New measurements of the nuclear spin-lattice relaxation times of ${}_{}{}^{12}{}_{}{}^{}\mathrm{B}$ implanted in Au, Pd, and Pt have established lower limits of 60, 185, and 270 sec °K, respectively, of $T_{1}T$ for ${}_{}{}^{12}{}_{}{}^{}\mathrm{B}$ in these metals. In conjunction with prior measurements of the effective moment of ${}_{}{}^{12}{}_{}{}^{}\mathrm{B}$ in these metals, these $T_{1}T$ values show that the Knight shift of ${}_{}{}^{12}{}_{}{}^{}\mathrm{B}$ in Au is positive, while in Pd and Pt it is negative. Using a common enhancement factor in these metals, one finds the value of the ${}_{}{}^{12}{}_{}{}^{}\mathrm{B}$ magnetic dipole moment to be $\mu =(+{1.00285}_{-0.000\mathrm{}14}^{+0.000\mathrm{}15}){\mu }_N$.

The ${}_{}{}^{12}{}_{}{}^{}\mathrm{B}$ electric quadrupole moment has been measured for the first time using the asymmetry of the ${}_{}{}^{12}{}_{}{}^{}\mathrm{B}$ resonance lines in Be foil under magnetic-field reversal and the estimated field gradient at ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ lattice positions. The result is $Q\left({}_{}{}^{12}{}_{}{}^{}\mathrm{B}\right)=(+0.030\mathrm{}\pm 0.008)\times {10}^{-24\mathrm{}}$ ${\mathrm{cm}}^2$.

• Received 1 June 1970

DOI:https://doi.org/10.1103/PhysRevC.2.1219