We have developed a technique for deducing the average primary excitation energy and mass of a hot nuclear system using the average energies and multiplicities of the decay products. Monte Carlo simulations show that we can account for all of the initial energy and mass in heavy-ion fusion reactions. For data from the reaction ${}_{}{}^{20}{}_{}{}^{}$Ne${+}^{27}$Al at 19.2 MeV/nucleon we find that the composite system formed after preequilibrium emission consists of 42.4 nucleons, on average, at an excitation energy of 4 MeV/nucleon. Similar data for Si+Si imply that the excitation energy per nucleon of these incompletely fused systems saturates near 3 MeV/nucleon with increasing beam energy.

• Received 15 May 1989

DOI:https://doi.org/10.1103/PhysRevC.40.1647