Isospin Dependence of Fragmentation
Soisson, Sarah Nicole
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Multifragmentation reactions have been used to study many of the complexities of the nucleus. Recently, work has been done to tie observables from multifragmentation reactions to astrophysical observables used in supernova explosions. To make this connection, it is necessary to have a highly excited, equilibrated system. The creation of a highly excited system is done for this dissertation by the reaction of one projectile, ??S, on three targets, ???????Sn and ^natAu at 45 MeV/nucleon. The forward array using silicon technology, FAUST, was used to collect the fragments produced from the excited projectiles. The motivation for this study was to isotopically identify the fragmenting source and to understand the relationship between its N/Z and the resulting fragmentation. This can then be used to constrain theoretical models which predict the evolution of supernova explosions. Using an isotropically identified source, the resulting fragmentation of the projectile has been studied. It is shown that there are dependencies on the fragment mass distribution, fragment charge distribution and source excitation energy from the source N/Z. Looking more specifically at the fragments produced, it was found that there is a parallel velocity anisotropy in the particle emission. This anisotropy is found to be a direct result of the presence of an external Coulomb field. Using DIT+SMM theoretical calculations, the anisotropy has been found to be dependent on the distance at which the projectile breaks up from the target (external Coulomb field). As the parallel velocity is related to the angle of emission, it is of interest to extract out the average kinetic energy of each isotope to determine if there are differences in the average kinetic energy by the angle of emission. It is found that the average kinetic energy is dependent on the emission angle in the quasi-projectile frame. Because of this, care should be taken when comparing between systems to ensure similar regions are being compared. However, the observation that the average kinetic energy changes as a function of the emission angle is not dependent on the presence of an external Coulomb field. Using DIT+SMM calculations, the differences between the average kinetic energy from different angles of emission are seen even when no external Coulomb field is present. These changes are attributed to the angular momentum. In all cases, a statistical framework, supplied by DIT+SMM calculations, can explain many phenomena seen from a fragmenting nucleus. However, the accuracy of the model varies when moving from a neutron-poor to a neutron-rich source.