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194 Advanced Mine Ventilation

Figure 12.3 Cyclone dust sampler.
Source: By Hartmann, John Wiley, 1982.

12.2.3 GCA Beta-Ray Sampler

GCA developed a gravimetric sampler that used beta ray for mass measurement.
Respirable dust is collected inside the instrument by impaction on a thin, grease-
coated plastic [4]. The mass of dust collected over a short time period (usually
1 min) is measured by the change in attenuation of beta radiation caused by the buildup
of dust on the disk. The instrument weighs 6.6 lb and is intrinsically safe for use in coal
mines. It is battery-powered and completely self-contained. At the end of the sampling
period, the average dust concentration over the period is read out on a digital display.
The source for beta ray was a piece of C 14 with a half-life of 5700 years. This in-
strument, although very handy, did not receive a government approval as the previous
two instruments did because of several drawbacks. The main objection was that it was
not size selective. Second, it tended to give a lower than MRE dust concentration