Decays ofTa176,Lu176, andLu176mto Levels inHf176

Abstract

The locations of 48 energy levels in $^{176}\mathrm{Hf}$ have been deduced from $\ensuremath{\gamma}$-ray singles, conversion-electron, and $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidence measurements on the $\mathrm{E}\mathrm{C}\ensuremath{-}{\ensuremath{\beta}}^{+}$ decay of $^{176}\mathrm{Ta}$. Over $300\ensuremath{\gamma}$-ray transitions have been observed in the $^{176}\mathrm{Ta}$ decay spectrum, and about 140 of these have been definitely assigned to the $^{176}\mathrm{Hf}$ level scheme on the basis of 75 $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidence spectra. Spin and parity assignments are proposed for 27 levels besides the ground-state rotationalband members. Less extensive $\ensuremath{\gamma}$-ray singles data from $^{176}\mathrm{Lu}$ and $^{176m}\mathrm{Lu}$ decay have also been obtained; these are found to be consistent with the $^{176}\mathrm{Hf}$ level structure proposed on the basis of $^{176}\mathrm{Ta}$ decay data. Two ${0}^{+}$ excitations in $^{176}\mathrm{Hf}$ identified at 1150 and 1293 keV are found to display quite different decay properties. Evidence for the existence of a series of low-spin four-quasiparticle states near 3 MeV is cited. The $^{176}\mathrm{Hf}$ level structure is compared with available theoretical calculations, and a preliminary interpretation of several unusual features of the level scheme is presented.