Temperatures of Exploding Nuclei

Breakup temperatures in central collisions of ¹⁹⁷Au+¹⁹⁷Au at bombarding energies E/A0ex0ex=0ex0ex50 to 200 MeV were determined with two methods. Isotope temperatures, deduced from double ratios of hydrogen, helium, and lithium isotopic yields, increase monotonically with bombarding energy from 5 to 12 MeV, in qualitative agreement with a scenario of chemical freeze-out after adiabatic expansion. Excited-state temperatures, derived from yield ratios of states in ⁴He, 5,6Li, and ⁸Be, are about 5 MeV, independent of the projectile energy, and seem to reflect the internal temperature of fragments at their final separation from the system.