Radon Content in Schools from Cluj and Oneşti Cities

Radon content in schools from Cluj and Oneşti cities

Radon content in schools from Cluj and Oneşti cities

C. Cosma, Corina Rudei, Irina Ciobotaru, Kinga Hening

“Babeş-Bolyai” University, Faculty of Physics, 3400-Cluj-Napoca, Romania

ABSTRACT

This paper is based on a comparative analysis between the Radon concentrations obtained in Cluj-Napoca and Oneşti Cites with other measurements made in Romania, as Bucharest, Bihor, Stei and Oradea, measurements that were made in schools, kinder-gardens and dwellings. The values (numbers) obtained in the Transilvanian study are 2-3 times higher than the ones obtained in Moldova. The results from the three studies are almost similar. The differences are due to the geological differences, different measurement conditions and different periods in the year when the studies were made, type of buildings.

INTRODUCTION

The main radionuclides that are important from the radiological protection point of view are radon, thoron and their short-life family products. Radon is present everywhere, in rocks, water, soil, it comes from solid and liquid materials, it’s present in the air and in natural gases. Radon, because it is a radioactive gas and the only α emitter of this type, is very mobile. The first indications of a possible radon prone area1 for Cluj-Napoca City were the relatively high radon concentration (1 nCi/L) in the old water supply plant. The implication of this gas on our health is very serious. Through inhalation, Radon gets into our lungs, and through blood circulation it reaches the other organs. The irradiation its-self is not very dangerous, but the attached elements (radionuclides) on the respiratory paths are, from where they directly irradiate the bronchi and the bronchi mucus and also the bronchi epithelium that covers the interior surface of the lungs, so the irradiation is very significant. The risk of irradiation is higher if the concentration of Radon is increased.

Between the indoor radon exposure and the lung cancer risk seems to be a direct relation, that’s why determinating radon concentrations in buildings is very important for characterizing the indoor air quality. The detectors used for this study are of CR-39 type, the most sensitive nuclear track detector investigated so far, because it gives an answer to all alpha energies. For the measurements of the Rn activity concentrations integrated in the time unit was used RadoSys2000.

In order to determinate the Rn concentrations in air and to make possible an analysis of lung cancer risk due to Rn exposure, we placed CR39detectors in 28 schools and high schools from Cluj-Napoca and 14 detectors in schools and kindergartens from Oneşti. The detectors were exposed in average for 35 days in secretariats, principles’ offices and libraries, at appreciatively 1m from the ground. The measurements were made in warm season, spring to summer, and the appreciations for the whole year average is determinated due to other studies performed2 which proved that radon concentrations are 2 or 3 times higher in winter seasons than in summer. The values obtained in the schools from Cluj-Napoca City are higher comparing to the ones obtained in Oneşti.

EXPERIMENTAL METHOD

As the “ion explosion spike” model sustains, the forming mechanism of the tracks is the following: the charged particle on its trajectory ionizes the atoms of solid materials. There appear forces, which remove the ionized atoms creating numerous holes and interstitially defects. This process will take place if the big void charge does not decrease fast from the particles trajectory and if the appearing forces are high sufficiently to remove the atoms. With chemical methods these tracks can be observed with an optical microscope.

The CR-39 track detectors used for this study are made of plastic (polyetilen membranes) and they are sensitive to alpha radiation, with energies between 0.2-8Mev. The detector is placed inside of a small box called radapot, which allows the air inside. The volume of the radapot is V=0.0000402 m3. The radon daughters which contaminated the detector are then corrodated with a NaOH solution with a concentration C=7.02mol in a thermostat at t=90oC. The developing time is 4.5h.

The tracks after the developing are read using the Radosys2000 system, where the electronic microscope is attached to the computer. The number of tracks from the detector is proportionally with the radon concentration from the radapot. From the tracks number, based on a calibration of Radosys2000, it can be calculated the concentration with an extent of V=0.0000402m3.

RESULTS AND DISSCUTION

After developing and measuring the detectors placed in the schools from Cluj-Napoca and Oneşti, with RadoSys2000 system, the results obtained are enclosed in the following table and graphic. The annual values were approximated by increasing the measured ones by 1,5, using the results and formulas deduced in other studies3, 2, as they admitted that the for the values found in winter the ratio is 3:1and were due to slightly increased radon potential of the region, and on peoples’ tendency to save heat in the cold season, on the other hand.

Table 1

Measured and Estimated Radon Concentrations in Cluj-Napoca and Oneşti

Place / Values / Geometric Average (Bq/m3) / Arithmetic average
(Bq/m3) / 0-100 Bq/m3 / 100-200 Bq/m3 / >200 Bq/m3 / Excess
200 Bq (%)
Cluj-Napoca / Summer Measured / 83,49 / 91,85 / 20 / 6 / 2 / 0,071
Annual Estimated / 106,9 / 275,53 / 17 / 6 / 5 / 0,178
Oneşti / Summer Measured / 75,438 / 113 / 10 / 4 / - / -
Annual Estimated / 113,5 / 125,57 / 6 / 6 / 2 / 0,142

Fig.1 Lognormal Distribution for Radon in Schools from Cluj-Napoca and Oneşti

The lognormal distribution obtained is limited between 39 Bq/m3 and 556,5 Bq/m3, annual estimated values. Usually, in basements of buildings, the Rn concentration presents rather high values than in other places because the aerating process is very weak and it permits radionuclid accumulation, as the 556,5 Bq/m3 value indicates, value that was obtained in a semi-basement space, in order to compare it with other obtained values. As the means show, the values obtained in Cluj-Napoca are higher than the ones obtained in Oneşti and the mean is near 300 Bq/m3; that can be rather alarming.

The “Public Health” Institute and “Joszef Stefan” Institute from Ljubliana, Slovenia realized a resembling study upon Rn concentrations in 100 schools and kindergartens from Bucharest. The measurements were made in wintertime and the track detectors were also placed there for 35 days. A lognormal distribution was obtained, limited between 43 Bq/m3 and 447 Bq/m3, an arithmetic average of 146 Bq/m3 and a geometric average of 129,18 Bq/m3. The results from the three studies are almost similar. The differences are due to the geological differences, different measurement conditions, and different periods in the year when the studies were made, type of buildings. If we compare arithmetic means, we notice that Cluj-Napoca has the most increased Rn potential from these three studies, followed by Bucharest and Oneşti.

Indoor radon concentrations at ground floor level have been measured in 20012, in Cluj-Napoca, in 46 detached houses, as well as in 35 flats in blocks, in cold season. The average values found were 183.04+75.33 Bq/m3 for houses and of 69.64+23.47 Bq/m3 for flats. The values found then were rather high and the average value found for houses in the cold season resembles those found in Ukraine3 respectively in Sweden4. Indoor radon values in Cluj-Napoca City are 2-3 times higher than other values found in Romania5.

The influence of constructions materials upon indoor Rn concentrations is very well illustrated if we compare the measurements made in the schools from Cluj-Napoca with 80 measurements made in Stei area, a zone at 15 km far from an Uranium mine2; in a few homes, Uranium waste was used in constructions materials. The medium value obtained was 240 Bq/m3, higher than the one obtained in the schools from Cluj-Napoca, it can be noticed a difference of 148,15 Bq/m3. In Stei measurements, there can be observed rather high concentrations (234 Bq/m3 and 269 Bq/m3), but also maximum values like 1070 Bq/m3 and 1231 Bq/m3. In the schools measured in Cluj-Napoca, the values obtained are variant, from 26 Bq/m obtained in "School nr. 21" from Mănăştur ward to 399 Bq/m3 obtained in "Grup Şcolar Transporturi" in Gheorghieni ward.

The radon measurements made in these schools contribute to a map of the Radon from the air for Romania, in order to establish for the future a maximum exposure admitted value for the population. It has been demonstrated that the lung cancer apparition risk due to Rn exposure is higher as the age is lower, that's why we have chosen placing the detectors in schools.

REFERENCES

1. A. S z a b o, Ape şi Gaze Radioactive în România. Editura Dacia, Cluj-Napoca, 1978, p245

2. C. C o s m a, D. R i s t o i u, C. C î n d e a, S. R â m b o i u, Season and building material influence on indoor radon concentration in houses from Transylvania, Studia Universitatis Babeş-Bolyai, Physica, XLVI, 1, 2001, pag. 42

3. T. A. P a v e l k o, I. P. L o s, Indoor 222Rn levels and irradiation doses on the territory of Ukraine. Radiation Measurements, 25, 595, 1995

4. G. P e r h a g e n, Z. L i a n g , et al., J. Residential radon exposure and lung cancer in Swedish women. Health Phys, 63, 179, 1991

5. C. M i l u, R.G h e o r g h e et al. Air exposure to radon and thoron daughters in Romanian houses. Rom J Biophys 1993; 3: 157-162