Side arm method. Steady state static system

1 Side arm method. Steady state static system 

Smith s original treatment was one-dimensional, i.e. it ignored the possibility that radial as well as longitudinal atom concentration gradients 

Flow of gas in which is generated a constant concentration of atoms 

The Wrede—Harteck gauge consists of a small chamber in communication with the atom—molecule mixture via a hole whose dimensions are small compared with the mean free path. The chamber is coated with an efficient catalyst so that, ideally, every atom which enters is recombined. Because the atom flux is unidirectional, a pressure difference (AP) between the pressure outside and inside the gauge will characterise the stationary condition, such that 

In contrast to the use of large Sf ratios, where attention is focussed on the wall of the tube, Wood and Wise [62, 63] have used short tubes to determine j for the material simulating the end plate. They investigated the recombination efficiency of several metals for H atoms. In the later study [63], their terminal probe was in the form of a heated spiral filament of the metal under investigation. The decrease in energy necessary to maintain the filament at constant temperature was measured and assumed to be proportional to the atom concentration at the cross-section occupied by the filament. The method is preferable to the use of thermocouple probes, whose change in temperature might affect the atom decay profiles. Wood and Wise attribute differences in their results obtained 

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