New Neutron-Deficient Isotopes of Tantalum

Bombardment of ${\mathrm{Ho}}_2$ ${\mathrm{O}}_3$ with ${\mathrm{N}}^{14}$ ions in the Berkeley heavy-ion linear accelerator has resulted in the discovery of new isotopes of tantalum which have been assigned as ${\mathrm{Ta}}^{173}$ and ${\mathrm{Ta}}^{174}$. They have half-lives of 3.7 hr and 1.3 hr, respectively. Tantalum-172 was not observed and is believed to have a half-life shorter than 30 minutes. Gamma-ray spectra have been obtained for these two isotopes and for ${\mathrm{Ta}}^{175}$. Tantalum-175, with an 11-hr half-life, has also been produced by 48-Mev alpha-particle bombardment of ${\mathrm{Lu}}_2$ ${\mathrm{O}}_3$, and its conversion-electron spectrum was studied. From these data a decay scheme is proposed using nine of the observed transitions and assigning spins to three members of the ground-state rotational band.