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

Laser spectroscopy has been used to study Y-86-90,Y-92-102 and isomeric states of Y-87-90,Y-93,Y-96,Y-97,Y-98. Nuclear charge radii differences, magnetic dipole and electric quadrupole moments have been obtained. Information on the nature of the Z approximate to 40, N approximate to 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 defonned rigid prolate shape occurs but prior to this, although the nuclear deformation is increasing with N, a proportionate increase in softness is also observed. (c) 2007 Elsevier B.V. All rights reserved.