Complete-Fusion Collisions in Heavy-Ion Reactions

Cross sections for compound-nucleus formation were experimentally measured for the ${\mathrm{O}}^{16}$+${\mathrm{Al}}^{27}$, ${\mathrm{Ne}}^{20}$+${\mathrm{Al}}^{27}$, and ${\mathrm{O}}^{16}$+${\mathrm{Co}}^{59}$ systems by means of mica track detectors. It was shown that the cross section for compound-nucleus formation (complete fusion) above 100 MeV decreases with increasing energy of the bombarding particles, whereas the reaction cross sections increase slightly. An attempt was made to explain this behavior by considering a sharp cutoff in the spin distribution of the compound nuclei.