Monte Carlo Simulation Studies for Medical and Astrophysical Applications

Monte Carlo simulations have become an increasingly important topic in high energy physics over the last few decades especially as a method for studying systems with a large number of degrees of freedom, such as tracking high energy particles through detector geometries. In this thesis, Monte Carlo simulation studies were performed to estimate performance characteristics for three different geometries of a future breast PET/MR insert for a clinical PET/MR scanner, and to reproduce the measured EPIC pn-CCD camera background on board the ESA X-ray satellite XMM-Newton. PET performance characteristics for sensitivity and spatial resolution of the insert were investigated and are found to show significant improvements for two of the probed geometries in both sensitivity and spatial resolution near the center of the field of view, with spatial resolutions better than 1.6 mm FWHM, compared to modern clinical PET/MR scanners with roughly 4 mm FWHM. A blurring in the radial direction, referred to as the radial elongation effect, is seen towards the outer regions of the field of view, deteriorating the spatial resolution. Future studies are suggested to explore the impact of Depth Of Interaction (DOI) detectors on the spatial resolution across the whole field of view and especially on the mitigation of the radial elongation effect. In X-ray astronomy, a sound understanding of the background picked up by X-ray satellites operating in a space environment is crucial, since weak sources must be observable in the presence of a strong background. Foundations for a modern Geant4 simulation environment, inspired by earlier background simulations and enabling enhanced future studies, were developed and used to reproduce the quantum efficiency and background of the EPIC pn-CCD camera with a reasonable agreement with measurements.