The Effects of Deformation on Proton Emission Rates

Orateur : Michael TAYLOR (The University of Manchester, Oxford Road, Manchester, M13 9PL, UK)

The proton drip line defines one of the fundamental limits to nuclear stability. Nuclei lying beyond this locus are energetically unbound to the emission of a constituent proton from their ground state. Nuclear structure information on these proton emitting nuclei has historically been extracted from a comparison of the measured proton decay half-lives with those predicted by tunnelling calculations. Proton decay rates for near-spherical nuclei in the region N=50-82 have been shown to be well reproduced by simple WKB calculations using spectroscopic factors derived from a low-seniority spherical shell-model calculation, however ; more sophisticated models are required for deformed nuclei. Proton emission rates are highly sensitive to nuclear deformation but in all known cases the deformation has never been experimentally determined. Currently, proton emission calculations rely on theoretically determined deformations making experimentally determined values highly sought after for these theoretical models. To address this logical weakness a new plunger device, DPUNS (Differential Plunger for Unbound Nuclear States), was developed to measure the lifetimes of low-lying excited states in proton emitting nuclei. The accurate determination of excited-state lifetimes above proton emitting states can be used to evaluate the extent of deformation in the system. With the aid of state-of-the-art theoretical models, decay half-lives can be calculated for the measured deformation and compared with those determined experimentally. This presentation will report on the first study in a programme of experiments to investigate the effect of deformation on proton emission rates.

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