Experiments have been conducted to study (a) the development and annealing properties of the latent damage trails produced by radon/thoron alpha particles in plastic Solid State Nuclear Track Detectors (SSNTDs), and (b) the diffusion properties of radon and thoron in various media by using SSNTDs. The information thus obtained has been employed for (a) the optimization of the conditions for the construction of radon/thoron dosimeters for uranium/thorium mines, and (b) the use of SSNTDs for prospection and estimation of uranium and thorium. The results indicate that these gases can diffuse even through rocks, and cellulose nitrate detectors, LR-115 and CA80–15, can be profitably employed in dosimetry, prospection, and for the discrimination between uranium and thorium deposits.