NMR studies on polarized12B implanted in highly oriented pyrolytic graphite

NMR measurements on12B nuclei implanted in a thin sheet of highly oriented pyrolytic graphite (Grafoil) have been made to study the magnitude of the polarization of12B and its electric quadrupole coupling. The magnitude of the residual polarization of12B held in carbon material is of crucial importance to the experiment measuring the average polarization of12B produced in the muon capture by12C. It was found that the polarization of12B can be maintained at 101.0±2.2% in Grafoil under a magnetic field of 3 kG. The electric quadrupole coupling was determined to bee 2 qQ/h=+1207.3±8.2 kHz. From the magnitude and the sign of the electric field gradienteq, the location of12B was found to be a substitutional site in the carbon lattice. The anomalous B-C bond involving thesp 2 hybrid orbitals with partially filledp z electrons is also discussed.