Preface

      The detection of ionizing radiation using luminescence methods has been at the forefront of radiation research ever since the earliest discoveries of radiation, radioactivity, and the structure of the atom. The list of pioneering names in the discovery of radiation is lengthy and impressive – Wilhelm Roentgen, Edmond and Henri Becquerel, Ernest Rutherford, Marie Curie, James Chadwick, and numerous others. Many of these pioneers used luminescence of one type or form in their studies, including (using the modern names) phosphorescence, thermoluminescence, and optically stimulated luminescence. Today’s researchers use these techniques and others related to them in a wide range of radiation detection and measurement applications, including personal, environmental, medical, and space dosimetry, and embrace both very low as well as very high radiation dose regimes.

      The genesis of this book is a course, given by the author, to graduate students at Oklahoma State University. The intended readers are graduate students (and undergraduate students who are performing research in these areas), and other beginning researchers in this field of study (e.g., postdoctoral fellows and new researchers entering the field). More experienced researchers may also find the book helpful to refresh their conceptual understanding of the topics. The benefit to the reader will be to see how the techniques relate in a holistic manner and to see how the fundamental processes that describe the phenomena can be used to explain many different experimental characteristics.

      To new researchers entering the field, the array of measurement and data analysis techniques can be bewildering. Experimental collection of the data may seem simple on first introduction, but useful and reliable analysis requires attention to small details and knowledge of fundamental principles, along with very careful experimental technique. A phrase I often used with my students was that they will spend most of their time learning how to do the experiment properly before they have a reliable data set for analysis. And then what of that analysis? How should they interpret the results that they obtain? What is the best analytical approach, and why?

      What this book is: This book presents a course of instruction for beginning students, or for more-experienced researchers new to the field, into three of the main and currently used luminescence phenomena in radiation dosimetry, namely, thermoluminescence (TL), optically stimulated luminescence (OSL), and radiophotoluminescence (RPL). The book outlines the theoretical background of each technique and stresses the connections between them. In doing so, the book treats luminescence techniques for radiation dosimetry holistically, beginning with the basic concepts and showing how the three techniques are related within the processes of energy storage, charge transfer, and defect interactions.

The book emphasizes pedagogy rather than the latest research. State-of-the-art research is included only if it demonstrates a principle or opens new insight into physical mechanisms. Thus, the primary purpose of the book is to teach beginning researchers in the field about the three techniques, their similarities and distinctions, and their applications. The intent is to provide the reader with the building blocks with which they can examine the latest research and have a sufficient understanding of it to enable them to raise questions and conceive future research programs to answer those questions.

      A note on the Exercises: To emphasize the book as a teaching tool, several substantial Exercises are introduced at various points in the book for the reader to test their understanding of the subject matter being discussed. These include derivations of important relationships, or numerical simulations, or solutions to differential equations, etc., in order to demonstrate the various processes. Some are prescriptive, but others are open ended, requiring the reader to draw their own conclusions from the results of the Exercises. The Exercises also include analysis of real experimental data. For this purpose, the book has a companion website where the reader will find some original data sets (TL, OSL, RPL) that may be used by the reader to analyse using the material learned from the book. New data and new problems may be introduced via the web site in the future and in this way the book will be updated and refreshed for future students. In this sense, the author hopes that the book will serve as a “living” teaching tool.

      Although it is recommended that the Exercises be worked one by one in the order given, the reader may wish to skip some of the Exercises if they do not align strongly with the reader’s own research interests. Many of them are lengthy. While most are designed for the individual reader, supervisors and advisors may decide that some may be better solved as group exercises, perhaps as part of a tutorial. Some may even form the basis of internal research projects and reports.

      What this book is not: Firstly, the book is not a course in radiation dosimetry. That topic is adequately covered in many excellent existing textbooks.

      Secondly, the book is not an updated summary of the latest research on luminescence dosimetry. It is not a review. Several books exist on the topics of TL, OSL, and (to a much lesser extent) RPL. Each, by and large, is a summary of the latest research and newest developments and applications of the techniques (at the times that the books were written) and generally deal with the chosen topic (i.e. TL, OSL, or RPL) in isolation. For example, several texts exist on TL and related thermally stimulated processes, introducing the standard energy band diagrams and kinetic equations, analysis of TL glow curves, and subsequent applications. One can also identify similar texts on OSL. (Only one text, of which this author is aware, deals with RPL.) Rarely, however, do the published books relate one technique to another, except in passing. This is especially true of RPL and its relationship to TL and/or OSL.

      Nor does the book present a list of references to all the latest research or pivotal developments. The original material is for the reader to find in independent study. Only when the author has judged that additional reading would be useful, or that the meaning requires more explanation, are references to the original literature included. Readers who wish to avail themselves of the latest research are advised to refer to the proceedings of relevant conferences in the field and to original, peer-reviewed literature. The author hopes that this book will assist in an understanding of the material readers find in those publications.

To achieve the goals outlined above, the book is constructed in two parts. Part I deals with theory, models, and kinetics. It can be considered as a “tool-box” into which the reader can delve to help form an understanding of the underlying principles which govern luminescence phenomena. In the same way that a designer of a new aircraft or of a sophisticated automobile will need an understanding of the basic principles of mechanics, materials, and aerodynamics, so too should the budding researcher into luminescence dosimetry have at hand a similar understanding of the basics of electronic processes in solids, particularly the kinetics of charge generation and storage, stimulation, and recombination. Armed with this “tool-box” the reader can more fully appreciate the experimental phenomena described in Part II.

Part II discusses several real examples of the fundamentals outlined in Part I. The intent is to illustrate how the principles developed in Part I have been used in experiments to measure, understand, and exploit the properties of luminescence materials, especially as they relate to radiation dosimetry. To learn from the wisdom of Albert Einstein, knowing the luminescence properties of a material is one thing, but real progress is made only when we understand them. The author’s hope is that the reader can use the items in the “tool-box” and apply them to the properties of real materials in order to gain that understanding, and perhaps lead to greater creativity and innovation. As a caveat, however, the reader may be wise to recall the words of Prussian Field Marshal Helmuth von Moltke, which the author paraphrases as few theories survive first contact with an experiment.