A combination study of indoor radon and in situ gamma spectrometry measurements in Greek dwellings

The aim of the present study was to investigate of a possible correlation between indoor radon and indoor gamma dose rates deduced by in situ gamma spectrometry measurements by using a portable HPGe detector. Indoor radon and high resolution in situ gamma spectrometry measurements were performed in 60 apartments in Thessaloniki, the second largest city of Greece. Geometric mean radon concentration is 52 Bq m(-3). The mean total absorbed dose rate in air due to gamma radiation is 56 +/- 9 nGy h(-1). The contribution of the different radionuclides to the total indoor gamma dose rate in air is 41% due to 40K, 36% due to the thorium series and 23% due to the uranium series. No correlation was found between indoor gamma dose rate due to the uranium series and indoor radon for ground and first floor apartments. For upper floor apartments (above the second floor) a weak correlation is observed. The mean annual effective dose due to radon is 1.15 mSv, i.e., more than four times higher compared to the effective dose due to gamma radiation (0.27 mSv).     

Study of a Greek area with enhanced indoor radon concentrations

In this paper the focus is on Arnea Chalkidikis, an area in Greece with granitic geological background and indications of possible elevated radon concentration indoors. Data are reported of indoor radon measurements with etched track detectors and those are used for dosimetric estimations. Moreover, data are reported on soil gas and soil radon concentrations in Arnea, as well as radon and uranium concentrations in water samples. From the measured radon concentrations in water samples the contribution to the overall dose has been calculated. For a period of 1 month, indoor radon and progeny activity has also been monitored in the dwelling that has the maximum indoor radon concentration in Greece. This dwelling is in Arnea and the dose delivered to the inhabitants has been calculated. The mean annual effective dose due to indoor radon was 4.5 mSv and about 11% of this was due to the use of water. Mean soil gas concentration and soil radon concentration were (90 +/- 30) kBq m(-3) (p<0.05) and (30 +/- 5) kBq m(-3) (p<0.05) respectively. Mean uranium concentration of the water samples was (98 +/- 13) mBq l(-1) (p<0.05).     

A comparison study between radon concentration in schools and other workplaces

The Nuclear Technology Laboratory of the Aristotle University of Thessaloniki has since 1999 an open research project of indoor radon measurements in Greek workplaces. Since now 1380 measurements in 690 workplaces have been performed. Most (75 %) of the workplaces were offices in schools. The remaining 25 % were offices, mainly in public buildings. In the present study, a possible correlation between radon concentration in schools and other workplaces is investigated and discussed.     

Simultaneous measurements of indoor radon, radon-thoron progeny and high-resolution gamma spectrometry in Greek dwellings

Simultaneous indoor radon, radon-thoron progeny and high-resolution in situ gamma spectrometry measurements, with portable high-purity Ge detector were performed in 26 dwellings of Thessaloniki, the second largest town of Greece, during March 2003-January 2005. The radon gas was measured with an AlphaGUARD ionisation chamber (in each of the 26 dwellings) every 10 min, for a time period between 7 and 10 d. Most of the values of radon gas concentration are between 20 and 30 Bq m(-3), with an arithmetic mean of 34 Bq m(-3). The maximum measured value of radon gas concentration is 516 Bq m(-3). The comparison between the radon gas measurements, performed with AlphaGUARD and short-term electret ionisation chamber, shows very good agreement, taking into account the relative short time period of the measurement and the relative low radon gas concentration. Radon and thoron progeny were measured with a SILENA (model 4s) instrument. From the radon and radon progeny measurements, the equilibrium factor F could be deduced. Most of the measurements of the equilibrium factor are within the range 0.4-0.5. The mean value of the equilibrium factor F is 0.49 +/- 0.10, i.e. close to the typical value of 0.4 adopted by UNSCEAR. The mean equilibrium equivalent thoron concentration measured in the 26 dwellings is EEC(thoron) = 1.38 +/- 0.79 Bq m(-3). The mean equilibrium equivalent thoron to radon ratio concentration, measured in the 26 dwellings, is 0.1 +/- 0.06. The mean total absorbed dose rate in air, owing to gamma radiation, is 58 +/- 12 nGy h(-1). The contribution of the different radionuclides to the total indoor gamma dose rate in air is 38% due to 40K, 36% due to thorium series and 26% due to uranium series. The annual effective dose, due to the different source terms (radon, thoron and external gamma radiation), is 1.05, 0.39 and 0.28 mSv, respectively.     

A passive radon dosemeter suitable for workplaces

The results obtained in different international intercomparisons on passive radon monitors have been analysed with the aim of identifying a suitable radon monitoring device for workplaces. From this analysis, the passive radon device, first developed for personal dosimetry in mines by the National Radiation Protection Board, UK (NRPB), has shown the most suitable set of characteristics. This radon monitor consists of a diffusion chamber, made of conductive plastic with less than 2 cm height, containing a CR-39 film (Columbia Resin 1939), as track detector. Radon detectors in workplaces may be exposed only during the working hours, thus requiring the storage of the detectors in low-radon zones when not exposed. This paper describes how this problem can be solved. Since track detectors are also efficient neutron dosemeters, care should be taken when radon monitors are used in workplaces, where they may he exposed to neutrons, such as on high altitude mountains, in the surroundings of high energy X ray facilities (where neutrons are produced by (gamma, n) reactions) or around high energy particle accelerators. To this end, the response of these passive radon monitors to high energy neutron fields has been investigated.     

Long-term measurements of radon equilibrium factor in Greek dwellings

The time variation of the radon equilibrium factor F was measured every four hours in the Nuclear Technology Laboratory of the Aristotle University of Thessaloniki (in northern Greece) during October 1998-April 1999. The time dependence of the mean weekly value of radon equilibrium factor F is relatively small. During October 1999-May 2000 the radon equilibrium factor was measured in 25 apartments randomly distributed in Thessaloniki. The mean value of the equilibrium factor F is 0.47 +/- 0.09, close to the typical value of 0.4 adopted by UNSCEAR.     

Status of the European indoor radon map

Since 2006 a European map of indoor radon (Rn) concentration is in the making. So far 20 countries have contributed with national data, allowing a fair coverage of parts of Europe. This paper presents the current (September 2010) state of the map, discusses its rationale, presents some statistical findings and addresses a few problems which arose during the work. It also briefly presents the European Atlas of Natural Radiation project, of which the Rn map will be part, and further, planned maps of environmental natural radioactivity.     

Hourly indoor radon measurements in a research house

This paper reports and discusses the behaviour of radon concentration with time in an uninhabited dwelling. The relationship between variations in radon concentrations and indoor-outdoor temperatures and wind intensity has also been discussed. Radon concentration was measured hourly in a house located at a height of 800 m in the Lombard Prealps, at the top of the Valassina valley. The wind velocity and indoor-outdoor temperatures were measured by means of a meteorological station located on the terrace of the house. The data were analysed using the LBL model for indoor-outdoor air exchange and the models for the indoor accumulation of radon due to exhalation from building materials and pressure-driven infiltrations located underground. The role of wind and indoor-outdoor temperatures were analysed. The agreement of measurements with modelling clearly demonstrates the importance of the different sources of indoor radon. As the investigation was conducted in an uninhabited house, the measurements were not affected by the behaviour of people, e.g. opening and closing of windows. Measurements of the outdoor atmospheric concentrations of (222)Rn provide an index of the atmospheric stability, the formation of thermal inversions and convective turbulence.     

The newest international trend about regulation of indoor radon

On the basis of recent epidemiological findings, many international and national organisations have revised their recommendations and regulations on radon exposure in dwellings and workplaces, or are in the process to do it. In particular, new recommendations and regulations were recently published (or are going to be) by World Health Organization, Nordic Countries, International Commission on Radiological Protection, International, Atomic Energy Agency (and the other international organisations sponsoring the International Basic Safety Standards), European Commission. Although with some differences, these new documents recommend lower radon concentrations in indoor air, especially in dwellings, compared with previous ones. Moreover, preventive measures in all new buildings are more and more considered as one of the most cost-effective way to reduce the radon-related lung cancers, compared with previous approach restricting preventive measures in radon-prone areas only. A comprehensive national action plan, involving several national and local authorities, is generally considered a necessary tool to deal with the many complex actions needed to reduce the risk from radon exposure in an effective way.     

Radon in workplaces: first results of an extensive survey and comparison with radon in homes

Extensive radon surveys have been carried out in many countries only in dwellings, whereas surveys in workplaces are rather sparse and generally restricted to specific workplaces/activities, e.g. schools, spas and caves. Moreover, radon-prone areas are generally defined on the basis of radon surveys in dwellings, while radon regulations use this concept to introduce specific requirements in workplaces in such areas. This approach does not take into account that work activities and workplace characteristics can significantly affect radon concentration. Therefore, an extensive survey on radon in different workplaces have been carried out in a large region of Italy (Tuscany), in order to evaluate radon distribution in workplaces over the whole territory and to identify activities and workplace characteristics affecting radon concentration. The results of this extensive survey are compared with the results of the survey carried out in dwellings in the same period. The workplaces monitored were randomly selected among the main work activities in the region, including both public and industrial buildings. The survey monitored over 3500 rooms in more than 1200 buildings for two consecutive periods of ～6 months. Radon concentration was measured by means of passive nuclear track detectors.     

Invariants of the Jacobi-Porstendorfer room model for radon progeny in indoor air

The Jacobi-Porstend?rfer room model, describing the dynamical behaviour of radon and radon progeny in indoor air, has been successfully used for decades. The inversion of the model-the determination of the five parameters from measured results which provide better information on the room environment than mere ratios of unattached and attached radon progeny-is treated as an algebraic task. The linear interdependence of the used equations strongly limits the algebraic invertibility of experimental results. For a unique solution, the fulfilment of two invariants of the room model for the measured results is required. Non-fulfilment of these model invariants by the measured results leads to a set of non-identical solutions and indicates the violation of the conditions required by the room model or the incorrectness or excessive uncertainties of the measured results. The limited and non-unique algebraic invertibility of the room model is analysed numerically using our own data for the radon progeny.     

Application of the advanced radon diagnosis methods in the indoor building environment

The health risk and dose calculations from exposure to indoor radon and its decay products are generally based on long-term integral measurements and standard ICRP recommendations. In this context, the results of assessments predicate more about human activities inside the building instead of a quality and an effectiveness of applied measures against the radon. The present paper is focused on a set of different measuring techniques and methods practically used for a classification of buildings regarding to the radon protection requirements. The fundamental quantitative and qualitative procedures of radon transport pathways and radon sources analysis, commonly named as radon diagnostic methods are performed in detail.     

Simulation of the concentrations and distributions of indoor radon and thoron

The technique of computational fluid dynamics (CFD) was used to study the concentrations and distributions of indoor radon (222Rn) and thoron (220Rn) as well as their progeny in three dimensions. According to the simulation results, in a naturally ventilated room, the activity distribution of 222Rn is homogeneous except for the places near air diffuser (supply and exhaust) locations. The concentration of 220Rn exponentially decreases with the distance from the source wall which is considered independently. However, as the ventilation rate increased, the concentrations of both 222Rn and 220Rn decreased and their activity distributions become complicated due to the effect of turbulent flow. It suggests that the impact factors of monitoring conditions (sampling site, airflow characteristics, etc.) should be taken into account in obtaining representative concentrations of 222Rn/220Rn for dose assessment. Both the simulation results of activities and their distributions agreed well with the experimental results in a laboratory room. It suggests that the CFD models may be applicable for the estimation of indoor 222Rn and 220Rn as well as their progeny.     

A representative survey of indoor radon in the sixteen regions in Mexico City

Mexico City, also called Federal District, covers an area of 1504 km(2), and has more than 8 million inhabitants. It is located more than 2200 m above sea level in a zone of high seismic activity, and founded on an ancient lake. At present it is one of the most crowded and contaminated cities in the world, with thermal inversions. Chemical contaminants and aerosol particles in the environmental air are high most of the year. Due to these geological, environmental and socioeconomic conditions, Federal District presents very peculiar characteristics, which are important for understanding the distribution and measurements of indoor radon concentration. In this work the results of 3 year (1998-2000) measurements of indoor radon levels in the Federal District are presented. For the detector distribution and measurements, the actual political administrative divisions of the Federal District, consisting of 16 very well defined zones, was used. Nuclear track detection methodology was selected for the measurement, with a passive device close-end-cup system with CR-39 (Lantrack) polycarbonate as the detection material, with one step chemical etching, following a very well established protocol developed at the Instituto de Física, UNAM. Calibration was carried out at the Oak Ridge National Laboratory, and verification at the Instituto de Física chamber. The results show that the arithmetical mean values of the indoor radon concentration for each region of the Federal District follow a non-homogenous distribution.     

Seasonal variation of indoor radon concentration in dwellings of Alexandria city, Egypt

Inhalation of radon ((222)Rn) and daughter products are a major source of natural radiation exposure. Keeping this in view, seasonal indoor radon measurement studies have been carried out in 68 dwellings belonging to 17 residential areas in Alexandria city, Egypt. LR-115 Type 2 films were exposed for four seasons of 3 months each covering a period of 1 y for the measurement of indoor radon levels. Assuming an indoor occupancy factor of 0.8 and a factor of 0.4 for the equilibrium factor of radon indoors, it was found that the estimated annual average indoor radon concentration in the houses surveyed ranged from 45 ± 8 to 90 ± 13 Bq m(-3) with an overall average value of 65 ± 10 Bq m(-3). The observed annual average values are greater than the world average of 40 Bq m(-3). Seasonal variation of indoor radon shows that maximum radon concentrations were observed in the winter season, whereas minimum levels were observed in the summer season. The season/annual ratios for different type of dwellings varied from 1.54 to 2.50. The mean annual estimated effective dose received by the residents of the studied area was estimated to be 1.10 mSv. The annual estimated effective dose is less than the recommended action level (3-10 mSv y(-1)).     

Assessment of test duration effect in indoor radon measurement by Monte Carlo simulations

To better understand the effect of various test durations on indoor radon measurement results in Canada, Monte Carlo simulations were performed for test durations of 1 month (30 d), 2 months (61 d), 3 months (91 d) and 6 months (183 d). For each of the specified test durations, a total of 1500 Monte Carlo simulations were performed. Each simulation was compared with the result of a 1-y measurement. On average, the radon concentration estimated from a 30-d test differed by about ±22 % from the value of a 1-y measurement. The difference reduced to about ±17 % for a 61-d test, ±14 % for a 91-d test and ±9 % for a half-year test. Health Canada's recommendation of a 3-month radon test performed during the heating season resulted in an estimated radon concentration, on average, ～20 % higher than the value determined from a 1-y measurement. This ensures a conservative estimate of the annual average radon concentration, as there is some risk at any radon level. Therefore, to avoid an underestimation of radon exposure and to ensure appropriate levels of precision and accuracy are met, the results from this study suggest that a radon measurement duration of 3 months or longer during the heating season (from October through to April) is needed.     

Anomalous indoor radon concentration in a dwelling in Qatif City, Saudi Arabia

An indoor radon survey was carried out recently in nine cities of Saudi Arabia using nuclear track detectors (NTD)-based passive radon detectors. The survey included Qatif City in the Eastern Province of Saudi Arabia, where 225 detectors were collected back successfully. It was found that the average indoor radon concentration in the dwellings was 22 +/- 15 Bq m(-3). However, one of the dwellings showed an anomalous radon concentration of 535 +/- 23 Bq m(-3). This finding led to a detailed investigation of this dwelling using active and passive techniques. In the active technique, an AlphaGUARD 2000 PRQ radon gas analyser was used. In the passive technique, CR-39 based passive radon detectors were used in all the rooms of the dwelling. Radon exhalation from the wall and the floor was also measured using the can technique. The active measurement confirms the passive one. Before placing the passive radon detectors in all the rooms of the two-storey building, the inhabitant was advised to ventilate his house regularly. The radon concentration in the different rooms was found to vary from 124 to 302 Bq m(-3). Radon exhalation from the floor and the wall of the room with the anomalous radon concentration was found to vary from 0.5 to 0.8 Bq m(-2) h(-1). These low radon exhalation rates suggest that the anomalous radon concentration is most probably due to underground radon diffusion into the dwelling through cracks and joints in the concrete floor.     

Regional variations pattern of indoor radon levels in some areas of Punjab and Haryana

The indoor radon concentration levels and their regional variationspattern, for two consecutive half-year periods, in a wide rangeof dwellings of some regions of Punjab and Haryana states havebeen studied. The objective was to find the relation betweenthe variations of indoor radon levels with the sub-soil andlocal geology, type of building materials utilised in the dwellingsof the region. Keeping this in view, indoor radon measurementshave been carried out in the dwellings of 30 villages aroundthe Tusham Ring Complex, Bhiwani district, Haryana, known tobe composed of acidic volcanics and associated granites, alongwith 11 villages of Amritsar District, Punjab. The indoor radonconcentration in the dwellings around Tusham (Haryana) was foundto vary from 120 ± 95 to 915 ± 233 Bq m^–3,whereas radon levels varied from 60 ± 37 to 235 ±96 Bq m^–3 for the dwellings studied in Punjab. We believethat local geology including embedded granitic rocks, and sub-soil,as well as building materials having higher radioactive content,is the major contributor for the higher indoor radon levelsobserved particularly in the dwelling around Tusham Ring complex,where some dwellings are showing higher radon concentrationsthan the ICRP recommendations. The environmental samples fromsome areas of Punjab state and around the Tusham Ring Complexof Haryana state have also been analysed for radon exhalationstudies. Higher values for radon exhalation rates have beenobserved for the Tusham's soil/rock specimens, as compared withsoil samples of the Amritsar region of Punjab.     

A study of indoor radon levels in rural dwellings of Ezine (Canakkale, Turkey) using solid-state nuclear track detectors

Indoor radon activity level and radon effective dose (ED) rate have been carried out in the rural dwellings of Ezine (Canakkale) during the summer season using Radosys-2000, a complete set suitable to radon concentration measurements with CR-39 plastic alpha track detectors. The range of radon concentration varied between 9 and 300 Bq m(-3), with an average of 67.9 (39.9 SD) Bq m(-3). Assuming an indoor occupancy factor of 0.8 and 0.4 for the equilibrium factor of radon indoors, it has been found that the 222Rn ED rate in the dwellings studied ranges from 0.4 to 5.2 mSv y(-1), with an average value of 1.7 (1.0) mSv y(-1). There is a possibility that low radon concentrations exist indoors during the summer season in the study area because of relatively high ventilation rates in the dwellings. A winter survey will be needed for future estimation of the annual ED.     

Analysis of the main factors affecting the evaluation of the radon dose in workplaces: the case of tourist caves

High concentrations of radon exist in several workplaces like tourist caves mainly because of the low ventilation rates existing at these enclosures. In this sense, in its 1990 publication, the ICRP recommended that high exposures of radon in workplaces should be considered as occupational exposure. In developed caves in which guides provide tours for the general public great care is needed for taking remedial actions concerning radon, because in some circumstances forced ventilation may alter the humidity inside the cave affecting some of the formations or paintings that attract tourists. Tourist guides can work about 1900 h per year, so the only option to protect them and other cave workers from radon exposure is to apply an appropriate system of radiation protection mainly based on limitation of exposure by restricting the amount of time spent in the cave. Because of the typical environmental conditions inside the caves, the application of these protecting actions requires to know some indoor air characteristics like particle concentration, as well as radon progeny behaviour in order to get more realistic effective dose values In this work the results of the first two set of radon measurements program carried out in 10 caves located in the region of Cantabria (Spain) are presented.