The excitation function and lifetime $T_i=(45\mathrm{}\pm 5)$ ns of a ${}_{}{}^{237}{}_{}{}^{}\mathrm{Np}$ fission isomer were measured using the ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}\mathrm{}(p,2n)\mathrm{}$ reaction and the fission-in-flight method. The analysis of the delayed-to-prompt fission ratio provided an excitation energy of (2.85 ± 0.4) MeV for the isomeric state and a branching ratio of 1.9 × ${10}^{-3\mathrm{}}$ between $\gamma$ and fission decays.

NUCLEAR REACTIONS ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}\mathrm{}(p,2n)\mathrm{}$; $E_p=9.75, 11.6, 12.5$ MeV. Measured ${}_{}{}^{237}{}_{}{}^{}\mathrm{Np}_{}^m{}_{}{}^{}$ isomeric decay curve and delayed-to-prompt fission ratios. Deduced partial half-lives $T_{\mathrm{if}}$, $T_{i\gamma }$ and the branching ratio.

• Received 1 March 1977

DOI:https://doi.org/10.1103/PhysRevC.16.1919