Abstract
Given the rather short half-life of thoron (220Rn), at 56 s, its contribution to radiation exposure is often over-looked. Nevertheless, in a thorium (232Th) rich environment potential hazard does exist, in particular regarding prolonged duration exposures to 220Rn and its short-lived alpha-particle emitting progeny [polonium (216Po)]. Herein, concerning the geology and major soil types in the Malaysian state of Perak, an activity concentration map has been established for 220Rn in soil gas, with the use made of a RAD7 detector and the THORON protocol for in-situ measurements. The detector has been coupled to a soil probe driven to a depth of 0.8 m. The activity concentration of 220Rn in the soil ranged from undetectable to 563 kBq m- 3 with a mean value of 38 +/- 11 kBq m- 3. Granite and Triassic-Jurassic formations in the region showed more elevated 220Rn activity while Qua-ternary and Silurian formations revealed low 220Rn values. Moreover, while elevated 220Rn activity concentra-tions were found in peat, riverine, and granite source soils, the activity concentrations in marine and other soils were low. A primary map of 220Rn in the soil gas has been developed based on geogenic impact assessment, with a greater 220Rn activity concentration in the central part of the state.