Delayed neutron emission in the semi-gross theory of nuclear β-decay

The semi-gross theory of nuclear β-decay enables one to estimate some β-decay properties such as half-lives and delayed neutron emission probabilities (Pn-values) in the region far from the β-stability line. This theory has been obtained by refining the conventional gross theory to take into account some shell effects of the parent nucleus. In this theory, the one-particle energy-levels are assumed to be discrete and non-uniform, and the one-particle strength function depends on the orbital and total angular momenta of the decaying nucleon. The Pn-values obtained with use of the semi-gross theory are lower than the experimental values in many cases. In order to get more reasonable Pn-values, the strength of the semi-gross theory in each small energy interval is spread with a width depending on the excitation energy. Modified Pn-values thus obtained are compared with the experimental data as well as those estimated by the semi-gross theory.