Improvement to the gross theory of β decay by inclusion of change in parity

Abstract

An improvement to the single-particle structure is made to the gross theory, which is a global $\ensuremath{\beta}$-decay model. The gross theory is based on the sum rule of the intensity of the $\ensuremath{\beta}$-decay transition and a strength function. This model provides reasonable results for $\ensuremath{\beta}$-decay rates and delayed neutrons for the entire nuclear mass region. An attempt is made to improve the gross theory of nuclear $\ensuremath{\beta}$ decay by considering the change in parity at the single-particle level of ground-state nuclei. In this treatment, the nuclear matrix elements are suppressed when the parity of the single neutron and proton levels is different for the allowed transition. The assignment of parity is performed using the Woods-Saxon--type single-particle potential. The discrepancies from experimental half-lives, which appeared in the vicinity of the magic numbers of neutrons and protons, are systematically improved in the nuclear mass region.