WELCOME 1

A Study of Determination of the Natural Radionuclides in Soil Samples Collected from Different Locations of Barendra Region of Rajshahi and Mining Region of Dinajpur TITLE OF THESIS 2

AIM & MOTIVATION Finally all results were compared with each other and also with other results in different locations worldwide including Bangladesh.  To determine the activity concentrations of Naturally occurring radionuclides 238 U, 232 Th and 40 K and their progeny present in soil samples collected from two regions (Barendra region, Rajshahi and Mining region, Dinajpur) in Banladesh.  Two regions have geological significance.  There was no such study of these two regions in the past.  The aim of this thesis was also the determination of the radiological hazard parameters such as Radium Equivalent Activity (Ra eq ), Gamma Dose Rate (D), External Hazard Index (H ex ) and Annual Effective Dose Equivalent (D eff ) for individuals living in both regions. 3

EXPERIMENTAL FACILITIES  There are many principles, methods and techniques used to determine the amount of radioactivity in the environment.  One of the widely used techniques is gamma-ray spectrometry which is common to all low-level radioanalysis.  We planned to carry out the measurements using high resolution γ-ray spectroscopy with an HPGe detector (ORTEC) in a low background configuration in Health Physics Division, Atomic Energy Centre (AEC), Dhaka.  It is a semiconductor detector.  Germanium detectors of any type cannot operate at room-temperature and it is kept at 77K by liquid nitrogen cryostat during operation. 4

EXPERIMENTAL FACILITIES Fig.3: A typical germanium detector cooled by a reservoir of liquid nitrogen. 5 Detector in cap

Fig.4: Photograph of laboratory setup for radioactivity measurement. Fig.5: (a) Door closed tightly against shield body (b) Liquid nitrogen cryostat (c) Detector located near centre of shield volume (d) Cylindrical lead material and (e) an inner layer of copper.  The detector was enclosed with a cylindrical lead shield to reduce the background radiation from various natural radiation sources. EXPERIMENTAL FACILITIES 6

 The detector was connected to a Preamplifier, Shaping Amplifier, High Voltage Power Supply, Multichannel Analyzer (MCA), PC, PC Monitor and Printer.  Data acquisition, display and analysis of gamma-ray spectra were performed using a commercial software. Fig.6: Showing shaping amplifier and high voltage power supply and data readout device. EXPERIMENTAL FACILITIES 7

BLOCK DIAGRAM OF THE DETECTOR Detector High Purity Germanium (HPGe) Crystal Diameter 5.14cm Length 4.13 cm Volume cm 3 Detector-window distance 0.3 cm Face dead-layer thickness 0.07 cm Liquid nitrogen Dewar volume 30 liter, ORTEC Preamplifier Resistive feedback REP11 Operating Operating bias volts DC Polarity Positive Shaping time 6 µsec. Leakage current <50 pA Test point volts at operating bias Cool down time 6hours Resolution FWHM for 60 Co 2.3 keV Relative efficiency 19.6% Fig.7: Block diagram of HPGe detector system. Table 1: ORTEC detector specifications. 8

EXPERIMENTAL PROCEDURE Sample collection :  Soil samples were collected from 22 locations of Barendra region and Mining region, separately. The geographical representations of the locations are shown in Fig.8 and Fig.9.  All samples were carefully collected at 5cm-10cm depth from the soil-surface by using shovel and each of the samples weighed approximately 1kg. Fig.9: Map of the Mining Region samples (Dinajpur district). Fig.8: Map of Barendra Region samples (Godagari, Rajshahi). 9

Fig.10: Sample collected in polyethylene bags and a soil sample label.  The samples were packed in dried cleaned polyethylene bags shown in Fig.10. The bags were then labeled with sample codes and sealed.  Finally the samples were transferred to the radiation detection laboratories of the Health Physics division, AEC, Dhaka. EXPERIMENTAL PROCEDURE 10

EXPERIMENTAL PROCEDURE Sample preparation:  The collected samples were transferred from the polyethylene bags to the stainless steel bucket and a crowbar was used to break the big soil stone separately.  Then the samples were dried at 105°C-110°C until a constant weight was achieved.  Each of the dried samples was ground to fine powder in an agate motor separately.  The powdered samples were then sieved using a fine aperture mesh screen (mesh size 2µm; Fig.11) in order to remove extraneous items like plant material, roots, pebbles etc.  Each of the samples was transferred to cylindrical plastic- container (Fig.12). The containers were approximately of equal size and shape.  The samples were stored for at least four weeks before counting in order to attain Secular Equilibrium. Fig.12: Cylindrical plastic soil sample container. Fig.11: A standard sieve of 2μm mesh size. 11

EXPERIMENTAL PROCEDURE Detector Characterization:  Detector Resolution: Resolution is defined by- Where, E 1 -E 2 is the energy difference between the peaks, C 1 -C 2 is the channel difference of the two photo-peaks. ∆C is the number of the channel under FWHM in the peak. The resolution of the HPGe detector was found to be 2.80 keV at FWHM of the 1332 keV peak of 60 Co. Fig.13: The energy resolution of the HPGe detector measured from the 1332keV photo- peak of 60 Co. Counts Channel numbers 12

EXPERIMENTAL PROCEDURE  Energy Calibration : The gamma reference sources 137 Cs (monoenergetic gamma source), 60 Co and 40 K were chosen for energy calibration due to a wide range of gamma-ray energies emitted over the entire energy range of interest. The linear relationship between the gamma-ray energies and channel numbers is evidenced in Fig.14 and can be parameterized by the following equation: Known Gamma Sources Gamma ray energy (keV) Channel No. of the centrids full energy peaks Cs Co K Table 2: Energy Calibration of the HPGe Detector Fig.14: Energy Calibration curve of the detector. 13

 Detector Efficiency: Absolute detector efficiency at energy is Where, P γ is the absolute intensity of the transition of energy E or the fraction of transitions taking place. In the present study, 10 transitions or gamma ray lines of the radionuclide 152 Eu were used to perform the efficiency calibration. The values of the efficiency are given in Table 3. EXPERIMENTAL PROCEDURE Line no Energy (keV) Efficiency (%) Table 3: Values of efficiency for different energies of transitions in 152 Eu radionuclide. Fig.15: Efficiency curve of the detector using 10 transitions in 152 Eu radionuclide. 14

Measurements and Data Analysis :  A background measurement was counted for 5000 sec. with no radiation source present around the high-purity germanium detector.  Then, all prepared samples were measured for 5000 sec.  The resultant spectrum of each sample was acquired, one each of the two sets are displayed in Fig.16 and 17.  Actually, for both cases, Net count is equal to the Gross count minus Background count (Fig.), which is carried out by software itself.  No 137 Cs line was obtained at keV in both regions. EXPERIMENTAL PROCEDURE Fig.: Actual Net count 15

EXPERIMENTAL PROCEDURE Fig.16: Spectrum of the gamma-rays from one soil sample of Barendra region. 16

EXPERIMENTAL PROCEDURE Fig.17: Spectrum of the gamma-rays from one soil sample of Mining region. 17

EXPERIMENTAL PROCEDURE  The activity concentration of individual radionuclides in soil samples were measured by using following equation: where, N = Net counts per second (c.p.s) P γ = Transition probability of gamma ray ε = Efficiency in percent W = Weight of the sample in gm  Error in every measurements of activity concentration of individual radionuclides in soil samples were measured by using following equation: where, σ = standard deviation A s = Sample count rate in c.p.s. A b = Background count rate in c.p.s. T s = Sample count time T b = background count time 18

EXPERIMENTAL PROCEDURE  Radiological Hazard Parameters such as Radium Equivalent Activity (Ra eq ), Gamma Dose Rate (D), External Hazard Index (H ex ) and Annual Effective Dose Equivalent (D eff ) are calculated by using following equations, respectively, Ra eq (Bq.kg -1 ) = C Ra C Th C K D (nGy.h -1 ) = 0.462C Ra C Th C K H ex = (C Ra /370) + (C Th /259) + (C K /4810) D eff (µSv.y -1 )=D (nGy.h -1 )×8760 h×0.2×0.7Sv.Gy -1 ×10 -3 Where, C Ra, C Th and C K are the activity concentrations of 226 Ra, 232 Th and 40 K in Bq.kg -1 19

RESULTS AND DISCUSSION  The activity concentrations of 238 U and 232 Th for both regions are calculated from the average activity concentration of daughter nuclides [ 214 Pb (295.2 keV), 214 Pb (351.9 keV), 214 Bi (609.3 keV), 214 Bi ( keV)] and [ 212 Pb (238.6 keV), 208 Tl (583.1 keV), 228 Ac (911.2 keV), 228 Ac (968.9 keV)], respectively.  The activity concentrations of 40 K are determined directly by measurement of the gamma-ray transitions at keV.  The activity concentrations of 238 U, 232 Th and 40 K for different soil samples of Barendra and Mining regions are presented in Table 4. These values are displayed in Fig

RESULTS AND DISCUSSION Location Sample codes Activity concentration in Bq.kg U 232 Th 40 K Barendra Region, Godagari, Rajshahi RGMM42.7± ± ±2.3 RGSM31.9± ± ±2.3 RGCB35.6± ± ±2.3 RGDG33.4± ± ±2.4 RGKH37.5± ± ±2.4 RGAT38.3± ± ±2.4 RGBP35.4± ± ±2.4 RGJB34.9± ± ±2.4 RGBM40.2± ± ±2.3 RGKP37.0± ± ±2.4 RGMD37.3± ± ±2.4 Mean36.7± ± ±2.4 For Barendra region soil samples, it is found that –  Activity concentration of 238 U ranges from 31.9±1.3 to 42.7±1.4 Bq/kg with mean 36.7±1.4 Bq/kg.  Activity concentration of 232 Th ranges from 52.9±1.6 to 68.9±1.7 Bq/kg with mean 59.7±1.7 Bq/kg.  Activity concentration of 40 K ranges from 232.5±2.3 to 320.6±2.4 Bq/kg with mean 282.5±2.3 Bq/kg. Table 4(a): Activity concentrations of radionuclides 238 U, 232 Th and 40 K for Barendra region. 21

Location Sample codes Activity concentration in Bq.kg U 232 Th 40 K Mining region, Dinajpur DFSA37.3± ± ±2.3 DFTP42.4± ± ±2.5 DFCP38.6± ± ±2.4 DPCM48.3± ± ±2.3 DPSM31.3± ± ±2.3 DPVP33.8± ± ±2.4 DHHL29.5± ± ±2.4 DBSA36.5± ± ±2.5 DBJN32.5± ± ±2.5 DNSP34.9± ± ±2.4 DNSA43.0± ± ±2.4 Mean37.1± ± ±2.4 RESULTS AND DISCUSSION For Mining region soil samples, it is found that –  Activity concentration of 238 U ranges from 31.3±1.3 to 48.3±1.5 Bq/kg with mean 37.1±1.4 Bq/kg.  Activity concentration of 232 Th ranges from 44.5±1.5 to 81.9±1.9 Bq/kg with mean 56.9±1.7 Bq/kg.  Activity concentration of 40 K ranges from 222.0±2.3 to 475.7±2.5 Bq/kg with mean 343.7±2.4 Bq/kg. Table 4(a): Activity concentrations of radionuclides 238 U, 232 Th and 40 K for Mining region. 22

RESULTS AND DISCUSSION  The mean values of 238 U and 232 Th concentrations are similar for both the regions. The mean of 40 K concentration in Mining region is higher than that in Barendra region. Fig.18: Comparison of the concentration of 238 U, 232 Th and 40 K for different soil samples for both regions. 23

RESULTS AND DISCUSSION Locations Average activity concentration in Bq.kg U 232 Th 40 K Chittagong Pabna Dhaka Nine southern districts Jessore Sitakunda Kuakata Sea Beach Cox’s Bazar Sylhet Rangpur Lalmonirhat Kurigram Barendra region Mining region  The average activity concentrations in the soil samples of the two regions are presented along with those of other places in Bangladesh. The values are presented in Table 5 and graphically displayed in Figs.6.3a and 6.3b. Table 5: Average activity concentration of 238 U, 232 Th and 40 K in soil samples for different regions within Bangladesh. 24

RESULTS AND DISCUSSION Districts Concentration range in Bq.kg U 232 Th 40 K Jamalpur15 – 3912 – – 739 Kushtia24 – 5442 – Tangail & satkhira39 – 6743 – Jessore – – 674 Comilla6 – 4821 – – 470 Brahmanbaria7 – – 509 Munshiganj25 – 4935 – – 827 Narayanganj26 – 6725 – – 700 Ishwardi22 – 5631 – – 662 Rangpur3 – 4346 – – 663 Dinajpur17 – 3722 – – 544 Sylhet Barendra region32 – 4353 – – 321 Mining region31 – 4845 – – 476 Table 6: Concentration range of 238 U, 232 Th and 40 K in soil samples from different Districts of Bangladesh.  The ranges of activity concentrations in the soil samples of the two regions are presented along with those of other places in Bangladesh. The values are presented in Table 6. 25

RESULTS AND DISCUSSION  238 U and 232 Th concentrations in both regions are about 2.5 times less than those in the high radioactivity zones (Rangpur, Lalmonirhat, Kurigram). Fig.19a: Comparison of concentration of 238 U and 232 Th in soil samples for different regions within Bangladesh.  238 U content in the two regions is comparable with the values of other districts in Bangladesh except that in Sylhet where the value is about 50% higher.  232 Th content in the two regions is also comparable except that in Sylhet and Kuakata Sea Beach where the values are 110% and 50% higher, respectively. 26

RESULTS AND DISCUSSION  The 40 K activity concentration of the former is about 6 times less than that in the high radioactivity zones (Rangpur, Lalmonirhat and Kurigram). Fig.19b: Comparison of activity concentration of 40 K in soil samples for different regions within Bangladesh.  The concentrations of 40 K in these two regions are much lower than the values in all other districts. 27

RESULTS AND DISCUSSION Countries Average activity concentration in Bq.kg U 232 Th 40 K Egypt USA China Japan Malaysia India Iran Denmark Poland Greece Romania Spain Saudi Arabia Nigeria Turkey Pakistan West Bank-Palestine Worldwide average Barendra region Mining region  The average activity concentrations of 238 U, 232 Th and 40 K of the two regions are shown along with the values of other countries. The values of 238 U, 232 Th and 40 K are presented in Table 7 and graphically displayed in Fig.20a and 20b. Table 7: Comparison of radioactivity level of the soil samples of different countries with that of the present work. 28

 The 238 U concentrations in both regions are comparable with these of most of other countries of the world. In fact, they are roughly equal to the world average Fig.20a: Comparison of average activity concentration of 238 U and 232 Th for soil samples in different countries. RESULTS AND DISCUSSION  The 232 Th concentrations of the two regions, on the other hand, are higher than those of most other countries and are almost double the world average. 29

RESULTS AND DISCUSSION  The 40 K concentrations of the two regions are smaller than the values of most countries and about 25% lower than the world average. Fig.20b: Comparison of activity concentration of 40 K in soil samples in different countries. 30

RESULTS AND DISCUSSION The following Radiological hazard parameters are calculated from the measured activity concentrations of the radionuclides 238 U, 232 Th and 40 K in soil samples. (a) Radium Equivalent Activity (Ra eq ), (b) Absorbed Dose Rate in Air (D), (c) External Hazard Index (H ex ) and (d) Annual Effective Dose Equivalent (D eff ). The values of these parameters are presented in Table 8 & 9. 31

RESULTS AND DISCUSSION Locations Sample codes Radium Equivalent Activity, Ra eq (Bq/kg) Absorbed Dose Rate, D (nGy/h) External Hazard Index, H ex Annual Effective Dose, D eff (10 -6 Sv) Barendra Region, Godagari, Rajshahi RGMM RGSM RGCB RGDG RGKH RGAT RGBP RGJB RGBM RGKP RGMD Mean Table 8: Radium Equivalent Activity, Dose Rate, External Hazard Index and Annual Effective Dose Equivalent for samples in Barendra region. 32

RESULTS AND DISCUSSION Table 9: Radium Equivalent Activity, Dose Rate, External Hazard Index and Annual Effective Dose Equivalent for samples in Mining region. Locations Sample codes Radium Equivalent Activity, Ra eq (Bq/kg) Absorbed Dose Rate, D (nGy/h) External Hazard Index, H ex Annual Effective Dose, D eff (10 -6 Sv) Mining Region, Dinajpur DFSA DFTP DFCP DPCM DPSM DPVP DHHL DBSA DBJN DNSP DNSA Mean

RESULTS AND DISCUSSION Table 10: Values of Radium Equivalent Activity, Ra eq. Table 11: Values Absorbed Dose Rate, D. Fig.21: Radium Equivalent Activity (Ra eq ) of two regions along with safety limit. Fig.22: Absorbed Dose Rate (D) of two regions along with worldwide mean. Ra eq (Bq.kg -1) MinimumMaximumMean Barendra Region Mining Region Safety limit (by OECD) 370 D (nGy/h) MinimumMaximumMean Barendra Region Mining Region Worldwide mean57 34

RESULTS AND DISCUSSION Table 11: Values of External Hazard Index, H ex. Table 12: Values of the Annual Effective Dose Equivalent, D eff. Fig.23: External Hazard Index (H ex ) of two regions along with safety limit. Fig.24: Annual Effective Dose Equivalent (D eff ) of two regions along with worldwide mean. H ex MinimumMaximumMean Barendra Region Mining Region Safety limit (by ICRP) 1 D eff (µSv.y -1 ) MinimumMaximumMean Barendra region Mining Region Worldwide mean70 35

 The activity concentrations of 238 U and 232 Th in the samples of the two regions are found to be similar, the 40 K concentration of Mining region is slightly higher.  The average 238 U concentration in the samples of the present study is similar with the world average. On the other hand, the average 232 Th concentration is double of the world average. The average 40 K concentration is lower than the world average.  No 137 Cs is found in the samples of the present study. It seems that there is no fresh nuclear fallout in places under study.  Radiological hazard parameters of the two regions were estimated and compared with the world averages.  The natural radioactivity in the Barendra and Mining region poses no threat to general public there. CONCLUSION 36

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