High-precision quadrupole moment reveals significant intruder component in 33Al20 ground state

TL;DR

This study precisely measures the quadrupole moment of 33Al20, revealing a significant intruder component in its ground state, indicating a transition from deformed to normal isotopic structures near the island of inversion.

Contribution

It provides the first precise quadrupole moment measurement of 33Al20 and demonstrates a substantial intruder configuration component using beta-NQR and shell model comparisons.

Findings

33Al has at least 50% intruder configurations in its ground state

The measured quadrupole moment is Qs= 141(3) mb

Supports the transition from deformed to normal isotopes near N=20

Abstract

The electric quadrupole moment of the 33Al20 ground state, located at the border of the island of inversion, was obtained using continuous-beam beta-detected nuclear quadrupole resonance (beta-NQR). From the measured quadrupole coupling constant Q = 2.31(4) MHz in an alpha-Al2O3 crystal, a precise value for the electric quadrupole moment is extracted: Qs= 141(3) mb. A comparison with large-scale shell model calculations shows that 33Al has at least 50% intruder configurations in the ground state wave function, favoring the excitation of two neutrons across the N = 20 shell gap. 33Al therefore clearly marks the gradual transition north of the deformed Na and Mg nuclei towards the normal Z>14 isotopes.