We propose a method for a laboratory determination of the actual concentration of subsoil radon and of its exhalation rate from uranium-containing sediments. The method is based on gamma-ray spectrometry paired with a. systematic theoretical study of radioactive processes. It may help understand the relationship between radon exhalations and seismic activity. It also provides a low-cost technique for prospecting uranium ores, and can be used to improve the precision of thermoluminescence dating. (C) 2000 Elsevier Science Ltd. All rights reserved.