Mechanisms for light charged particle emission in the reactions 247 and 337 MeVAr40+natAg

Abstract

Light charged particles from the reactions 247 and 337 MeV ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ ${+}^{\mathrm{nat}}$Ag have been measured in singles and in coincidence with fission-like products. Most of the ${}_{}{}^1{}_{}{}^{}\mathrm{H}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ in coincidence with fusion-fission and quasifission can be accounted for by evaporation from the composite nucleus or by the fragments. Multiplicities are determined for ${}_{}{}^1{}_{}{}^{}\mathrm{H}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ in association with evaporation residues, fusion-fission, and quasifission. The probability for composite nucleus emission decreases with increasing spin zone of the emitter and gives a view of the role of emitter lifetime. The ratio of composite-nucleus multiplicities for quasifission/fusion-fission is about 1/2 ((1/4) for 337 MeV ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ (247 MeV ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$) which implies a similar ratio for the lifetimes of the respective composite nuclei between thermalization and scission. Energy spectra and angular distributions of particles (in coincidence with fusion-fission and quasifission) are consistent with emission from a strongly distorted nuclear system en route toward scission. Prethermalization emission of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ is observed at 10° in comparable amounts for peripheral collisions (quasifission and fusion-fission) and for central collisions.