Examining the cooling of hot nuclei

Abstract

Energy spectra have been measured for helium and hydrogen isotopes emitted from highly excited residues produced in central ${}^{129}$Xe + ${}^{\mathrm{nat}}$Cu collisions at $E/A=30$ MeV. The observed differences between the spectra for ${}^{3}$He and ${}^{4}$He 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.