| Popis: |
The experimental data on helium adsorption isotherms for molecular sieve have been extended from 10−7 to 10−11 Torr. A commercially available cryopump CVR 1008 made by Excalibur was used for this investigation. It was found that, in general, the experimental points fall on a curve predicted by the Dubinin and Radushkevich theory down to 1×10−10 Torr. Below this pressure the slope gets steeper and possible causes for this behavior are being studied. When compared with bare copper surfaces, a 1.8-mm-thick layer of bonded molecular sieve 5A adsorbs almost 108 times more helium per unit area. The pumping speed remains high for leaks Q |
