No abstract

Gamma-ray production cross sections and spectra have been updated for the latest version of JENDL-3 (JENDL-3.2). Problems of g-ray production data contained in the previous version JENDL-3.1 were examined, and they have been mostly resolved in the present work. In the medium-heavy mass region, capture g-ray spectra for incident neutron energies below 10keV were re-calculated with the statistical model taking account of experimentally determined branching ratios for primary transitions. For natural elements, line gamma rays due to inelastic scattering were explicitly given in JENDL-3.2 up to several MeV. Capture cross sections of some light nuclides were evaluated by considering a p-wave capture behavior indicated by recent measurements. Gamma-ray production data for 66 nuclides have been compiled into JENDL-3.2 in the ENDF-6 format.

Results of evaluation of neutron cross sections are presented for 27 fission product nuclides selected as being most important for fast reactor calculation. The cross sections considered are total, elastic scattering, inelastic scattering and capture cross sections in the energy range from thermal to 15 MeV. Thermal and resonance cross sections were calculated from resonance parameters. The calculated thermal capture cross section was adjusted by the measured value by adding a background cross section of 1/v form. A modified multi-level Breit.Wigner formula was developed to avoid the well-known occurrence of negative values in elastic scattering cross section. Smooth cross sections above resonance region were calculated with the spherical optical model and the statistical theory, taking account of neutron width fluctuation and level interference. The calculation was adjusted by capture data when available. The joining between the resonance and smooth cross sections was performed with the aid of statistical examination using Monte Carlo method. Present results are discussed in comparison with other evaluated data sets. Numerical results are stored on magnetic tape in the ENDF/B format.

Conventional formulas of the neutron cross sections based on the statistical model are modified so as to keep equality between the total cross section and the sum of the partial cross sections by taking into account the effects of the cascade process accompanied by the emission of 7-rays from the compound nuclear states, and of other processes which compete with the neutron scattering and capture. T h e modifications are applied to the cross-section formulas with width-fluctuation correction and resonanceresonance interference, according to the statistical distribution law of the level widths and spacings, respectively. Examples of calculations are shown for 238U, logag, Io3Rh andDiscussions are given concerning the contributions of the cascade process, the competing processes, the width-fluctuation and resonance-interference effects.

Three versions of Japanese Evaluated Nuclear Data Library (JENDL) are briefly explained. The first version, JENDL-1, was made aiming mainly at application to fast reactors. The second version, JENDL-2, was built as a bigger general purpose evaluated nuclear data library. It stores nuclear data for 181 nuclides. It has, however, some drawbacks particularly for fusion neutronics calculation. To remove these drawbacks of JENDL-2 and further extend its applicability, the third version, JENDL-3, has now been made. JENDL-3 includes photon-production data for some nuclides, in addition to the data contained in JENDL-2.