DOUBLE-DIFFERENTIAL NEUTRON EMISSION CROSS-SECTIONS OF 14-MEV NEUTRON-INDUCED REACTIONS ON NA AND PB

The energy and angular distribution of secondary neutrons from the int eraction of 14-MeV neutrons with sodium and natural lead were investig ated. Absolute double-differential neutron emission cross sections wer e measured for reaction angles from 30 degrees to 150 degrees in steps of 15 degrees in the secondary neutron energy range 2-14 MeV using th e time-of-flight facility at the Institut fur Radiumforschung und Kemp hysik, Vienna. Systematic uncertainties in these measurements could be reduced to less than 3-5% (depending on secondary neutron energy) res ulting in total uncertainties of less than 5% for a large part of the studied range in angle and energy for Pb and of less than 8% for Na. T hese results agree with previous measurements within the relatively la rge uncertainties of the latter. The measured cross sections were comp ared to the results of statistical model calculations using the quantu m mechanical theory of Feshbach, Kerman, and Koonin for preequilibrium emission and also with calculations based on the exciton model and th e Kalbach-Mann systematics for the shape of the angular distributions. For compound nucleus decay, the Hauser-Feshbach model was used in bot h cases. Very good agreement was found with both predictions in the ca se of lead; in the case of sodium, noticeable discrepancies do show th e limits of applicability of any statistical model for light nuclei.