Level lifetimes and shape transitions for A=100 nuclei

Subnanosecond lifetime and nuclear spectroscopic measurements of levels in neutron-rich nuclei near A=100 have revealed a uniquely abrupt shape transition as N increases above 50. Just at the onset of deformation at N=60 spherical Sr and Y nuclei abruptly obtain a saturated deformation, and the shape transition is slightly less abrupt for the Sr nuclei. The level lifetime results discussed were all obtained using the FEST technique for b-g-g triple coincidences by the TRISTAN collaboration at the TRISTAN mass-separator at the High Flux Beam Reactor at Brookhaven