Evidence for the asymmetry dependence of the nuclear caloric curve seen in fusion reactions *

The nuclear equation of state emerges from the microscopic nucleon-nucleon interaction. The leading uncertainty in the EoS is in regards to the energy due to neutron-excess. We study here in particular one facet of the EoS: the caloric curve. Reactions of 78,86Kr + 12C @ 15, 25, 35 MeV/u were conducted. The mean excitation energy of the compound nucleus is varied via the beam energy, and the mean neutron excess of the compound nucleus is varied by changing the projectile isotope. Light charged particles were measured with good energy and good position resolution with the FAUST (Forward Array Using Silicon Technology). The velocity of heavy residues were measured by time of flight. Temperatures are extracted using both kinetic and population approaches. Mean excitation energies are calculated from the measured residue velocities. The caloric curves thus constructed show a dependence on the neutron excess, with systematically higher temperatures for the more neutron-rich system.