Quasi-elastic scattering for the nuclear ground state structure: An intriguing case of $^{30}$Si

TL;DR

This study investigates the ground state structure of $^{30}$Si using quasi-elastic scattering and theoretical models, revealing shape fluctuations and structural changes compared to $^{28}$Si, with implications for nuclear shape evolution.

Contribution

It combines experimental scattering data with coupled-channels and shell-model calculations to explore shape coexistence and fluctuations in $^{30}$Si, a novel approach for this isotope.

Findings

$^{28}$Si is uniquely oblate in its ground state.

$^{30}$Si shows no well-defined shape, indicating shape fluctuations.

Structural change occurs between $^{28}$Si and $^{30}$Si.

Abstract

Quasi-elastic (QEL) scattering measurements have been performed using the $^{28, 30}$Si projectiles off the $^{90}$Zr target at energies around the Coulomb barrier. Coupled-channels (CC) calculations were carried out in a large parameter space of quadrupole and hexadecapole deformations for the N=Z, $^{28}$Si and N=Z+2, $^{30}$Si nuclei. $^{28}$Si at the N=Z line is observed to be uniquely oblate shaped in its ground state. In contrast, for $^{30}$Si with just two additional neutrons -- oblate, prolate, and spherical CC descriptions are equally compatible with the measurements. To further investigate the nuclear structure evolution with varying neutron number, shell-model calculations were performed. These calculations reveal a sudden change in the nuclear structure aspects at $^{30}$Si in going from $^{28}$Si to $^{30}$Si. Combined reaction and structure analyses consistently indicate that $^{30}$Si does not possess a well-defined intrinsic shape, and it is a potential candidate for ``shape fluctuations" in its ground state.