Measurements of time delays for projectile-like fragments in the reaction 40Ar+Ge at 44 MeV/nucleon

Crystal-blocking angular distributions have been measured for projectile-like fragments produced in bombarding a 10-μm Ge crystal with a 1.76-GeV 40Ar beam. Long time delays of the order of (6-12)×10-18 s were extracted and gave a direct indication of important evaporation effects. The measured times can be reproduced using a broad distribution of primary fragments of the type predicted by the abrasion model, but with excitation energies from 15 to 50 MeV, which are higher than predicted by the model. The measured times can also be reproduced assuming a narrow primary mass distribution with highly excited fragments having excitation energies of about 150 MeV.