Development of polarized HD target for LEPS experiment (1)

We develop the method to obtain the polarized proton and deuteron target using the cryogenic technique. In 2008, we firstly completed the cryogenic system to polarize proton in the HD sample and produced firstly the polarized HD sample. The HD sample was cooled down to 15 mK in the period of 2 months with a magnetic field of 17 T, and the polarization and the relaxation time for H and D were measured at 300 mK and at 1 T. We measured the first experimental data at various temperatures and magnetic fields. The H polarization degree is 41.4$\pm$ 3.1\%, and the D polarized degree is 13.1$\pm$ 1.9\%. The polarization degrees measured are lower than those expected, but the reason of the low polarization is considered to be due to non-linear relation between the NMR signal height and the polarization degree. The H relaxation time is 2550$\pm$ 380 hours, and the D relaxation time is 1740$\pm$ 170 hours. The relaxation time is found to be acceptable to produce a new polarized HD target for replacement in continuous experiments.