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30 October 2018 Photon counting performance of amorphous selenium and its dependence on detector structure
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Abstract
Photon counting detectors (PCD) have the potential to improve x-ray imaging; however, they are still hindered by high costs and performance limitations. By using amorphous selenium (a-Se), the cost of PCDs can be significantly reduced compared with modern crystalline semiconductors, and enable large-area deposition. We are developing a direct conversion field-shaping multiwell avalanche detector (SWAD) to overcome the limitation of low carrier mobility and low charge conversion gain in a-Se. SWAD’s dual-grid design creates separate nonavalanche interaction (bulk) and avalanche sensing (well) regions, achieving depth-independent avalanche gain. Unipolar time differential (UTD) charge sensing, combined with tunable avalanche gain in the well region allows for fast response and high charge gain. We developed a probability-based numerical simulation to investigate the impact of UTD charge sensing and avalanche gain on the photon counting performance of different a-Se detector configurations. Pulse height spectra (PHS) for 59.5 and 30 keV photons were simulated. We observed excellent agreement between our model and previously published PHS measurements for a planar detector. The energy resolution significantly improved from 33 keV for the planar detector to ∼7  keV for SWAD. SWAD was found to have a linear response approaching 200  kcps  /  pixel.
© 2018 Society of Photo-Optical Instrumentation Engineers (SPIE) 2329-4302/2018/$25.00 © 2018 SPIE
Jann Stavro, Amir H. Goldan, and Wei Zhao "Photon counting performance of amorphous selenium and its dependence on detector structure," Journal of Medical Imaging 5(4), 043502 (30 October 2018). https://doi.org/10.1117/1.JMI.5.4.043502
Received: 21 June 2018; Accepted: 17 September 2018; Published: 30 October 2018
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