The low-lying structure of ${}^{188,190,192}\mathrm{W}$ has been studied following $\beta$ decays of the neutron-rich mother nuclei ${}^{188,190,192}\mathrm{Ta}$ produced following the projectile fragmentation of a 1-GeV-per-nucleon ${}^{208}\mathrm{Pb}$ primary beam on a natural beryllium target at the GSI Fragment Separator. The $\beta$-decay half-lives of ${}^{188}\mathrm{Ta}$, ${}^{190}\mathrm{Ta}$, and ${}^{192}\mathrm{Ta}$ have been measured, with $\gamma$-ray decays of low-lying states in their respective W daughter nuclei, using heavy-ion $\beta -\gamma$ correlations and a position-sensitive silicon detector setup. The data provide information on the low-lying excited states in ${}^{188}\mathrm{W}$, ${}^{190}\mathrm{W}$, and ${}^{192}\mathrm{W}$, which highlight a change in nuclear shape at ${}^{190}\mathrm{W}$ compared with that of lighter W isotopes. This evolution of ground-state structure along the W isotopic chain is discussed as evidence for a possible proton subshell effect for the $A~$ 190 region and is consistent with maximization of the $\gamma$-softness of the nuclear potential around $N~116$.

• Received 18 September 2009

DOI:https://doi.org/10.1103/PhysRevC.80.064308