Determination of Natural and Artificial Radionuclides in Soil Samples of Bhola District, Bangladesh
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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 Bhola District, Bangladesh 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 Barisal 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 Patuakhali District 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 upazilas: Bhola Sadar Upazila, Daulatkhan Upazila, Burhanuddin Upazila, Tazumuddin Upazila, Lalmohan 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.