Nuclear shapes of highly deformed bands inHf171,172and neighboring Hf isotopes

Abstract

A Gammasphere experiment was carried out to search for triaxial strongly deformed (TSD) structures in $^{171,172}\mathrm{Hf}$ and the wobbling mode, a unique signature of nuclei with stable triaxiality. Three strongly deformed bands in $^{172}\mathrm{Hf}$ and one in $^{171}\mathrm{Hf}$ were identified through $^{48}\mathrm{Ca}$($^{128}\mathrm{Te}$, xn) reactions. Linking transitions were established for the band in $^{171}\mathrm{Hf}$ and, consequently, its excitation energies and spins (up to $111/2\ensuremath{\hbar}$) were firmly established. However, none of the $^{172}\mathrm{Hf}$ sequences were linked to known structures. Experimental evidence of triaxiality was not observed in these bands. The new bands are compared with other known strongly deformed bands in neighboring Hf isotopes. Theoretical investigations within various models have been performed. Cranking calculations with the Ultimate Cranker code suggest that the band in $^{171}\mathrm{Hf}$ and two previously proposed TSD candidates in $^{170}\mathrm{Hf}$ and $^{175}\mathrm{Hf}$ are built on proton $({i}_{13/2}{h}_{9/2})$ configurations, associated with near-prolate shapes and deformations enhanced with respect to the normal deformed bands. Cranked relativistic mean-field calculations suggest that band 2 in $^{175}\mathrm{Hf}$ has most likely a near-prolate superdeformed shape involving the $\ensuremath{\pi}{i}_{13/2}\ensuremath{\bigotimes}\ensuremath{\nu}{j}_{15/2}$ high-$j$ intruder orbitals. It is quite likely that the bands in $^{172}\mathrm{Hf}$ are similar in character to this band.