Ammonia as a polarized solid target material—a review

The enormous efforts towards dynamically polarized ammonia and deuterated ammonia (d-ammonia) with their reasonable high polarizable nucleon contents (quality factor) are reviewed. The early attempts are also a story of failures until a radiation doping method for NH3 was successfully demonstrated in the end of the 1970s. Some years later the outcome of intense studies and new developments (with pitfalls, too) was the availability of the highly polarizable target materials 14NH3, 15NH3, 14ND3 and 15ND3, all of them doped for the dynamic nuclear polarization (DNP) by radiation. These materials have been used in new particle physics experiments which, up to that time, suffered either from the lower quality factors or from the modest polarization resistance against radiation damage of the existing alcohol and diol target materials.