ebook img

New halide scintillators for γ-ray detection Mikhail S. Alekhin PDF

143 Pages·2013·5.54 MB·English
Save to my drive
Quick download

Preview New halide scintillators for γ-ray detection Mikhail S. Alekhin

New halide scintillators for γ-ray detection Mikhail S. Alekhin New halide scintillators for gamma ray detection Proefschrift ter verkrijging van de graad van doctor aan de Technische Universiteit Delft, op gezag van de Rector Magnificus prof. ir. K.C.A.M. Luyben, voorzitter van het College voor Promoties, in het openbaar te verdedigen op 26 november 2013 om 15:00 uur door Mikhail Sergeevich ALEKHIN Master of Science in Physics, Lomonosov Moscow State University geboren te Podolsk, USSR Dit proefschrift is goedgekeurd door de promotor: Prof. dr. P. Dorenbos Samenstelling promotiecommissie: Rector Magnificus, voorzitter Prof. dr. P. Dorenbos Technische Universiteit Delft, promotor Prof. dr. E. H. Brück Technische Universiteit Delft Prof. dr. A. Meijerink Universiteit Utrecht Prof. dr. C. R. Ronda Universiteit Utrecht Prof. dr. L. D. A. Siebbeles Technische Universiteit Delft Prof. dr. C. W. E. van Eijk Technische Universiteit Delft Dr. K. W. Krämer Universität Bern, Zwitserland Prof. dr. H. T. Wolterbeek Technische Universiteit Delft, reservelid This research was financially supported by the Dutch Technology Foundation STW (project 07644 “The ultimate scintillator”). Cover design: Dmitry Kileynikov Printed by: Proefschriftmaken.nl | | Uitgeverij BOXPress ISBN: 978-90-8891-738-7 Table of contents List of acronyms and abbreviations iv Chapter 1 Introduction 1 Chapter 2 Scintillation materials 3 2.1 Scintillation mechanisms 3 2.1.1 Interaction of γ-rays with matter 3 2.1.2 Interaction of electrons with matter, thermalization and transport 4 2.1.3 Emission 5 2.1.4 Self-absorption of emission 6 2.2 Scintillator requirements 6 2.2.1 Light yield 7 2.2.2 Non-proportionality 7 2.2.3 Energy resolution 8 2.2.4 Decay time 9 2.2.5 Other requirements 9 2.3 Scintillation materials overview 10 2.4 Applications 11 2.4.1 High energy physics 11 2.4.2 Medical diagnostics 12 2.4.3 Space explorations 13 2.4.4 Scientific investigations in nuclear physics 13 2.5 Selection of the studied compounds 14 Chapter 3 Experimental Techniques 17 3.1 X-ray excited luminescence and thermoluminescence 17 3.2 VUV excitation and emission spectroscopy 18 3.3 Diffuse reflectance 19 3.4 Pulse-height measurements 19 3.4.1 Light yield 19 3.4.2 Non-proportionality of energy response 21 3.5 Scintillation time profiles 22 i Chapter 4 Improvement of LaBr :5%Ce scintillation properties by Li+, 3 Na+, Mg2+, Ca2+, Sr2+, and Ba2+ co-doping 25 4.1 Introduction 26 4.2 Crystal growth 26 4.3 Results and discussion 27 4.3.1 Proportionality improvement of LaBr :Ce and CeBr 27 3 3 4.3.2 Light yield and energy resolution of LaBr :Ce,Sr 29 3 4.3.3 Scintillation properties of LaBr :Ce co-doped with Li, Na, Mg, 3 Ca, Sr, and Ba 34 4.4 Summary and conclusion 40 Chapter 5 Optical properties and defect structure of Sr2+ co-doped LaBr :5%Ce scintillation crystals 43 3 5.1 Introduction 43 5.2 Crystal growth 44 5.3 Results 45 5.3.1 Optical properties 45 5.3.2 Time response 49 5.4 Discussion 52 5.4.1 Three different Ce3+ sites 52 5.4.2 Re-absorption of Ce3+ emission and its decay time 54 5.4.3 Point defects in LaBr :Ce,Sr 55 3 5.5 Conclusion 58 Chapter 6 Scintillation properties of and self-absorption in SrI :Eu2+ 61 2 6.1 Introduction 61 6.2 Crystal growth 62 6.3 Results 62 6.3.1 Excitation and emission spectra 62 6.3.2 Photoelectron yield 70 6.3.3 Decay time measurements 74 6.4 Discussion 76 6.5 Conclusion 81 Chapter 7 Self-absorption in SrI :2%Eu2+ between 78 K and 600 K 83 2 7.1 Introduction 83 7.2 Experimental methods 84 7.3 Results and discussions 85 7.3.1 Photoelectron yield studies 85 ii 7.3.2 Decay time studies 87 7.3.3 Probability of self-absorption 88 Chapter 8 Non-proportional response and energy resolution of pure SrI and SrI :5%Eu scintillators 91 2 2 8.1 Introduction 91 8.2 Experiment 92 8.3 Results 93 8.3.1 Scintillation non-proportionality to X-rays 94 8.3.2 Energy resolution of X-ray total absorption peaks 95 8.3.3 Scintillation non-proportionality to K-shell photoelectrons 98 8.4 Discussion 100 8.5 Conclusion 103 Chapter 9 Optical and scintillation properties of CsBa I :Eu2+ 105 2 5 9.1 Introduction 105 9.2 Crystal growth 106 9.3 Results 106 9.3.1 Excitation and emission spectra 106 9.3.2 Light yield and energy resolution 109 9.3.3 Decay time 113 9.4 Discussion 114 9.4.1 Optical properties 114 9.4.2 Light yield and energy resolution 116 9.4.3 Decay time and probability of self-absorption 117 9.5 Summary and conclusion 119 Summary 121 Samenvatting 125 Acknowledgements 129 Curriculum Vitae 131 List of publications 133 iii List of acronyms and abbreviations a Probability of Self-absorption η Quantum Efficiency APD Avalanche Photo Diode Bq Becquerel CB Conduction Band CT Computed Tomography e Electron FWHM Full Width at Half Maximum h Hole HPGe High Purity Germanium Detector LHC Large Hadron Collider LY Light Yield NPMT Number of photoelectrons produced in photo multiplier tube phe nPR Non-proportional Response ph Photon phe Photoelectron PMT Photo Multiplier Tube R Energy Resolution SiPM Silicon Photo Multiplier SLYNCI Scintillator Light Yield Non-proportionality Characterization Instrument SPECT Single-Photon Emission Computed Tomography SSL Steady-State X-ray Excited Luminescence STE Self Trapped Exciton TE Trapped Exciton ToF PET Time-of-Flight Positron Emission Tomography UV Ultraviolet VUV Vacuum Ultraviolet VB Valence Band XRD X-ray Diffraction iv Chapter 1 Introduction A scintillator is a material that converts the energy of an ionizing particle into a flash of light. Scintillation materials are used for the detection of ionizing particles and measurement of their types and energies. The position of an interaction between an ionizing particle and a scintillator and the moment of this interaction can also be determined. ee ee ee Conduction band ee ee γ photon Forbidden gap phonon hh hh hh Valence band hh hh Fig. 1. Schematic of the scintillation mechanism. A typical inorganic scintillator is an insulator with 4-12 eV gap between the top of the valence band (VB) and the bottom of the conduction band (CB), the so called forbidden gap, see Fig. 1. In the VB, all electrons (e) are bound to atoms. When excited into the CB, electrons leave holes (h) in the VB. Both electrons in the CB and holes in the VB can move freely within the crystal. The general idea of a scintillation material is to find an effective way to recombine all the excited electrons in the CB with the holes in the VB via a photon emission. For this, one requires efficient e-h transport to efficient luminescence centers. In 1895, Wilhelm Röntgen discovered X-ray radiation by observing a faint glow from barium platinocyanide. Visual scintillation counting was introduced by Crookes and Regener in 1908 [1]. The photomultiplier was applied to scintillation counting by Curran and Baker in 1944 [1, 2]. An intensive search for scintillation materials started after the discovery of NaI:Tl by Robert Hofstadter in late 1940s [3]. Tens of compounds have been discovered and successfully applied since then. New halide scintillators for gamma ray detection 2013 - M. S. Alekhin Chapter 1 Today, the search for new scintillation materials is a separate scientific branch with numerous institutes and industries involved. Scintillator research is driven by the ever- increasing requirements for more advanced applications. Among them are medical diagnostics, high energy physics, space exploration, oil well logging, and different scientific investigations. There are various types of scintillation materials: inorganic single crystals, ceramic, plastic, liquid, and organic scintillators. Single crystal inorganic scintillators are the most efficient and wide-spread ones, and are the subject of this thesis. Thesis outline: chapter 2 of this thesis reviews all the steps of scintillation mechanisms, from interaction of γ-rays and high energy electrons with matter to emission from luminescence centers and its self-absorption. Several well-known compounds, applications, and application requirements are discussed. The choice of the studied materials is motivated. Chapter 3 explains the principles of the experimental techniques used. Chapters 4-9 are devoted to the studied compounds. In chapter 4, a new outstanding LaBr :5%Ce,Sr scintillator is presented. Its energy resolution, γ-ray 3 and electron response proportionality are considerably improved as compared to standard LaBr :5%Ce. The effects of Li+, Na+, Mg2+, Ca2+, Sr2+, and Ba2+ co-dopants 3 on light yield, energy resolution, proportionality, decay time, and charge carrier trap creation of LaBr :Ce are also discussed. In chapter 5, attention is paid to the optical 3 properties and lattice point defects of LaBr :Ce,Sr. Three different Ce3+ sites are 3 revealed and their possible origins are discussed. Chapter 6 deals with scintillation properties and self-absorption in SrI :Eu. Temperature, sample size and Eu 2 concentration appear to strongly affect the emission spectrum, decay time and light yield of SrI :Eu. A model of self-absorption is introduced to explain this behavior. In 2 chapter 7, the scintillation properties and probability of self-absorption in SrI :2%Eu 2 are compared to those of SrI :5%Eu. Studies of non-proportionality of pure SrI and 2 2 SrI :5%Eu at temperatures between 80 K and 600 K gain attention in Chapter 8. 2 Chapter 9 is devoted to the optical and scintillation properties of CsBa I :Eu, which 2 5 appears to have similar amount of self-absorption as SrI :Eu. Finally, the thesis is 2 summarized. References: [1] J. B. Birks, The theory and practice of scintillation counting, Macmillan, New York, 1964. [2] S. C. Curran and W. R. Baker, Rev Sci Instrum 19 (1948) 116. [3] R. Hofstadter, Phys Rev 75 (1949) 796. 2

Page 1. New halide scintillators for γ-ray detection. Mikhail S. Alekhin. Page 2. Page 3. New halide scintillators for gamma ray detection. Proefschrift.
See more

The list of books you might like

Upgrade Premium
Most books are stored in the elastic cloud where traffic is expensive. For this reason, we have a limit on daily download.