The new isotopes ${}_{72}{}^{163}{}_{}{}^{}\mathrm{Hf}$ [$T_{\frac{1}{2}}=40.0\mathrm{}\left(6\right)\mathrm{}$ s] and ${}_{72}{}^{162}{}_{}{}^{}\mathrm{Hf}$ [$T_{\frac{1}{2}}=37.6\mathrm{}\left(8\right)\mathrm{}$ s] were produced in ${}_{60}{}^{142}{}_{}{}^{}\mathrm{Nd}$ (${}_{12}{}^{24}{}_{}{}^{}\mathrm{Mg}$, $\mathrm{xn}$) reactions and transported to a measuring station by use of the He-jet technique. Decay properties were observed with $\alpha$, $\gamma$, and $\gamma -\gamma$ spectroscopy. The $Z$ assignment of the new isotopes was based on a cross bombardment, ${}_{12}{}^{24}{}_{}{}^{}\mathrm{Mg}$+${}_{59}{}^{141}{}_{}{}^{}\mathrm{Pr}$, and on results of $\gamma$-x-ray coincidence measurements. The mass assignment was deduced from measured excitation functions. Beta-delayed $\gamma$ rays were identified, 11 for ${}_{}{}^{163}{}_{}{}^{}\mathrm{Hf}$ and 3 for ${}_{}{}^{162}{}_{}{}^{}\mathrm{Hf}$, and level schemes for ${}_{71}{}^{163}{}_{}{}^{}\mathrm{Lu}$ and ${}_{71}{}^{162}{}_{}{}^{}\mathrm{Lu}$ are proposed based on the results of intensity and $\gamma -\gamma$ coincidence measurements. A small $\alpha$ branch [$I_{\alpha }={0.0087 }_{(-37\mathrm{}}^{+17)}$%] with a decay energy of $E_{\alpha }=4308\mathrm{}$ (10) keV was found in the decay of ${}_{}{}^{162}{}_{}{}^{}\mathrm{Hf}$. The reduced $\alpha$ width $W_{\alpha }={2.6}_{(-1.2\mathrm{}}^{+0.6)}$ for ${}_{}{}^{162}{}_{}{}^{}\mathrm{Hf}$ is in accordance with those for neighboring nuclei. With the new ${}_{}{}^{162}{}_{}{}^{}\mathrm{Hf}$ $\alpha$-decay energy, mass values were derived for ${}_{72}{}^{162}{}_{}{}^{}\mathrm{Hf}$, ${}_{74}{}^{166}{}_{}{}^{}\mathrm{W}$, ${}_{76}{}^{170}{}_{}{}^{}\mathrm{Os}$, ${}_{78}{}^{174}{}_{}{}^{}\mathrm{Pt}$, and ${}_{80}{}^{178}{}_{}{}^{}\mathrm{Hg}$. The new masses as well as values deduced for two-proton binding energies are compared with predictions of current mass formulas.

RADIOACTIVITY ${}_{}{}^{163,162}{}_{}{}^{}\mathrm{Hf}$ from ${}_{}{}^{142}{}_{}{}^{}\mathrm{Nd}$(${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$,$\mathrm{xn}$); measured $E_{\gamma }$, $I_{\gamma }$, $E_{\alpha }$, $I_{\alpha }$, and $T_{\frac{1}{2}}$; ${}_{}{}^{163,162}{}_{}{}^{}\mathrm{Lu}$ deduced level schemes; deduced reduced $\alpha$ width for ${}_{}{}^{162}{}_{}{}^{}\mathrm{Hf}$; deduced mass values for ${}_{}{}^{162}{}_{}{}^{}\mathrm{Hf}$, ${}_{}{}^{166}{}_{}{}^{}\mathrm{W}$, ${}_{}{}^{170}{}_{}{}^{}\mathrm{Os}$, ${}_{}{}^{174}{}_{}{}^{}\mathrm{Pt}$, and ${}_{}{}^{178}{}_{}{}^{}\mathrm{Hg}$. He-jet technique; Ge(HP), Ge(Li), and Si surface-barrier detectors.

• Received 22 January 1982

DOI:https://doi.org/10.1103/PhysRevC.25.3091