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University of Coimbra, LRN-Laboratory of Natural Radioactivity, Department of Earth Sciences, Portugal(1);IATV-Instituto do Ambiente, Tecnologia e Vida, Coimbra, Portugal.(2);University of Coimbra, CITEUC-Center for Earth and Space Research, Department of Earth Sciences, Portugal(3);The requirements for radiological protection regarding radioactive substances in water intended for human consumption are established in the Council Directive 2013/51/EURATOM of 22 October 2013. In Portugal, the Directive was transposed to the Decree-Law 152/2017, of December 7, which states that the entities managing water supply must establish a quality control program based on a risk assessment. The risk assessment must consider the results of previous monitoring programs of both groundwater and surface water sources and the results of radionuclides measured in raw water, among others. To aid the entities managing water supply, risk maps of radon (Rn-222), uranium (U-238 and U-234), radium (Ra-226) and polonium (Po-210) were developed for mainland Portugal by the Laboratory of Natural Radioactivity of University of Coimbra using: (i) results from measurements performed in water samples retrieved from the database of the national regulation authority responsible for water and waste services (ERSAR); (ii) the terrestrial gamma dose rate map at the scale of 1:1 000 000; (iii) uranium concentration (n = 2681) and (iv) radium activity concentration (n = 609) measured in bedrock samples. ERSAR’s database comprises radon (n = 9473), gross alpha and beta (n = 10500), Po-210 (n = 1188), Ra-226 (n = 1143), U-234 (n = 1127) and U-238 (n = 1129) results from 5874 distinct groundwater and surface water sources. In this work, data are presented, methods and challenges for risk mapping of radon and terrestrial radionuclides in water samples are discussed.

Thoron contribution to the inhaled dose is often neglected due to its shorter half-life and lack of strong gamma emissions that hinder its measurement. However, numerous studies report a significant contribution of thoron and/or its progeny to the dose received by the population. In the present work, radon and thoron exhalation rate and emanation coefficient were measured simultaneously with the accumulation method with an AlphaGuard DF2000 monitor in granite samples collected in high background radiation areas located in Central Portugal. The samples were also analyzed by gamma-ray spectrometry using an Ortec NaI(Tl) detector to determine 226Ra and 224Ra assuming secular equilibrium in the respective decay series. The relationship between radon and thoron exhalation rate and emanation coefficient, and the activity concentrations of their parent isotopes, are investigated. Radon exhalation and emanation are generally higher than thoron’s, however, thoron exhalation rate may exceed the radon exhalation rate in porphyritic granodiorites. Weak correlations are observed between radon and thoron, suggesting they must be estimated independently for the assessment of thoron’s contribution to the dose received by the population. Variations of the radon exhalation rate, radon and thoron emanation coefficient, and the activity concentration of radium (226Ra and 224Ra) are observed linked to the geologic time of emplacement of granitic intrusions during the Variscan orogeny.