Tóm tắt luận án tiếng anh NGHIÊN cứu và PHÁT TRIÊN PHƯƠNG PHÁP đo LIỀU bức xạ GAMMA và NƠTRON DÙNG LIỀU kế MÀNG MỎNG NHUỘM màu

Introduction The research subject Dose controlling field associated with sustainable developments of Nuclear Physics, Nuclear Technology, Radiation Technology and related fields in the national economy such as industry, agriculture, health This field which has diversified high development and application aims to exactly control the distribution of irradiated doses on the irradiated objects Radiation dosimetry is generally based on evaluation of absorption energy in which radiation is directly transmitted to matter by heat increasing, or evaluation of absorption energy in which absorbed energy is detected by secondary processes in materials such as ionization, structural change, chemical reaction, biology, discoloration of materials, etc Dyed PVA film dosimeters use organic materials which are the same tissues, so they are popularly made dosimeters in gamma dose measurements, particularly in the field of radiation process Thin film dosimeters may also be used to measure neutron doses and different radiations, but they are less noticeable because it is difficult for estimating the sensitivity in the study dose range due to exactly known-less dose response The thesis is expected to detect the dose response functions and sensitive of the thin film dosimeters used to measure gamma and neutron doses with the wide dose range with logical mathematic function and suitable dyes With the plan to build and operate a new research reactor to make radioactive isotopes and to serve the future nuclear power program, gamma and neutron dose fields shall be important to control the radiation doses, to ensure the safety for operating people and using radioactive materials, as well as related technologies That is the reasons why we DEVELOPMENT choose ON the subject GAMMA AND "RESEARCH AND NOTRON DOSE MEASUREMENT METHODS USE DYED FILM DOSIMETER" The aims of this thesis To manufacture dyed organic film dosimeter which can measure both gamma and neutron dose, and to determine the sensitivity, dose range and the dose response function The object and scope of the thesis Research and manufacture dyed organic film dosimeter for controlling gamma high dose in radiation processing and neutron dose at the channel No.2 of the Dalat nuclear research reactor Studying problems - Research, manufacture and application of dyed the films for measurement gamma and neutron dose; - To study the factors which affect the working quality of the dyed film dosimeters for measurement gamma and neutron doses, and to propose suitable dosimeters - Identification of dose response functions for the dyed films - Choose the dosimeters with the best particularities These experiments were carried out at Institute for Nuclear Science and Technology, Hanoi Irradiation Center, Nuclear Research Institute, Vietnam Atomic Energy Institute The structure of the thesis The thesis is divided into three chapters, including: Chapter I Overview of research; Chapter II Research methods and equipments; Chapter III Results and Discussion The scientific significance and the contributions of the thesis The thesis has successfully studied and manufactured the dyed PVA film dosimeter which can control gamma radiation dose in wide dose range with the optimal radiation sensitivity In addition, the thesis is the first study to investigate the properties of the PVA thin films when they are exposed on the thermal neutron source at channel of the Dalat nuclear research reactor From the research results, the thesis has published scientific papers The reality meaning of the thesis The thesis has contributed to the development of a new dosimeter which is capable of controlling both the gamma dose with a wide dose range and neutron doses in the research reactor Chapter I Overview of study 1.1 Overview of study situation 1.1.1 The study situation in the world The studies of the dyed PVA film dosimeter for the gamma dose control in the world are highly developed and widely applied such as the radiation processing, medical and also in reactors However, these studies were only surveyed effects of films when they were exposed by gamma irradiation with different dose ranges The specificity dose response curve for each study dose range has not been established correctly In addition, the study of neutron dose with the dyed PVA film is less well studied in the world 1.1.2 The study situation in Vietnam Chemical dosimeters and solid dosimeters are almost exclusively used in gamma dose control, or used to determine the environmental dose Research and manufacture of dosimeters in neutron dose control is also an open field 1.2 Methods of common dose measurement 1.2.1 Dosimeter classification With difference configurations and components as also working process, there are the primary dosimeter and the second dosimeter With the quality, precision level and usage, there are four types of dosimeters: Dosimeter system of first level Standard, Dosimeter system of secondary Standard, Dosimeter system of standard transfer, Routine dosimeter system 1.2.2 Some criterions for dosimeters selection with different dose ranges 1.2.2.1 Some criterions for dosimeters selection With the usage target, they are used to use some criterions for dosimeters selection such as relative dose measurement or absolute dose measurement, the accuracy or repeatability of the dose measurements, the total dose or dose rate, measurement while they were online or offline, dose ranges, type of radiation and radiation energy, spatial resolution, type of equipment for dose measurement, price of dosimeter, private density of dosimeter and mechanical quality 1.2.2.1 Dose range for dosimeters The subjects of radiation processing and radiation technology are used in the high dose ranges from several hundred gray to hundreds of kilogray 1.2.3 Unit of dose measurement and determination a) Absorbed dose: Gray (Gy) unit, which 1Gy = 1J / kg b) Absorption dose rate: Gy / s, which 1Gy / s = 1J / s.kg = 1W / kg c) Kerma and Kerma rate: The Kerma unit and the Kerma rate are the same as the unit of dose measure and rate d) Energy leakage line: The energy leakage line is the energy which is lost from the surface of a unit of volume considered and determined by the expression J /  , where J is the density vector of energy line and  is the absorpted material density e) Dose equilibrium equation: The dose equilibrium equation is written as follows: dE where dEk J dEb    dm dm  dm dEk dEb J , dm and dm  is the sum of the initial kinetic energy, the energy consumed by the braking process and the energy leakage line of the charged particles f) Radiation dose: The unit in the SI system is C / kg The unit commonly used is Roentgen R Radiation dose rate: The unit in the SI system is C / kg / s The unit commonly used is R / h or mR / h g) Equivalent dose: The equivalent absorbed dose or equivalent dose of H is the quantity to evaluate the degree of danger of the radiation, by caculation of the absorbed dose D and the the radiation weighting factor WR: H  D.WR h) Radiation chemical yield G and activated molecular probability: G values are measured by the number of chemical changes for 100 eV of the absorbed energy of ionizing radiation 1.2.4 Some dosimeters for high control 1.2.4.1 Calorimetry Calorimetry is a method of directly measuring the absorption energy of a substance with radiation The absorption dose D (Gy) is determined by the formula: D T C m where, T is the temperature rise with unit [K], C the heat capacity of the calorimeter with unit [JK-1], m is the mass of the calorimeter with unit [kg] 1.2.4.1 Dose measurement method based on ionization of gases According to the Bragg-Gray principle, the absorbed dose can be calculated by the formula: Dm  W.Sm P Where W is the ionic pair energy in the gas (J / ion), Sm is the ratio of lost energy for a unit of density of the surveyed material and air, P is the number of ion pairs generated in a unit of gas volume (pair / kg) 1.2.4.2 Chemical dosimeter Chemical dosimeters are secondary dosimeters in which absorbed dose is determined from a chemical change produced on irradiation: where, product yield unit is mol.kg-1, G is in units of active molecules per 100 eV Some typical chemical dosimeters: Gas-phase dosimeter, Liquid dosimeter, Fricke dosimeter, cerium sulfate dosimeter and solid-State dosimeter Summarization of Chapter I In this chapter, the thesis gives the overviews of the study situation and the method of measuring gamma and neutron radiation dose using dyed PVA film In addition, in this chapter we have listed some of the commonly dose measurement methods which are used in high-dose radiation control technology Chapter II Research methods and equipment 2.1 Interaction of radiation with PVA matter 2.1.1 Effects of cross-linking and degradation of polymer Effects of cross-linking and degradation are not reversible effects, significantly altering the structure and properties of polymers 2.1.2 Gas separation effect In the irradiation process with PVA by the gamma source, the gass products released are very strong In this process, the common gases are H2, CH4, CO2, CO 2.1.3 Radiation oxidation and after irradiated of polymer In many cases oxygen has a significant effect on the radiolysis of polymers and leads to their oxidation The radiation oxidation rate depends on the concentration of oxygen in the polymer, the effect of the dose rate, the temperature effect and the pressure effect 2.1.4 Destruction of the structure Structural destruction is divided into two such as group of point defects and group of size defect The first group of point defects consists of holes, atoms apart of nodes, atoms and centers of color The group of size defect consist variables, displacements, and empty spaces 2.1.5 Transformation of the physical properties of the irradiated polymer Irradiation on polymer materials often changes the physical properties of materials such as electrical charge, mechanics, memory effect, and heat shrinkage 2.1.6 Radiation protection and radiation sensitivity increase a) Radiation protection for polymer: Radiation resistance increases if polymer is added special material which called protective additive b) Sensitivity increase with radiation-chemical processes in the polymer: The polymer is added additives which impulse radiationchemical process and lead to desirable effects 2.2 The trasmitable process of radiation energy to matter 2.2.1 Linear energy transfer coefficient The L-LET energy transfer coefficient of the charged particle in the material is determined by the formula: L  dE dl , where dE is the average loss energy of the charged particle on the dl line 2.2.2 Energy transfer model The energy transfer model is a typical function of a dosimeter or study material in that it depends on the dose rate and role of the background n0 when it is irradiated It is determined by the following formulary: D D  k0  k0   n D   n s 1  e D '   n e D '   where, n (D) is quantity of activated elements, D is dose, D’ is dose rate that is proportional to the rate of energy transfer imparted to the material, the coefficients ns, k0 and n0 are defined as follow: ns  pC  n  pq , k0  p  q , n  n 0  where p and q were the probabilities that one sensitive element will be activated and reactivated per unit of time, respectively 2.2.3 Different formula of the energy transfer model + Different formulas of the energy transfer model incluse: Saturated exponential formula of quantum theory and theory of particle track structure, Formula of exponential function, Polynomial, Linear formula, Super-high dose effect + Dose rate effect: Dose rate effect may occur in some dosimeters Experiments show that in the same material, it can be caused different effects with different radiations and energies + Duality of dose-response curve and radiation incident analysis: Total dose Dsum is determined: Dsum  Di  D or D  Dsum  Di , where, Di is incident dose When D  the incident dose is small, D  Ds and D  the incident dose is large, D  DL 2.3 Analysis of the dosimeters results by spectrophotometer 2.3.1 Analysis of the dosimeters results by spectrophotometer When light goes through a substance, it will be occurred the phenomenon that matter molecules absorbed or radiated of energy and it is determined by the formula: where, E1 and E0 are the energy levels of the molecule in initial state and final state respectively,  is frequency of electromagnetic radiation which is absorbed or emitted, h is Planck constant and h=6.262x10-34 J.s,  is wavelength 2.3.2 Lambert-Beer law I0   C d  I where,  is absorbance coefficient, C unit is mol/l, d unit is cm and D log is optical density The equation is only true for monochromatic rays 2.5.3 Equipment construction The measuring system consists of the following parts: light source, monochromatic component, specimen holder, detector and spectral recorder Summarization of Chapter II The main contents presented in Chapter are: + The interaction process with radiation has caused a change in the structure of the polymer and leaded to chemical and physical changes in this material + The variation of the polymer when it interacted with radiation through the transpotation of radiation to matter is based on the theory of linear energy transfer coefficients and the energy transfer model + Overview of the method of reading the dose from the analysis of optical density on the spectrometer system Chapter III Results and Discussion 3.1 Study dose measurement of gamma radiation using dyed PVA film dosimeter 3.1.1 Gamma radiation source 60Co The 60Co radioactive source is made in the form of a power source and covered with a thin metal layer to remove emition radiation  from the 60 Co source The activity of the 60 Co source used in the radiation processing facilities at the study time was 173.30 kCi at a distance of 45 cm 3.1.2 Manufacturing the dyed PVA film dosimeter 3.1.2.1 Preparation of materials and chemiclas To Include: The PVA powder; four different colors such as Methylene blue, Methyl red, Methyl orange and Crystal violet; additives such as Sulfate cadmium, Lithium hydroxide monohydrate, Boric acid, Natri borat decahidrat and Lithium fluoride 3.1.2.2 Procedures of manufacture a) Preparation of dye For convenience in dye mixing with colloidal solutions, dyes are prepared in the form of 10-3M Methylene blue, 0.4 x 10-3M methyl red, 10-3M methyl oranges and 10- 3M crystal violet solutions b) Preparation of dyed films Prepare films with the following characteristics: The PVA films dyed with different colors; films with PVA powder masses in the solutions were 1.47%, 2.94%, 5.88% and 7.35%; films with different additives 3.1.3 Color change and absorption spectra of the dyed films with different colors From Figures 3.4 to 3.7, the amplitude of these absorption bands decreased gradually with the increase of dose of gamma rays Figure 3.4: The absorption spectra of unirradiated and irradiated MB-PVA films measured at wavelength range 500-750 nm for different doses Figure 3.5: The absorption spectra of unirradiated and irradiated MO-PVA films measured at wavelength range 300-600 nm for difference doses 10 Figure 3.6: The absorption spectra of unirradiated and irradiated MR-PVA films measured at wavelength range 400-600 nm for difference doses Figure 3.7: The absorption spectra of un-irradiated and irradiated CV-PVA films measured at wavelength range 540-650 nm for difference doses 3.1.4 Determination of dose-response curve of the dyed PVA film dosimeter Figure 3.8 and Table 3.2 depicted the fitted values for the dyed PVA films with different colors by the energy transfer model: Figure 3.8: Descriptive dose-response curve of the dyed PVA film with different colors at specific absorption wavelengths Table 3.2: The coefficient values are fitted by the energy transfer model Phim no ns no/ ns k R2 Methyl red 0.8140.011 0.2760.021 2.9500.227 0.0360.005 0.98664 Crystal violet 1.0520.014 0.2140.030 4.9160.689 0.0230.005 0.99426 Methyl orange 0.1590.007 0.0510.006 3.1180.404 0.0240.005 0.96574 Melthylene blue 1.3990.031 0.1900.020 7.3630.788 0.0300.002 0.99435 3.1.5 Evaluation of radiation sensitivity of indicator dyes To assess the color variability of the dyed PVA films which were irradiated by the gamma source, we determined the color sensitivity 11 of a dosimeter by the formula: s  n0 ns , where, n0 and ns are respectively number of the activated element at D=0 and D=∞ These results showed that The MB-PVA dyed films were the best dosimeters 3.1.6 Study the effect of PVA solution concentration on the dyed PVA films The changes in optical density values per unit thickness of the dyed PVA films are determined by the formula: A / d  ( A0  A) / d where, A0 and A were values of optical density for the un-irradiated and irradiated films by the gamma source at 668 nm wavelength, respectively; d was film thickness Uncertainty of the film density value is ± 2% The dyed PVA films were the best using when the changes in optical density values per unit thickness were the largest at 2.94% PVA (Table 3.2, Figure 3.9 and Figure 3.10) Table 3.2: The optical density values of un-irradiated and irradiated films with different PVA concentration Optical density values %PVA d [mm] un-irradiated irradiated 1.47 0.01 1.458 1.211 2.94 0.02 1.574 0.741 5.88 0.05 1.698 0.576 7.35 0.06 1.711 0.442 Figure 3.9: The changes in optical density values of the un-irradiation BMB/PVA films with %PVA differences at the 668 nm wavelength 12 Figure 3.10: The change A/d values of the BMB/PVA films with %PVA differences at the 668 nm wavelength 3.1.7 The effective investigation of additives on the optical density values of the unirradiation and irradiation dyed PVA films Evaluate the color uniformity and thickness of the films after they are made by casting The results show that the sampling method ensures with the color uniformity of the sample is high (Table 3.3) Table 3.3: The effective investigation of additives on the optical density values of the unirradiation and irradiation dyed PVA films No 10 TB Stdev % d(mm) BMB0 1.561 1.585 1.639 1.591 1.534 1.592 1.585 1.529 1.566 1.555 1.574 0.032 2% 0.02 BMB2 1.812 1.725 1.851 1.858 1.791 1.754 1.807 1.780 1.771 1.756 1.791 0.042 2% 0.02 Optical density values LMB1 LMB2 CMB 1.345 1.119 1.301 1.349 1.122 1.3 1.352 1.178 1.353 1.334 1.102 1.311 1.399 1.077 1.311 1.348 1.12 1.301 1.394 1.096 1.3 1.399 1.101 1.338 1.316 1.129 1.31 1.403 1.124 1.353 1.364 1.115 1.318 0.032 0.022 0.022 2% 2% 2% 0.02 0.02 0.02 NMB 2.026 2.083 2.141 2.009 2.144 2.061 2.141 2.063 2.025 2.062 2.076 0.051 2% 0.02 The results presented in Table 3.3 and Figure 3.11 shows that the NMB film has the highest optical density value and then the BMB2 film Thus, the addition of sodium borate decahidrate and boric acid to the dyed PVA film increased the color of the film without the additives (BMB0) clearly In contrast, the addition of sulfite cadmium and lithium hydroxide monohydrate reduced the film color compared to that before adding it 13 Figure 3.11: The average optical density values of the films before and after gamma irradiation at 668nm absorption peaks Figure 3.12 describes the change in optical density before and after gamma irradiation at the specific absorption wavelengths of the dyed PVA films with different additives Figure 3.12: The change in optical density of films at 668 nm after being exposed by gamma source at 25 kGy The results A in Figure 3.9 show that the dyed PVA film with additive has improved the radiation sensitivity of the film compared to the PVA film without additive Films containing the LiOH.H2O additive reduce the radiation sensitivity of the film The boric acid improves the best sensitivity of the film with other additive 3.1.8 Investigate the effect boric acid mass on quality of the dyed PVA films In this study, MB/PVA film with 2.94% PVA was exposed to gamma source at 25 kGy Figure 3.13 depicts the optical density values of MB/PVA films with different boric acid masses at 668 nm before gamma irradiation and the results show that when the mass of boric acid increased to 150 mg, the density values also increased The optical aspect of the previous 14 film also increased The optical density of the film decreases rapidly when the mass of boric acid added to the solution is greater than 150 mg Figure 3.13: Change of optical density on the dyed PVA films with the different boric acid mass before gamma irradiation at the 668nm wavelength Results from measurement and invesgation on the Figure 3.14 shows that the optical density change increases when boric acid mass increases to 100mg and decreases quickly when the boric acid mass is greater than 100mg Figure 3.14: the change A/d values of the dyed PVA films with boric acid differences at 668 nm wavelength 3.1.9 Evaluation uncertainty of the dyed PVA film for controlling gamma dose as regular measurement Uncertainty of the dyed PVA film is 2.40% with trust 68% or 4,8% with the trust 95% This uncertainty in allowed limit for the regular measurement at industrial irradiation equipment is small than 10% 15 3.2 Study some properties of the dyed PVA films irradiated by thermal-neutron source at the channel No.2 of the Dalat nuclear research reactor 3.2.1 Thermal neutron source at Channel 2, Da Lat nuclear research reactor The measured thermal neutron flux at an outer position of the beam line was determined by neutron activation method using Au thin foils Neutron dose rate and dose were determined by the thermal neutron flux with conversional coefficient from neutron flux to dose following 10CFR-20 (USA) standard The gamma dose rate which controlled by TLD dosimeter at irradiation position was 0.0027 Gy/h with uncertainty