Radon and Thoron Progeny Measurements in Dwellings of Northern Greece

Radon progeny concentration is measured with a total alpha counting system in 185 dwellings in the town of Thessaloniki. The Equilibrium Equivalent radon Concentration (EEC Rn) follows a lognormal distribution with an arithmetic and geometric mean value of 28 Bq/m and 16 Bq/m respectively. Simultaneous in situ alpha and gamma spectroscopy measurements were performed in 60 schools of Thessaloniki. The mean Equilibrium Equivalent Concentration of radon and thoron is 22 Bq/m and 0.9 Bq/m respectively. The minimum, maximum and mean total absorbed dose rate in air due to gamma radiation is 13 nGy/h, 88 nGy/h and 47 nGy/h respectively. The contribution of the different radionuclides to the total gamma dose rate in air is 39% due to K, 33.5% due to thorium series, 27 % due to uranium series and about 0.5% due to Cs from the Chernobyl accident. For schools that were under construction or constructed the first years after the Chernobyl accident, Cs act also as an indoor source term, however with small contribution to the total dose rate. The mean annual effective dose equivalent due to gamma radiation is 0.29 mSv, comparable to the 0.2 mSv due to thoron progeny and about five times smaller than the value of 1.36 mSv due to radon progeny. The mean annual effective dose equivalent due to thoron progeny is about 13% of the total effective dose equivalent due to radon progeny and thoron progeny. No correlation was found between radon and thoron progeny and the absorbed gamma dose rates in air due to uranium and thorium series respectively. Radon and thoron progeny was measured every 4 hours in the Nuclear Technology Laboratory of the Aristotle University of Thessaloniki for more than a year. The mean EEC Rn on a weekly basis varies from 16 Bq/m up to 155 Bq/m. The time dependence variation of EEC thoron progeny is smaller than the radon progeny. The mean annual effective dose equivalent due to radon and thoron progeny is 3.8 mSv and 1 mSv respectively. The mean annual effective equivalent dose due to thoron progeny is about 21% of the total effective dose equivalent due to radon progeny and thoron progeny. The effective dose equivalent due to thoron progeny is sometimes comparable to the effective dose equivalent due to radon progeny.