Partial Pressure Analysis Using A Two-Chamber Gauge Together with an Ion–Electron Converter

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Abstract
A two-chamber device has been developed together with a very sensitive ion detecting system. The hot filament is placed in a separately pumped vacuum chamber, thus eliminating interaction effects of the filament with the residual gas. Electrons from the filament pass through a very small conductance orifice into the ionization chamber. The ions are detected with a tube-shaped ion–electron converter followed by a surface barrier detector. Single ion pulses can be counted and from the pulse height distributions the counting efficiency can be calculated for different ionic species. With counting losses of 3% or less for all ions, a background current of 4×10−21 A was measured. This leads to a minimum detectable partial pressure of about 10−15 Torr which can be extrapolated to an ultimate sensitivity of 10−17 Torr. The mass resolution of the magnetic analyzer is 190 (FWHM definition).

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