Direct Evidence for a Narrow Window at High Angular Momentum in Incomplete-Fusion Reactions

Alpha-gamma coincidence measurements have been made with reactions of 142-MeV ¹⁶O on ¹⁴⁶Nd leading to the noncollective nuclei ¹⁵²Dy and ¹⁵¹Dy. The side-feeding pattern in coincidence with forward energetic alpha particles peaks at $J=30$ with full width at half maximum {~}10, indicating that central collisions do not participate, while that for backward alpha particles extends down to $J=0$. The data are consistent with the generalized critical-angular-momentum model of incomplete fusion.