IAEA SAFETY GUIDES - gnssn - International Atomic Energy Agency

This publication is no longer validPlease see http://www-ns.iaea.org/standards/TABLE VI. VALUES OF Z FOR USE IN THE TWO FILTER METHOD FORMEASURING THORONt T, t 2 z10 1 11 0.0126210 60 70 0.0572410 10 110 0.5159110 10 1010 6.3142030 1 11 0.0671330 60 70 0.1849830 10 110 1.6998930 10 1010 18.98648120 1 11 0.60925120 60 70 0.88502120 10 110 8.48933120 10 1010 75.32111Note: Z is the decay correction factor (min);t is the sampling time (min);T, is the start of the counting period (min);T2 is the end of the counting period (min) (T = 0 at the end of the sampling period).then manipulated with forceps. If glass fibre filters are used, correction must bemade for self-absorption.The two filter method usually has relatively low count rates, partly because ofa high degree of plateout of the freshly formed and hence mostly unattached RaA.It has been suggested to correct for this effect by adding aerosols to the air stream.Because of the low count rates, the background radiation of the alpha counterbecomes significant. This should be checked periodically, especially in mining applications,as the counters may gradually accumulate contamination by radon daughtersthrough plateout.5.1.5. The two filter method for thoronPrincipleThe two filter method for thoron is identical to the two filter method for radonexcept for the following:30