Nuclear structure of 238Np from neutron-capture and alpha -decay measurements.

Abstract

The experimental measurements made in this investigation include secondary $\ensuremath{\gamma}$ rays and conversion electrons from thermal neutron capture in $^{237}\mathrm{Np}$, primary $\ensuremath{\gamma}$ rays from average resonance capture with a 2-keV neutron beam and from resonance capture with thermal neutrons, and $\ensuremath{\alpha}$ particles and $\ensuremath{\gamma}$ rays, singles and coincidences, from $^{242}\mathrm{Am}^{m}$ $\ensuremath{\alpha}$ decay. From these data and those of previous investigations, 69 excited levels in $^{238}\mathrm{Np}$ with energies 700 keV were identified and, of these, 46 were placed in 13 rotational bands with assigned Nilsson configurations. The results are found to be in good agreement with a semiempirical model calculation. A special feature is the observation of four different $K=0$ rotational bands in the low-energy structure of $^{238}\mathrm{Np}$. Experimentally determined Gallagher-Moszkowski and Newby matrix elements show reasonable agreement with calculated values.