1 VIETNAM ATOMIC ENERGY INSTITUTE **************** NGUYEN THI THU HA STUDY AND DEVELOP LITHIUM ALUMINATE (LiAlO2) MATERIAL FOR PHOTON DOSIMETRY Major Nuclear and atomic physics Code 9 44 01 06 Supervi[.]
MINISTRY OF EDUCATION AND TRAINING MINISTRY OF SCIENCE AND TECHNOLOGY VIETNAM ATOMIC ENERGY INSTITUTE **************** NGUYEN THI THU HA STUDY AND DEVELOP LITHIUM ALUMINATE (LiAlO2) MATERIAL FOR PHOTON DOSIMETRY Major: Nuclear and atomic physics Code: 9.44.01.06 Supervisors: Dr Trinh Van Giap Dr Nguyen Trong Thanh SUMMARY OF DOCTORAL DISSERTATION OF PHYSICS Hanoi – 2023 ABSTRACT Pasive dosimetry has been widely used in the fields of personal dosimetry, environmental dosimetry and materias research Passive dosimeters have the ability to register autonomously the absorbed doses accumulated over extended periods of time for radiation exposure workers, nuclear reactors and hospital radiotherapy More and more medical facilities are applying radioactive sources in treatment and sterilization, so the need for a highly sensitive and reliable dosimeter are essential There are may types of thermoluminescent dosimeters that have been researched and manufactured such as CaSO4: Dy; LiF: Mg, Ti; LiF: Mg, Cu, P; Li2B4O7: Cu; Al2O3:C…, these are comonly used dosimeters in photon dosimetry In terms of, thermoluminescence properties, lithium-containing compounds have high luminescence intensity, including LiAlO2 This material has been studied and applied for various application Its application as in radiation detection and dosimetry Research and development of this material for photon and neutron dosimetry has great potential in practice In the country, there have been studies on manufacturing hermoluminescent materials applied in dosimetry such as Li2B4O7: Cu; LiF: Mg, Cu, P; Li2B4O7: Cu, Ag, P CaSO4: Dy Radiation dosimeters must exhibit some properties such as accuracy, detection limit, linear dose response, fading, reusability, etc Not all dosimeters can meet the requirements of: sensitivity, durability, tissue equivalence, linear dose range, etc., so although there are many different types of dosimeters However, currently dosimeter materials still attract the attention of many research groups In the world, there have been a number of authors doing research on LiAlO materials, but at present this material has not become a commercial dosimetry material Therefore, the author "Research and development of lithium aluminate (LiAlO2) materials for photon dosimetry" is of scientific and practical significance From above requirements, the thesis focuses on the following three main objectives: - Studying on synthesis method of pure gamma phase LiAlO2 material - Study and survey the structural and morphological characteristics of LiAlO2 after being synthesized - Research and investigate some dosimetry characteristics of LiAlO2 after being irradiated gamma, beta radiation In this thesis, LiAlO2 after being synthesized by three different methods, were investigated for their structural and morphological characteristics by typical techniques of X-ray diffraction (XRD) and Scanning electron microscopy (SEM) After being irradiated gamma, beta and neutron, the LiAlO2 was measured thermoluminescence on a Harshaw reader Using analytical methods, fitting methods, kinetic models, some characteristic results of dose response, trapping parameters were studied and reported Studying an artificial neural network to identify and evaluate the dose of LiAlO2 material is also studied and presented in the thesis In addition to the introduction, conclusions, and references, the thesis is devided to chapters: Chapter Overview study of radiation interaction with matter, units and methods of passive dosimetry methods, and overview of LiAlO2 material Chapter describe experimentally synthesizing LiAlO2 material by three different methods Study and investigate structural and morphological of LiAlO2 material by X-ray diffraction (XRD) and Scanning electron microscopy techniques Research and investigate some dosimetry characteristics of LiAlO2 material by thermoluminescence method Study and build a program to analyze the thermoluminescent glow curve of LiAlO2 material using first order kinetic, second order kinetic and general order kinetic models Chapter present the synthesis results and investigate the structural and morphological characteristics of LiAlO2 material after being synthesized Study results of thermoluminescent glow curves, dose response characteristic, and trapping parameters of LiAlO2 after being synthesized The results of studying thermoluminescent glow curve of LiAlO2 material by deconvolution method using kinetic models The results of applying an artificial neural network to identify and evaluate the dose of LiAlO2 material after being fabricated Chapter initially study and apply an artificial neural network to identify, evaluate the dose and determine kinetic parameters of LiAlO2 material Overview study 1.1 Interaction of radiation with matter 1.1.1 Direct and indirect ionization Direct ionizing: Direct ionizing radiation is radiation made up of charged particles with kinetic energy large enough to cause an ionizing effect (eject electrons out of an atom's shell) Indirect ionizing: Indirect ionizing radiation is a type of radiation consisting of components that have no electrical charge (electromagnetic radiation, neutrons) but when interacting with the environment they can produce direct ionizing radiation 1.1.2 Interaction of ionization radiation with matter Interaction of alpha particles with matter: Alpha decay is the phenomenon in which the nucleus AZX automatically emits a nucleus 42He and becomes a daughter nucleus A−4 Z−2Y described by the following equation: A ZA → 42He + A−4 (1.1) Z−2Y Interaction of beta particles with matter: Beta decay is the phenomenon in which the nucleus automatically emits electrons, positrons After decay, the parent nucleus does not change the mass A, but the charge Z changes by one unit There are three types of beta decay Including: - decay, + decay and electron capture are described by the following equations: A A − ̅ (1.2) ZX → Z+1Y + e + υ A A + ZX → Z−1Y + e + υ A 𝑒 − + AZX → Z−1 Y+υ (1.3) (1.4) Interaction of gamma rays and X-rays with matter: X-ray and gamma-ray radiation are indirect ionizing radiation (no charge, no mass), ionizing ability is considered poor compared to particles electrically charged, but have great penetrating power, depending on their energy Therefore, it is necessary to shield with heavy materials (lead) X-ray and gamma radiation have many applications in medicine (imaging, radiotherapy), industry (sterilization), agriculture (mutation), etc Due to their high penetrating power, gamma rays and X-rays travel a long distance during their interaction with matter, and then there are three main effects that can occur: photoelectric effect, compton scattering effect and pairing effect Interaction of neutrons with matter: Neutron radiation is indirect (noncharged) ionizing radiation, with a large mass and very strong penetrating power Neutrons are shielded with lightweight hydrogen-rich materials such as water, paraffin, and polyethylene Neutron beams have many industrial and medical applications Neutrons are produced by nuclear fission or nuclear reaction Neutrons interact with matter through three effects: elastic scattering, inelastic scattering, and neutron capture Elastic scattering and inelastic scattering lead to slowing down of fast neutrons and intermediate neutrons Neutron capture occurs only for thermal neutrons leading to nuclear reactions 1.2 Quantities, units and passive dosimetry methods 1.2.1 Quantities and units of dosimetry The pursose of radiation dosimetry is the determine the energy that has been absorbed in matter under the influence of ionizing radiation Ionizing radiation includes alpha, beta, X-rays, gamma rays and neutrons Absorption mechanism and efficency depends on the type and energy of the radiation as well as the composition of the absorber When exposed to radiation, the biological effects that occur to different cells are different and completely dependent on the type of radiation The effect of ionizing radiation is assessed through the radiation dose that living body must receive in radiation activities as well as daily activities A system of units and standards has been developed to evaluate different biological effects for different types of radiation These quantities and units are accepted by the International Commission on Radiological Units (ICRU) and the International Commission on Radiation Protection (ICRP) include the following quantities: radioactivity, absorbed dose and absorbed dose rate, Kerma, personal dose equivalent, equivalent dose, ambient dose equivalent, effective dose, dose limit 1.2.2 Dosimetry methods To detect and determine the amount of energy absorbed in matter under the radiation exposure, we usually rely on physicochemical changes caused by the interaction between radiation and matter Up to now there have been many methods capable of detecting and measuring different types of radiation such as: ionizaion chamber, thermoluminescence and optically stimulate luminescence methods Based on the formation of color centers is a colorization method of glass and plastics In addition, the method of using film, calorimetry, etc 1.2.3 Thermoluminescence dosimetry The kinetic studies of the TL process began with the publication of Urbach (1930), followed by the groups of Radall and Wilkins (1945), Garlick and Gibson (1948) These studies have established the relationship between the temperature, shape and size of the TL peak with trap parameters such as trap depth E, frequency factor s and kinetic order b Next, a series of studies present the relationship between trap parameters and TL experimental data The First order kinetics (Randall-Wilkins model) I(T) = IM exp [1 + E kT ( T−TM TM )− T2 T2 M (1 − 2kT E ) exp [ E kT ( T−TM TM )] − 2kTM E ] (1.5) The advantage of Eq 1.5 is that it has only two free parameters, namely the TL intensities (IM) and the temperature at the glow peak maximum (TM), which can be obtained directly from the experimental glow curve The Second order kinetics (Garlick and Gibson model) I(T) = 4IM exp ( E kT ( T−TM TM )) [ T2 T2 M (1 − 2kT E ) exp ( E T−TM ) kT TM + + (1 − 2kTM E −2 )] (1.6) The General order kinetics (May and Partridge model) I(T) = IM (b) b b−1 exp ( E T−TM kT TM ) [(b − 1) (1 − đó, 2kT E ) T T2 M exp ( ZM = + (b − 1) E T−TM kT TM 2kTM E − ) + ZM ] b b−1 (1.7) (1.8) 1.2.4 Kinetic parameters of thermoluminescence dosimetry The detecting of thermoluminescent signal using photomultiplier, photodiot The result gives a thermoluminescence glow curve that can have one or more TL peaks at different temperrature and intensity locations The shape of the glow curve describes the distribution of localized levels in the band gap of the material, the area under the curve reflects the cumulative dose during the interaction of ionizing radiation with material Each peak on the glow curve is characterized by TM (the temperature at the top of the peak), the activation energy E and frequency factor s… are the characteristic kinetic parameters determining the existence of a charge capture state in the band gap of the material 1.2.5 Thermoluminescence dosimetry materials There are many natural or synthetic materials that hae thermoluminescent properties However, not all materials are suitable for radiation dosimetry For the aim of radiation dosimetry, thermoluminescent materials need to satisfy the following requirements: relatively simple TL glow curve; dosimetric peak temperature in range of 180 – 300 0C; high sensitivity; low fading; linear dose response; effective atomic number (Zeff) equivalent to living body tissue In recent years, many materials have been successfully studied and widely used The most commonly used materials are LiF: Mg, Ti (TLD-100) Following are some materials with commercial names such as: LiF: Mg, Cu, P (TLD-100H); CaF2: Dy (TLD-200); Al2O3:C (TLD-500) CaSO4: Dy (TLD-900) … 1.3 Overview of LiAlO2 material 1.3.1 LiAlO2 material and applications in radiation dosimetry LiAlO2 is an insulator that can be grown into three distinct crystal structures which are referred to in the literature as α-phase (α- LiAlO2), β-phase (βLiAlO2), and γ-phase (γ- LiAlO2) Table 1.3: Some properties of lithium aluminate material Chemical formular Molar mass Appearance Density of γ- LiAlO2 Density of β- LiAlO2 Density of α- LiAlO2 Melting point Solubility in the water LiAlO2 65,92 g·mol−1 White crystalline powder 2,615 g/cm3, solid 2.61 g/cm3, solid 3,401 g/cm3, solid 1,625 °C (2.957 °F; 1.898 K) Insoluble In personal dosimetry, the information indicates the amount of ionizing radiation to which the dosimeter wearer has been exposed Exposure dose information is very important for the health of people who frequently work in radioactive environments The dosimeter is a passive cumulative dosimeter The radiation energy accumulation is based on the electron and hole capture mechanism when the ionizing radiation interact with the dosimetric material by the corresponding traps These traps are the localized energy levels in the band gap of material 1.3.2 Overview of LiAlO2 material on domestic and foreign The synthesis method of LiAlO2 material by solid phase reaction has been reported by many authors In which the lithium salt with alumina is mixed and sintered at high temperature in air, the reaction produces a gamma phase lithium aluminate compound (γ-LiAlO2) Kinoshita et al synthesized γ-LiAlO2 by reacting alumina with alkali carbonate or alkali hydroxide Becerril et al obtained γ-LiAlO2 consisting of a small amount LiAl5O8 from the reaction Li2CO3 and Al2O3 powder at 1000 0C Recently, γ-LiAlO2 was synthesized by fusing and solgel Optically stimulate luminescence (OSL) characteristic of lithium aluminate was first studied in 2008 by Mittani et al Dhabekar et al described the TL glow curve of LiAlO2: Ce and LiAlO2: Mn The TL properties of LiAlO2: Mn were also studied by Teng et al The TL glow curve of undoped LiAlO2 was also presented by Lee et al… In recent years in Vietnam, there have been a number of establishments: Institute of Materials Science; Institute of Physics; Nha Trang Institute of Technology Research and Application – under the Vietnam Academy of Science and Technology; Nuclear Research Institute; Hue University; … has been studying on a number of TL materials for application in radiation dosimetry such as: CaSO4:Dy; Al2O3; Li2B4O7:Cu; … Qua tìm hiểu tình hình nghiên cứu nước đối tượng vật liệu tác giả thấy LiAlO2 vật liệu có nhiều tiềm đo liều xạ chưa nghiên cứu Với lý đo đề cập trên, tác giả tập trung tiến hành nghiên cứu phát triển vật liệu LiAlO2 cho ứng dụng đo liều photon Experimental methods and techniques 2.1 Methods and experiments to synthesize of LiAlO2 material 2.1.1 Main equipments used to synthesize of LiAlO2 material Figure 2.1: some equipments used to synthesize LiAlO2 material 2.1.2 Synthesized LiAlO2 material methods Mixing citric acid with LiNO3/Al(NO3)3.9H2O Clear solution Evaporation at < 80 0C Adjust pH values with NH4OH LiAlO2 powder Calcination at different temperatures Drying at 110 0C Figure 2.2: Synthesize procedure of γ-LiAlO2 material by sol-gel method Mixing Li2CO3 with γ-Al2O3 Milling 6h Calcination LiAlO2 powder Figure 2.3: Synthesize procedure of γ-LiAlO2 powder by solid state method Mixing LiNO3 with Al(NO3)3.9H2O in deionized Mixing C10H16N2O8 with C6H8O7, pH=9 Drying on hot plate at 200 0C Heating and stirring; pH=9 Calcination γ-LiAlO2 Figure 2.4: Synthesize procedure of γ-LiAlO2 powder by sol-gel with EDTA method 2.2 Experimental investigation of structural characteristics of LiAlO2 2.2.1 X-ray diffraction analysis X-ray diffraction (XRD): X-ray diffraction is a non-destructive analytical technique that provides information on crystal structure, state, crystal orientation, and other structural parameters, such as mean grain size or crystal defects The nature of X-ray diffraction is the phenomenon in which X-ray beams diffract on the crystal faces of a solid X-ray diffraction measurements performed on a German D8 Advanced–Bruker machine at the Institute of Materials and Sciences Figure 2.5: Image and structure of X-ray diffraction (XRD) 2.2.2 Scanning electron microscope analysis Scanning electron microscope (SEM) is a type of electron microscope that can produce high-resolution images of the surface of a specimen by using a narrow electron beam scanned over the sample surface The morphology of LiAlO2 materials after sintering was measured on the S-4800 SEM system of Hitachi of Japan at the Institute of Materials and Sciences Figure 2.6: The image and principle of Scanning electron microscopy (SEM) 2.3 Methods and experiments to study dosimetry characteristics of LiAlO2 2.3.1 Irradiation of LiAlO2 material - Gamma irradiation using 137Cs source with activity was ~ 1.1Ci; Figure 2.7: Callibration room and decay diagram of 137Cs source - Beta irradiation is 90Sr with activity was 1.5GBq (40.54 mCi) Figure 2.8: Source and decay diagram of 90Sr 2.3.2 Thermoluminescent devices Thermoluminescence signal measurements were performed on a Harshaw 4000 TLD reader at Institute for Nuclear Science and Technology and a Harshaw 3500 TLD reader of the Institute of Materials Science values still had some impurities appearing in the structure of synthesized material 3.1.2 X-ray diffraction results Figure 3.1 presents the results of XRD measurements of synthesized materials by sol-gel method with the different sintered temperatures: 600 0C, 800 C, 900 0C and 1000 0C Figure 3.1: XRD patterns of the material synthesized by sol-gel method and calcined at different temperatures (a) 600 0C; (b) 800 0C, (c) 900 0C and (d) 1000 0C Figure 3.2 shows the results of XRD measurements of synthesized materials by sol-gel method and solid state method with the different sintered temperatures: 900 0C 1000 0C Figure 3.2: XRD patterns of the material synthesized by solid state method and calcined at different temperatures (a) 900 0C, (b) 1000 0C and (c) using sol-gel method and calcined at (c) 900 0C, (d) 1000 0C Figure 3.3 presents the results of XRD patterns of synthesized materials by sol-gel combined EDTA method with the different sintered temperatures: 600 C, 800 0C, 900 0C and 1000 0C 11 Figure 3.3: XRD patterns of the synthesized LiAlO2 by sol-gel combined EDTA with different calcined temperatures (a) 600 0C, (b) 800 0C, (c) 900 0C and (d) 1000 0C The X-ray diffraction results of LiAlO2 material were synthesized by three different methods all obtained gamma phase structure at temperature higher than 900 0C The lattice constants and density were determined as: a= 5.16870 Å, c= 6.26790 Å, and δ= 2.615 g/cm³ 3.1.3 Scanning electron microscopy results Figure 3.4: SEM images synthesized γ-LiAlO2 calcined at 900 0C by the different synthesis methods: (a) sol-gel; (b) solid state and (c) sol-gel combined EDTA From the survey results on the structure and morphology of LiAlO2 materials, it is shown that the struture and morphology strongly depend on the sintering temperature and synthesized method 3.2 Investigation results on dosimetry properties of LiAlO2 material 3.2.1 Background and detection limit of LiAlO2 material Detection limit (DL) was determined as three standard deviations (σ) of 10 background values of LiAlO2 (DL = × σ) The standard deviation of LiAlO2 is σ = 2,04 nC, the detection limit is DL = 6,12 nC 3.2.2 Homogeneity of synthesized LiAlO2 material Uniformity is a very important factor in the synthesis of dosimetric materials The results of testing the uniformity of synthesized materials are shown in Figure 3.5 The results obtained have a standard deviation of 2,58 % Thus, the LiAlO2 12 material synthesized by sol-gel combined with EDTA method is accepted in radiation dosimetry Figure 3.5: The results of dosimetry samples of LiAlO2 synthesized by sol-gel combined with EDTA after being irradiated gamma radiation mGy at heating rate 0C/s The uniformity is calculated according to the following equation and the results are presented in Table 3.1 𝐷 −𝐷𝑚𝑖𝑛 𝐻(%) = 𝑚𝑎𝑥 × 100 (3.1) 𝐷 𝑚𝑖𝑛 Bảng 3.1: The results of uniformity evaluation of LiAlO2 material Sample (nC) 1383,47 Sample Sample Sample Sample (nC) (nC) (nC) (nC) 1369,44 1342,22 1293,25 1359,71 Dmax = 1383,47 nC; Dmin = 1293,25 nC Uniformity H(%) = (1383,47-1293,25)/1293,25×100 = 6,98% 3.2.3 Linearity LiAlO2 material was divided into three groups that was de-signaled and irradiated gamma radiation: 4mGy, 6mGy 8mGy The material groups are designaled and irradiated gamma radiation: 10mGy, 20mGy 40mGy Figure 3.6 shows a graph of the linearity of LiAlO2 in dose range 4-40 mGy Figure 3.6: Graph of the linearity of LiAlO2 in dose range 4-40 mGy 13 3.2.4 The TL signal sensivity of LiAlO2 material Measurements were made under the same experimental conditions: same heating rate, same exposure dose, same reader equipment Figure 3.7 presents the investigate results of the TL sensitivity of LiAlO2 material compared with TLD 100 and α-Al2O3:C comercial materials Survey experiments show that the sensitivity of TLD 100 and α-Al2O3:C are 1.2 and 17.5 times higher than LiAlO2 materials, respectively Hình 3.7: Sensitivity results of LiAlO2 compared with TLD 100 and α-Al2O3:C 3.2.5 Study the reusability of LiAlO2 material Reusability of dosimetry materials is also factor to evaluated because many materials effected by irradiation, temperature, thermal sensitivity, etc during measurements To test the reusability of LiAlO2 material, ten dosimetry cycles were repeated including: irradiation, heat treatment and dosimetry steps under the same conditions The reusability results of LiAlO2 materials are presented in Table 3.2 Table 3.2: The reusability results of LiAlO2 material after being irradiated gamma radiation 4mGy Cycles TL (103 nC) 2.47 2.39 2.42 Mean value Standard deviation 2.46 2.50 2.36 2.41 2.52 2.44 2.44× 103 (nC) 2.09 % 10 2.49 3.2.6 Dose response of LiAlO2 material It is necessary to determine the dose response of LiAlO2 material The dose response curve describes the relationship between the TL intensity and the exposure dose Figure 3.8 shows the dose response of LiAlO2 synthesized by sol-gel and sol-gel combined with EDTA with dose range from 0.3 to 2.4 Gy 14 The dot is the experiment point at the different dose values and the solid line is the fitting line Figure 3.8: Dose response of LiAlO2 synthesized by sol-gel (left side) and sol-gel combined with EDTA (right side) methods 3.2.7 Fading of TL signal after being irradiated of LiAlO2 Fading is very important parameter of dosimetry materials This factor evaluates the ability to store information in dosimetry time Figure 3.9 shows that fading of LiAlO2 material synthesized by sol-gel after being irradiated gamma 0.3 Gy and stored at different time Figure 3.9: Fading of LiAlO2 material synthesized sol-gel method The results showed that the fading of LiAlO2 material synthesized sol-gel method decreases by about 2% after 30 days at the dosimetry peak, and the signal almost stable after 90 days Figure 3.10 describes the fading of LiAlO2 material synthesized sol-gel combined with EDTA The results showed that the signal at the dosimetry peak decreases by nearly 3%, then the signal slowly decreased about 1.2% After 30 days, the TL signal decrease by 6% and almost stable after 90 days 15 Figure 3.10: Fading of LiAlO2 material synthesized sol-gel combined with EDTA method 3.3 Investigation the TL curve and trap parameters of LiAlO2 3.3.1 TL curve shape of LiAlO2 after being irradiated gamma, beta Figure 3.11 presents the results of TL glow curve of γ-LiAlO2 material synthesized sol-gel combined with EDTA irradiated gamma and beta The obtained TL glow curve appears two peaks of 117 0C and 231 0C 231 0C peak was selected as the dosimetric peak Figure 3.11: The TL glow curve of γ-LiAlO2 synthesized by sol-gel combined with EDTA irradiated: 1-90Sr souce; 2- 137Cs source 3.3.2 Investigation TL curves when various heating rate TL glow curve of LiAlO2 materials were gamma irradiated 0.3 Gy and measured at different heating rates are shown in Figure 3.12 TL glow curve appears two peaks, the second peak was selected as the dosimetric peak The maximum position of peaks tends to shift towards the high temperature as the heating rates increase At heating rate of 0C/s, the position of dosimetric peak is about 203 ± 0C, when increasing the heating rate to 10 0C/s, the position of 16 dosimetric peak is about 250 ± 0C The shape of the curves does not change when various heating rates Figure 3.12: The TL glow curve of LiAlO2 with different heating rates 3.3.3 Investigate trapping parameters of LiALO2 The kinetic parameters are physics quntities that characterize a electrongcapture trap, giving the maximum temperature of peak (Tm), activation energy (E), frequency factor (s) and lifetime (τ) for which the charge is trapped in the trap at a certain temperature These parameters represent the stability of a trap when the material interacts with factor such as temperature, light etc The kinetic parameters are studied by the following methods: 3.3.3.1Various heating rate method Correlation between the factors ln(Tm2/β) and 1/kTm are presented in equation (3.1) These parameters are determined from experimental results 𝑇2 𝐸 𝐸 𝑙𝑛 ( 𝛽𝑀 ) = 𝑘𝑇 + 𝑙𝑛 (𝑘𝑠) 𝑀 (3.1) where, Tm is the maximum temperature of dosimetric peak, β is linear heating rate, and k is Boltzmann constant Figure 3.13 shows that the correlation between ln(TM2/β) and 1/kTM of the dosimetric peak with different heating rates From the linear fittings, the slope and intercept gives the activation energy (E) and the frequency factor (s) are E = 0.81 (eV) and s = 1.09×107 (s-1) 17 Figure 3.13: Determine E and s from correlation between ln(Tm2/β) and 1/kTm at dosimetric peak 3.3.3.2 Peak shape method Chen’s peak method was developed by R Chen to determine the kinetic values of activation energy (E), frequency factor (s) and kinetic order (b) using the experimental parameters: Tm, T1 and T2 are the peak temperature at maximum (IM) and the temperature on either side of the temperature at the maximum, corresponding to half intensity IM/2, respectively The value μg can be obtained from the experimental parameters The results of kinetic parameters of LiAlO2 material by Chen’s method presented in Table 3.3 Table 3.3 Kinetic parameters of LiAlO2 material gamma irradiated 0.3 Gy at heating rate of 0C/s Tm(0C) Tm(K) T1(K) T2(K) µg 117 ± 392 ± 365 ± 417 ± 0.49 0.68 8.58×1011 231 ± 506 ± 470 ± 549 ± 0.54 1.38 1.10×1018 E(eV) s(s-1) 3.4 Analysis results of TL glow curves of LiAlO2 by deconvolution method To find the optimal mode as well as to determine the kinetic models that are most suitable for LiAlO2 material, so a program is built to analysize the TL glow curve by deconvolution method according to different models 18 Figure 3.14 shows experimental glow curve of LiAlO2 synthezed by solgel with EDTA method was gamma irradiated 0.3 Gy Fitting curve using the two order general expressions with component six peaks and FOM factor is 1.08x10-2 Figure 3.14: GOK fitting of γ-LiAlO2 deconvoluted with six peaks in sequential after gamma irradiated 0.3 Gy with heating rate 0C/s From obtained results indicate that the LiAlO2 material is best matched with the general kinetic order model with kinetic order b=1.79 Comparative data between first-order, second-order, and general-order models are presented in Table 3.4 Table 3.4: Trapping parameters of synthesized LiAlO2 by sol-gel with EDTA method after being irradiated gamma 0,3 Gy Đỉnh Nhiệt độ (0C) 136± 1,65 248± 1,65 FOM Mơ hình bậc (FOK) E(eV) s(s-1) 0,80 2,17E+09 0,84 2,73E+07 1,65×10-2 Mơ hình bậc (SOK) E(eV) s(s-1) 0,95 1.94E+11 1,05 3.07E+09 1,72×10-2 Mơ hình bậc tổng qt (GOK) E(eV) s(s-1) 0,75 5.30E+08 1,03 1.97E+09 1,08×10-2 Investigate the influence of E and b In Figure 3.15a shows parameters of dosimetric peak (P5) for GOK model such as s, b, TM and IM were kept constant while E is varying As observed from 19 the Figure, the curve becomes broader on either side of the glow peak as the value of E decreases Figure 3.18: Effects of activation energy E (a) and kinetic order b (b) on TL glow curve of LiAlO2 synthesized by sol-gel with EDTA method Figure 3.15b is normalized glow curves of different values of b, keeping s, E, TM and IM of dosimetric peak This Figure shows that as the value of b increases, the higher temperature side of the glow peak becomes broader, while the lower temperature side of the peak is not affected by changes in b Apply results of artificial neural network to identify and evaluate the dose of LiAlO2 material An artificial neural network is an information processing model that imitates the information processing method of biological neural systems It is made up of a large number of elements (called processors or neurons) connected to each other through links (called link weights) that work as a unified whole to solve a specific problem Figure 4.1: Diagram of application model for identification and evaluation of LiAlO material 20 Within the framework of the thesis, initially focus on studying the multilayer linear network, the back error propagation algorithm for the LiAlO2 material Inputs are TL intensity of corrsponding to 176 different temparature points Outputs are factor such as: material type, exposure dose, heating rate, peak (Tm1) and peak (Tm2) Figure 4.1 shows the diagram of application model for identification and evaluation of LiAlO2 material Figure 4.2 shows the matching curve between outputs of network and real data after learning 109 times Figure 4.2: The matching curve between network output and real data (after 109 learning times) The result after learning 109 times, the linear fitting line Y=T, is a descriptive matching function between output (target) and output after the learning process of the network, the fitting line shows the linearity and the good fitting index: R≈ (70% of the total input for training); R= 0,99998 (15% of the total input for validation); R= 0,99999 (15% of the total input for testing); R≈ (for all inputs) 21 Identify and evaluate the exposure dose of LiAlO2 written by C# languauge Figure 4.3: Display neural network structure settings CONCLUSION The thesis has accomplished the research objectives and contents, the main results obtained including: - Overview of the interaction of radiation with matter; quantities, units and passive dosimetry methods; and overview of LiAlO2 material in the world and in the country; - Studied and investigated the structure and morphology of LiALO2 material after being synthesized by typical techniques of X-ray diffraction (XRD) and scanning electron microscopy (SEM) The results show that when the material is heated below the temperature of 900 0C, the structure of the material has a small contribution of impurities; - The synthesized LiAlO2 material by sol-gel combined with EDTA is the most optimal with: pH = 9; gel forming temperature 90 – 95 0C; gel treatment temperature 200 – 300 0C; sintering temperature greater than 900 0C The 22 - - - - - - results are shown that the structure and morphology of LiAlO2 strongly depend on the sintering temperature and synthesize method; Studied the dosimetric characteristics of LiAlO2 material with the background value and detection limit of 23.4 nC and 6.12 nC, respectively; the uniformity of LiAlO2 material is 6.98%; the good linearity of LiAlO2 material with dose range 4-40 mGy, it is possible estimate the fluctuation of measured dose compared to the exposure dose 8,8%, the satisfaction according to IEC-62387 is 11% The experiment results show that the sensitivity of commercial TLD100 and α-Al2O3:C material are 1.2 and 17.5 times higher than LiAlO2 material; Studied the reusability by repeating 10 dosimetric cycles of LiAlO2 material including irradiation, heat treatment and dosimetry steps under the same conditions The reusability of LiAlO2 material with standard deviation of 10 measurements are 3.63% and the distribution of the measurements is quite uniform The synthesized LiAlO2 material by sol-gel combined with EDTA method with good sensitivity and reusability; Investigated the good dose response of LiAlO2 material after being gamma irradiated with dose range – 40 mGy and 0.3-2.4 Gy The LiAlO2 material has applicability in personal and enviromental dosimetry; Studied the fading of LiAlO2 material after being gamma irradiated 90 days at dosimetric peak The results show that the fading of synthesized LiAlO2 material by sol-gel and sol-gel combined with EDTA methods decrease about giảm khoảng 2% and 6%, respectively; The TL glow curve LiAlO2 material appears a clear peak which is considered as the dosimetric peak located in the temperature range 200-300 0C: (1) the dosimetric peak at 249 0C for the synthesized LiAlO2 by sol-gel method; (2) the dosimetric peak at 231 0C for the synthesized LiAlO2 by sol-gel combined with EDTA method The shape of the TL glow curve of LiAlO2 material strongly depend on synthesize method Compared the work of K K Gupta et al in 2017 [91] shows that the dosimetric peak of LiAlO2 is quite similar to that of K K Gupta’s group; Investigated the TL signal of LiAlO2 material when changing the heating rate The results show that the height of dosimetric peak tends to decrease when the heating rate is increased, this phenomenon is due to the influence of thermal quenching and is only significantly affected when the heating rate is low However, when the heating rate is greater than 0C/s the height of dosimetric peak decreases more slowly and tends to change insignificantly The shape of the TL glow curve of LiAlO2 material does not change as the heating rate changes; 23 - Conducted and calculated kinetic parameters of LiAlO2 material using different methods From the above results, the process of TL formation in LiAlO2 materials can describe as follows: the irradiation forms electron-hole pairs, the electrons move to the conduction band and then they are captured on the traps (corresponding to the trap depth from 0.63 – 1.30 eV Thermal stimulation, causing electrons from the traps to be released, they move to the conduction band, and then recombine with the hole at the recombination center and form a TL signal; - Built a program to analyze thermoluminescent glow curves of LiAlO2 based on Matlab language using first order, second order, and general order kinetic models Used Levenberg-Marquard iterative algorithm to the fitting The fitting algorithm requires the initial parameters to be sufficiently precise to ensure convergence and minimize the number of iterations The quality of the matching is verified by the FOM quantity The results show that the synthesized LiAlO2 material is the most suitable with the general order kinetic model - Initially applied artificial neural network is written based on Matlab language to identify and evaluate the exposure dose of LiAlO2 After training 109 times for good application results In addition, a program is written in C#, initially we studied and applied collecting, calculating, processing, storing, identifying, and evaluting the dose of LiAlO2 Some results of the thesis that can be considered as new contribution including: - Studied and developed an optimal method to synthesize LiAlO2 material that have not been studied in Vietnam, which can be applied in radiation dosimetry; - Provide data on structure, morphology and some dosimetry characteristics of LiAlO2 after being synthesized, which can be applied in personal and environmental dosimetry; - Studied and developed a program based on Matlab language to investigate more detail about thermoluminescent glow curves of LiAlO2 using deconvolution method; - Initial application of artificial neural network to identify and evaluate the exposure dose of LiAlO2 material Recommendations for future studies as follows: In order to have a complete evaluation of LiAlO2 materials applied in radiation dosimetry by TL and OSL methods, more comprehensive and complete studies are needed Some recommendations need to be studied in the near future: 24 - Study and investigate the dosimetry characteristics of LiAlO2 materials by OSL method; - Study and investigate the dosimetry characteristics of LiAlO2 materials when dopping with other elements; - Study and synthesize LiAlO2 material using 6Li component for application in neutron dosimetry PAPERS PUBLISHED DURING THE DISSERTATION Nguyen Thi Thu Ha, Trinh Van Giap, Nguyen Trong Thanh (2020), “Synthesis of lithium aluminate for application in radiation dosimetry”, Material Letters, Volume 267,15 May 2020, 127506 Nguyen Thi Thu Ha, Trinh Van Giap, and Bui Duc Ky (2022), “Synthesis and characterization of lithium aluminate for passive dosimetry”, World Journal of Nuclear Science and Technology, Vol 12, No 1, January 2022 Nguyễn Thị Thu Hà, Trịnh Văn Giáp, Vũ Hoài (2022), “Nghiên cứu xây dựng quy trình tổng hợp vật liệu LiAlO2”, TNU Journal of Science and Technology, T 227, S 16, 124-131 Nguyễn Thị Thu Hà, Trịnh Văn Giáp, Bùi Đức Kỳ (2022), “Nghiên cứu tổng hợp phân tích đường cong tích phân nhiệt phát quang LiAlO2”, Tạp chí khoa học cơng nghệ Việt Nam, ISSN: 1859-4794 chấp nhận đăng ngày 02/12/2022 Nguyễn Thị Thu Hà, Trịnh Văn Giáp, Bùi Đức Kỳ (2023), “Nghiên cứu khảo sát đặc trưng đo liều gamma LiAlO2”, Tạp chí khoa học cơng nghệ Việt Nam, gửi ngày 21/03/2023 Nguyen Thi Thu Ha, Trinh Van Giap, Nguyen Trong Thanh, Bui Duc Ky, Vu Hoai, Nguyen Huyen Trang (2019), “Research to make lithium aluminate powder by sol-gel method applied in radiation dosimetry”, Báo cáo poster Hội nghị Khoa học Công nghệ hạt nhân toàn quốc lần thứ 13 (VINANST 13) ngày 7-9/8/2019 Quảng Ninh 25