The $\alpha$ decay of ${}_{}{}^{235}{}_{}{}^{}\mathrm{Np}$ has been studied by quantitative $\alpha$ singles and $\alpha -\gamma$ coincidence techniques, and the $\beta$ decay of ${}_{}{}^{231}{}_{}{}^{}\mathrm{Th}$ by quantitative $\gamma$-ray singles and $\gamma -\gamma$ two-parameter coincidence measurements with semiconductor detectors. Rotational bandheads in ${}_{}{}^{231}{}_{}{}^{}\mathrm{Pa}$ at 102.30, 174.10, and 183.47 keV are given the Nilsson assignments $\left[\Omega \pi \right(N{n}_z\Lambda \left)\right] \frac{3}{2}+\left(651\right)\mathrm{}$, $\frac{5}{2}-\left(523\right)\mathrm{}$, and $\frac{5}{2}+\left(642\right)\mathrm{}$. Decay schemes for ${}_{}{}^{235}{}_{}{}^{}\mathrm{Np}$ and ${}_{}{}^{231}{}_{}{}^{}\mathrm{Th}$ are presented as well as a transition intensity balance for ${}_{}{}^{231}{}_{}{}^{}\mathrm{Th}$ which includes $\beta$ branchings. Energy level spacings and $\alpha$, $\beta$, and $\gamma$ transition probabilities are interpreted in terms of a strong Coriolis interaction among the even-parity rotational bands and admixtures in the wave functions are given for the observed levels.

• Received 12 January 1973

DOI:https://doi.org/10.1103/PhysRevC.7.2545