Total kinetic energy release in the fast-neutron-induced fission of Np237

Abstract

The total kinetic energy (TKE) release in the fast neutron-induced fission of $^{237}\mathrm{Np}$ was measured for neutron energies from ${E}_{n}=2.6--100\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$ at the Los Alamos Neutron Science Center at the Weapons Neutron Research facility. The post-TKE release decreases nonlinearly with increasing incident neutron energy and can be represented as $\mathrm{TKE}\phantom{\rule{0.16em}{0ex}}(\mathrm{MeV})=(174.38\ifmmode\pm\else\textpm\fi{}0.72)--(5.11\ifmmode\pm\else\textpm\fi{}0.5821){\mathrm{log}}_{10}{E}_{n}$ for ${E}_{n}>1\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$. Analysis of the fragment mass distributions indicates that the decrease in TKE with increasing ${E}_{n}$ is a consequence of the fading out of shell effects at high excitation energies (resulting in an increase of symmetric fission) and the decrease of the total kinetic energy associated with asymmetric fission with increasing ${E}_{n}$.