Journal of Pure Applied and Industrial Physics, Vol.6(4), 57-64, April 2016 ISSN 0976-5727 (Print) (An International Research Journal), www.physics-journal.org ISSN 2319-8133 (Online

Determination of Natural and Artificial Radionuclides in Soil Samples of ,

Md. Arafat Hossain1, Khondokar Nazmus Sakib2 and Md. Masum Billah3

1Lecturer in Physics, Govt. Fazilatunnesa Mahila College, Bhola, BANGLADESH. 2Lecturer in Physics, Mawlana Bhashani Science and Technology University, BANGLADESH. 3Lecturer in Physics, Jessore University of Science and Technology, BANGLADESH.

(Received on: April 20, 2016)

ABSTRACT

Though there is no enough information about radioactivity in Bhola district of Bangladesh due to lack of measurement, geographical position and natural resources of this area are in favour of radioactivity. For this reason, concentration of radionuclides in 21 soil samples have been studied and evaluated. Soil samples were collected from 21 locations of Bhola district. Experimental results were obtained by using a High Purity Germanium (HPGe) Detector and the radioactive standard sources supplied by IAEA were used to determine the efficiency. The measuring time of all samples is 5000 seconds.

Keywords: HPGe detector, soil, Radionuclides, 40K, 226Ra, 232Th.

1. INTRODUCTION

In our daily life we come across both natural as well as manmade sources of radiation. The natural radioactivity present in soil and rocks whereas man-made sources are nuclear installation, radio nuclides, electronic devices and radiation sources used in industry. Although radionuclides are just a mare material of environment it reminds us the use in medical science, nuclear power plant, industry as well as the horrible day of Hiroshima & Nagasaki. Radiation may be artificial or natural, or radiation dose may be small or large, it creates some biological effects. For these reason the whole world has became aware of radionuclides and many splendid works has been done monitoring radioactivity. Some countries in Asia have recently started nuclear programmers to achieve nuclear power. By this time, some successful nuclear explosions have already been carried out by our neighboring countries-India, Pakistan and China. Therefore, the probability of radioactive contamination of the environment of Bangladesh may further be increased. There is no information about radioactivity in the soils

57 Md. Arafat Hossain, et al., J. Pure Appl. & Ind. Phys. Vol.6 (4), 57-64 (2016) samples of Bhola District so far. For this reason, the concentrations of the natural radio nuclides in twenty one surface soil samples in municipal area of Bhola district have been studied and evaluated.

2. MATERIALS AND METHODS

2.1. Description of study area

Bhola District is an administrative district (zila) in south-western Bangladesh. It is established as a district at 1 February 1984. It is located in the Division and has an area of 3403.48 km².It is bounded by Lakshmipur and Barisal Districts to the north, the Bay of Bengal to the south, by Lakshmipur and Noakhali districts, the (lower) Meghna river and Shahbazpur Channel to the east, and by and the Tetulia river to the west. The total population of Bhola district is 20,37,201 and population density is 500/Sq Km. Bhola district comprises the following : Bhola Sadar , Upazila, Burhanuddin Upazila, , , Char Fasson Upazila, Manpura Upazila.

Figure 1: Map of Bhola District, Bangladesh. This map indicates the location of the Upazilas studied.

2.2. Sampling and samples preparation

Soil samples were collected during 2009 from 21 locations in the municipal area of Bhola district in the north east of Bangladesh. Samples were collected from a depth of 0 – 3 inch. Lands of slightly dry soil were chosen maintaining some criteria mentioned below: 1. The collection area should be undisturbed open terrain.

58 Md. Arafat Hossain, et al., J. Pure Appl. & Ind. Phys. Vol.6 (4), 57-64 (2016) 2. There should be very little or no runoff soil during heavy rain, particularly in rainy season.

After removing the stones and vegetation, all soil samples were dried up at room temperature, sieved, placed in the plastic 400 cm3 containers and left for four weeks to reach radioactive equilibrium. Then the samples were weighted by a weighting balance supplied by Shanghai, Japan. Each soil sample weighted between 250 to 400gm is chosen for the experiment. Then all the samples were put into the cylindrical plastic pot of equal size, collected from local market. All the samples were then rested for at least 24 or 26 days. All samples were analyzed with gamma ray detector.

Table 1: Sample Codes and corresponding Locations of Bhola District

Upazila (Date) Sample Code Specific Location 1.Bhola Sadar BS10 314,Norona Sarak,Ward-1 (10.10.2009) BS11 Gp Towar, Charnoabad BS12 Majhibari, Bapta 2.Borhanuddin BB07 Sub-Divisional Engineer Office, Water Development Board (10.10.2009) BB08 Brac Office BB09 Howladar Enterprise, South Bus-Stand 3.Doulotkhan BD13 Thana Office (10.10.2009) BD14 High School BD15 Char Borolamsidhoni 4.Tojumuddin BT16 Shosibhuson (12.10.2009) BT17 High School BT18 Thana Office Building(East) 5.Lalmohon BL04 Molla Boro Jam-E-Masjid(East) (12.10.2009) BL05 Bohumukhi High School(Opposite Pourobhaban) BL06 Zila Parisad Dakbanglo 6.Charfashion BC01 Hafizia Orfahanage(Bus-Stand Left Turn) (20.12.2009) BC02 Thana Masjid(Pond Side) BC03 Al-Madina Jam-E-Masjid(Kobor Sthan) 7.Monpura BM19 Char Jotin,Hazirhatt (21.12.2009) BM20 Char Johiruddin BM21 Thana Office Square 2.3. Experimental setup

The spectrometry system consisted of a high purity germanium (HPGe) detector, Pre- amplifier (supplied by Oxford instrument Inc. Nuclear measurement group, U.S.A), High voltage supplier (HV supply model ORTEC 459), Amplifier, MCA card memory containing a commercial software EMCAPLUS (silena) version 1.012 (supplied by silena, Germany). The contents of the memory after a measurement lasting 5000s can be displayed on a CRT screen of a monitor coupled with the PC. The digital recording of the content of each channel can be printed out through a printer (Model LQ-570+) supplied by EPSON,Japan. The resolution of the (HPGe) detector was found 2.80keV at FWHM of the 1332keV peak of 60Co. The shielding arrangement surrounding the detector was fabricated in the form of a circular cylinder having 21 inch in height using lead and steel. The top was covered by round movable steel and a lead

59 Md. Arafat Hossain, et al., J. Pure Appl. & Ind. Phys. Vol.6 (4), 57-64 (2016) plate. 226Ra activity of the samples was determined by the help of its daughters (214Pb and 214Bi) and 232Th activity of the sample was determined by the help of its daughters (228Ac). Average Radioactivity of different soil samples were determined and are given in Table 2. The activity of each radionuclide 214Pb, 214Bi, 228Ac,40K were then calculated using the following formula:

N  100  1000 A  (1) P    W Where, N=Net counts per second (c.p.s) = (sample c.p.s-back ground c.p.s) Pɣ =Probability of radionuclide ߝ= Efficiency in%. W=Weight of the sample in kg.

Table 2 : Average Radioactivity of different soil samples.

Upazila Code 214pb 214pb 214Bi 214Bi 228Ac 228Ac 40K (295.21keV) (351.92keV) (609.31keV) (1120.07keV) (911.07keV) (969.11 (1460.8 Bq/kg Bq/kg Bq/kg Bq/kg Bq/kg keV) keV) Bq/kg Bq/kg 1.Bhola Sadar BS10 BS11 BS12 2.Borhanuddin BB07 BB08 BB09 3.Doulotkhan BD13

BD14 BD15 4.Tojumuddin BT16 BT17 BT18 5.Lalmohon BL04

BL05 22.3967 ± 0.002476 29.86837 ± 0.003013 ± 29.86837 0.004953 ± 33.27494 0.004347 ± 34.40806 0.003506 ± 58.60002 0.002774 ± 75.08077 0.006676 ± 775.0719 BL06 6.Charfashion BC01 BC02 BC03 7.Monpura BM19 BM20 BM21

3. RADIATION HAZARD INDICES CALCULATION

The distribution of 226Ra, 232Th and 40K is not uniform. Uniformity with respect to exposure to radiation has been defined in terms of radium equivalent activity (Raeq) in Bq/kg to compare the specific activity of materials containing different amounts of 226Ra, 232Th and 40K. It is calculated using the following relation (UNSCEAR, 2000):

Raeq = CRa + 1.43CTh +0.07CK (2)

226 232 40 where CRa, CTh and CK are the activity concentrations of Ra, Th and K in Bq/kg, respectively. While defining Raeq activity according to Eq. (2), it has been assumed that 370 Bq/kg of 226Ra or 259 Bq/ kg of 232Th or 4810 Bq/kg of 40K produce the same gamma dose rate.

60 Md. Arafat Hossain, et al., J. Pure Appl. & Ind. Phys. Vol.6 (4), 57-64 (2016) The external gamma absorbed dose rate in the air at lm above ground level was calculated from the measured activities of 226Ra, 232Th and 40K in soil assuming that the other radionuclides, such as 137Cs, 90Sr and the 235U series can be neglected as they contribute very little to the total dose from environmental background. The calculations were performed according to the following equation (UNSCEAR, 2000):

D = 0.462CRa + 0.604CTh + 0.042CK (3) where D is the dose rate in nGy/h and CRa, CTh and CK are the specific activities (Bq/kg) of 226Ra, 232Th and 40K, respectively. The external hazard index, Hex, is defined as (UNSCEAR, 2000):

Hex = CRa/370 + CTh/259 + CK / 4810 (4) 226 232 40 where CRa, CTh and CK are the specific activities (Bq/kg) of Ra, Th and K, respectively. The value of this index must be less than unity in order to keep the radiation hazard insignificant. To estimate annual effective dose rates, the conversion coefficient from absorbed dose in air to effective dose (0.7SvGy−1) and an outdoor occupancy factor (0.2) proposed by UNSCEAR, 2000 are used. Therefore, the annual effective dose rate (mSvy−1) was calculated by the formula:

Deff(Sv) = D(nGy/h) × (24 × 365)(h) × 0.7 × 0.2 (5)

Table 3: Specific activities of radionuclides (226Ra, 40K, 232Th) in soil samples at different locations in Bhola District.

Location Sample code Radioactivity of 226Ra Radioactivity of 232Th Radioactivity of 40K (Bq/Kg) (Bq/Kg) (Bq/Kg) 1.Bhola Sadar BS10 28.50809 71.27736 852.874 BS11 31.02974 62.63376 859.9272 BS12 20.99517 47.14026 710.7567 2.Borhanuddin BB07 21.56256 54.82963 762.3734 BB08 37.48429 61.90442 714.8643 BB09 26.98772 61.50725 828.7731 3.Doulotkhan BD13 33.4064 75.20153 862.0375 BD14 30.97862 50.32272 674.9434 BD15 69.27992 72.35898 768.3552 4.Tojumuddin BT16 93.81951 62.65477 116.167 BT17 87.74462 56.61306 844.0236 BT18 23.81067 48.01489 633.7713 5.Lalmohon BL04 23.49986 66.9511 851.2551 BL05 16.02263 46.14574 757.3391 BL06 16.37663 67.9966 709.668 6.Charfashion BC01 13.19229 51.09571 844.0298 BC02 12.82836 52.27484 792.0667 BC03 11.46364 44.61048 759.4041 7.Monpura BM19 38.66298 55.9684 1073.662 BM20 41.18964 69.74073 980.1315 BM21 43.72588 51.35824 880.0867 Average 33.56072 58.39482 758.7522

61 Md. Arafat Hossain, et al., J. Pure Appl. & Ind. Phys. Vol.6 (4), 57-64 (2016)

Table 4: Radium equivalent activity, gamma absorbed dose rate, annual effective dose and external hazard index for soil samples at different locations in Bhola.

Location Sample code Radium Equivalent Dose Rate D External Hazard Annual Effective -6 Activity Raeq (Bq/kg) (nGy/h) Index Hex Dose Deff (10 Sv) 1.Bhola Sadar BS10 190.1359 92.04297 0.529564 649.457 BS11 180.7909 88.28347 0.504472 618.6849 BS12 138.1587 68.02427 0.386519 474.0268 2.Borhanuddin BB07 153.3351 75.09868 0.428472 525.4783 BB08 176.0481 84.73231 0.488943 599.6391 BB09 172.9572 84.42718 0.482722 592.0098 3.Doulotkhan BD13 201.2872 97.06106 0.559859 686.6108 BD14 150.1861 73.05467 0.418343 513.056 BD15 226.5381 107.9831 0.626363 768.171 4.Tojumuddin BT16 191.5475 86.06711 0.519628 637.2714 BT17 227.7829 110.1813 0.631204 774.108 BT18 136.836 66.61992 0.3815 467.8716 5.Lalmohon BL04 178.8278 87.04811 0.498988 611.9585 BL05 135.0248 67.08272 0.378924 464.7127 BL06 163.2885 78.44201 0.454336 557.1982 6.Charfashion BC01 145.3412 72.4059 0.40841 500.8735 BC02 143.0261 70.76751 0.401175 492.0016 BC03 128.4149 64.1359 0.361104 442.8583 7.Monpura BM19 193.8541 96.76101 0.543803 666.9204 BM20 170.178 82.64311 0.473912 581.2057 BM21 190.1359 92.04297 0.529564 649.457 Average 171.1283 83.09073 0.476562 584.4557

Figure 2: Radium equivalent activity, dose rate, annual effective dose and external hazard index at different locations in Bhola.

62 Md. Arafat Hossain, et al., J. Pure Appl. & Ind. Phys. Vol.6 (4), 57-64 (2016) 4. RESULTS

It was found that, the soil specific activity ranges from 11.46 – 93.82 Bq/kg for Radium-226 (226Ra), 44.61 – 75.20 Bq/kg for Thorium-232(232Th) and 116.17 – 1073.62 Bq/kg for Potassium-40 (40K), with mean values of 33.56 Bq/kg, 58.40 Bq/kg and 758.75 Bq/kg respectively (Table 3). We did not get artificial radionuclide (137Cs) in any kind of samples of Bhola district. Radium equivalent activity(Raeq), gamma absorbed dose rate, The external hazard index(Hex), annual effective dose rate for different soil samples were 171.1283 Bq/kg, 83.09073 nGy/h, 0.476562, 584.4557 µSv respectively (Table 4).

5. DISCUSSION

Bhola district is one of the border . Radionuclides in 21 soil samples have been studied and evaluated due to unavailable Information about radioactivity in Bhola. For soil samples radium equivalent activity (Raeq), gamma absorbed dose rate, the external hazard index (Hex), annual effective dose rate were 171.1283 Bq/kg, 83.09073 nGy/h, 0.476562, 584.4557 µSv respectively. The average value of gamma dose rate obtained in this study is less than to the world average 57 nGy/h. All values obtained for radium equivalent activity are less than 370 Bq/kg, which are acceptable for safe use OECD 1979. The calculated results for annual effective dose of soil samples were less than the average world recommended value of 1.0 mSv. The calculated values of Hex for the soil samples is less than unity, and therefore, according to the Radiation Protection 112 (European Commission, 1999) report, soil from these regions is safe. We did not get artificial radionuclide (137Cs) in any kind of samples of Bhola district. All values of activity in the soil samples were lower than the permissible limit. So people of Bhola district were safe to use soil in agriculture and construction. This radioactivity monitoring study is significantly devoted to measure the effective dose to the environment where people live in. This type of study may be continued to establish a complete database of environmental radioactivity dissymmetry. This study may lead the researchers to improve necessary safety measures.

6. CONCLUSION: The average dose rates and other calculated hazard in- dices were less than the average world recommended values. So, the soil was suitable for normal use.

ACKNOWLEDGMENTS

The study was supported by the Atomic energy center, Dhaka, Bangladesh. Thanks to Prof. Dr. Nasima Ferdous and Dr. Md. Mustafizur Rahman for their helpful discussion and advice.

REFERENCES

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