Study Of The Surface Recombination In The Production Of A Dense Polarized Hydrogen Atomic-Beam At Low-Temperature

The surface recombination of atomic hydrogen occurring during the cooling process in the production of a high density hydrogen atomic beam is treated. Several types of material, coatings and cryogenic layers have been investigated in order to find a good recombination inhibiting surface at low temperature. Adding a small amount of N 2 gas to the hydrogen gas in the dissociator was found to reduce strongly the recombination rate in a range of a few degrees around 35 K. From the density measurements of the atomic beam it was possible to extract the behaviour of the recombination coefficient γ as a function of the temperature. Comparing this behaviour with theoretical models allows the determination of the adsorption energy of H on the actual surface of the accommodator. Without the addition of N 2 the density behaviour is mostly characterized by the recombination probability of H on H 2 O. The deduced value of the adsorption energy of H on H 2 O is 470 K, which agrees with previous results. The adsorption energy of H on a cryogenic layer of N 2 is determined for the first time and found to be 180 K.