Isomeric Transitions in the Rare-Earth Elements

A search was made for isomeric transitions in the rare-earth elements with half-lives greater than 5 microseconds and less than ∼30 minutes which arise in the decay of photoexcited nuclei. Four isomeric transitions were found and identified as follows: ${\mathrm{Tb}}^{158}$, $50 \mathrm{kev}<E<\mathrm{}200\mathrm{} \mathrm{kev}$, 11.0±0.1 sec, $M3\mathrm{}$ or $E3\mathrm{}$; ${\mathrm{Ho}}^{163}$, 305 kev, 0.8±0.1 sec, $E3\mathrm{}$; ${\mathrm{Er}}^{165,167,\mathrm{o}\mathrm{r}169}$, 213 kev, 2.5±0.1 sec, $E3\mathrm{}$; ${\mathrm{Lu}}^{174}$, 133 kev, 75±2 μsec, $E2\mathrm{}$. These results are compared with the predictions of the nuclear models which have been proposed by Nilsson and Gottfried.