Dependence of neutron yield on fragment mass for several low-energy fissioning systems

Abstract

Neutron-yield functions for $^{245}\mathrm{Cm}$($n$,$f$), $^{252}\mathrm{Cf}$(sf), $^{254}\mathrm{Cf}$(sf), $^{254}\mathrm{Es}$($n$,$f$), and $^{256}\mathrm{Fm}$(sf) are derived with an iterative method in which successive approximations to the pre-neutron-emission (initial) mass distribution are compared with the post-neutron-emission (final) mass distribution. Initial mass distributions are deduced from kinetic energy measurements of the fragments. Final mass distributions are determined from radiochemical measurements of fission product mass yields. The $^{252}\mathrm{Cf}$(sf) neutron-yield function so derived agrees well with functions determined directly by neutron counting. All neutron-yield functions exhibit a saw-toothed character. The masses for which maximum neutron emission occurs and for which minimum neutron emission occurs are within \ifmmode\pm\else\textpm\fi{} 2 mass units of being complementary masses for the observed fissioning system, with the exception of the $^{245}\mathrm{Cm}$($n$,$f$) reaction. The effect of the neutron-yield function on various mass and energy correlations deduced from kinetic energy measurements is discussed.NUCLEAR REACTIONS, FISSION $^{254}\mathrm{Cm}$($n$,$f$), $^{252}\mathrm{Cf}$(sf), $^{254}\mathrm{Cf}$(sf), $^{254}\mathrm{Es}$($n$,$f$), $^{256}\mathrm{Fm}$(sf). Deduced neutron yields, fragment mass and energy distributions.