Silicon Pixel Detectors - Performance after Irradiation and Application in Three-dimensional Imaging
Year: 2019
Type: dissertation
Abstract: This dissertation addresses two applications of silicon pixel detectors as tracking devices, namely the applications in high energy physics experiments and in a novel tomographic technique termed material budget imaging.For current and future experiments in high energy physics, one of the main challenges for the development of silicon detectors is the immense radiation fluence received over the years of operation.In this thesis, the performance of silicon pixel detectors for the tracking detector of the Compact Muon Solenoid (CMS) experiment is investigated for fluences of up to $\Phi_{eq}= 1.39\times10^{15}$n/cm$^2$ close to the expected lifetime fluence of the innermost layer of the barrel pixel detector. Measurements conducted at the DESY II Test Beam Facility show, that the maximum collected charge is reduced significantly by the high radiation fluences, but that an efficiency of above 99 % can be maintained when applying reasonable bias voltages.The voltage required to fully deplete the sensor rises up to around 600 V.The effective Lorentz angle of unirradiated detector modules and a module irradiated to a fluence of $\Phi_{eq}= 4\times10^{14}$n/cm$^2$ was determined for various bias voltages using a 1.34 T magnetic field.The findings imply that the high bias voltages required for an efficient operation of radiation damaged pixel detectors will impair the resolution of the detector modules significantly.The second application investigated is the use of silicon pixel detectors for an imaging technique aiming to reconstruct the three-dimensional material distribution of arbitrary samples.Using the high-resolution EUDET-type Beam Telescopes available at the DESY II Test Beam Facility to measure the scattering angle of relativistic particles when traversing a sample allows for the determination of its projected material budget in two dimensions.A rotation of the sample and an inverse Radon transform facilitates a reconstruction of the sample's internal structure.Simulations of this technique are presented as well as the first acquired three-dimensional material budget images.The simulations and an evaluation of the underlying two-dimensional images indicate a possible resolution of this method of less than 20 $\mu$m at a sufficiently high contrast-to-noise ratio.The potential and the limits of material budget imaging as well as possible future applications and developments are discussed.
Author: Schütze, Paul
Institution: Deutsches Elektronen-Synchrotron DESY
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W3104217262