MSc Thesis Presentation: Gamma-Gamma Angular Correlation Measurements with Griffin

MSc Thesis Presentation

Candidate: Andrew MacLean

Abstract

The assignment of spins and parities to excited nuclear states plays an important role in determining nuclear structure. In a γ - γ cascade from an excited nuclear state an anisotropy is found in the spatial distribution of the second γ-ray, γ2, with respect to the first γ-ray, γ1. By defining the direction of γ1 to be the z-axis (setting θ = 0), the intermediate level in general will have an uneven distribution of m-states. This uneven population of m-states causes anisotropy in the angular correlation of the second γ-ray with respect to the first. The anisotropy depends on the sequence of spin-parity values for the nuclear states involved, the multipolarities, and mixing ratios of the emitted γ-rays.

            These γ-ray angular correlations can be used for the assignment of spins and parities to the nuclear states, and thus provide a powerful means to elucidate the structure of nuclei away from stability. The goal of his work is to explore the sensitivity of the new Gamma-Ray Infrastructure For Fundamental Investigations of Nuclei (GRIFFIN) 16 clover-detector γ-ray spectrometer, at TRIUMF-ISAC, to such γ - γ angular correlations. Firstly, establishing a methodology for γ - γ angular correlation measurements for a well-known 4+ →2+→0+ γ- γ cascade from the 60Co decay will be demonstrated. Also, as a verification of the method a data set was also collected from 66Ga to analyze various angular correlations. The optimization of the performance for these measurements tests were preformed through both experimental measurements and Geant4 simulation. Results from the decay of 60Co, 66Ga as well as 62Ga will be shown in this presentation.

Examination Committee:

Dr. Robert Wickham, Chair

Dr. Carl Svensson, Advisory

Dr. Paul Garrett, Member