Particle Emission in Heavy-Ion Reactions

Abstract

Light charged particles produced at 0 deg in the interaction of 167-MeV ${\mathrm{O}}^{16}$ ions with Al, Ni, Ag, and Au thick targets have been analyzed magnetically with nuclear-emulsion detectors. The spectra obtained are compared with extensive statistical-model calculations, which include both the effects of angular momentum and of multiple particle emission. The spectra from light targets are seen to be sensitive to the equilibrium shape of the compound nucleus, since rotational effects that depend on this shape are large for these nuclei. For ${\mathrm{O}}^{16}$ on Au the de-excitation of the compound nucleus is found to be dominated by neutron emission, and a comparison of the calculations with neutron spectra seems to show that the nucleus fissions with highest probability after about 5±1 stages of neutron emission. Owing to the increased competition of neutron emission, charged-particle evaporation for the heavier elements decreases so much that the observed spectra are dominated by direct reaction products. These products, particularly the Li isotopes, are seen to arise from a breakup of the incident ${\mathrm{O}}^{16}$, and the energetics of this process are considered.