Beta Decay and Electron Capture Branching to the Levels ofPu239

Abstract

The experimental $log\mathrm{ft}$ values of the ${\mathrm{Np}}^{239}$ beta decay and ${\mathrm{Am}}^{239}$ electron capture are analyzed according to the asymptotic selection rules proposed by Alaga for deformed nuclei. It is found that, with a reasonable choice of state assignments from the Nilsson energy level diagram, a consistent interpretation can be given of the observed $log\mathrm{ft}$ values. All "allowed" transitions are retarded by at least an order of magnitude, whereas the "first forbidden" transitions observed here proceed with normal $\mathrm{ft}$ values. The interesting case of an "allowed" transition with $log\mathrm{ft}>\mathrm{}8\mathrm{}$ is discussed.