Probing the Collective Degrees of Freedom at the Proton Drip Line in the Extremely Neutron Deficient Hg-172

Abstract

Excited states in the extremely neutron-deficient isotope Hg-172 have been established for the first time. The Ru-96(Kr-78,2n) reaction was employed to populate excited states in Hg-172 with a cross section sigma approximate to 15 nb. The highly selective Recoil-Decay Tagging (RDT) technique was used to obtain clean in-beam gamma-ray spectra for Hg-172. The yrast ground-state band has tentatively been established up to I = 6 (h) over bar. The data have been interpreted within the framework of total Routhian surface and quasiparticle random phase approximation calculations. In addition to the well-known features of shape coexistence previously observed in light Hg isotopes, the systematic trends in the energy of the yrast 2(+) and 4(+) states in the chain of Hg isotopes indicate a pronounced vibrational collectivity which is reduced in strength, but at the same time shows a higher degree of harmonicity, as the neutron number decreases below the neutron midshell.