Collective structure of the neutron-rich nuclei, 110Ru and 112Ru

The collective structure of 110Ru and 112Ru has been studied at the IGISOL facility through the beta decay of 110Tc and 112Tc. Neutron-rich technetium isotopes were produced by the 238U(p,f) reaction at 20 MeV bombarding energy. The new isotope 112Tc was found to decay with a half-life of 280(30) ms. The observed energies of the 2+ and 4+ ground state band levels in 108,110,112Ru are almost the same. However, a steady energy decrease of the proposed gamma band head is observed with increasing neutron number, suggesting importance of triaxiality in these nuclei. In fact, only in 192Os the second 2+ state has been observed at lower excitation than in 112Ru. The static deformation of 108,110,112Ru isotopes has been investigated in microscopic lattice Hartree-Fock calculations. The obtained potential energy surface predict that these isotopes are deformed (β ≅ 0.3), with a quasidegeneracy associated with γ-deformation, and suggest that the γ-asymmetry softness increases with the neutron number for neutron-rich ruthenium isotopes. (orig.)