Collection of radon decay products — a uranium exploration technique

Abstract

The spontaneous deposition of short-lived radon decay products onto solid surfaces (“collectors”) provides the basis for a simple and efficient way of prospecting for uranium. The alpha activity of two of the decay products, 218Po and 214Po, can be measured by conventional counting techniques following the exposure of a collector to a radon source. Laboratory studies have shown: (a) radon decay products can be collected on a wide variety of materials; (b) the number of radon decay products increases with the collector surface area; (c) a negative charge applied to the collectors enhances the number of decay products collected; (d) the shape of the collectors is relatively unimportant; and (e) reproducibility is about ± 5% of the measured value. Field tests on known uranium anomalies involved suspending collectors for an overnight exposure, in either covered holes or inverted containers buried in soil. Subsequent removal of the collectors was immediately followed by counting the alpha activity. Anomalies were readily detected at three different test sites. Replicate measurements at selected sites both on an hour-to-hour and on a day-to-day basis showed remarkably good agreement. Some anomalies were also outlined using activity measurements from collectors suspended above soil aliquots in sealed containers. Because the half-lives of two of the thoron ( 220Rn) decay products are much longer than those of the radon ( 222Rn) decay products, a thoron correction can be applied to the original activity measured from the collectors, thus discriminating against thoron in thorium-rich terrains. The counting of radon decay products deposited onto collectors is an effective method for delineating radon anomalies in uranium exploration. The field techniques are simple to apply, and results are available after very short exposure times (about 18 hours) and after short counting intervals (5 minutes).