M. G. Mustafa

Mechanisms of fragment production in heavy-ion reactions at intermediate energies

Comparative analysis of three typical models of nuclear disintegration, the statistical multifragmentation model (SMM), the quantum statistical model (QSM) and a generalized evaporation model (GEM), is carried out. The thermodynamical properties of a decaying system as well as observable characteristics in heavy ion collisions predicted by the different models are discussed. It is shown that these models yield quite similar results for low charge yields at higher excitation energies (E/A>6 MeV per nucleon) and it is suggested that the coincidence measurements of the intermediate mass fragment multiplicity and the neutron and proton multiplicity (or alternatively, the total bound charge) may be very useful for deducing the decay mechanism. The GEM is shown to differ from the other models in predicting a high Z residue peak.

Equilibration and Multifragmentation in Heavy Ion Reactions

Modeling of multifragmentation measurements from heavy ion reactions generally requires separate treatment of the initial fast part of the reaction, during which energetic nucleons are emitted, and of a quasi-equilibrated system where sufficient degrees of freedom have been excited, so that statistical approaches may be applied. Some of the more sophisticated fast cascade models, e.g., Quantum molecular dynamics (QMD), might also produce fragment yields, however, transport models have not yet been able to satisfactorily reproduce fragmentation properties of nuclear reactions.

Interpretation of ion-range recoil data obtained from activated-foil measurements of nuclear excitation functions.

Ion-range recoil data were obtained during activated-foil measurements of excitation functions for proton-, deuteron-, and triton-induced reactions on selected targets. These data were analyzed by using the Lindhard, Scharf, and Schiott range-energy theory. An important feature of our analysis was the use of angular distributions from the recent Kalbach systematics based on multistep compound and multistep direct reactions. Furthermore, we used the ({ital p},{ital n}) data to fix the parameters of LSS theory, and then applied the theory to ({ital d},{ital n}), ({ital d},2{ital n}), ({ital t},2{ital n}), ({ital t},{alpha}) and ({ital d},{alpha}) reactions. The adjustments to the LSS-theory parameters were less than 10%. The comparisons of the data with calculations demonstrate several important aspects of the reaction mechanisms, e.g., transition from equilibrium to direct reaction, breakup of the deuteron and triton in the reaction entrance channel, and pickup for triton-induced reactions. Overall, the ion-range measurements give a consistent picture of the reaction mechanisms involved.