Effective Radiation Dose From Indoor Rn-220 Concentration

Equilibrium equivalent concentration of thoron (EECTh)were measured in theNuclearrnPhysics laboratory of the Addis AbabaUniversity over a period of 21 days in the monthsrnof April andMay 2017. The laboratory is located in the first floor of the Department’srnbuilding. The method, used in this work, is based on gross beta counting of filteredrnaerosol samples counted over successive time intervals using an end-windowGeiger-rnMüller detection system. i.e., grab sampling of air followed by absolute beta countingrnwas used to determine thoron concentration.rnThe gross beta-count was then fitted to a mathematical model using least-squarernfitting method. The concentrations of the radon and thoron daughter products wererndetermined from the best fit. Equilibrium Equivalent Concentrations of Radon andrnThoron were calculated from the concentrations of the progeny. This EEC was usedrnto determine the effective indoor inhalation dose due to thoron.rnIt was found that the effective annual effective doses for thoron inhalation by therninhabitantswere found to vary in the range (0.06 - 0.20mSv/y) with a mean of 0.1 mSvrny .rnThese results are close to the maximum permissible dose (0.1mSv/y) to the publicrndue to thoron progeny recommended by (ICRP, 1990).rnxi

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