Irradiated ammonia (NH3) as target material for polarized proton targets

Dymamic proton polarization measurements in irradiated NH3 were performed at 1 K and 0.5 K in a magnetic field of 2.5 T. The paramagnetic radicals in the frozen ammonia beads were created by irradiation with 20 MeV electrons from the injection linac of the Bonn 2.5 GeV electron synchrotron. During the irradiation the ammonia beads were cooled in liquid argon at about 90 K. Electron paramagnetic resonance measurements identified the created radicals as NH2. Samples of NH3 yielded a maximum proton polarization of 35% at 1 K and 66% at a temperature of 0.5 K. They exhibited short polarization build-up times of 2 min at 1 K and 9 min at 0.5 K. The radiation resistance of the polarization of NH3 is better than that of butanol. The radiation damage can be repaired by annealing. (orig.)