Levels in Zr90: Theoretical

An attempt is made to describe the seven levels of Zr90 below 3.6 Mev in terms of the proton configurations (2p12)2, (2p121g92), and (1g92)2. The level positions and the compositions of the two 0+ states are determined for Gaussian and Yukawa forces of various ranges and exchange characters. The experimental data are well reproduced for a reasonable choice of the force parameters, the best fit being obtained with a Serber exchange mixture and a range of about 1.5 fermis. The experimental values of the half-lives of the excited states can also be reconciled with these simple configurational assignments. The most serious discrepancy is in the half-life of the first excited (0+) state, which we calculate to be 1.35×10-8 sec, as compared to the observed value of (6.0±1.5)×10-8 sec. The remaining discrepancies in the energies and half-lives are in the direction of the effects produced by a slight deformation of the Sr88 core.