9
RADON AND THORON PROGENY MEASUREMENTS
IN DWELLINGS OF NORTHERN GREECE

A. Clouvas, S. Xanthos and M. Antonopoulos-Domis
Nuclear Technology Laboratory, Department of Electrical and Computer
Engineering, Aristotle University of Thessaloniki, GR-54006 Thessaloniki

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 222 Rn) follows a log-normal
distribution with an arithmetic and geometric mean value of 28 Bq/m 3 and 16 Bq/m 3
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 3 and 0.9 Bq/m 3 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 40 K, 33.5% due to thorium
series, 27 % due to uranium series and about 0.5% due to 137 Cs from the Chernobyl accident. For
schools that were under construction or constructed the first years after the Chernobyl accident, 137 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 222 Rn on a
weekly basis varies from 16 Bq/m 3 up to 155 Bq/m 3 . 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.

Key words: Radon progeny; Thoron progeny; In situ ã -spectrometry