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

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.