Formation and decay of the composite system in 40Ar-induced reactions at 15 MeV/nucleon.

Abstract

The reactions $^{40}$Ar${+\mathrm{}}^{27}$Al, $^{45}$Sc, $^{58}$Ni, $^{90}$Zr are studied at 600 MeV bombarding energy. The experiments employ several large-area detectors of different kinds to identify heavy fragments and measure their multiplicity. Two- and three-fragment channels are observed in all reactions and their cross sections are determined. The existence of four-fragment channels is suggested by the experiment; their contribution is, however, too weak for a detailed analysis. In addition to the multifragmentation processes, the emission of light particles is also observed, the average charge of all emitted particles being slightly smaller than expected from experiments at lower energies. The predominant source of light particles is the evaporation from hot fragments. In the light systems the existence of three fragments is ascribed to a fast disintegration process, whereas in the heaviest system a major part of such channels could also arise from a sequential fission process.