Irradiated NH3 and ND3 - two new target materials for polarized targets

A study of dynamic nuclear polarization (DNP) in NH3 and ND3 was made at the Bonn 2.5 GeV electron synchrotron. The paramagnetic radicals in the polycrystalline ammonia beads were created by irradiation in the high intensity 20 MeV electron beam (> 1014 electrons/sec) of the injection linac. During irradiation the ammonia beads, produced by dropping into liquid nitrogen, were cooled in liquid argon at approx. 90K. DNP measurements were performed at 1K, 0.5K, and 0.2K in a 2.5T magnetic field. Samples of NH3, prepared in this way, yielded a maximum proton polarization of 66% at a temperature 0f 0.5K with a short polarization build-up time of 9 minutes. ND3 could be polarized at a temperature of 0.2K up to 31%. The radiation resistance of the polarization of NH3 is better than that of butanol. 23 references, 4 figures, 2 tables