COLLECTIVITY IN LIGHT ZIRCONIUM ISOTOPES - EVOLUTION WITH NEUTRON NUMBER AND ANGULAR-MOMENTUM

Considerable data have recently been collected on light zirconium isotopes. We present new measurements on 84Zr and some unpublished results on 82Zr. We have performed calculations on 82,84,86Zr using an extension to the IBM which allows a collective core to couple to up to four unpaired fermions (two broken pairs). The role of vibrational collectivity is clear in the N = 44 and N = 46 nuclei, but collective rotation becomes the dominant mode below N = 44. The relative positions of the neutron and proton Fermi surfaces are crucial in determining the complexity of the decay path down the yrast states, being dominated by proton configurations for N less-than-or-equal-to 44 but showing strong competition between neutron and proton structures when N > 44.