Electron-capture and alpha-decay properties of ${\mathrm{Pu}}^{237}$, ${\mathrm{Pu}}^{235}$, and the new isotope ${\mathrm{Pu}}^{233}$ have been measured. The over-all half-lives are 44±2 days for ${\mathrm{Pu}}^{237}$, 26±2 minutes for ${\mathrm{Pu}}^{235}$, and 20±2 minutes for ${\mathrm{Pu}}^{233}$. Two alpha groups, one of 5.65±0.02 Mev and one of 5.36±0.02 Mev, were detected in the decay of ${\mathrm{Pu}}^{237}$, one group of 5.85±0.02 Mev in the decay of ${\mathrm{Pu}}^{235}$, and one of 6.30±0.02 Mev in the decay of ${\mathrm{Pu}}^{233}$. The partial alpha half-lives corresponding to these alpha groups are, for ${\mathrm{Pu}}^{237}$, (1.7±0.4)×${10}^4$ years and (4.6±0.6)×${10}^3$ years, respectively; for ${\mathrm{Pu}}^{235}$, (1.7±0.4) years; and for ${\mathrm{Pu}}^{233}$, 11±4 days. On the basis of the experimental data it has been possible to calculate hindrance factors for the alpha decay and $log\mathrm{ft}$ values for the electron-capture decay of the three isotopes and to correlate their properties with the alpha and electron-capture systematics.

• Received 7 March 1957

DOI:https://doi.org/10.1103/PhysRev.106.1228