DYNAMIC NUCLEAR-POLARIZATION WITH A CYCLOTRON-RESONANCE MASER AT 5-T

DNP (dynamic nuclear polarization) experiments at 5 T are reported, in which a cyclotron resonance maser (gyrotron) is utilized as a 20 W, 1 40 GHz microwave source to perform the polarization. MAS (magic angle spinning) NMR spectroscopy with DNP has been performed on samples of p olystyrene doped with the free radical BDPA (alpha,gamma-bisdiphenylen e-beta-phenylallyl) at room temperature. Maximal DNP enhancements of a pproximately 10 for H-1 and approximately 40 for C-13 are observed and are considerably larger than expected. The DNP and spin relaxation me chanisms that lead to these enhancements at 5 T are discussed.