Examining the cooling of hot nuclei

Energy spectra have been measured for helium and hydrogen isotopes emitted from highly excited residues produced in central 129Xe + natCu collisions at E/A=30 MeV. The observed differences between the spectra for 3He and 4He nuclei can be attributed to the time dependent evaporative cooling of the residues. This cooling dynamics is also reflected in a characteristic dependence of isotope ratios on the kinetic energy of the emitted particles in reasonable agreement with present evaporative models.