Si-48: An atypical nucleus?

Abstract

Based on the relativistic Hartree-Fock formalism and one of the most advanced Lagrangian PKA1, we investigate the properties of the exotic nucleus 48Si. We found that 48Si may be an atypical nucleus characterized by i) the onset of doubly magicity, ii) its location at the drip line, iii) the presence of a doubly semibubble (central depletion of the neutron and proton density profiles) in the ground state, and iv) the occurrence of pairing reentrance at finite temperature. These phenomenons are not independent from each others. We illustrate for instance that the doubly semibubble reduces the spin-orbit splitting of low-l orbitals and modifies the splitting of relevant pseudospin partners, favoring N = 34 as a new magic number for neutron rich nuclei. Since 48Si is predicted doubly magic, it could have an extra stability which puts it at the drip line. Moreover, 48Si may have interesting excited states which may induce pairing reentrance at finite temperature. While not being new, these phenomenons are found to serendipitously occur together in 48Si, from our theoretical calculation. Theoretical nuclear modelings are known to be poorly predictive in general, and we asset our confidence in the prediction of our modeling on the fact that the predictions of PKA1 in various regions of the nuclear chart have systematically been found correct and more specifically in the region around 48Si, our approach correctly reproduce the known features of neighboring nuclei. Whether our predictions are confirmed or not, 48Si provides a concrete benchmark for the understanding of the nature of nuclear forces.