Shape coexistence in the neutron-deficient 188Hg investigated via lifetime measurements
Abstract
Shape coexistence in the Z ≈ 82 region has been established in mercury, lead and polonium isotopes. Even-even mercury isotopes with 100 ≤ N ≤ 106 present multiple fingerprints of this phenomenon, which seems to be no longer present for N ≥ 110. According to a number of theoretical calculations, shape coexistence is predicted in the 188Hg isotope. The 188Hg nucleus was populated using two different fusion-evaporation reactions with two targets, 158Gd and 160Gd, and a beam of 34S, provided by the Tandem-ALPI accelerators complex at the Laboratori Nazionali di Legnaro. The channels of interest were selected using the information from the Neutron Wall array, while the γ rays were detected using the GALILEO γ-ray array. The lifetimes of the excited states were determined using the Recoil Distance Doppler-Shift method, employing the dedicated GALILEO plunger device. Using the two-bands mixing and rotational models, the deformation of the pure configurations was obtained from the experimental results. The extracted transition strengths were compared with those calculated with the state-of-the-art symmetry-conserving configuration-mixing (SCCM) and five-dimentional collective Hamiltonian (5DCH) approaches in order to shed light on the nature of the observed structures in the 188Hg nucleus. An oblate, a normal- and a super-deformed prolate bands were predicted and their underlying shell structure was also discussed.