The ground-state spontaneous-fission half-lives of ${}_{}{}^{233}{}_{}{}^{}\mathrm{U}$, ${}_{}{}^{234}{}_{}{}^{}\mathrm{U}$, ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$, and ${}_{}{}^{236}{}_{}{}^{}\mathrm{U}$ were redetermined using solutions of highly enriched uranium in spinner detectors. The following values were obtained: >2.7×${10}^{17}$ years for ${}_{}{}^{233}{}_{}{}^{}\mathrm{U}$; (1.42±0.08)×${10}^{16}$ years for ${}_{}{}^{234}{}_{}{}^{}\mathrm{U}$; (9.8±2.8)×${10}^{18}$ years for ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$; (2.43±0.13)×${10}^{16}$ years for ${}_{}{}^{236}{}_{}{}^{}\mathrm{U}$. The values for ${}_{}{}^{234}{}_{}{}^{}\mathrm{U}$ and ${}_{}{}^{236}{}_{}{}^{}\mathrm{U}$ are in agreement with the systematics for spontaneous-fission half-lives of even-even nuclides. The spontaneous-fission of the odd-$A$ uranium isotopes 233 and 235 is considerably hindered (hindrance factors >1.3 and 3, respectively).

RADIOACTIVITY, FISSION ${}_{}{}^{233}{}_{}{}^{}\mathrm{U}$(sf), ${}_{}{}^{234}{}_{}{}^{}\mathrm{U}$(sf), ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$(sf), ${}_{}{}^{236}{}_{}{}^{}\mathrm{U}$(sf); measured $T_{\frac{1}{2}}$ of sf, spinner detector.

• Received 3 October 1980

DOI:https://doi.org/10.1103/PhysRevC.23.1110