Jannin, S., et al., High field dynamic nuclear polarization at 6.7&T: Carbon-13 polarization above 70% within 20 min. Chem. Phys. Lett., 2012. 549(0): p. 99-102.
In most applications of dissolution-DNP, the polarization of nuclei with low gyromagnetic ratios such as 13C is enhanced directly by irradiating the ESR transitions of radicals with narrow ESR lines such as Trityl at low temperatures T = 1.2 K in polarizing fields B0 ⩽ 5 T. In a field B0 = 6.7 T at T = 1.2 K, DNP with TEMPO leads to a rapid build-up of proton polarization P(1H) = 91% with τDNP(1H) = 150 s. CP at low temperatures yields a polarization P(1H → 13C) in excess of 70% within 20 min. After rapid dissolution to room temperature, this is 122 000 times larger than the Boltzmann polarization at 300 K and 6.7 T.