Rapid onset of collectivity in the vicinity of 78Ni

TL;DR

This study investigates the rapid development of collective nuclear behavior near 78Ni, revealing significant core polarization and confirming the fragile, easily polarizable nature of this doubly-magic nucleus through experimental gamma-ray measurements and theoretical calculations.

Contribution

It provides new experimental data and theoretical analysis demonstrating the collective character and core polarization effects in nuclei near 78Ni, highlighting its fragile doubly-magic nature.

Findings

Measured excitation energies of 84Ge states indicating collectivity

Confirmed the new single particle state ordering after shell closures

Established 78Ni as a fragile, easily polarized doubly-magic core

Abstract

gamma-rays following the B and B-n decay of the very neutron rich 84Ga produced by photo-fission of 238U have been studied at the newly built ISOL facility of IPN Orsay: ALTO. Two activities were observed and assigned to two B-decaying states: 84gGa, I = (0\^-) and 84mGa, I = (3\^-, 4\^-). Excitation energies of the 2+1 and 4+1 excited states of 84Ge were measured at E(2+1) = 624.3 keV and E(4+1) = 1670.1 keV. Comparison with HFB+GCM calculations allows to establish the collective character of this nucleus indicating a substantial N=50 core polarization. The excitation energy of the 1/2+1 state in 83Ga known to carry a large part of the neutron 3s1/2 strength was measured at 247.8keV. Altogether these data allow to confirm the new single particle state ordering which appears immediately after the double Z=28 and N=50 shell closure and to designate 78Ni as a fragile and easily polarized doubly-magic core.