15_26_86 - Hydrogen H 2 0.43 Oxygen O 2 0.96 Carbon...

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RELATIVE SENSITIVITY OF BAYARD-ALPERT IONIZATION GAUGES TO VARIOUS GASES Paul Redhead The ion current I + in a hot-cathode ionization gauge is given by I + = KI e P . The gauge constant is K = ( I + / I e )(1/ P ), where I e is the electron current, and P the pressure. The sensitivity is given by S = KI e = I + / P . The constant K is independent of pressure below about 10 -3 Pa. Relative sensitivities for different Bayard-Alpert ionization gauges may differ by as much as ± 15% as a result of differences in applied voltages, electron current, and electrode structure. The table below presents the average of the measurements of 12 ex- perimenters on Bayard-Alpert ionization gauges in various gases. The sensitivity relative to nitrogen is tabulated. Gas Relative sensitivity S / S (N 2 ) Helium He 0.18 Neon Ne 0.31 Argon Ar 1.4 Krypton Kr 1.9 Xenon Xe 2.7 Nitrogen N 2 1.00
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Unformatted text preview: Hydrogen H 2 0.43 Oxygen O 2 0.96 Carbon monoxide CO 1.0 Carbon dioxide CO 2 1.4 Water H 2 O 0.93 Sulfur hexafluoride SF 6 2.3 Mercury Hg 3.5 Methane CH 4 1.6 Ethane C 2 H 6 2.6 Propane C 3 H 8 3.5 Butane C 4 H 10 4.3 Ethene C 2 H 4 1.3 Propene C 3 H 6 1.8 Acetylene C 2 H 2 0.61 Allene C 3 H 4 1.3 1-Propyne (Methyl acetylene) C 3 H 4 1.4 Benzene C 6 H 6 3.8 References 1. Hollanda, R., J. Vac. Sci. Technol ., 10 , 1133, 1973. 2. Nakayama, K., and Hojo, H., Jap. J. Appl. Phys ., Suppl. 2, part 1, p. 113, 1974. 3. Tilford, C. R., J. Vac. Sci. Technol.A , 1 , 152, 1983. 4. Tilford, C. R., in Physical Methods of Chemistry, vol.6, Determination of Thermodynamic Properties , B. W. Rossiter and R. C. Baetzoid, Eds., pp. 101-173, John Wiley, New York, 1992. 15-12...
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