A new γ ray with an energy of 100.7 keV has been observed in the decay of ${}_{}{}^{180}{}_{}{}^{}\mathrm{Hf}_{}^{\mathrm{m}}{}_{}{}^{}$. This line is interpreted as the transition between the $I^{\pi }$${=8\mathrm{}}^{+}$ level at 174 keV and the $9^{\mathrm{-}}$ isomeric state in ${}_{}{}^{180}{}_{}{}^{}\mathrm{Ta}$ following the 113-keV endpoint β decay of ${}_{}{}^{180}{}_{}{}^{}\mathrm{Hf}_{}^{\mathrm{m}}{}_{}{}^{}$. The laboratory branching ratio is 2.3×${10}^{\mathrm{-}4}$ compared to the electromagnetic decay mode of ${}_{}{}^{180}{}_{}{}^{}\mathrm{Hf}_{}^{\mathrm{m}}{}_{}{}^{}$. A possible second branch to a proposed $7^{\mathrm{-}}$ level in ${}_{}{}^{180}{}_{}{}^{}\mathrm{Ta}$ is not seen. Even when the enhancement due to bound state β decay in a stellar environment is included, the observed branch is not sufficient to explain the abundance of ${}_{}{}^{180}{}_{}{}^{}\mathrm{Ta}_{}^{\mathrm{m}}{}_{}{}^{}$ in the universe.

• Received 26 December 1984

DOI:https://doi.org/10.1103/PhysRevC.31.1505