Shape transitions in exotic Si and S isotopes and tensor-force-driven Jahn-Teller effect

TL;DR

This paper investigates shape transitions in neutron-rich Si and S isotopes using shell-model calculations with a new Hamiltonian, highlighting the role of tensor forces and Jahn-Teller effects in nuclear shape evolution.

Contribution

The study introduces a new Hamiltonian based on V_MU interaction to explain shape transitions and tensor-force effects in exotic isotopes, with detailed comparisons to experimental data.

Findings

Excellent agreement with experimental excitation energies and B(E2) values.

Identification of rapid shape transitions near N=28.

Evidence of tensor-force-driven Jahn-Teller effects influencing nuclear shapes.

Abstract

We show how shape transitions in the neutron-rich exotic Si and S isotopes occur in terms of shell-model calculations with a newly constructed Hamiltonian based on V_MU interaction. We first compare the calculated spectroscopic-strength distributions for the proton 0d_5/2,3/2 and 1s_1/2 orbitals with results extracted from a 48Ca(e,e'p) experiment to show the importance of the tensor-force component of the Hamiltonian. Detailed calculations for the excitation energies, B(E2) and two-neutron separation energies for the Si and S isotopes show excellent agreement with experimental data. The potential energy surface exhibits rapid shape transitions along the isotopic chains towards N=28 that are different for Si and S. We explain the results in terms of an intuitive picture involving a Jahn-Teller-type effect that is sensitive to the tensor-force-driven shell evolution. The closed sub-shell nucleus 42Si is a particularly good example of how the tensor-force-driven Jahn-Teller mechanism leads to a strong oblate rather than spherical shape.