MEASUREMENTS OF DOUBLE-DIFFERENTIAL NEUTRON EMISSION CROSS-SECTIONS OF NB, MO, TA, W AND BI FOR 14 AND 18MEV NEUTRONS

Double-differential neutron emission cross sections have been measured for Nb, Mo, Ta, W and Bi at 14MeV incident energy, and for Nh and Bi at 18MeV using Tohoku University Dynamitron TOF spectrometer. The experimental results indicated problems in current evaluations both for energy spectra and angular distributions. Angle-integrated neutron emission spectra and angular distributions of secondary neutrons were analyzed, respectively, by the statistical multi-step model code EXIFON and the systematics by Kalbach-Mann and by Kalbach. The energy spectra were reproduced successfully by EXIFON except for Bi, and the angular distributions were followed by the systematics over wide range of outgoing energy and target mass if the emission spectra calculated by EXIFON were employed for generation of angular distributions.