  In this work, we devise a fast and effective nuclear spin hyperpolarization
scheme, which is in principle magnetic field and temperature independent. We
use this scheme to experimentally demonstrate polarizations of up to 66% for
phosphorus donor nuclear spins in bulk silicon, which are created within less
than 100 us in a magnetic field of 0.35 T at a temperature of 5 K. The
polarization scheme is based on a spin-dependent recombination process via
weakly-coupled spin pairs, for which the recombination time constant strongly
depends on the relative orientation of the two spins. We further use this
scheme to measure the nuclear spin relaxation time and find a value of approx.
100 ms under illumination, in good agreement with the value calculated for
nuclear spin flips induced by repeated ionization and deionization processes.
