دانلود رایگان مقاله انگلیسی انتقال بار شبیه سازی شده در آشکارسازهای شمارش فوتون - الزویر 2018

Abstract

The purpose of this study is to review and compare simulation methods for describing the transport of charge clouds in silicon based semiconductor detectors and investigate the effects on energy spectrum for silicon based photon counting strip detectors. Charge clouds and detailed carrier transport are sim ulated and compared using two different approaches including analytical and  Monte Carlo schema. The results of the simulations are evaluated using pulse height spectra (PHS) for a silicon strip detector with edge on geometry at two  energies (25 and 75 keV) at various x-ray absorption locations relative to the  pixel boundary and detector depth. The findings confirm carrier diffusion plays a large role in the charge sharing effect in photon counting detectors, in particular when the photon is absorbed near the pixel boundary far away from the pixel electrode. The results are further compared in terms of the doublecounting probability for x-ray photons absorbed near the pixel boundary as a function of the threshold energy. Monte Carlo and analytical models show reasonable agreement (2% relative error in swank factor) for charge sharing effects for a silicon strip detector with edge-on geometry. For 25 keV mono-energetic photons absorbed at 5 µm from the pixel boundary, the theoretical threshold energy at 10% double-counting probability based on charge sharing is 5.5, 8.5 and 9.2 keV for absorption depths of 50, 250 and 450 µm from the electrode, respectively. The transport of charge clouds affects the spectral characteristics of photon counting detectors and the double-counting probability results show the theoretical threshold energy to avoid double-counting as a function of x23 ray energy and x-ray interaction locations for silicon and can be considered for future studies of charge sharing effects.

Conclusion

Charge clouds and their transport affect the spectral characteristics of photon counting detectors. These effects are most pronounced when interactions occur near pixel boundaries and can be simulated with Monte Carlo and analytical tools. Results of the model comparison show reasonable agreement for the pulse-height spectra simulations (2% relative error in Swank factor) between the bubble-line and ARTEMIS models when considering a silicon strip detec339 tor with two mono-energetic beams (25 and 75 keV). The comparison results indicate that carrier diffusion plays a large role in photon-counting detectors, particularly when the photon is absorbed near the pixel boundary far away from the pixel electrode. In addition, the double-counting probability and percentage for x-ray photons absorbed near the pixel boundary as a function of the threshold energy has been simulated. This work contributes to our understanding of modeling efforts designed to guide future studies of charge-sharing effects in different detection materials, detector arrangements, absorption locations and at different levels of x-ray energy thresholds.