Electric quadrupole moment of $^{25}$Na.

Among the many Na isotopes, whose electric quadrupole moments $Q$ are known, the precision of the $Q$ moment of $^{25}$Na ($I^{\pi }$=5/2$^{+}$, $T_{1/2}$=59.1s) has been extremely poor, which prevents us from the quantitative discussion of nuclear structure of the Na isotopes. In the present experiment, the $Q$ moment of $^{25}$Na has been determined precisely by means of $\beta $-NMR technique. Polarized $^{25}$Na nuclei were produced through the projectile fragmentation process in the $^{26}$Mg on Be collisions at 100$A$ MeV. The NMR/NQR were observed on the $^{25}$Na nuclei implanted in NaCl and/or TiO2 single crystals, by means of the asymmetric emission of $\beta $ rays. As a result, the absolute values of the magnetic and the $Q$ moments were precisely determined to be 3.6832(3) $\mu _{N}$ and 1.0(4) mb, respectively. The obtained $Q$ moment is much precise than the old value --64(44) mb. The present $Q$ is reproduced well by the shell model value --2.7 mb.