HEXITEC is a spectroscopic imaging X-ray detector technology developed at the STFC Rutherford Appleton Laboratory for X-ray and γ-ray spectroscopic imaging applications. Each module has 80 × 80 pixels on a 250 μm pixel pitch, and has been implemented successfully in a number of applications. This paper presents the HEXITEC 2 × 2 detector system, a tiled array of 4 HEXITEC modules read out simultaneously, which provides an active area of 16 cm2. Systems have been produced using 1 mm thick Cadmium Telluride (CdTe) and 2 mm thick Cadmium Zinc Telluride (CdZnTe) sensor material. In this paper the system and data processing methods are presented, and the performance of the systems are evaluated. The detectors were energy calibrated using an 241Am sealed source. Three types of charge sharing correction were applied to the data-charge sharing addition (CSA), charge sharing discrimination (CSD), and energy curve correction (ECC) which compensates for energy lost in the inter-pixel region. ECC recovers an additional 34 % of counts in the 59.5 keV peak in CdTe compared to the use of CSD; an important improvement for photon-starved applications. Due to the high frame rate of the camera system (6.3 kHz) an additional End of Frame (EOF) correction was also applied to 6.0 % of events to correct for signals that were readout whilst the signal was still forming. After correction, both detector materials were found to have excellent spectroscopic performance with a mean energy resolution (FWHM) of 1.17 keV and 1.16 keV for CdZnTe and CdTe respectively. These results successfully demonstrate the ability to construct tiled arrays of HEXITEC modules to provide larger imaging areas.

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The performance of Li + ion batteries (LIBs) is hindered by steep Li + ion concentration gradients in the electrodes. Although thick electrodes (≥300 μm) have the potential for reducing the proportion of inactive components inside LIBs and increasing battery energy density, the Li + ion concentration gradient problem is exacerbated. Most understanding of Li + ion diffusion in the electrodes is based on computational modeling because of the low atomic number (Z) of Li. There are few experimental methods to visualize Li + ion concentration distribution of the electrode within a battery of typical configurations, for example, coin cells with stainless steel casing. Here, for the first time, an interrupted in situ correlative imaging technique is developed, combining novel, full-field X-ray Compton scattering imaging with X-ray computed tomography that allows 3D pixel-by-pixel mapping of both Li + stoichiometry and electrode microstructure of a LiNi 0.8 Mn 0.1 Co 0.1 O 2 cathode to correlate the chemical and physical properties of the electrode inside a working coin cell battery. An electrode microstructure containing vertically oriented pore arrays and a density gradient is fabricated. It is shown how the designed electrode microstructure improves Li + ion diffusivity, homogenizes Li + ion concentration through the ultra-thick electrode (1 mm), and improves utilization of electrode active materials.

HR GaAs:Cr is a well known material, used for room-temperature X-ray detector applications. While GaAs:Cr detectors have typically shown good performance at 25̂C, there may be benefits of running the detector at lower temperatures where leakage currents are lower. The aim of this study was to evaluate the energy resolution across the temperature range −10̂C to 30̂C which is easily achievable using compact electrical cooling solutions. Using HR GaAs:Cr detectors that were flip-chip-bonded to STFC's PIXIE ASIC, it was possible to measure the spectroscopic performance of the material as a function of temperature. Both HR GaAs:Cr sensors were of 500 μm thickness and mobility-lifetime products measured at room temperature comprised 0.5⋅10−4 and 1.7⋅10−4 cm2V−1 for sensors dated from 2016 and 2018, respectively. Using an 241Am sealed source, pulse height spectra were measured for pixel arrays with pitches of 250 and 500 μm for temperatures in the range -10̂C to 30̂C. By varying the operating voltage of the detectors it was also possible to study the variation in the charge transport properties of the HR GaAs:Cr over the same temperature range.