Highest polarizations in deuterated compounds

Unlike the proton, which can be almost completely polarized even at temperatures as high as 1 K, achieving a high polarization in a deuteron system is a much more complicated task. The reason for that is the much lower magnetic moment of the deuteron compared to that of the proton. Since the nuclear polarization is determined by the ratio of the magnetic to the thermal energy, the only way to further enhance the deuteron polarization consists of reducing the effective temperature. Speaking in terms of the spin temperature theory, the nuclear Zeeman temperature has to be minimized. This can be done most effectively by using paramagnetic centers, which experience only a weak non-Zeeman interaction. In deuterated alcohols or diols such centers can be provided by either an irradiation with ionizing particles or by chemical doping with radicals of the trityl family. Both methods led to a substantial improvement of the maximum polarization in these substances. Values of about 80% have been measured in trityl-doped D-butanol and D-propanediol.