ESTIMATION OF INDOOR RADON CONCENTRATIONS IN THE AIR OF RESIDENTIAL HOUSES AND MINES IN THE REPUBLIC OF MOLDOVA *

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1 ESTIMATION OF INDOOR RADON CONCENTRATIONS IN THE AIR OF RESIDENTIAL HOUSES AND MINES IN THE REPUBLIC OF MOLDOVA * I. URSULEAN, L. COREŢCHI, I. CHIRUŢĂ, S. VÎRLAN National Centre of Public Health, Chişinău, Republic of Moldova Received November 15, 2012 This study was conducted to review the latest research in radon problem carried out in the Republic of Moldova. The main aim of this paper was focused on the need for a National Radon Strategy (NRS) and a National Action Plan (NAP) for NRS implementation. Both NRS and NAP has to be correlated with other national policies, such as Smoking Reducing or Energy Efficiency. Development of a Radon Database including a map of radon concentrations, as well as a set of requirements for new housing construction, would be among the main components of NAP. Key words: air radon concentration, radon database. 1. INTRODUCTION Radon is a chemically inert radioactive gas. It is formed by the natural radioactive decay of uranium in rock, soil, and water. Naturally existing, low levels of uranium occur widely in Earth's crust. Radon is responsible for the majority of the mean public exposure to natural ionizing radiations [5]. Radon (55%) Natural sources (excluding Radon) (26%) Medical X- rays (11%) Nuclear Medicine (4%) Consumer Products (3%) Other (<1%) * Paper presented at the First East European Radon Symposium FERAS 2012, September 2 5, 2012, Cluj-Napoca, Romania. Rom. Journ. Phys., Vol. 58, Supplement, P. S291 S297, Bucharest, 2013

2 S292 I. Ursulean et al. 2 Radon gas from produces by natural sources can be accumulated in buildings, especially in confined areas such as basements. The radon concentrations in a building are dependent on the concentration of radium in subjacent ground and surrounding soil, geological bed rock, radioactivity of building materials, ventilation conditions, meteorological conditions and human activities. UNSCEAR Report (United Nations Scientific Committee on the Effects of Atomic Radiation, 2000) estimated the annual average dose per capita from natural sources amounting to 2.4 ms/year, radon contribution being about 55% (Fig. 1). Fig. 1 Annual average (dose ms/year) per capita from natural sources. It is well known that constant exposure to high concentration of radon gas may cause lung cancer [3, 4, 7, 8]. In accordance with the National Radiation Protection norms, a high indoor radon concentration for dwellings is considered the level which exceeds 150 Bqm -3 in new buildings and 200 Bqm -3 in old buildings [6]. 2. MATERIAL AND METHODS Measurements were made onto the soils surface with radiometer type RTM which has continuously air pumping mechanism (Fig. 2). Fig. 2 Measurement system scheme of radon concentration in soil.

3 3 Estimation of indoor radon concentrations in residential houses and mines S293 Determination of radon ( 222 Rn) concentration was performed by quantitative analysis of its short-lived decay products by means of ionization chamber. Due to the fact that some electrons are released during the emission of alpha particles resulting 218 Po nucleus acquires for a short time a positive charge. Positively charged ions accumulate under the influence of electric field on the surface of a semiconductor sensor. The number of 218 Po ions collected is proportional to the concentration of radon present in the air inside the enclosure. 218 Po is an unstable isotope with a half-life of 3.5 min, and the sensor can record only about half of the particles emitted from its decay, which are directed towards the sensor surface. The relationship between 222 Rn and 218 Po decays recorded can be determined after approximately 5 half-disintegration, i.e. after about 15 minutes, which is a minimum measurement interval for 222 Rn concentration. However, the decay chain is continued by 214 Pb, 214 Bi (beta particles) and 214 Po (alpha particles). This means that each of 218 Po decay produces further detectable 214 Po decay that occurs with a delay of about 3 hours, limited to the period of half-decay of these radio nuclides. The energy released as a result of 218 Po and 214 Po disintegration is different allowing the analysis of these nuclides by alpha spectroscopy. Radiometer RTM , used for the measurements, has two modes of measuring 222 Rn concentration Slow, taking into account not only the disintegration of 218 Po, but also 214 Po, and Fast, which provides only 218 Po decay calculation. Quick registration advantage is a reflection of the rapid concentration fluctuations, while the slow mode has a sensitivity of 2 times, which in turn reduces the statistical error of measurement according to the number of decays detected. For 222 Rn measurement in different rock types same activity unit treatment was applied, 30-minute air pump mode to continuously pump unit. Performing radon concentration measurements consist of removing various barriers that might influence radon emanation from soil and its accumulation in the metal room. The metal camera is designed to create a closed circuit, appliance connection are made through two tubes, one output and one input. Such device pumps air containing radon exhaled from the soil, which accumulate inside the metal room (Fig. 3). Fig. 3 Measurements with RTM radiometer.

4 S294 I. Ursulean et al Rn concentrations measurements were performed during on different soil types in the main cities of Moldova. 3. RESULTS AND DISCUSSIONS The results of radon concentrations monitoring in the air samples collected from different buildings placed on the territory of the Republic of Moldova between 1991 and 2011 are given in the paper. Investigations have concluded that the 222 Rn concentrations ( Bqm -3 ) in most cases do not exceed the reference level, with the exception in 1998 year when a level of about 1800 Bqm -3 have been detected (fig. 4). Fig. 4 Radon concentration (Bq/m 3 ) detected in the indoor air samples of different objects on the territory of Republic of Moldova. In 2007, 430 measurements were made in 61 rooms: unit housing (27), private house (2), socio-cultural monument (11), industrial building (21). It was established that Rn activity measurements presented values lower than 100 Bqm -3, 7 measurements had activities higher than 100 Bqm -3 while only in two locations were measured more than 200 Bqm -3. In 2008, 280 indoor measurements were made in 39 areas. Measurements have revealed values of 222 Rn activity less than 100 Bqm -3 in the majority of cases. Only 2 locations, representing 1% of all investigated houses within the territory of Republic of Moldova exceeds the level of 200 Bqm -3 for radon concentration (fig. 5).

5 5 Estimation of indoor radon concentrations in residential houses and mines S295 Fig. 5 The means of indoor 222 Rn activity, investigated during the years. The analysis of 222 Rn concentrations in air samples results from 294 cases demonstrate that the values recorded ranged between 15.0 Bqm -3 and Bqm -3. Our research reported the exceeding of the maximum allowable level of radon concentration indoor in two cases of 1993 (280 Bqm -3 and 368 Bqm -3 ), 10 cased in 1995 (from 201 Bqm -3 to 681 Bqm -3 ) and 3 cases in 1998 (from 212 Bqm -3 to 1930 Bqm -3 ) [1] (Table 1). Concentration, Table 1 The record of exceeded values of the 222 Rn concentrations The years and the number of the measurement Bq/m In the period of were performed measurements of 222 Rn concentrations in several stone mines from Cricova village and underground

6 S296 I. Ursulean et al. 6 galleries located on the territory of Chișinău and Mileştii Mici village. The air samples were collected from mines at different depths: 50 to 85 m. The study demonstrated that values of 222 Rn concentrations were classified within the acceptable limits, ranging from 92 Bqm -3 to Bqm -3 in the majority of cases. The overtaking (211.6 Bqm -3 ) was registered on in an underground gallery of Mileştii Mici village, at a depth of 70 m (Table 2). Table 2 The values of the 222 Rn concentrations detected in air samples stone mines and underground galleries located on the territory of Republic of Moldova Sampler place Concentration, Data of sampler Bqm -3 Underground gallery, Mileştii Mici, 70 m Underground gallery, Mileştii Mici, 60 m Underground gallery, Chişinău, 85 m Underground gallery, Chişinău, 50 m Stone mine No. 5, Cricova Industrial complex of stone mine extraction, Cricova The measurements of Radon concentrations made during the period of by German expert in the field of radon monitoring Dr. Thomas Streil (radiometer SARAD radon Scout nr.7, Radon Scout Plus Nr.84, SARAD Dose man Pro No.193, SARAD Myriam No.265) in underground galleries of Chişinău and Mileştii Mici village, in several mines of the Orhei Town, showed values exceeding the maximum allowable concentrations in all the samples of underground galleries, ranging between 200 Bqm -3 and 1800 Bqm -3 [2] (Fig. 6). Fig. 6 The concentrations of 222 Rn, detected in underground galleries of Chişinău and Mileştii mici village and in some mines of Orhei, 2006 year.

7 7 Estimation of indoor radon concentrations in residential houses and mines S CONCLUSIONS 1. The results require the need of radon concentrations monitoring carried out in dynamics, with the subsequent elaboration of the radon concentrations maps. It is necessary in developing of the maps to use 5 indicators: the indoor radon measurements, geology, and radioactivity in air, soil permeability and foundation type. The radon genesis is based on specific conditions, definite locality, to form the principles which are used in mapping of radon concentration. 2. The implementation of the extended national programme for radon monitoring in dwellings and the estimation of the public exposure from radon in different types of houses and building materials need to be more developed in the near future. 3. The implementation of the programme for mines monitoring and underground gallery workers are suggested. 4. The extension of the measurement areas together with evaluation of radon concentration in living houses and all existing working mines in the Republic of Moldova is necessary. REFERENCES 1. Coretchi, L., Bahnarel, I., Strail, T., Investigations of radon concentration in the Republic of Moldova. European Conference on Individual Monitoring of Ionizing Radiation, Athens, Greece, March, 8 12, p. 266, Coretchi, L., Streil, T., Bahnarel I., Radon mapping strategy in the Republic of Moldova. Third European IRPA Congress Abstracts. Helsinki, Finland, p. 80, European Commission JRC, Radon Prevention and Remediation (RADPAR) Project Recommendations, International Commission on Radiation Protection, Protection against radon-222 at home and work, ICRP Publication 65. Ann. ICPR, 23(2), James Mc Laughlin. Radon: past, present and future, First East European Radon Symposium, Cluj-Napoca, Romania, 2012, p Norme fundamentale de radioprotecţie. Cerinţe şi reguli igienice (NFRP-2000), Monitorul Oficial al R. Moldova nr.40-41/111 din Tomasek L., E. Kunz, T. Muller, J. Hulka, A. Heribanova, J. Matzner, V. Placek, I. Burian, J. Holecek. Radon exposure and lung cancer risk Czech cohort study on residential radon. Science of the Total Environment, Vol. 272 (1 3), 14 May 2001, p Всемирная Организация Здравоохранения. Радон и рак, Информационный бюллетень ВОЗ N 291, сентябрь 2009 г.