Electric quadrupole moment of the ^33Al ground state

The ground-state Q moment of ^33Al has been measured by applying the β-ray-detected nuclear magnetic resonance technique to spin-polarized ^33Al fragments produced in the projectile fragmentation reaction. The obtained Q moment, |Q_exp(^33Al)| = 132(16) emb, shows a significant deviation from the theoretical value predicted in the shell model calculation with the USD interaction. The deviation will be discussed in context of possible erosion of the N = 20 shell gap, by comparing the experimental Q and theoretical predictions from the large scale shell model calculation and the particle-vibration coupling calculation.