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84 5 Scintillator upgrade source of background. For more detailed studies about the background sources beside these in the scintillation detector, further studies with more simulated events and a better knowledge of the contamination levels are necessary.
Chapter 6 Summary and future work In this thesis possible scintillators for a COBRA upgrade were investigated. Emphasis was laid on inorganic crystal scintillators with high light yield, high stopping power, moderate price and low intrinsic background contamination. The scintillator materials NaI:Tl, CsI:Tl, BGO and CWO were short-listed. A Monte Carlo simulation and a price research helped to choose the optimal crystal size. CsI:Tl seemed to be the most promising choice and was studied further. A strong dependence of the scintillator energy resolution from the crystal dimensions, the readout area and the spectral matching of the scintillator emission spectrum and readout quantum efficiency required further studies. A second Monte Carlo simulation compared different readout devices and indicates, that a readout of CsI:Tl with APDs is possible for this crystal size. A COBRA upgrade with CsI:Tl was designed and implemented into the COBRA simulation framework VENOM. Monte Carlo studies of this upgrade demonstrated that CsI:Tl is not as suitable as anticipated for the COBRA experiment. The cosmogenic 134 Cs is expected to be the main background of CsI:Tl and reduces the detection efficiency for the neutrino accompanied transitions of 116 Cd into the first excited state by one order of magnitude. This prevents a direct detection of the 2νββ-decay of 116 Cd into the first excited state even for half-lives, being equal to the lower half-life limit. The background contribution was reduced by considering the position of involved CsI crystals, for events with one involved CZT and two involved CsI detector. A further background reduction for all events with more than two involved detectors, by considering the angle correlations between the detectors is expected. With the current simulation, this is only promising for events with multiple CZT hits, owing to the lager CsI crystal 85
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A DESIGN STUDY FOR A COBRA UPGRADE
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I hereby declare that I have create
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vi Abstract
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viii Überblick
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x Contents 4.1.2 Scintillation proc
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xii Contents
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2 1 Introduction The CdZnTe detecto
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4 2 Neutrino physics mass scales no
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6 2 Neutrino physics Ground states
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8 2 Neutrino physics mi: 〈mνe〉
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10 2 Neutrino physics
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12 3 The COBRA experiment CdZnTe (C
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14 3 The COBRA experiment 1420:480:
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16 3 The COBRA experiment Figure 3.
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18 3 The COBRA experiment They are
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20 3 The COBRA experiment Therefore
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22 4 Scintillation detectors search
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24 4 Scintillation detectors Figure
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26 4 Scintillation detectors spectr
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28 4 Scintillation detectors SCINTI
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30 4 Scintillation detectors emissi
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32 4 Scintillation detectors activa
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Page 64 and 65: 52 5 Scintillator upgrade ergy phys
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Page 98 and 99: 86 6 Summary and future work dimens
Page 100 and 101: 88 A FIRST APPENDIX Scintillator De
Page 102 and 103: 90 A FIRST APPENDIX A.2 Reports abo
Page 104 and 105: 92 A FIRST APPENDIX trons than a st
Page 106 and 107: 94 B SECOND APPENDIX Figure B.1: Am
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Page 116 and 117: 104 Bibliography [13] H. V. Klapdor
Page 118 and 119: 106 Bibliography [43] T. Y. Kim et
Page 120: Typeset September 29, 2010
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