Precision measurement of the electric quadrupole moment of 31Al and determination of the effective proton charge in the sd-shell

TL;DR

This study precisely measures the electric quadrupole moment of 31Al using two NMR techniques, compares results with shell-model calculations, and suggests a revised effective proton charge for sd-shell nuclei.

Contribution

First direct comparison of continuous rf and adiabatic fast passage NMR techniques for 31Al quadrupole measurement and refined effective proton charge value.

Findings

Measured |Q(31Al)| = 134.0(16) mb

Proton effective charge e_p=1.1 e fits sd-shell data better

Ground state dominated by normal sd-shell configurations

Abstract

he electric quadrupole coupling constant of the 31Al ground state is measured to be nu_Q = |eQV_{zz}/h| = 2196(21)kHz using two different beta-NMR (Nuclear Magnetic Resonance) techniques. For the first time, a direct comparison is made between the continuous rf technique and the adiabatic fast passage method. The obtained coupling constants of both methods are in excellent agreement with each other and a precise value for the quadrupole moment of 31Al has been deduced: |Q(31Al)| = 134.0(16) mb. Comparison of this value with large-scale shell-model calculations in the sd and sdpf valence spaces suggests that the 31Al ground state is dominated by normal sd-shell configurations with a possible small contribution of intruder states. The obtained value for |Q(31Al)| and a compilation of measured quadrupole moments of odd-Z even-N isotopes in comparison with shell-model calculations shows that the proton effective charge e_p=1.1 e provides a much better description of the nuclear properties in the sd-shell than the adopted value e_p=1.3 e.