Cooling Mechanism of Spin Polarized Atomic Hydrogen Adsorbed on Dilute 3He-4He Mixture Film

We cooled down the two-dimensional (2-D) spin-polarized atomic hydrogen (H...) adsorbed on a small surface called cold spot, whose temperature was kept much colder than the rest of the sample cell. The 2-D density of H … was controlled by an input flux of H... into the sample cell. We investigated the surface recombination of H... adsorbed on 3% 3 He 3 He- 4 He mixture. ESR at 129GHz was carried out to detect H... by mirror cavity with the cold spot located at the confocal point. We calculated the thermal boundary resistance between the absorbed H... and the mixture. From the temperature dependence of the surface recombination together with calculated boundary resistance, we obtained the temperature dependence of (epsilon)a. The result agrees with the previous measurement. Two-D H…on the mixture film was cooled well down to 40mK.