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

Laser spectroscopy has been used to study 86–90,92–102Y and isomeric states of 87–90,93,96,97,98Y. Nuclear charge radii differences, magnetic dipole and electric quadrupole moments have been obtained. Information on the nature of the Z≈40Z≈40, N≈60N≈60 sudden onset of deformation has been derived from all three parameters. It is seen that with increasing neutron number from the N=50N=50 shell closure that the nuclear deformation becomes increasingly oblate and increasingly soft. At N=60N=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.