Speaker
Description
Detector systems utilising the small pixel effect, such as HEXITEC, display high rates of charge sharing due to the similar scales of the charge carrier clouds generated by hard X-ray interactions and the pixel pitch of the detector.
Charge sharing distributes the complete interaction energy of event across multiple readout channels – with losses occurring due to truncation of fractional pixel signals by the energy threshold and inter-pixel trapping. As charge sharing may occur due to charge carrier cloud diffusion/repulsion or multiple photon interaction processes (i.e. detector fluorescence), charge sharing signals degrade the energy and spatial resolution of a detector system.
To preserve system performance, charge sharing signals are typically excluded using Charge Sharing Discrimination (CSD), or the fractional pixel signals are summed without energy-loss or position correction, known as Charge Sharing Addition (CSA) [1]. For photon-limited applications such as medical imaging, CSD results in sensitivity losses of ≈ 67% at 141 keV, whilst CSA significantly degrades energy resolution. The development of charge sharing reconstruction approaches based on the physical process responsible for a charge sharing event allows correction for inter-pixel signal losses and determination of the event interaction position – avoiding the limitations of both CSD and CSA.
Charge sharing interaction process has been demonstrated to correlate with event shape for 2-pixel events [2]. We present a range of energy-analysis methods, based on event shape analysis, which identify the most-likely interaction process responsible for charge sharing events up to 4 pixels in size (characterising >99.996% of events at 141 keV). This allows pre-established methods for energy [3, 4] and position [5] correction to be applied only to events, or sub-processes within complex events, which require correction. Position correction methods for 2-pixel events have also been generalised to allow correction of fractional sub-processes within events. This correction toolkit is sufficient for energy and position correction of all 2-pixel events and most 3-pixel events; achieving improved spatial resolution, 2-3x increased sensitivity when compared with CSD and reduced energy resolution degradation when compared to CSA.