  Polarized negative muons were used to study the behaviour of the boron
acceptor centre in synthetic diamond produced by the chemical vapour deposition
(CVD) method. The negative muon substitutes one of the electrons in a carbon
atom, and this muonic atom imitates the boron acceptor impurity in diamond. The
temperature dependence of the muon spin relaxation rate and spin precession
frequency were measured in the range of 20 - 330 K in a transverse magnetic
field of 14 kOe. For the first time a negative shift of the muon spin
precession was observed in diamond. It is tentatively attributed to an
anisotropic hyperfine interaction in the boron acceptor. The magnetic
measurements showed that the magnetic susceptibility of the CVD sample was
close to that of the purest natural diamond.
