Thoron activity concentration in Malaysian soil gas: geogenic impact assessment

Abstract

Given the rather short half-life of thoron (220Rn), at 56 s, its contribution to radiation exposure is often overlooked. 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 Quaternary and Silurian formations revealed low 220Rn values. Moreover, while elevated 220Rn activity concentrations 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.