Fast-timing lifetime measurements of the 33/2⁺ and 25/2^- states in ¹⁸⁹Hg: oblate excitations

Abstract The lifetimes of the $I^{\pi}=33/2^{+}$ and $I^{\pi}=25/2^{-}$ states with $E_x=2674.6$ keV and $E_x=1917.3$ keV, respectively, in $^{189}$Hg have been determined by using the fast-timing techniques with the HPGe and LaBr$_{3}$:Ce array via the $^{175}$Lu($^{19}$F,5$n$)$^{189}$Hg reaction at a beam energy of 100 MeV. The deduced $B(E2)$ strengths have been discussed in relation to the systematics of the previously reported $B(E2)$ strengths in the heavy mercury isotopes. The transition quadrupole moments $Q_t$ are derived from present experimental data. The $Q_t$ values together with the excitation energies of the (+,0)(+,1/2) and (+,0)(-,1/2) bands are interpreted in terms of the Nilsson-Strutinsky-Bogoliubov model(CNSB) calculations suggesting oblate excitations in $^{189}$Hg.