Studies of the Beta Decay of Light Projectile Fragments Far from Stability

Nuclei far from stability can be produced by the fragmentation of beams at the National Superconducting Cyclotron Laboratory at Michigan State University, and separated by the Reaction Product Mass Separator. Since these fragments maintain a significant fraction of the momentum of the beam broadened by the reaction dynamics, the beta decay of these nuclei can be observed only after they come to rest in a thick layer of material such as an active silicon detector. Here decay products such as the emitted beta particle and any beta-delayed charged particles can be detected and often their energy determined. New techniques to study beta decay and beta delayed particle emission from projectile fragmentation have been developed. Problems such as the determination of absolute partial and total decay rates, contamination by other isotopes, background and daughter activity, fitting procedures where only a small number of events are available or where data are contaminated with other activity or background and energy calibration are discussed. Techniques for their management are presented. The Nuclear Shell Model, with an empirical Hamiltonian based upon tabulated nuclear structure information from stable or close to stability nuclei, will benefit particularly from information of the structure of nuclei far from stability for two reasons. At first, observables such as beta decay rates can be measured and compared to predictions. Any deviations might give insight into the limitations of the present Hamiltonians. Later as more information is gathered, a significant body of excited states will be compiled facilitating a new fit of the matrix elements of the Hamiltonian including far-from-stability configurations. It is however difficult to extract the standard quantities such as beta decay matrix elements from the data in a form comparable to the predicted values. Many levels will be unbound to nuclear decay, often to the emission of two or more particles. The distribution in phase space of all of these particles must somehow be interpreted with a reasonably simple model in order to extract beta decay matrix elements. In this thesis, a simple model is presented in order to interpret such data. This model incorporates the generalized density of states concept into the standard model of beta decay to bound levels.