Coulomb excitation of the |Tz|= 12, A=23 mirror pair

Abstract

Background: Electric-quadrupole (E2) strengths relate to the underlying quadrupole deformation of a nucleus and present a challenge for many nuclear theories. Mirror nuclei in the vicinity of the line of N=Z represent a convenient laboratory for testing deficiencies in such models, making use of the isospin symmetry of the systems.Purpose: Uncertainties associated with literature E2 strengths in Mg23 are some of the largest in Tz=|12| nuclei in the sd shell. The purpose of the present paper is to improve the precision with which these values are known, to enable better comparison with theoretical models. Methods: Coulomb-excitation measurements of Mg23 and Na23 were performed at the TRIUMF-ISAC facility using the TIGRESS spectrometer. They were used to determine the E2 matrix elements of mixed E2/M1 transitions. Results: Reduced E2 transition strengths, B(E2), were extracted for Mg23 and Na23. Their precision was improved by factors of approximately 6 for both isotopes, while agreeing within uncertainties with previous measurements. Conclusions: A comparison was made with both shell-model and ab initio valence-space in-medium similarity renormalization group calculations. Valence-space in-medium similarity renormalization group calculations were found to underpredict the absolute E2 strength, in agreement with previous studies.