Quadrupole moments of neutron-deficient 20,21Na

The electric-quadrupole coupling constant of the ground states of the proton drip line nucleus 20Na (Iπ=2+Iπ=2+, T1/2=447.9 msT1/2=447.9 ms) and the neutron-deficient nucleus 21Na (Iπ=3/2+Iπ=3/2+, T1/2=22.49 sT1/2=22.49 s) in a hexagonal ZnO single crystal were precisely measured to be |eqQ/h|=690±12 kHz|eqQ/h|=690±12 kHz and 939±14 kHz939±14 kHz, respectively, using the multi-frequency β-ray detecting nuclear magnetic resonance technique under presence of an electric-quadrupole interaction. An electric-quadrupole coupling constant of 27Na in the ZnO crystal was also measured to be |eqQ/h|=48.4±3.8 kHz|eqQ/h|=48.4±3.8 kHz. The electric-quadrupole moments were extracted as |Q(Na20)|=10.3±0.8 efm2 and |Q(Na21)|=14.0±1.1 efm2, using the electric-coupling constant of 27Na and the known quadrupole moment of this nucleus as references. The present results are well explained by shell-model calculations in the full sd-shell model space.