Natural Airborne Radioactivity at Kjeller, Norway

Abstract

WE have recently been investigating airborne concentrations of radon and thoron daughters, by monitoring the β-activity of a small asbestos filter through which air is drawn at a rate of about 25 l./min. A shielded end-window counter tube is mounted above the filter, giving an overall counting efficiency of 22 per cent for potassium carbonate samples. The filter is changed daily, and decay measurements have shown that recorded activity is almost entirely due to radium B and C. Assuming equilibrium concentrations of radon and radium A, B and C, an equilibrium counting-rate in counts per minute can be multiplied by 0.714 to obtain an estimate of the radon concentration in curie × 10⁻¹⁸ per cm.³ of air.