Radiation Protection Dosimetry Advance Access published December 30, 2013 Radiation Protection Dosimetry (2013), pp. 1–4

doi:10.1093/rpd/nct346

RADON CONCENTRATIONS IN DIFFERENT TYPES OF DWELLINGS IN ISRAEL L. Epstein1,2,*, J. Koch1, T. Riemer1, I. Orion2 and G. Haquin1 1 Radiation Safety Division, Soreq Nuclear Research Center, Yavne 81800, Israel 2 Department of Nuclear Engineering, Ben-Gurion University of the Negev, Beer Sheva 84105, Israel *Corresponding author: [email protected]

The average radon concentration in Israeli dwellings was assessed by combining the results of a 2006 radon survey in singlefamily houses with the results of a 2011 radon survey in apartments of multistorey buildings. Both surveys were based on long-term measurements using CR-39 detectors. The survey in multistorey buildings was intended to assess the influence of recent practices in the local building industry on the radon concentrations. These practices include the use of building materials with higher concentrations of the natural radionuclides in the last 20 y than before, as well as the improvement in sealing techniques over that period. Another practice in place since the early 1990 s is the building of a shielded area in every apartment that is known as an RSS (residential secure space). The RSS is a room built from massive concrete walls, floor and ceiling that can be hermetically sealed and is intended to protect its residents from a missile attack. The influence of the above-mentioned features on radon concentrations was estimated by dividing the participating apartments into two groups: apartments in buildings >20 y, built using building materials with low concentrations of the natural radionuclides, regular sealing and without an RSS and apartments in buildings newer than 10 y, built using building materials with higher concentrations of the natural radionuclides, improved sealing and including an RSS. It was found that the average radon concentration in apartments in new buildings was significantly higher than in old buildings and the average radon concentration in single-family houses was significantly higher than in apartments in multistorey buildings. Doses due to indoor radon were estimated on the basis of the updated information included in the 2009 International Commission on Radiological Protection statement on radon.

INTRODUCTION Radon (222Rn), the only gaseous element in the 238U decay chain, has a sufficiently long half-life (3.825 d) that allows it to travel easily from its place of origin (the ground or the building materials) to the air. Radon accumulates in closed spaces like underground mines or inside buildings. It can reach relatively high concentrations in areas where high concentrations of 238 U and especially of its decay product, 226Ra, exist in the ground. In apartments in multistorey buildings (above the ground level) the main contributors to the radon concentration are the exhalation rate from the building materials and the ventilation rate(1). Radon is known as the main contributor to the exposure of the population to natural sources of ionising radiation. The exposure occurs as a result of the inhalation of the radon decay products which are attached to the aerosols in the air. Most of the dose comes from the alpha and beta particles emitted from the four short-lived decay products of radon: 218Po, 214 Pb, 214Bi and 214Po. A radon survey in single-family houses was performed in Israel and its results were published in 2006(2). The survey included almost 2000 dwellings and its goal was to determine the average radon concentration in single-family houses and to identify

radon-prone areas. The 2006 radon survey was based on long-term measurements using CR-39 solid-state nuclear track detectors (SSNTD). It was found that the average radon concentration in single-family houses is equal to 47 Bq m23 and that a correlation exists between the indoor radon concentration and the geological group on which the dwelling is built. In the present study results of a radon survey conducted in 2011 in apartments of multistorey buildings are presented. The results of the two surveys are then combined in order to assess the average radon concentration in Israeli dwellings and the annual dose to the population of Israel due to radon inhalation. METHODS The radon survey in multistorey buildings was intended to assess the influence of the recent practices in the local building industry on the radon concentrations. These practices include the use of building materials with higher concentrations of the natural radionuclides, in particular 226Ra, in the last 20 y than before. In addition, improvement in sealing techniques, as part of the tendency to build energy saving dwellings experienced in the last 20 y, reduced the ventilation rate in living spaces. Another practice since

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Received 27 August 2013; revised 1 December 2013; accepted 4 December 2013

L. EPSTEIN ET AL.

RESULTS In order to analyse the measurements, the CR-39 detectors were divided into three sub-samples: (1) detectors that were placed inside apartments in old buildings; (2) detectors that were placed inside the living/bed room of apartments in new buildings; (3) detectors that were placed inside the RSS of apartments in new buildings. The geometric means and the geometric standard deviation of the radon concentrations of the three subsamples are presented in Table 1. Figure 1 presents the distribution of radon concentrations in old and new buildings (in the living/bed rooms). Figure 2 shows the distribution of radon

Table 1. Average radon concentrations in old buildings, in RSS in new buildings and in living/bed rooms in new buildings.

Living/bed rooms in old buildings Living/bed rooms in new buildings RSS in new buildings

Geometric mean (Bq m23)

Geometric standard deviation

22.9

1.6

41.3

1.5

43.6

1.6

concentrations in RSS and in living/bed rooms in new buildings. It can be seen that the distribution of radon concentrations in Figures 1 and 2 approximate a log– normal distribution, as seen in the Israeli 2006 survey of single-family houses as well as in other national radon surveys(3). t-tests were performed in order to test the statistical significance of the differences between the sub-samples. It was found that a significant difference exists between the average radon concentration inside new and old buildings (P , 0.001). This confirms the assumption that the combined effect of the practices in new buildings (higher concentrations of 226Ra in the building materials, better sealing and the presence of an RSS) causes higher indoor radon concentrations. A paired t-test was conducted to assess the statistical significance of the differences between the radon concentrations in the RSSs and in the living/bed rooms of the same apartments. The test showed that there is a significant difference between the two subsamples with higher concentrations in the RSS ( p¼0.04). The assumption that the combination of the higher density of the building materials in the walls of the RSS, the higher 226Ra activity in the building materials and the improved sealing causes higher radon concentrations in RSSs than in the living/bed rooms was therefore confirmed. The difference between radon concentrations in single-family houses and apartments in multistorey buildings was also tested using a t-test and it was found to be significant (P , 0.001). It was found that the average radon concentration in Israeli dwellings, according to the distribution of the population in all dwelling types (single-family houses and apartments in old and new multistorey buildings), is equal to 31 Bq m23. The annual average dose to the population of Israel was estimated based on the average radon concentrations indoors and outdoors, the fraction of time spent indoors (0.8) and an equilibrium factor between the radon and its decay products (0.4 indoors(3) and 0.6 outdoors(3,4)). The average radon concentration outdoors was assumed to be 10 Bq m23(3,4). The conversion factor from radon concentration to dose that was used is based on the updated information included in the 2009 International Commission on Radiological Protection (ICRP) Statement on Radon(5). According to the statement, based on recent findings on the health effects attributable to exposure to residential radon, the effective dose per unit exposure to radon is higher by around a factor of 2 than previously thought. This increase results in an effective dose per unit exposure of 12 nSv per Bq h m23. Using this conversion factor, the annual average dose to the population of Israel due to radon inhalation was found to be 1.2 mSv. The dose calculation could be subject to change when a new dose coefficient is published by the ICRP.

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the early 1990s is the mandatory building of a shielded area in every apartment that is known as an RSS (residential secure space). The RSS is a room built from massive concrete walls, floor and ceiling that can be hermetically sealed and is intended to protect its residents from a missile attack. In many apartments the RSS is used as a bedroom. The combined influence of the above-mentioned features on the radon concentration was estimated by dividing the apartments participating in the survey into two groups: apartments in buildings older than 20 y, built using building materials with lower concentrations of 226Ra, regular sealing and without an RSS and apartments in buildings newer than 10 y, built using building materials with higher concentrations of 226 Ra, improved sealing and including an RSS. The measurements were conducted using CR-39 SSNTDs that were placed in one of the bedrooms or the living room for a minimal period of 3 months. A second detector was placed in the RSS of apartments in new buildings. A sample of 300 apartments throughout the country was selected to participate in the survey, onethird of which were in new buildings.

RADON CONCENTRATIONS IN ISRAELI DWELLINGS

Figure 2. The distribution of radon concentrations in RSS and in living/bed rooms in new buildings.

CONCLUSIONS The results of the 2006 radon survey in singlefamily houses in Israel were combined with the results of a recent survey of radon concentrations in multistorey buildings in order to assess the average dose to the population of Israel due to radon inhalation. It was found that the average radon concentration in apartments in new buildings was

significantly higher than in old buildings and the average radon concentration in single-family houses was significantly higher than in apartments in multistorey buildings. More research is needed in order to estimate the relative contribution of changes in the ventilation rate and in the 226Ra concentration in the building materials to changes in the radon concentration.

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Figure 1. The distribution of radon concentrations in old and new buildings (in the living/bed rooms).

L. EPSTEIN ET AL.

The average radon concentration in Israeli dwellings was found to be 31 Bq m23. The annual average dose due to radon inhalation was found to be 1.2 mSv.

FUNDING This work was partially supported by the Israeli National Coal Ash Board. REFERENCES

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1. Leung, J. K. C., Tso, M. Y. W. and Ho, C. W. Behavior of 222 Rn and its progeny in high-rise buildings. Health Phys. 75, 303– 312 (1998).

2. Haquin, G., Riemer, T., Margaliot, M., Shamai, Y., ShiravSchwartz, M. and Kenett, R. Radon survey of Israel. The 23rd Conference of the Nuclear Societies in Israel, 15–16 February 2006, Dead Sea, Israel. Dan Knassim Ltd. (2006). 3. UNSCEAR. Effects of ionizing radiation, UNSCEAR 2006 Report (2008). 4. Haquin, G., Riemer, T., Perrino, C., Lahav, D. and Margaliot, M. Atmospheric radon and radon decay products in Ashdod, Israel. Living with global changes in environmental sciences. In: Proc. Int. Conf. Israel Society of Ecological and Environmental Quality Sciences (ISEEQS), 30 May–1 June 2005, Rehovot, Israel (2005). 5. International Commission on Radiological Protection. Lung cancer risk from radon and progeny and statement on radon. ICRP Publication 115. Ann. ICRP 40(1). Elsevier (2010).

Radon concentrations in different types of dwellings in Israel.

The average radon concentration in Israeli dwellings was assessed by combining the results of a 2006 radon survey in single-family houses with the res...
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