Spectral correction algorithm for multispectral CdTe x-ray detectors

Abstract

Compared to the dual energy scintillator detectors widely used today, pixelated multispectral X-ray detectors show the potential to improve material identification in various radiography and tomography applications used for industrial and security purposes. However, detector effects, such as charge sharing and photon pileup, distort the measured spectra in high flux pixelated multispectral detectors. These effects significantly reduce the detectors' capabilities to be used for material identification, which requires accurate spectral measurements. We have developed a semi analytical computational algorithm for multispectral CdTe X-ray detectors which corrects the measured spectra for severe spectral distortions caused by the detector. The algorithm is developed for the Multix ME100 CdTe X-ray detector, but could potentially be adapted for any pixelated multispectral CdTe detector. The calibration of the algorithm is based on simple attenuation measurements of commercially avaiable materials using standard laboratory sources, making the algorithm applicable in any X-ray setup. The validation of the algorithm has been done using experimental data acquired with both standard lab equipment and synchrotron radiation. The experiments show that the algorithm is fast, reliable even at X-ray flux up to 5 Mph/s/mm 2 , and greatly improves the accuracy of the measured X-ray spectra, making the algorithm very useful for both security and industrial applications where multispectral detectors are used.

A generic model of semiconductor-based photon-counting detectors for spectral CT

“…where kB is the Boltzmann's constant (= 1.38×10 -23 J/K), T is absolute temperature (= 313.15 K), z is the distance between the interaction location and the anode (along the direction of the electric field), d is the thickness of the detector, q is the elementary charge (= 1.60×10 -19 C), U is the bias voltage (= 1000 V), N is the number of electron-hole pairs liberated (= Edep/ΔE; Edep is energy deposited in each interaction and ΔE is the energy per electron-hole pair), 𝜀 is the permittivity, and 𝜎 / is the initial diameter of the charge cloud. 4 For 𝜎 / , another Monte Carlo simulation was designed, with a cubicle detector sized 50×50×50 mm 3 and a point source at its center that irradiated 10 5 electrons for each energy in the 1-150 keV range. The diameter covering 95% of the total charge was considered the initial charge cloud diameter (𝜎 / ) for the simulated detector material.…”

Material classification using basis material decomposition from spectral X-ray CT

“…[53]. In this work we therefore use the correction algorithm proposed by Dreier et al [54] to correct the spectral distortions in the PCD used. The LAC curve is corrected by the correction of the measured flat field and attenuated spectra, for which the comprehensive semianalytical interpretations based on the physical reason of the different interactions are used.…”

“…In a recent paper [53] we showed that the correction of the detector's spectral response for these distortions is required to correct the measured LACs and significantly enhance the material classification performance. A correction algorithm presented by Dreier et al [54] was used to correct for the spectral distortions occurring in the PCD.…”

“…Our method does not use the calibration phase used by Brambilla et al [47] to learn the detector's spectral response for different combinations of thicknesses of the basis materials, and thereby estimate Z eff values of unknown materials from x-ray radiography acquisitions. Instead we use the correction algorithm [54] to correct for the spectral distortions in the PCD and directly relate the resulting corrected LAC of a given material to the LAC expressed as in the formula for basis material decomposition.…”

Intrinsic XRF corrections in Timepix3 CdTe spectral detectors

“…The number of electron/hole pairs created is proportional to the energy deposited [3,4]. One of the limitations of HPDs is the intrinsic X-ray fluorescence (XRF) emission from the detector semiconductor sensor [5]. These fluorescence photons can travel away from the initial interaction position and can interact in neighbouring pixels or even escape the detector.…”