The correlation between radon exposure and the increased probability of lung cancer is widely recognized. In Portugal, several efforts have been made to estimate the radon potential in granitic rocks, however, existing knowledge on sedimentary rocks is limited. For this reason, extensive representative sampling was conducted in the well-known Lower and Middle Jurassic of the Lusitanian Basin (Central Portugal) to evaluate the radon potential of latter type of rocks. This paper compares the variability of 226Ra and 222Rn activity, emanation coefficient, and radon production rate in several lithologies deposited on paleoenvironments ranging from distal continental to deep marine. To reach this goal, 190 samples were collected in 16 well-studied outcrop sections. 226Ra and 222Rn activity varies between 2.8-119.6 and 0.1-19.6 Bq/kg, respectively. Higher values are linked to sandstones, fine-grained siliciclastics, marls and black shales. The emanation coefficient is lower in lithologies presenting a low siliciclastic/carbonate ratio, namely in dolostones, dolomitic limestones, limestones and marly limestones, with median values ranging between 6.5 and 9.7%. The distribution of radon production rate in the different lithological groups varies between 1.7 and 241.1 Bq.m-3.h-1, increasing in samples of continental source (sandstones and fine-grained siliciclastics) and proximal marine with major continental influence (dolostones), as well as from marls and black shales associated to deeper marine environments. The variability of the radon potential in sedimentary rocks varies according to lithology but, since the typical organization of these rocks in layers, the dip of these ones in each structural block also contribute to increase the variability.
Keywords: Emanation; Lower-Middle Jurassic; Lusitanian basin; Radon potential; Sedimentary rocks; Terrestrial radionuclides.
Copyright © 2020 Elsevier Ltd. All rights reserved.