Fissile Nuclei of Medium Mass with Nanosecond Lifetimes

Targets of ${}_{56}{}^{}{}_{}{}^{}\mathrm{Ba}_{}^{138}{}_{}{}^{}$ to ${}_{83}{}^{}{}_{}{}^{}\mathrm{Bi}_{}^{209}{}_{}{}^{}$ have been bombarded with various heavy ions, ${}_5{}^{}{}_{}{}^{}\mathrm{B}_{}^{11}{}_{}{}^{}$ to ${}_9{}^{}{}_{}{}^{}\mathrm{F}_{}^{19}{}_{}{}^{}$. In a number of cases fission has been observed to occur from nuclei that must have mean lives of several nanoseconds and cross sections of the order of 10 μb. There are strong indications that the major reactions responsible for producing these products are of the compound-nucleus type. This type of fission appears to be rather common for $Z\approx 66$ and $Z\approx 84$.