Compound nucleus fission at high angular momentum studied in the reactionXe132+Si30

Reaction products from the bombardment of ${}_{}{}^{132}{}_{}{}^{}\mathrm{Xe}$ onto ${}_{}{}^{30}{}_{}{}^{}\mathrm{Si}$ at energies between 5.4 MeV/u and 8.2 MeV/u have been measured by a time-of-flight system combined with an ionization chamber. At all energies fission fragments are found to be well separated from deep inelastic reaction products. The rapidly increasing excitation function for fission shows an onset at $65-70\hslash$. This value and an $l_{\mathrm{crit}}$ of $98\hslash$ at 8.2 MeV/u are compatible with the concept of a fissioning compound nucleus. However, at the highest bombarding energies the $Z$ distributions indicate the emission of charged particles which is difficult to reconcile with the idea of a fully equilibrated compound nucleus. Incomplete momentum transfer reactions (incomplete fusion) followed by fission are considered as an explanation for the strong increase of the width of the $Z$ distribution with excitation energy. Consequences for the formation of compound nuclei at high angular momenta are discussed.