Unhindered ${\frac{11}{2}}^{-}\to {\frac{11}{2}}^{-}$ $\beta$-ray transitions with $log\mathrm{ft}$ values of 5.0 to 5.4 have been observed in the decay of ${}_{}{}^{139}{}_{}{}^{}\mathrm{Eu}$, ${}_{}{}^{139}{}_{}{}^{}\mathrm{Sm}_{}^m{}_{}{}^{}$,, and a new isotope ${}_{}{}^{135}{}_{}{}^{}\mathrm{Pm}$. These transitions show no noticeable retardation and are not "shape forbidden." The shape of ${\frac{11}{2}}^{-}$ states with odd $N$ is not very different from the (prolate) shape of adjacent ${\frac{11}{2}}^{-}$ states with odd $Z$.

RADIOACTIVITY $\beta$ decay between ${\frac{11}{2}}^{-}$ states of ${}_{}{}^{139}{}_{}{}^{}\mathrm{Eu}$, ${}_{}{}^{139}{}_{}{}^{}\mathrm{Sm}$, ${}_{}{}^{139,137,135}{}_{}{}^{}\mathrm{Pm}$, ${}_{}{}^{137,135}{}_{}{}^{}\mathrm{Nd}$. Deduced $log\mathrm{ft}$ values and shape differences.

• Received 6 January 1975

DOI:https://doi.org/10.1103/PhysRevC.12.2111