EVIDENCE FOR GAMMA-VIBRATIONS AND SHAPE EVOLUTIONS THROUGH THE TRANSITIONAL HG-184,HG-186,HG-188,HG-190 NUCLEI

Constrained Hartree-Fock-Bogoliubov calculations based on Gogny's forc e have been performed to determine the potential energy surfaces, coll ective masses, and moments of inertia used to build a five-dimension c ollective Hamiltonian treating quadrupole motion in the Hg-184,Hg-186, Hg-188,Hg-190 isotopes. Many collective states have been predicted at low excitation energy, some of them forming gamma-vibrational bands. T o expand experimental information on gamma bands, high statistics meas urements on the beta(+) and electron capture decay of Tl-190(g,m) and Tl-186(g,m) have been performed at the ISOCELE facility. For the first time, gamma bands have been identified in Hg-190 and Hg-186. These ne w results together with previous experimental information available on the ground state and K=0 excited bands in Hg-184,Hg-186,Hg-188,Hg-190 form a database which has been analyzed and discussed in the present theoretical framework. It is argued that the first K=0 excited band in Hg-190 is a beta-vibrational band, and that Hg-186 is, a nucleus in w hich shape coexistence occurs not only for the K=0 bands but also for the gamma bands.