High proton polarization at high temperature with single crystals of aromatic molecules

Protons in single crystals of naphthalene doped with pentacene and p-terphenyl doped with pentacene have been polarized up to 32% and 18%, respectively. Such polarization has been achieved at liquid nitrogen temperature in a magnetic field of 3kG by means of microwave-induced optical nuclear polarization. We also measured the polarization by the neutron transmission method. The relaxation time at 77K in 7G was found to be about 3h and the enhancement of the obtained polarization compared with thermal polarization reached 8×104. This method is applicable to neutron experiments.