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52 5 Scintillator upgrade ergy physics and nuclear experiments, medical, accelerator and space physics studies. The version geant4.9.2.p01, was used. It is available at http:// geant4.cern.ch/. ROOT is an object orientated programming framework, which provides tools and methods for data handling, analysis and plotting. It was developed at CERN and can be found at http://root.cern.ch. The ROOT version V5.20.00-sl5-x86 64.gcc4.1.2 was used during this thesis. 5.1 Monte Carlo studies for the upgrade design The aim of this thesis is to develop a design of a COBRA upgrade with a high detection efficiency for the decay of 116 Cd into the first excited state. Besides having a low intrinsic background, the scintillation detector should achieve a high detection efficiency and a good energy resolution, be compact in size and should have a moderate price. The number of possible scintillating materials was reduced in the previous chapter to NaI:Tl, CsI:Tl, BGO and CWO. This section evaluates the optimal crystal size, for these scintillators. Simulations with the application ”ScintBlock” determined the efficiency of different scintillator sizes for absorption of photons and are presented in 5.1.1—“Scintillator size”. Price researches for considered scintillator crystals are presented in 5.1.2—“Price research”. The high light yield of CsI:Tl, its easier handling compared to NaI:Tl and the good matching with the compact semiconductor read-outs favours this scintillation material. The section 5.1.3—“Electronic readout” determines the optimal readout device for CsI:Tl crystals, considering in the previous section determine crystals dimensions. The influence of the size of the active area and the quantum efficiency of the readout device were estimated with the simulation ”CsI”, considering the optical properties of the crystal. 5.1.1 Scintillator size Finding an affordable scintillation detector with adequate detection efficiency requires the consideration of different aspects. In favour of
5.1 Monte Carlo studies for the upgrade design 53 cost and the amount of needed shielding material, smaller scintillators would be preferable. Whereas, a good detection efficiency for gamma rays requires bigger scintillators. For finding an optimal size of NaI:Tl, CsI:Tl, BGO and CWO crystals, the absorption efficiency of different scintillator crystals for gamma rays was determined with the simulation ”ScintBlock”. GEANT4 APPLICATIONS ”SCINTBLOCK” The setup of this simulation consists of a volume of 2.5×2.5×5 m 3 filled with air. Within this, a cage of 2×2×4 m 3 containing nitrogen gas and, as default, a 1×1×1 m 3 CsI scintillator block is positioned. The user can change the size and the material of the target interactively via the commands /SB/det/setScintLength and /SB/det/setScintMat. The kind of the simulated particles and the physic processes are set in the PhysicsList class. All electromagnetic processes are defined for photons, charged leptons and charged hadrons. The primary kinematic consists of a single particle which hits the target perpendicular to the input face. The type of the particle and its energy are set in the PrimaryGeneratorAction class, and can be changed via the G4 build-in commands /gun/particle and /gun/energy of the ParticleGun class. As default a single 511 keV photon is initialised. SIMULATION AND DATA ANALYSIS Initially, a record of the number of the event (event ID), the number of the particle in the respective event (track ID), the kind of the particle (particle), the initial energy (Ei), the place of the interaction (x,y,z), the energy deposited in the scintillator (Edep), the kind of the interaction (process) and the amount of recorded steps (step) was printed for every step with an interaction in the scintillator volume. In order to understand the tracking of a particle, this detailed output was used to reconstruct samples of simulated events. An event of the simulation of a 500 keV gamma ray in NaI is shown in table 5.1. The initial photon is back-scattered and produces three Compton electrons (track ID 4, 3 and 2) before leaving the scintillator. This is recorded as transportation process (trans). The Compton electrons number 4 and 3 loose their energy by ionization processes (eIoni) and the electron number 2 emits Bremsstrahlung (eBrems) before being absorbed. The Bremsstrahlungs photon is absorbed by the photo effect (phot) and the produced photo electron (track ID 6) is stopped nearby. In total 840 simulations with different macros were started, changing the photon energy, the crystal material and the crystal size. For each simulation, the impact of 50000 monoenergetic photons (one after the
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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
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 32 and 33: 20 3 The COBRA experiment Therefore
Page 34 and 35: 22 4 Scintillation detectors search
Page 36 and 37: 24 4 Scintillation detectors Figure
Page 38 and 39: 26 4 Scintillation detectors spectr
Page 40 and 41: 28 4 Scintillation detectors SCINTI
Page 42 and 43: 30 4 Scintillation detectors emissi
Page 44 and 45: 32 4 Scintillation detectors activa
Page 46 and 47: 34 4 Scintillation detectors descri
Page 50 and 51: 38 4 Scintillation detectors group
Page 56 and 57: 44 4 Scintillation detectors AVALAN
Page 60 and 61: 48 4 Scintillation detectors gap. T
Page 62 and 63: 50 4 Scintillation detectors photoc
Page 66 and 67: 54 5 Scintillator upgrade event ID
Page 68 and 69: 56 5 Scintillator upgrade Ephoton (
Page 70 and 71: 58 5 Scintillator upgrade back side
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Page 74 and 75: 62 5 Scintillator upgrade vice. The
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Page 78 and 79: 66 5 Scintillator upgrade Figure 5.
Page 84 and 85: 72 5 Scintillator upgrade In 3.1 %
Page 86 and 87: 74 5 Scintillator upgrade were repo
Page 90 and 91: 78 5 Scintillator upgrade crystal p
Page 92 and 93: 80 5 Scintillator upgrade and gamma
Page 94 and 95: 82 5 Scintillator upgrade Backgroun
Page 96 and 97: 84 5 Scintillator upgrade source of
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
Page 108 and 109: 96 B SECOND APPENDIX Figure B.5: Am
Page 110 and 111: 98 B SECOND APPENDIX B.2 Geant4 Gea
Page 112 and 113: 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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