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.

Lifetime measurements in the yrast band of 187Hg

“…Though, a number of lifetime measurements were performed in the even-even isotopes of Hg nuclei of this mass region, the lifetime measurements in odd-A Hg isotopes region are very rare. Earlier in [30] Y. Zheng, et al reported the lifetimes of (propsed) isomeric states 33/2 + and 25/2 + in 189 Hg. Also in 191 Hg, Jin H, et al [31] reported lifetimes of a few low spin states of the yrast band measured via recoil distance Doppler-shift techniques.…”