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Radon concentration and radon effective dose rate in dwellings of some villages in the district of Ajloun, Jordan
Applied Radiation and Isotopes 70 (2012) 1579–1582
Contents lists available at SciVerse ScienceDirect
Applied Radiation and Isotopes journal homepage: www.elsevier.com/locate/apradiso
Radon concentration and radon effective dose rate in dwellings of some villages in the district of Ajloun, Jordan H.M. Al-Khateeb a,n, A.A. Al-Qudah b, F.Y. Alzoubi a, M.K. Alqadi a, K.M. Aljarrah a a b
Department of Physics, Jordan University of Science and Technology, P.O. Box 3030 Irbid 22110, Jordan Department of Physics, College of Science/Girl Branch, University of Ha’il, P.O. Box 2440, Hail, Saudi Arabia
a r t i c l e i n f o
abstract
Article history: Received 1 October 2011 Received in revised form 21 March 2012 Accepted 10 April 2012 Available online 13 April 2012
Indoor and soil radon concentrations were measured in the villages of Ayn-Jana, Ishtafena, Samta and Umm-Yanabe’ in the district of Ajloun, Jordan. Several factors that are strongly related to the radon concentrations are considered whether in soil such as its type or indoors such as room occupation type, floor level and building materials. In the village of Ayn-Jana, our results showed that the average radon concentration decreases gradually as the floor level increases. The highest concentration was found to be in the ground floor (35.575.0 Bq m 3) and the lowest was in the second floor (22.973.2 Bq m 3). Regarding the effect of ventilation rate in the same village, storage rooms revealed the highest concentration (38.875.4 Bq m 3) while the lowest concentration was in living rooms (33.874.4 Bq m 3). In the four villages, it was found that the highest radon concentration was in the dwellings made of clay (45.776.7 Bq m 3) and the lowest was in dwellings made of brick (33.976.4 Bq m 3). In general, the average indoor radon concentration in these villages was 36.372.3 Bq m 3 and it corresponds to an average effective dose rate of 0.9270.06 mSv yr 1. These indoor radon concentrations as well as the annual effective dose are below the action level recommended by ICRP. The average radon concentration in soil of these villages was about 2.5570.20 kBq m 3, and it ranges from 2.0870.12 kBq m 3 in the village of Ayn-Jana to 3.6270.13 kBq m 3 in the village of Ishtafena. & 2012 Elsevier Ltd. All rights reserved.
Keywords: Radon Indoor air Effective doses Different floor Building material Jordan
1. Introduction Radon is a natural inert gas produced continuously from decay of radium in natural decay chains of uranium and thorium in soil, rocks and water all over the earth. The radioisotope 222Rn (usually called radon), produced from the decay of 238U, is the main source of radiation exposure to human life (ICRP, 1993). Radon has a longer half-life (3.83 days), while other isotopes, 220Rn (usually called Thoron) and 219Rn (usually called Actinon), produced from 232 Th and 235U respectively, are usually less significant because of their much shorter half-lives. Therefore, radon is the most dominant hazardous radionuclide. If radon is inhaled, it decays in lungs by means of alpha-emission and causes damages as the emitted alpha particles strike the lung tissues, resulting in lung cancer in the long term (ICRP, 1993; Bochicchio et al., 1988; Field et al., 2000). Radon is considered to be the second leading cause of lung cancer after smoking.
n Corresponding author. Current address: Basic Sciences Department, College of Medicine, King Saud Bin Abdulaziz University for Health Sciences, P.O. Box 22490, Riyadh 11426, Saudi Arabia. Fax: þ 966 1 252 0088x47130. E-mail addresses: [email protected], [email protected] (H.M. Al-Khateeb).
0969-8043/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apradiso.2012.04.009
Worldwide studies were conducted to measure and tabulate radon concentration in soil, air and water to end up with recommendations as well as to build databases (UNSCEAR, 2000; Al-Kofahi et al., 1992; Abu-Jarad et al., 2003; Magalhaes et al., 2003; Srivastava, 2004; Akrama et al., 2005; Diyuna et al., 2005; Friedmann, 2002; Pouloa et al., 2005). In Jordan, several indoor radon surveys have been carried out. For example, AlKofahi et al. (1992) studied radon levels in the city of Irbid while Abumurad et al. (1997) and Khatibeh et al. (1997) conducted comprehensive studies of radon levels covering the main cities in Jordan. Rabadi and Abumurad (2008) measured radon concentrations in dwellings, soil and water of Ajloun city. As a complementary, we measured radon concentrations indoor and in soil in the villages of Ayan-Jana, Ishtafena, Samta and Umm-Yanabe’ in the district of Ajloun, in order to assess public exposure to radon. The district of Ajloun has more than 130,000 inhabitants, who constitute about 4% of the Jordan’s total population. Ajloun city lies in northwest of Jordan at about 70 km from Amman, capital Jordan, and at about 770 m above sea level. The villages under investigation lie in forests of green oak and pine trees around the city and they are at about 900–1100 m above sea level. No standard pattern for houses in these villages is noticed and they typically consist of three up to four rooms built of stones, cement and bricks while old houses are made of clay and stone.
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H.M. Al-Khateeb et al. / Applied Radiation and Isotopes 70 (2012) 1579–1582
the formula
2. Experiment
C ¼ C o rt o =ro t,
In this study we used a time-integrated passive radon dosimeter containing CR-39 solid state nuclear track detectors (SSNTDs). The CR-39 detector (500 mm thick) is the diglycol carbonate (C12H18O7) supplied by Pershore Molding Ltd., UK. The dosimeter consists of a closed cylindrical chamber, with the CR-39 detector stuck to its bottom surface, and has a small hole in its top surface covered by sponge to allow the diffusion of radon into and prevent other components. A detailed description of these dosimeters can be found elsewhere (Abumurad et al., 1994, Al-Bataina et al., 1997). In this study, 350 dosimeters were distributed randomly over the area of interest in summer season. One hundred dosimeters were installed into the soil at a depth of 40 cm (above this depth the soil is usually unstable due to the plowing it undergoes for planting purposes) and the rest were distributed indoors. In each dwelling, three dosimeters at least were distributed to cover the living room, bedroom and storage room (one dosimeter in each room). For multi-floor dwellings, additional dosimeters were installed in the living rooms of each floor above the ground. Twenty days later for soil dosimeters and 3 months later for indoors ones, detectors were collected and etched using 30% KOH solution for 9 h at 70 1C, then washed with distilled water and dried to be ready for alpha tracks counting. An optical microscope, with proper magnification, was used to count manually the number of tracks per square centimeter for at least 30 different sectors of each detector to obtain an arithmetic average track density. To convert the track density of alpha particles into radon concentration, a calibration factor obtained by Al-Batania in the School of Physics and Space Research at Birmingham University, England (Al-Bataina et al., 1997) was used. During the calibration, dosimeters were placed inside the radon chamber for 48 h at a concentration of 90 kBq m 3. To make this calibration suitable for all radon levels (in air, water and soil), Al-Bataina placed 10 dosimeters inside the radon chamber at once. After 5 h the first dosimeter was taken out and the track density of its CR-39 detector was measured. After 10 h the second dosimeter was taken out to measure the track density of its detector. After 15 h, the third dosimeter was taken out and so on until the rest of dosimeters were taken out. By plotting radon dose (concentration (kBq m 3)xtime (h) versus the density of tracks (no. of tracks/ cm2) a linear relationship was found between these variables. The radon concentration C in units of Bq m 3 can be calculated using
ð1Þ
where Co is the radon concentration of the calibration chamber (90 kBq m 3), to is the calibration exposure time (48 h), ro is the measured tracks density of the calibrated dosimeters (3.31 104 tracks cm-2), r is the measured tracks density of the CR-39 detectors used in the study, t is the exposure time and C is the radon concentration to be determined. It is important to estimate the annual effective dose rate (ED) for radon exposure. According to the UNSCEAR (2000) report, indoor effective dose rate of radon in units of mSv yr 1 can be calculated by the following formula ED ¼ C annual FTDð24 hÞð365Þð106 Þ,
ð2Þ 3
where Cannual is the annual radon concentration (in Bq m ), F is the indoor radon equilibrium factor (0.4), T is the indoor occupancy time (0.8) and D is the dose conversion factor (9.0 nSv h 1 per 1 Bq m 3). In order to use our data, which was measured during summer season, to estimate the annual effective dose rate, we have to figure out the relationship between average annual radon concentration and summer radon concentration. Depending on a study done by Kullab et al. (2001) to estimate the seasonal variation of indoor radon concentration in specific locations in Jordan, we can write ( ) 1:37C summer for ground floors C annual ¼ , ð3Þ 1:04C summer for first floors where Csummmer is the average radon concentration in the summer season. Due to the unavailability of data for the second floor, we used the same formula for the first floors to estimate annual radon concentrations for the second floors.
3. Results and discussion In this study, indoor radon concentrations were measured in the villages of Ayn-Jana, Ishtafena, Samta and Umm-Yanabe’ in the district of Ajloun, Jordan. Factors affecting radon concentration were studied such as floor level, room type and building materials. Table 1 reflects the variation of radon concentration over the different floor levels. It shows the minimum, maximum, arithmetic average and the standard deviation for radon concentration in the dwellings of Ayn-Jana village. It is clear that the
Table 1 Indoor radon concentration for different floors in Ayn-Jana village.
n
Floor number
Min. concentration (Bq m 3)
Max. concentration (Bq m 3)
Average concentration (Bq m 3)
Average radon effective dose (mSv yr 1)n
Ground floor First floor Second floor
13.7 72.8 16.4 72.2 15.0 73.0
87.4 7 10.0 48.8 7 6.0 36.8 7 4.2
35.5 7 5.0 27.9 7 3.6 22.9 7 3.2
1.23 70.19 0.73 70.11 0.60 70.09
Under the assumption made for Eq. (3) above.
Table 2 Indoor radon concentration for different kinds of rooms in Ayn-Jana village. Kind of room
Min. concentration (Bq m-3)
Max. concentration (Bq m 3)
Average concentration (Bq m 3)
Indoor occupancy factorn
Annual radon Effective dose (mSv yr 1)
Living room Bedroom Storage room
14.8 7 1.9 15.5 7 2.9 13.7 7 2.8
74.27 9.6 79.27 5.8 74.77 4.2
33.87 4.4 35.57 4.6 38.87 5.4
0.38 0.34 0.02
0.474 70.063 0.443 70.061 0.028 70.004
n Under the assumption that on average, the people in the investigation area stay in bedrooms for 8 h, in living rooms for 9 h, in kitchens for 1.5 h and in storage rooms for half an hour.
H.M. Al-Khateeb et al. / Applied Radiation and Isotopes 70 (2012) 1579–1582
average radon concentration decreases as the floor level increases and this variation may be attributed to how close or how far the floor is from ground since soil represents the main source of indoor radon in addition to many other reasons such as the fact that upper floors are better ventilated than lower floors that are exposed to dust and other forms of contaminations. These variations of radon concentrations were reflected on the average estimated annual radon doses (ED) for which the highest dose (1.2370.19 mSv yr 1) belongs to the ground floor and the lowest (0.6070.09 mSv yr 1) belongs to the second floor. Table 2 shows the variation of radon concentrations for different types of rooms in the Ayn-Jana village. Storage rooms have a slightly higher radon concentration among others with an average of about 38.875.4 Bq m 3, while a lower average concentration of about 33.8 74.4 Bq m 3 was found in living rooms. This may be because the living rooms are better ventilated than storage rooms. Bedrooms are less used than living rooms but more used than storage rooms and therefore their average radon concentration falls in between. To estimate the annual effective radon doses in different room types, it is necessary to partition the indoor occupancy factor among them. Table 2 shows this
Radon Concentration (Bq m-3)
100 90 80 70
Clay Stone Concrete Brick
60 50 40 30 20 10 0
Any-Jana
Ishtafena Samta Ajloun Villages
Um Yanabe'
Fig. 1. The variation of radon concentrations for different types of building materials in the four villages (radon concentrations of living rooms on the ground floor). Note that there are no dwellings made of clay in the village of Samta.
partitioning as well as the annual effective radon doses. The minimum value of annual radon dose was in storage rooms and the maximum value was in living rooms. These results reverse the average radon concentration results because the indoor occupation factor plays an important role in determining the annual radon dose. To estimate the effect of building materials on the radon concentration, Fig. 1 shows the variation of radon concentrations for different types of building materials in the four villages (radon concentrations of living rooms on the ground floor). It is clear that the highest radon concentration was in the dwellings made of clay and may be attributed to the age and poor maintenance of these dwellings compared to others. Furthermore, the exhalation of radon from the walls and floors of clay dwellings is higher than that of modern dwellings because of the cracks and defective joints in their walls and floors. On the other hand, the lowest average radon concentration was detected in the dwellings made of brick because walls are usually thin and empty; this reduces the exhalation rate of radon. In general, the average radon concentration indoors in these villages was 36.372.3 Bq m 3 and it corresponds to an average effective dose rate of 0.9270.06 mSv yr 1. These indoor radon concentrations as well as the annual effective dose are below the action level recommended byICRP (1993). Radon concentrations in soil were measured in the four villages. Table 3 shows the minimum, maximum and average radon concentration in kBq m 3. The highest soil radon concentration (3.6270.13 kBq m 3) was detected in the Ishtafena village and the lowest (2.08 70.12 kBq m 3) was in Ayn-Jana village. The average soil radon concentrations in the villages of the Ayn-Jana, Samta and Umm-Yanabe’ are approximately the same and it may return to the similarity of their geological location. The high soil radon concentration in Ishtafena village may be attributed to the excavation activity of the earth crust in that region as a result of building and road construction activities accompanied by utilizing a very hard and expensive stone layer that covers the top of the ground in most parts of this village. The average radon concentration in the soil of these villages was about 2.55 70.20 kBq m 3. To the best of our knowledge, there are no previous reports of radon concentration in our chosen fields of study; however there are some reported data on radon levels in nearby areas such as Ajloun city itself. Table 4 lists our results accompanied by others
Table 3 Soil radon concentration in the villages of Ajloun. Village
Min. concentration (kBq m 3)
Max. concentration (kBq m 3)
Average concentration (kBq m 3)
Ayn-Jana Samta Umm-Yanabe’ Ishtafena
0.257 0.02 1.047 0.04 0.487 0.02 2.38 7 0.07
4.39 7 0.16 4.52 7 0.22 4.36 7 0.19 5.11 7 0.18
2.08 70.12 2.15 70.13 2.36 70.09 3.62 70.13
Table 4 Radon concentration comparison. Region
Indoor radon concentration (Bq m3)
Soil radon concentration (kBq m 3)
Reference
Villages Studied here Ajloun Ajloun Ajloun Jordan
36.3 7 2.3 27.6 7 1.8 40.08 7 27.00 52.0* 56.7*
2.557 0.20 3.407 1.4 – – –
Present study Rabadi and Abumurad (2008) Abumurad et al. (1997) Khatibeh et al. (1997) Abumurad, et al. (1997)
n
Errors are unavailable
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for indoor and soil radon concentrations. Our results for indoor radon are higher than those measured by Rabadi and Abumurad (2008) but lower than those measured by Abumurad et al. (1997) and Khatibeh et al. (1997). Moreover, our results are less than the average national indoor radon concentration of Jordan. Soil radon results of this study are in good agreement with the results from Rabadi and Abumurad (2008).
4. Conclusion Indoor radon concentrations have been measured in four villages of the district of Ajloun, Jordan. These concentrations were measured according to a variety of effective factors such as room type, floor level and building materials. In the Ayn-Jana village, it was found that the radon concentration decreases gradually with floor level. Regarding ventilation rate of rooms in the same village, it was found that the highest radon concentration was in the storage room and the lowest in the living rooms. In all villages under investigation, it was found that the highest radon concentration was in the dwellings made of clay (45.776.7 Bq m 3) and the lowest was in dwellings made of brick (33.976.4 Bq m 3). The average indoor radon concentration for the whole survey was about 36.372.3 Bq m 3 and corresponds to an annual effective dose of 0.9270.06 mSv yr 1. The average soil radon concentration of these villages was found to be 2.55 70.20 kBq m 3. Acknowledgments The authors would like to thank the Deanship of Research at Jordan University of Science and Technology for financially supporting this project. Also, thanks go to Prof. Jing Chen for reading the manuscript. References Abu-Jarad, F., Fazal-ur-Rehman, Al-Jarallah, M.I., Al-Shukri, A., 2003. Indoor radon survey in dwellings of nine cities of the eastern and western provinces of Saudi Arabia. Radiat. Prot. Dosim. 106, 227–232.
Abumurad, K., Kullab, M., Al-Bataina, B., Ismail, A., Lehlooh, A., 1994. Estimate of radon concentrations inside houses in some Jordanian regions. Mu’tah J. Res. Stud. B9, 9–21. Abumurad, K., Al-Bataina, B., Ismail, A., Kullab, M., Al-Eloosy, A., 1997. A survey of radon levels in Jordanian dwellings during an autumn season. Radiat. Prot. Dosim. 69, 221–226. Akrama, M., Khattaka, N.U., Iqbalb, A., Qureshia, A.A., Ullaha, K., Qureshia, I.E., 2005. Measurement of radon concentration in dwellings of Skardu city, Pakistan. Radiat. Meas. 40, 695–698. Al-Bataina., B.A., Ismail, A.M., Kullab, M.K., Abumurad, K.M., Mustafa., H., 1997. Radon measurements in different types of natural waters in Jordan. Radiat. Meas. 28, 591–594. Al-Kofahi, M.M., Khader, B.R., Lehlooh, A.D., Kullab, M.K., Abumurad, K.M., AlBataina, B.A., 1992. Measurement of radon 222 in Jordanian dwellings. Nucl. Tracks Radiat. Meas. 20, 377–382. Bochicchio, F., Forastiere, F., Abeni, D., Rapiti, E., 1988. Epidemiologic studies on lung cancer and residential exposure to radon in Italy and other countries. Radiat. Prot. Dosim. 78, 33–38. Diyuna, C., Xingbaoa, Y., Ruiying, H., 2005. Indoor radon survey in indoor environments in Zhuhai city, China. Radiat. Meas. 39, 205–207. Field, R.W., Steck, D.J., Brus, C.P., Neuberger, J.S., Fisher, E.F., Platz, C.E., et al., 2000. Residential gas exposure and lung cancer: the Iowa radon lung cancer study. Am. J. Epidemiol. 151, 1091–1102. Friedmann, H., 2002. Radon in Austria. In: Bukart, W., Shorabi, M., Bayer A. (Eds), Proceeding of the Fifth International Conference on High Levels of Natural Radiation and Radon Areas: Radiation Dose and Health Effects. Munich, Germany, 4–7 September, 2000, p. 162. ICRP, 1993. Protection against radon-222 at home and at works Ann. ICRP 23(2).(ICRP Publication 65). Khatibeh, A.J.A.H., Ahmad, N., Matiullah, M.A., Kenawy, K.M., Abu-murad, K.M., Kullab, M., et al., 1997. Measurement of indoor radon concentration levels in some cities of Jordan. Radiat. Meas. 28, 589–590. Kullab, M.K., Al-Bataina, B.A., Ismail, A.M., Abumurad, K.M., 2001. Seasonal variation of radon-222 concentrations in specific locations in Jordan. Radiat. Meas. 34, 361–364. Magalhaes, M.H., Amaral, E.C.S., Sachet, I., Rochedo, E.R.R., 2003. Radon-222 in Brazil: an outline of indoor and outdoor measurements. J. Environ. Radioact. 67, 131–143. Pouloa, S.R., Nemanb, R., Netob, J.C.H., Iunesb, P.J., Guedesb, S., Balanc, A.M.O.A., et al., 2005. Radon surveys in Brazil using CR-39. Radiat. Meas. 39, 657–700. Rabadi, R.R., Abumurad, K.M., 2008. Radon surveys in Ajloun city using CR-39 Detector. Radiat. Meas. 43, S449–S451. Srivastava, A., 2004. An overview of indoor radon study carried out in dwellings in India and Bangladesh during the last decade using solid state nuclear track detectors. J. Environ. Radioact. 78, 113–121. UNSCEAR, 2000. United Nations Scientific Committee on the Effect of Atomic Radiation (UNSCEAR). Sources and Effects on Ionizing Radiation. United Nation, New York.
Contents lists available at SciVerse ScienceDirect
Applied Radiation and Isotopes journal homepage: www.elsevier.com/locate/apradiso
Radon concentration and radon effective dose rate in dwellings of some villages in the district of Ajloun, Jordan H.M. Al-Khateeb a,n, A.A. Al-Qudah b, F.Y. Alzoubi a, M.K. Alqadi a, K.M. Aljarrah a a b
Department of Physics, Jordan University of Science and Technology, P.O. Box 3030 Irbid 22110, Jordan Department of Physics, College of Science/Girl Branch, University of Ha’il, P.O. Box 2440, Hail, Saudi Arabia
a r t i c l e i n f o
abstract
Article history: Received 1 October 2011 Received in revised form 21 March 2012 Accepted 10 April 2012 Available online 13 April 2012
Indoor and soil radon concentrations were measured in the villages of Ayn-Jana, Ishtafena, Samta and Umm-Yanabe’ in the district of Ajloun, Jordan. Several factors that are strongly related to the radon concentrations are considered whether in soil such as its type or indoors such as room occupation type, floor level and building materials. In the village of Ayn-Jana, our results showed that the average radon concentration decreases gradually as the floor level increases. The highest concentration was found to be in the ground floor (35.575.0 Bq m 3) and the lowest was in the second floor (22.973.2 Bq m 3). Regarding the effect of ventilation rate in the same village, storage rooms revealed the highest concentration (38.875.4 Bq m 3) while the lowest concentration was in living rooms (33.874.4 Bq m 3). In the four villages, it was found that the highest radon concentration was in the dwellings made of clay (45.776.7 Bq m 3) and the lowest was in dwellings made of brick (33.976.4 Bq m 3). In general, the average indoor radon concentration in these villages was 36.372.3 Bq m 3 and it corresponds to an average effective dose rate of 0.9270.06 mSv yr 1. These indoor radon concentrations as well as the annual effective dose are below the action level recommended by ICRP. The average radon concentration in soil of these villages was about 2.5570.20 kBq m 3, and it ranges from 2.0870.12 kBq m 3 in the village of Ayn-Jana to 3.6270.13 kBq m 3 in the village of Ishtafena. & 2012 Elsevier Ltd. All rights reserved.
Keywords: Radon Indoor air Effective doses Different floor Building material Jordan
1. Introduction Radon is a natural inert gas produced continuously from decay of radium in natural decay chains of uranium and thorium in soil, rocks and water all over the earth. The radioisotope 222Rn (usually called radon), produced from the decay of 238U, is the main source of radiation exposure to human life (ICRP, 1993). Radon has a longer half-life (3.83 days), while other isotopes, 220Rn (usually called Thoron) and 219Rn (usually called Actinon), produced from 232 Th and 235U respectively, are usually less significant because of their much shorter half-lives. Therefore, radon is the most dominant hazardous radionuclide. If radon is inhaled, it decays in lungs by means of alpha-emission and causes damages as the emitted alpha particles strike the lung tissues, resulting in lung cancer in the long term (ICRP, 1993; Bochicchio et al., 1988; Field et al., 2000). Radon is considered to be the second leading cause of lung cancer after smoking.
n Corresponding author. Current address: Basic Sciences Department, College of Medicine, King Saud Bin Abdulaziz University for Health Sciences, P.O. Box 22490, Riyadh 11426, Saudi Arabia. Fax: þ 966 1 252 0088x47130. E-mail addresses: [email protected], [email protected] (H.M. Al-Khateeb).
0969-8043/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apradiso.2012.04.009
Worldwide studies were conducted to measure and tabulate radon concentration in soil, air and water to end up with recommendations as well as to build databases (UNSCEAR, 2000; Al-Kofahi et al., 1992; Abu-Jarad et al., 2003; Magalhaes et al., 2003; Srivastava, 2004; Akrama et al., 2005; Diyuna et al., 2005; Friedmann, 2002; Pouloa et al., 2005). In Jordan, several indoor radon surveys have been carried out. For example, AlKofahi et al. (1992) studied radon levels in the city of Irbid while Abumurad et al. (1997) and Khatibeh et al. (1997) conducted comprehensive studies of radon levels covering the main cities in Jordan. Rabadi and Abumurad (2008) measured radon concentrations in dwellings, soil and water of Ajloun city. As a complementary, we measured radon concentrations indoor and in soil in the villages of Ayan-Jana, Ishtafena, Samta and Umm-Yanabe’ in the district of Ajloun, in order to assess public exposure to radon. The district of Ajloun has more than 130,000 inhabitants, who constitute about 4% of the Jordan’s total population. Ajloun city lies in northwest of Jordan at about 70 km from Amman, capital Jordan, and at about 770 m above sea level. The villages under investigation lie in forests of green oak and pine trees around the city and they are at about 900–1100 m above sea level. No standard pattern for houses in these villages is noticed and they typically consist of three up to four rooms built of stones, cement and bricks while old houses are made of clay and stone.
1580
H.M. Al-Khateeb et al. / Applied Radiation and Isotopes 70 (2012) 1579–1582
the formula
2. Experiment
C ¼ C o rt o =ro t,
In this study we used a time-integrated passive radon dosimeter containing CR-39 solid state nuclear track detectors (SSNTDs). The CR-39 detector (500 mm thick) is the diglycol carbonate (C12H18O7) supplied by Pershore Molding Ltd., UK. The dosimeter consists of a closed cylindrical chamber, with the CR-39 detector stuck to its bottom surface, and has a small hole in its top surface covered by sponge to allow the diffusion of radon into and prevent other components. A detailed description of these dosimeters can be found elsewhere (Abumurad et al., 1994, Al-Bataina et al., 1997). In this study, 350 dosimeters were distributed randomly over the area of interest in summer season. One hundred dosimeters were installed into the soil at a depth of 40 cm (above this depth the soil is usually unstable due to the plowing it undergoes for planting purposes) and the rest were distributed indoors. In each dwelling, three dosimeters at least were distributed to cover the living room, bedroom and storage room (one dosimeter in each room). For multi-floor dwellings, additional dosimeters were installed in the living rooms of each floor above the ground. Twenty days later for soil dosimeters and 3 months later for indoors ones, detectors were collected and etched using 30% KOH solution for 9 h at 70 1C, then washed with distilled water and dried to be ready for alpha tracks counting. An optical microscope, with proper magnification, was used to count manually the number of tracks per square centimeter for at least 30 different sectors of each detector to obtain an arithmetic average track density. To convert the track density of alpha particles into radon concentration, a calibration factor obtained by Al-Batania in the School of Physics and Space Research at Birmingham University, England (Al-Bataina et al., 1997) was used. During the calibration, dosimeters were placed inside the radon chamber for 48 h at a concentration of 90 kBq m 3. To make this calibration suitable for all radon levels (in air, water and soil), Al-Bataina placed 10 dosimeters inside the radon chamber at once. After 5 h the first dosimeter was taken out and the track density of its CR-39 detector was measured. After 10 h the second dosimeter was taken out to measure the track density of its detector. After 15 h, the third dosimeter was taken out and so on until the rest of dosimeters were taken out. By plotting radon dose (concentration (kBq m 3)xtime (h) versus the density of tracks (no. of tracks/ cm2) a linear relationship was found between these variables. The radon concentration C in units of Bq m 3 can be calculated using
ð1Þ
where Co is the radon concentration of the calibration chamber (90 kBq m 3), to is the calibration exposure time (48 h), ro is the measured tracks density of the calibrated dosimeters (3.31 104 tracks cm-2), r is the measured tracks density of the CR-39 detectors used in the study, t is the exposure time and C is the radon concentration to be determined. It is important to estimate the annual effective dose rate (ED) for radon exposure. According to the UNSCEAR (2000) report, indoor effective dose rate of radon in units of mSv yr 1 can be calculated by the following formula ED ¼ C annual FTDð24 hÞð365Þð106 Þ,
ð2Þ 3
where Cannual is the annual radon concentration (in Bq m ), F is the indoor radon equilibrium factor (0.4), T is the indoor occupancy time (0.8) and D is the dose conversion factor (9.0 nSv h 1 per 1 Bq m 3). In order to use our data, which was measured during summer season, to estimate the annual effective dose rate, we have to figure out the relationship between average annual radon concentration and summer radon concentration. Depending on a study done by Kullab et al. (2001) to estimate the seasonal variation of indoor radon concentration in specific locations in Jordan, we can write ( ) 1:37C summer for ground floors C annual ¼ , ð3Þ 1:04C summer for first floors where Csummmer is the average radon concentration in the summer season. Due to the unavailability of data for the second floor, we used the same formula for the first floors to estimate annual radon concentrations for the second floors.
3. Results and discussion In this study, indoor radon concentrations were measured in the villages of Ayn-Jana, Ishtafena, Samta and Umm-Yanabe’ in the district of Ajloun, Jordan. Factors affecting radon concentration were studied such as floor level, room type and building materials. Table 1 reflects the variation of radon concentration over the different floor levels. It shows the minimum, maximum, arithmetic average and the standard deviation for radon concentration in the dwellings of Ayn-Jana village. It is clear that the
Table 1 Indoor radon concentration for different floors in Ayn-Jana village.
n
Floor number
Min. concentration (Bq m 3)
Max. concentration (Bq m 3)
Average concentration (Bq m 3)
Average radon effective dose (mSv yr 1)n
Ground floor First floor Second floor
13.7 72.8 16.4 72.2 15.0 73.0
87.4 7 10.0 48.8 7 6.0 36.8 7 4.2
35.5 7 5.0 27.9 7 3.6 22.9 7 3.2
1.23 70.19 0.73 70.11 0.60 70.09
Under the assumption made for Eq. (3) above.
Table 2 Indoor radon concentration for different kinds of rooms in Ayn-Jana village. Kind of room
Min. concentration (Bq m-3)
Max. concentration (Bq m 3)
Average concentration (Bq m 3)
Indoor occupancy factorn
Annual radon Effective dose (mSv yr 1)
Living room Bedroom Storage room
14.8 7 1.9 15.5 7 2.9 13.7 7 2.8
74.27 9.6 79.27 5.8 74.77 4.2
33.87 4.4 35.57 4.6 38.87 5.4
0.38 0.34 0.02
0.474 70.063 0.443 70.061 0.028 70.004
n Under the assumption that on average, the people in the investigation area stay in bedrooms for 8 h, in living rooms for 9 h, in kitchens for 1.5 h and in storage rooms for half an hour.
H.M. Al-Khateeb et al. / Applied Radiation and Isotopes 70 (2012) 1579–1582
average radon concentration decreases as the floor level increases and this variation may be attributed to how close or how far the floor is from ground since soil represents the main source of indoor radon in addition to many other reasons such as the fact that upper floors are better ventilated than lower floors that are exposed to dust and other forms of contaminations. These variations of radon concentrations were reflected on the average estimated annual radon doses (ED) for which the highest dose (1.2370.19 mSv yr 1) belongs to the ground floor and the lowest (0.6070.09 mSv yr 1) belongs to the second floor. Table 2 shows the variation of radon concentrations for different types of rooms in the Ayn-Jana village. Storage rooms have a slightly higher radon concentration among others with an average of about 38.875.4 Bq m 3, while a lower average concentration of about 33.8 74.4 Bq m 3 was found in living rooms. This may be because the living rooms are better ventilated than storage rooms. Bedrooms are less used than living rooms but more used than storage rooms and therefore their average radon concentration falls in between. To estimate the annual effective radon doses in different room types, it is necessary to partition the indoor occupancy factor among them. Table 2 shows this
Radon Concentration (Bq m-3)
100 90 80 70
Clay Stone Concrete Brick
60 50 40 30 20 10 0
Any-Jana
Ishtafena Samta Ajloun Villages
Um Yanabe'
Fig. 1. The variation of radon concentrations for different types of building materials in the four villages (radon concentrations of living rooms on the ground floor). Note that there are no dwellings made of clay in the village of Samta.
partitioning as well as the annual effective radon doses. The minimum value of annual radon dose was in storage rooms and the maximum value was in living rooms. These results reverse the average radon concentration results because the indoor occupation factor plays an important role in determining the annual radon dose. To estimate the effect of building materials on the radon concentration, Fig. 1 shows the variation of radon concentrations for different types of building materials in the four villages (radon concentrations of living rooms on the ground floor). It is clear that the highest radon concentration was in the dwellings made of clay and may be attributed to the age and poor maintenance of these dwellings compared to others. Furthermore, the exhalation of radon from the walls and floors of clay dwellings is higher than that of modern dwellings because of the cracks and defective joints in their walls and floors. On the other hand, the lowest average radon concentration was detected in the dwellings made of brick because walls are usually thin and empty; this reduces the exhalation rate of radon. In general, the average radon concentration indoors in these villages was 36.372.3 Bq m 3 and it corresponds to an average effective dose rate of 0.9270.06 mSv yr 1. These indoor radon concentrations as well as the annual effective dose are below the action level recommended byICRP (1993). Radon concentrations in soil were measured in the four villages. Table 3 shows the minimum, maximum and average radon concentration in kBq m 3. The highest soil radon concentration (3.6270.13 kBq m 3) was detected in the Ishtafena village and the lowest (2.08 70.12 kBq m 3) was in Ayn-Jana village. The average soil radon concentrations in the villages of the Ayn-Jana, Samta and Umm-Yanabe’ are approximately the same and it may return to the similarity of their geological location. The high soil radon concentration in Ishtafena village may be attributed to the excavation activity of the earth crust in that region as a result of building and road construction activities accompanied by utilizing a very hard and expensive stone layer that covers the top of the ground in most parts of this village. The average radon concentration in the soil of these villages was about 2.55 70.20 kBq m 3. To the best of our knowledge, there are no previous reports of radon concentration in our chosen fields of study; however there are some reported data on radon levels in nearby areas such as Ajloun city itself. Table 4 lists our results accompanied by others
Table 3 Soil radon concentration in the villages of Ajloun. Village
Min. concentration (kBq m 3)
Max. concentration (kBq m 3)
Average concentration (kBq m 3)
Ayn-Jana Samta Umm-Yanabe’ Ishtafena
0.257 0.02 1.047 0.04 0.487 0.02 2.38 7 0.07
4.39 7 0.16 4.52 7 0.22 4.36 7 0.19 5.11 7 0.18
2.08 70.12 2.15 70.13 2.36 70.09 3.62 70.13
Table 4 Radon concentration comparison. Region
Indoor radon concentration (Bq m3)
Soil radon concentration (kBq m 3)
Reference
Villages Studied here Ajloun Ajloun Ajloun Jordan
36.3 7 2.3 27.6 7 1.8 40.08 7 27.00 52.0* 56.7*
2.557 0.20 3.407 1.4 – – –
Present study Rabadi and Abumurad (2008) Abumurad et al. (1997) Khatibeh et al. (1997) Abumurad, et al. (1997)
n
Errors are unavailable
1581
1582
H.M. Al-Khateeb et al. / Applied Radiation and Isotopes 70 (2012) 1579–1582
for indoor and soil radon concentrations. Our results for indoor radon are higher than those measured by Rabadi and Abumurad (2008) but lower than those measured by Abumurad et al. (1997) and Khatibeh et al. (1997). Moreover, our results are less than the average national indoor radon concentration of Jordan. Soil radon results of this study are in good agreement with the results from Rabadi and Abumurad (2008).
4. Conclusion Indoor radon concentrations have been measured in four villages of the district of Ajloun, Jordan. These concentrations were measured according to a variety of effective factors such as room type, floor level and building materials. In the Ayn-Jana village, it was found that the radon concentration decreases gradually with floor level. Regarding ventilation rate of rooms in the same village, it was found that the highest radon concentration was in the storage room and the lowest in the living rooms. In all villages under investigation, it was found that the highest radon concentration was in the dwellings made of clay (45.776.7 Bq m 3) and the lowest was in dwellings made of brick (33.976.4 Bq m 3). The average indoor radon concentration for the whole survey was about 36.372.3 Bq m 3 and corresponds to an annual effective dose of 0.9270.06 mSv yr 1. The average soil radon concentration of these villages was found to be 2.55 70.20 kBq m 3. Acknowledgments The authors would like to thank the Deanship of Research at Jordan University of Science and Technology for financially supporting this project. Also, thanks go to Prof. Jing Chen for reading the manuscript. References Abu-Jarad, F., Fazal-ur-Rehman, Al-Jarallah, M.I., Al-Shukri, A., 2003. Indoor radon survey in dwellings of nine cities of the eastern and western provinces of Saudi Arabia. Radiat. Prot. Dosim. 106, 227–232.
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