BREAKUP OF HIGHLY EXCITED CL-35 PROJECTILES ON A GOLD TARGET AT 30 A MEV - AN EXCLUSIVE ANALYSIS

Projectile excitation and breakup have been studied in the reaction Cl-35 + Au-197 at 30 A MeV. Differential cross sections and energy distributions were measured. The absolute cross sections of 98 different exit channels made of as many as 7 coincident charged fragments have been determined. Such exclusive measurements allow event-by-event reconstruction of the excited primary nuclei. By selecting specific exit channels, we studied the decay of hot nuclei over a wide range of excitation energy. The behaviour of the excited nuclei is consistent with a statistical description. The fragmentation mechanism was also investigated. Although the lowest excited channels are well reproduced by a standard sequential-binary-decay model, evidence is observed for an evolution with excitation energy of the time scale for particle emission. Model calculations have been performed which show that the lifetime of the excited chlorine projectile should decrease by a factor of 4 when the excitation energy increases from 2.3 A to 4.3 A MeV.