Study of neutron-deficient nucleus 224Np and its {α} decay by particle-number-conserving method in the framework of deformed shell model

The particle-number-conserving (PNC) method in the framework of the deformed shell model (DSM) is employed to study the properties of the newly discovered short-lived neutron-deficient nucleus 224Np and its {α}-decay. The calculated energy of {α}-particle lies within 300 keV of the experimental data. This is the first application of the PNC method to the region of neutron-deficient nuclei. This work provides the first attempt to combine the microscopic PNC theory with empirical formulas to study the nuclear {α} decay. The configurations of ground states are assigned as {π}5/2-[523]{⊗}{ν}5/2+[633] for 224Np, {π}1/2-[530]{⊗}{ν}3/2+[642] for 220Pa, {π}3/2+[651]{⊗}{ν}1/2-[501] for 216Ac, and {π}7/2-[514]{⊗}{ν}3/2-[501] for 212Fr. The absence of the Z = 92 subshell closure in 224Np is explained by analyzing the proton single-particle levels. Low-lying excited statesare predicted for nuclei along the {α}-decay chain by the PNC method. Based on the PNC predicted {α}-decay energy and the assigned configurations, the {α}-decay half-lives are calculated by the empirical formulas, in which the angular momentum taken away by the {α} particle is taken into account. The angular momentum have an important effect on the {α}-decay half-life. The errors of the empirical formulas calculation are in two orders of magnitude with the experimental data.