Quadrupole Moments of Neutron-Deficient

The electric-quadrupole coupling constant of the ground states of the proton drip line nucleus 20 Na(I � = 2 + , T1/2 = 447.9 ms) and the neutron-deficient nucleus 21 Na(I � = 3/2 + , T1/2 = 22.49 s) in a hexagonal ZnO single crystal were precisely measured to be |eqQ/h| = 690 ± 12 kHz and 939 ± 14 kHz, respectively, using the multi-frequency �-ray detecting nuclear magnetic resonance technique under presence of an electric-quadrupole interaction. A electric-quadrupole coupling constant of 27 Na in the ZnO crystal was also measured to be |eqQ/h| = 48.4 ±3.8 kHz. The electric-quadrupole moments were extracted as |Q( 20 Na)| = 10.3 ± 0.8 e fm 2 and |Q( 21 Na)| = 14.0 ± 1.1 e fm 2 , using the electric-coupling constant of 27 Na 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.