THERMAL ACCOMMODATION OF SPIN-POLARIZED HYDROGEN ON LIQUID-HE SURFACES BELOW 0.25-K

We have measured the thermal accommodation of spin-polarized hydrogen gas on superfluid He films at saturation thickness in the temperature range 0.1 0.25 K. The measurements have been performed as a function of He3 concentration by monitoring the thermal flux between two parallel plates maintained at slightly differing temperatures. The measuring arrangement was designed to secure homogeneous He3 coverages and to minimize uncontrolled thermal gradients. No dependence of the accommodation coefficient on the He3 concentration is observed within the resolution of the measurements of 30%. The results are consistent with recent surface-sticking measurements, assuming that thermal accommodation proceeds on both He3 and He4 surfaces via sticking-evaporation collisions; i.e., inelastic surface scattering is negligible. © 1990 The American Physical Society.