Evidence For Thermal Equilibration In Multifragmentation Reactions Probed With Bremsstrahlung Photons

The production of nuclear bremsstrahlung photons (E-gamma > 30 MeV) has been studied in inclusive and exclusive measurements in four heavy-ion reactions at 60A MeV. The measured photon spectra, angular distributions, and multiplicities indicate that a significant fraction of the hard photons is emitted in secondary nucleon-nucleon collisions from a thermally equilibrated system. The observation of the thermal component in multifragment Ar-36 + Au-197 reactions suggests that the breakup of the thermalized source produced in this system occurs on a rather long time scale.