EXCITATION-ENERGIES AND TEMPERATURES OF HOT NUCLEI PRODUCED IN THE REACTIONS OF CU-63-197 AT 35A MEV(AU)

Observations of heavy remnants emitted at forward angles with high vel ocities and high associated particle multiplicities have been used to select central collisions of 35A MeV Cu-63 With Au-197. The data indic ate that these remnants, both fission fragments and evaporation residu elike products, result from the deexcitation of nuclei with A similar to 225-240 having excitation energies of similar to 800-1300 MeV. Simi lar particle multiplicities are observed for both evaporative and fiss ion decay channels. Modeling the results with hybrid codes which treat entrance channel dynamics followed by sequential statistical decay re quires the inclusion of some delay in the fission channel to produce h eavy remnants with mass A greater than or equal to 130, but the trend of the predicted velocities of these heavy remnants is different from that of the experiments. Calculations with a dynamic model based on th e molecular dynamics approach have also been performed and lead to sim ilar results. He and Li isotope yield ratios and the apparent temperat ures derived from those ratios are similar to those previously reporte d for excited nuclei in this mass region. Temperatures derived from ot her yield ratios are also similar once a self-consistent treatment, ta king into account population and decay of known excited states, is app lied. The derived temperatures show little variation with excitation e nergy, suggesting that a Limiting temperature may be reached at relati vely low excitation energy, although the interpretation of this result and the determination of the actual initial value of this temperature is model dependent. Comments on the application of the double isotope yield ratio technique to extraction of the nuclear caloric curve are made.