Energy calibration of a Timepix4 detector assembly with a compact quasi-monochromatic X-ray system

Timepix4 is an application-specific integrated circuit (ASIC) developed by the Medipix4 international collaboration. It features a 448 × 512 pixel matrix that can be bump-bonded to pixelated sensors of various materials and thicknesses optimized for specific uses. Among its potential applications, Timepix4 can be utilized for spectral imaging, provided that an accurate energy calibration is performed to ensure precise measurements across all pixels. This calibration procedure was previously carried out using synchrotron X-ray beams, which provide a monochromatic and high-statistics source essential for pixel-by-pixel calibration. Building on this established protocol, which combines X-ray measurements with the detector internal test pulses, we introduce an alternative approach that employs a quasi-monochromatic (QM) X-ray beam generated by an X-ray tube in conjunction with a mosaic crystal. This configuration enables flexible implementation under standard laboratory conditions, minimizing the need for accelerator facilities with limited access. To validate this method, data acquired with an additional X-ray fluorescence (XRF) system were analyzed, demonstrating that the mixed calibration approach (combining QM data and test pulses) reduces discrepancy between measured and nominal energies to within 5%, compared to about 20% when relying solely on test pulses and less than 2% when using synchrotron radiation. Moreover, this improvement is accompanied by a significant decrease in the standard deviation of the measured photopeak, reflecting enhanced consistency across the pixel matrix. These findings highlight the potential of QM-based calibration as an effective and accessible alternative for achieving accurate Timepix4 energy calibration for a wide variety of spectral imaging applications.