Investigations into the relaxation of polarized nuclear target materials inhomogeneously broadened EPR lines at hv > kT

Processes of relaxation in inhomogeneously broadened lines of frozen solutions of Cr compounds in 1,2-propylene glycol were studied within the short-wave region of the mm- wavelength range at helium temperatures (hν/kT > or approximately 1). It is shown that EPR spectrum lines are inhomogeneously broadened due to the g-factor anisotropy. The values of g-factor tensor components differ negligibly for all the substances. Initiation of dynamic polarization of nuclei is a result of dynamic cooling of a dipole-dipole reservoir of the electronic spin system. Recommendations on the selection of an optimum concentration of paramagnetic centers in order to receive a maximum nuclear polarization are presented