Magnetic substate populations of product nuclei in the /sup 11/B(d,p)/sup 12/B reaction have been measured in an energy range Esub(d) = 1.3-3.0 MeV at recoil angles of thetasub(R) = 55/sup 0/, 45/sup 0/ and 27/sup 0/-37/sup 0/. A static magnetic field (3 kG) was applied normal to the reaction plane to keep the nuclear orientation. Quadrupole effects on the implanted /sup 12/B in Ta were utilized to perturb the Zeeman splitting. NMR transitions were induced, and detected by the asymmetry change in the ..beta..-decay of /sup 12/B. From this information, the magnetic substate populations were determined, for the unique assignment of which the sign of the quadrupole interaction had to be known. For this purpose, a p-..gamma.. angular correlation was measured, which determined the alignment of the first excited state of /sup 12/B. A comparison of the present result with theoretical predictions is given, together with the resultant information about j-mixings in the /sup 12/B states.