Mid Term Review

The Asymmetric Two-Centre Shell Model and its Applications

Mr Jacob Buete
Department Nuclear Physics

For the last two decades the search for superheavy elements (SHEs) has relied on a beam of 48Ca aimed at heavier and heavier targets. This combination has produced the last 6 SHEs, but has the fundamental limitation that heavier targets are both less stable and harder to produce. To bypass this limitation we must understand the reason that 48Ca is so effective in these reactions, and then use that understanding to find the next SHE `wunderkind'.

One possible explanation for the efficacy of 48Ca is its `doubly-magic' nature --- both its proton and neutron numbers fall in line with observed shell structure (or `magic numbers') indicating a tightly-bound, stable, nucleus. Decades of experimentation has shown that reactions involving magic or doubly-magic nuclei provide higher fusion yields.

However, this explanation does not account for the observed differences in fusion yield between 48Ca and 40Ca – both are doubly-magic, but 40Ca  shows a higher yield of quasifission even when controlling for the same compound nucleus. Current theories point to the high N/Z ratio of 48Ca --- matching that of the targets --- being beneficial as it removes the rapid N/Z equalisation that occurs with 40Ca in similar reactions. This enables 48Ca to maintain its structure, and hence its magicity, longer than would otherwise be possible.

To explore the evolution of shell structure in these reactions I propose using the Asymmetric Two-Centre Shell Model (ATCSM), an analytic model in which the asymmetry, deformation, and separation of the target and projectile can be prescribed via their independent potential wells. The seminar will provide an overview of the ATCSM and the efforts to rederive the model following the discovery of errors in the original publications. I will also cover the benchmarking and testing before presenting preliminary calculations of shell structure and and derived shell corrections.

 

Zoom link : https://anu.zoom.us/j/21284009858?pwd=SitxZEtueXFxVE90WE1CeUlwK0l3UT09

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