The Decay ofHo166

The disintegration of ${\mathrm{Ho}}^{166}$ (27.3 hr) has been studied by scintillation counter coincidence techniques. Gamma rays of 1.53 Mev and 1.61 Mev are present in low intensity, in addition to the previously identified 80-kev and 1.36-Mev transitions. Both the 1.36-Mev and the 1.53-Mev gamma rays are in coincidence with the 80-kev transition. For the 80-kev $E2\mathrm{}$ transition the $K$-conversion coefficient has been measured as 1.9±0.2 and the total conversion coefficient as 7.6±1.5. The $\beta$ branching has been determined from $\beta -\gamma$ and $\gamma -\gamma$ coincidence measurements and by a comparison of the $\beta -\gamma$ coincidences with ${\mathrm{Tm}}^{170}$. The results indicate a ground state branch of ∼25 percent, a branch of ∼74 percent to the 80-kev state, a branch of ∼1 percent to a state at 1.44 Mev and a branch of ∼0.3 percent to a state at 1.61 Mev in ${\mathrm{Er}}^{166}$. The spin of ${\mathrm{Ho}}^{166}$ is probably 2-.