Inelastic Scattering Of 31-Mev Alpha Particles From Zn-64 And Zn-66

The ($\ensuremath{\alpha},{\ensuremath{\alpha}}^{\ensuremath{'}}$) reaction on ${\mathrm{Zn}}^{64}$ and ${\mathrm{Zn}}^{66}$ has been studied using the 31-MeV $\ensuremath{\alpha}$-particle beam from the Massachusetts Institute of Technology cyclotron, with an over-all energy resolution of 80-120 keV. Angular distributions are presented, both for levels with known spin, and for levels whose spin and parity have not been previously determined. New ${3}^{\ensuremath{-}}$, ${4}^{+}$, and ${5}^{\ensuremath{-}}$ assignments are made both by comparison with levels of known spin and with the distorted-wave Born approximation. Good angular distributions are presented for the weak states at 1.81 MeV (${2}^{+}$) and 2.32 MeV (${4}^{+}$) in ${\mathrm{Zn}}^{64}$. They are both out of phase with the ${2}^{+}$ and ${4}^{+}$ single-excitation states. The slope of the angular distribution for the 2.32-MeV (${4}^{+}$) level is shallower than for the single-excitation ${4}^{+}$ state, while the slopes are the same for the ${2}^{+}$ states. Transition strengths in ${\mathrm{Zn}}^{64}$ and ${\mathrm{Zn}}^{66}$ are compared. Fractionation of ${3}^{\ensuremath{-}}$ strength in ${\mathrm{Zn}}^{64}$ has been observed, but it is smaller than that found in the calcium isotopes.