Theses of PhD dissertation DETERMINATION OF PARAMETERS THAT INFLUENCE THE INDOOR RADON LEVEL

Theses of PhD dissertation DETERMINATION OF PARAMETERS THAT INFLUENCE THE INDOOR RADON LEVEL MIHÁLY MINDA Chemistry and Environmental Sciences Doctoral School Advisor: DR. JÁNOS SOMLAI university lecturer University of Pannonia Radiochemistry Department Veszprém, 2009

l. Premises The radioactive gas radon is the most important natural source of human exposure to ionizing radiation. Present epidemiological researches show that the excess relative risk per 100 Bq/m 3 increase in the observed radon concentration was 0.08 (Darby et al., 2006). The indoor radon surveys started in the 1970ies all over the world. In most countries seasonal (about 3 months) measuring periods were used. The determination of the annual indoor radon activity concentration (indoor radon level) was formed shorter than one year s measuring results, experiences and statistical analysis (Wrixon et al. 1988; Pinel et al. 1995; Miles, 2001, Bochicchio et al. 2005, Karpinska et al. 2004) One of the most important aims was to find parameters that can predict higher than average radon activity concentrations in an area. It was recognized almost at the beginning of radon surveys that the highest radon levels are mainly caused by geological formations under the houses (Gunby et al. 1993, Hámori et al. 2006; Keller et al. 1992; Mose et al. 1992, Somlai et al. 2006a). But some parameters of the house structure (Arvela 1995; Gunby et al. 1993; Levesque et al. 1997, Hunter et al. 2005, Bossew et al. 2007, Kemski et al. 2006, Mireles et al. 2007, Somlai et al. 2006b) and the way of life (Katona et al. 2004, 2005, Orlando et al. 2004, Bossew et al. 2007) can also influence the radon levels. Radon Map can be prepared, which could be useful for professionals and municipalities, for efficiently finding areas at which high concentrations of indoor radon frequently occurs. The Joint Research Center of the European Union intends to map Europe concerning the indoor radon, using the measured yearly averages of radon activity concentrations (The 8 th International Workshop on the Geological Aspects of Radon Risk Mapping, Prague, 2008). The RAD Laboratory (founded in 1992) measured the radon activity concentrations in almost all the homes in Mátraderecske between 1992-1994. The nationwide radon survey started in 1994, and the work still continues in these days. The RAD Laboratory has measured the annual mean of radon activity concentrations, i.e. radon level in more than 19 000 Hungarian homes between 1994 and 2008 (Hámori et al., 2006). I work at RAD Laboratory from 2005. In the first year my tasks were the distribution, collection, etching, and counting of tracks of the detectors. Then I took part in the organizations of the public relation of the RAD Laboratory, I gave lectures with demonstrations in the settlements before the detector distributions, and I prepared and directed the students laboratory works. 13 325 houses were also known by structures. Their analysis started in autumn 2005. The present PhD dissertation introduces the methods, the results and the discussion of this analysis. 2. Aims To survey all of the houses in Hungary is impossible due to financial problems, but it would be also insensate from the professional point of view. International and national surveys show that there are houses in which low indoor radon level are very probable. The most effective approach is using the large database of the measured dwellings to discover the parameters which influence the indoor radon level. During my work the measurements and the analysis of the Hungarian indoor radon levels had the following aims: 1. To set data s of the 13 325 houses, which were known by structures, into the database. 2. To identify whether in which cases are acceptable the estimation of the indoor radon level; cases: from one or from two or from three measured seasonal radon activity concentrations. 3. To determine those parameters that influences the indoor radon level. 4. To map indoor radon of Hungary. 3. Methods 3.1. Measurement The indoor radon activity concentrations were measured by closed CR-39 track detectors, the detector container being a plastic cylinder with a threaded cap (diameter 4 cm, height 6 cm). In a given room, the radon activity concentration was measured three times, each measurement lasting about 3 months (autumn, winter, and spring). The radon level was calculated from the three (rarely two) seasonal measured radon activity concentrations. (Because of the too large error radon levels were not determined in dwellings from where we had only one seasonal data.) 3.2. Sample taking The rooms sampled were based on volunteers, where local physics teachers facilitated the distribution of samplers. 3.3. Estimation of the indoor radon level A whole year (four seasons) radon survey was made in 628 dwellings of Mórágyblock. Using a strict mathematical statistical procedure I made comparison between the real indoor levels and the estimated indoor radon levels which originated from one or two or three measured seasonal radon activity concentrations, using this survey s data. 1 2

I introduced the Borak-factor (Borak et al., 1989), which gives the ratio of the houses where the absolute values of the difference of the estimated radon levels and the real radon level is not larger than the 50% of the real radon level. 3.4. Determination of parameters that influence the indoor radon level If the set of dwellings were homogenous from the point of view of geology, of the house structure and of the life style of inhabitants, then the distribution of dwellings on the radon levels can be approximated by lognormal distribution (Miles, 1998a; Miles 1998b, Minda et al., 2009). 13 325 dwellings were grouped according to all kinds of known parameters. Hungary was divided into geological units by the help of geologists. All of the statistical parameters of the groups were given, such as number of houses of the group, the maximum, the minimum, the arithmetic mean, the arithmetic standard deviation, the geometric mean, the geometric standard deviation of the indoor radon level, and the indoor radon index of the group. Indoor radon index is the ratio of the measured houses above 200 Bq/m 3 within the group. I elaborated a mathematical statistical procedure to determine the indoor radon index and its error. The radon index and its error made the groups comparison and the parameters determination which dominantly influence the indoor radon level possible. 3.5. Radon maps Radon maps of Hungary were drawn of different topography (counties, grids, geological units) and different values (maximum, average, indoor radon index). 4. Results and theses 1. To estimate the annual mean of indoor radon activity concentration measurements are required at least in three seasons: autumn, winter and spring. International recommendations on areas with similar climate to Hungary should use the three measured seasonal radon activity concentrations to estimate the annual mean. 2. I devised a mathematical statistical procedure to determine the indoor radon index and its error. By the help of this procedure on the basis of 19 710 measured houses data I proved that a) the geological formation under the house, the room s level, the housetype (one- or many-storied), the basement under the room and the wall s materials dominantly influence the indoor radon level. b) the isolating material under the room, the wall covering, number of the doors of the room, the distance of the detector from the floor, the room s heating-length during winter, the fuel used for heating, the heating-apparatus, the mode of the ventilation of the room don t influence the indoor radon level significantly. c) the highest indoor radon levels can be observed and also expected in the one-storied, no-basement, adobe houses built on the bedrock of volcanic rocks, of granites bodies and on young sedimentary formations with high concentrations of radium. 3. I made radon maps of Hungary on different topography (counties, geological units and 10 10 km grid), rendering the different values (maximum, mean, indoor radon indexes) of the measured houses in the units. These radon maps are used in the database of the European Joint Research Center and in the 2006 and 2007 annual reports of OKSER (Fig. 1) Figure 1. The indoor radon indexes of one-storied, no basement houses in geological units 1 Vas-Zalai dombság; 2 Kisalföld; 3 Bakony; 4 Mórágyi rög, Tolna; 5 Nagyalföld, Heves; 6 Sajóhidvég; 7 Nagyalföld, Szabolcs-Szatmár; 8 Nagyalföld, Pest- Budapest; 9 Nagyalföld, Bács-Kiskun, Csongrád; 10 Mezőföld; 11 Északidombság; 12 Nagyalföld, Békés; 13 Vértes-Pilis-Budai hegység; 14 Baranya- Somogy-Tolnai dombság; 15 Bükk; 16 Mórágyi rög, Baranya; 17 Velencei hegység; 18 Mátra; 19 Sajó-Hernád völgy; 20 Börzsöny; 21 Cserhát; 22 Zemplén; 23 Mecsek. 3 4

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