HEXITEC: A High-Energy X-ray Spectroscopic Imaging Detector for Synchrotron Applications

Abstract

HEXITEC is a compact high energy X-ray spectroscopic imaging detector system developed by the STFC Rutherford Appleton Laboratory (UK). The system is based on the high density compound semiconductor cadmium telluride and consists of an 80 × 80 array of pixels on a 250 m pitch with each channel capable of measuring X-ray spectra in the energy range 2 -200 keV with an energy resolution of 800 eV. The system operates at room temperature and removes the need for large cryogenic cooling systems used by other systems covering similar energy ranges. The system has applications at synchrotrons in experiments where mechanical, structural or chemical information is required from thick samples or to determine the chemical composition of samples containing multiple high Z materials. In this article the operation of the system is described, the sensor performance characterised and a simple example of spectroscopic imaging at a synchrotron beamline demonstrated.

Characterization of the Uniformity of High-Flux CdZnTe Material

“…The spectroscopic performance of all 10 of the HF-CdZnTe detectors were evaluated using the same method and the results are summarized in Table 1 . Across the sample of 10 detectors, an average FWHM of 0.83 keV was measured, which is comparable to the best energy resolution previously measured with the Acrorad Schottky-anode CdTe using the HEXITEC ASIC [ 16 ]. It is worth noting that one of the key advantages of the CdZnTe is that, unlike the CdTe, it does not require the bias voltage to be cycled periodically to avoid bias-induced polarization.…”

“…The best performing detectors show pixel to pixel variations of 5.5% (D185735) while the worst shows 12.2% (D185740). The uniformity of the best HF-CdZnTe detectors compares well to that of Schottky CdTe detectors, which have previously been tested with HEXITEC that also show pixel to pixel variations of ~5% [ 16 ]. In the rest of this section, the different types of non-uniformity observed in the HF-CdZnTe detectors will be examined in more detail.…”

“…The Fano-limited energy resolution (Δ E Fano ) is described by Equation (1): where F is the Fano factor and W is the electron hole pair creation energy; these have values of 0.1 and 4.62 eV ehp-1 in CdZnTe material [ 18 ]. In recent years, the spectroscopic performance of CdZnTe and CdTe detectors has improved dramatically, with FWHM measured at 59.54 keV of the order 1–2 keV [ 9 , 16 , 19 , 20 ], compared to the theoretical Fano-limited minimum of 0.39 keV.…”

“…Each HEXITEC module, see Figure 1 b, is mounted in a HEXITEC ‘GigE’ data acquisition system (DAQ) [ 16 ]. The DAQ contains the entirety of the readout electronics, including the analogue-to-digital converters (ADCs) that digitize the analogue voltages readout from the chip.…”

Edge-subtraction X-ray ptychographic imaging with pink beam synchrotron radiation and a single photon-counting detector

“…Here we demonstrate a new modality for edge-subtraction ptychography that makes use of multiple undulator harmonics and a multiple threshold X-ray Photon Counting Detector (XPCD) -the Pixirad-1/Pixie-III 11 -as an harmonic selector. The nature of the Pixie-III is such that the acceptable count rate is significantly higher compared to a hyperspectral detector 12 , resulting in faster acquisition times while still offering energy discriminating capabilities. The detector is capable of operating at more than 500 Hz, with 10 5 counts s −1 pixel −1 , giving the potential of spectroscopic ptychography at 2.6 • 10 7 photons mm −2 s −1 .…”