Inelastic Scattering of 31-MeV Alpha Particles fromZn64andZn66

The ($\alpha ,{\alpha }^{\prime }$) reaction on ${\mathrm{Zn}}^{64}$ and ${\mathrm{Zn}}^{66}$ has been studied using the 31-MeV $\alpha$-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 $3^{-}$, $4^{+}$, and $5^{-}$ 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 $3^{-}$ strength in ${\mathrm{Zn}}^{64}$ has been observed, but it is smaller than that found in the calcium isotopes.