Anomalous and normal angular distributions in Ni(18O,16O) reactions

Differential cross sections are measured for ⁵⁸Ni, ⁶⁰Ni, ⁶²Ni, ⁶⁴Ni(¹⁸O, ¹⁶O) reactions to both ground and excited (2⁺) states of the residual Ni nuclei at incident ¹⁸O laboratory energies of 65, 57, and 50 MeV. Anomalous, forward-rising, angular distributions are seen for ⁵⁸,⁶⁰Ni(¹⁸O, ¹⁶O) 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.