THERMOLUMINESCENCE CHARACTERISTICS OF SILICON …eprints.utm.my/id/eprint/48926/25/MohdHilmiSahiniMFS2014.pdf · 11.19 and 12.27 respectively, which is higher than that of soft tissue

THERMOLUMINESCENCE CHARACTERISTICS OF SILICON OPTICAL FIBRE

DOPED WITH YTTERBIUM AND YTTERBIUM – TERBIUM AS PHOTON

DOSIMETER.

MOHD. HILMI BIN SAHINI

UNIVERSITI TEKNOLOGI MALAYSIA

THERMOLUMINESCENCE CHARACTERISTICS OF SILICON OPTICAL FIBRE

DOPED WITH YTTERBIUM AND YTTERBIUM – TERBIUM AS PHOTON

DOSIMETER.

MOHD. HILMI BIN SAHINI

A thesis submitted in fulfillment of the

requirements for the award of the degree of

Master of Science (Physics)

Faculty of Science

University Teknologi Malaysia

JUNE 2014

ACKNOWLEDGEMENT

My most humble and sincere thanks to first and foremost, my supervisor, Prof.

Dr. Husin Wagiran for his believe in me and opportunities given to further my studies.

Not to forget, Dr. Imam Hossain who also had helped throughout the completion of this

research.

To my extraordinary family, thanks for their endless love and support in

completing this study. My profound thanks to my fiancée, Nor Amiera for her patience

and support for me. They have truly been the foundation under this author.

I would like to express my immense gratitude to En. Hassan Ali, Science Officer

of Department of Oncology And Radiation Therapy, Hospital Sultan Ismail for his

generous assistance and expertise in this research.

I wanted to thank the government of Malaysia in providing a funded Master

scholarship. Not to forget also the Ministry of Higher Education of Malaysia for

providing research grant for this research.

ABSTRACT

The study of SiO2 commercial optical fiber explores the useful

thermoluminescence (TL) properties and reveals its potential as a TL dosimeter. The

present work describes the TL dose response, reproducibility, fading and minimum

detectable dose of SiO2: Yb and SiO2: Yb, Tb optical fibers as compared to TLD-100.

The optical fibers were placed in a solid phantom and irradiated with 6 and 10 MV X-

rays using LINAC Primus MC 3339 and 1.25 MeV gamma ray from gamma cell.

Scanning electron microscopy analysis was performed to determine the dopant

concentration and the effective atomic number, Zeff. The dopant concentration of Yb for

SiO2: Yb optical fiber was found ranging between 0.23 – 0.35 mol% and for SiO2: Yb,

Tb; the dopant concentration of Yb and Tb were in the range of 0.03 – 1.46 mol% and

0.12 – 0.39 mol% respectively. The Zeff value for SiO2: Yb and SiO2: Yb, Tb were

11.19 and 12.27 respectively, which is higher than that of soft tissue (7.42), but close to

bone (11.6 – 13.8). In term of TL dose response and sensitivity, SiO2: Yb, Tb optical

fiber demonstrated better results than SiO2: Yb optical fiber, but both TL materials were

still inferior when compared to TLD-100. SiO2: Yb, Tb optical fiber had the lowest

percentage lost in fading of about 5.83%, 15.65% and 18.55% for day 7, 21 and 28

respectively, compared to SiO2: Yb optical fiber which has higher fading of about

55.17% and 95.87% for day 14 and 30 respectively. SiO2: Yb, Tb optical fiber shows

good reproducibility results compared to SiO2: Yb optical fiber. The minimum

detectable dose of SiO2: Yb and SiO2: Yb, Tb optical fibers were 333 mGy and 19 mGy

respectively. In general, it can be concluded that SiO2: Yb, Tb optical fiber is a much

better optical fiber to be developed as a new TL dosimeter compared to SiO2: Yb

optical fiber.

ABSTRAK

Kajian gentian optik komersial SiO2 meneroka ciri luminesens terma (TL)

berguna dan keupayaan sebagai dosimeter TL. Kajian ini membincangkan sambutan

dos luminesens terma, kebolehulangan, kepudaran dan dos pengesanan minimum

gentian optik SiO2: Yb dan SiO2: Yb, Tb dan berbanding TLD-100. Gentian optik

diletakkan di dalam fantom pepejal dan disinarkan dengan sinar-X 6 dan 10 MV

menggunakan LINAC Primus MC 3339 dan sinar gama 1.25 MeV dari sel gama.

Analisis mikroskop pengimbas elektron (SEM) dilakukan bagi menentukan kepekatan

dopan dan nombor atom berkesan, Zeff. Kepekatan dopan Yb bagi gentian optik SiO2

ialah dalam julat 0.23 – 0.35 mol% dan kepekatan dopan Yb dan Tb bagi SiO2 : Yb, Tb

masing-masing ialah 0.03 – 1.46 mol% dan 0.12 – 0.39 mol%. Nilai Zeff bagi gentian

optik SiO2 : Yb dan SiO2 : Yb, Tb masing-masing ialah 11.19 dan 12.27, iaitu lebih

tinggi daripada nilai tisu lembut (7.42), tetapi hampir dengan tulang (11.6 – 13.8). Dari

aspek sambutan luminesens terma, SiO2 : Yb, Tb memberi keputusan yang lebih baik

berbanding SiO2 : Yb, tetapi kedua-dua bahan masih tidak dapat menandingi TLD-100.

Gentian optik SiO2 : Yb, Tb mempunyai peratus kepudaran yang lebih rendah iaitu

5.83%, 15.65% dan 18.55% masing-masing pada hari ke-7, 21 dan 28 berbanding

dengan SiO2 : Yb yang mempunyai peratus kepudaran yang lebih tinggi sebanyak

55.17% dan 95.17% pada hari ke-14 dan 30. Hasil kajian menunjukkan gentian optik

SiO2 : Yb, Tb menunjukkan keputusan sifat kebolehulangan yang lebih baik berbanding

gentian optik SiO2 : Yb. Dos pengesanan minimum bagi gentian optik SiO2 : Yb dan

SiO2 : Yb, Tb masing-masing ialah 333 mGy dan 19 mGy. Secara umum dapat

disimpulkan bahawa gentian optik SiO2 : Yb, Tb adalah lebih sesuai untuk dimajukan

sebagai dosimeter TL berbanding gentian optik SiO2 : Yb.

TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION v

ACKNOWLEDGEMENT vi

ABSTRACT vii

ABSTRAK viii

TABLE OF CONTENTS ix

LIST OF TABLES xiii

LIST OF FIGURES xv

LIST OF SYMBOLS xix

LIST OF ABRIVIATIONS xxi

LIST OF APPENDICES xxii

1 INTRODUCTION 1

1.1 Research Background 1

1.2 Objective of the Research 3

1.3 Statement of Problem 4

1.4 Scope of the Research 5

1.5 Significance of the Research 6

2 LITERATURE REVIEW 7

2.1 Introduction 7

2.2 Radiation Dosimeter 8

2.3 Thermoluminescence 8

2.3.1 Thermoluminescence Phenomena 9

2.3.2 Thermoluminescence Dosimeter System 10

2.3.3 Thermoluminescence Dosimeter 11

2.4 Characteristics of Thermoluminescence Material 13

2.4.1 Dose Linearity 14

2.4.2 Glow Curve 16

2.4.3 Energy Dependance 17

2.4.4 Fading 19

2.4.5 Sensitivity 20

2.4.6 Stability and Reproducibility 20

2.4.7 Effective Atomic Number 21

2.4.8 Minimum Detectable Dose 21

2.5 Silicon Dioxide Optical Fiber 22

2.5.1 SiO2 structure 24

2.5.2 Intrinsic Point-Defects 26

2.5.3 Oxygen Deficient Centers 27

2.5.4 Oxygen Associated Hole Center 28

2.5.5 Extrinsic Point-Defects 29

2.6 Rare Earth Impurity 30

3 RESEARCH METHODOLOGY 31

3.1 Material and Sample Preparation 31

3.2 Pre-Irradiation Annealing 32

3.3 Exposure to Irradiation 34

3.3.1 Linear Accelerator (LINAC) 34

3.3.2 Cobalt-60 36

3.3.3 Energy Response 38

3.3.4 Fading Determination 38

3.3.5 Reproducibility 38

3.3.6 Minimum Detectable Dose 38

3.4 Read-out Equipment 39

3.4.1 Dark Current 40

3.4.2 PMT Noise 41

3.4.3 Background Noise 41

3.5 Scanning Electron Microscope (SEM) 41

4 RESULTS AND DISCUSSION 44

4.1 Scanning Electron Microscope (SEM) Analysis 44

4.2 Dopant Concentration 46

4.3 Effective Atomic Number 49

4.4 TL Glow Curve 52

4.5 TL Dose Response 54

4.5.1 TL Response to X-ray Photon Irradiation 54

4.5.2 Comparison of Yb-doped with Yb-Tb

doped SiO2 Optical Fiber for 6 and 10 MV

Photons Irradiation

61

4.5.3 Comparison of SiO2 Doped Optical Fiber

with TLD-100 for 6 and 10 MV Photons

Irradiation

62

4.5.4 Comparison of Yb- and Yb-Tb Doped with

Ge- and Al-Doped SiO2 Optical Fibers for

6 and 10 MV Photons Irradiation

65

4.5.5 TL Response to Gamma Ray Irradiation 66

4.5.6 Comparison of Yb-Doped with Yb-Tb

Doped Optical Fiber for 1.25 MeV Gamma

Ray Irradiation

70

4.5.7 Comparison of Doped Optical Fiber with

TLD-100 for 1.25 MeV Gamma Ray

Irradiation

71

4.6 Energy Response 73

4.7 Fading 75

4.8 Reproducibility 78

4.9 Minimum Detectable Dose 81

5 CONCLUSION 82

5.1 Summary 82

5.2 Recommendation and Future Research 84

REFERENCES

Appendix A - D

85

91

LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 Characteristics of TL phosphors 15

3.1 TLDs material specification 36

3.2 Time of irradiation using Cobalt-60 41

4.1 Summary of dopant concentration for Yb-doped SiO2 optical

fiber

50

4.2 Summary of dopant concentration for Yb and Tb in Yb-Tb

doped SiO2 optical fiber

52

4.3 Summary of Zeff for Yb-doped optical fiber 54

4.4 Summary of Zeff for Yb-Tb doped optical fiber 55

4.5 TL response of Yb-doped SiO2 optical fiber for 6 MV

photons energy

59

4.6 TL response of Yb-Tb doped SiO2 optical fiber for 6 MV

photons energy

60

4.7 TL response of TLD-100 for 6 MV photons energy 61

4.8 TL response of Yb-doped SiO2 optical fiber for 10 MV

photons energy

63

4.9 TL response of Yb-Tb doped SiO2 optical fiber for 10 MV

photons energy

64

4.10 TL response of TLD-100 for 10 MV photons energy 65

4.11 Summary of sensitivity of TL materials compared with

TLD-100 for 6 MV photon.

69

4.12

Summary of sensitivity of TL materials compared with

TLD-100 for 10 MV photon

70

4.13 Summary of TL response of TL dosimeters for 6 and 10 MV

photons energy

71

4.14 TL response of Yb-doped SiO2 optical fiber for 1.25 MeV

gamma ray energy

72

4.15 TL response of Yb-Tb doped SiO2 optical fiber for 1.25

MeV gamma ray energy

73

4.16 TL response of TLD-100 for 1.25 MeV gamma ray

energy

75

4.17 Summary of sensitivity of TL materials compared with

TLD-100 for 1.25 MeV gamma ray energy

78

4.18 Reproducibility data for Yb-doped SiO2 optical fiber 86

4.19 Reproducibility data for Yb-Tb doped SiO2 optical fiber 86

4.20 Summary of minimum detectable dose 87

LIST OF FIGURES

FIGURE NO. TITLE PAGE

2.1 Energy level diagram of the thermoluminescence process 11

2.2 Schematic diagram of a typical TLD reader 13

2.3 Linearity curve in a plot of TL as a function of dose 18

2.4 Comparison of first order (b=1), second order (b=2) and

intermediate order (b=1.5) TL glow peak

20

2.5 Photon energy response for a new indicated TLD materials 21

2.6 Different propagation mode in single-mode and multi-

mode optical fiber

26

2.7 Structure of an optical fiber 27

2.8 SiO4 tetrahedral structure is the most common structure

unit for SiO2

28

2.9 Structure of the amorphous silicon, with Si atom in grey

and O atoms in black

30

2.10 X-band electron paramagnetic resonance spectrum of E’

center

32

3.1 A furnace or TLD oven for annealing process 37

3.2 Linear accelerator Primus MLC 3339 used for photon

irradiation

39

3.3 A gamma cell used for gamma ray irradiation 41

3.4 Harshaw 3500 TL reader 44

3.5 Nova NanoSEM 450 used for SEM analysis 47

4.1 The spectrum of Yb-doped SiO2 optical fiber 49

4.2 The spectrum of Yb-Tb doped SiO2 optical fiber 49

4.3 The dopant concentration of Yb-doped SiO2 optical fiber 51

4.4 The dopant concentration of Yb in Yb-Tb doped SiO2

optical fiber

52

4.5 The dopant concentration of Tb in Yb-Tb doped SiO2

optical fiber

53

4.6 The Zeff of Yb-doped optical fiber 55

4.7 The Zeff of Yb-Tb doped optical fiber 56

4.8 The glow curve of Yb-Tb doped SiO2 optical fiber at 6 MV

photon irradiation for dose 1 -4 Gy

57

4.9 The glow curve of TLD-100 at 6 MV photon irradiation for

dose 1 -4 Gy

57

4.10 TL response (nC mg-1

) of Yb-doped SiO2 optical fiber

subjected to 6 MV photon irradiation

59


) of Yb-Tb doped SiO2 optical fiber


61


) of TLD-100 subjected to 6 MV

photon irradiation

62



subjected to 10MV photon irradiation

63




65


) of TLD-100 subjected to 10 MV

photon irradiation

66

4.16 The graph shows the TL response of Yb and Yb-Tb doped

SiO2 optical fiber for 6 MV photon energy versus dose

67

4.17 The graph shows the TL response of Yb and Yb-Tb doped

SiO2 optical fiber for 10 MV photon energy versus dose

67

4.18 TL response of Yb-, Yb-Tb doped SiO2 optical fiber and

TLD-100 for 6 MV photons

68

4.19 TL response of Yb-, Yb-Tb doped SiO2 optical fiber and

TLD-100 for 10 MV photons

69



subjected to 1.25 MeV gamma ray irradiation

72



subjected to 1.25 MeV gamma ray irradiation

74


) of TLD-100 subjected to 1.25 MeV

gamma ray irradiation

75

4.23 The graph shows the TL response of Yb- and Yb-Tb doped

SiO2 optical fiber for 1.25 MeV gamma ray energy versus

dose

76

4.24 TL response of Yb-, Yb-Tb doped SiO2 optica fiber and

TLD-100 for 1.25 gamma ray energy

77

4.25 The graph shows the energy response of Yb-doped SiO2

optical fiber for 6 and 10 MV photon irradiation

79

4.26 The graph shows the energy response of Yb-Tb doed SiO2

optical fiber for 6 and 10 MV photon irradiation

80

4.27 The graph shows the energy response of TLD-100 for 6

and 10 MV photon irradiation

80

4.28 The fading of Yb-doped SiO2 optical fiber subjected to 6

MV photon irradiation

82

4.29 The fading of Yb-Tb doped SiO2 optical fiber subjected to

6 MV photon irradiation

83

4.30 The reproducibility of Yb-doped SiO2 optical fiber at 6


84

4.31 The reproducibility of Yb-Tb doped SiO2 optical fiber at 6


85

LIST OF SYMBOLS

Zeff The effective atomic number

γ Gamma

β Beta

µ Micro

Gy Gray

ŋ The efficiency of the thermoluminescence emission

m Mass

ε Ratio between the energy

D Absorbed dose

M TL signal

k Boltzmann’s constant

Fc The inverse of the calibration factor

(µen / ρ)i The mass energy absorption coefficient

Wi The fraction of that element

S TL signal

k Kilo

s Second

ºC Degree Celsius

pC PikoCoulomb

nC NanoCoulomb

an Weight fraction contribution

Zn The atomic number of the element-n

mg Milligram

F(d) Dose response at dose D

Do The response at the lowest dose

B TL background signal

The standard deviation

F The calibration factor

MV Megavoltz

MeV Mega electron voltz

keV Kilo electron voltz

R Regression coeffiecient

LIST OF ABBREVIATIONS

TLD Thermoluminescence dosimetry

TL Thermoluminescence

SEM Scanning electron microscope

LINAC Linear accelerator

MOS Metal oxide semiconductor

CRN Continuous random network

ODC Oxygen deficient centers

EPR Electron paramagnetic resonance

NBOHC Non bridging oxygen hole center

UV Ultra violet

POR Peroxy radical

STH Self-trapped hole

RE Rare earth

CT Computed tomography

PMMA Polymethylmethacrylate

SSD Source-surface distance

MU Monitor unit

PMT Photomultiplier tube

LIST OF APPENDICES

Appendix Title Page

A Dopant Concentration Calculation 97

B Effective Atomic Number, Zeff Calculation 99

C Minimum Detectable Dose 102

D Propagation Error 104

CHAPTER 1

INTRODUCTION

1.1 Research Background

In radiotherapy and radio diagnosis, in order to map dose in tissues, there exist a

need for highly sensitivity in vivo dosimetry systems of high spatial resolution,

commercially available thermoluminescence dosimeters (TLDs) being limited to a

capability of few millimeters. The spatial resolution and dynamic range required of a

dosimeter to accurately evaluate the radiotherapy dose distribution of such complex

three-dimensional geometries, especially at the micro spatial resolution scale, is

becoming more challenging. Major advantages in using optical fibers or optical fibers

sensors for radiation detection and monitoring are: real-time interrogation capabilities,

possibility to design spatially resolved solutions and in-vivo investigation (Sporea et al.

2012).

The foundation of thermoluminescence (TL) theory appear to be due to Randall

and Wilkins (1945) and by Garlick and Gibson (1948) (Mckeever et al. 1988),

providing expressions for the shape of a glow peak in terms of temperature, heating

rate, and the characteristic of the trap. LiF has been developed commercially by

Harshaw Chemical Company and made available as TLD 100, TLD 100H, TLD 600

and TLD 700 depending on the quantity of Li present. The Li concentration determines

how the element will respond to neutrons, and an activator is required for the material to

be thermoluminescent. The effective atomic number of LiF (Zeff = 8.04) is close enough

to the value of Zeff for tissue make it almost tissue equivalent.

Studies of potential radiation therapy applications of the optical fiber TL

dosimetric system have been undertaken by several groups. Since then, much research

has been carried out for a better understanding and improvement of the material

characteristics as well as to develop new TL materials. As stated by Espinosa et al.

(2006), that optical fibers could be very attractive for using in a variety of radiation

dosimetry applications due to its small size, flexibility, low cost and commercially

available. Abdulla et al. (2001) has carried out a TL study on commercially available

Ge-doped silica based fiber optic in the dose range from 1 to 120 Gy and has fast fading

rate (2% within 6 hours and 6% within 30 days).

Hashim et al. (2009) work was also based on commercially available Ge-doped

optical fiber and compared to aluminum doped optical fiber. The TL dosimeters were

exposed by a wide range of sources, from low energy photons to megavoltage, through

neutrons and charged particles. The results showed that Ge-doped optical fiber had

linear dose response until at least 4 Gy for 6 MV photons, and up to 3.5 Gy for 6, 9and

12 MeV electrons irradiation. A linear dose response was found for 2.5 MeV protons

irradiations.

Another study from Hashim et al. (2010) was done by using oxygen atoms as a

dope to pure SiO2 optical fibers by using ion implantation technique. The O2- , Ge- and

Al- doped optical fibers were exposed to 6 MV photons and separately to 6, 9 and 12

MeV electrons. The results show the superior TL response to be that of the Ge-doped

optical fibers followed by the O2-doped fibers and lastly Al-doped fibers.

Encouraging results from such studies have paved the way in development of

the fiber radiation dosimeters specifically TL dosimetric characterization and properties

such as the glow curves parameters, energy dependence, relative energy response and

dose rate effect.

In many TLD applications, the main purpose is to determine the dose absorbed

in human tissue. For this reason, it is desirable that the TLD has an energy response

equal to that human tissue. In composite materials, for photon interactions the atomic

number cannot be represented uniquely across the entire energy region, as in the case of

elements, by a single number known as effective atomic number, Zeff (Shivaramu et al.

2000). It is very useful in medical radiation dosimetry for the calculation of dose in

radiation therapy and medical imaging. TL materials with Zeff = 7.42 or near this

number are called tissue equivalent.

1.2 Objectives of the Research

The objectives of this study are:

a) To determine the Zeff of Ytterbium, Yb and Ytterbium-Terbium, Yb-Tb doped

SiO2 and compare them with Zeff of tissue and bone.

b) To determine the dose response (dose linearity and sensitivity) and energy

response and compare them with LiF: Mg, Ti.

c) To determine the fading, reproducibility and minimum detectable dose of Yb

and Yb-Tb doped SiO2 optical fiber.

1.3 Statement of the Problem

Among the wide choice of radiation dosimeters that can be used for application

in radiotherapy, brachytherapy, diagnosis radiology and radiation protection of the

patient, thermoluminescence dosimetry (TLD) now become the well-established

technique for radiation detection. But it also has several restrictions including being

hygroscopic and having relatively poor spatial resolution – up to few millimeters.

In in-vivo dosimetry, the radiotherapist faces problem to set the exposure in

real-time to ensure that the proper dose is delivered to the desired region. Because, it

only provides integrated dose information after some time of irradiation of patient.

Other limitations of TLD are poor dose reproducibility, limited dynamic range and

sensitivity and in certain cases nonlinear response. This study intended to investigate

the alternative dosimetric material base on SiO2 optical fiber as a TL dosimeter.

Recently, several research groups have started to use SiO2 optical fibers as a

radiation dosimeter to measure the absorbed dose by patients, in particular overcoming

the spatial resolution limitations of existing TL dosimeter system (Yaakob et al., 2011)

and for certain dopant and dopants concentrations, sufficient TL yield to serve the

associated sensitivity needs (Wagiran et al., 2012). However, the manufacturers did not

specify the amount of dopant added in the optical fiber. Therefore, in this research, the

concentration of dopant for Tb-Yb and Yb-doped SiO2 optical fiber will also be

determined.

In regard to the potential of Ytterbium, Yb and Ytterbium-Terbium, Yb-Tb

doped optical fiber for therapeutic dosimetry application, studies have been carried out

to investigate the TL response of this candidate dosimeter for various types of radiation

beam. It is important to investigate the possible linear dose response between the

absorbed dose and the TL intensity over a wide range of dose as well as the energy

response of the dosimeters.

1.4 Scope of the Research

This study may provide a basis for applying TL phenomena in several

dosimetric situations. Their general characteristics such as linearity, energy response,

reproducibility, fading, sensitivity and atomic effective number, may provide

information to introduce Yb-Tb and Yb-doped SiO2 optical fiber as a new TL material.

This dosimeter may be suitable for many types of application particularly in radiation

therapy.

The irradiation of the core of the optical fiber exposed at dose level ranging

from 0.5 – 4.0 Gy of X-ray irradiation using Primus MLC 3339 linear accelerator

machine (LINAC) at 6 and 10 MV X-ray beams and 1.0 – 10.0 Gy for 1.25 MeV

gamma rays using Cobalt-60. The determination of fading effect of Tb-Yb and Yb-

doped optical fiber has been done using 6 MV X-ray irradiation at 4.0 Gy. Readings of

TL yield are obtained on 30 days following the time of exposure, and the

reproducibility characteristic were examined using 6 MV X-ray with dose 4 Gy

produced by LINAC.

This study has also been carried out to determine dopant concentration and

effective atomic number, with Zeff for Tb-Yb and Yb-doped optical fiber using a

scanning electron microscope (SEM). By using SEM, the composition of the elements

present in the fiber and the effective atomic number was determined.

1.5 Significance of the Research

The ability to manufacture silica fibers of relatively small diameter provides the

possibility of producing a thermoluminescence dosimeter offering high spatial

resolution. It is a further expectation that such fibers will provide radiation

measurements close to that of an ideal Bragg-Grayy cavity. This is important in the

accurate evaluation of absorbed radiation dose, being a critical consideration for non-

tissue equivalent probes such as doped silica glass.

There are a lot of advantages of doped silica glass fiber dosimeters. For

example, unlike conventional TLDs, the fibers are impervious to water; it then becomes

possible to locate the fiber dosimeter within a particular tissue of interest. With the

flexibility of silica glass fibers, this further suggests the possible use of fibers in a

variety of vascular procedures that involve appreciable radiation doses, in particular, in

intra-coronary artery brachytherapy.

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THERMOLUMINESCENCE CHARACTERISTICS OF SILICON …eprints.utm.my/id/eprint/48926/25/MohdHilmiSahiniMFS2014.pdf · 11.19 and 12.27 respectively, which is higher than that of soft tissue