CRYOSORPTION PUMPING OF H-2 AND HE WITH METALS AND METAL-OXIDES AT 4.3-K

Pressures below 10(-10) torr can be maintained in large LHe cooled UHV systems by increasing the available active cryosorbing surface area. Clean metal oxides (metal sponges) can provide the required surface ar ea increase for higher adsorption capacities as well as for enhancing the pumping speed at extremely low pressures. Metal sponges have sever al advantages over the conventional cryosorbers viz. molecular sieves and charcoals. The adsorption isotherms of H-2 and He at 4.3 K on meta ls (Al, stainless steel, Nb) and metal oxides (Al2O3, Nb2O5) are given here in the pressure range 10(-14) - 10(-6) torr. An extractor gauge is used at LHe temperature to obtain this isotherm data.