X-Ray Fluorescence Imaging With the Medipix2 Single-Photon Counting Detector

Abstract

Abstract-Material-resolved X-ray imaging or colour X-ray imaging is of a great interest for many applications ranging from physics, industry to medicine and biology. X-ray Àuorescence offers a method for producing such images if the energies and positions of origin of the Àuorescent photons can be adequately resolved.This paper describes application of the Medipix2 single photon counting imaging detector (256 256 pixels each of 55 55 m size) for this purpose.The basics of the method are explained including details of the energy calibration of all 65 k individual pixels. The effect of charge sharing is discussed and a method for its characterisation based on numerical calculation presented. The charge sharing calculation is then used to generate the Medipix2 detector response matrix, which is subsequently used for analysis of measured spectra in detector pixels.

Tutorial on X-ray photon counting detector characterization

“…In contrast to using synchrotron radiation or radioactive isotopes that the detector is directly illuminated, the excitation source (laboratory X-ray source or radioactive isotope) and the detector are generally placed perpendicularly to each other in the method using XRF [64], both facing to the fluorescent targets. This experimental setup could significantly improve the fluorescence-to-scatter ratio (FSR) [65].…”

“…1, the Kα energy of each fluorescent target is determined as the average of Kα2 and Kα1 energies. When the fluorescent target has a Z less than around 70, typically these two sub-fluorescence lines are too close to be separated even with a spectrometer with high energy resolution, let alone the use of a photon counting detector with a relatively lower energy resolution in several keVs [33, 64]. For Z>70, in contrast, both of these two sub-fluorescence lines can be clearly distinguished with high energy resolution spectrometers, but this is not the case with a photon counting detector.…”

“…Therefore, when the photon counting detector is illuminated by X-rays or gamma rays in the form of mono-energetic spectrum, a low-energy tail can be observed beside the detected pulse height peak [1, 55]. The low-energy tail exhibits stronger for those with small pixels and high insufficient charge collection [10, 36, 64, 66]. This observation is generally performed with energy response calibration and energy resolution determination using synchrotron radiation, radioactive isotopes and XRF with fluorescent materials.…”

Application of Factorisation Methods to Analysis of Elemental Distribution Maps Acquired with a Full-Field XRF Imaging Spectrometer

“…There is no obvious choice for the type of detector for such applications as typically the energy resolution of position-sensitive detectors is compromised by physical effects, like charge division [ 23 ], and by technical constraints. Different types of detectors have been tried by other groups for such applications: a detector based on a Charge Coupled Device (CCD) used in a special spectroscopic mode [ 21 , 24 , 25 , 26 ], a pixel detector [ 27 , 28 ], a gaseous Micro Hole Strip Plate (MHSP) detector [ 29 ], and a gaseous detector based on the technology of Thick Gas Electron Multiplier (THGEM) [ 22 ], called THCOBRA. Application of the Gas Electron Multiplier (GEM) detector with the resistive divider readout has also been tried [ 30 ].…”

A hybrid Monte Carlo model for the energy response functions of X-ray photon counting detectors

“…Uher et al used a Gaussian function to describe the spread of charges, and fitted the energy response functions of a 300um Si based Medipix2 detector with X-ray fluorescence [10]. Campbell and Das did a similar work with some minor improvement, and further used the response functions for spectral restoration [11].…”