Quadrupole Effects in NMR Spectra on Short-Lived β-Radioactive Nuclei, ¹²B and ¹²N

Quadrupole effects in NMR on ¹² B( T _1/2 =20 ms) and ¹² N( T _1/2 =11 ms) have been investigated by using the polarized nuclei produced and implanted through nuclear reactions and the resultant asymmetric β decay. The implantation media were polycrystalline bcc metals (Nb, Mo, Ta and W), TiB ₂ and ZrB ₂ . To increase the observable effects in NMR, a frequency-modu-lated r.f. field was employed. The spectra in bcc metals show the characteristics of quadrupole interaction for nuclear spin \(I{=}1\hslash\), and the determined coupling constants depend largely on the periodic groups of the related elements. The spectra in the bcc metals together with those in the fcc metals (Al, Cu, Pt and Au) indicate that the major implanted sites are interstitial. From the results on TiB ₂ and ZrB ₂ and the known values on ¹¹ B, the ratio of quadrupole moments is determined as | Q ( ¹² B)/ Q ( ¹¹ B)|=0.42±0.04, and the moment of ¹² B is deduced to be | Q ( ¹² B)|=0.017 ₁ ±0.001 ₆ b.