The fully energy-damped yields for the 36Ar + 12C and 20Ne + 28Si reactions at Ec.m. = 47.0 MeV and 45.5 MeV, respectively, are explored using particle-particle-γ coincidence data. These reactions reach a similar excitation energy of E*CN= 59.5 MeV in the 48Cr compound nucleus as was obtained in an earlier particle-particle coincidence study of the 24Mg + 24Mg reaction. The overall mass and total kinetic energy distributions of the fission fragments are found to be well reproduced by statistical-model calculations. These calculations are also found to reproduce structure seen in the excitation-energy spectra for the 20Ne + 28Si and 24Mg + 24Mg exit channels for all three reactions. In previous excitation-function measurements, strong heavy-ion resonance behavior has been observed in elastic and inelastic cross sections for the 24Mg - 24Mg system. There has been speculation that peaks observed in the corresponding excitation-energy spectra at more negative Q values may also be a consequence of this resonance phenomenon. The observation of very similar behavior with the asymmetric-mass entrance channels makes it less likely, though, that the peaks arise from any special configuration of the compound system. Instead, an analysis of the γ-ray data and the results of statistical-model calculations support the conclusion that most of the observed high-lying structure can be accounted for in terms of statistical fission from a fully energy- and shape-equilibrated compound nucleus. For the 24Mg + 24Mg entrance channel, however, comparisons with the statistical model indicate a reduction of high-angular-momentum partial cross sections, leading to the 24Mg + 24Mg fission channel. For the first time, we are able to deduce the nature of the competition between the resonance and statistical-fission mechanisms in this mass region.
ASJC Scopus subject areas
- Nuclear and High Energy Physics