Dynamic nuclear polarization of electron-beam irradiated and TEMPO-doped samples

Kumada, Takayuki   ; Noda, Yohei*; Ishikawa, Norito   

We compared dynamic nuclear polarization (DNP) behavior of electron-beam irradiated and TEMPO-doped samples. Both of the growth and decay rates of the nuclear polarization of the irradiated samples linearly increased with the irradiation dose, whereas those of the doped sample were quadratically proportional to the TEMPO concentration. This result suggests that the irradiated samples are polarized due to pair of free radicals produced in a spur, whereas the doped sample is polarized by unspecified TEMPO radical pairs accidentally located nearby. We suggest that higher polarization is expected by optimizing irradiation temperature, on which the radical-radical distance in the pair depends.