Experiments with ‘‘doubly’’-spin-polarized atomic hydrogen

We analyze and reinterpret experiments with electron- and nuclear-spin (‘‘doubly’’)-polarized hydrogen (H↓?) in a cell with a very low concentration of magnetic impurities. The destabilizing magnetic relaxation due to remaining impurities ($G_i^s$) is found to be suppressed by increasing the thickness of the helium film covering the walls of the cell. Using recent information on surface three-body recombination, we obtain good quantitative agreement with more recent experiments if we assume thermal gradients, up to ΔT/T≃0.1. We extract both the value and field dependence for the three-body surface recombination [$L_3^s$=1.5(2)×${10}^{\mathrm{-}24}$ ${\mathrm{cm}}^4$ ${\mathrm{s}}^{\mathrm{-}1}$ at B=8 T]. We also extract the magnetic field dependence of the impurity relaxation.