First characterization of a GaAs-based Timepix4 detector assembly for X-ray imaging applications

Abstract The experimental characterization of a Timepix4 detector assembly with a 500 μm gallium arsenide (GaAs) sensor was performed for X-ray imaging in the 20–50 keV energy range. GaAs offers 70% or more absorption efficiency below 50 keV and higher stopping power than silicon, while its moderate atomic number suppresses fluorescence yield and thereby improves image contrast in X-ray imaging relative to high-Z materials. The Timepix4-based detector, controlled by a dedicated FPGA-based DAQ system, operates in two modes: data-driven for full spectroscopy and frame-based for simple single-threshold photon counting. Flat-field uniformity and spatial resolution were assessed in frame-based mode, and pixel-wise energy calibration and charge-sharing analysis were carried out in data-driven mode. Spatial resolution was mainly determined by the 55 μm pixel pitch, with a measured FWHM ranging from 45 to 70 μm showing variations depending on energy and threshold in frame-based operation. The system achieved sub-percent flat-field uniformity and 6% energy calibration accuracy with combined internal and external references. These results establish GaAs-Timepix4 detectors as a promising solution for spectral X-ray imaging in the medium-energy range.