Contribution of alpha cluster exchange to elastic and inelasticO16+Ne20scattering

Angular distributions for elastic and inelastic transitions in ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ + ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ scattering have been measured at $E\left({}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}\right)=50\mathrm{}$ MeV. For the $0^{+}$, $2^{+}$, and $4^{+}$ members of the ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ ground-state rotational band, the angular distributions exhibit pronounced backward peaking characteristic of an $\alpha$-cluster exchange mechanism. The analysis of the ground-state transition in the first-order elastic transfer model yields no satisfactory fit although microscopic cluster form factors and full recoil corrections are employed. A coupled channels calculation for the $0^{+}$, $2^{+}$, and $4^{+}$ transitions reveals very strong coupling effects, indicating that the coherent superposition of first-order optical model and distorted-wave Born-approximation amplitudes may not be an adequate model for these reactions.