Nuclear shell model and analytical SU(3) description of 28Si

Abstract

We analyze the 28Si nucleus using an analytical SU(3)-based model as well as state of the art numerical shell model calculations. In principle, spherical, oblate and prolate structures can coexist at low energies. However, we found that the spherical shape in 28Si does not survive because the 1d5/2-2s1/2 nearly degenerated doublet gains huge amounts of quadrupole correlations, which favors deformed bands. Although the standard USDB interaction reproduces the oblate ground state and the vibrational band, it fails at establishing a prolate band. A modification of the USDB interaction must be introduced to reproduce the experimental spectrum. Our calculations suggest that the oblate ground state is mostly 0p-0h, whereas the prolate band consists mainly of 4p-4h excitations into the 1d3/2 orbital