Rotational Energy and the Diffuseness of the Boundary between Fusion and Strongly Damped Collisions

Differences in the kinetic energies of the fragments produced in the scission of the pairs of similar composite nuclei ${}_{}{}^{59}{}_{}{}^{}\mathrm{Cu}$-${}_{}{}^{60}{}_{}{}^{}\mathrm{Zn}$ and ${}_{}{}^{83}{}_{}{}^{}\mathrm{Y}$-${}_{}{}^{88}{}_{}{}^{}\mathrm{Zr}$ are interpreted as resulting from angular momentum fractionation. The energies indicate that some partial waves with angular momenta $10\hslash$ to $15\hslash$ below the sharp-cutoff fusion limit lead to strongly damped collisions.