Emission of light particles in 32S induced reactions

The reactions 32S + 16O, 27Al, and 40Ca were studied at the 221 MeV 32S beam of the MP tandem+postaccelerator combination of the Max-Planck Institute for Nuclear Physics. The experimental methodics consisted of the coincident detection of both heavy reaction products in two large area ionization chambers and two preswitched parallel plate shower counters. The method of analysis used the conservation laws of charge, mass, energy, and momentum in order to calculate from the measured parameters of the heavy fragments their charge, mass, and momentum defects against the incident channel which were caused by emission of light particles. The exit channels show large mean charge defects of 2.01 (16O), 2.94 (27Al), and 4.16 (40Ca) charge units. Two-particle exit channels contribute only to the 16O reactions with about 3%, even three-body exit channels are only found at this system and a charge defect of 2 e. In all other reaction channels more than three reaction channels are present. After the transformation of the momentum defects - i.e. the vector sum of the momenta of the light particles - into the c.m. system no indications for the existence of direct or fast emission processes result. Rather shape and position of the momentum defect distributions can be reproduced by means of Monte Carlo calculations under the assumption of sequential decay mechanisms. For the three-particle exit channels of the 16O reactions which can be identified as sequential α-decays the transformation of the momentum defects to the laboratory system of the emitting nucleus is possible. The fit of Maxwell distributions to the energy spectra of the α particles in the laboratory system yields a mean nuclear temperature of about 2 MeV. From the anisotropy of the angular distributions in the laboratory system angular momenta of the emitting fragments are calculated. (orig./HSI)