A Classic Thesis Style - Johannes Gutenberg-Universität Mainz

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108 noise and radiation damage Probability density 0.18 0.16 0.14 0.12 0.1 0.08 0.06 0.04 0.02 before irradiation three days exposure seven days exposure 0 60 80 100 120 140 160 ADC (chn) Figure 71: Noise spectra of a green sensitive Photonique SSPM-0701BG-TO18 device that was exposed to background irradiation close to the beam-line during one week of normal beam operation. Damage is shown for 3 and 7 days of exposure. Probability density 0.1 0.08 0.06 0.04 0.02 before irradiation after irradiation 0 80 90 100 110 120 130 140 150 160 170 ADC (chn) (a) without radiation shielding Probability density 0.07 0.06 0.05 0.04 0.03 0.02 0.01 before irradiation after irradiation 0 80 90 100 110 120 130 140 150 160 170 ADC (chn) (b) with radiation shielding Figure 72: (a) Noise spectra of blue sensitive Photonique SSPM-0611B1MM devices before and after irradiation close to the beam-line. (b) Same type of SiPM but protected by a radiation shield. A reduced damage is observed for the shielded SiPM. consequence of an increase in the after-pulsing probability according to the Monte Carlo simulation. Blue sensitive Photonique SSPM-0611B1MM devices were exposed to half of the full dose and the noise spectra with and without shielding are shown in Fig. 72. The shielding effect is clear but damage due to high energy neutrons is still observable. The device SSPM-0611B1MM seems to present a smaller damage than the green sensitive SiPM SSPM-0701BG-TO18 for the same irradiation period of 3 days. A heat treatment (annealing) was attempted to reduce the observed damage. SiPMs were kept in a controlled temperature oven at 80° during two weeks. ADC spectrum for a randomly generated window is shown in Fig.73 for the green sensitivity device. Pedestal shifts have been subtracted for easer comparison. Only a partial recovery can be
6.5 damage characterisation with a monte carlo model 109 Probability density 0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0 Not irradiated SiPM Irradiated SiPM After annealing 60 80 100 120 140 160 ADC (chn) Figure 73: Annealing at 80° results only in partial recovery of the SiPM exposed to the radiation field in the experimental hall. Green sensitivity SiPM histograms are shown before and after irradiation for a randomly generated integration window. The same histogram is shown after the heat treatment. observed in these histograms. Longer heating time did not produce any further improvement. 6.5 characterisation of radiation damage in silicon photomultipliers with a monte carlo model 6.5.1 The Monte Carlo model for the detector output A complete model for the MPHD of SiPM was derived based on a Monte Carlo simulation. For the model, Poisson distributed photoelectron and dark signals are generated independently. Each of these signals can cause optical cross-talk and after-pulses according to a given probability distribution. For this set of pixels the distribution in time is generated with respect to an integration time window. Single pixels can contribute with varying gain to the generation of the detector output. Finally, the noise is added. The free parameters of the simulation are: mean signal amplitude (A), gain variation (σG), dark pulse rate (r), optical cross-talk probability (popt), after-pulse probability (p aft), trap lifetime (τ), mean number of detected photons (λ), pedestal position (xped), and noise amplitude (σped). In the following, the simulated processes are explained. As SiPM are a set of APD connected in parallel many of their properties are thus inherited. Its dark count rate, r, is the sum of all the APD dark count rates. After-pulses appear in each pixel after a photon (or a thermically generated charge carrier) triggers an avalanche due to trapped carriers that are released after some time-delay. The afterpulse probability, paft, is defined as the fraction of events in which one additional signal is generated after the detection of a photon. It is the product of the trapping probability and the triggering probability, both
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M E A S U R E M E N T O F T H E U N
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A B S T R A C T The new stage of th
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C O N T E N T S i kaon electroprodu
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Part I K A O N E L E C T R O P R O
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4 introduction Lorentz invariance.
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10 introduction This allows us to w
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12 introduction K ¡p γ ∗ Λ(Σ
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22 introduction Figure 9: Total cro
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E X P E R I M E N TA L S E T U P A
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2.3 target 27 Figure 11: Schematic
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2.4 kaos spectrometer 2.4 kaos spec
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M MWPC L F 2.4 kaos spectrometer 31
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Table 3: Spectrometers properties 2
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2.4 kaos spectrometer 35 Figure 16:
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2.4.5.1 Read out electronics 2.4 ka
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2.4 kaos spectrometer 39 channels.
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2.5 kaos single arm trigger 41 64MB
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2.6 spectrometer b 43 Figure 23: Sc
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2.7 coincidence setting 45 to be im
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2.9 kinematical setting 49 (GeV/c)
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52 detection efficiencies and data
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A Classic Thesis Style - Johannes Gutenberg-Universität Mainz

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