ANALYSES OF 14-MEV NEUTRON-TRANSPORT IN BERYLLIUM

The 14 MeV netron transport in beryllium is analyzed on the basis of an S(N)-transport procedure with rigorous treatment of the neutron scattering and double-differential cross-sections (DDX-data) from the nuclear data files ENDF/B-VI and EFF-1 (European Fusion File). The latter one uses the Los Alamos (LANL) data evaluation for the beryllium cross-sections. Comparisons with conventional S(N)/P(l) transport calculations in one- and two-dimensional geometry show that their quality depends on the way of representing and processing the DDX-data on the files. If the DDX-data are given in the Legendre approximation (EFF-1 file) rigorous S(N) and approximative S(N)/P(l) transport calculations agree perfectly. If the DDX data are given in the more appropriate angular representation (ENDF/B-VI file), enabling the DDX data processing without making any use of the Legendre approximation, rigorous S(N) and approximative S(N)/P(l) calculations disagree significantly. Calculations of integral beryllium experiments show that it is not possible at present to draw a final conclusion on the quality of the EFF-1 and ENDF/B-VI beryllium date evaluations although they show remarkable differences. There are, however, indications that the 14 MeV (n, 2n) cross-section in ENDF/B-VI is too low and that the secondary-energy distribution of the EFF-1 neutron emission cross-section at low secondary energies is too high. Further integral experiments, especially measurements of neutron leakage spectra, are needed for a reliable assessment of the quality of the beryllium data evaluations.