A simple passive collector for direct measurement of radon flux from soil

A simple technique for measurement of the soil-atmosphere radon flux has been developed by fastening a charcoal canister inside a PVC cylindrical container. This device, which is deployed at the ground surface for approximately 16 hours, captures radon emanating from the soil by adsorption onto the charcoal surface. After recovery of the canister and measurement of the radon daughter activity on a NaI detector, the radon flux may be calculated if the adsorption efficiency of radon onto the charcoal is known. This parameter was determined by exposure of charcoal canisters to²²⁶Ra-spiked barium palmitate filter sources for timed intervals. Since this compound is known to emanate 100% of the²²²Rn generated during radium decay, it forms a useful flux standard. The accuracy of our flux measurements was assessed by comparison to a more established technique, the enclosed-chamber or accumulator method. Concentration measurements were made for the chamber over a less than 2-hour period while the canister flux measurements were based on single overnight deployments. The experiment was repeated 5 times at two different sites and the two techniques generally agreed within a 95% confidence interval.