Lifetime measurements probing collectivity in the ground-state band of Mg32

Abstract

The signatures of inversion between normal and intruder configurations of particle-hole excitations across the $N=20$ shell gap in the neutron-rich isotope $^{32}\mathrm{Mg}$ have long been of keen interest. Electromagnetic transition rates in the ground-state band are key quantities that provide insights into collective properties associated with the contributions of the 2p2h and 4p4h intruder configurations. The combination of TRIPLEX, GRETINA, and the S800 spectrograph enables model-independent lifetime measurements to determine electromagnetic transition rates in rare isotopes. The reduced $E2$ transition rates in $^{32}\mathrm{Mg}$ between the ${2}_{1}^{+}$ and ${0}_{1}^{+}$ states and between the ${4}_{1}^{+}$ and ${2}_{1}^{+}$ states have been measured, the latter representing the first experimental $B(E2)$ value for this transition. The $B(E2)$ strengths indicate large collectivity and strong contributions from the 2p2h and 4p4h intruder configurations that may change with spin in the ground-state band of $^{32}\mathrm{Mg}$.