RADON EXHALATION FROM BUILDING MATERIALS USED IN YEMEN

RADON EXHALATION FROM BUILDING MATERIALS USED IN YEMEN Abstract The present article seeks to determine the annual effective doses of 222Rn exposure, effective radium content and radon exhalation rates in some building materials from the local market of Ibb province, Yemen. A total of 33 samples of building materials were collected from the target area. The radon exhalation rate and effective radium content in these samples were measured using solid-state nuclear track detector, which has become an important tool in every investigation of the radon levels in the surrounding environment. Surface exhalation rate has been found to vary from 178.90 to 1267.6 mBq m−2 h−1, whereas mass exhalation rate has been found to vary from 5.51 to 33.25 mBq kg−1 h−1. All the values of effective radium content in all samples under test were found to be quite lower than the permissible value of 370 Bq kg−1 recommended by Organization for Economic Cooperation and Development. Annual effective doses have also been estimated. INTRODUCTION Radioactivity is widely spread in the earth’s environment and it is found in various geological formation, e.g. soils, rocks, plants, water and air(1, 2). Most building materials derived from soil and rocks contain the natural radionuclides such as uranium (238U) and thorium (232Th) and their daughter products and singly occurring potassium (40K)(3). Concentrations of radionuclides present in building materials vary depending upon the local geology of each region in the world(4, 5). The building industry also uses large amounts of waste from other industries(6). These radioactive elements are sources of three radioactive decay series. Radon gas is one of the decay products of these series. It consists of three isotopes, namely: (1) 222Rn (called radon, belongs to 238U decay series); (2) 220Rn (called thoron, belongs to 232Th decay series); and (3) 219Rn (called action, belongs to 235U decay series). 222Rn has 3.82 days half-life, whereas 220Rn (55.6 s) and 219Rn (3.96 s) have much shorter half-lives than 222Rn. That is why 220Rn and 219Rn are given less importance in environmental studies(7, 8). Radon (222Rn), as an emitter of α-particles with energy 5.48 MeV, is the most crucial and dangerous radioactive gaseous element in the science of environmental radioactivity(9, 10). Most individuals spend more than 80% of their time indoors and the rest is spent on outdoor activities. The internal and external radiation exposure from building materials creates prolonged exposure situations(11). The external radiation exposure is caused by the gamma emitting radionuclides, which in the uranium series mainly belongs to the decay chain segment starting with 226Ra. The internal (inhalation) radiation exposure is largely due to 222Rn, and marginally to 220Rn, and their short lived decay products(12). The study of alpha activity in building materials is very important because alpha radiation is 1000 times more carcinogenic than gamma radiation(4). The noble gas 222Rn, although not so noble in its health hazard effect, is chemically inert and can move through the Earth and structural materials(9, 10). Once the radon atoms are formed by the decay of the parent 226Ra, they move either by diffusion or by transport mechanisms or by both(13, 14). Radon exhalation is a complex phenomenon depending upon a number of parameters such as effective radium content in soil, soil morphology, soil moisture, vegetation, temperature, atmospheric pressure, rainfall and soil grain size(15). The amount of the produced radon from the grains that finally enters by recoil effect and diffusion process in the porous system of the material is defined as ‘effective radium content’(16). Recently, several interesting studies of people exposed to radon have confirmed that radon in homes and workplaces represent a serious health hazard(3, 17, 18). The exposure of people to high concentrations of indoor radon for long periods causes pathological effects and functional respiratory changes, which consequently lead to an increased risk of developing lung cancer(19–21). The aim of this study is to determine the annual effective doses of 222Rn exposure, effective radium content and radon exhalation rates in some building materials from local market of Ibb province in Yemen by solid-state nuclear track detectors (CR-39). Such studies can be useful for keeping reference records and developing data panels to ascertain changes in the environmental radioactivity due to nuclear, industrial and other human activities over time(22). Ibb province is located between Thamar and Taiz provinces. The capital city of Ibb province is ~193 km to the south of Sana’a, the capital city of Yemen. Figure 1 shows Ibb’s location(23). The province has a total area of 5383 km2 and it is located at latitude 13°58′48″ and longitude 44°10′48″(24). Figure 1. View largeDownload slide Map showing the study area in Ibb(23). Figure 1. View largeDownload slide Map showing the study area in Ibb(23). MATERIALS AND METHODS For the purposes of this study, a total of 33 samples of building materials were collected from different companies and stores in Ibb, comprising 15 slab samples and 18 porous powdery building material samples. The concentration and exhalation rate of radon have been determined using CR-39 detectors because of their ability to register tracks at different levels of sensitivity(25–27). The CR-39 polymer sheets of TASTRAK were produced and provided by Track Analysis Systems Ltd. (TASL), Bristol, UK. The polymeric detector samples, for the present study, were cut to a size of 1.5 × 1.5 cm2 and adhered to a plastic can of known dimension (7 cm in diameter and 11 cm in height)(28–31). To avoid the track contribution from thoron in the can, the CR-39 detectors were kept at distance ~7 cm or more from the sample in accordance with the protocol(32–36). This is because the half-life time of 220Rn (55.6 s) is ~0.00017 that of radon 222Rn (3.82 d). This shows that most of the thoron will decay inside the building material and radon diffusion length, so that, thoron would be still in the order of 2 or 3 cm(37–39). Two types of experiments for measurement of radon exhalation rates of building materials were used: The container was placed inversely on the surface of the tile samples of building materials. These samples were washed, cleaned, dried and used without crushing as used naturally. The contact between the chamber and the building material parts was sealed with silicon(40). The powder samples were dried in an oven at a temperature of 80°C for 24 h to remove all the moisture content(19, 27), crushed to fine grain size (100 μm)(20). Then each sample of 125 g weight was placed at the bottom of a cylindrical sealed can. The mouth of the cylindrical can was sealed with a cover and fitted with CR-39 plastic track detectors at the top inner surface so that they were facing the specimen(14, 41, 42). The cover was sealed by silicon and duct tape from the outside in order to avoid radon leakage(43). The sample was left for 1 month to allow radioactive equilibrium to reach between 226Ra, 222Rn and their decay products. Furthermore, in order to ensure the radioactive equilibrium of 226Ra, 222Rn and their decay products, it is important to ensure that no 222Rn is lost from the sample container(20, 44). During the exposure period of 3 months(10, 15), the sensitive side of the detector is exposed freely to the emergent radon from the sample in the can so that it could record the tracks of alpha-particles resulting from the decay of radon. At the end of the expose time, the detectors were removed and chemically etched for 9 h in 6.25 N NaOH at 70 ± 1°C(21). After this chemical treatment, these CR-39 solid-state nuclear track detectors were washed in distilled water in order to stop the chemical reaction, dried in air and the tracks were counted using an optical microscope at a magnification of ×400. The mass exhalation and surface exhalation rate of radon were obtained from the following expressions(10, 31, 45):   EA=CλRnVA[T+(1/λRn(e−λRnT−1))] (1)  EM=CλRnVM[T+(1/λRn(e−λRnT−1))] (2)where, EA is the surface exhalation rate (Bq m−2 h−1), EM is the mass exhalation rate (Bq kg−1 h−1), C is the integrated radon exposure (Bq m−3 h), A is the total surface area of the building material sample from which radon is exhaled (3.85×10−3m2), V is the effective volume of the emanation container or can (m3), M is the mass of the powder sample (0.125 kg), λRn is the decay constant of radon (h−1) and T is the exposure time in hour. The risk of lung cancer from domestic exposure due to radon and its daughter nuclides can therefore be computed directly from the effective dose equivalents. The radiation hazards due to radon and its daughters are calculated from the radon exhalation rates of building material samples. The contribution of indoor radon concentration from building materials can be calculated from the following relation(46):   C¯Rn=EA×S(λRn+λV)×Vr (3)where, C¯Rn is radon concentration in construction materials contributing to indoor radon, Vr is the room volume (m3) and λV is air exchange rate (h−1). In these calculations, the maximum radon concentration from building materials was assessed by assuming the room to be a cavity with the ratio S/Vr = 2.0 m−1, where S and Vr are the internal surface area and volume of the room, respectively, and the air exchange rate λV was taken to be 0.5 h−1(47, 48). The annual effective doses of 222Rn exposure were estimated using the following equation(49):   ERn=C¯Rn×Fe×Ta×DRn (4)where, ERn is the annual effective dose of 222Rn (Sv y−1), Ta is the annual work time = 7000 hy−1, DRn the dose conversion factor for 222Rn decay products [Sv/Bq h m−3 (EERC)] and Fe is the equilibrium factor. The value of Fe was assumed to be 0.4(49). The effective radium content was measured for the same samples using CR-39 detectors because of its capability to register tracks at different levels of registration sensitivity(10, 31, 50). After the sealing of the can, the activity concentration of radon begins to increase with time T as follows(10, 51):   CRn=CRa(1−e−λRnT) (5)where, CRa is the effective radium content(10, 31, 34, 52) of the building material sample. Also CRa is called the effective radium concentration(53, 54), as this is the fraction of total radium which contributes to radon exhalation(55). The effective radium content was calculated by using the following relation(15, 56):   CRa(Bqkg−1)=hρAKTeM (6)where, h is the distance between the detector and the top of the solid sample, ρ is the radon track density (track cm−2), K is the calibration factor for radon (0.16 track cm−2d−1/Bq m−3) which was calibrated in previous work(57) and Te is the effective exposure time (in days), which is related to the actual exposure time T and decay constant for 222Rn according to the following equation(58, 59):   Te=[T−1λRn(1−e–λRnT)] (7) The exposure time, in these measurements, was 90 days. Radon exhalation from the building materials contributes towards indoor radon. In this regard, previous studies have been carried out in different parts of the world and extensive data are available in the literature. In the current survey, most of the houses in the studied area are built of blocks (mixtures of cement sand and gravel aggregates in definite proportions). Some of the houses were made up of bricks and Sand and most of them also contain interior decoration made of ceramics, gypsum, marble and granite. These houses are in fact constructed on the Earth’s crust, which is essentially composed of rocks and soil. RESULTS AND DISCUSSION The surface radon exhalation rates from the solid slab samples ranged from 275.24 ± 5.43 to 1267.6 ± 11.84 mBq m−2 h−1, with a mean of 661.69 ± 8.56 mBq m−2h−1, whereas the surface exhalation rates from the powdery samples ranged from 178.90 ± 6.76 to 1079.53 ± 9.70 mBq m−2 h−1, with a mean of 462.46 ± 10.02 mBq m−2h−1. The mass radon exhalation rates from the powdery samples ranged from 5.51 ± 0.2 to 33.25 ± 0.30 mBq kg−1h−1 with a mean of 4.24 ± 0.31 mBq kg−1 h−1. The values of exhalation rates of building materials vary from one building material to another. This variation can be attributed to the difference in the nature of the samples, and effective radium content in the samples. To estimate the contribution of building materials to indoor radon concentrations(10), a room with an air exchange rate of 0.5 h−1 was assumed as mentioned above. The radon concentration contribution to indoor radon in the room due to exhalation from the solid slab samples building materials was found to range from 1.10 ± 0.02 to 5.07 ± 0.05 Bq m−3, with a mean of 2.65 ± 0.03 Bqm−3 (Table 1). The smallest accumulated radon concentration per day in a room with its entire floor and walls decorated with M2, denoting Yemen marble, would be 26.42 Bq m−3. Thus, on average, the sample M2 would contribute only slightly to the radon concentration in Yemen homes. On the other hand, the largest accumulated radon concentration per day was 121.656 and 103.634 Bq m−3 for samples Gra1 and Gra2, denoting Yemen granite and china granite, respectively. Table 3. Radon contribution to indoor radon, surface and mass exhalation rates, annual effective doses and effective radium content, together with the statistical uncertainties (1σ) for the powdery different building material samples. S. no.  Sample ID  Size (cm3)  Radon surface exhalation rate (mBq m−2 h−1)  Radon contribution (Bq m−3)  Radon mass exhalation rate (mBq kg−1 h−1)  Effective radium content (Bq kg−1)  Annual effective dose (μSv y−1)  1  C1  342.65  207.96 ± 7.88  0.83 ± 0.03  6.40 ± 0.24  0.69  20.96  2  C2  338.80  243.12 ± 6.07  0.97 ± 0.02  7.49 ± 0.19  0.79  24.51  3  C3  338.80  507.66 ± 10.73  2.03 ± 0.04  15.64 ± 0.33  1.66  51.17  4  WC1  338.80  276.76 ± 6.07  1.11 ± 0.02  8.52 ± 0.19  0.90  27.90  5  WC2  342.65  455.67 ± 10.85  1.82 ± 0.04  14.03 ± 0.33  1.50  45.93  6  WC3  342.65  553.53 ± 9.39  2.21 ± 0.04  17.05 ± 0.29  1.83  55.80  7  Sa1  346.50  178.90 ± 6.76  0.72 ± 0.03  5.51 ± 0.21  0.60  18.03  8  Sa2  346.50  428.14 ± 10.41  1.71 ± 0.04  13.19 ± 0.32  1.43  43.16  9  Sa3  346.50  339.46 ± 6.62  1.36 ± 0.03  10.45 ± 0.20  1.13  34.22  10  Sa4  346.50  633.04 ± 35.51  2.53 ± 0.14  19.50 ± 1.09  2.11  63.81  11  Sa5  346.50  463.31 ± 6.76  1.85 ± 0.03  14.27 ± 0.21  1.55  46.70  12  Gy1  331.10  325.70 ± 6.76  1.30 ± 0.03  10.03 ± 0.21  1.04  32.83  13  Gy2  327.25  441.91 ± 10.98  1.77 ± 0.04  13.61 ± 0.34  1.39  44.54  14  Gr1  327.25  526.01 ± 7.22  2.10 ± 0.03  16.20 ± 0.22  1.66  53.02  15  Gr2  346.50  449.55 ± 8.62  1.80 ± 0.03  13.85 ± 0.27  1.50  45.31  16  Gr3  342.65  474.02 ± 10.52  1.90 ± 0.04  14.60 ± 0.32  1.57  47.78  17  So1  342.65  740.08 ± 9.57  2.96 ± 0.04  22.79 ± 0.29  2.44  74.60  18  So2  342.65  1079.53 ± 9.70  4.32 ± 0.04  33.25 ± 0.30  3.56  108.82  S. no.  Sample ID  Size (cm3)  Radon surface exhalation rate (mBq m−2 h−1)  Radon contribution (Bq m−3)  Radon mass exhalation rate (mBq kg−1 h−1)  Effective radium content (Bq kg−1)  Annual effective dose (μSv y−1)  1  C1  342.65  207.96 ± 7.88  0.83 ± 0.03  6.40 ± 0.24  0.69  20.96  2  C2  338.80  243.12 ± 6.07  0.97 ± 0.02  7.49 ± 0.19  0.79  24.51  3  C3  338.80  507.66 ± 10.73  2.03 ± 0.04  15.64 ± 0.33  1.66  51.17  4  WC1  338.80  276.76 ± 6.07  1.11 ± 0.02  8.52 ± 0.19  0.90  27.90  5  WC2  342.65  455.67 ± 10.85  1.82 ± 0.04  14.03 ± 0.33  1.50  45.93  6  WC3  342.65  553.53 ± 9.39  2.21 ± 0.04  17.05 ± 0.29  1.83  55.80  7  Sa1  346.50  178.90 ± 6.76  0.72 ± 0.03  5.51 ± 0.21  0.60  18.03  8  Sa2  346.50  428.14 ± 10.41  1.71 ± 0.04  13.19 ± 0.32  1.43  43.16  9  Sa3  346.50  339.46 ± 6.62  1.36 ± 0.03  10.45 ± 0.20  1.13  34.22  10  Sa4  346.50  633.04 ± 35.51  2.53 ± 0.14  19.50 ± 1.09  2.11  63.81  11  Sa5  346.50  463.31 ± 6.76  1.85 ± 0.03  14.27 ± 0.21  1.55  46.70  12  Gy1  331.10  325.70 ± 6.76  1.30 ± 0.03  10.03 ± 0.21  1.04  32.83  13  Gy2  327.25  441.91 ± 10.98  1.77 ± 0.04  13.61 ± 0.34  1.39  44.54  14  Gr1  327.25  526.01 ± 7.22  2.10 ± 0.03  16.20 ± 0.22  1.66  53.02  15  Gr2  346.50  449.55 ± 8.62  1.80 ± 0.03  13.85 ± 0.27  1.50  45.31  16  Gr3  342.65  474.02 ± 10.52  1.90 ± 0.04  14.60 ± 0.32  1.57  47.78  17  So1  342.65  740.08 ± 9.57  2.96 ± 0.04  22.79 ± 0.29  2.44  74.60  18  So2  342.65  1079.53 ± 9.70  4.32 ± 0.04  33.25 ± 0.30  3.56  108.82  C, cement; WC, white cement; Sa, sand; Gy, gypsum; Gr, gravel; So, soil. Table 3. Radon contribution to indoor radon, surface and mass exhalation rates, annual effective doses and effective radium content, together with the statistical uncertainties (1σ) for the powdery different building material samples. S. no.  Sample ID  Size (cm3)  Radon surface exhalation rate (mBq m−2 h−1)  Radon contribution (Bq m−3)  Radon mass exhalation rate (mBq kg−1 h−1)  Effective radium content (Bq kg−1)  Annual effective dose (μSv y−1)  1  C1  342.65  207.96 ± 7.88  0.83 ± 0.03  6.40 ± 0.24  0.69  20.96  2  C2  338.80  243.12 ± 6.07  0.97 ± 0.02  7.49 ± 0.19  0.79  24.51  3  C3  338.80  507.66 ± 10.73  2.03 ± 0.04  15.64 ± 0.33  1.66  51.17  4  WC1  338.80  276.76 ± 6.07  1.11 ± 0.02  8.52 ± 0.19  0.90  27.90  5  WC2  342.65  455.67 ± 10.85  1.82 ± 0.04  14.03 ± 0.33  1.50  45.93  6  WC3  342.65  553.53 ± 9.39  2.21 ± 0.04  17.05 ± 0.29  1.83  55.80  7  Sa1  346.50  178.90 ± 6.76  0.72 ± 0.03  5.51 ± 0.21  0.60  18.03  8  Sa2  346.50  428.14 ± 10.41  1.71 ± 0.04  13.19 ± 0.32  1.43  43.16  9  Sa3  346.50  339.46 ± 6.62  1.36 ± 0.03  10.45 ± 0.20  1.13  34.22  10  Sa4  346.50  633.04 ± 35.51  2.53 ± 0.14  19.50 ± 1.09  2.11  63.81  11  Sa5  346.50  463.31 ± 6.76  1.85 ± 0.03  14.27 ± 0.21  1.55  46.70  12  Gy1  331.10  325.70 ± 6.76  1.30 ± 0.03  10.03 ± 0.21  1.04  32.83  13  Gy2  327.25  441.91 ± 10.98  1.77 ± 0.04  13.61 ± 0.34  1.39  44.54  14  Gr1  327.25  526.01 ± 7.22  2.10 ± 0.03  16.20 ± 0.22  1.66  53.02  15  Gr2  346.50  449.55 ± 8.62  1.80 ± 0.03  13.85 ± 0.27  1.50  45.31  16  Gr3  342.65  474.02 ± 10.52  1.90 ± 0.04  14.60 ± 0.32  1.57  47.78  17  So1  342.65  740.08 ± 9.57  2.96 ± 0.04  22.79 ± 0.29  2.44  74.60  18  So2  342.65  1079.53 ± 9.70  4.32 ± 0.04  33.25 ± 0.30  3.56  108.82  S. no.  Sample ID  Size (cm3)  Radon surface exhalation rate (mBq m−2 h−1)  Radon contribution (Bq m−3)  Radon mass exhalation rate (mBq kg−1 h−1)  Effective radium content (Bq kg−1)  Annual effective dose (μSv y−1)  1  C1  342.65  207.96 ± 7.88  0.83 ± 0.03  6.40 ± 0.24  0.69  20.96  2  C2  338.80  243.12 ± 6.07  0.97 ± 0.02  7.49 ± 0.19  0.79  24.51  3  C3  338.80  507.66 ± 10.73  2.03 ± 0.04  15.64 ± 0.33  1.66  51.17  4  WC1  338.80  276.76 ± 6.07  1.11 ± 0.02  8.52 ± 0.19  0.90  27.90  5  WC2  342.65  455.67 ± 10.85  1.82 ± 0.04  14.03 ± 0.33  1.50  45.93  6  WC3  342.65  553.53 ± 9.39  2.21 ± 0.04  17.05 ± 0.29  1.83  55.80  7  Sa1  346.50  178.90 ± 6.76  0.72 ± 0.03  5.51 ± 0.21  0.60  18.03  8  Sa2  346.50  428.14 ± 10.41  1.71 ± 0.04  13.19 ± 0.32  1.43  43.16  9  Sa3  346.50  339.46 ± 6.62  1.36 ± 0.03  10.45 ± 0.20  1.13  34.22  10  Sa4  346.50  633.04 ± 35.51  2.53 ± 0.14  19.50 ± 1.09  2.11  63.81  11  Sa5  346.50  463.31 ± 6.76  1.85 ± 0.03  14.27 ± 0.21  1.55  46.70  12  Gy1  331.10  325.70 ± 6.76  1.30 ± 0.03  10.03 ± 0.21  1.04  32.83  13  Gy2  327.25  441.91 ± 10.98  1.77 ± 0.04  13.61 ± 0.34  1.39  44.54  14  Gr1  327.25  526.01 ± 7.22  2.10 ± 0.03  16.20 ± 0.22  1.66  53.02  15  Gr2  346.50  449.55 ± 8.62  1.80 ± 0.03  13.85 ± 0.27  1.50  45.31  16  Gr3  342.65  474.02 ± 10.52  1.90 ± 0.04  14.60 ± 0.32  1.57  47.78  17  So1  342.65  740.08 ± 9.57  2.96 ± 0.04  22.79 ± 0.29  2.44  74.60  18  So2  342.65  1079.53 ± 9.70  4.32 ± 0.04  33.25 ± 0.30  3.56  108.82  C, cement; WC, white cement; Sa, sand; Gy, gypsum; Gr, gravel; So, soil. For the powdery materials, they ranged from 0.72 ± 0.03 to 4.32 ± 0.04 Bq m−3. The sand sample (Sa1) showed the lowest value, and the daily accumulated radon concentration in a room was estimated at 17.16 Bq m−3. On the other hand, the soil sample (So2) gave the highest value observed in this type of study. Where the daily accumulated radon concentration in a room was estimated to be 103.63 Bq m−3. To study the contribution of building materials to indoor radon concentrations with air changes per hour (ACH), two scenarios were considered: Case I: radon exhalation from a granite countertop Consider a granite countertop (0.67 m × 2.50 m × 0.025 m) installed in a kitchen with an area of 20 m2 and a height of 2.5 m(60), with the assumption that 25% of the kitchen volume is occupied by kitchen wares and furniture, and assuming as well that the kitchen is ventilated with the minimum required ACH of 0.3 h−1, for granite countertops having the highest radon exhalation rate (30.42 Bq m−2 d−1) observed in this study, as shown in Table 2, the radon concentration in the kitchen will be 0.37 Bq m−3. It can be concluded that kitchen granite countertops, under normal ventilation, contribute very little to the radon concentration for the range of radon exhalation rates reported here. Similar assessments were reported in the literature(19, 60). Based on more data available recently, it was assessed that the average radon concentration in Yemen homes is 4 Bq m−3(61). It indicates that on average, granite countertops could contribute to <1% of radon concentration in Yemen homes. Table 1. Radon contribution to indoor radon, surface exhalation rate and annual effective doses, together with the statistical uncertainties (1σ) for the solid slab different building material samples. S. no.  Sample ID  Radon surface exhalation rate (m Bq m−2 h−1)  Radon contribution (Bq m−3)  Annual effective dose (μSv y−1)  1  M1  527.53 ± 10.84  2.11 ± 0.04  53.18  2  M2  275.24 ± 5.43  1.10 ± 0.02  27.74  3  M3  513.77 ± 6.87  2.06 ± 0.03  51.79  4  M4  336.40 ± 6.28  1.35 ± 0.03  33.91  5  Gra1  1267.61 ± 11.84  5.07 ± 0.05  127.78  6  Gra2  1079.53 ± 13.51  4.32 ± 0.05  108.82  7  Ce1  827.23 ± 11.63  3.31 ± 0.05  83.39  8  Ce2  564.23 ± 6.46  2.26 ± 0.03  56.87  9  Ce3  382.27 ± 8.15  1.53 ± 0.03  38.53  10  Ce4  342.52 ± 5.70  1.37 ± 0.02  34.53  11  RB1  519.89 ± 8.00  2.08 ± 0.03  52.40  12  RB2  593.28 ± 6.04  2.37 ± 0.02  59.80  13  T  758.43 ± 6.87  3.03 ± 0.03  76.45  14  CB1  889.93 ± 8.27  3.56 ± 0.03  89.70  15  CB2  1047.42 ± 12.53  4.19 ± 0.05  105.58  S. no.  Sample ID  Radon surface exhalation rate (m Bq m−2 h−1)  Radon contribution (Bq m−3)  Annual effective dose (μSv y−1)  1  M1  527.53 ± 10.84  2.11 ± 0.04  53.18  2  M2  275.24 ± 5.43  1.10 ± 0.02  27.74  3  M3  513.77 ± 6.87  2.06 ± 0.03  51.79  4  M4  336.40 ± 6.28  1.35 ± 0.03  33.91  5  Gra1  1267.61 ± 11.84  5.07 ± 0.05  127.78  6  Gra2  1079.53 ± 13.51  4.32 ± 0.05  108.82  7  Ce1  827.23 ± 11.63  3.31 ± 0.05  83.39  8  Ce2  564.23 ± 6.46  2.26 ± 0.03  56.87  9  Ce3  382.27 ± 8.15  1.53 ± 0.03  38.53  10  Ce4  342.52 ± 5.70  1.37 ± 0.02  34.53  11  RB1  519.89 ± 8.00  2.08 ± 0.03  52.40  12  RB2  593.28 ± 6.04  2.37 ± 0.02  59.80  13  T  758.43 ± 6.87  3.03 ± 0.03  76.45  14  CB1  889.93 ± 8.27  3.56 ± 0.03  89.70  15  CB2  1047.42 ± 12.53  4.19 ± 0.05  105.58  M, marble; RB, red brick; CB, concrete block; Gra, granite; Ce, ceramic; T, tiles. Table 1. Radon contribution to indoor radon, surface exhalation rate and annual effective doses, together with the statistical uncertainties (1σ) for the solid slab different building material samples. S. no.  Sample ID  Radon surface exhalation rate (m Bq m−2 h−1)  Radon contribution (Bq m−3)  Annual effective dose (μSv y−1)  1  M1  527.53 ± 10.84  2.11 ± 0.04  53.18  2  M2  275.24 ± 5.43  1.10 ± 0.02  27.74  3  M3  513.77 ± 6.87  2.06 ± 0.03  51.79  4  M4  336.40 ± 6.28  1.35 ± 0.03  33.91  5  Gra1  1267.61 ± 11.84  5.07 ± 0.05  127.78  6  Gra2  1079.53 ± 13.51  4.32 ± 0.05  108.82  7  Ce1  827.23 ± 11.63  3.31 ± 0.05  83.39  8  Ce2  564.23 ± 6.46  2.26 ± 0.03  56.87  9  Ce3  382.27 ± 8.15  1.53 ± 0.03  38.53  10  Ce4  342.52 ± 5.70  1.37 ± 0.02  34.53  11  RB1  519.89 ± 8.00  2.08 ± 0.03  52.40  12  RB2  593.28 ± 6.04  2.37 ± 0.02  59.80  13  T  758.43 ± 6.87  3.03 ± 0.03  76.45  14  CB1  889.93 ± 8.27  3.56 ± 0.03  89.70  15  CB2  1047.42 ± 12.53  4.19 ± 0.05  105.58  S. no.  Sample ID  Radon surface exhalation rate (m Bq m−2 h−1)  Radon contribution (Bq m−3)  Annual effective dose (μSv y−1)  1  M1  527.53 ± 10.84  2.11 ± 0.04  53.18  2  M2  275.24 ± 5.43  1.10 ± 0.02  27.74  3  M3  513.77 ± 6.87  2.06 ± 0.03  51.79  4  M4  336.40 ± 6.28  1.35 ± 0.03  33.91  5  Gra1  1267.61 ± 11.84  5.07 ± 0.05  127.78  6  Gra2  1079.53 ± 13.51  4.32 ± 0.05  108.82  7  Ce1  827.23 ± 11.63  3.31 ± 0.05  83.39  8  Ce2  564.23 ± 6.46  2.26 ± 0.03  56.87  9  Ce3  382.27 ± 8.15  1.53 ± 0.03  38.53  10  Ce4  342.52 ± 5.70  1.37 ± 0.02  34.53  11  RB1  519.89 ± 8.00  2.08 ± 0.03  52.40  12  RB2  593.28 ± 6.04  2.37 ± 0.02  59.80  13  T  758.43 ± 6.87  3.03 ± 0.03  76.45  14  CB1  889.93 ± 8.27  3.56 ± 0.03  89.70  15  CB2  1047.42 ± 12.53  4.19 ± 0.05  105.58  M, marble; RB, red brick; CB, concrete block; Gra, granite; Ce, ceramic; T, tiles. Case II: radon exhalation from a floor area If a room has a floor area of 20 m2 and a height of 2.5 m as assumed in scenario 1 and its entire floor is decorated with ceramic tiles, slate or granite, and 10% of the room volume is occupied by furniture, the radon concentration, Bq m−3, due to radon exhalation from the floor can be determined by Eq. (4). The resulting radon concentrations are calculated for materials of various radon exhalation rates and for various air change rates, as shown in Table 2. One can infer from Table 2 that even if the entire floor was covered with a material of a relatively high radon exhalation rate, as granites studied here 30.42 Bq m−2 d−1, it would contribute only 1.83 Bq m−3 to a tightly sealed house (minimum required ACH of 0.3 per hour). This is only 1% of the action level for radon in dwellings(62). Higher ventilation rates will reduce the contribution proportionally. In the worst case scenario and when the mechanical ventilation system failed completely and no natural ventilation alternative was provided (ACH = 0), the indoor radon concentration would rise but not above an action level of 200 Bq m−3 for radon in dwellings(62). The effective radium content in powdery samples was calculated using Eq. (6). And the results are provided in Table 3. RECs range from 0.6 to 3.56 Bq kg−1 with a mean value of 1.52 Bq kg−1, whereas in the solid slabs samples this parameter could not be determined. All the values of effective radium content in all samples under test were found to be quite lower than the permissible value recommended by Organization for Economic Cooperation and Development(63). Table 2. Estimate steady-state radon concentration (Bq m−3) due to radon exhalation from floor material with various air change rates. Sample  EA (Bqm−2d−1)  ACH = 3  ACH = 1  ACH = 0.3  ACH = 0.15  ACH = 0  Marble  13.02  0.08  0.24  0.78  1.53  31.97  Ceramic  19.85  0.12  0.36  1.20  2.33  48.75  Tiles  21.92  0.13  0.40  1.32  2.58  53.81  Granite  30.42  0.19  0.56  1.83  3.58  74.69  Sample  EA (Bqm−2d−1)  ACH = 3  ACH = 1  ACH = 0.3  ACH = 0.15  ACH = 0  Marble  13.02  0.08  0.24  0.78  1.53  31.97  Ceramic  19.85  0.12  0.36  1.20  2.33  48.75  Tiles  21.92  0.13  0.40  1.32  2.58  53.81  Granite  30.42  0.19  0.56  1.83  3.58  74.69  Table 2. Estimate steady-state radon concentration (Bq m−3) due to radon exhalation from floor material with various air change rates. Sample  EA (Bqm−2d−1)  ACH = 3  ACH = 1  ACH = 0.3  ACH = 0.15  ACH = 0  Marble  13.02  0.08  0.24  0.78  1.53  31.97  Ceramic  19.85  0.12  0.36  1.20  2.33  48.75  Tiles  21.92  0.13  0.40  1.32  2.58  53.81  Granite  30.42  0.19  0.56  1.83  3.58  74.69  Sample  EA (Bqm−2d−1)  ACH = 3  ACH = 1  ACH = 0.3  ACH = 0.15  ACH = 0  Marble  13.02  0.08  0.24  0.78  1.53  31.97  Ceramic  19.85  0.12  0.36  1.20  2.33  48.75  Tiles  21.92  0.13  0.40  1.32  2.58  53.81  Granite  30.42  0.19  0.56  1.83  3.58  74.69  Finally, it is necessary to estimate the radon emanation potential from building materials to evaluate the radiation risk to the inhabitants. Thus, the assessment of the annual effective dose expected to be received by populations due to radon and its progenies were based on the calculations of radon exhalation rates. The minimum, maximum and mean annual effective doses were found to be 27.74, 127.78 and 66.70 μSv y−1 for the slabs samples, and 18.03, 108.82 and 46.62 μSv y−1 for the powdery samples. The slabs samples giving the lowest values of the annual effective dose were marble (M2) from Yemen (Taiz); the lowest dose value from the powdery samples was attributed to the Sa1, denoting Yemen sand. The highest dose from the slabs samples came from granite in Yemen and the highest dose in the powdery samples came from So2, denoting Yemen. The results obtained are shown in Tables 3 and 1. The results of the current study have been compared with already published data (Table 4). Table 4. Comparison between surface exhalation rates (EA) and mass exhalation rates (EM) of some building materials in different countries. Material  Country  EA (mBq m−2 h−1)  EM (m Bq kg−1 h−1)  Reference  Cement  Sudan  379  4.5  (65)  Indian  263.3–401.6  12.1–18.4  (66)  Libya  523.2  20.4  (10)  Yemen  243.12–492.37  6.405–15.164  Present work  White cement  Libya  550.9  20.8  (10)  Indian  417–437  13.8–20.1  (66)  Yemen  276.76–553.53  8.524–17.048  Present work  Sand  Pakistan  205–291    (67)  Pakistan  366–649    (7)  Libya  722.2  27.4  (10)  Yemen  178.90–633.04  5.510–19.497  Present work  Ceramic  Sudan  240    (65)  Canada  8.33–125    (60)  Libya  69.5–73.7    (10)  Yemen  382.27–827.23    Present work  Granite  Libya  733.2–17 221.2    (10)  Greece  1240–3540    (68)  KSA  333–1250    (69)  Yemen  1079.53–1267.61    Present work  Gypsum  Egypt  26.28    (30)  Libya  147.5–365.5  17.4–43.1  (10)  Yemen  325.70–441.91  10.031–13.610  Present work  Brick  Pakistan  184–231    (7)  Pakistan  245–365    (67)  Libya  123.7–1625.1    (10)  Yemen  519.89–593.28    Present work  Gravel  Canada  45.83–4245.83    (19)  Pakistan  168–322    (7)  Yemen  449.55–526.01  13.85–16.20  Present work  Marble  Libya  142.3–970.6    (10)  Italy  65.4    (43)  Canada  4.17–25    (60)  Algeria  35–66    (70)  Yemen  275.24–527.53    Present work  Soil  Libyan  58.3–506.9  1.2–17.4  (14)  KSA  45–8400  135–251  (59)  India    6–56  (36)  Pakistan  114–416    (67)  Egypt  480–15 370  8.31–233.70  (31)  Yemen  740.08–1079.53  22.794–33.248  Present work  Material  Country  EA (mBq m−2 h−1)  EM (m Bq kg−1 h−1)  Reference  Cement  Sudan  379  4.5  (65)  Indian  263.3–401.6  12.1–18.4  (66)  Libya  523.2  20.4  (10)  Yemen  243.12–492.37  6.405–15.164  Present work  White cement  Libya  550.9  20.8  (10)  Indian  417–437  13.8–20.1  (66)  Yemen  276.76–553.53  8.524–17.048  Present work  Sand  Pakistan  205–291    (67)  Pakistan  366–649    (7)  Libya  722.2  27.4  (10)  Yemen  178.90–633.04  5.510–19.497  Present work  Ceramic  Sudan  240    (65)  Canada  8.33–125    (60)  Libya  69.5–73.7    (10)  Yemen  382.27–827.23    Present work  Granite  Libya  733.2–17 221.2    (10)  Greece  1240–3540    (68)  KSA  333–1250    (69)  Yemen  1079.53–1267.61    Present work  Gypsum  Egypt  26.28    (30)  Libya  147.5–365.5  17.4–43.1  (10)  Yemen  325.70–441.91  10.031–13.610  Present work  Brick  Pakistan  184–231    (7)  Pakistan  245–365    (67)  Libya  123.7–1625.1    (10)  Yemen  519.89–593.28    Present work  Gravel  Canada  45.83–4245.83    (19)  Pakistan  168–322    (7)  Yemen  449.55–526.01  13.85–16.20  Present work  Marble  Libya  142.3–970.6    (10)  Italy  65.4    (43)  Canada  4.17–25    (60)  Algeria  35–66    (70)  Yemen  275.24–527.53    Present work  Soil  Libyan  58.3–506.9  1.2–17.4  (14)  KSA  45–8400  135–251  (59)  India    6–56  (36)  Pakistan  114–416    (67)  Egypt  480–15 370  8.31–233.70  (31)  Yemen  740.08–1079.53  22.794–33.248  Present work  Table 4. Comparison between surface exhalation rates (EA) and mass exhalation rates (EM) of some building materials in different countries. Material  Country  EA (mBq m−2 h−1)  EM (m Bq kg−1 h−1)  Reference  Cement  Sudan  379  4.5  (65)  Indian  263.3–401.6  12.1–18.4  (66)  Libya  523.2  20.4  (10)  Yemen  243.12–492.37  6.405–15.164  Present work  White cement  Libya  550.9  20.8  (10)  Indian  417–437  13.8–20.1  (66)  Yemen  276.76–553.53  8.524–17.048  Present work  Sand  Pakistan  205–291    (67)  Pakistan  366–649    (7)  Libya  722.2  27.4  (10)  Yemen  178.90–633.04  5.510–19.497  Present work  Ceramic  Sudan  240    (65)  Canada  8.33–125    (60)  Libya  69.5–73.7    (10)  Yemen  382.27–827.23    Present work  Granite  Libya  733.2–17 221.2    (10)  Greece  1240–3540    (68)  KSA  333–1250    (69)  Yemen  1079.53–1267.61    Present work  Gypsum  Egypt  26.28    (30)  Libya  147.5–365.5  17.4–43.1  (10)  Yemen  325.70–441.91  10.031–13.610  Present work  Brick  Pakistan  184–231    (7)  Pakistan  245–365    (67)  Libya  123.7–1625.1    (10)  Yemen  519.89–593.28    Present work  Gravel  Canada  45.83–4245.83    (19)  Pakistan  168–322    (7)  Yemen  449.55–526.01  13.85–16.20  Present work  Marble  Libya  142.3–970.6    (10)  Italy  65.4    (43)  Canada  4.17–25    (60)  Algeria  35–66    (70)  Yemen  275.24–527.53    Present work  Soil  Libyan  58.3–506.9  1.2–17.4  (14)  KSA  45–8400  135–251  (59)  India    6–56  (36)  Pakistan  114–416    (67)  Egypt  480–15 370  8.31–233.70  (31)  Yemen  740.08–1079.53  22.794–33.248  Present work  Material  Country  EA (mBq m−2 h−1)  EM (m Bq kg−1 h−1)  Reference  Cement  Sudan  379  4.5  (65)  Indian  263.3–401.6  12.1–18.4  (66)  Libya  523.2  20.4  (10)  Yemen  243.12–492.37  6.405–15.164  Present work  White cement  Libya  550.9  20.8  (10)  Indian  417–437  13.8–20.1  (66)  Yemen  276.76–553.53  8.524–17.048  Present work  Sand  Pakistan  205–291    (67)  Pakistan  366–649    (7)  Libya  722.2  27.4  (10)  Yemen  178.90–633.04  5.510–19.497  Present work  Ceramic  Sudan  240    (65)  Canada  8.33–125    (60)  Libya  69.5–73.7    (10)  Yemen  382.27–827.23    Present work  Granite  Libya  733.2–17 221.2    (10)  Greece  1240–3540    (68)  KSA  333–1250    (69)  Yemen  1079.53–1267.61    Present work  Gypsum  Egypt  26.28    (30)  Libya  147.5–365.5  17.4–43.1  (10)  Yemen  325.70–441.91  10.031–13.610  Present work  Brick  Pakistan  184–231    (7)  Pakistan  245–365    (67)  Libya  123.7–1625.1    (10)  Yemen  519.89–593.28    Present work  Gravel  Canada  45.83–4245.83    (19)  Pakistan  168–322    (7)  Yemen  449.55–526.01  13.85–16.20  Present work  Marble  Libya  142.3–970.6    (10)  Italy  65.4    (43)  Canada  4.17–25    (60)  Algeria  35–66    (70)  Yemen  275.24–527.53    Present work  Soil  Libyan  58.3–506.9  1.2–17.4  (14)  KSA  45–8400  135–251  (59)  India    6–56  (36)  Pakistan  114–416    (67)  Egypt  480–15 370  8.31–233.70  (31)  Yemen  740.08–1079.53  22.794–33.248  Present work  CONCLUSION The two highest values of radon exhalation observed in the studied solid slabs samples came from the Yemeni granite and the Chinese granite. For this reason, these two materials are not favorable for decorative use and should be replaced by other alternatives. For the powdery sample, the soil was found to have a high level of radon exhalation. However, there exists only a small number of houses which are made of mud alone. Without ventilation, elevated radon levels could arise. In general, the current results are within the world-wide range of values found in soil, and this range is within the safe limits recommended by the United Nations Scientific Committee on the Effects of Atomic Radiation(64). The effective radium content and annual effective dose equivalents are within the safe limits recommended by Organization for Economic Cooperation and Development (OECD)(63), European Commission (EC)(3) and United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR)(64). 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For Permissions, please email: journals.permissions@oup.com This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Radiation Protection Dosimetry Oxford University Press

RADON EXHALATION FROM BUILDING MATERIALS USED IN YEMEN

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Abstract

Abstract The present article seeks to determine the annual effective doses of 222Rn exposure, effective radium content and radon exhalation rates in some building materials from the local market of Ibb province, Yemen. A total of 33 samples of building materials were collected from the target area. The radon exhalation rate and effective radium content in these samples were measured using solid-state nuclear track detector, which has become an important tool in every investigation of the radon levels in the surrounding environment. Surface exhalation rate has been found to vary from 178.90 to 1267.6 mBq m−2 h−1, whereas mass exhalation rate has been found to vary from 5.51 to 33.25 mBq kg−1 h−1. All the values of effective radium content in all samples under test were found to be quite lower than the permissible value of 370 Bq kg−1 recommended by Organization for Economic Cooperation and Development. Annual effective doses have also been estimated. INTRODUCTION Radioactivity is widely spread in the earth’s environment and it is found in various geological formation, e.g. soils, rocks, plants, water and air(1, 2). Most building materials derived from soil and rocks contain the natural radionuclides such as uranium (238U) and thorium (232Th) and their daughter products and singly occurring potassium (40K)(3). Concentrations of radionuclides present in building materials vary depending upon the local geology of each region in the world(4, 5). The building industry also uses large amounts of waste from other industries(6). These radioactive elements are sources of three radioactive decay series. Radon gas is one of the decay products of these series. It consists of three isotopes, namely: (1) 222Rn (called radon, belongs to 238U decay series); (2) 220Rn (called thoron, belongs to 232Th decay series); and (3) 219Rn (called action, belongs to 235U decay series). 222Rn has 3.82 days half-life, whereas 220Rn (55.6 s) and 219Rn (3.96 s) have much shorter half-lives than 222Rn. That is why 220Rn and 219Rn are given less importance in environmental studies(7, 8). Radon (222Rn), as an emitter of α-particles with energy 5.48 MeV, is the most crucial and dangerous radioactive gaseous element in the science of environmental radioactivity(9, 10). Most individuals spend more than 80% of their time indoors and the rest is spent on outdoor activities. The internal and external radiation exposure from building materials creates prolonged exposure situations(11). The external radiation exposure is caused by the gamma emitting radionuclides, which in the uranium series mainly belongs to the decay chain segment starting with 226Ra. The internal (inhalation) radiation exposure is largely due to 222Rn, and marginally to 220Rn, and their short lived decay products(12). The study of alpha activity in building materials is very important because alpha radiation is 1000 times more carcinogenic than gamma radiation(4). The noble gas 222Rn, although not so noble in its health hazard effect, is chemically inert and can move through the Earth and structural materials(9, 10). Once the radon atoms are formed by the decay of the parent 226Ra, they move either by diffusion or by transport mechanisms or by both(13, 14). Radon exhalation is a complex phenomenon depending upon a number of parameters such as effective radium content in soil, soil morphology, soil moisture, vegetation, temperature, atmospheric pressure, rainfall and soil grain size(15). The amount of the produced radon from the grains that finally enters by recoil effect and diffusion process in the porous system of the material is defined as ‘effective radium content’(16). Recently, several interesting studies of people exposed to radon have confirmed that radon in homes and workplaces represent a serious health hazard(3, 17, 18). The exposure of people to high concentrations of indoor radon for long periods causes pathological effects and functional respiratory changes, which consequently lead to an increased risk of developing lung cancer(19–21). The aim of this study is to determine the annual effective doses of 222Rn exposure, effective radium content and radon exhalation rates in some building materials from local market of Ibb province in Yemen by solid-state nuclear track detectors (CR-39). Such studies can be useful for keeping reference records and developing data panels to ascertain changes in the environmental radioactivity due to nuclear, industrial and other human activities over time(22). Ibb province is located between Thamar and Taiz provinces. The capital city of Ibb province is ~193 km to the south of Sana’a, the capital city of Yemen. Figure 1 shows Ibb’s location(23). The province has a total area of 5383 km2 and it is located at latitude 13°58′48″ and longitude 44°10′48″(24). Figure 1. View largeDownload slide Map showing the study area in Ibb(23). Figure 1. View largeDownload slide Map showing the study area in Ibb(23). MATERIALS AND METHODS For the purposes of this study, a total of 33 samples of building materials were collected from different companies and stores in Ibb, comprising 15 slab samples and 18 porous powdery building material samples. The concentration and exhalation rate of radon have been determined using CR-39 detectors because of their ability to register tracks at different levels of sensitivity(25–27). The CR-39 polymer sheets of TASTRAK were produced and provided by Track Analysis Systems Ltd. (TASL), Bristol, UK. The polymeric detector samples, for the present study, were cut to a size of 1.5 × 1.5 cm2 and adhered to a plastic can of known dimension (7 cm in diameter and 11 cm in height)(28–31). To avoid the track contribution from thoron in the can, the CR-39 detectors were kept at distance ~7 cm or more from the sample in accordance with the protocol(32–36). This is because the half-life time of 220Rn (55.6 s) is ~0.00017 that of radon 222Rn (3.82 d). This shows that most of the thoron will decay inside the building material and radon diffusion length, so that, thoron would be still in the order of 2 or 3 cm(37–39). Two types of experiments for measurement of radon exhalation rates of building materials were used: The container was placed inversely on the surface of the tile samples of building materials. These samples were washed, cleaned, dried and used without crushing as used naturally. The contact between the chamber and the building material parts was sealed with silicon(40). The powder samples were dried in an oven at a temperature of 80°C for 24 h to remove all the moisture content(19, 27), crushed to fine grain size (100 μm)(20). Then each sample of 125 g weight was placed at the bottom of a cylindrical sealed can. The mouth of the cylindrical can was sealed with a cover and fitted with CR-39 plastic track detectors at the top inner surface so that they were facing the specimen(14, 41, 42). The cover was sealed by silicon and duct tape from the outside in order to avoid radon leakage(43). The sample was left for 1 month to allow radioactive equilibrium to reach between 226Ra, 222Rn and their decay products. Furthermore, in order to ensure the radioactive equilibrium of 226Ra, 222Rn and their decay products, it is important to ensure that no 222Rn is lost from the sample container(20, 44). During the exposure period of 3 months(10, 15), the sensitive side of the detector is exposed freely to the emergent radon from the sample in the can so that it could record the tracks of alpha-particles resulting from the decay of radon. At the end of the expose time, the detectors were removed and chemically etched for 9 h in 6.25 N NaOH at 70 ± 1°C(21). After this chemical treatment, these CR-39 solid-state nuclear track detectors were washed in distilled water in order to stop the chemical reaction, dried in air and the tracks were counted using an optical microscope at a magnification of ×400. The mass exhalation and surface exhalation rate of radon were obtained from the following expressions(10, 31, 45):   EA=CλRnVA[T+(1/λRn(e−λRnT−1))] (1)  EM=CλRnVM[T+(1/λRn(e−λRnT−1))] (2)where, EA is the surface exhalation rate (Bq m−2 h−1), EM is the mass exhalation rate (Bq kg−1 h−1), C is the integrated radon exposure (Bq m−3 h), A is the total surface area of the building material sample from which radon is exhaled (3.85×10−3m2), V is the effective volume of the emanation container or can (m3), M is the mass of the powder sample (0.125 kg), λRn is the decay constant of radon (h−1) and T is the exposure time in hour. The risk of lung cancer from domestic exposure due to radon and its daughter nuclides can therefore be computed directly from the effective dose equivalents. The radiation hazards due to radon and its daughters are calculated from the radon exhalation rates of building material samples. The contribution of indoor radon concentration from building materials can be calculated from the following relation(46):   C¯Rn=EA×S(λRn+λV)×Vr (3)where, C¯Rn is radon concentration in construction materials contributing to indoor radon, Vr is the room volume (m3) and λV is air exchange rate (h−1). In these calculations, the maximum radon concentration from building materials was assessed by assuming the room to be a cavity with the ratio S/Vr = 2.0 m−1, where S and Vr are the internal surface area and volume of the room, respectively, and the air exchange rate λV was taken to be 0.5 h−1(47, 48). The annual effective doses of 222Rn exposure were estimated using the following equation(49):   ERn=C¯Rn×Fe×Ta×DRn (4)where, ERn is the annual effective dose of 222Rn (Sv y−1), Ta is the annual work time = 7000 hy−1, DRn the dose conversion factor for 222Rn decay products [Sv/Bq h m−3 (EERC)] and Fe is the equilibrium factor. The value of Fe was assumed to be 0.4(49). The effective radium content was measured for the same samples using CR-39 detectors because of its capability to register tracks at different levels of registration sensitivity(10, 31, 50). After the sealing of the can, the activity concentration of radon begins to increase with time T as follows(10, 51):   CRn=CRa(1−e−λRnT) (5)where, CRa is the effective radium content(10, 31, 34, 52) of the building material sample. Also CRa is called the effective radium concentration(53, 54), as this is the fraction of total radium which contributes to radon exhalation(55). The effective radium content was calculated by using the following relation(15, 56):   CRa(Bqkg−1)=hρAKTeM (6)where, h is the distance between the detector and the top of the solid sample, ρ is the radon track density (track cm−2), K is the calibration factor for radon (0.16 track cm−2d−1/Bq m−3) which was calibrated in previous work(57) and Te is the effective exposure time (in days), which is related to the actual exposure time T and decay constant for 222Rn according to the following equation(58, 59):   Te=[T−1λRn(1−e–λRnT)] (7) The exposure time, in these measurements, was 90 days. Radon exhalation from the building materials contributes towards indoor radon. In this regard, previous studies have been carried out in different parts of the world and extensive data are available in the literature. In the current survey, most of the houses in the studied area are built of blocks (mixtures of cement sand and gravel aggregates in definite proportions). Some of the houses were made up of bricks and Sand and most of them also contain interior decoration made of ceramics, gypsum, marble and granite. These houses are in fact constructed on the Earth’s crust, which is essentially composed of rocks and soil. RESULTS AND DISCUSSION The surface radon exhalation rates from the solid slab samples ranged from 275.24 ± 5.43 to 1267.6 ± 11.84 mBq m−2 h−1, with a mean of 661.69 ± 8.56 mBq m−2h−1, whereas the surface exhalation rates from the powdery samples ranged from 178.90 ± 6.76 to 1079.53 ± 9.70 mBq m−2 h−1, with a mean of 462.46 ± 10.02 mBq m−2h−1. The mass radon exhalation rates from the powdery samples ranged from 5.51 ± 0.2 to 33.25 ± 0.30 mBq kg−1h−1 with a mean of 4.24 ± 0.31 mBq kg−1 h−1. The values of exhalation rates of building materials vary from one building material to another. This variation can be attributed to the difference in the nature of the samples, and effective radium content in the samples. To estimate the contribution of building materials to indoor radon concentrations(10), a room with an air exchange rate of 0.5 h−1 was assumed as mentioned above. The radon concentration contribution to indoor radon in the room due to exhalation from the solid slab samples building materials was found to range from 1.10 ± 0.02 to 5.07 ± 0.05 Bq m−3, with a mean of 2.65 ± 0.03 Bqm−3 (Table 1). The smallest accumulated radon concentration per day in a room with its entire floor and walls decorated with M2, denoting Yemen marble, would be 26.42 Bq m−3. Thus, on average, the sample M2 would contribute only slightly to the radon concentration in Yemen homes. On the other hand, the largest accumulated radon concentration per day was 121.656 and 103.634 Bq m−3 for samples Gra1 and Gra2, denoting Yemen granite and china granite, respectively. Table 3. Radon contribution to indoor radon, surface and mass exhalation rates, annual effective doses and effective radium content, together with the statistical uncertainties (1σ) for the powdery different building material samples. S. no.  Sample ID  Size (cm3)  Radon surface exhalation rate (mBq m−2 h−1)  Radon contribution (Bq m−3)  Radon mass exhalation rate (mBq kg−1 h−1)  Effective radium content (Bq kg−1)  Annual effective dose (μSv y−1)  1  C1  342.65  207.96 ± 7.88  0.83 ± 0.03  6.40 ± 0.24  0.69  20.96  2  C2  338.80  243.12 ± 6.07  0.97 ± 0.02  7.49 ± 0.19  0.79  24.51  3  C3  338.80  507.66 ± 10.73  2.03 ± 0.04  15.64 ± 0.33  1.66  51.17  4  WC1  338.80  276.76 ± 6.07  1.11 ± 0.02  8.52 ± 0.19  0.90  27.90  5  WC2  342.65  455.67 ± 10.85  1.82 ± 0.04  14.03 ± 0.33  1.50  45.93  6  WC3  342.65  553.53 ± 9.39  2.21 ± 0.04  17.05 ± 0.29  1.83  55.80  7  Sa1  346.50  178.90 ± 6.76  0.72 ± 0.03  5.51 ± 0.21  0.60  18.03  8  Sa2  346.50  428.14 ± 10.41  1.71 ± 0.04  13.19 ± 0.32  1.43  43.16  9  Sa3  346.50  339.46 ± 6.62  1.36 ± 0.03  10.45 ± 0.20  1.13  34.22  10  Sa4  346.50  633.04 ± 35.51  2.53 ± 0.14  19.50 ± 1.09  2.11  63.81  11  Sa5  346.50  463.31 ± 6.76  1.85 ± 0.03  14.27 ± 0.21  1.55  46.70  12  Gy1  331.10  325.70 ± 6.76  1.30 ± 0.03  10.03 ± 0.21  1.04  32.83  13  Gy2  327.25  441.91 ± 10.98  1.77 ± 0.04  13.61 ± 0.34  1.39  44.54  14  Gr1  327.25  526.01 ± 7.22  2.10 ± 0.03  16.20 ± 0.22  1.66  53.02  15  Gr2  346.50  449.55 ± 8.62  1.80 ± 0.03  13.85 ± 0.27  1.50  45.31  16  Gr3  342.65  474.02 ± 10.52  1.90 ± 0.04  14.60 ± 0.32  1.57  47.78  17  So1  342.65  740.08 ± 9.57  2.96 ± 0.04  22.79 ± 0.29  2.44  74.60  18  So2  342.65  1079.53 ± 9.70  4.32 ± 0.04  33.25 ± 0.30  3.56  108.82  S. no.  Sample ID  Size (cm3)  Radon surface exhalation rate (mBq m−2 h−1)  Radon contribution (Bq m−3)  Radon mass exhalation rate (mBq kg−1 h−1)  Effective radium content (Bq kg−1)  Annual effective dose (μSv y−1)  1  C1  342.65  207.96 ± 7.88  0.83 ± 0.03  6.40 ± 0.24  0.69  20.96  2  C2  338.80  243.12 ± 6.07  0.97 ± 0.02  7.49 ± 0.19  0.79  24.51  3  C3  338.80  507.66 ± 10.73  2.03 ± 0.04  15.64 ± 0.33  1.66  51.17  4  WC1  338.80  276.76 ± 6.07  1.11 ± 0.02  8.52 ± 0.19  0.90  27.90  5  WC2  342.65  455.67 ± 10.85  1.82 ± 0.04  14.03 ± 0.33  1.50  45.93  6  WC3  342.65  553.53 ± 9.39  2.21 ± 0.04  17.05 ± 0.29  1.83  55.80  7  Sa1  346.50  178.90 ± 6.76  0.72 ± 0.03  5.51 ± 0.21  0.60  18.03  8  Sa2  346.50  428.14 ± 10.41  1.71 ± 0.04  13.19 ± 0.32  1.43  43.16  9  Sa3  346.50  339.46 ± 6.62  1.36 ± 0.03  10.45 ± 0.20  1.13  34.22  10  Sa4  346.50  633.04 ± 35.51  2.53 ± 0.14  19.50 ± 1.09  2.11  63.81  11  Sa5  346.50  463.31 ± 6.76  1.85 ± 0.03  14.27 ± 0.21  1.55  46.70  12  Gy1  331.10  325.70 ± 6.76  1.30 ± 0.03  10.03 ± 0.21  1.04  32.83  13  Gy2  327.25  441.91 ± 10.98  1.77 ± 0.04  13.61 ± 0.34  1.39  44.54  14  Gr1  327.25  526.01 ± 7.22  2.10 ± 0.03  16.20 ± 0.22  1.66  53.02  15  Gr2  346.50  449.55 ± 8.62  1.80 ± 0.03  13.85 ± 0.27  1.50  45.31  16  Gr3  342.65  474.02 ± 10.52  1.90 ± 0.04  14.60 ± 0.32  1.57  47.78  17  So1  342.65  740.08 ± 9.57  2.96 ± 0.04  22.79 ± 0.29  2.44  74.60  18  So2  342.65  1079.53 ± 9.70  4.32 ± 0.04  33.25 ± 0.30  3.56  108.82  C, cement; WC, white cement; Sa, sand; Gy, gypsum; Gr, gravel; So, soil. Table 3. Radon contribution to indoor radon, surface and mass exhalation rates, annual effective doses and effective radium content, together with the statistical uncertainties (1σ) for the powdery different building material samples. S. no.  Sample ID  Size (cm3)  Radon surface exhalation rate (mBq m−2 h−1)  Radon contribution (Bq m−3)  Radon mass exhalation rate (mBq kg−1 h−1)  Effective radium content (Bq kg−1)  Annual effective dose (μSv y−1)  1  C1  342.65  207.96 ± 7.88  0.83 ± 0.03  6.40 ± 0.24  0.69  20.96  2  C2  338.80  243.12 ± 6.07  0.97 ± 0.02  7.49 ± 0.19  0.79  24.51  3  C3  338.80  507.66 ± 10.73  2.03 ± 0.04  15.64 ± 0.33  1.66  51.17  4  WC1  338.80  276.76 ± 6.07  1.11 ± 0.02  8.52 ± 0.19  0.90  27.90  5  WC2  342.65  455.67 ± 10.85  1.82 ± 0.04  14.03 ± 0.33  1.50  45.93  6  WC3  342.65  553.53 ± 9.39  2.21 ± 0.04  17.05 ± 0.29  1.83  55.80  7  Sa1  346.50  178.90 ± 6.76  0.72 ± 0.03  5.51 ± 0.21  0.60  18.03  8  Sa2  346.50  428.14 ± 10.41  1.71 ± 0.04  13.19 ± 0.32  1.43  43.16  9  Sa3  346.50  339.46 ± 6.62  1.36 ± 0.03  10.45 ± 0.20  1.13  34.22  10  Sa4  346.50  633.04 ± 35.51  2.53 ± 0.14  19.50 ± 1.09  2.11  63.81  11  Sa5  346.50  463.31 ± 6.76  1.85 ± 0.03  14.27 ± 0.21  1.55  46.70  12  Gy1  331.10  325.70 ± 6.76  1.30 ± 0.03  10.03 ± 0.21  1.04  32.83  13  Gy2  327.25  441.91 ± 10.98  1.77 ± 0.04  13.61 ± 0.34  1.39  44.54  14  Gr1  327.25  526.01 ± 7.22  2.10 ± 0.03  16.20 ± 0.22  1.66  53.02  15  Gr2  346.50  449.55 ± 8.62  1.80 ± 0.03  13.85 ± 0.27  1.50  45.31  16  Gr3  342.65  474.02 ± 10.52  1.90 ± 0.04  14.60 ± 0.32  1.57  47.78  17  So1  342.65  740.08 ± 9.57  2.96 ± 0.04  22.79 ± 0.29  2.44  74.60  18  So2  342.65  1079.53 ± 9.70  4.32 ± 0.04  33.25 ± 0.30  3.56  108.82  S. no.  Sample ID  Size (cm3)  Radon surface exhalation rate (mBq m−2 h−1)  Radon contribution (Bq m−3)  Radon mass exhalation rate (mBq kg−1 h−1)  Effective radium content (Bq kg−1)  Annual effective dose (μSv y−1)  1  C1  342.65  207.96 ± 7.88  0.83 ± 0.03  6.40 ± 0.24  0.69  20.96  2  C2  338.80  243.12 ± 6.07  0.97 ± 0.02  7.49 ± 0.19  0.79  24.51  3  C3  338.80  507.66 ± 10.73  2.03 ± 0.04  15.64 ± 0.33  1.66  51.17  4  WC1  338.80  276.76 ± 6.07  1.11 ± 0.02  8.52 ± 0.19  0.90  27.90  5  WC2  342.65  455.67 ± 10.85  1.82 ± 0.04  14.03 ± 0.33  1.50  45.93  6  WC3  342.65  553.53 ± 9.39  2.21 ± 0.04  17.05 ± 0.29  1.83  55.80  7  Sa1  346.50  178.90 ± 6.76  0.72 ± 0.03  5.51 ± 0.21  0.60  18.03  8  Sa2  346.50  428.14 ± 10.41  1.71 ± 0.04  13.19 ± 0.32  1.43  43.16  9  Sa3  346.50  339.46 ± 6.62  1.36 ± 0.03  10.45 ± 0.20  1.13  34.22  10  Sa4  346.50  633.04 ± 35.51  2.53 ± 0.14  19.50 ± 1.09  2.11  63.81  11  Sa5  346.50  463.31 ± 6.76  1.85 ± 0.03  14.27 ± 0.21  1.55  46.70  12  Gy1  331.10  325.70 ± 6.76  1.30 ± 0.03  10.03 ± 0.21  1.04  32.83  13  Gy2  327.25  441.91 ± 10.98  1.77 ± 0.04  13.61 ± 0.34  1.39  44.54  14  Gr1  327.25  526.01 ± 7.22  2.10 ± 0.03  16.20 ± 0.22  1.66  53.02  15  Gr2  346.50  449.55 ± 8.62  1.80 ± 0.03  13.85 ± 0.27  1.50  45.31  16  Gr3  342.65  474.02 ± 10.52  1.90 ± 0.04  14.60 ± 0.32  1.57  47.78  17  So1  342.65  740.08 ± 9.57  2.96 ± 0.04  22.79 ± 0.29  2.44  74.60  18  So2  342.65  1079.53 ± 9.70  4.32 ± 0.04  33.25 ± 0.30  3.56  108.82  C, cement; WC, white cement; Sa, sand; Gy, gypsum; Gr, gravel; So, soil. For the powdery materials, they ranged from 0.72 ± 0.03 to 4.32 ± 0.04 Bq m−3. The sand sample (Sa1) showed the lowest value, and the daily accumulated radon concentration in a room was estimated at 17.16 Bq m−3. On the other hand, the soil sample (So2) gave the highest value observed in this type of study. Where the daily accumulated radon concentration in a room was estimated to be 103.63 Bq m−3. To study the contribution of building materials to indoor radon concentrations with air changes per hour (ACH), two scenarios were considered: Case I: radon exhalation from a granite countertop Consider a granite countertop (0.67 m × 2.50 m × 0.025 m) installed in a kitchen with an area of 20 m2 and a height of 2.5 m(60), with the assumption that 25% of the kitchen volume is occupied by kitchen wares and furniture, and assuming as well that the kitchen is ventilated with the minimum required ACH of 0.3 h−1, for granite countertops having the highest radon exhalation rate (30.42 Bq m−2 d−1) observed in this study, as shown in Table 2, the radon concentration in the kitchen will be 0.37 Bq m−3. It can be concluded that kitchen granite countertops, under normal ventilation, contribute very little to the radon concentration for the range of radon exhalation rates reported here. Similar assessments were reported in the literature(19, 60). Based on more data available recently, it was assessed that the average radon concentration in Yemen homes is 4 Bq m−3(61). It indicates that on average, granite countertops could contribute to <1% of radon concentration in Yemen homes. Table 1. Radon contribution to indoor radon, surface exhalation rate and annual effective doses, together with the statistical uncertainties (1σ) for the solid slab different building material samples. S. no.  Sample ID  Radon surface exhalation rate (m Bq m−2 h−1)  Radon contribution (Bq m−3)  Annual effective dose (μSv y−1)  1  M1  527.53 ± 10.84  2.11 ± 0.04  53.18  2  M2  275.24 ± 5.43  1.10 ± 0.02  27.74  3  M3  513.77 ± 6.87  2.06 ± 0.03  51.79  4  M4  336.40 ± 6.28  1.35 ± 0.03  33.91  5  Gra1  1267.61 ± 11.84  5.07 ± 0.05  127.78  6  Gra2  1079.53 ± 13.51  4.32 ± 0.05  108.82  7  Ce1  827.23 ± 11.63  3.31 ± 0.05  83.39  8  Ce2  564.23 ± 6.46  2.26 ± 0.03  56.87  9  Ce3  382.27 ± 8.15  1.53 ± 0.03  38.53  10  Ce4  342.52 ± 5.70  1.37 ± 0.02  34.53  11  RB1  519.89 ± 8.00  2.08 ± 0.03  52.40  12  RB2  593.28 ± 6.04  2.37 ± 0.02  59.80  13  T  758.43 ± 6.87  3.03 ± 0.03  76.45  14  CB1  889.93 ± 8.27  3.56 ± 0.03  89.70  15  CB2  1047.42 ± 12.53  4.19 ± 0.05  105.58  S. no.  Sample ID  Radon surface exhalation rate (m Bq m−2 h−1)  Radon contribution (Bq m−3)  Annual effective dose (μSv y−1)  1  M1  527.53 ± 10.84  2.11 ± 0.04  53.18  2  M2  275.24 ± 5.43  1.10 ± 0.02  27.74  3  M3  513.77 ± 6.87  2.06 ± 0.03  51.79  4  M4  336.40 ± 6.28  1.35 ± 0.03  33.91  5  Gra1  1267.61 ± 11.84  5.07 ± 0.05  127.78  6  Gra2  1079.53 ± 13.51  4.32 ± 0.05  108.82  7  Ce1  827.23 ± 11.63  3.31 ± 0.05  83.39  8  Ce2  564.23 ± 6.46  2.26 ± 0.03  56.87  9  Ce3  382.27 ± 8.15  1.53 ± 0.03  38.53  10  Ce4  342.52 ± 5.70  1.37 ± 0.02  34.53  11  RB1  519.89 ± 8.00  2.08 ± 0.03  52.40  12  RB2  593.28 ± 6.04  2.37 ± 0.02  59.80  13  T  758.43 ± 6.87  3.03 ± 0.03  76.45  14  CB1  889.93 ± 8.27  3.56 ± 0.03  89.70  15  CB2  1047.42 ± 12.53  4.19 ± 0.05  105.58  M, marble; RB, red brick; CB, concrete block; Gra, granite; Ce, ceramic; T, tiles. Table 1. Radon contribution to indoor radon, surface exhalation rate and annual effective doses, together with the statistical uncertainties (1σ) for the solid slab different building material samples. S. no.  Sample ID  Radon surface exhalation rate (m Bq m−2 h−1)  Radon contribution (Bq m−3)  Annual effective dose (μSv y−1)  1  M1  527.53 ± 10.84  2.11 ± 0.04  53.18  2  M2  275.24 ± 5.43  1.10 ± 0.02  27.74  3  M3  513.77 ± 6.87  2.06 ± 0.03  51.79  4  M4  336.40 ± 6.28  1.35 ± 0.03  33.91  5  Gra1  1267.61 ± 11.84  5.07 ± 0.05  127.78  6  Gra2  1079.53 ± 13.51  4.32 ± 0.05  108.82  7  Ce1  827.23 ± 11.63  3.31 ± 0.05  83.39  8  Ce2  564.23 ± 6.46  2.26 ± 0.03  56.87  9  Ce3  382.27 ± 8.15  1.53 ± 0.03  38.53  10  Ce4  342.52 ± 5.70  1.37 ± 0.02  34.53  11  RB1  519.89 ± 8.00  2.08 ± 0.03  52.40  12  RB2  593.28 ± 6.04  2.37 ± 0.02  59.80  13  T  758.43 ± 6.87  3.03 ± 0.03  76.45  14  CB1  889.93 ± 8.27  3.56 ± 0.03  89.70  15  CB2  1047.42 ± 12.53  4.19 ± 0.05  105.58  S. no.  Sample ID  Radon surface exhalation rate (m Bq m−2 h−1)  Radon contribution (Bq m−3)  Annual effective dose (μSv y−1)  1  M1  527.53 ± 10.84  2.11 ± 0.04  53.18  2  M2  275.24 ± 5.43  1.10 ± 0.02  27.74  3  M3  513.77 ± 6.87  2.06 ± 0.03  51.79  4  M4  336.40 ± 6.28  1.35 ± 0.03  33.91  5  Gra1  1267.61 ± 11.84  5.07 ± 0.05  127.78  6  Gra2  1079.53 ± 13.51  4.32 ± 0.05  108.82  7  Ce1  827.23 ± 11.63  3.31 ± 0.05  83.39  8  Ce2  564.23 ± 6.46  2.26 ± 0.03  56.87  9  Ce3  382.27 ± 8.15  1.53 ± 0.03  38.53  10  Ce4  342.52 ± 5.70  1.37 ± 0.02  34.53  11  RB1  519.89 ± 8.00  2.08 ± 0.03  52.40  12  RB2  593.28 ± 6.04  2.37 ± 0.02  59.80  13  T  758.43 ± 6.87  3.03 ± 0.03  76.45  14  CB1  889.93 ± 8.27  3.56 ± 0.03  89.70  15  CB2  1047.42 ± 12.53  4.19 ± 0.05  105.58  M, marble; RB, red brick; CB, concrete block; Gra, granite; Ce, ceramic; T, tiles. Case II: radon exhalation from a floor area If a room has a floor area of 20 m2 and a height of 2.5 m as assumed in scenario 1 and its entire floor is decorated with ceramic tiles, slate or granite, and 10% of the room volume is occupied by furniture, the radon concentration, Bq m−3, due to radon exhalation from the floor can be determined by Eq. (4). The resulting radon concentrations are calculated for materials of various radon exhalation rates and for various air change rates, as shown in Table 2. One can infer from Table 2 that even if the entire floor was covered with a material of a relatively high radon exhalation rate, as granites studied here 30.42 Bq m−2 d−1, it would contribute only 1.83 Bq m−3 to a tightly sealed house (minimum required ACH of 0.3 per hour). This is only 1% of the action level for radon in dwellings(62). Higher ventilation rates will reduce the contribution proportionally. In the worst case scenario and when the mechanical ventilation system failed completely and no natural ventilation alternative was provided (ACH = 0), the indoor radon concentration would rise but not above an action level of 200 Bq m−3 for radon in dwellings(62). The effective radium content in powdery samples was calculated using Eq. (6). And the results are provided in Table 3. RECs range from 0.6 to 3.56 Bq kg−1 with a mean value of 1.52 Bq kg−1, whereas in the solid slabs samples this parameter could not be determined. All the values of effective radium content in all samples under test were found to be quite lower than the permissible value recommended by Organization for Economic Cooperation and Development(63). Table 2. Estimate steady-state radon concentration (Bq m−3) due to radon exhalation from floor material with various air change rates. Sample  EA (Bqm−2d−1)  ACH = 3  ACH = 1  ACH = 0.3  ACH = 0.15  ACH = 0  Marble  13.02  0.08  0.24  0.78  1.53  31.97  Ceramic  19.85  0.12  0.36  1.20  2.33  48.75  Tiles  21.92  0.13  0.40  1.32  2.58  53.81  Granite  30.42  0.19  0.56  1.83  3.58  74.69  Sample  EA (Bqm−2d−1)  ACH = 3  ACH = 1  ACH = 0.3  ACH = 0.15  ACH = 0  Marble  13.02  0.08  0.24  0.78  1.53  31.97  Ceramic  19.85  0.12  0.36  1.20  2.33  48.75  Tiles  21.92  0.13  0.40  1.32  2.58  53.81  Granite  30.42  0.19  0.56  1.83  3.58  74.69  Table 2. Estimate steady-state radon concentration (Bq m−3) due to radon exhalation from floor material with various air change rates. Sample  EA (Bqm−2d−1)  ACH = 3  ACH = 1  ACH = 0.3  ACH = 0.15  ACH = 0  Marble  13.02  0.08  0.24  0.78  1.53  31.97  Ceramic  19.85  0.12  0.36  1.20  2.33  48.75  Tiles  21.92  0.13  0.40  1.32  2.58  53.81  Granite  30.42  0.19  0.56  1.83  3.58  74.69  Sample  EA (Bqm−2d−1)  ACH = 3  ACH = 1  ACH = 0.3  ACH = 0.15  ACH = 0  Marble  13.02  0.08  0.24  0.78  1.53  31.97  Ceramic  19.85  0.12  0.36  1.20  2.33  48.75  Tiles  21.92  0.13  0.40  1.32  2.58  53.81  Granite  30.42  0.19  0.56  1.83  3.58  74.69  Finally, it is necessary to estimate the radon emanation potential from building materials to evaluate the radiation risk to the inhabitants. Thus, the assessment of the annual effective dose expected to be received by populations due to radon and its progenies were based on the calculations of radon exhalation rates. The minimum, maximum and mean annual effective doses were found to be 27.74, 127.78 and 66.70 μSv y−1 for the slabs samples, and 18.03, 108.82 and 46.62 μSv y−1 for the powdery samples. The slabs samples giving the lowest values of the annual effective dose were marble (M2) from Yemen (Taiz); the lowest dose value from the powdery samples was attributed to the Sa1, denoting Yemen sand. The highest dose from the slabs samples came from granite in Yemen and the highest dose in the powdery samples came from So2, denoting Yemen. The results obtained are shown in Tables 3 and 1. The results of the current study have been compared with already published data (Table 4). Table 4. Comparison between surface exhalation rates (EA) and mass exhalation rates (EM) of some building materials in different countries. Material  Country  EA (mBq m−2 h−1)  EM (m Bq kg−1 h−1)  Reference  Cement  Sudan  379  4.5  (65)  Indian  263.3–401.6  12.1–18.4  (66)  Libya  523.2  20.4  (10)  Yemen  243.12–492.37  6.405–15.164  Present work  White cement  Libya  550.9  20.8  (10)  Indian  417–437  13.8–20.1  (66)  Yemen  276.76–553.53  8.524–17.048  Present work  Sand  Pakistan  205–291    (67)  Pakistan  366–649    (7)  Libya  722.2  27.4  (10)  Yemen  178.90–633.04  5.510–19.497  Present work  Ceramic  Sudan  240    (65)  Canada  8.33–125    (60)  Libya  69.5–73.7    (10)  Yemen  382.27–827.23    Present work  Granite  Libya  733.2–17 221.2    (10)  Greece  1240–3540    (68)  KSA  333–1250    (69)  Yemen  1079.53–1267.61    Present work  Gypsum  Egypt  26.28    (30)  Libya  147.5–365.5  17.4–43.1  (10)  Yemen  325.70–441.91  10.031–13.610  Present work  Brick  Pakistan  184–231    (7)  Pakistan  245–365    (67)  Libya  123.7–1625.1    (10)  Yemen  519.89–593.28    Present work  Gravel  Canada  45.83–4245.83    (19)  Pakistan  168–322    (7)  Yemen  449.55–526.01  13.85–16.20  Present work  Marble  Libya  142.3–970.6    (10)  Italy  65.4    (43)  Canada  4.17–25    (60)  Algeria  35–66    (70)  Yemen  275.24–527.53    Present work  Soil  Libyan  58.3–506.9  1.2–17.4  (14)  KSA  45–8400  135–251  (59)  India    6–56  (36)  Pakistan  114–416    (67)  Egypt  480–15 370  8.31–233.70  (31)  Yemen  740.08–1079.53  22.794–33.248  Present work  Material  Country  EA (mBq m−2 h−1)  EM (m Bq kg−1 h−1)  Reference  Cement  Sudan  379  4.5  (65)  Indian  263.3–401.6  12.1–18.4  (66)  Libya  523.2  20.4  (10)  Yemen  243.12–492.37  6.405–15.164  Present work  White cement  Libya  550.9  20.8  (10)  Indian  417–437  13.8–20.1  (66)  Yemen  276.76–553.53  8.524–17.048  Present work  Sand  Pakistan  205–291    (67)  Pakistan  366–649    (7)  Libya  722.2  27.4  (10)  Yemen  178.90–633.04  5.510–19.497  Present work  Ceramic  Sudan  240    (65)  Canada  8.33–125    (60)  Libya  69.5–73.7    (10)  Yemen  382.27–827.23    Present work  Granite  Libya  733.2–17 221.2    (10)  Greece  1240–3540    (68)  KSA  333–1250    (69)  Yemen  1079.53–1267.61    Present work  Gypsum  Egypt  26.28    (30)  Libya  147.5–365.5  17.4–43.1  (10)  Yemen  325.70–441.91  10.031–13.610  Present work  Brick  Pakistan  184–231    (7)  Pakistan  245–365    (67)  Libya  123.7–1625.1    (10)  Yemen  519.89–593.28    Present work  Gravel  Canada  45.83–4245.83    (19)  Pakistan  168–322    (7)  Yemen  449.55–526.01  13.85–16.20  Present work  Marble  Libya  142.3–970.6    (10)  Italy  65.4    (43)  Canada  4.17–25    (60)  Algeria  35–66    (70)  Yemen  275.24–527.53    Present work  Soil  Libyan  58.3–506.9  1.2–17.4  (14)  KSA  45–8400  135–251  (59)  India    6–56  (36)  Pakistan  114–416    (67)  Egypt  480–15 370  8.31–233.70  (31)  Yemen  740.08–1079.53  22.794–33.248  Present work  Table 4. Comparison between surface exhalation rates (EA) and mass exhalation rates (EM) of some building materials in different countries. Material  Country  EA (mBq m−2 h−1)  EM (m Bq kg−1 h−1)  Reference  Cement  Sudan  379  4.5  (65)  Indian  263.3–401.6  12.1–18.4  (66)  Libya  523.2  20.4  (10)  Yemen  243.12–492.37  6.405–15.164  Present work  White cement  Libya  550.9  20.8  (10)  Indian  417–437  13.8–20.1  (66)  Yemen  276.76–553.53  8.524–17.048  Present work  Sand  Pakistan  205–291    (67)  Pakistan  366–649    (7)  Libya  722.2  27.4  (10)  Yemen  178.90–633.04  5.510–19.497  Present work  Ceramic  Sudan  240    (65)  Canada  8.33–125    (60)  Libya  69.5–73.7    (10)  Yemen  382.27–827.23    Present work  Granite  Libya  733.2–17 221.2    (10)  Greece  1240–3540    (68)  KSA  333–1250    (69)  Yemen  1079.53–1267.61    Present work  Gypsum  Egypt  26.28    (30)  Libya  147.5–365.5  17.4–43.1  (10)  Yemen  325.70–441.91  10.031–13.610  Present work  Brick  Pakistan  184–231    (7)  Pakistan  245–365    (67)  Libya  123.7–1625.1    (10)  Yemen  519.89–593.28    Present work  Gravel  Canada  45.83–4245.83    (19)  Pakistan  168–322    (7)  Yemen  449.55–526.01  13.85–16.20  Present work  Marble  Libya  142.3–970.6    (10)  Italy  65.4    (43)  Canada  4.17–25    (60)  Algeria  35–66    (70)  Yemen  275.24–527.53    Present work  Soil  Libyan  58.3–506.9  1.2–17.4  (14)  KSA  45–8400  135–251  (59)  India    6–56  (36)  Pakistan  114–416    (67)  Egypt  480–15 370  8.31–233.70  (31)  Yemen  740.08–1079.53  22.794–33.248  Present work  Material  Country  EA (mBq m−2 h−1)  EM (m Bq kg−1 h−1)  Reference  Cement  Sudan  379  4.5  (65)  Indian  263.3–401.6  12.1–18.4  (66)  Libya  523.2  20.4  (10)  Yemen  243.12–492.37  6.405–15.164  Present work  White cement  Libya  550.9  20.8  (10)  Indian  417–437  13.8–20.1  (66)  Yemen  276.76–553.53  8.524–17.048  Present work  Sand  Pakistan  205–291    (67)  Pakistan  366–649    (7)  Libya  722.2  27.4  (10)  Yemen  178.90–633.04  5.510–19.497  Present work  Ceramic  Sudan  240    (65)  Canada  8.33–125    (60)  Libya  69.5–73.7    (10)  Yemen  382.27–827.23    Present work  Granite  Libya  733.2–17 221.2    (10)  Greece  1240–3540    (68)  KSA  333–1250    (69)  Yemen  1079.53–1267.61    Present work  Gypsum  Egypt  26.28    (30)  Libya  147.5–365.5  17.4–43.1  (10)  Yemen  325.70–441.91  10.031–13.610  Present work  Brick  Pakistan  184–231    (7)  Pakistan  245–365    (67)  Libya  123.7–1625.1    (10)  Yemen  519.89–593.28    Present work  Gravel  Canada  45.83–4245.83    (19)  Pakistan  168–322    (7)  Yemen  449.55–526.01  13.85–16.20  Present work  Marble  Libya  142.3–970.6    (10)  Italy  65.4    (43)  Canada  4.17–25    (60)  Algeria  35–66    (70)  Yemen  275.24–527.53    Present work  Soil  Libyan  58.3–506.9  1.2–17.4  (14)  KSA  45–8400  135–251  (59)  India    6–56  (36)  Pakistan  114–416    (67)  Egypt  480–15 370  8.31–233.70  (31)  Yemen  740.08–1079.53  22.794–33.248  Present work  CONCLUSION The two highest values of radon exhalation observed in the studied solid slabs samples came from the Yemeni granite and the Chinese granite. For this reason, these two materials are not favorable for decorative use and should be replaced by other alternatives. For the powdery sample, the soil was found to have a high level of radon exhalation. However, there exists only a small number of houses which are made of mud alone. Without ventilation, elevated radon levels could arise. In general, the current results are within the world-wide range of values found in soil, and this range is within the safe limits recommended by the United Nations Scientific Committee on the Effects of Atomic Radiation(64). The effective radium content and annual effective dose equivalents are within the safe limits recommended by Organization for Economic Cooperation and Development (OECD)(63), European Commission (EC)(3) and United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR)(64). 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