Isospin character of transitions to the 21+ and 31- states of 90,92,94,96Zr.

Abstract

The elastic and inelastic scattering of 35.4 MeV alpha particles by $^{90,92,94,96}\mathrm{Zr}$ have been measured to investigate the isospin mixing of transitions to the ${2}_{1}^{+}$ and ${3}_{1}^{\mathrm{\ensuremath{-}}}$ states. The data have been analyzed using a deformed optical model potential and a folding model assuming transition densities of either the standard collective model type or resulting from random-phase approximation calculations. For the ${2}_{1}^{+}$ states of $^{90,92,94}\mathrm{Zr}$, both models give B(E2)\ensuremath{\uparrow} values which are in excellent agreement with those determined from Coulomb excitation or lifetime measurements. Both models of analysis suggest a sharp drop in the B(E2)\ensuremath{\uparrow} at $^{96}\mathrm{Zr}$ relative to the value at $^{90,92,94}\mathrm{Zr}$, in agreement with an earlier measurement of alpha-particle scattering. Deduced ${\mathit{M}}_{\mathit{n}}$/${\mathit{M}}_{\mathit{p}}$ ratios for $^{92,94,96}\mathrm{Zr}$ are considerably larger than their respective ratios of N/Z. General agreement is found between folding model calculations for alpha-particle scattering and $^{6}\mathrm{Li}$ scattering when using the same random-phase approximation (RPA) transition densities. A small shift in phase is observed between the oscillations in the calculated inelastic angular distributions and the measured ones. A possible means to reproduce this shift is presented, but the changes required appear to be too large to be physically meaningful.