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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[.]

VIETNAM ATOMIC ENERGY INSTITUTE

****************

NGUYEN THI THU HA

STUDY AND DEVELOP LITHIUM ALUMINATE (LiAlO 2 ) MATERIAL FOR

PHOTON DOSIMETRY

Major: Nuclear and atomic physics Code: 9.44.01.06

Supervisors:

1 Dr Trinh Van Giap

2 Dr Nguyen Trong Thanh

SUMMARY OF DOCTORAL DISSERTATION OF PHYSICS

Hanoi – 2023

MINISTRY OF EDUCATION AND TRAINING MINISTRY OF SCIENCE AND TECHNOLOGY

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 và 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 LiAlO2materials, 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 4 chapters:

Chapter 1 Overview study of radiation interaction with matter, units and methods of passive dosimetry methods, and overview of LiAlO2 material Chapter 2 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 3 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 4 initially study and apply an artificial neural network to identify, evaluate the dose and determine kinetic parameters of LiAlO2 material

1 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 24He and becomes a daughter nucleus A−4Z−2Y described by the following equation:

A → He24Z

A +A−4Z−2Y (1.1)

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:

X → Y + e− Z+1AZ

A + υ̅ (1.2)

X → Y + e+ Z−1AZ

A + υ (1.3)

𝑒−+ X →AZ Z−1AY+ υ (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

(non-charged) 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)

The advantage of Eq 1.5 is that it has only two free parameters, namely

the TL intensities (I M ) and the temperature at the glow peak maximum (T M), which can be obtained directly from the experimental glow curve

The Second order kinetics (Garlick and Gibson model)

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) và 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 (β- LiAlO2), and γ-phase (γ- LiAlO2)

Table 1.3: Some properties of lithium aluminate material

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 LiAlO 2 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 gel 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…

sol-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 trong nước về đối tượng vật liệu này tác giả thấy rằng LiAlO2 là vật liệu mới có nhiều tiềm năng trong đo liều bức xạ và chưa được nghiên cứu Với những lý đo được

đề cập ở trên, tác giả tập trung tiến hành nghiên cứu và phát triển vật liệu LiAlO2

cho ứng dụng trong đo liều photon

2 Experimental methods and techniques

2.1 Methods and experiments to synthesize of LiAlO2 material

2.1.1 Main equipments used to synthesize of LiAlO 2 material

Figure 2.1: some equipments used to synthesizeLiAlO2 material

2.1.2 Synthesized LiAlO 2 material methods

Figure 2.2: Synthesize procedure of γ-LiAlO2 material by sol-gel method

Mixing citric acid with

LiNO 3 /Al(NO 3 ) 3 9H 2 O

Clear solution

Drying at

110 0 C

Adjust pH values with

NH 4 OH Evaporation at < 80 0 C

Calcination

at different temperatures LiAlO 2

powder

Figure 2.3: Synthesize procedure of γ-LiAlO2 powder by solid state method

Figure 2.4: Synthesize procedure of γ-LiAlO2 powder by sol-gel with EDTA method

2.2 Experimental investigation of structural characteristics of LiAlO 2

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

Milling 6h Calcination LiAlO

Figure 2.6: The image and principle of Scanning electron microscopy (SEM) 2.3 Methods and experiments to study dosimetry characteristics of LiAlO 2

2.3.1 Irradiation of LiAlO 2 material

- Gamma irradiation using 137 Cs source with activity was ~ 1.1Ci;

Figure 2.7: Callibration room and decay diagram of 137 Cs 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

Figure 2.9: Pictures of Harshaw 3500 (a) and Harshaw 4000 (b)

2.4 Deconvolution method to analysize TL glow curve of LiAlO2

To better understand about TL glow curves of LiAlO2 material, we built a soft program on Matlab language and using the different order kinetics expression to fitting with experimental curves We used Levenberg-Marquad iteractive algorithm to do the matching The quality of fitting is verified by the

FOM factor These basic TL kinetics equations can be transformed into I=I (IM,

E, TM, T) The initial values of E, TM, IM and b are estimated by using the kinetics

equations, where IM and TM, can be obtain directly from the experimental glow

curve The Figure of Merit (FOM) is calculated to see the deviation between the two curves The procedure continues by sequentially changing the fitting parameters until a minimum value of FOM is obtained

(2.1)

where: y e and y f represent the experimental TL intensity data and the values of the fitting function, respectively The summation p extends over all experimental

points

3 Study and develop Results of LiAlO 2 material

3.1 Synthesis results and investigate characteristics of LiAlO2

3.1.1 Effect of sintering temperature and pH value on the phase structure of synthesized materials

Samples after being adjusted to pH values and heat treated, sintered at different temperatures for 4 hours First, the sintered material at 600 0C, the main product obtained are about 80% ((Al2Li(OH)6)2CO3H2O) and 20 % (LiOH.H2O

or Li2CO3) When the temperature was elevated to 800 0C, the intensity of the reflection of Al2Li(OH)6CO3.xH2O decreased to 48.8 %, while that of LiOH.H2O disappeared, and a weak reflection of Li2CO3 appeared up to 15 %, especially up

to 36.2 % to γ-LiAlO2 appearance Further increase of temperature to 900 0C, the pure γ-LiAlO2 material was reached 100% with pH=1±0.1 value and other pH

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

0C, 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 0 C; (b) 800 0 C, (c) 900 0 C and (d) 1000 0 C 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 và 1000 0C

Figure 3.2: XRD patterns of the material synthesized by solid state method and

calcined at different temperatures (a) 900 0 C, (b) 1000 0 C and (c) using sol-gel method

and calcined at (c) 900 0 C, (d) 1000 0 C Figure 3.3 presents the results of XRD patterns of synthesized materials by sol-gel combined EDTA method with the different sintered temperatures: 600

0C, 800 0C, 900 0C and 1000 0C

Figure 3.3: XRD patterns of the synthesized LiAlO2 by sol-gel combined EDTA with different calcined temperatures (a) 600 0 C, (b) 800 0 C, (c) 900 0 C and (d) 1000 0 C 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 0 C 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 LiAlO 2 material

Detection limit (DL) was determined as three standard deviations (σ) of 10 background values of LiAlO2 (DL = 3 × 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 LiAlO 2 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