Systematics of Spontaneously Fissioning Isomers

Excitation functions have been measured for the production of fission isomers by ($\alpha ,xn$) reactions for bombarding energies of 20-29 MeV and by ($d,2n$), ($d,p$), and ($d,pn$) reactions for bombarding energies of 9-14 MeV. Excitation functions for ($\alpha ,xn$) reactions were measured for targets of ${}_{}{}^{233}{}_{}{}^{}\mathrm{U}$, ${}_{}{}^{234}{}_{}{}^{}\mathrm{U}$, ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$, ${}_{}{}^{236}{}_{}{}^{}\mathrm{U}$, ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$, ${}_{}{}^{237}{}_{}{}^{}\mathrm{Np}$, ${}_{}{}^{239}{}_{}{}^{}\mathrm{Pu}$, ${}_{}{}^{240}{}_{}{}^{}\mathrm{Pu}$, ${}_{}{}^{242}{}_{}{}^{}\mathrm{Pu}$, and ${}_{}{}^{244}{}_{}{}^{}\mathrm{Pu}$. Excitation functions for deuteron reactions were measured for targets of ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$, ${}_{}{}^{237}{}_{}{}^{}\mathrm{Np}$, ${}_{}{}^{239}{}_{}{}^{}\mathrm{Pu}$, ${}_{}{}^{240}{}_{}{}^{}\mathrm{Pu}$, ${}_{}{}^{242}{}_{}{}^{}\mathrm{Pu}$, ${}_{}{}^{244}{}_{}{}^{}\mathrm{Pu}$, and ${}_{}{}^{243}{}_{}{}^{}\mathrm{Am}$. New or more accurate half-lives were determined for the following fission isomers: ${}_{}{}^{235m}{}_{}{}^{}\mathrm{Pu}$, 30 ± 5 nsec; ${}_{}{}^{238m}{}_{}{}^{}\mathrm{Pu}$, 6.5 ± 1 nsec;