With the use of $\alpha$ spectroscopy and the helium gas-jet technique the $\alpha$ decay of the previously unknown isotopes, ${}_{}{}^{159}{}_{}{}^{}\mathrm{Hf}$, ${}_{}{}^{160}{}_{}{}^{}\mathrm{Hf}$, and ${}_{}{}^{161}{}_{}{}^{}\mathrm{Hf}$, was observed. These hafnium nuclides were produced by bombarding targets of ${}_{}{}^{144}{}_{}{}^{}\mathrm{Sm}$ and ${}_{}{}^{147}{}_{}{}^{}\mathrm{Sm}$ with ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ ions accelerated in the Oak Ridge isochronous cyclotron. The decay characteristics and mass assignments (made on the basis of yield curve measurements, cross bombardments, and parent-daughter relationships) of the three new $\alpha$ emitters are as follows: (1) ${}_{}{}^{159}{}_{}{}^{}\mathrm{Hf}$, $E_{\alpha }=5.09\mathrm{}\pm 0.01$ MeV, $T_{\frac{1}{2}}=5.6\mathrm{}\pm 0.5$ sec; (2) ${}_{}{}^{160}{}_{}{}^{}\mathrm{Hf}$, $E_{\alpha }=4.77\mathrm{}\pm 0.02$ MeV, $T_{\frac{1}{2}}\sim 12$ sec; and (3) ${}_{}{}^{161}{}_{}{}^{}\mathrm{Hf}$, $E_{\alpha }=4.60\mathrm{}\pm 0.01$ MeV, $T_{\frac{1}{2}}=17\mathrm{}\pm 2$ sec. The latter two isotopes with neutron numbers of 88 and 89 are of some interest with respect to $\alpha$-decay systematics in the 82-neutron region. The only 88-neutron $\alpha$ emitters known up to now are naturally occurring ${}_{}{}^{152}{}_{}{}^{}\mathrm{Gd}$ and long-lived ${}_{}{}^{154}{}_{}{}^{}\mathrm{Dy}$, while ${}_{}{}^{161}{}_{}{}^{}\mathrm{Hf}$ is the first 89-neutron nuclide to exhibit $\alpha$ decay.

• Received 2 January 1972

DOI:https://doi.org/10.1103/PhysRevC.7.2010