a design study for a cobra upgrade to - Institut für Kern- und ...

More documents

Recommendations

Info

16 3 The COBRA experiment Figure 3.1: Current COBRA prototype set-up at the LNGS, with neutron shield, Faraday cage, lead and copper shield and CZT inside a copper case, called Nest [19]. protons and are subsequently captured by 10 B(n, α) 7 Li reactions [21]. Faraday cage: The Faraday cage is a 2×1×1 m 3 copper box, inside the neutron shield. It is hosting the further shielding assembly and the charge sensitive preamplifier outside the lead shield. It was constructed, to minimize the Rn concentration of the inner set-up, but is not working satisfying and will be improved in the future. Lead and copper shield: The inner set-up is hosted in the Faraday cage, surrounded by 10 cm of copper and a 20 cm lead layer. Lead, with its high density of about 11 g/cm 3 and its large atomic number Z of 82, is well qualified for the absorption of high energetic gammas. It also has a low cross section for thermal neutron capture and cosmogenic interaction, but contains the radioisotope 210 Pb. Commercial lead can be acquired in different low activity qualities with for instance 40 or minimal 3 Bq/kg [11]. Copper, having a lower Z and density compared to lead, is less suitable for the shielding, but is also less likely to be contami-
3.2 Background shielding 17 nated with primordial nuclei. Therefore, it is used as an additional layer, shielding the decay products emitted by 210 Pb and its daughter nuclides 210 Bi and 210 Po in the lead layer. Although copper can be produced by electrolyse with a low U and Th contamination, it has a rather high cross section for thermal neutron capture and for the cosmogenic production of radioactive isotopes like 60 Co. Accordingly, the exposure of copper, used in a low level experiment, at the earth surface should be minimised. Nest: The inner set-up is a 10×10×10 cm 3 copper case, called Nest, where 64 CZT crystals can be installed. These are arranged in a 4×4×4 array, by mounting 16 crystal on each of four delrin holders. This is shown on the right side of figure 3.2. Five Teflon tubes feed into the central copper casing, being used for flushing the Nest with nitrogen in order to reduce the radon concentration in the inner set-up. Additionally, wire mounted calibration sources can be fed through these tubes into the inner Nest, enabling frequent energy calibration without opening the shielding structure. The COBRA prototype set-up uses CZT crystals, supplied by eV- Microelectronics (former eV-Products), with dimensions of about 1×1×1 cm 3 and a mass of ≈6.5 g. These CZT crystals have low radioactive contamination [22] of: 40 K: A < 3.7 mBq/kg 238 U: A < 7.3 mBq/kg 232 Th: A < 2.2 mBq/kg Figure 3.2: a) CZT detector with colourless passivation and coplanar grid anode [23]. b) Inner copper case (Nest), containing 64 CdZnTe detectors on four Delrin holders [19].
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 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 74 and 75: 62 5 Scintillator upgrade vice. The
Page 76 and 77: 64 5 Scintillator upgrade lecting e
Page 78 and 79:
66 5 Scintillator upgrade Figure 5.
Page 80 and 81:
Page 82 and 83:
Page 84 and 85:
72 5 Scintillator upgrade In 3.1 %
Page 86 and 87:
74 5 Scintillator upgrade were repo
Page 88 and 89:
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
show all

a design study for a cobra upgrade to - Institut für Kern- und ...

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?