«William Geoffrey West A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Nuclear Engineering ...»
75. Nam, Y.-M. and Kim, J.-L. Thermoluminescence properties of LiF:Mg,Cu,Na,Si pellets in radiation dosimetry. Radiat. Prot. Dosim. 100, 467-470 (2002).
76. Tang, K. Dependence of thermoluminescence in LiF:Mg,Cu,Na,Si phosphor on Na dopant concentration and thermal treatment. Radiat. Meas. 37, 133-140 (2003).
77. Tang, K., Zhu, H., Shen, W. and Liu, B. A new high sensitivity thermoluminescent phosphor with low residual signal and good stability to heat treatment: LiF:Mg,Cu,Na,Si.
Radiat. Prot. Dosim. 100, 239-242 (2002).
78. West, W. G., Kearfott, K. J. and Kalchik, A. F. An affordable optically stimulated luminescent dosimeter reader utilizing multiple excitation wavelengths. (Ann Arbor, Michigan: The University of Michigan) (2011).
79. McKeever, S. W. S., Moscovitch, M. and Townsend, P. D. Thermoluminescence dosimetry materials: Properties and uses. (Ashford: Nuclear Technology Publishing) (1995) ISBN 1870965191.
80. Randall, J. T. and Wilkins, M. H. F. Phosphorescence and electron traps. I. The study of trap distributions. Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences. 184, 365-389 (1945).
81. Horowitz, Y. S. and Yossian, D. Computerised glow curve deconvolution:
Application to thermoluminescence dosimetry. Radiat. Prot. Dosim. 60(1995).
82. Harvey, J. A., Haverland, N. P. and Kearfott, K. J. Characterization of the glow peak
fading properties of six common thermoluminescent materials. (Ann Arbor, Michigan:
The University of Michigan) (2010).
83. Sidran, M. An infrared stimulable phosphor dosimeter with time lapse indication.
Applied Optics. 8, 79-84 (1969).
84. Furetta, C., Pani, R., Pellegrini, R. and Driscoll, C. M. H. A computational method to assess the time elapsed since exposure using thermoluminescence dosemeters. Radiation Effects. 88, 59-67 (1986).
85. Budzanowski, M., Vergara, J. C. S., Ryba, E., Bilski, P., Olko, P. and Waligorski, M.
P. R. Estimation of the time elapsed between exposure and readout using peak ratios of LiF:Mg, Cu, P (MCP-N, GR200A). Radiat. Prot. Dosim. 85, 149-152 (1999).
86. Spurny, Z. Simultaneous estimation of exposure and time elapsed since exposure using multipeaked thermoluminescent phosphors. Health Phys. 21, 755-761 (1971).
87. Nakajima, T. and Hashizume, T. On applicability of TL fading to estimation of time after irradiation. Health Phys. 16, 782-783 (1969).
88. Moscovitch, M. Automatic method for evaluating elapsed time between irradiation and readout in LiF-TLD. Radiat. Prot. Dosim. 17, 165-169 (1986).
89. Lakshmanan, A. R., Bhatt, B. C. and Bhatt, R. C. Simultaneous determination of dose and elapsed time after radiation exposure using CaSO4:Na,Dy. Radiat. Prot. Dosim. 27, 15-20 (1989).
91. Furetta, C., Tuyn, J. W. N., Louis, F., Azorin-Nieto, J., Gutiérrez, A. and Driscoll, C.
M. H. A method for determining simultaneously the dose and the elapsed time since irradiation using TLDs. International Journal of Radiation Applications and Instrumentation. Part A. Applied Radiation and Isotopes. 39, 59-69 (1988).
92. Weinstein, M., German, U., Dubinsky, S. and B. Alfassi, Z. On the determination of the post-irradiation time from the glow curve of TLD-100. Radiat. Prot. Dosim. 106, 121Blakemore, J. S. and Rahimi, S. Models for mid-gap centers in gallium arsenide.
(Elsevier) (1984) ISBN 0080-8784.
94. Grimmeiss, H. G. and Ledebo, L. A. Photo-ionization of deep impurity levels in semiconductors with non-parabolic bands. Journal of Physics C: Solid State Physics. 8, 2615 (1975).
95. Singarayer, J. S. and Bailey, R. M. Component-resolved bleaching spectra of quartz optically stimulated luminescence: Preliminary results and implications for dating.
Radiat. Meas. 38, 111-118 (2004).
96. Huntley, D. J., Short, M. A. and Dunphy, K. Deep traps in quartz and their use for optical dating. Canadian Journal of Physics. 74, 81-91 (1996).
97. Jaek, I., Kerikmae, K., Lust, A. Optically stimulated luminescence of some thermoluminescence detectors as an indicator of absorbed radiation dose. Radiat. Prot.
Dosim. 100, 459-462 (2002).
98. Pradhan, A. S. Emission spectra and influence of sunlight on thermoluminescence of dysprosium doped CaSO4 and CaF2. Radiat. Prot. Dosim. 47, 151-154 (1993).
The preceding papers detail a series of experiments ultimately conducted to analyze the OSL properties, using multiple excitation wavelengths, of a number of TL materials. Additionally, the effect of sunlight on the OSL response of α-Al2O3:C was explored in detail, and a novel and inexpensive OSL reader with unique capabilities was designed, built and found to be experimentally useful. Ultimately, the course of research detailed herein resulted in several significant observations, described below.
CaF2:Mn, Li2B4O7:Cu, LiF:Mg,Ti, CaSO4:Dy and CaSO4:Dy+P exhibited little to no OSL signal in the UV region, when using visible light stimulation. In the case of CaF2:Mn, CaSO4:Dy and CaSO4:Dy+P, additional research at higher excitation frequencies and/or with the capability to measure emission frequencies other than UV could reveal an OSL response. In the case of Li2B4O7:Cu and LiF:Mg,Ti, the evidence suggests that alternative OSL reader configurations would not result in a favorable OSL sensitivity.
CaSO4:Tm and KBr exhibited relatively modest but detectable OSL responses in the experiments. The presence of OSL signals resulting from different excitation light frequencies in these materials suggested that different electron traps were being accessed by the OSL reader in a manner analogous, and related, to the polling of traps at different temperatures in TL. While their luminance was significantly lower than that of
induced by the different excitation wavelengths. Specifically, the signals resulting from lower-energy stimulation appeared to decay more quickly at room temperature than those resulting from higher-energy stimulation. This behavior supports the correlation between OSL signals resulting from various excitation frequencies and TL peaks resulting from different temperatures. Further investigations at higher doses, using stronger or different-wavelength excitation light sources and/or collecting non-UV emission wavelengths is indicated to more precisely characterize and quantify these materials’ OSL behaviors.
LiF:Mg,Cu,Na,Si (KLT-300) and, to an even greater extent, LiF:Mg,Cu,Si, (New-KLT-300) exhibited significant OSL output in the UV range when exposed to visible light. The apparent OSL sensitivity of both materials, most especially LiF:Mg,Cu,Si, while less than that of α-Al2O3:C using the experimental setup, may ultimately meet or exceed the sensitivity of this commercially-used OSL dosimetry material, given improved experimental conditions. In addition, these materials, like CaSO4:Tm and KBr, also exhibited differences in the OSL signals’ decay time constants when using lower- versus higher-frequency light excitation. These differences corresponded in quality and approximate quantity to the trap structure demonstrated by TL measurements of these same materials.
The experiments described above provide substantial new information regarding the OSL properties of a number of substances. Based on these results, it was determined that a significant OSL response exists for CaSO4:Tm, LiF:Mg,Cu,Na,Si and LiF:Mg,Cu,Si. In addition, it was found that the fading rates of OSL signals over time
rates and the excitation wavelengths that correspond to them correlate well with the TL behavior of the materials. Further investigation into the OSL properties of CaSO4:Tm, LiF:Mg,Cu,Na,Si and LiF:Mg,Cu,Si is indicated by this research, and it is hoped that the initial work performed during the course of this dissertation may provide a foundation upon which other investigations may be built.
More generally, this dissertation highlights the substantial experimental resources and time required to partially characterize, from an OSL behavior standpoint, a very limited number of candidate materials. Future research in this area would benefit greatly from quicker and more efficient methods of identifying materials that may possess favorable OSL properties. The application of solid state band theory in predicting the energy level structure and recombination properties, as well as the use of recently-developed techniques in the area of computational solid state chemistry, may provide these methods. While much effort has been made in this area related to the development of advanced semiconductors for the electronics and computer industry, and textbooks in this area(1) may focus examples on such materials as gallium arsenide and silicon for that reason, these techniques could theoretically be applied in the radiation dosimetry space. Computational chemistry, in particular, has reached a maturity at which it may be possible for non-materials scientists to predict which materials and dopants will yield the luminescence properties that are desired, and to refine or optimize the existing materials being employed. Codes based on a quantum-mechanical approach to understanding solid state structure, such as the projector-augmented wave (PAW) method and the linearized muffin-tin orbital (LMTO) method, as well as statistical methods such
predict both optical absorption and luminescence properties(2). Each of these codes has its particular strengths and weaknesses and the ease of use varies amongst them. As such, while learning to use one or more of them properly and designing a search methodology to identify promising OSL compounds is not a trivial exercise, the long-term benefits to such an effort could be significant.
1. Singleton, J. Band theory and electronic properties of solids. (Oxford, United Kingdom: Oxford University Press) (2001).
2. Dronskowski, R. Computational chemistry of solid state materials. (Weinheim, Germany: Wiley-VCH) (2005) ISBN 978-3-527-31410-2.