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

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 Hg-189 have been determined by using the fast-timing techniques with the HPGe and LaBr3:Ce array via the Lu-175(F-19, 5n)Hg-189 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 Hg-189.