A survey of 222Rn concentrations in dwellings of the town of Metsovo in north-western Greece

Radon and radioactivity at a town overlying Uranium ores in northern Greece

Extensive measurements of (222)Rn in the town of Xanthi in N Greece show that the part of the town overlying granite deposits and the outcrop of a uranium ore has exceptionally high indoor radon levels, with monthly means up to 1500 Bq m(-3). A large number of houses (40%) in this part of the town exhibit radon levels above 200 Bq m(-3) while 11% of the houses had radon levels above 400 Bq m(-3). Substantial interannual variability as well as the highest in Europe winter/summer ratios (up to 12) were observed in this part of the town, which consist of traditional stone masonry buildings of the late 19th-early 20th century. Measurements of (238)U and (232)Th content of building materials from these houses as well as radionuclide measurements in different floors show that the high levels of indoor radon measured in these buildings are not due to high radon emanation rates from the building materials themselves but rather due to high radon flux from the soil because of the underlying geology, high radon penetration rates into the buildings from underground due to the lack of solid concrete foundations in these buildings, or a combination thereof. From the meteorological variables studied, highest correlation with indoor (222)Rn was found with temperature (r(2) = 0.65). An indoor radon prognostic regression model using temperature, pressure and precipitation as input was developed, that reproduced indoor radon with r(2) = 0.69. Hence, meteorology is the main driving factor of indoor radon, with temperature being the most important determinant. Preliminary flux measurements indicate that the soil-atmosphere (222)Rn flux should be in the range 150-250 Bq m(-2) h(-1), which is in the upper 10% of flux values for Europe.

Occupational exposure during remediation works at a uranium tailings pile

The aim of this study was to assess by different approaches the occupational exposure during the remediation of a tailings dam in an abandoned uranium mining site, with an area of about 13.3 ha and an estimated volume of 1.39 million m³. A hypothetical scenario was created in which the workers involved in the remediation activities were exposed to radiation through both internal and external pathways. It was intended to assess quantitatively the potential exposure of the workforce involved in the remediation works, focussing particularly on the inhalation of radon and on the gamma irradiation from the contaminated soil. Different methodologies were considered based on a deterministic and a probabilistic approach for dose assessment and risk assessment, respectively. The deterministic approach typically employs a highly "conservative" single value for each input parameter. The probabilistic approach employs sensitivity and uncertainty analysis of input parameters using probabilistic distributions of the sensitive parameters. The results indicate that annual effective dose limit for occupational exposure (worst scenario case created) may reach a significant fraction of occupational radiation protection limits. This is also stressed by the values obtained for the occupational risk estimated by Monte Carlo methodology using probabilistic distributions for the input parameters. The results also showed that the pathway with the highest dose does not necessarily correspond to the pathway with the highest risk. Nevertheless, it is well known that probabilistic analysis generally produces more realistic results.

Natural radioactivity measurements in the city of Ptolemais (Northern Greece)

Specific activities of the natural radionuclides (238)U, (226)Ra, (232)Th and (40)K were measured by means of gamma-ray spectrometry in surface soil samples collected from the city of Ptolemais, which is located near lignite-fired power plants. The mean activity values for (238)U, (226)Ra, (232)Th and (40)K were found to be 42+/-11, 27+/-6, 36+/-5 and 496+/-56 Bq kg(-1), respectively. These values fall within the range of typical world and Greek values for soil. The indoor radon concentration levels, which were also measured in 66 dwellings by means of SSNTD, ranged from 12 to 129 Bq m(-3), with an average value of 36+/-2 Bq m(-3). This value is close to world and Greek average values for indoor radon concentrations. The total effective dose due to outdoor external irradiation of terrestrial origin and to indoor internal irradiation from the short-lived decay products of (222)Rn was estimated to be 1.2 mSv y(-1) for adults, which is lower than the global effective dose due to natural sources of 2.4 mSv y(-1).

The effect of moisture content on radon diffusion through soil: assessment in laboratory and field experiments

The diffusion of radon through soil is strongly affected by the degree of water saturation of the soil pores. In the present work, a laboratory technique for studying radon diffusion has been developed and applied to determine diffusion coefficients in a sandy loam, containing various amounts of water, from null to saturation. The results indicate that, once the soil pore volume becomes saturated to values above approximately 20%, the diffusion of radon is markedly hampered; the bulk diffusion coefficient drops from 1.2 x 10(-6) to 2 x 10(-9) m2 s(-1) as soil saturation increases from 20 to 90%. The effect of soil moisture was further evaluated in field experiments conducted on soil of the same matrix. Comparison between results obtained by the two methods showed that laboratory studies may provide a good indication of radon diffusion coefficients to be expected in situ. However, values determined in the field were systematically lower than those assessed in the laboratory, illustrating the key role of structural differences between undisturbed and repacked soil.

Radon activity levels and effective doses in the Perama Cave, Greece

An investigation of atmospheric radon levels in the Perama Cave, North-western Greece, has been carried out using CR-39 detectors. The detectors were placed at various locations along the guided cave pathway and exposed during different sampling periods. Mean concentrations amounting to 925 +/- 418 and 1,311 +/- 352 Bq m-3 were recorded in the summer and winter months, respectively. As the Perama Cave is one of the most popular in Greece, attracting more than 85,000 tourists per year, the quantification of effective doses to staff and visitors was an issue of importance. Doses less than 5.1 microSv per visit were calculated for tourists and around 1.8 mSv y-1 for seasonal guides, employed for periods of high visiting frequency. The annual exposure of permanent guides was estimated to fall between 3 and 10 mSv, which is the range of action levels recommended by the ICRP.

Radon concentrations in some dwellings of Tunisia

Indoor air radon concentrations are still unknown in Tunisia. For the first time, they have been determined in several regions of the country using open alpha track dosimeters containing LR-115 film. Measurements were taken in 69 dwellings located around greater Tunis during 1 y, changing dosimeters every 2 mo. In 12 other locations, devices were placed during 2 winter months. The median of 1,217 measurements was 40 Bq m(-3) and 93.4% of them were less than 100 Bq m(-3). The highest concentration was 392 Bq m(-3). In Tunis, concentrations were higher during winter. Indoor air radon figures varied with geographic location: the highest values were found in Jendouba, Gafsa, Beja, and Tataouine government districts where phosphate and lead mines and deposits are present. This first study showed that indoor air radon concentrations are low in Tunisia, but further studies should be performed in localized areas, taking into consideration the geology, the climatic variations, and the building material.

Estimate of annual average radon concentration in the normal living area from short-term tests

Most residential radon guidelines refer to annual average radon concentration in the normal living area. However, decisions on whether a house needs mitigation are usually based on short term radon tests. Depending on where detectors are placed and when tests are performed, results of those measurements can differ significantly from the annual average radon concentration in the normal living area. We provide a practical method based on survey results in 5486 Canadian houses to estimate annual average radon levels from results of screening tests. The average ratio of radon concentration in the basement to that of the upper floors in a house is determined, and the average relative seasonal variations of radon levels in the basement and of the upper floors are identified. Based on these relative quantities, estimate factors are derived for four different combinations of detector location and the living area and tabulated for different calendar periods of radon testing. The annual average radon level can be estimated by multiplying the result of a short-term screening test with the appropriate estimate factor given in this study.

Soil gas radon: a tool for exploring active fault zones

The profile of soil gas radon was monitored in five active fault sites in northern and northwestern Greece. Measurements were carried out during summer months, using CR-39 solid state nuclear track detectors (SSNTDs). The spatial distribution of radon along lines traversing the fault zones revealed anomalies, clearly connected to the local tectonic structure. Specifically, increased radon signals evolved on the radon background level, in the vicinity of the faults' axes and the signal-to-background ratio ranged from 2 to 13. The consistency of this pattern confirms that the radon technique is powerful in the detection and mapping of active fault zones.

Indoor radon levels and influencing factors in houses of Patras, Greece

Measurements of indoor radon concentrations were performed in 28 low-rise houses and 30 apartments in Patras area from December 1996 to November 1997, using nuclear track detectors. The investigation was focused on the effects of season and floor number, as well as on the existence of a basement in low-rise houses on indoor radon levels. It was found that the differences in mean radon concentrations between adjacent seasons, in a number of 61 selected sampling sites distributed in 28 houses, were statistically significant. As expected, a maximum was found in winter and a minimum in summer. The differences in mean radon concentration on different floors of the same houses were also statistically significant and followed a linear decrease from underground to 2nd floor. In addition, indoor radon concentrations in the ground floor were found to be influenced by the existence or not of a basement. The average annual radon concentration was found to be 41 Bq m(-3) for the houses, 28 Bq m(-3) for the apartments and 38 Bq m(-3) for all the dwellings. These values lead to an average effective dose equivalent of 1.1, 0.7 and 0.9 mSv y(-1), respectively. Residents living on the underground in low-rise houses, during winter, where the average effective dose equivalent is 2.1 mSv y(-1), attain the higher risk.

Radon survey in Greece--risk assesment

A large scale radon survey using track etch detectors has been carried out from 1995 to 1998 in Greece in order to estimate the radon concentrations in Greek dwellings and the exposure of the Greek population to radon. The total data set consisted of 1,277 samples. Residential potential alpha energy concentration values ranged between (0.024 +/- 0.009) and (8 +/- 1) WLM per year (P < 0.05) and effective doses between (0.09 +/- 0.04) and (28 +/- 4) mSv (P < 0.05). The mean lifetime risk for the Greek population due to radon was found to be 0.4%.