Influence of thermal radiation on the vapor pressure of condensed hydrogen (and isotopes) between 2 and 4.5 K

Abstract

It has previously been established that H/sub 2/ emission from condensates and adsorbates on He-cooled cryopumps is enhanced by incident thermal radiation and this effect has produced anomalously high values for the H/sub 2/ saturated vapour pressure. Also it has been indicated that the effect depends on the substrate used. The subject is reviewed and additional information is given on the desorption characteristics of HD and D/sub 2/. Studies made at CERN with three types of cryopump are discussed. The pumps had stainless steel and silver cryosurfaces and blackened baffles whose temperature determined the nature of the incident thermal radiation. The apparent rise in saturated vapour pressure of condensed hydrogen and its isotopes was attributed to the relase of phonons from the substrate by photons which traversed the condensate without absorption. (11 refs)