Study of natural radioactivity in Mansehra granite, Pakistan: environmental concerns

Radiation Protection Dosimetry Advance Access published October 31, 2013 Radiation Protection Dosimetry (2013), pp. 1–13

doi:10.1093/rpd/nct271

STUDY OF NATURAL RADIOACTIVITY IN MANSEHRA GRANITE, PAKISTAN: ENVIRONMENTAL CONCERNS Aziz Ahmed Qureshi1,*, Istiaq khan Jadoon2, Ali Abbas Wajid2, Ahsan Attique2, Adil Masood2, Muhammad Anees2, Shahid Manzoor1, Abdul Waheed1 and Aneela Tubassam1 1 Radiation Physics Laboratory, Physics Department, COMSATS Institute of Information Technology, Chak Shahzad, Park Road, Islamabad, Pakistan 2 Department of Earth Sciences, COMSATS Institute of Information Technology, Abbotabad, Pakistan *Corresponding author: [email protected] Received 12 April 2013; revised 11 October 2013; accepted 12 October 2013

INTRODUCTION Human beings are exposed to radiation. Out of 370 naturally occurring nuclides in environment, 70 are radionuclides. Radionuclides are unstable nuclides whose decay yields harmful radiations such as alphaand beta-particles and gamma-rays. The gammaradiation is the major source of damage to the living cells and tissues. The sources of the radiations are terrestrial, extraterrestrial and anthropogenic. The radiation of terrestrial origin comes from various earthly materials which contain various amounts of 238U and 232Th and their decay products and 40K. The level of radiation in any area depends on local geological conditions. Higher radiation levels are associated with igneous rocks, such as granite, granodiorites and syenites, and lower levels with sedimentary rocks with some exceptions where shales and phosphate rocks are a source of high radiation(1). Granites are the most commonly occurring plutonic bodies in mountain belts and crustal areas occupying thousands of square kilometres. In terms of natural radioactivity, granitic rocks exhibit an enhanced elemental concentration of uranium (1 –10 ppm), thorium (5–30 ppm) and potassium (33 191 ppm) compared with the average abundance of these elements in mantle and the earth crust as a whole(2). Mansehra Granite is a large plutonic body that covers a vast area between Muzaffarabad re-entrant and the Indus River. Location of Mansehra is shown in Figure 1. Mansehra Granite is used as building

and decorational material. A part of Mansehra Granite covering densely populated area of Mansehra city was studied for the assessment of radiological hazards using a high purity germanium (HPGe) gamma-spectrometer. On average 80 % of the radiation exposure to world population is attributed to terrestrial sources(3). The present study aims at investigating natural radioactivity in Mansehra Granite with reference to environmental concerns and as a building material. This study not only supplements the earlier studies carried out on a nearby Ambela Granitic Complex (AGC), Pakistan, but also assesses radioactivity and its hazards in a densely populated part of Mansehra city. The understanding and awareness about radiation in the outdoor and indoor environment is important for determining the population exposure to radiation. The outdoor exposure is from the geological formations, sand, soil etc. to which human beings are exposed. The indoor exposure is due to the gammarays radiating from the building material and alpha radiation from the decay of radon. Worldwide surveys have been carried out to determine the radiation indices of building materials. For health hazards linked with radiation exposure, the ICRP-103 (1994)(4) has adopted strong measures for minimising such exposures, for which limits have been set. For occupational workers, a dose limit of 20 mSv y21 averaged on 5 y has been fixed, which may be up to 50 mSv y21 but total dose should not exceed 100 mSv in 5 y. For general public, the criterion limit is 1 mSv y21 but in exceptional cases it may be up to 5 mSv y21.

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A part of Mansehra Granite was selected for the assessment of radiological hazards. The average activity concentrations of 226 Ra, 232Th and 40K were found to be 27.32, 50.07 and 953.10 Bq kg21, respectively. These values are in the median range when compared with the granites around the world. Radiological hazard indices and annual effective doses were estimated. All of these indices were found to be within the criterion limits except outdoor external dose (82.38 nGy h21) and indoor external dose (156.04 nGy h21), which are higher than the world’s average background levels of 51 and 55 nGy h21, respectively. These values correspond to an average annual effective dose of 0.867 mSv y21, which is less than the criterion limit of 1 mSv y21 (ICRP-103). Some localities in the Mansehra city have annual effective dose higher than the limit of 1 mSv y21. Overall, the Mansehra Granite does not pose any significant radiological health hazard in the outdoor or indoor.

A. A. QURESHI ET AL.

Figure 1. Location map of Mansehra, Pakistan, showing road network, Indus River, Tarbela Dam and Karakorum Highway leading to China.

Assessment of natural radioactivity is therefore important for implementing the precautionary measures wherever the radiation is found higher than the average background levels. MATERIALS AND METHODS Study area, sample collection and preparation Natural radioactivity in Mansehra Granite area was measured in and around the town of Mansehra, located in Khyber Pakhtunkhwa Province, North Pakistan. The study area is located between 348200 0000 N to 348210 2100 N latitude and between 738100 3000 E to 738120 1000 E longitude. The Mansehra Granite is the western most pluton recognised in the Lesser Himalayan granite belt that outcrops as a large body west of the western syntaxes of the Himalayas(5). For more details, see the regional geological map of Northern Pakistan (Figure 2). Sampling was done on a grid pattern, plotted over a Mansehra area, in such a way that it covered both the granitic bodies and majority of local populace as shown in Figure 3. In total, 30 samples were collected and each sample corresponded to a specific latitude and longitude value on map (Table 1). The sampling grid was plotted using six N-S trending lines labelled as A B C D E F and five E-W trending lines 1–5. The distance between two adjacent N-S trending lines was 500 m, while it was 625 m in case of E-W trending lines.

The rock samples were crushed and ground to obtain sand sized particles. Sand size particles allow radionuclide measurements with precise results. The samples were dried in an electric oven at 1108C for 24 h in order to remove moisture for the free movement of radon in the rock medium. After the removal of moisture, sample net weight was noted. Each sample was sealed in standard 1000-ml Marinelli beaker and stored for 1 month in order to attain the secular equilibrium(6). Activity concentration measurements Activity concentrations of 226Ra, 232Th and 40K in the Mansehra Granite samples were measured using HPGe gamma-spectrometer. The HPGe detector is encased with adequate outer lead and inner Cu –Sn shielding, which reduced the background by a factor of 95 %. Background spectra were taken fortnightly for 20 000 s to check the background level of radioactivity in the laboratory. Weekly gamma-ray measurements of the reference material were also done for 20 000 s for the calibration of the system. The gamma-ray photo peaks corresponding to 295 keV (214Pb), 352 keV (214Pb), 609 keV (214Bi), 1120 keV (214Bi) and 1764 keV (214Bi) for 226Ra and 239 keV (212Pb), 583 keV(208Tl), 911 keV (228Ac), 2614 keV (208Tl) were considered for identifying 232 Th in the samples. 40K was recognised from its single peak of 1460.80 keV. Spectrum acquisition of

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Figure 2. Regional geological map of Northern Pakistan showing study area (Mansehra) along with tectonic settings (after Ahsan and Chaudhry, 2008). Box shows Mansehra district. Various tectonic features are denoted by MKT (Main Karakoram Thrust), MMT (Main Mantle Thrust), MCT (Main Central Thrust), MBT (Main Boundary Thrust), KBT (Kashmir Boundary Thrust), PT (Panjal Thrust) and NF (Nathia Gali Fault).

granite samples was also taken for 20 000 s and the spectra were stored in the computer. The analyses of 226 Ra and 232Th were carried out on the basis of the peaks of their respective daughter products (214Pb and 214Bi for 226Ra; 228Ac and 208Tl for 232Th) in equilibrium with their parent radionuclides. The activity concentration of 40K was based upon its single peak of 1460.80 keV(7).

Radiation indices measurements Unintentional exposure to the radiations is broadly termed as radiological hazard. Hazards from radiation may arise from exposure or from intake of radioactive materials which directly affects the living tissues. The assessments of radiation hazard indices represent methods for the calculation of collective

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A. A. QURESHI ET AL.

Figure 3. Grid laid over Google Map of Mansehra area for the sampling purpose. Most of the populated area of city is located in the SE of the map. Rocky area is located in the NWof the studied area.

impact of the activity concentration of 226Ra, 232Th and 40K present in a material in a single quantity. Various types of hazard indices have been defined, by Beretka and Mathew(8), UNSCEAR(3, 9), Nordic(10) and European Commission (EC)(11). Exposure to radiations can either be outdoor (gamma-radiation in open air) or indoor (gamma-radiations and radon inside buildings). Based on activity concentrations of 226 Ra, 232Th and 40K outdoor and indoor indices and corresponding annual effective doses of Mansehra Granite were calculated. The details of the calculation of radiological hazards are given below.

Gamma index A number of indices to account for the assessment of excessive gamma-radiation originating from the building materials and its relation to annual dose rate have been proposed by various authors. One of such hazard index called as gamma activity concentration index or simply the gamma index (Ig) has been introduced to account for the combined impact of 226Ra, 232 Th and 40K as radiological hazard associated with a building material. Ig for any building material is

calculated using the following equation: Ig ¼

ARa ATh AK þ þ 300 200 3000

ð1Þ

where ARa, ATh and AK are the specific activities of 226 Ra, 232Th and 40K, respectively, in any material. The resultant value of Ig is in numbers which corresponds to annual dose rate due to the gammaradiation. For materials used in bulk, the value of Ig  0.5 correspond to a dose rate criterion of 0.3 mSv y21; whereas for materials with restricted use, the Ig  6 corresponds to a criterion of 1 mSv y21(11). Thus Ig can be used for identifying safe materials for construction or decorative purpose. As per EC(11) the building materials with Ig value 2 may be used as a construction material without any restriction. The materials with Ig . 6 should be avoided in normal construction except in exceptional cases for restricted use. Radium equivalent activity (Raeq) In order to find out the exact gamma-dose rate of a building material, a common radiological index namely radium equivalent activity (Raeq) has been

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STUDY OF NATURAL RADIOACTIVITY Table 1. Activity mass concentration of 226Rn, 232Th and 40K and their total in Mansehra Granite along with Th/Ra ratios. No.

Sample no.

Sample coordinates Latitude

1 A1 348210 21.6000 N 2 A2 348210 01.4200 N 3 A3 348200 41.2400 N 4 A4 348200 21.0600 N 5 A5 348200 00.8800 N 6 B1 348210 21.6000 N 7 B2 348210 1.4200 N 8 B3 348200 41.2400 N 9 B4 348200 21.0500 N 10 B5 348200 00.8800 N 11 C1 348210 21.6000 N 12 C2 348210 21.4200 N 13 C3 348200 41.2400 N 14 C4 348200 21.0600 N 15 C5 348200 00.8800 N 16 D1 348210 21.5800 N 17 D2 348210 21.4100 N 18 D3 348200 41.2300 N 19 D4 348200 21.0500 N 20 D5 348200 0.8700 N 21 E1 348210 21.5600 N 22 E2 348210 1.4100 N 23 E3 348200 41.2200 N 24 E4 348200 21.0500 N 25 E5 348200 00.8800 N 26 F1 348210 21.5900 N 27 F2 348210 21.4000 N 28 F3 348200 41.2300 N 29 F4 348200 21.0500 N 30 F5 348200 00.8800 N Maximum Minimum Average Crustal average(1) Building material average(3)

Activity mass concentrations

Longitude 738100 30.1600 E 738100 30.1600 E 738100 30.1600 E 738100 30.1600 E 738100 30.1600 E 738100 50.2800 E 738100 50.2800 E 738100 50.2800 E 738100 50.2800 E 738100 50.2800 E 738110 10.4200 E 738110 10.4200 E 738110 10.4200 E 738110 10.4200 E 738110 10.4200 E 738110 30.5500 E 738110 30.5500 E 738110 30.5500 E 738110 30.5500 E 738110 30.5500 E 738110 50.6800 E 738110 50.6800 E 738110 50.6800 E 738110 50.6800 E 738110 50.6800 E 738120 10.8000 E 738120 10.8000 E 738120 10.8000 E 738120 10.8000 E 738120 10.8000 E – – – – –

226

Ra

22.66 22.91 50.91 25.72 27.37 17.56 18.35 22.88 28.52 5.70 24.80 27.72 29.45 36.92 31.33 24.62 34.85 36.71 38.37 34.91 23.64 26.68 23.46 33.93 17.98 31.80 26.96 34.68 32.19 29.64 50.91 17.56 27.32 35 50

232

Th

23.47 34.74 55.62 87.01 77.40 24.27 26.21 43.99 73.91 11.13 26.85 39.97 31.37 71.77 56.64 26.30 48.43 65.77 83.24 52.54 43.25 76.46 38.85 63.19 28.70 51.5 45.65 70.77 63.80 63.77 87.01 26.30 50.07 30 50

40

K

1227.82 948.53 366.47 197.65 1037.51 1151.42 1215.83 1165.98 805.85 203.30 1141.12 1113.85 1179.02 1160.15 700.56 1087.99 826.12 993.42 1024.53 922.73 1036.11 963.96 960.40 1090.15 984.11 1000.76 741.96 873.22 976.77 1004.78 1227.82 197.65 953.10 400 500

Ratios Total

Th/Ra

1273.95 1006.18 473.00 310.38 1142.28 1193.25 1260.39 1232.85 908.28 220.13 1192.77 1181.54 1239.84 1268.84 788.53 1138.91 909.40 1095.90 1146.14 1010.18 1192.77 1181.54 1239.84 1268.84 788.53 1138.91 909.4 1095.9 1146.14 1010.18 1365.74 241.51 1030.49 465.00 600.00

1.04 1.52 1.09 3.38 2.83 1.38 1.43 1.92 2.59 1.95 1.08 1.44 1.07 1.94 1.81 1.07 1.39 1.79 2.17 1.51 1.83 2.87 1.66 1.86 1.60 1.62 1.69 2.04 1.98 2.15 3.38 1.04 1.78 0.86 1

Sample no. B5 not included in the calculation.

introduced to evaluate the total gamma-dose rate of 226 Ra, 232Th and 40K present in the building materials. Raeq is calculated using the following equation by Beretka and Mathew(8): Raeq ¼ ARa þ 1:43ATh þ 0:077AK

ð2Þ

In formulating equation (2), it is assumed that 10 Bq kg21 of 226Ra, 7 Bq kg21 of 232Th and 130 Bq kg21 of 40K produce an equal gamma-ray dose. By calculating the Raeq it becomes possible to place a single regulatory limit on the activity of natural radionuclides in building materials rather than to limit 226 Ra, 232Th and 40K separately. Raeq should be lower than the criterion limit of 370 Bq kg21 which, as per Al-Trabulsy et al.(12), corresponds to an annual effective dose of 1.5 mS y21.

External hazard criterion (Hex) Radiation exposure to an individual depends on the concentrations of 226Ra, 232Th and 40K in the surrounding material and the time spent in the radiation area. The radiation exposure is denoted as external hazard criterion (Hex). The Hex can be evaluated using the following equation introduced by Beretka and Mathew(3): Hex ¼

ARa ATh AK þ þ 370 259 4810

ð3Þ

The Hex value should be less than unity for probability of risk to be negligible. The Hex value of unity corresponds to an exposure of 1.5 mGy y21 and upper limit Raeq of 370 Bq kg21.

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A. A. QURESHI ET AL.

Outdoor external dose (Dout) 21

Outdoor external dose rate (Dout), in nGy h , is calculated at 1 m above the ground level containing homogenously mixed terrestrial radionuclides, 226Ra, 232 Th and 40K by converting the activity concentration of 226Ra, 232Th and 40K into nGy h21 using three conversion factors (CFs). The CFs are 0.462 nGy h21 Bq21 kg21 for 226Ra, 0.604 nGy h21 Bq21 kg21 for 232Th and as 0.0417 nGy h21 Bq21 kg21 for 40 K. The Dout of an area is calculated using the following equation given in the UNSCEAR(9). While formulating the equation, it is assumed that 137Cs, 90 Sr and the 235U decay series has insignificant contribution to the total dose from environmental background(3). Dout ¼ 0:462ARa þ 0:604ATh þ 0:042AK

ð4Þ

dose (Eout) is estimated from the net outdoor external gamma-radiation dose rate Dout by taking into account the total stay of the individual in the radiation area [or occupancy factor (OF)] and CF to convert the Dout to effective dose received by a person. The Eout is calculated using the following equation proposed by UNSCEAR(9): Eout ¼ Dout  8760  OF  CF

ð7Þ

where Dout is the outdoor external gamma-radiation dose (nGy h21) calculated for the study area, 8760 is the hours in a y, OF is the occupancy factor (0.2), which corresponds to the time spent in the radiation area and CF is the conversion factor (0.7`  1026 Sv y21) from absorbed dose (Dout) in air to effective dose received by the person. By putting the values of OF and CF, equation (7) is modified to equation (8). Eout ¼ Dout 1:226  103 ðmSv y1 Þ

ð8Þ

Indoor hazard criterion (Hin) In addition to gamma-rays, 222Rn is also an internal exposure within a building. The radio-toxicity of 226Ra becomes twice due to 222Rn and its short-lived daughters. The combined internal exposure to gamma-rays and radon has been defined by Krieger(13) as indoor external hazard criterion (Hin). The Hin is calculated from the formula given below by Krieger(13): Hin ¼

ARa ATh AK þ þ 185 259 4810

ð5Þ

For the safe use of materials in the construction of buildings, a criterion limit of Hin  1 mSv y21 has been proposed by Krieger(13) and Beretka and Mathew(8).

Indoor effective dose (Ein) Annual indoor effective dose (Ein) is again calculated on the basis of OF and converting the absorbed dose (Din) in air to effective dose received by the person using the conversion factor (0.7 `  1026 Sv y21). The time spent in the indoor is taken as 80 %. Therefore, the time spent in the indoors is 8760`  0.8 h y21. The equation for calculating Ein may be deduced as follows: Ein ¼ Din ð8760  0:8h y1  0:7  106 Þ ðmSv y1 Þ Ein ¼ Din 4:905  103 ðmSv y1 Þ

ð9Þ ð10Þ

Indoor external dose (Din) The use of a building material demands that radioactive emissions must fall in safe limits; otherwise, health hazards may arise from its usage. Indoor absorbed gamma-dose rate (Din) for a standard room ` 5 m ` 2.8 m with wall having a dimension of 4 m thickness of 20 cm in nGy h21 is calculated using the following equation by EC(11). Din ¼ 0:92ARa þ 1:1ATh þ 0:084AK

ð6Þ

Annual effective doses Outdoor effective dose (Eout) The radiological hazard of an area is assessed from the impact of annual radiation dose exerted by the radiation sources in the area like rocks, sand, soil and other building materials. Annual outdoor effective

RESULTS AND DISCUSSION Activity concentration The activity concentration of 226Ra, 232Th and 40K in Mansehra Granite varies between 17.56 and 50.91, 26.30 and 87.01, and 197.65 and 1227.82 Bq kg21 with an average value of 27.32, 50.07 and 953.10 Bq kg21, respectively, shown in Table 1. Values of activity concentration of 226Ra are highest in Sample A3 with low value of 40K. Similarly, the activity of 232Th is highest in Sample A4 with a low value of 40K. These two samples are rich in quartz and low in feldspars and ore minerals. The activity values in all other samples are of typical granite type. The average activity concentration of 226Ra (27.32 Bqkg21) in Mansehra Granite is lower than the average crustal concentration of 35 Bq kg21(9) and

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STUDY OF NATURAL RADIOACTIVITY

average of 50 Bq kg21 in building materials(3). The activity concentrations of 232Th and 40K (50.07 and 953.10 Bq kg21) are higher than the average crustal concentration of 30 and 400 Bq kg21. The activity concentration of 40K is much higher than average value of 500 Bq kg21 in building materials. If activity concentration of 226Ra, 232Th and 40K present in Mansehra Granite with the crustal average of 35, 30 and 400 Bq kg21 is compared, the 226Ra is lesser than by a factor of 0.78, 232Th is more than by a factor of 1.43 and 40K is more than by a factor of 2.38. The 232 Th/226Ra ratio of 1.78 also indicates that the Mansehra Granite contains more thorium. Overall, the concentrations of 226Ra and 232Th in the Mansehra Granite samples are in normal range of these elements in the granites. The uranium and thorium occur as small patches at isolated locations in the Mansehra Granite. For comparison, the activity mass concentrations of 226Ra, 232Th and 40K in the Mansehra Granite with other countries from world over are represented in Table 2. The concentrations of these radionuclides in granite samples vary over a wide range(14 – 36). The minimum values of 226Ra are found in Saudi Arabia and Brazil (10 Bq kg21) and maximum value (1184 Bq kg21) is found in Egypt/Gable El Misikit. The second highest value (659 Bq kg21) is from Ambela Granitic Complex (AGC), Pakistan. The minimum and maximum values of 232Th are found in granites of Turkey (6 Bq kg21) and AGC, Pakistan (598 Bq kg21). As far as 40K is concerned, the minimum and maximum values are found in granites of Brazil (51 Bq kg21) and Egypt/Wadi Karim (4819 Bq kg21). Values of 226Ra, 232Th and 40K in the Mansehra Granite show a medium range that is typical of granites.

Gamma index (Ig) The values of Ig in 30 samples of Mansehra Granite are given in Table 3. The range and average of Ig values is 0.142–0.886 and 0.657. The average gamma-dose delivered by Mansehra Granite is close to 0.5 that corresponds to an annual effective dose rate slightly .0.3 mSv y21. The Mansehra Granite can be exempted from all types of restrictions as far as radiological hazards are concerned.

External hazard criterion (Hex) The Hex calculated from 30 samples of Mansehra Granite during present study range from 0.101 to 0.638 and an average of 0.465 (Table 3). This value is much less than the criterion limit of unity(8) and hence the Mansehra Granite is suitable for the construction purpose. Outdoor external dose (Dout) The Dout of Mansehra Granite ranges from 17.83 to 110.73 nGy h21 with an average value of 82.38 nGy h21 (Table 3). The average value is higher than the world’s average background level of 51 nGy h21 for soil, as per UNSCEAR(9) report. Indoor hazard criterion (Hin) The value of Hin in the Mansehra Granite samples is 0.541 with a range from 0.116 to 0.742, which is less than the criterion limit of ,1(8). Hence, the annual effective dose is ,1 mSv y21, indicating that the internal hazards are less than the recommended value. Indoor external dose (Din) The values of Din for Mansehra Granite are given in Table 3. The average and the range values are 156.04 nGy h21 and 33.75–208.83 nGy h21. These values are higher than the world’s average background level of 55 nGy h21 as per UNSCEAR report (37). Annual effective dose The outdoor effective dose Eout of Mansehra Granite has an average value of 0.103 mSv y21 with a range of 0.021 to 0.166 mSv y21. The annual indoor effective dose (Ein) has an average value of 0.764 mSv y21 with a range of 0.165– 1.021 mSv y21. The total annual outdoor and indoor effective dose ranges from 0.177 to 1.189 mSv y21 with an average value of 0.867 mSv y21, which is lower than the criterion limit of unity for the general public(4). In general, the annual effective dose of Mansehra Granite falls in safe limits. However, there are localities in the Mansehra city where the annual effective doses are more than the criterion limit. COMPRISON ON RADIATION INDICES

Radium equivalent activity (Raeq) The values of the Raeq of Mansehra Granite are in the range of 37.24 to 230.90 Bq kg21 with an average of 171.91 Bq kg21. The average is less than the criterion limit of 370 Bq kg21(8) and as such the Mansehra Granite does not pose any radiological hazard when used for the construction purpose.

A comparison of outdoor and indoor radiation indices along with annual effective doses of Mansehra Granite with other granites of the world is given in Table 4(14, 17, 21, 35, 36, 38 – 43). From the review of data summarised in Table 4, following facts can be deduced; † The Ig of Mansehra Granite (0.65) is well below the limit of unity. The Ig of Nigeria (1.38) and

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A. A. QURESHI ET AL. Table 2. Comparison of specific gamma activity (Bq kg21) concentration of Mansehra Granite Pakistan with some other granites of the world. No.

Country

Specific activity concentration 226

1 Pakistan (Mansehra Granite) 2 Pakistan (Ambela Granite) 3 Turkey (Granodiorite) 4 Turkey/Kaymaz 5 Turkey/Sivrihisar 6 Iran 7 Italy 8 Saudi Arabia 9 Saudi Arabia 10 Brazil 11 Slovak 12 Germany 13 Greece 14 China 15 Algeria 16 India 17 Cameron 18 Nigeria 19 Africa 20 Belgium 21 Brazil 22 Brazil 23 China 24 Australia 25 Italy 26 Holland 27 Sweden 28 Finland 29 Malaysia 30 Portugal 31 S. Africa 32 Spain 33 India 34 India 35 Egypt/Gable El Misikat 36 Egypt Wadi Karim 37 Egypt/Homert Waggat North 38 Egypt/Gable El Aradiya 39 Egypt/Eastern Desert 40 Egypt 41 Ghana/Kasoa 42 Ghana/Winwba 43 Ghana/Apam 44 Ghana/Otuam 45 Average of 137 granite samples world over. Maximum Minimum Average Crustal average Building material average

232

Ra

27 659 77 306 67 130 24 31 10 10 49 76 18 23 12 93 14 81 23 68 82 91 95 40 162 64 107 94 86 117 92 80 119 53 1184 56 489 126 13 57 88 66 76 67 42 1184 10 119 35 50

Sweden (1.30) is more than limit of unity; whereas Ig of Ambela Granitic Complex (AGC) of Pakistan has exceptionally high value of 5.60.

†

Th

50 598 6 248 153 83 27 27 29 13 54 70 17 36 7 306 31 249 42 77 168 152 158 253 490 91 110 163 134 105 153 123 172 74 40 54 109 25 14 53 56 45 54 46 73 598 6 112 30 50

40

References

K

Total

953 1203 140 1266 1058 1287 528 534 664 51 1376 1465 367 891 74 1074 536 508 811 1129 1297 1819 1256 1340 1540 1206 1226 1223 1019 1490 1151 1289 1082 750 705 4819 1590 480 405 1041 818 785 696 677 1055 4819 51 1037 400 500

1030 2460 223 1820 1278 1500 579 592 703 74 1479 1611 402 950 93 1473 581 838 876 1274 1547 2062 1509 1633 2192 1361 1443 1480 1239 1712 1396 1492 1373 877 1929 4929 2188 631 432 1151 962 896 826 790 1170 4929 74 1268 465 600

Present study (14) (15) (16) (16) (17) (18) (19) (20) (21) (22) (23) (24) (25) (26) (27) (28) (29) (30) (30) (30) (31) (31) (31) (30) (32) (31) (31) (31) (31) (31) (31) (31) (27) (33) (34) (33) (33) (35) (23) (36) (36) (36) (36) (31) – – (1) (3)

The Raeq of Mansehra Granite (171.91 Bq kg21) has a median value when compared with the granites exposed in India (247.00 Bq kg21), Turkey

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STUDY OF NATURAL RADIOACTIVITY Table 3. Outdoor and indoor hazards indices and annual effective dose of Mansehra Granite, Pakistan. No.

Sample no.

1 A1 2 A2 3 A3 4 A4 5 A5 6 B1 7 B2 8 B3 9 B4 10 B5 11 C1 12 C2 13 C3 14 C4 15 C5 16 D1 17 D2 18 D3 19 D4 20 D5 21 E1 22 E2 23 E3 24 E4 25 E5 26 F1 27 F2 28 F3 29 F4 30 F5 Maximum Minimum Average *Limits, **world’s averages Reference

Outdoor hazard indices

Indoor hazard indices

Annual effective doses

Ig

Raeq, Bq kg21

Hex

Dout, nGy h21

Hin

Din, nGy h21

Eout, mSv

Ein, mSv

Total Eout þ Ein, mSv

0.602 0.566 0.570 0.587 0.824 0.564 0.597 0.685 0.733 0.142 0.597 0.664 0.648 0.869 0.621 0.576 0.634 0.782 0.886 0.687 0.640 0.793 0.593 0.792 0.531 0.697 0.565 0.761 0.752 0.753 0.886 0.142 0.657 ,1*

150.64 145.50 158.56 165.22 217.75 140.80 149.32 175.41 196.09 37.24 150.94 170.50 164.96 228.69 166.13 145.88 167.59 207.08 236.09 180.95 165.13 210.06 152.84 208.06 134.68 182.35 149.25 202.95 198.44 198.03 230.09 37.24 171.91 370*

0.407 0.393 0.429 0.447 0.589 0.381 0.404 0.474 0.530 0.101 0.408 0.461 0.446 0.618 0.449 0.394 0.453 0.560 0.638 0.489 0.446 0.568 0.413 0.562 0.364 0.493 0.403 0.549 0.536 0.535 0.568 0.101 0.465 ,1*

75.85 71.12 72.40 72.68 102.66 70.79 75.01 85.76 91.42 17.83 75.26 83.40 81.72 108.78 77.90 72.63 79.81 98.11 110.73 86.34 80.25 98.71 74.35 99.30 60.68 87.53 70.97 95.18 94.13 94.11 110.73 17.83 82.38 51**

0.468 0.455 0.566 0.516 0.662 0.428 0.453 0.536 0.607 0.116 0.475 0.536 0.525 0.718 0.534 0.461 0.547 0.659 0.742 0.583 0.510 0.640 0.476 0.654 0.413 0.579 0.476 0.642 0.623 0.615 0.662 0.116 0.541 ,1*

144.90 135.18 137.34 135.19 193.32 134.97 142.98 162.72 172.01 33.75 143.64 158.58 155.92 205.73 147.17 138.62 151.43 185.59 208.83 163.73 152.21 185.77 141.15 187.94 126.84 165.97 134.38 179.61 177.91 177.80 205.73 33.75 156.04 55**

0.092 0.087 0.088 0.089 0.125 0.086 0.091 0.105 0.112 0.012 0.092 0.102 0.100 0.133 0.095 0.089 0.097 0.120 0.135 0.105 0.098 0.121 0.091 0.121 0.074 0.107 0.087 0.166 0.165 0.115 0.166 0.012 0.103

0.710 0.662 0.673 0.662 0.947 0.661 0.701 0.797 0.843 0.165 0.704 0.777 0.764 1.008 0.721 0.679 0.742 0.909 1.023 0.802 0.746 0.910 0.692 0.921 0.621 0.813 0.658 0.880 0.872 0.871 1.023 0.165 0.764

0.802 0.749 0.761 0.751 1.072 0.747 0.792 0.902 0.955 0.177 0.796 0.879 0.864 1.141 0.816 0.768 0.839 1.029 1.158 0.907 0.844 1.031 0.783 1.042 0.695 0.920 0.745 1.046 1.037 0.986 1.189 0.177 0.867 *1

–

–

(4)

(11)

(8)

(8)

(11)

(8)

(11)

Safe limits with reference have also been reported for comparison.

†

†

(244.30 Bq kg21), Ghana Kasoa (232.16 Bq kg21) etc. with odd values of a Libyan (19 Bq kg21) and a Brazilian granite (504.62 Bq kg21) against a criterion value of 370 Bq kg21. The Hex of Mansehra Granite (0.46) is comparable with most of the granites of the world except very high value of AGC of Pakistan with a value of 4.3 when compared with the criterion limit of unity. Like most of the granites of world the Dout of Mansehra Granite (82.38 nGy h21) is higher than the world’s average value of 51 nGy h21, except very low values in a Libyan (8.90) and a Nigerian (0.04) granite.

† The Hin of Mansehra Granite (0.54) is comparable with rest of the granites of the world except the AGC of Pakistan with a value of 6.1 against a criterion limit of unity. † The Din of Mansehra Granite (156.04 nGy h21) is higher than all the values reported in the table except the AGC of Pakistan with a value of 716 nGy h21 against world’s average of 55 nGy h21. † Annual outdoor effective dose (Eout) of Mansehra Granite (0.103 mSv) is comparable with the granites of the world except AGC of Pakistan and a Iranian granite with a value of 0.90 and 0.79 mSv, respectively. The annual indoor effective dose

Page 9 of 13

A. A. QURESHI ET AL. Table 4. Comparison of radiological hazard indices of Mansehra Granite, Pakistan, with some other countries of the world. No.

Country

Outdoor hazard indices Ig

1

Indoor hazard indices

Annual effective dose

Raeq (Bq kg21)

Hex

Dout, nGy h21

Hin

Din, nGy h21

Eout, mSv

Ein, mSv

References

Pakistan

0.65

171.91

0.46

82.38

0.54

156.04

0.103

0.764

Pakistan (AGC*) 3 Iran 4 Sweden 5 Egypt 6 Ghana/Kasoa 7 Pakistan 8 India 9 Italy Rosa 10 China Rosa 11 Brazil 12 Turkey 13 Turkey 14 Nigeria *Limits, **world’s averages Reference

5.60

–

4.30

716.00

6.10

–

0.90

–

Present study (14)

– 1.30 – – 0.42 0.90 – – – 0.92 – 1.38 ,1*

340.20 – 65.51 232.16 110.50 247.00 129.16 235.91 504.61 244.30 112.00 – 370*

0.86 1.00 0.21 0.48 0.31 – 0.75 0.63 1.36 – 0.31 1.04 ,1*

– 166.00 32.50 109.90 54.90 114.00 171.91 147.11 320.72 – – 0.04 51**

1.26 1.30 0.18 0.72 0.37 – 0.88 0.73 1.76 – 0.43 – ,1*

1.47 – – – – – – – – – 104.00 – 55**

0.79 – – – 0.27 0.14 – – – – – –

– – – 0.54 – 0.56 – – – – 0.51 0.12

(17) (21) (35) (36) (38) (39) (40) (40) (40) (41) (42) (43)

(11)

(8)

(8)

(9)

(8)

(9)

2

1** (4)

–

AGC*, Ambela Granitic Complex.

Figure 4. Relatively high annual effective dose rate (Eout þ Ein) area shown in brown shade in the mid southern part of the Mansehra city.

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STUDY OF NATURAL RADIOACTIVITY

†

(Ein) of Mansehra Granite (0.764 mSv) is slightly higher than the other locations of the world except AGC of Pakistan with a value of 6.67 mSv. The total annual effective dose (Eout þEin) of Mansehra Granite has an average value of 0.867 mSv y21, which is lower than the criterion limit of unity for the general public. However, over a small portion of Mansehra city located around 738190 0000 longitude and 348340 0000 latitude the annual effective dose rates (Eout þEin) are relatively higher as shown in Figure 4. It is recommended to abstain from constructing basements in this area to avoid the prolonged exposure to natural gamma and alpha radiations. Moreover, proper ventilation should be incorporated in the design of the house to be built with Mansehra Granite specifically in this relatively hot area. The Ein/Eout ratio in Mansehra Granite is 7.4, which is higher than ratios in the normal granites, which vary from 4 to 5. The Ein/Eout ratio in Mansehra Granite is equal to the ratio of AGC of Pakistan, which is 7.4. This may be due to the similar tectonic feature of the two granites.

CONCLUSIONS The natural radioactivity levels of Mansehra Granite, Pakistan, have been assessed by using HPGe gammaray spectrometer. The results show that the average activity concentration of 226Ra (27.32 Bq kg21) is lower than the crustal average of 35 Bq kg21. The average activity concentrations of 232Th and 40K are higher than the corresponding typical crustal averages of 30 and 400 Bq kg21 but lower than most of the granites of the world. As far as outdoor hazard indices are concerned, the Ig (0.657) corresponds to an annual effective dose slightly higher than the criterion limit of 0.3 mSv y21 for materials used in bulk quantity. The Raeq (171.91 Bq kg21) and Hex (0.465) are less than their criterion limits of 370 Bq kg21 and 1, respectively. The Dout 1 m above the Mansehra Granite with an average value of 82.38 nGy h21 is higher than the global average of 51 nGy h21. The Hin is lower than the criterion limit of unity whereas the average value of Din (156.04 nGy h21) is about three times higher than the global average of 55 nGy h21. The annual effective dose (Eout þ Ein) of Mansehra Granite has an average value of 0.867 mSv y21, which is lower than the criterion limit of unity for the general public. However, over a small portion of Mansehra city, the annual effective dose (Eout þ Ein) is higher than the criterion limit of unity. Constructing basements in this area should be avoided. Proper ventilation should be designed for the houses to be built with Mansehra Granite specifically in relatively hot area. By summing up the work done on Mansehra Granite, it is concluded that all outdoor and indoor

hazard indices are below their criterion limits. Therefore, from the radiological point of view, the Mansehra Granite as a building stone does not pose any significant radiological hazard. The Mansehra Granite tiles, slabs and countertops may be used without any restriction with radiological hazard point of view. Similarity of Ein/Eout ratio in Mansehra Granite and AGC of Pakistan which (7.4) is indicative of similar tectonic and genetic signatures of the two granites. The Mansehra Granite was emplaced as three phases spread over time and space; it would therefore be advisable to extend the radiological study to encompass larger area of Mansehra pluton to assess the radiological hazards of three phases. The present study should be considered as a preliminary database for further work in future. ACKNOWLEDGEMENTS Authors are thankful to Dr Khalid Jamil for critically reading the manuscript and useful discussion/suggestions on the subject. Authors are also thankful to Mr Usman Ali, Lab., assistant for providing help in sample preparation and other laboratory work. REFERENCES 1. ICRP. International Commission on radiation protection against Radon-222 at home and at work. ICRP Publication 65. Ann. ICRP 23(2), Pergamon Press (1994). 2. Marble Institute of America. Truth about granite and radon exhalation. Marble Institute of America (2007). 3. UNSCEAR. Sources and effects of ionizing radiation. Report to the General Assembly, with Scientific Annexes (1993). 4. ICRP Publication. www.icrp.org/ICRP. Publication 103. Ann. ICRP 37(2–4)-F. The Recommendations of the International Commission on Radiological Protection (2007). 5. Shams, F. A. Granites of NW Himalayas in Pakistan. In: Shams, F. A. Eds. Granite of Himalayas, Karakoram and Hindukush. Institute of Geology, Punjab University, pp. 75–122 (1983). 6. Hamby, D. M. and Tynybekov, A. K. Uranium, thorium, and potassium in soils along the shore of Lake Issyk-Kyol in the Kyrghyz Republic. Environ. Monit. Assess. 73(2), 101–108 (2002). 7. IAEA. Technical report 309. Construction and use of calibration facilities for radiometric field equipment (1989). 8. Beretka, J. and Mathew, P. J. Natural radioactivity of Australian building materials, industrial wastes and by products. Health Phys. 48, 87 (1985). 9. UNSCEAR Report to the General Assembly, with scientific annexes. Sources and effects of ionizing radiation (Vol. I) (2000). 10. Nordic. Naturally occurring radiation in the Nordic countries: recommendations. The Flag-Book Series, the Radiation Protection Authorities in Denmark, Finland, Iceland, Norway and Sweden, Reykjavik (2000).

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