Diamond Detectors for Ionizing Radiation - HEPHY

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CHAPTER 7. RADIATION HARDNESS 40 10 2 Cross section (mb) 10 ⇓ π + p total π + p elastic 10 -1 1 10 10 2 10 3 πp 1.2 2 3 4 5 6 7 8 910 20 30 40 10 2 πd 2.1 3 4 5 6 7 8 910 20 30 40 50 60 Center of mass energy (GeV) ⇓ π ± d total Cross section (mb) 10 π – p total π – p elastic 10 -1 1 10 10 2 10 3 Laboratory beam momentum (GeV/c) Figure 7.2: Nuclear interaction cross section plots for pions and protons. 7.3.1.1 Collection Distance In g. 7.4, the charge collection distance values in the pumped state are shown vs. pion uence for various samples. The letter in the sample name indicates the wafer, from which the samples were cut. Apart from E1, always two corresponding samples from a wafer were irradiated, which behave similar. It turned out that the higher the collection distance in the virgin state is, the faster it drops with irradiation. This behavior could be explained by the linear model. The vertical trap density in the detector before irradiation is higher at the substrate side than on the growth side, as discussed in section 5.1.1. Thus the local charge collection distance is low on the substrate side and high at the growth side. Intense irradiation is expected to introduce additional traps, equally distributed along the beam track. The sum trap density now increases signicantly on the growth side, shrinking the local charge
CHAPTER 7. RADIATION HARDNESS 41 Carbon Shield Beam Pipe Diamond Sample Sample Holder Al Foil Slide Tray Light-tight Box π Beam Ionization Chamber xyz Table Figure 7.3: The irradiation setup. collection distance, while there is only a negligible relative trap density increase at the substrate side. In other words, regions with a high charge collection distance are more susceptible to radiation damage than those with low d c , which are relatively indierent. Similar behaviour applies to the global (mean) charge collection distance, as observed in the experiment. The measurements show that the signal decrease of the initially highest charge collection distance samples is about 40% after 10 15 cm ,2 . This corresponds to the estimated uence at the LHC at a radius of 7 cm from the vertex within 10 years of operation. However, the irradiation damage is less severe than expected from the collection distance decrease, as the collection distance is calculated from the mean signal. When comparing the signal pulse height spectra in the pumped state before and after irradiation (g. 7.5), it is visible that the radiation does not simply scale the whole distribution, but has more eect on initially higher signals, while there is almost no eect on very low signals. The Landau tail suers from irradiation, the most probable value of the distribution is less aected and the rising edge almost stays the same. This agrees with the linear model damage discussed above, when we consider the inhomogeneity of CVD diamond. Regions with higher local collection distance are more aected by radiation than others, causing the strong eect on the Landau tail. 7.3.1.2 Beam Induced Charge The ionisation process of 300 MeV c ,1 pions crossing the diamond is very similar to that of the electrons from the 90 Sr source, because pions with this momentum deposit approximately 110% of the MIP energy in diamond of 650 m thickness [17]. The basic dierence between the two types of irradiation is the ux, or intensity. While each single electron is observed during the characterization, there is a high pion ux during irradiation, which allows to measure aDCcurrent, or average Q=t, respectively. During beam-o periods, the current in the samples is essentially zero. When beginning the irradiation with a virgin sample, the beam induced current increases in the rst couple of seconds due to the pumping eect. However, as the ux was not constant throughout the irradiation, it is more convenient for further analysis to look at the beam induced charge instead of the current.
Page 1 and 2: Diploma Thesis Diamond Detectors fo
Page 3 and 4: CONTENTS 3 7 Radiation Hardness 37
Page 5 and 6: CHAPTER 1. SYNOPSIS 5 primarily sil
Page 7 and 8: CHAPTER 2. INTRODUCTION 7 Figure 2.
Page 9 and 10: Chapter 3 Material Properties 3.1 G
Page 11 and 12: CHAPTER 3. MATERIAL PROPERTIES 11 Q
Page 13 and 14: CHAPTER 3. MATERIAL PROPERTIES 13 d
Page 15 and 16: Chapter 4 Solid State Detector Theo
Page 17 and 18: CHAPTER 4. SOLID STATE DETECTOR THE
Page 19 and 20: CHAPTER 4. SOLID STATE DETECTOR THE
Page 21 and 22: CHAPTER 5. DETECTOR MATERIAL COMPAR
Page 27 and 28: CHAPTER 6. CHARACTERIZATION 27 6.1.
Page 29 and 30: CHAPTER 6. CHARACTERIZATION 29 and
Page 31 and 32: CHAPTER 6. CHARACTERIZATION 31 Lid
Page 33 and 34: CHAPTER 6. CHARACTERIZATION 33 Figu
Page 35 and 36: CHAPTER 6. CHARACTERIZATION 35 300
Page 37 and 38: Chapter 7 Radiation Hardness 7.1 Ra
Page 39: CHAPTER 7. RADIATION HARDNESS 39 7.
Page 43 and 44: CHAPTER 7. RADIATION HARDNESS 43 ev
Page 45 and 46: CHAPTER 7. RADIATION HARDNESS 45 2
Page 47 and 48: CHAPTER 7. RADIATION HARDNESS 47 no
Page 49 and 50: CHAPTER 8. DETECTOR GEOMETRIES 49 F
Page 51 and 52: CHAPTER 8. DETECTOR GEOMETRIES 51 S
Page 53 and 54: CHAPTER 8. DETECTOR GEOMETRIES 53 i
Page 55 and 56: Chapter 9 Summary The possible appl
Page 57 and 58: Acknowledgements First of all, I am
Page 59 and 60: APPENDIX A. ABBREVIATIONS AND SYMBO
Page 61 and 62: APPENDIX A. ABBREVIATIONS AND SYMBO
Page 63 and 64: Bibliography [1] Austrian Academy o
Page 65: BIBLIOGRAPHY 65 [29] A. Hrisoho, Fr

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