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Description
The upgrade of photon light sources to diffraction-limited storage rings, alongside the demands of techniques such as Hyperspectral X-ray Tomography, requires spectroscopic X-ray imaging detectors capable of operating at significantly higher photon fluxes than previous generations permitted. HEXITEC$_{\textrm{MHz}}$, developed at STFC, is the latest generation of the HEXITEC spectroscopic X-ray imaging detector family. Coupled to HF-CdZnTe sensor material and achieving a 1 MHz continuous frame rate, HEXITEC$_{\textrm{MHz}}$ delivers high-resolution spectroscopy across 2–200 keV at fluxes exceeding 10⁶ ph s⁻¹ mm⁻², representing a greater than hundred-fold improvement on the 9.1 kHz frame rate of the original HEXITEC system. Sensor characterisation measurements have demonstrated an energy resolution of 1.2 keV FWHM at fluxes of 10⁶ ph s⁻¹ mm⁻², confirming that high spectroscopic performance is maintained under high-flux conditions [1, 2].
HEXITEC$_{\textrm{MHz}}$ is designed as a compact, deployable instrument with a camera head footprint of ~6 cm × 6 cm × 30 cm, requiring only a 12 V supply and a small chiller unit for operation, with data transmitted via fibre optic. Maintaining the 250 μm pixel pitch of the original ASIC, the system achieves its 1 MHz frame rate through an integrating front-end architecture, in-pixel digitisation, and high-speed serialisers. This paper presents the full HEXITEC$_{\textrm{MHz}}$ camera system, covering the ASIC pixel architecture, in-FPGA data correction and compression algorithms, DAQ control software and firmware, and hardware- and software-triggered acquisition modes.
Working with Pacific Northwest National Laboratory, a series of measurements using a 160 keVp W X-ray source validated HEXITEC$_{\textrm{MHz}}$ across several experiments. Spectroscopic radiography of Au, Pt, and Au+Pt samples confirmed the system's ability to differentiate elements separated by only one atomic number. The system's suitability for time-resolved studies was further demonstrated through dynamic spectroscopic radiography of ion drift of critical materials in solution within a magnetic field, achieving a temporal resolution of 100 ms. Combined Radiography, Energy and Angular Diffraction Imaging (READI) was also demonstrated on powder samples. These results highlight the 100 ms dynamic imaging capability in particular as a distinctive strength, positioning HEXITEC$_{\textrm{MHz}}$ as a versatile platform for high-flux spectroscopic X-ray imaging across a broad range of scientific applications.
[1] M.C Veale et al., Preliminary characterisation of the HEXITEC$_{\textrm{MHz}}$ spectroscopic X-ray imaging detector, J. Inst. 18 (2023) P07048 doi:10.1088/1748-0221/18/07/P07048.
[2] B. Cline et al., Characterisation of HEXITEC$_{\textrm{MHz}}$ - A 1 MHz continuous frame rate spectroscopic X-ray imaging detector system, Nuc. Inst. Meth. A. 1057 (2023) 168718 doi:10.1016/j.nima.2023.168718.