Measurement of naturally occurring/fallout radioactive elements and ...

J Radioanal Nucl Chem (2011) 287:647–655 DOI 10.1007/s10967-010-0819-7

Measurement of naturally occurring/fallout radioactive elements and assessment of annual effective dose in soil samples collected from four districts of the Punjab Province, Pakistan S. U. Rahman • Matiullah • F. Malik M. Rafique • J. Anwar • M. Ziafat • A. Jabbar

•

Received: 10 August 2010 / Published online: 6 September 2010 Ó Akade´miai Kiado´, Budapest, Hungary 2010

Abstract Soil samples were collected from different localities of districts Jhelum, Chakwal, Rawalpindi and Attock, Punjab Province, Pakistan with an aim to measure naturally occurring radionuclides, namely 226Ra, 232Th, 40 K and fallout 137Cs radionuclide using a P-type coaxial high purity germanium (HPGe) c-ray spectrometer. Measured specific activities of 226Ra, 232Th and 40K in these soil samples ranged from 26.02 ± 7.11 to 93.54 ± 8.13 Bq kg-1, 29.34 ± 2.58 to 114.41 ± 2.80 Bq kg-1 and 348.15 ± 3.20 to 752.98 ± 4.20 Bq kg-1, respectively. Activity due to 137Cs was observed in some locations which ranged from 0.4 ± 0.2 to 7.8 ± 0.3 Bq kg-1. From the measured activity concentrations, radium equivalent activity concentrations were determined followed by calculations of mean absorbed dose rate and mean annual effective dose for the inhabitants of the studied area. The mean radium equivalent activity, internal and external hazard indices values came out to be 179.26 ± 11.93 Bq kg-1, 0.64 ± 0.05 and 0.48 ± 0.03, respectively.

S. U. Rahman J. Anwar A. Jabbar Department of Physics, CIIT, Islamabad, Pakistan Matiullah F. Malik Physics Division, PINSTECH, Islamabad, Pakistan M. Rafique Department of Physics, University of Azad Jammu & Kashmir, Muzaffarabad, Azad Kashmir, Pakistan M. Ziafat KRL, Kahuta, Rawalpindi, Pakistan S. U. Rahman (&) Department of Medical Physics, Nuclear Medicine, Oncology and Radiotherapy Institute (NORI), Islamabad, Pakistan e-mail: [email protected]

Indoors and outdoor average annual effective dose values were found to be 0.42 ± 0.03 and 0.10 ± 0.01 mSv, respectively. Present data have been compared with the published data for other parts of the world and found to be safe for public and environment. Keywords HPGe c-ray spectrometry Health risks Radium equivalent activity Annual effective dose Soil sampling

Introduction Radiation of natural origin at the earth’s surface consists of two components namely cosmic rays and terrestrial radiation. The latter component mainly originates from the primordial radioactive nuclides that were originated in the early stage of formation of the solar system. Uranium, thorium and potassium are the main elements which contribute towards the natural terrestrial radioactivity [1]. Natural environmental radioactivity and the associated external exposure due to the gamma radiation depend primarily on the geological and geographical conditions [2]. The naturally occurring radio nuclides present in the soil, rocks and water are not uniformly distributed all over the world. Terrestrial gamma rays derive essentially from 40K and the radio nuclides belonging to 238U and 232Th series that are present in the earth’s crust. Apart from these natural sources, modern scientific and technological activities also contribute to the radiation level in the environment [3–8]. 137 Cs is regarded as the most important constituent of worldwide radioactive fallout. Sixty percent of the collective effective dose equivalent commitment from external radiation associated with past atmospheric nuclear weapon

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testing may be attributed to 137Cs. In the case of an accidental release of fission products from a nuclear power plant, cesium isotopes are especially significant due to their volatility and large inventory that builds up in the reactor over time. Therefore, measurement of 137Cs levels in soil is necessary in the environment of a studied area as such a data would serve as the baseline data. Its presence in soil would be an indicator that the area under study might have received some fallout radioactivity in the past [4, 9]. Radio nuclides present in the environment may enter human body through air, food and water and may adversely affect human health at higher radiation dose levels [10, 11]. Humans and other living organisms are continuously exposed to ionizing radiations from natural and anthropogenic sources which are present everywhere in the environment. The level of background radiations vary significantly from area to area and hence radiation doses to be received by the general public [12, 13]. Therefore, knowledge about the distribution pattern of both anthropogenic and natural radio nuclides plays an important role in controlling the expected health risks to the general public. The present study deals with the measurement of specific activities of 226Ra, 232Th, 40K and 137Cs, calculation of the radium equivalent activity, external and internal hazard indices, absorbed dose and annual effective dose equivalent for the studied area. This data will help to decide whether the studied region is in an area of normal or high background radiation and will set a baseline for the determination of radioactivity level in the region.

S. U. Rahman et al.

Attock of the Punjab province, Pakistan. These districts are hilly, extending from the outer ranges of the Himalayas and including most of the salt ranges and are shown in Fig. 1. These districts are located in the northern part of the Punjab province. The selected area included major part of salt range and Pothwar plateau. The latitude and longitude of the studied region ranged from 33°100 000 N to 33°540 3000 N and 73°20 3700 E to 73°260 3000 E, respectively with an area of 22,254 km2. Geologically, the area is bounded on the east by the Jhelum River which separates it from Kashmir territory, on the west by the Indus River on the north by the Margalla Hills, and on the south by the Salt Range. The climate of the area is subhumid to subtropical continental type, receiving maximum rainfall from July to September. Temperature in the studied areas usually drop to below 0 °C in January and reaches above 40 °C in June [14, 15]. Materials and methods Sampling methodology The soil samples were collected from each district, namely, Jhelum, Chakwal, Rawalpindi and Attock from 60 selected locations. For soil samples, undisturbed level surfaces situated sufficiently away from the public road and buildings were selected. The soil samples were collected by grabbing the top 5 cm layer. The samples were packed in polythene bags, sealed, properly marked according to the location of sampling site, labeled and brought to the laboratory for processing before analysis.

Description of the studied area

Sample preparation

The studied area wherefrom soil samples were collected consisted of districts Jhelum, Chakwal, Rawalpindi and

For activity measurements, the soil samples were first dried in the sun for few days. The samples were then crushed and

Fig. 1 Shaded portion of the map showing the studied area of four districts of the Punjab Province, Pakistan

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Measurement of naturally occurring/fallout radioactive elements

649

oven dried at 110 °C until the moisture of the samples removed completely and the sample weight became constant. The dried samples were then ground, powdered and passed through sieve of mesh size 2 mm. These samples were then sealed in radon impermeable plastic containers. The geometrical dimensions of these samples were kept identical as described by the calibration requirement [16]. The samples and reference material were stored for more than 40 days to attain secular equilibrium between 226Ra and its short lived decay products.

rays absorbed dose in air at 1 m above the ground surface was calculated for 226Ra, 232Th and 40K radio nuclides, for general public of the studied area using the following expression: D nGy h1 ¼ 0:427CRa þ 0:662CTh þ 0:043CK ð2Þ where CK, CRa and CTh are the specific activity concentrations of potassium, uranium and thorium, respectively. In the above conversions, it is assumed that all the decay products of 226Ra and 232Th are in radioactive equilibrium with their precursors.

Radiometric analysis Radiometric analyses of different samples were carried out using a high resolution gamma ray spectrometry system. The spectrometry system consisted of an HPGe detector having an active volume of 180 mm3 with relative efficiency 30% with respect to NaI(Tl) detector and operating voltage 3000 V. To reduce the environmental gamma background radiation, the detector was shielded with lead bricks of thickness 10 cm and internally lined with 3 mm copper foil. For acquisition of data and analysis, a multi-channel analyzer card with inbuilt power supply, preamplifier and amplifier was installed in a personal computer. The IAEA reference material was employed for the efficiency calibration of the system. The spectra of the references were collected for 65000 s each. The gamma ray spectrum was recorded using PC based software GENIE-2000. The detector had energy resolution of 2.5 keV (FWHM) for 1332 keV line of 60Co. The concentration of 226Ra was assessed through the photo peaks of its daughters: 214Pb (295, 352 keV) and 214Bi (609, 1120 keV) whereas the concentration of 232Th was determined through the photo peaks of 228Ac (338, 911, 968.9 keV). 137Cs and 40K were measured directly from their 662 and 1460.83 keV c ray peaks, respectively [17, 18].

Annual effective dose The annual effective dose equivalent expected to be received by the general public due to the radioactivity in soil was calculated using the following relation. Indoor ðnSvÞ ¼ ðAbsorbed doseÞ nGy h1 8760 h 0:8 0:7 Sv Gy1

ð3Þ

Outdoor ðnSvÞ ¼ ðAbsorbed doseÞ nGy h1 8760 h 0:2 0:7 Sv Gy1

ð4Þ

The annual effective dose equivalent was calculated using a conversion factor of 0.7 Sv Gy-1, which converts absorbed dose in air to human effective dose in adults. The occupancy factor used was 0.2 for outdoor and 0.8 for indoors [1]. Internal and external hazard index The internal and external hazard indexes are calculated by the following expressions: Hin ¼ ARa =185 þ ATh =259 þ AK =4810

ð5Þ

Radium equivalent activity

Hex ¼ ARa =370 þ ATh =259 þ AK =4810

ð6Þ

Having measured activity concentration of 226Ra, 232Th and 40K in all the collected samples, radium equivalent activity (Raeq) was calculated by using the following relation [19, 20].

where ARa, ATh and AK are the activities of 226Ra, 232Th and 40K in Bq kg-1, respectively. The value of internal and external radiation hazard index must be less than unity in order to keep the radiation hazard to be insignificant.

Raeq ¼ ARa þ 1:43ATh þ 0:077AK

ð1Þ

where ARa, ATh and AK are the mean activities of 226Ra, Th and 40K in Bq kg-1, respectively. According to this formula, 1 Bq kg-1 of 226Ra, 0.7 Bq kg-1 of 232Th or 13 Bq kg-1 of 40K produce the same gamma ray dose.

Results and discussion

232

Calculation of air absorbed gamma radiation dose rate Effects of gamma radiation are normally expressed in terms of absorbed dose rate in air. The terrestrial gamma

Tables 1, 2, 3, 4 show measured activity concentration of Ra, 232Th, 40K and 137Cs in the soil samples collected from 60 different locations of districts Jhelum, Chakwal, Rawalpindi and Attock. As may be seen in these tables, the activity concentration of 226Ra, 232Th, 40K and 137Cs range from 26.02 ± 7.11 (Chakwal) to 93.54 ± 8.13 (Jhelum), 29.34 ± 2.58 (Jhelum) to 114.41 ± 2.80 (Rawalpindi),

226

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S. U. Rahman et al.

Table 1 Measured activity concentration (Bq kg-1) of 226Ra, 232Th, 40 K and 137Cs in soil samples of district Jhelum, Punjab Province, Pakistan Sample

226

Ra

232

Th

40

K

137

Cs

Table 3 Measured activity concentration (Bq kg-1) of 226Ra, 232Th, 40 K and 137Cs in soil samples of district Rawalpindi, Punjab Province, Pakistan Sample

226

Ra

232

Th

40

K

137

Cs

J1

45.12 ± 8.13

39.9 ± 2.60

572.7 ± 3.08

2.2 ± 0.2

R-1

71.54 ± 8.13

57.80 ± 2.80 707.92 ± 3.08 1.3 ± 0.2

J2

77.01 ± 8.13

52.2 ± 2.80

640.3 ± 3.08

3.1 ± 0.3

R-2

70.10 ± 8.13

52.70 ± 2.80 752.98 ± 4.20 4.3 ± 0.3

J3 J4

64.08 ± 8.01 67.50 ± 7.21

31.2 ± 2.58 62.46 ± 2.80

550.22 ± 3.20 640.33 ± 3.08

0.7 ± 0.2 1.6 ± 0.2

R-3 R-4

49.40 ± 7.21 34.67 ± 8.01

39.21 ± 2.58 730.45 ± 3.08 0.5 ± 0.2 53.24 ± 2.80 617.81 ± 3.08 0.7 ± 0.2

J5

70.10 ± 8.01

43.00 ± 2.60

460.16 ± 3.20

2.3 ± 0.2

R-5

34.5 ± 8.13

65.02 ± 2.80 640.33 ± 3.08 1.7 ± 0.2

J6

36.5 ± 7.21

29.34 ± 2.58

481.24 ± 3.08

1.7 ± 0.2

R-6

48.01 ± 7.21

45.56 ± 2.60 595.28 ± 4.20 3.6 ± 0.3

J7

68.13 ± 8.13

38.02 ± 2.58

694.38 ± 3.08

0.5 ± 0.2

R-7

54.60 ± 7.21

44.03 ± 2.60 572.01 ± 3.08 ND

J8

53.75 ± 8.01

67.6 ± 2.60

532.04 ± 3.20

1.2 ± 0.2

R-8

73.55 ± 8.13

31.24 ± 2.58 527.69 ± 3.52 0.5 ± 0.2

J9

39.08 ± 7.11

85.43 ± 2.80

573.7 ± 3.20

4.3 ± 0.3

R-9

72.69 ± 8.13

51.19 ± 2.80 460.10 ± 3.52 7.8 ± 0.3

J10

93.54 ± 8.13

70.56 ± 2.58

397.65 ± 3.08

3.5 ± 0.3

R-10

40.24 ± 8.01

68.60 ± 2.80 617.80 ± 3.08 2.7 ± 0.2

J11

42.87 ± 7.21

53.24 ± 2.80

348.15 ± 3.20

ND

R-11

63.50 ± 8.13

39.93 ± 2.80 527.93 ± 3.08 ND

J12

49.62 ± 8.13

62.82 ± 2.80

419.54 ± 3.08

ND

R-12

64.08 ± 8.13

46.70 ± 2.80 640.33 ± 3.08 0.9 ± 0.2

J13

75.42 ± 8.01

81.52 ± 2.80

660.22 ± 3.08

1.2 ± 0.2

R-13

57.70 ± 8.13

34.30 ± 2.80 437.57 ± 3.08 ND

J14

87.21 ± 8.13

48.02 ± 2.60

517.67 ± 3.08

5.4 ± 0.3

R-14

76.35 ± 8.13

73.45 ± 2.80 632.28 ± 3.52 2.5 ± 0.2

J15

48.53 ± 7.21

61.50 ± 2.60

513.32 ± 3.20

ND

R-15

53.37 ± 7.21 114.41 ± 2.80 591.57 ± 4.20 1.2 ± 0.2

Range

36.5–93.5

29.3–85.4

348.2–694.4

0.5–5.4

Range

34.5–76.4

31.2–114.4

Mean

61.23 ± 7.78

52.59 ± 2.67

533.44 ± 3.13

2.3 ± 0.2

Mean

57.62 ± 7.87

54.49 ± 2.74 603.47 ± 3.39 2.3 ± 0.2

ND not detected

226

Ra

232

Th

40

K

137

Cs

A-1

64.08 ± 8.13

37.37 ± 2.80

662.86 ± 3.08

1.4 ± 0.2

A-2

47.13 ± 8.13

67.58 ± 2.81

572.75 ± 4.20

2.1 ± 0.2

A-3

58.62 ± 8.13

38.91 ± 2.81

505.16 ± 4.20

0.8 ± 0.2

A-4

29.72 ± 7.21

54.16 ± 2.81

413.43 ± 3.52

1.2 ± 0.2

A-5

46.45 ± 8.01

67.35 ± 2.60

539.82 ± 3.52

ND

A-6

84.62 ± 8.13

41.64 ± 2.60

427.05 ± 4.20

3.8 ± 0.3

A-7

76.03 ± 8.13

32.03 ± 2.58

698.32 ± 4.20

2.5 ± 0.3

A-8 A-9

42.67 ± 7.11 39.78 ± 8.01

62.87 ± 2.81 94.22 ± 2.81

524.17 ± 3.08 674.43 ± 4.20

ND ND

A-10

55.21 ± 8.13

69.46 ± 2.80

711.34 ± 4.20

6.7 ± 0.3

A-11

73.32 ± 7.21

47.50 ± 2.58

524.45 ± 3.08

2.2 ± 0.2

A-12

36.54 ± 8.13

58.23 ± 2.60

702.89 ± 3.08

0.4 ± 0.2

A-13

81.67 ± 7.21

63.90 ± 2.81

560.15 ± 4.20

3.2 ± 0.2

A-14

74.05 ± 8.13

39.43 ± 1.60

478.34 ± 3.52

ND

A-15

63.56 ± 8.13

72.04 ± 2.80

625.28 ± 3.52

2.3 ± 0.2

Range

29.7–84.6

32.03–94.2

413.4–711.3

0.4–6.7

Mean

58.23 ± 7.86

56.45 ± 2.65

574 ± 3.72

2.4 ± 0.2

ND not detected

348.15 ± 3.20 (Jhelum) to 752.98 ± 4.20 (Rawalpindi) and 0.4 ± 0.2 (Attock) to 7.8 ± 0.3 (Rawalpindi), respectively. Wide variation in specific activity within each district is observed. This non-uniform behavior of

123

0.5–7.8

ND not detected

Table 2 Measured activity concentration (Bq kg-1) of 226Ra, 232Th, 40 K and 137Cs in soil samples of district Attock, Punjab Province, Pakistan Sample

437.6–753.0

radionuclides may be attributed to their uneven and irregular distribution in earth crust, differences of geological structures and also to various topographical and agricultural activities. Figure 2a–c depicts the correlation between the activities of 226Ra, 232Th and 40K, respectively. In all the three cases, the regression was found linear and positive. It is obvious that the correlations are rather weak, with correlation coefficients of 0.004, 0.007 and 0.027, respectively, but agreed with a previous study on the correlation between 226 Ra, 232Th and 40K [21] The mean activity concentration of 226Ra is found to be higher than many countries listed in the Table 5 [21–23, 25–29] and lower only than that of Turkey [24]. However, the concentration of 232Th is found to be lower than the Japan, Turkey, Indian Punjab and Mid-Rechna, Pakistan. The levels of 40K are found to be lower than those of many countries like Japan, Turkey, Bangladesh, Mid Rechna and Lahore Pakistan. Considering the Worldwide average concentrations of natural radionuclides UNSCEAR 2000 [2] the 226Ra, 232Th and 40K concentrations within the study area are found to be slightly high. From the measured activity of 226Ra, 232Th and 40K, radium equivalent activity, absorbed gamma radiation dose rate, annual effective dose equivalent (indoor and outdoor), internal and external hazard indices have been calculated and are shown in Tables 6, 7, 8, and 9. The distribution of 226 Ra, 232Th and 40K in soil is not uniform. Uniformity in respect of exposure to radiation has been defined in terms


651

Table 4 Measured activity concentration (Bq kg-1) of 226Ra, 232Th, 40 K and 137Cs in soil samples of district Chakwal, Punjab Province, Pakistan Sample

226

Ra

232

Th

40

K

137

Cs

C-1

66.09 ± 8.13

37.37 ± 2.60

595.28 ± 3.08

ND

C-2

51.44 ± 8.13

49.66 ± 2.80

550.22 ± 3.08

0.8 ± 0.2

C-3 C-4

56.90 ± 8.01 52.29 ± 8.13

41.47 ± 2.80 30.71 ± 2.58

550.25 ± 3.52 662.86 ± 3.08

2.1 ± 0.2 ND

C-5

70.10 ± 8.13

61.43 ± 2.80

505.16 ± 3.08

ND

C-6

43.65 ± 7.21

45.21 ± 2.60

703.49 ± 4.20

3.7 ± 0.3

C-7

76.32 ± 8.01

84.47 ± 2.80

577.68 ± 3.52

0.9 ± 0.2

C-8

26.02 ± 7.11

35.84 ± 2.60

397.32 ± 3.08

ND

C-9

57.43 ± 7.11

63.05 ± 2.80

682.21 ± 4.20

2.1 ± 0.2

C-10

38.39 ± 7.21

46.65 ± 2.80

364.45 ± 4.20

2.5 ± 0.2

C-11

65.42 ± 8.01

78.46 ± 2.80

621.04 ± 3.52

0.8 ± 0.2 ND

C-12

89.16 ± 8.13

42.72 ± 2.58

573.71 ± 4.20

C-13

46.67 ± 8.13

57.53 ± 2.58

422.54 ± 3.08

2.4 ± 0.2

C-14

62.28 ± 8.13

52.04 ± 2.80

498.21 ± 3.08

ND

C-15

35.53 ± 7.11

36.25 ± 2.60

501.32 ± 3.52

ND

Range

26.0–89.2

30.7–84.5

364.4–703.5

0.8–3.7

Mean

55.85 ± 7.78

50.86 ± 2.7

547.0 ± 3.5

1.7 ± 0.2

ND not detected

of radium equivalent activity (Raeq) in Bq kg-1 to compare the specific activity of materials containing different amounts of 226Ra, 232Th and 40K. It is calculated through the Eq. 1. The calculated Raeq value obtained in this study is minimum in district Chakwal (107.86 ± 11.06 Bq kg-1) whereas it is maximum in district Rawalpindi (262.53 ± 11.54 Bq kg-1). The mean radium equivalent activity in this study is 179.26 ± 11.93 Bq kg-1. The radium equivalent activity in the soil of the studied area is below the recommended limit of 370 Bq kg-1 [20]. In order to calculate the dose rate in air for the samples collected from the area under study, Eq. 2 was used [30]. The absorbed dose rate in air due to the terrestrial gamma rays at 1 m above the ground was calculated for all of the 60 sites. Equation 2 assumes that all the decay products of 226 Ra and 232Th are in radioactive equilibrium with their precursors. The dose rate ranged from 51.92 ± 4.89 to 123.97 ± 5.11 nGy h-1 with a mean dose rate value of 85.04 ± 5.27 nGy h-1. As may be seen in Tables 5, 6, 7, and 8, that most of the values for the gamma ray dose rate are higher than the world average value of 55 nGy h-1 [30] which is due to the variations in the soil formation geology. The annual effective dose equivalent was calculated for all the four districts of Punjab, namely Jhelum, Chakwal, Rawalpindi and Attock using Eqs. 3 and 4. These calculations assume that people spend 80% their time indoors and 20% outdoors. The values obtained ranged from 0.25 ± 0.02 to 0.61 ± 0.02 mSv for indoors and 0.06 ± 0.01 to

Fig. 2 a Correlation between 226Ra and 232Th concentrations; b correlation between 226Ra and 40K concentrations; c correlation between 232Th and 40K concentrations

0.15 ± 0.01 mSv for outdoors with average values of 0.42 ± 0.03 and 0.10 ± 0.01 mSv, respectively. These values are within the permissible dose equivalent limit (i.e., 1 mSv y-1) [31]. The external radiation hazard, Hex and internal radiation hazard, Hin were calculated using Eqs. 5 and 6. External hazard index has been calculated for the specific activity data given in Tables 1, 2, 3, 4 and presented in Tables 6, 7, 8, 9. The calculated values of Hin and Hex ranged from 0.36 ± 0.05 to 0.86 ± 0.05 and 0.29 ± 0.03 to 0.71 ± 0.03, respectively. For the materials to be used in construction, the external hazard index should be less than unity. Similarly, internal hazard index should also be less than unity to have negligible hazardous effects of radon and its short-lived progeny to the respiratory organs [21]. The values of external and internal hazard indices in the present study are less than unity, indicating that the soil from these districts is safe and can be used as a construction material without posing any significant harmful effects to the inhabitants. The activity levels of 137Cs in some of the locations was below the detection limit and in other regions, it ranged

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S. U. Rahman et al.

Table 5 The average concentrations of the natural radionuclides in soil samples (in Bq kg-1) from different parts of the world Mean activity concentration (Bq kg-1)

Country

References

226

232

40

Egypt

18.7

24.7

331.0

–

Ebaid et al. [22]

Japan

32.4

54

794

–

Selvasekarapandian [23]

Taiwan

30

44

431

–


Ireland

37

26

350

–


Turkey

79

62

574

–

Baykara et al. [24]

Venezuela

27

31

357

5

La Breque [25]

World average Indian Punjab

50 56.74

50 87.42

500 143.04

– –

UNSCEAR [2] Singh et al. [26]

Bangladesh

33

16

574

7

Miah et al. [27]

Southern Punjab, Pakistan

21.7

31.1

393.2

1.6

Fatima et al. [28]

Lahore, Pakistan

25.8

49.2

561.6

–

Akhtar et al. [29]

Mid-Rechna, Pakistan

49.0

62.4

670.6

3.5

Jabbar et al. [21]

Punjab Province, Pakistan

58.23

53.60

564.48

2.18

Present study

Ra

Th

137

K

Cs

Table 6 Calculated values of radium equivalent activity, absorbed dose rate, annual effective dose equivalent (indoor and outdoor), external and internal hazard indices in the district of Jhelum, Punjab province, Pakistan Sample

Radium equivalent activity (Bq kg-1)

Absorbed dose rate (nGy h-1)

Indoor annual effective dose equivalent (mSv y-1)

Outdoor annual effective dose equivalent (mSv y-1)

Internal hazard index

External hazard index

J1

146.28 ± 12.08

70.31 ± 5.32

0.34 ± 0.03

0.09 ± 0.01

0.52 ± 0.05

0.40 ± 0.03

J2

200.96 ± 12.37

94.97 ± 5.46

0.47 ± 0.03

0.12 ± 0.01

0.75 ± 0.06

0.54 ± 0.03

J3

151.06 ± 11.95

71.68 ± 5.27

0.35 ± 0.02

0.09 ± 0.01

0.58 ± 0.05

0.41 ± 0.03

J4

206.12 ± 11.45

97.70 ± 5.06

0.48 ± 0.02

0.12 ± 0.01

0.74 ± 0.05

0.56 ± 0.03

J5

167.02 ± 11.97

78.19 ± 5.28

0.38 ± 0.03

0.10 ± 0.01

0.64 ± 0.05

0.45 ± 0.03

J6

115.51 ± 11.14

55.70 ± 4.92

0.27 ± 0.02

0.07 ± 0.01

0.41 ± 0.05

0.31 ± 0.03 0.48 ± 0.03

J7

175.97 ± 12.06

84.12 ± 5.31

0.41 ± 0.03

0.10 ± 0.01

0.66 ± 0.05

J8

191.38 ± 11.97

90.58 ± 5.28

0.44 ± 0.03

0.11 ± 0.01

0.66 ± 0.05

0.52 ± 0.03

J9

205.42 ± 11.36

97.91 ± 5.03

0.48 ± 0.02

0.12 ± 0.01

0.66 ± 0.05

0.55 ± 0.03

J10

225.06 ± 12.06

103.75 ± 5.31

0.51 ± 0.02

0.13 ± 0.01

0.86 ± 0.05

0.61 ± 0.03

J11

145.81 ± 11.46

68.52 ± 5.07

0.34 ± 0.02

0.08 ± 0.01

0.51 ± 0.05

0.39 ± 0.03

J12

171.76 ± 12.37

80.82 ± 5.46

0.40 ± 0.03

0.10 ± 0.01

0.60 ± 0.06

0.46 ± 0.03

J13

242.83 ± 12.25

114.56 ± 5.41

0.56 ± 0.03

0.14 ± 0.01

0.86 ± 0.05

0.66 ± 0.03

J14 J15

195.74 ± 12.08 176.00 ± 11.17

91.29 ± 5.32 83.51 ± 4.94

0.45 ± 0.03 0.41 ± 0.02

0.11 ± 0.01 0.10 ± 0.01

0.76 ± 0.05 0.61 ± 0.05

0.53 ± 0.03 0.48 ± 0.03

Range

115.5–242.8

55.7–114.6

0.27–0.56

0.07–0.14

0.41–0.86

0.31–0.66

Mean

181.13 ± 11.85

85.57 ± 5.23

0.42 ± 0.02

0.1 ± 0.01

0.66 ± 0.05

0.49 ± 0.03

from 0.4 ± 0.2 to 7.8 ± 0.3 Bq kg-1, which might be due to fallout of previous worldwide nuclear explosion and reactor accidents. As result of nuclear activities, 137Cs enter into the atmosphere and most of the fallout radiation accumulates in the soil. In this study, the observed 137Cs concentrations are consistent with the world average.

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Conclusion Gamma activity from naturally occurring radionuclides namely 226Ra, 232Th, 40K and artificially radionuclide 137Cs has been measured in soil samples which were collected from four districts, namely Jhelum, Chakwal, Rawalpindi


653

Table 7 Calculated values of radium equivalent activity, absorbed dose rate, annual effective dose equivalent (indoor and outdoor), external and internal hazard indices in the district of Attock, Punjab province, Pakistan Sample


A1

168.56 ± 12.37

Absorbed dose rate (nGy h-1) 80.60 ± 5.46





0.40 ± 0.03

0.10 ± 0.01

0.63 ± 0.06

0.46 ± 0.03

A2

187.87 ± 12.47

89.49 ± 5.51

0.44 ± 0.03

0.11 ± 0.01

0.63 ± 0.06

0.51 ± 0.03

A3

153.15 ± 12.47

72.51 ± 5.51

0.36 ± 0.03

0.09 ± 0.01

0.57 ± 0.06

0.41 ± 0.03

A4

139.00 ± 11.50

66.32 ± 5.09

0.32 ± 0.02

0.08 ± 0.01

0.46 ± 0.05

0.38 ± 0.03

A5

184.33 ± 12.00

87.63 ± 5.29

0.43 ± 0.03

0.11 ± 0.01

0.62 ± 0.05

0.50 ± 0.03

A6

177.05 ± 12.17

82.06 ± 5.37

0.40 ± 0.03

0.10 ± 0.01

0.71 ± 0.05

0.49 ± 0.03 0.47 ± 0.03

A7

175.60 ± 12.14

83.70 ± 5.36

0.41 ± 0.03

0.10 ± 0.01

0.68 ± 0.05

A8

172.94 ± 11.36

82.38 ± 5.03

0.40 ± 0.02

0.10 ± 0.01

0.58 ± 0.05

0.47 ± 0.03

A9

226.45 ± 12.35

108.36 ± 5.46

0.53 ± 0.03

0.13 ± 0.01

0.72 ± 0.06

0.61 ± 0.03

A10

209.31 ± 12.46

100.14 ± 5.50

0.49 ± 0.03

0.12 ± 0.01

0.71 ± 0.06

0.56 ± 0.03

A11

181.63 ± 11.14

85.30 ± 4.92

0.42 ± 0.02

0.10 ± 0.01

0.69 ± 0.05

0.49 ± 0.03

A12

173.93 ± 12.08

84.38 ± 5.32

0.41 ± 0.03

0.10 ± 0.01

0.57 ± 0.05

0.47 ± 0.03

A13

216.18 ± 11.55

101.26 ± 5.12

0.50 ± 0.02

0.12 ± 0.01

0.80 ± 0.05

0.58 ± 0.03

A14 A15

167.27 ± 10.69 214.72 ± 12.40

78.29 ± 4.68 101.72 ± 5.48

0.38 ± 0.02 0.50 ± 0.03

0.10 ± 0.01 0.12 ± 0.01

0.65 ± 0.05 0.75 ± 0.06

0.45 ± 0.03 0.58 ± 0.03

Range

139.0–226.4

66.32–108.4

0.32–0.53

0.08–0.13

0.46–0.72

0.38–0.61

Mean

183.2 ± 11.94

86.94 ± 5.27

0.43 ± 0.03

0.11 ± 0.01

0.65 ± 0.05

0.49 ± 0.03

Table 8 Calculated values of radium equivalent activity, absorbed dose rate, annual effective dose equivalent (indoor and outdoor), external and internal hazard indices in the district of Rawalpindi, Punjab province, Pakistan Sample


R1

208.70 ± 12.37






0.49 ± 0.03

0.12 ± 0.01

0.76 ± 0.06

0.56 ± 0.03

R2

203.44 ± 12.46

97.20 ± 5.51

0.48 ± 0.03

0.12 ± 0.01

0.74 ± 0.06

0.55 ± 0.03

R3

161.72 ± 11.14

78.46 ± 4.92

0.38 ± 0.02

0.10 ± 0.01

0.57 ± 0.05

0.44 ± 0.03

R4

158.37 ± 12.25

76.61 ± 5.41

0.38 ± 0.03

0.09 ± 0.01

0.52 ± 0.06

0.43 ± 0.03

R5

176.78 ± 12.37

85.31 ± 5.46

0.42 ± 0.03

0.10 ± 0.01

0.57 ± 0.06

0.48 ± 0.03

R6

159.00 ± 11.25

76.26 ± 4.98

0.37 ± 0.02

0.09 ± 0.01

0.56 ± 0.05

0.43 ± 0.03 0.44 ± 0.03

R7

161.61 ± 11.16

77.06 ± 4.93

0.38 ± 0.02

0.09 ± 0.01

0.58 ± 0.05

R8

158.86 ± 12.09

74.78 ± 5.33

0.37 ± 0.03

0.09 ± 0.01

0.63 ± 0.05

0.43 ± 0.03

R9

181.32 ± 12.40

84.71 ± 5.48

0.42 ± 0.03

0.10 ± 0.01

0.69 ± 0.06

0.49 ± 0.03

R10

185.91 ± 12.25

89.16 ± 5.41

0.44 ± 0.03

0.11 ± 0.01

0.61 ± 0.06

0.50 ± 0.03

R11

161.25 ± 12.37

76.25 ± 5.46

0.37 ± 0.03

0.09 ± 0.01

0.61 ± 0.06

0.44 ± 0.03

R12

180.17 ± 12.37

85.81 ± 5.46

0.42 ± 0.03

0.10 ± 0.01

0.66 ± 0.06

0.49 ± 0.03

R13

140.44 ± 12.37

66.16 ± 5.46

0.32 ± 0.03

0.08 ± 0.01

0.54 ± 0.06

0.38 ± 0.03

R14 R15

230.07 ± 12.40 262.53 ± 11.54

108.41 ± 5.48 123.97 ± 5.11

0.53 ± 0.03 0.61 ± 0.02

0.13 ± 0.01 0.15 ± 0.01

0.83 ± 0.06 0.85 ± 0.05

0.62 ± 0.03 0.71 ± 0.03

Range

140.4–262.5

66.2–124.0

0.32–0.61

0.08–0.15

0.54–0.85

0.38–0.71

Mean

182.01 ± 12.05

86.63 ± 5.32

0.42 ± 0.03

0.11 ± 0.01

0.65 ± 0.05

0.49 ± 0.03

and Attock of the Punjab, province. Mean radium equivalent activity was found to be 179.26 ± 11.93 Bq kg-1 which is below the recommended limit of 370 Bq kg-1. The estimated dose rate due to the presence of 226Ra,

232

Th, 40K in the soil of studied area ranged from 51.92 ± 4.89 to 123.97 ± 5.11 nGy h-1 with a mean dose rate value of 84.63 ± 5.27 nGy h-1. The indoor and outdoor annual effective dose equivalent values ranged from

123

654

S. U. Rahman et al.

Table 9 Calculated values of radium equivalent activity, absorbed dose rate, annual effective dose equivalent (indoor and outdoor), external and internal hazard indices in the district of Chakwal, Punjab province, Pakistan Sample


C1

165.37 ± 12.08






0.39 ± 0.03

0.10 ± 0.01

0.62 ± 0.05

0.45 ± 0.03

C2

164.82 ± 12.37

78.50 ± 5.46

0.39 ± 0.03

0.10 ± 0.01

0.58 ± 0.06

0.44 ± 0.03

C3

158.5712.28

75.41 ± 5.42

0.37 ± 0.03

0.09 ± 0.01

0.58 ± 0.05

0.43 ± 0.03

C4

147.25 ± 12.06

71.16 ± 5.31

0.35 ± 0.03

0.09 ± 0.01

0.54 ± 0.05

0.40 ± 0.03

C5

196.84 ± 12.37

92.32 ± 5.46

0.45 ± 0.03

0.11 ± 0.01

0.72 ± 0.06

0.53 ± 0.03

C6

162.47 ± 11.25

78.82 ± 4.98

0.39 ± 0.02

0.10 ± 0.01

0.56 ± 0.05

0.44 ± 0.03 0.65 ± 0.03

C7

241.59 ± 12.28

113.35 ± 5.42

0.56 ± 0.03

0.14 ± 0.01

0.86 ± 0.05

C8

107.86 ± 11.06

51.92 ± 4.89

0.25 ± 0.02

0.06 ± 0.01

0.36 ± 0.05

0.29 ± 0.03

C9

200.12 ± 11.44

95.59 ± 5.07

0.47 ± 0.02

0.12 ± 0.01

0.70 ± 0.05

0.54 ± 0.03

C10

133.16 ± 11.54

62.95 ± 5.11

0.31 ± 0.02

0.08 ± 0.01

0.46 ± 0.05

0.36 ± 0.03

C11

225.44 ± 12.28

106.58 ± 5.42

0.52 ± 0.03

0.13 ± 0.01

0.79 ± 0.05

0.61 ± 0.03

C12

194.42 ± 12.14

91.02 ± 5.36

0.45 ± 0.03

0.11 ± 0.01

0.77 ± 0.05

0.52 ± 0.03

C13

161.47 ± 12.06

76.18 ± 5.31

0.37 ± 0.03

0.09 ± 0.01

0.56 ± 0.05

0.44 ± 0.03

C14 C15

175.06 ± 12.37 125.96 ± 11.10

82.47 ± 5.46 60.73 ± 4.91

0.40 ± 0.03 0.30 ± 0.02

0.10 ± 0.01 0.07 ± 0.01

0.64 ± 0.06 0.44 ± 0.05

0.47 ± 0.03 0.34 ± 0.03

Range

107.9–225.4

51.9–106.6

0.25–0.52

0.06–0.13

0.36–0.79

0.29–0.61

Mean

170.70 ± 11.91

81.04 ± 5.26

0.4 ± 0.03

0.1 ± 0.01

0.61 ± 0.05

0.46 ± 0.03

0.25 ± 0.02 to 0.61 ± 0.02 mSv and 0.06 ± 0.01 to 0.15 ± 0.01 mSv with average values of 0.42 ± 0.03 and 0.10 ± 0.01 mSv, respectively. The external and internal hazard indices have been found to be less than 1. A weak correlation between the concentrations of 226Ra, 232Th and 40 K was found with correlation coefficients of 0.004, 0.007 and 0.027, respectively. 137Cs has also been detected in some locations of the studied area which ranged from 0.4 ± 0.2 to 7.8 ± 0.3 Bq kg-1 and is consistent with the world average. The results of this study can be used as a baseline data for preparing a radiological map of the study area.

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