measurements of radon gas concentrations in ...

Radiation Protection Dosimetry (2014), Vol. 158, No. 2, pp. 156 – 161 Advance Access publication 12 September 2013

doi:10.1093/rpd/nct219

MEASUREMENTS OF RADON GAS CONCENTRATIONS IN DWELLINGS OF AL-MADINAH AL-MUNAWARAH PROVINCE IN SAUDI ARABIA R. I. Mohamed1,*, Z. Z. Alfull2 and N. D. Dawood2 1 Department of Physics, Al-Azhar University, Cairo, Egypt 2 Department of Physics, Taibah University, Al-Madinah Al-Munawarah, Saudi Arabia *Corresponding author: [email protected] Received April 27 2013, revised August 15 2013, accepted August 17 2013

INTRODUCTION Radon (222Rn) is a radioactive gas. It is generated in building materials and in soil by alpha decay of 226Ra. Radon is a member of the natural radioactive series, which is a long chain stating with 238U. The radioactive half-life of 222Rn (3.8 d) is long enough to allow 222Rn to migrate into indoor air, and its concentration builds up in buildings with poor ventilation(1 – 3). Radon contributes a large part of the radiation exposure of the general public, and it might produce lung cancer if inhaled in high concentration for a long period(4 – 6). There has been an increasing interest in indoor radon measurements if an average person spends .80 % of their time either in a home or in a workplace(7). A survey has been carried out to measure the indoor radon concentration in 800 dwellings situated in different sites of eastern and western AlMadinah Al Munawarah; the dwellers are affected mainly by the continuous inhalation of radon daughters. These radon daughters expose the lung tissue after inhalation and thereby potentially increase the risk of lung cancer(8). Not everyone exposed to elevated radon

levels will develop lung cancer. The amount of time between exposure and the onset of the disease may be many years. As with other environmental pollutants, there is some uncertainty about the magnitude of the health hazards of radon. The concentration of indoor radon depends up on a number of parameters such as climate, building materials, geology, living environment and so on. It has been estimated that exposure to radon daughters in US houses is responsible for about 10 % of the total risk of lung cancer(9). Most of the ‘active’ systems developed to date for radon dosimetry are expensive and suitable only for environmental dosimetry(10). In order to carry out environmental and personal dosimetry on a large scale, one needs to employ a light and an inexpensive system having convenient dimensions and which is easy to handle. CR-39 plastic detectors are used as a tool for this experimental work because of its versatile advantages such as simple in construction and use(11), insensitive to light, low cost and high efficiency.

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Indoor radon concentration levels in a large number of dwellings in Al-Madinah Al-Munawarah Province have been measured. Al-Madinah Al-Munawarah is in the western region of Saudi Arabia. It is the second holiest city in Islam after Mecca, because it is the burial place of the Islamic Prophet Muhammad. The city was divided into four regions: western (contains nine sites), eastern (contains six sites), northern (contains nine sites) and southern (contains five sites). Radon gas concentration was measured using the closed chamber technique employing 2` 32 cm2 sheets of CR-39 solid-state nuclear track detectors. The detectors were kept for a period of 5 to 6 months from September 2010 to February 2011 in order to expose to radon gas. The results of the survey in the western and eastern sites showed that the overall minimum, maximum and average radon concentration levels were + 1.6 Bq m23) was found in Al 20+ + 1.6, 27+ + 3.2 and 21+ + 2.5 Bq m – 3, respectively. The lowest average radon concentration (20+ Anabes and Al Suqya in the western region and Bani Dhafar in the eastern region, while the highest average concentration + 2.5 Bq m23 (27+ + 3.2 Bq m23) was found in Teeyba in the western region and Al ’Aridh in the eastern region, with an average of 21+ in the western and eastern sites of Al-Madinah Al-Munawarah. Also in the northern region, the minimum radon concentration + 1.6 Bq m23 in Sayyed al Shuhadd and Hai Nasr. In the southern was 20+ + 1.6 Bq m23 in Oyun, while the maximum was 42+ + 2.6 Bq m23 region, the minimum radon concentration was 25+ + 2.6 Bq m23 at Hai Al Hejrah, while the maximum value was 37+ at Al Awali and Dawadia. The average radon concentration was 26+ + 2.5 Bq m23 for Al-Madinah Al-Munawarah (western, eastern, northern and southern regions). The corresponding annual effective dose E (mSv y21) to public from 222Rn and its progeny was estimated to be 0.66 mSv y21 as an average value for Al-Madinah Al-Munawarah. The authors concluded that all the dwellings monitored for indoor radon concentration and annual effective dose show values within the permissible level and this is a blessing from God that this area, which many visitors come from all over the world (to visit the burial place of the Prophet Muhammad), is safe. Consequently, the health hazards related to radiation are expected to be negligible. Occupants of these dwellings are relatively safe.

RADON CONCENTRATION LEVELS IN AL-MADINAH AL-MUNAWARAH

The aim of this study was to measure radon concentration in different dwellings and determine the annual dose rate received by the public in Al-Madinah AlMunawarah Province of Saudi Arabia. Surveys have been carried out in other cities in Saudi Arabia(1, 12 – 15), but no data on the radon concentration in Al-Madinah Al-Munawarah city dwellings were available. Another object was to provide a baseline for Al-Madinah AlMunawarah in Saudi Arabia in the radon concentration world atlas. STUDY AREA

MATERIALS AND METHODS In this work, Al-Madinah Al-Munawarah was divided into four regions: western (nine sites), eastern (six sites), northern (nine sites) and south (six sites) as shown in Figure 2. On an average, about 200 CR-39 detectors were distributed inside the dwellings of each

Figure 1. Location of Al-Madinah Al-Munawarah Province in Saudi Arabia.

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Al-Madinah Al-Munawarah Province in Saudi Arabia was chosen for this study because it is a great city that attracts thousands of visitors who come from all over the world to visit the site related to Prophet Muhammad. Al-Madinah Al-Munawarah, ‘the radiant city’ (officially), is a city in the Hejaz region of western Saudi Arabia, and serves as the capital of Al-Madinah

Province. It is the second holiest city in Islam and the burial place of the Islamic Prophet Muhammad, and it is historically significant for being his home after the Hijrah. Before the advent of Islam, the city was known as Yathrib, but was personally renamed by Muhammad. It is located in the western region of the Kingdom of Saudi Arabia with an area of 589 km2, with the Prophet’s Holy Mosque at a latitude of about 248280 N and a longitude of 398260 E. Figure 1 illustrates the location of Al-Madinah Al-Munawarah Province in Saudi Arabia(16).

R. I. MOHAMED ET AL.

selected site, a total of 800 CR-39 detectors. In each dwelling, one detector was placed at height of about 2 m above the floor. The study was conducted between September 2010 and February 2011.

Preparation of CR-39 detectors for exposure The method of the present investigations is based on solid-state nuclear track detector (SSNTDS). It is more suitable for long-term measurement of radon in large-scale surveys of both indoor and outdoor environments. The thickness of the CR-39 plastic detector sheet, obtained from PPG industries, Inc., Italy, was 700 mm. The detectors were cut into small pieces of size 2 cm` 2 cm. These detector strips were then kept fixed inside at the bottom and on the inner walls of a cylindrical plastic can of diameter 6.5 cm and height 4.6 cm using adhesive tape. A sponge membrane was used to cover the can. A circular opening of 2 cm diameter in the middle of the cover is sealed by a 5 mm thick sponge. Sponge is preferred to filter paper because it is more durable in handling. The design of the chamber ensures that the aerosol plastics and radon decay products are deposited on the sponge from outside and that only radon, among other gases,

diffuses to the sensitive volume of the chamber, as shown in Figure 3, which illustrates cross-sectional view of the used closed chamber technique. This configuration was used in order to maintain the same calibration conditions and to stop the thoron (220Rn) from entering the cup, while allowing the radon gas to pass through the sponge(17). The exposed detectors were collected after approximately 4 to 5 months and then chemically etched simultaneously at a constant temperature of 708C in 6.25 N NaOH for 7 h. The CR-39 calibration factor for radon measurement is 2.328 T cm22 (Bq m23 h)21 with +8.35 % combined uncertainty. The calibration was carried out in the Department of Radiation Measurement, National Institute for Standard, Egypt, where CR-39 was equipped in diffusion chambers and exposed to standard radon concentration for different periods. The calibration factor is the resultant track density per integrating concentration.

Tracks counting method The etched CR-39 detectors were scanned using an optical microscope at a magnification of 400 (`40

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Figure 2. The map of the studied area in Al-Madinah Al-Munawarah Province of Saudi Arabia.

RADON CONCENTRATION LEVELS IN AL-MADINAH AL-MUNAWARAH Table 1. Analysis of indoor radon concentrations, annual effective dose and annual absorbed dose in the western region in Al-Madinah Al-Munawarah. Sites

Number of houses

Total

Figure 3. Schematic diagram showing the geometry of CR39-based passive radon dosemeter.

objective and` 10 eyepiece). Using the actual area of field of view (1.45` 10 – 3 cm2), the track densities (number of tracks per cm2) due to radon and its daughters were measured. Total track densities (observed track density minus back ground track density) were calculated. The radon activity concentrations were calculated (in Bq m23) from the average track density by using the calibration factor of 2.328 T cm22 (Bq m23 h)21. RESULTS AND DISCUSSION

Annual effective dose, mSv y21

11

22+2.6

0.55

11 15

20+1.6 21+2.5

0.50 0.52

13 14 14 12 9 14

23+2.7 22+2.6 20+1.6 22+2.6 23+2.7 27+3.2

0.58 0.55 0.50 0.55 0.58 0.68

113

Average 21+2.5

Average 0.55

Table 2. Analysis of indoor radon concentrations, annual effective dose and annual absorbed dose in the eastern region in Al-Madinah Al-Munawarah. Sites

Al Iskan Al Khalidiyyah Al ’Aridh Jathm Mahzur Bani Dhafar Total

Number of Mean radon houses concentration, Bq m23


14 19

22+2.6 24+2.8

0.55 0.60

19 14 48 13

27+3.2 26+3.1 22+2.6 20+1.6

0.58 0.68 0.55 0.50

127

Average 21+2.5

Average 0.57

Radon concentration measurement Tables 1 and 2 present radon concentrations, annual effective and absorbed dose rate in the western and eastern regions, respectively. Track densities measured using CR-39 nuclear track detectors were converted into radon concentrations (using a calibration factor of 2.328 T cm22 (Bq m23 h)21). The concentration of radon was calculated using the following equation(17, 18): CRn ¼

r 1000; ft

ð1Þ

where CRn is the radon concentration in Bq m23, r is the track density (numbers of tracks per square centimetre, T cm22), f is the calibration factor for the dosemeter used in the survey in the units of T cm22 (Bq m23 h)21 and t is the exposure time in hours, h. The minimum and maximum radon concentrations with a standard deviation were 20+1.6 and 27+3.2, respectively, with an average of 20+2.5 in the western

area, while 27+3.2 and 20+1.6 Bq m23 in the eastern region, respectively. The minimum radon concentration in the northern region was 20+1.6 Bq m23 in Oyun, while the maximum was 42+1.6 Bq m23 in Sayyed al Shuhadd and Hai Nasr. Tables 3–5 present radon concentrations, annual effective and absorbed dose rate in the northern and southern regions, respectively. The minimum radon concentration in the northern region was 20+1.6 Bq m23 in Oyun, while the maximum was 42+1.6 Bq m23 in Sayyed al Shuhadd and Hai Nasr. The minimum radon concentration in the southern region was 25 Bq m23 at Hai Al Hejrah, while the maximum value was 37+2.6 Bq m23 at Al Awali and Dawadia. It is believed that the high radon level in this part of the province may be attributed to its geographic location—the average radon concentration was 26+2.5 Bq m23 for Al-Madinah Al-Munawarah (the four regions included). This value is still much lower than the

159


Al Usayfirin Al Anabis Al Qiblatayn Al Seeh Al Salam Al Suqya Al Deffa Orwah Teeyba

Mean radon concentration, Bq m23

R. I. MOHAMED ET AL. Table 3. Analysis of indoor radon concentrations, annual effective dose and annual absorbed dose in the northern region in Al-Madinah Al-Munawarah. Sites

Number of houses

Total


12 17 8 14

20+1.6 30+1.6 37+2.7 42+2.6

0.50 0.75 0.93 1.05

7 21

30+1.6 27+2.6

0.75 0.68

9

35+2.7

0.88

11 35

42+3.2 27+2.5

1.05 0.68

134

Annual effective dose (E) estimation According to the UNSCEAR report (2000)(19), the annual effective dose E (mSv y21) to the public from 222 Rn and its progeny is estimated using the following equation(20): E ¼ C F H T D;

where C denotes the 222Rn concentration (Bq m23), F is an equilibrium factor (0.4), H is the occupancy factor (0.8), T is time in hours in a year (8760 h y21) and D is the dose conversion factor (9.0` 1026 mSV Bq m23 h21), which is the effective dose received by adults per unit of 222Rn activity per unit of air volume. The average effective annual dose in AlMadinah Al-Munawarah is about 0.66 mSv y21. It has been recommended that the action levels of radon in dwellings should be set within a range of 3–10 mSv y21 (ICRP 1993, 2011)(4, 21).

Average 32+2.5 Average 0.80

Table 4. Analysis of indoor radon concentrations, annual effective dose and annual absorbed dose in the southern region in Al-Madinah Al-Munawarah. Sites

Total

14

25+2.6

0.68

19

27+2.8

0.63

15 7 11

37+3.2 35+3.1 37+2.6

0.93 0.88 0.93

35

35+1.6

0.50

101

Average 32+2.5

Average 0.75

CONCLUSION The observed level of radon gas concentration, annual effective dose and annual absorbed dose to the public from 222Rn in Al-Madinah Al-Munawarah Province are within the permissible level as set by monitoring agencies of different countries. Consequently, the health hazards related to radiation are expected to be negligible. Occupants of these dwellings are, therefore, relatively safe.

Annual effective Number of Mean radon houses concentration, Bq dose mSv y21 23 m

Hai Al Hejrah Hai Al Bahr AL ’Awali Qubaa Al Dowama Qurban

REFERENCES

Table 5. A comparison of the indoor radon gas concentrations in Al-Madinah Al-Munawarah and different sites in Saudi Arabia. Place

Al-Madinah Al-Munawarah Taif Hafr Al Batin Khafji Riyadh Al_Qaseem

Radon concentration, Bq m23 26+2.5 29+10 76+25 58+20 18.4+2.2 67+8

ð2Þ

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