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20 3 The COBRA experiment Therefore, a suitable scintillator material has to be found. For this thesis it is necessary to get an overview of the available scintillation detectors, the commercial prices and their properties, making them more or less suitable for this experiment. This is discussed in chapter 4—“Scintillation detectors”. The steps of developing the design for the upgrade are described in chapter 5—“Scintillator upgrade”. Further on, the gain of the planned upgrade was determined with Monte Carlo studies of the 2νββ decay of 116 Cd into the first excited state.
Chapter 4 Scintillation detectors Scintillation detectors consist of a scintillating material and a readout device, detecting the emitted scintillation light. This scintillation light is a radiation induced luminescence, emitted by dielectric materials. The process, which leads to the emission of scintillation light, consists thereby of a chain of processes, which depend on the atomic, molecular or crystalline properties of the scintillator [26]. Scintillating materials have been used for radiation detection since the beginning of the 20th century. The first application was a zinc sulfide screen, viewed with the naked eye to detect α-particles, developed by Crookes in 1903. The beginning of the modern scintillation detector was the invention of the photomultiplier tube (PMT). In 1944, four decades after the first visual scintillation counter, Curran and Baker detected the scintillation light of a ZnS screen with a PMT connected to an oscilloscope. With such an assembly Blau and Dryfus showed that the PMT current varies with the radiation intensity, making the use as dosimeter possible. Thereafter the search for scintillating materials developed rapidly. In 1947 Browser and Kallman studied the scintillation light produced by α-, β- and γ-rays in various materials like ZnS, CaWO4, ZnSO4 and naphthalene, which was the first organic and large volume scintillator. The good scintillation properties of thallium doped NaI was discovered by Hofstadter in 1948. The development of many scintillators followed quickly and is still ongoing [27, 28]. Today, scintillators are used in a broad field of applications. They are established in the fundamental research of particle and nuclear physics such as high energy physics (BaBar - CsI calorimeters), Dark Matter 21
Page 1 and 2: A DESIGN STUDY FOR A COBRA UPGRADE
Page 3: I hereby declare that I have create
Page 6 and 7: vi Abstract
Page 8 and 9: viii Überblick
Page 10 and 11: x Contents 4.1.2 Scintillation proc
Page 12 and 13: xii Contents
Page 14 and 15: 2 1 Introduction The CdZnTe detecto
Page 16 and 17: 4 2 Neutrino physics mass scales no
Page 18 and 19: 6 2 Neutrino physics Ground states
Page 20 and 21: 8 2 Neutrino physics mi: 〈mνe〉
Page 22 and 23: 10 2 Neutrino physics
Page 24 and 25: 12 3 The COBRA experiment CdZnTe (C
Page 26 and 27: 14 3 The COBRA experiment 1420:480:
Page 28 and 29: 16 3 The COBRA experiment Figure 3.
Page 30 and 31: 18 3 The COBRA experiment They are
Page 34 and 35: 22 4 Scintillation detectors search
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Page 40 and 41: 28 4 Scintillation detectors SCINTI
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70 5 Scintillator upgrade Figure 5.
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72 5 Scintillator upgrade In 3.1 %
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76 5 Scintillator upgrade Figure 5.
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78 5 Scintillator upgrade crystal p
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80 5 Scintillator upgrade and gamma
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82 5 Scintillator upgrade Backgroun
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84 5 Scintillator upgrade source of
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86 6 Summary and future work dimens
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88 A FIRST APPENDIX Scintillator De
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90 A FIRST APPENDIX A.2 Reports abo
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92 A FIRST APPENDIX trons than a st
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94 B SECOND APPENDIX Figure B.1: Am
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96 B SECOND APPENDIX Figure B.5: Am
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98 B SECOND APPENDIX B.2 Geant4 Gea
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100 B SECOND APPENDIX Cube, scint64
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102 B SECOND APPENDIX
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104 Bibliography [13] H. V. Klapdor
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106 Bibliography [43] T. Y. Kim et
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Typeset September 29, 2010
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