The 45.3-day nuclide ${}_{}{}^{237}{}_{}{}^{}\mathrm{Pu}$ decays primarily via electron capture. The only information available up to now concerning the nuclide's $\alpha$-decay properties has been the observation of two $\alpha$ groups with energies of 5.65 and 5.36 MeV. In the present study, the photon spectrum of ${}_{}{}^{237}{}_{}{}^{}\mathrm{Pu}$ was investigated with x- and $\gamma$-ray Ge(Li) detectors. A total of 21 transitions was found to belong to ${}_{}{}^{237}{}_{}{}^{}\mathrm{Pu}$ decay; of these, 16 were assigned to its $\alpha$-decay branch. An $\alpha$-decay scheme was constructed on the bases of transition energy fits and known ${}_{}{}^{233}{}_{}{}^{}\mathrm{U}$ levels (including some observed only in reaction studies). The amounts of direct $\alpha$-decay feedings were then calculated from intensity balances, and a total $\alpha$-branching of (4.2 ± 0.4) × ${10}^{-3\mathrm{}}$% was deduced. $\alpha$-decay hindrance factors identify the band heads of the $\left(\frac{5}{2}\right)\left[752\right]\mathrm{}$ and $\left(\frac{7}{2}\right)\left[743\right]\mathrm{}$ orbitals in ${}_{}{}^{233}{}_{}{}^{}\mathrm{U}$ at 298.9 and 503.5 keV, respectively. Contrastingly, the ${}_{}{}^{233}{}_{}{}^{}\mathrm{Pa}$ and ${}_{}{}^{233}{}_{}{}^{}\mathrm{Np}$ decay studies had assigned the $\left(\frac{7}{2}\right)\left[743\right]\mathrm{}$ state to the level at 298.9 keV.

RADIOACTIVITY ${}_{}{}^{237}{}_{}{}^{}\mathrm{Pu}$, measured $E_{\gamma }$, $I_{\gamma }$; deduced $\alpha /\mathrm{electron}$-capture ratio. ${}_{}{}^{233}{}_{}{}^{}\mathrm{U}$, deduced levels, $J^{\pi }$.

• Received 29 January 1979

DOI:https://doi.org/10.1103/PhysRevC.20.799