A Soil-Gas Emanation Measurement System Used for Radon–222

Abstract

The transfer of various gases through the soil-atmosphere interface is of interest to agronomists, meteorologists, biologists and many others. Such gases include carbon dioxide, water vapor and radon. A system applicable to measurements of the emanation of gases has been developed and used to investigate the emanation of radon-222. The instrumentation was designed so that the variation of soil gas emanation with time, wind speed, soil moisture, soil type, and geographical location could be studied. The system has measured a net transport through the earth-atmosphere interface of 1.1±0.6 atoms of radon-222 per square centimeter per second (mean of 27 means, eight samples each, ± standard deviation of 27 means). For a set of eight samples collected on a given site, the coefficient of variation was 0.3 to 0.4. The analysis of a single sample provided the amount of radon-222 collected with an error of about 5 per cent. The system is completely portable, including the power supply, and can be carried from a vehicle by two men. It was designed to minimize disturbance of the site at all times, providing air flow and pressure within the collecting apparatus comparable to those in nature during sampling. Sampling sites can be chosen as desired, and all equipment can be removed from the site when sampling is completed. During a sampling trip to the Rocky Mountains, the equipment was transported 3000 miles without any breakage. Throughout an experiment on the diurnal variation of radon emanation, two duplicate systems were operated 12 hours each without difficulty.