Triaxiality, chiral bands and gamma vibrations in A=99–114 nuclei

摘要

Prompt γ–γ–γ coincidence measurements of A=99–114 neutron-rich nuclei populated in the spontaneous fission of 252Cf were made with Gammasphere. The high statistics data, 5.7×10 11 triples and higher folds, opened up discoveries of new band structures and significant extensions of previously known bands. The new data for ground bands in 99,101Y, 101,105Nb, 105,107,109,111Tc and 111,113Rh when compared with one quasi-particle plus triaxial rotor calculation, revealed a smooth transition from axial symmetry in 99,101Y to maximize triaxiality in 111,113Rh. In 106Mo, 110,112Ru, pairs of △I=1 doublet bands are established to high spins. Their constant and equal kinetic moments of inertia, small energy differences between states of the same spin and very similar B(E2)/B(M1) ratios for each band in these nuclei suggest that these are chiral doublet bands. If they are not chiral, then a new symmetry is indicted. Extended one- and new two-phonon γ-vibrational bands are observed in 110,112Ru. The extended one-phonon bands in 104-108Mo, and 108-112Ru exhibit an unexpected reversal in the energy level staggering pattern with spin. The first one- and two-phonon γ-bands in an odd-A nucleus are seen in 105Mo with level energies almost identical to these same bands known in 104Mo.