  In this work we investigated the time behavior of the polarization of bulk
13C nuclei in diamond above the thermal equilibrium. This nonthermal nuclear
hyperpolarization is achieved by cross relaxation between two nitrogen related
paramagnetic defect species in diamond in combination with optical pumping. The
decay of the hyperpolarization at four different magnetic fields is measured.
Furthermore, we use the comparison with conventional nuclear resonance
measurements to identify the involved distances of the nuclear spin with
respect to the defects and therefore the coupling strengths. Also, a careful
look at the linewidth of the signal give valuable information to piece together
the puzzle of the hyperpolarization mechanism.
