Counter-flow leak detector

Figure 8.2 Vacuum distillation system with a helium counter-flow leak detector connected.

Flow Proportional Counter. The flow proportional counter covers a wide wavelength range and is generally used for wavelengths longer than 2 A (elements with Z < 27). This detector is illustrated in Fig. 8.24(a). The windows are thin (<6 pm) polymer film, coated on the inside surface with aluminum to permit a homogeneous electric field to be established within the detector. The thin windows allow the filler gas to leak out therefore a supply of filler gas is constantly provided to the detector through the inlet as shown in Fig. 8.24(a). The filler gas for a flow proportional counter is often 10% CH4, 90% Ar, a mixture called PIO gas. The pressure, flow, and temperature of the gas must be precisely controlled for accurate detector response. 

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