuclei to which the above method could not be applied. In addition, the DDXs for emission of charged particles (p, d, t, 3He and α-particle) were given for 2H, 9Be and elements heavier or equal to F. The present results give an overall good description of the measured DDX data of both the neutron and charged particles emission channels. The data were compiled in ENDF-6 format, and released in 1999 as a special purpose file of JENDL family, namely, JENDL Fusion File 99.

Calculation of Neutron Nuclear Data on Silicon Isotopes for JENDL-4

Neutron nuclear data on 92,94,95,96,97,98,99,100 Mo have been calculated for the evaluated nuclear data library JENDL-4. Simultaneously calculated are the total, elastic and inelastic scattering, (n, p), (n, d), (n, t), (n, 3He), (n, α), (n, np), (n, nd), (n; nα), (n, 2n), (n, 3n) reaction cross sections, the angular distributions of emitted particles, and the energy distributions of emitted particles and γrays. The statistical model was applied to calculate these quantities. Coupled-channel optical model parameters were used for neutrons. Preequilibrium and direct-reaction processes were taken into account in addition to the compound process. The present calculations are almost consistent with available experimental data. The calculated results are compiled into JENDL-4.

Uncertainty Analyses of Neutron Cross Sections for 235U in the Resonance Region

The latest version of the Japanese Evaluated Nuclear Data Library, JENDL-3.3, was released in May 2004. This library contains covariance data of 20 nuclides in order to clarify uncertainties in nuclear data for reactor design calculations. However, we could not evaluate the covariances of neutron cross sections for U in the resonance region below 30 keV (resolved resonance region: 10 5 eV–2.25 keV, unresolved resonance region: 2.25–30 keV), although the U covariances were completely prepared above 30 keV. The reasons for this incompleteness are that (1) the resolved resonance parameters of U were taken from the analysis of Leal et al., but they did not make available the covariances of the resonance parameters; (2) it was almost impossible to make covariance matrices of more than 3,000 resolved resonances, since a huge storage space was required. The neutron nuclear data of U are the most important for nuclear energy applications. Therefore, their uncertainties have been urgently required by the users involved in the evaluation of design accuracy for innovative nuclear reactors. The present work was undertaken to complete the uncertainty information on the U data contained in JENDL3.3. We have evaluated the covariances of the energy-averaged cross sections for U in certain energy intervals from experimental data instead of those of the resonance parameters, since it was extremely difficult to obtain the covariances of the resonance parameters as mentioned above. This paper deals with the evaluation method and results of the U cross-section covariances in the resonance region.

Status and evaluation methods of JENDL Fusion File and JENDL PKA/KERMA File

Abstract The status of evaluated nuclear data in the JENDL Fusion File and PKA/KERMA File is presented. The JENDL Fusion File was prepared in order to improve the quality of the JENDL-3.1 data especially on the double-differential cross sections (DDXs) of secondary neutrons and gamma-ray production cross sections, and to provide DDXs of secondary charged particles (p, d, t, 3 He and α-particle) for the calculation of PKA and KERMA factors. The JENDL Fusion File contains evaluated data of 26 elements ranging from Li to Bi. The data in JENDL Fusion File reproduce the measured data on neutron and charged-particle DDXs and also on gamma-ray production cross sections. Recoil spectra in PKA/KERMA File were calculated from secondary neutron and charged-particle DDXs contained in the Fusion File with two-body reaction kinematics. The data in the JENDL Fusion File and PKA/KERMA File were compiled in ENDF-6 format with an MF = 6 option to store the DDX data.

Evaluation of neutron nuclear data on antimony isotopes

Neutron nuclear data on 121,123,124,125,126Sb have been evaluated for the next version of JENDL general purpose file in the energy region from 10− 5 eV to 20 MeV. In the low-energy region, the latest resolved resonance parameters were taken into account for 121, 123Sb. The thermal capture cross sections of 125, 126Sb, for which no measurements exist, were determined by using a simplified formula. The statistical model was applied to calculate the cross sections above the resolved resonance region. In the calculations, coupled-channel optical model parameters were used for the interaction between neutrons and odd-mass targets. Preequilibrium and direct-reaction processes were considered in addition to the compound process. The present evaluation is consistent with available experimental data. The evaluated data are compiled into an ENDF-formatted data file.