Anomalous and Normal Angular Distributions in Ni(O18,O16) Reactions

Differential cross sections are measured for ${}_{}{}^{58,60,62,64}{}_{}{}^{}\mathrm{Ni}$(${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$) reactions to both ground and excited ($2^{+}$) states of the residual Ni nuclei at incident ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ laboratory energies of 65, 57, and 50 MeV. Anomalous, forward-rising, angular distributions are seen for ${}_{}{}^{58,60}{}_{}{}^{}\mathrm{Ni}$(${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$) reactions, in contrast to normal heavy-ion-induced transfer shapes obtained for the heavier Ni targets. A theoretical explanation is presented based on a weaker absorption than is usually employed for such heavy-ion transfer reactions.