A novel and fast way for energy calibrating the Medipix-2 low discrimination threshold

The Medipix-2 MXR is a single photon counting imaging detector developed at Cern. It provides 65,536 pixels in a 256 × 256 array, each equipped with low and high energy discriminators and a counter. The low (and high) threshold settings can be used to collect energy-resolved radiographic images. Applications include high-dynamic range, low-noise and material-resolved X-ray imaging. Each pixel has a different electronic gain and offset, so the energy calibration for each pixel needs to be determined separately. The Medipix detector provides only global low and high threshold settings, which are applied to all pixels. However, each pixel has additional 3-bit offset settings for the low and high thresholds. These settings can be used to fine-tune the thresholds for individual pixels and their calibration also needs to be determined. This paper describes a novel and fast method for calibrating the low energy discrimination threshold setting by using X-ray tube transmission spectra through different materials.