The experimental measurements made in this investigation include secondary $\gamma$ rays and conversion electrons from thermal neutron capture in ${}_{}{}^{237}{}_{}{}^{}\mathrm{Np}$, primary $\gamma$ rays from average resonance capture with a 2-keV neutron beam and from resonance capture with thermal neutrons, and $\alpha$ particles and $\gamma$ rays, singles and coincidences, from ${}_{}{}^{242}{}_{}{}^{}\mathrm{Am}_{}^m{}_{}{}^{}$ $\alpha$ 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 $K=0\mathrm{}$ 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.

• Received 11 September 1989

DOI:https://doi.org/10.1103/PhysRevC.41.484