The decays of ${\mathrm{Ta}}^{177}$ and ${\mathrm{Lu}}^{177}$ to levels in ${\mathrm{Hf}}^{177}$ have been investigated with beta-ray spectrometers, NaI(Tl) gamma-ray spectrometers, and fast coincidence and angular correlation techniques. Energy levels in ${\mathrm{Hf}}^{177}$ have been characterized according to their energy (kev), the Nilsson asymptotic quantum numbers ($N{n}_z\Lambda$), the total angular momentum and its component along the symmetry axis ($I, K$), and the parity ($\pi$) as follows: $0[514 \frac{7}{2}, \frac{7}{2}-]$; $112.97[514 \frac{9}{2}, \frac{7}{2}-]$; $249.7[514 \frac{11}{2}, \frac{7}{2}-]$; $321.34[624 \frac{9}{2}, \frac{9}{2}+]$; $447.9[624 \frac{11}{2}, \frac{9}{2}+]$; $420.95[642 \frac{3}{2}, \frac{3}{2}+]$; $488.8[642 \frac{5}{2}, \frac{3}{2}+]$; $585.8[642 \frac{7}{2}, \frac{3}{2}+]$; $509.0[512 \frac{5}{2}, \frac{5}{2}-]$; $605.5[512 \frac{7}{2}, \frac{5}{2}-]$; $746.04[633 \frac{7}{2}, \frac{7}{2}+]$; $848.2[633 \frac{9}{2}, \frac{7}{2}+]$; and $1058.38[503 \frac{7}{2}, \frac{7}{2}-]$. The levels at 447.9, 488.8, and 585.8 kev are tentative. The spins and parities have been uniquely determined by angular correlation and internal conversion data for the levels at 746.0 and 848.2 kev, if we assume the spins and parities of the levels at 0, 113.0, 249.7, and 321.3 kev are correct as determined from earlier work. For the level at 1058.4 kev the $\mathrm{ft}$ value is needed in addition to angular correlation and conversion data in order to determine the spin and parity uniquely. The spins of ${\mathrm{Lu}}^{177}$ and ${\mathrm{Hf}}^{177}$ have previously been measured directly as $\frac{7}{2}$, and the ${\mathrm{Ta}}^{177}$ spin is expected to be $\frac{7}{2}$ on the basis of other tantalum isotopes. The following half-lives were measured: 56.56 hr for ${\mathrm{Ta}}^{177}$, 0.32 nsec for the level at 113.0 kev, and 0.52 nsec for the level at 321.3 kev. The $\frac{K}{L}$ electron capture ratio to the 1058.4-kev level and the $\frac{\beta +}{K}$-capture ratio to the ground state determine the total decay energy to be 1166±6 kev.

• Received 24 March 1961

DOI:https://doi.org/10.1103/PhysRev.124.527