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«William Geoffrey West A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Nuclear Engineering ...»

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Investigations into the Optically Stimulated Luminescence Response of

Various Materials

by

William Geoffrey West

A dissertation submitted in partial fulfillment

of the requirements for the degree of

Doctor of Philosophy

(Nuclear Engineering and Radiological Sciences)

in the University of Michigan

2011

Doctoral Committee:

Professor Kimberlee J. Kearfott, Chair

Professor Rodney C. Ewing

Professor Ronald M. Gilgenbach

Professor Zhong He

Joseph A. Miklos © William Geoffrey West 2011 For Dad ii

ACKNOWLEDGEMENTS

I would like to thank my mother, Margie, for never letting me give up and always believing in me.

Sincere thanks also to my advisor, Professor Kimberlee Kearfott, for keeping me out of law school and reminding me of why I became a scientist in the first place.

Additional thanks also to those individuals that helped this research along the way:

Andrew Kalchik and Sara Bernal, my dedicated lab partners, for many long nights of work; Dr. Benjamin Warner and David Morris of Los Alamos National Laboratory for helping me to better understand radiation dosimetry and optics; and Dr. David Jordan for his help with all thing electrical and for mentoring me while I mentored him. A special thanks to Peggy Gramer, for always lending an ear and wise counsel when times were tough.

Finally, I want to thank my wife, Jennifer, for pushing me to finish what I started and for betting the farm on me.

iii

PREFACE

In the summer of 2002, as the world – and the United States in particular – were still adjusting to a world in which the threat of nuclear terrorism appeared to have increased dramatically, I was busy preparing to leave my job as a medical physicist and enter law and business school (to attain a JD/MBA) at the University of Michigan. This was a career change that I had been planning for many years and I had only to sign the acceptance papers and arrange my move. As I contemplated my new career direction, I received a remarkably timely phone call from Professor Kimberlee Kearfott, who had been my Master’s degree advisor several years prior. She mentioned that there was a project forming around the idea of using optically stimulated luminescence (OSL) techniques to improve our ability to detect illicit radiological materials, and that she thought that I might be interested. I told her that I had other plans in the works, but to tell me more since it sounded intriguing.

Over the course of an hour-long conversation, we discussed the importance of this type of work, the technical challenges, and the opportunities. Though the University of Michigan had a long history of groundbreaking research in the area of thermoluminescence dosimetry, OSL technology was relatively new and this area of scientific inquiry had not yet been explored at this institution. However, we both believed that if suitable materials could be indentified and techniques developed, it would permit a greater degree of ease and sophistication in extracting dose information from a

–  –  –

that it was important to make every attempt to advance the state of knowledge in this field and that a significant need existed in analyzing materials for potential use in OSL applications that had never been evaluated before.

By the end of this phone call, I had decided to change my plans for law and business school and pursue a Ph.D. instead. I wanted to do something that would, in some small way, advanced the science of radiation detection and characterization; and perhaps lead to additional research and/or applications that would improve the safety and security of every peace-loving person on our planet.

This dissertation is the final product of my research. It documents a series of initial experiments undertaken to learn optimal OSL techniques and to produce novel information regarding basic OSL properties of numerous materials; details the design, construction and testing of a custom OSL reader; and reveals the results of a set of final experiments intended to more fully characterize the OSL behavior, including fading properties, of a set of promising materials.

I hope you, the reader, find value in its contents.

–  –  –

DEDICATION

ACKNOWLEDGEMENTS

PREFACE

LIST OF FIGURES

LIST OF TABLES

CHAPTER 1: Introduction

CHAPTER 2: The Sunlight OSL Response of a Commercially Available α-Al2O3:C

Personnel Dosimetry Material

CHAPTER 3: The Optically Stimulated Luminescence of Various Known Thermoluminescent Materials

CHAPTER 4: An Affordable Optically Stimulated Luminescent Dosimeter Reader Utilizing Multiple Excitation Wavelengths

CHAPTER 5: OSL Investigation of KBr, CaSO4:Tm, CaSO4:Dy, CaSO4:Dy+P, LiF:Mg,Cu,Na,Si and LiF:Mg,Cu,Si

CHAPTER 6: Conclusions

–  –  –

Figure

1.1 Thermoluminescence (TL) glow curve for LiF:Mg,Cu,Na,Si 6 h after irradiation to 500 mGy with a 120 kVp x-ray beam.

1.2 Energy-level diagram showing the possible optical absorption transitions in a semiconductor..

1.3 Photo-ionization cross-section versus incident photon energy as predicted by the Lucovsky theoretical model.





1.4 Graphical depiction of the continuous-wave optically stimulated luminescence (CW-OSL), linearly-modulated OSL (LM-OSL) and pulsed OSL (POSL) readout techniques, shown from top to bottom

2.1 OSL response of a-Al2O3:C samples exposed to varying durations of direct sunlight…………

2.2 Peak OSL signal of a-Al2O3:C in units of equivalent dose versus total direct sunlight exposure.

2.3 OSL response of a-Al2O3:C samples exposed to varying durations of direct sunlight after receiving a 15 mGy beta dose.

2.4 Peak OSL signal of a-Al2O3:C versus duration of 100,000 lux direct sunlight exposure..37  

2.5 Solar radiation spectrum for direct light at both the top of the Earth’s atmosphere and at sea level

3.1 Optically stimulated luminescence (OSL) response during infrared light (λ = 830 nm) stimulation of unirradiated samples

3.2 Optically stimulated luminescence (OSL) response during blue light (λ = 470 nm) stimulation of unirradiated samples

3.3 Optically stimulated luminescence (OSL) response during infrared light (λ = 830 nm) stimulation of samples irradiated to 15 mGy.

3.4 Optically stimulated luminescence (OSL) response during blue light (λ = 470 nm) stimulation of samples irradiated to 15 mGy.

3.5 Optically stimulated luminescence (OSL) response during infrared light (λ = 830 nm) stimulation of samples irradiated to 1.5 Gy

3.6 Optically stimulated luminescence (OSL) response during blue light (λ = 470 nm) stimulation of samples irradiated to 1.5 Gy

3.7 Optically stimulated luminescence (OSL) peak signal height versus dose for CaSO4:Tm.

4.1 Basic layout of the optically stimulated luminescence (OSL) reader.............. 77 vii

4.2 Light emitting diode (LED) source assembly and iris plate with iris.............. 81   4.3 ‘Exploded view’ of the main optically stimulated luminescence (OSL) reader components..

4.4 Rendering of the optically stimulated luminescence (OSL) reader emission filter housing.

4.5 Rendering of the optically stimulated luminescence (OSL) reader sample holder assembly.

4.6 Circuit diagram of the excitation power supply.

4.7 Circuit diagram of the cooling fan/vacuum pump control system…………………………………………………………………………...……..98

4.8 Photograph of the optically stimulated luminescence (OSL) reader case when closed……………….

4.9 Screenshot of the optically stimulated luminescence (OSL) reader software interface………

4.10 Block diagram of the optically stimulated luminescence (OSL) reader software interface…

4.11 Circuit diagram of the photomultiplier tube (PMT) gating circuit................. 107  

4.12 Graph showing the results of the single channel analyzer (SCA) setup testing…….

4.13 Graph showing the results of the iris position optimization testing................ 112  

4.14 Optically stimulated luminescence (OSL) output graph from the OSL reader for samples of Luxel™ irradiated to 250 mGy and 500 mGy using Cs-137 gamma rays……...

5.1 Corrected optically stimulated luminescence (OSL) curves for KBr irradiated to 500 mGy dose in air using 120 kVp x-rays, at 6 h post-irradiation.

5.2 Corrected peak signal (CPS) curves for KBr irradiated to 500 mGy dose in air using 120 kVp x-rays.

5.3 Peak signal minus end signal (P-E) curves for KBr irradiated to 500 mGy dose in air using 120 kVp x-rays

5.4 Ratio of peak optically stimulated luminescence (OSL) signal minus end signal (P-E) values for KBr under red light excitation (λ = 625 nm) versus green light excitation (λ = 530 nm)

5.5 Thermoluminescence (TL) glow curves for KBr powder irradiated to 500 mGy dose in air using 120 kVp x-rays.

5.6 Corrected optically stimulated luminescence (OSL) curves for CaSO4:Tm irradiated to 500 mGy dose in air using 120 kVp x-rays, at 6 hours post-irradiation.... 147  

5.7 Corrected average signal (CAS) curves for CaSO4:Tm irradiated to 500 mGy dose in air using 120 kVp x-rays.

5.8 Corrected peak signal (CPS) curves for CaSO4:Tm irradiated to 500 mGy dose in air using 120 kVp x-rays

5.9 Corrected average signal (CAS) output ratios for CaSO4:Tm irradiated to 500 mGy dose in air using 120 kVp x-rays, as a function of time elapsed since irradiation. 149  

5.10 Thermoluminescence (TL) glow curves for CaSO4:Tm irradiated to 500 mGy dose in air using 120 kVp x-rays.

5.11 Corrected optically stimulated luminescence (OSL) curves for CaSO4:Dy irradiated to 500 mGy dose in air using 120 kVp x-rays, at 6 hours post-irradiation.... 151   viii

5.12 Peak signal minus end signal (P-E) curves for CaSO4:Dy irradiated to 500 mGy dose in air using 120 kVp x-rays.

5.13 Thermoluminescence (TL) glow curves for CaSO4:Dy irradiated to 500 mGy dose in air using 120 kVp x-rays.

5.14 Corrected optically stimulated luminescence (OSL) curves for CaSO4:Dy+P irradiated to 500 mGy dose in air using 120 kVp x-rays, at 6 hours post-irradiation.... 153  

5.15 Thermoluminescence (TL) glow curves for CaSO4:Dy+P irradiated to 500 mGy dose in air using 120 kVp x-rays.

5.16 Corrected optically stimulated luminescence (OSL) curves for LiF:Mg,Cu,Na,Si irradiated to 500 mGy dose in air using 120 kVp x-rays, at 6 hours post-irradiation.

5.17 Corrected average signal (CAS) curves for LiF:Mg,Cu,Na,Si irradiated to 500 mGy dose in air using 120 kVp x-rays.

5.18 Corrected peak signal (CPS) curves for LiF:Mg,Cu,Na,Si irradiated to 500 mGy dose in air using 120 kVp x-rays.

5.19 Corrected average signal (CAS) output ratios for LiF:Mg,Cu,Na,Si irradiated to 500 mGy dose in air using 120 kVp x-rays.

5.20 Afterglow optically stimulated luminescence (OSL) curves for LiF:Mg,Cu,Na,Si irradiated to 500 mGy dose in air using 120 kVp x-rays, at 6 hours post-irradiation.

5.21 Thermoluminescence (TL) glow curves for LiF:Mg,Cu,Na,Si irradiated to 500 mGy dose in air using 120 kVp x-rays.

5.22 Corrected average signal (CAS) curves for LiF:Mg,Cu,Na,Si, irradiated to 500 mGy dose in air using 120 kVp x-rays, with only green, cyan, blue and royal blue curves shown……

5.23 Corrected optically stimulated luminescence (OSL) curves for LiF:Mg,Cu,Si irradiated to 500 mGy dose in air using 120 kVp x-rays, at 6 hours post-irradiation.... 161  

5.24 Corrected optically stimulated luminescence (OSL) curves for LiF:Mg,Cu,Si, irradiated to 500 mGy dose in air using 120 kVp x-rays, at 30 days post-irradiation.... 162  

5.25 Corrected average signal (CAS) curves for LiF:Mg,Cu,Si irradiated to 500 mGy dose in air using 120 kVp x-rays.

5.26 Afterglow optically stimulated luminescence (OSL) curves for LiF:Mg,Cu,Si irradiated to 500 mGy dose in air using 120 kVp x-rays, at 5 days post-irradiation...... 164  

5.27 Total integrated optically stimulated luminescence (OSL) afterglow signal for LiF:Mg,Cu,Si irradiated to 500 mGy dose in air using 120 kVp x-rays, as a function of time since irradiation

5.28 Ratio of LiF:Mg,Cu,Si integrated optically stimulated luminescence (OSL) afterglow signals for green, cyan and blue light excitation relative to royal blue light excitation, as a function of time since irradiation.

5.29 Thermoluminescence (TL) glow curves for LiF:Mg,Cu,Si irradiated to 500 mGy dose in air using 120 kVp x-rays.

–  –  –

Table

3.1 Thermal annealing parameters used for material samples.……….…..………51

4.1 Light emitting diode (LED) emission specifications.

4.2 Digital acquisition (DAQ) board digital channel assignments

–  –  –

Optically stimulated luminescence (OSL) dosimetry relies upon the illumination of an irradiated sample with light to produce a stimulated emission of light proportional to the radiation dose which previously caused trapping of electrons in the material(1).



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