Radioactivity has always existed in the environment.The radioactive sources in the environment can be divided into two main categories: Natural radioactivity incluce radioactive isotopes from Earths surface or the primordial radioactive isotopes (the radioactive isotopes of decay chains of 40K,238U,232Th ) and cosmogenic radioisotopes which produced as a result of the interaction os cosmic rays with the Earths material; artificial radioactive isotopes (137Cs) which produced by manmade such as medical and industrial uses of radioisotopes,nuclear testing weapon,nuclear accidents,the operation of nuclear power plants and mining....
VIETNAM NATIONAL UNIVERSITY, HANOI VNU UNIVERSITY OF SCIENCE FACULTY OF PHYSICS Nguyen Thi Diem Determination of the activity concentration of plant samples by gamma-ray spectrometrometry Submitted in partial fulfillment of the requirements for the degree of Bachelor of Science in Nuclear Technology (Advanced program) Supervisors: Bui Văn Loat Assoc.Prof Vu Thi Kim Duyen,MSc Ha Noi - 2017 ACKNOWLEDGEMENT I would like to express my gratitude to my supervisor, Assoc.Prof Bui Van Loat and Master Vu Thi Kim Duyen for their trust in me which encouraged me to know the strength in myself and motivated me to work harder and achieve this success My sincere thanks are also extended to Center for Technology Environment Treatment where has helps me to finish the practical part of my research Besides, I would like to thank all teachers, lecturers, researchers and other seniors in Faculty of Physics, particularly Department of Nuclear Technology, VNU University of Science, who always create good conditions for students to study and research I would like to give special thanks to my family and all my friends who have supported and promoted me in studying and researching They have become my faith and motivation throughout a hard time Student, Nguyen Thi Diem List of Figure Fig.1.1 Schematic of the exponential decay of activity for 210Pb Fig.1.2 Radioactive decay chains of 232Th Fig.1.3 Radioactive decay chains of 238U .7 Fig.1.4 Radioactive decay chains of 235U .7 Fig.1.5 The pathway of radionuclides to man 10 Fig.2.1 The diagram of gamma -ray spectrometry system 13 Fig 3.1 Graph of the energy-channel dependence 18 Fig 3.2 The TN1 spectroscopy was measured in counting time t=197058s 19 Fig 3.3 Establishment of efficiency calibration curve 21 Fig.3.4 Comparison of 226Ra among plant samples in the present work 26 Fig.3.5 Comparison of 232Th among plant samples in the present work 27 Fig.3.6 Comparison of 40K among plant samples in the present work 28 List of Table Table 1.1 Some common cosmogenic nuclides Table 1.2 Some Man-made radionuclides Table 2.1 Sampling stations 12 Table 3.1 The energy-channel dependence .18 Table 3.4 The efficiency at full-absorption peak of gamma radiation 20 Table 3.2 Minimum Detectable Activity of gamma-ray system 21 Table 3.3 The activity value of radioactive isotopes 22 Table 3.4 Activity concentration of analytical samples 23 Table 3.5 Average activity concentration of 226Ra, 232Th, 40K 25 Table 3.6 Compare of activity concentration of 226Ra, 232Th, 40K (in Bq/kg) in some vegetable 26 Contents CHAPTER LITERATURE REVIEWS 1.1 Phenomenon and the radioactive decay law .3 1.1.1 The radioactive decay law .3 1.1.2 The radioactive decay chains 1.2 Radioactive in nature .5 1.2.1 Primordial Radioisotopes 1.2.2 Cosmogenic radioisotopes .8 1.3 Artificial radioisotopes .8 1.4 Transfer of the radioactive isotopes from soil into plant 1.5 Characteristic of radioactive concentration in plant samples 11 1.5.1 The original of radionuclides in plant samples 11 CHAPTER 12 MATERIALS AND EXPERIMENTAL METHODS 12 2.1 Collecting samples 12 2.1.1 Sampling stations 12 2.1.2 Preparation of samples 12 2.2 Equipment .13 2.3 Analytical Methods 14 2.3.1 Gamma spectrum analysis 14 CHAPTER 18 RESULTS AND DISCUSSION .18 3.1 Establishment of energy calibration and efficiency calibration curve 18 3.1.1 Establishment of energy calibration .18 3.1.2 Establishment of efficiency calibration curve .19 3.2 Results of the activity concentration in plant samples 22 3.2.1 Calculation of Radionuclides .22 3.1.2 Results and Discussion 26 Conclusion .30 REFERENCES 31 APPENDICES 33 Determination of the activity concentration of plant samples by gamma-ray spectrometry Student: Nguyen Thi Diem Student ID:13000151 Course: QH.2013.T.CQ Faculty: Physics Supervisors: Bui Van Loat Vu Thi Kim Duyen Abstract This study is aimed at the determination of contamination of natural radionuclides such as 226Ra, 232Th, 40K in plants This present work determined of activity concentration of radionuclides in plant samples (rice, bean, corn, potato), which was collected at Ha Noi, Hai Duong-Viet Nam, and Laos The samples were dried, sealed and kept in a cylindrical container and stored for a period of 30 days They were counted and quantified using high purity germanium (HPGe) detector to analyze spectrometer at respective progeny energy then calculated activity concentation of plant samples in analytical areas Radionuclides in analytical samples observed include 226 Ra, 232 Th, 40 K The activity concentration of these radionuclides was found in the following ranges: 0.21 to 2.47; 0.19 to 1.98; 27.66 to 382.87 (Bq/kg) respectively The data is discussed and compared with those given in another study such as USA, Iran, Southern Serbia 40 K, Keywords: Natural radionuclides, activity concentration, HPGe detector, Ra, 232Th 226 Introduction Radioactivity has always existed in the environment The radioactive sources in the environment can be divided into two main categories: Natural radioactivity include radioactive isotopes from Earth’s surface or the primordial radioactive isotopes ( the radioactive isotopes of decay chains of 40K, 238U, 232Th) and cosmogenic radioisotopes which produced as a result of the interaction of cosmic rays with the Earth’s material; artificial radioactive isotopes (137Cs) which produced by man-made such as medical and industrial uses of radioisotopes, nuclear testing weapon, nuclear accidents, the operation of nuclear power plants and mining… The radioisotopes in upper layers of the atmosphere have polluted the Earth The process depends on the meteor, the climate, the geochemist Besides, the other man-made also makes the change of distributing of radioisotopes as by- produced from nuclear fuel cycle and other from mining, fuel enrichment, fuel airborne particles may be intercepted by plants or return to the top soil These radioisotopes can be transferred to human through the food chain, so it caused danger to their health There are two ways to absorb radioactive into the plant,which is: deposition on leaves and fruit and deposition onto soil and uptake by plants through the roots Evaluation of the process radioisotopes moves from soil to plants is very importance Internal exposure and external exposure in the human body may grow up the probability of induced cancer and various radiation-induced problems in the body of human and may be detrimental to the whole population In particular, this study can estimate of radioisotopes in Ha Noi’s surface and compare it with near areas, such as Hai Duong province and Laos The content of the thesis includes three chapters: Chapter 1: Literature Reviews Chapter 2: Material and Methods Chapter 3: Results and Discussion CHAPTER LITERATURE REVIEWS 1.1 Phenomenon and the radioactive decay law 1.1.1 The radioactive decay law The radioactive atoms in a radioactive substance decay according to a random process The probability of a nucleus decaying in a time is independent of time It was noted three years after the discovery of radioactive that decay rate of a pure radioactive substance decreases in time according to an exponential law which is called the Radioactive decay law [6] In fact, the radioactive decay law transfers the nucleus unstable into another nucleus by emitting alpha, beta, gamma ray If no new nuclide are introduced into a given radioactive substance, this law predicts how the number of radioactive nuclide which are present at time t decreases with time The number dN, decaying in a time interval dt is proportional to N, and so: -dN Ndt (1.1) where λ is the decay constant which equals the probability per unit time for decay of an atom From equation (1.1), so: N (t ) Ne-t (1.2) where N, represents the original number of nuclide present at t=0 The half-life is the time requires for one-half of the original nuclide to decay, denoted by the symbol T1/2 Putting N=No/2, it follows that: T1/2 ln 0.693 ln (1.3) where the mean lifetime is the average time that a nucleus is likely to survive before it decays and equals 1/λ, the reciprocal of the decay constant The activity, A is the rate at which decays occur in a sample and can be obtained by differentiating equation (1.2) From (1.2) we have (1.4) equation: A(t) = λN(t) = Ao e-λt where Ao N0 is the initial activity at t=0, A is the activity at time t [6] (1.4) Fig.1.2 Schematic of the exponential decay of activity for 210Pb [6] 1.1.2 The radioactive decay chains N1(t) is the number of nuclide of the original radioactivity (the mother) and λ1 is its decay constant N2(t) is the number of nuclide of the radioactive product (the daughter) and λ2 is its decay constant The radioactive decay chain was described by two equation: dN1 (t) = -λ1N1 (t)dt (1.6) dN2 (t) = λ1N1 (t) - λ2 N2 (t)dt (1.7) From two equation, we use differentiating equation to get: (1.8) dN1 (t ) 1 N1 (t ) dt dN (t ) 2 N (t ) 1 N1 (t ) dt (1.9) The number of nuclide was called at t=0: N1(0)=N10 and N2(0)=N20 It follows that: N1 (t ) N10et N (t ) (1.10) N101 1t 2t (e e ) N 20e 2t 2 1 (1.11) By integrating equation (1.10) and (1.11) and using the initial condition N2(0)=0 the following results are obtained [1]: To check the accuracy of the efficiency calibration curve, I analyzed samples TN2 which were known the activity The results were determined by table 3.3 Table 3.3 The activity value of radioactive isotopes Element Reference (Bq) Research (Bq) 23.46 0.65 22.12 1.41 661.65 7.63 0.29 6.66 0.22 1460.82 37.66 1.12 34.26 1.21 Energy (keV) 338.19 232 Th 911.20 968.97 137 Cs 40 K From Table 3.3, The activity value of Reference is similar to the activity value of Research Therefore, Efficiency calibration curve is reasonable 3.2 Results of the activity concentration in plant samples 3.2.1 Calculation of Radionuclides We measured gamma spectrometry of analytical samples for a sufficiently large time to error area of analytical peaks less 15% The activity concentration was calculated based on gamma radiation line corresponding to the energy of it Plant samples were taken at random, weighed, sealed, and kept in a cylindrical plastic container The prepared samples were stored for a period of 30 days [12] The net count calculated from the background subtracted area prominent gamma energies in Table 3.1 corresponding to the counting time 99946s From the efficiency calibration curve (Fig 3.4), We determined the efficiency corresponding to energies and then determined the activity concentration 22 Table 3.4 Activity concentration of analytical samples Energy (keV) M1 M2 M4 M5 Count Rate (cps) 𝜀 238.63 0.0013 0.019 43.60 1.421 0.041 295.22 0.0006 0.017 18.41 1.611 0.052 338.32 0.0002 0.015 11.27 0.891 0.03 351.93 0.0012 0.014 35.60 2.03 0.06 583.19 0.0009 0.008 30.04 0.65 0.01 609.31 0.0012 0.008 45.49 2.59 0.08 1460.82 0.0003 0.004 10.66 66.89 2.16 238.63 0.0011 0.019 43.60 0.97 0.03 295.22 0.0012 0.017 18.41 3.14 0.09 351.93 0.0012 0.014 35.60 1.69 0.05 609.31 0.0005 0.008 45.49 1.21 0.04 1460.82 0.002 0.004 10.66 44.37 1.43 238.63 0.0007 0.019 43.60 0.67 0.02 295.22 0.0008 0.017 18.41 2.09 0.06 351.93 0.0008 0014 35.60 1.233 0.004 609.31 0.0005 0.008 45.49 0.99 0.03 1460.82 0.0061 0.004 10.66 125.55 4.04 238.63 0.0017 0.019 43.60 1.98 0.06 295.22 0.0006 0.017 18.41 2.11 0.06 351.93 0.0017 0.014 35.60 3.03 0.09 609.31 0.0009 0.008 45.49 2.55 0.07 1460.82 0.0151 0.004 10.66 382.82 1.75 23 I (%) H (Bq/kg) K2 K1 G3 G2 238.63 0.0004 0.019 43.60 0.086 0.003 295.22 0.0004 0.017 18.41 0.231 0,007 338.32 0.0004 0.015 11.27 0.192 0.007 351.93 0.0001 0.014 35.60 0.179 0.005 609.31 0.0006 0.008 45.49 0.273 0.008 1460.82 0.0392 0.004 10.66 145.06 4.68 238.63 0.0003 0.019 43.60 0.08 0.0021 295.22 0.0006 0.017 18.41 338.32 0.0002 0.015 11.27 351.93 0.0007 0.014 35.60 609.31 0.0005 0.008 45.49 0.279 0.008 1460.82 0.027 0.0034 10.66 151.13 4.87 238.63 6.9 10-4 0.019 43.60 0.73 0.02 295.22 3.5 10-4 0.017 18.41 1.02 0.03 338.32 4.1 10-4 0.015 11.27 2.14 0.32 351.93 5.8 10-4 0.014 35.60 0.95 0.03 583.19 5.7 10-4 0.008 30.04 1.94 0.06 609.31 8.8 10-4 0.008 45.49 2.08 0.06 1460.82 2.7 10-3 0.004 10.66 60.36 1.95 238.63 0.00063 0.019 43.60 0.671 0.021 295.22 0.00082 0.017 18.41 2.63 0.08 338.32 0.00017 0.015 11.27