The shape transition in the neutron-rich yttrium isotopes and isomers

Abstract Laser spectroscopy has been used to study 86–90,92–102 Y and isomeric states of 87–90,93,96,97,98 Y. Nuclear charge radii differences, magnetic dipole and electric quadrupole moments have been obtained. Information on the nature of the Z ≈ 40 , N ≈ 60 sudden onset of deformation has been derived from all three parameters. It is seen that with increasing neutron number from the N = 50 shell closure that the nuclear deformation becomes increasingly oblate and increasingly soft. At N = 60 a transition to a strongly deformed rigid prolate shape occurs but prior to this, although the nuclear deformation is increasing with N , a proportionate increase in softness is also observed.