Final PhD Seminar

The origins and nature of weak collectivity in nuclei

Mr Ben Coombes
Department Nuclear Physics

The structure of nuclei at closed shells and far from closed shells is understood in terms of the coupling of individual nucleons near the shell closure, and in terms of the rotor model far from the shell closures. The regions between these two extrema are much less well understood with no consensus on the process by which collectivity develops, nor on the nature of weak collectivity. The nature of weak collectivity and the emergence of nuclear collectivity is probed by measurements of electromagnetic observables in Te and Cd isotopes. The stable Te isotopes range from weakly-collective nuclides near the neutron mid-shell up to isotopes close to the N=82 shell closure. Recent advancements in computational power have allowed microscopic calculations on these isotopes which allow the direct comparison of experimental data, microscopic calculations, and collective model predictions.

The convergence of the 2+ and 4+ g factors to collective values from single-particle structures have been measured using the transient-field method and are discussed with reference to shell-model calculations. Suggestions are made on the origins of nuclear collectivity. Transition strengths in the Te isotopes have been measured through Coulomb excitation measurements, with enhanced B(E2) values observed that exceed the predictions of the shell-model calculations. These patterns are discussed in terms of the known indicators of emerging nuclear collectivity. The stable Cd isotopes lie closer to the mid-shell and may be expected to be more collective. The Cd isotopes also have the same number of valence proton holes as Te has proton particles and so may be expected to display similar behaviours. Transition strengths in the odd-mass Cd-111,113 isotopes are reported and discussed as coupling of collective excitations and an unpaired neutron


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