Some Observations of Natural Atmospheric Radioactivity

Abstract

The techniques that have been used for the measurement of atmospheric radioactivity are reviewed. The results of previous investigations are reviewed and discussed. Equations giving the amounts of radon and thoron daughter products collected with a filter paper or electrostatic precipitator are derived, and further equations giving the decay of activity after collection are deduced. The effect of the occurrence of non-equilibrium mixtures in the atmosphere is discussed, and it is shown that departures from equilibrium in the case of radon and its daughters would cause appreciable changes in the rate of decay of the collected activity. The construction and operation of an automatic sampler using an electrostatic precipitator and a scintillation counter for detection is described. By measuring the decay times of 34 samples it was found that the radon and its short-lived daughters are usually in equilibrium in the atmosphere. Over 300 measurements of air samples have been taken over a period of 19 weeks and show the dependence of the activity on weather conditions. Examples of the variations in activity during the course of a day are given, with the relevant meteorological factors. The estimated radon content of the air from an average of 90 daily readings taken in the early afternoon was 31 x 10⁻¹² c/m³, the maximum level being 400 x 10⁻¹² c/m³ and the smallest value 0.