<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mi>β</mml:mi><mml:mrow><mml:mo>−</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math>-delayed spectroscopy of neutron-rich tantalum nuclei: Shape evolution in neutron-rich tungsten isotopes

The low-lying structure of $^{188,190,192}\mathrm{W}$ has been studied following $\ensuremath{\beta}$ 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 $\ensuremath{\beta}$-decay half-lives of $^{188}\mathrm{Ta}$, $^{190}\mathrm{Ta}$, and $^{192}\mathrm{Ta}$ have been measured, with $\ensuremath{\gamma}$-ray decays of low-lying states in their respective W daughter nuclei, using heavy-ion $\ensuremath{\beta}\ensuremath{-}\ensuremath{\gamma}$ 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 $\ensuremath{\gamma}$-softness of the nuclear potential around $N~116$.