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RADON MAPPING IN CLUJ-NAPOCA CITY-A RADON PRONE AREA FROM ROMANIA

C. Cosma 1 D. Ristoiu 1 , A. Poffijn 2
1) University Babes-Bolyai, Faculty of Physics, 3400-Cluj-Napoca, Romania 2) University of Gent, Nuclear Physics Laboratory, 9000-Ghent, Belgium

Cluj Napoca City is the most important city from northwestern part of Romania, having about 350,000
inhabitants. The Somes river, also the most important river of this country region crosses the city from
west to east, but before it crosses a granite massive, named Maguri-Racatau, a region located at 35
Km on the upper part of this water course. The first indicators of a possible radon prone area for Cluj-Napoca
city and its neighboring was the water radon concentration from the old power supply of the
city with about 37 Bq/L (1nCi/L). Also in the east part of the city, where Someseni Spa is located,
some cold springs with radon content up to 360 Bq/L (9.5 nCi/L) were emphasized. At present the city
water supply is assured by two sources: the old source consisting in a chain of wells delving near
riverbed of Somes (4 Km upstream Cluj-Napoca) and the new accumulation lake of Tarnita (20 Km
from Cluj-Napoca) which collects the surface waters arising from Apuseni Mountains.
To see the radon potential of this region we measured in the last years the radon concentration of
indoor air in dwellings (detached houses and flats in blocks of flats) and the radon water content in the
city network water supply and also in some wells especially in two neighboring villages (Floresti and
Someseni) which are located on the Somes course. In addition we measured the radon exhalation and
soil radon content in this area. The integrated measurements of the indoor radon were made using
makrofol track detectors for three months exposure and RADIM device was used for continuos
monitoring. The radon content in water was measured using the LUK-3A device (Jiri Plch SMM,
Czech Republic) which was also used for radon soil measurement. The radon charcoal adsorption
method was used for radon flux exhalation and for radon soil content. The results for the indoor radon
show a difference between detached houses and flats, the mean value for winter season being high
enough for the both situations 183 Bq/m 3 and 70 Bq/m 3 respectively. The radon content in water was
followed at five points in the network water supply and in several wells. The values range from 1 Bq/l
to 32 Bq/L in the case of the network supply and from 12 Bq/L to 65 Bq/L in the case of the wells.
The radon content in soil shows values in the interval of 15-55 kBq/m 3 and the radon exhalation
presents an evident gradient perpendicular to the Somes riverbed. The variation of radon exhalation
was continuously measured for a month during April 1998. The average value of radon in soil for 49
sites was 32.5 kBq/m 3 and an average of 26.5 mBq/m 2 s was found in the case of the radon
exhalation. These data confirm a slightly increased radon potential of this area.
Key words: indoor radon, exhalation, radon in wells, soil gas, sedimentary rocks, charcoal adsorption,
Lucas cell.