Diamond Detectors for Ionizing Radiation - HEPHY

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CHAPTER 8. DETECTOR GEOMETRIES 50 300 V 641 µm (a) 0V 1.0 1.5 1.75 2.0 r [mm] 300 V 0V 641 µm (b) 0V Figure 8.2: Cross-section of a diamond sample, showing potentials and the electric eld without (a) and with (b) a grounded guard ring. the digital (or, binary) resolution RMS of RMS dr = p p 12 : (8.1) When the strip pitch is small enough, charge sharing between two or more electrodes occurs, and together with proper analysis tools, the particle track can be reconstructed with much higher resolution than digital, depending primarily on the SNR. Using a silicon detector (300 m thick) with a strip pitch ofp=50m and a high-quality amplier (e.g., the VA2), it is easy to obtain a spatial resolution of a few micrometers. 8.2.2 Measurements When a diamond strip detector is measured in a test beam, the particle track is monitored with a number of high-resolution silicon strip reference detectors. Half of the reference detectors are rotated by 90 in order to obtain x and y position information. A system of such detectors, shown in g. 8.3, is called \beam telescope". The RD42 telescope utilizes 8 planes of silicon strip detectors with a pitch of50m, which are read out by VA2 chips. The intrinsic resolution of this telescope is approximately 1:5 m.
CHAPTER 8. DETECTOR GEOMETRIES 51 Silicon Strip Reference Detectors Diamond Tracker Silicon Strip Reference Detectors Particle Track Figure 8.3: The RD42 beam telescope with a diamond tracker under test. In the past years, several diamond samples have been equipped with strip electrodes and measured in test beams [22, 39]. The rst diamond tracker, shown on the left side of g. 8.4, was built and tested in 1994. It was made of a 1 1cm 2 piece of CVD diamond; the strips had a 100 m pitch anda50minterstrip gap. Using a VIKING readout chip, a mean SNR of 9 was achieved and the spatial resolution was 26 m, slightly better than the digital resolution (29 m). In the meantime, the quality of the CVD diamond material has been dramatically improved. Furthermore, as the intention was to achieve better spatial resolution, the strip pitch was reduced to 50 m. With the best diamond sample available, which has an area of 1 1cm 2 , a mean SNR of 71 (most probable SNR=46) has been achieved with the VA2 readout chip. The measured spatial resolution of =15m approximately corresponds to the digital resolution for this strip pitch. Recently, a 2 4cm 2 CVD diamond tracker with a pitch of 50 m has been tested with VA2 amplier chips (right side of g. 8.4). With this conguration, a mean SNR of 30 and a spatial resolution of 14 m has been obtained. Apart from the slow, but low-noise VA2 chips, diamond strip detectors have also been tested with fast LHC front-end electronics. At the LHC, a bunch crossing occurs every 25 ns. In order to correlate the detector signal with a certain bunch crossing, the shaping time of the front-end electronics must be of the same order. Furthermore, the LHC amplier chips need an analog pipeline storage, since the trigger decision, i.e., the request for event data, comes a few microseconds later. The SCT128AHC readout chip [40] has been designed for the ATLAS experiment, having a shaping time of 21 to 25 ns and a 128 cell analog pipeline. Due to the short integration time, the noise gure of this chip is ENC 650 e + 70 e pF ,1 , much higher than the noise of the VA2 chip. The best available diamond detector, which was tested with the VA2 before, was later connected to the SCT128AHC readout chip without changing the strip pattern. This chip version is optimized for high capacitive load, i.e., silicon strip detectors, and thus not ideal for diamond detectors. Nevertheless, a mean SNR of 10 was demonstrated (most probable SNR=7.2) and a spatial resolution of =16:5mwas observed. Although the SNR gures of the same diamond strip detector measured with VA2 and SCT chips dier considerably, the spatial resolution is close to the digital resolution in
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
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Page 15 and 16: Chapter 4 Solid State Detector Theo
Page 17 and 18: CHAPTER 4. SOLID STATE DETECTOR THE
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Page 21 and 22: CHAPTER 5. DETECTOR MATERIAL COMPAR
Page 27 and 28: CHAPTER 6. CHARACTERIZATION 27 6.1.
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Page 31 and 32: CHAPTER 6. CHARACTERIZATION 31 Lid
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Page 39 and 40: CHAPTER 7. RADIATION HARDNESS 39 7.
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Page 57 and 58: Acknowledgements First of all, I am
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Page 63 and 64: Bibliography [1] Austrian Academy o
Page 65: BIBLIOGRAPHY 65 [29] A. Hrisoho, Fr

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