Photon event evaluation for conventional pixelated detectors in energy-dispersive X-ray applications

In principle, most X-ray sensitive pixelated detectors like CCDs or active pixel sensors (e.g. CMOS detectors) can be operated in single-photon counting (SPC) mode. In combination with rather simple data post-processing steps, this allows the exploitation of energy-dispersive properties similar to hybrid-pixel detectors and pnCCDs. For example, energy discrimination can be used to simultaneously measure the spatial distribution of various fluorescence lines on the detector chip or enable noise suppression in wavelength-dispersive measurements. Furthermore, due to the analysis of the charge distribution on the detector resulting from an absorbed X-ray photon, sub-pixel spatial resolution can be achieved. Where applicable, those additional features can be utilized without any hardware modification at the detector. There is a large potential for novel experiments and sensitivity gain in many laboratories already applying pixelated detectors, but only a few experiments indeed use this potential. The up until now published algorithms are hardly validated and rarely described in detail. Besides a thorough description of various algorithms for photon event evaluation, this work concentrates on a quantitative and qualitative comparison of such algorithms with respect to energy resolution, efficiency and photon recovery. For this purpose, the algorithms are tested on simulated data featuring various detector noise and charge-cloud size values and the influence of noise thresholds and photon density is discussed. Finally, we present two examples to demonstrate the advantages of photon event evaluation and highlight its benefits for X-ray spectroscopic applications.