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62 5 Scintillator upgrade vice. The length of the light guide depends on the number of devices and the readout size. A visualisation, using the visualisation system Heprep, is shown in fig. 5.3. With this developed Geant4 application, different aspects of the scintillation detector preparation were studied. DATA ANALYSIS Before starting the comparison between the readout devices, the influence of the housing finish, reflectivity and absorption length was studied. Therefore all 6 different kinds of housing finish were simulated with a PMT readout, covering the front faces of the crystal. The finish ”polished” yields highest amount of photo electrons. Ground, groundand polished-frontpainted yield around 75 % of the previous amount of photo electrons. The ground- and polished-backpainted finish only around 60 % of the photo electron yield, obtained with a polished surface. The influence of the surface finish on the uniformity of the signal for different source positions was not studied, but a higher uniformity of light collection for ground, than for polished surfaces is expected [29]. The further simulations were carried out with a ground surface finish and a reflectivity of 0.98. As main examination, the amount of photo electrons detected by different readout devices was evaluated. Therefore these 7 readout devices were simulated with different sizes of active area. In a first simulation, the readout devices covered the entire front facing crystal side, in another simulation, only commercially available sizes for the readout devices were taken into account. 10000 events with 662 keV photons were simulated and the amount of produced photo electrons was only recorded if the incident photon was completely absorbed. This was the case for about 5900 events. The mean values of the recorded photo electron number and the relative standard deviation for the different readout areas and quantum efficiencies are listed in table 5.5. RESULTS The crucial point of this simulation is the limited knowledge about the actual optical properties of individual crystals. This simulation can therefore give only an estimation of the expected numbers of detected photo electrons. Properties, like the optical absorption length, depend on the crystal quality and production process. The increase of the optical absorption length from 10 cm to 100 cm, improves the simulated amount of detected photons significantly by almost a factor of 10. This simulation is nevertheless useful for comparing the spectral matching and the influence of the size of different readout devices.
5.1 Monte Carlo studies for the upgrade design 63 kind of device size of out device number active area pe/keV σ/pe (%) PMT R6094 25 cm 2 4.05 2.07 PMT R5900 25 cm 2 4.50 1.99 PMT R669 25 cm 2 2.60 2.52 APD S8664-1010 1 cm 2 1.96 2.87 Si-PMT S10985-100C 0.36 cm 2 1.71 3.16 Si-PMT S10985-050C 0.36 cm 2 1.34 3.57 PIN S2744-08 4 cm 2 3.39 2.26 APD’ S8664-1010 25 cm 2 24.53 1.13 Si-PMT’ S10985-100C 25 cm 2 15.11 1.29 Si-PMT’ S10985-050C 25 cm 2 11.83 1.39 PIN’ S2744-08 25 cm 2 11.76 1.40 Table 5.5: Photo electron yield and relative standard deviation of the photo electron yield at 662 keV for quantum efficiencies of different readout devices. Different sizes of active areas were considered, by using size of one commercial device (A) and size of 25 cm 2 (A’). In table 5.5, it is shown, that semiconductor readout devices, especially the APD are superior to PMTs with the same active area. The APDs produce more photoelectrons than silicon PMTs and PIN diodes, due to a higher quantum efficiency than PIN diodes and a larger active area than Si-PMTs, which have dead layers between individual pixels. If only one commercially available readout device is attached to the crystal, the PMT, having by far the biggest active area, can detect more photo electrons than the other readout devices. This correlates with the relative variation of the amount of detected photo electrons, which has the main influence on the obtained energy resolution. The smallest relative variation of produced photo electrons have 25 cm 3 APDs with 1.13 % (RMS) and PMTs of about 2 % for commercial sizes. Single APD have a photo electron yield variation of 2.9 %, which is about one third more than the variation of PMTs. It can be seen, that PMTs with bialkali photo cathode still detect more photons than commercial APDs and Si-PMTs. The obtained photo electron yield variation considers the statistical variation of the production of optical photons, the variations of the col-
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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
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 64 and 65: 52 5 Scintillator upgrade ergy phys
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
Page 72 and 73: 60 5 Scintillator upgrade three dif
Page 76 and 77: 64 5 Scintillator upgrade lecting e
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
Page 114 and 115: 102 B SECOND APPENDIX
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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