Abstract
The production of HD targets relies on a longitudinal relaxation time switch mechanism. The longitudinal relaxation time of solid HD samples strongly depends on the concentration of ortho-hydrogen and para-deuterium in pure HD. At low temperatures these contaminants decay into H2 and D2 molecular ground states and the reduction of their concentration causes a dramatic increase of the longitudinal relaxation time of H and D in the HD solid. This is obtained by aging the. target sample, keeping it at about 10 mK temperature while a 15-17 Tesla magnetic field is applied. The ortho-hydrogen and paradeuterium concentrations in the HD gas to be polarized are therefore critical parameters for the whole polarization process. A careful procedure for distilling commercial HD gas and storing the purified gas has been developed. An accurate technique to analyze the HD gas before and after the polarization procedure, which is based on gas chromatography and Raman scattering, has also been setup to optimize the aging time as a function of the initial concentration of the contaminants.