Speaker
Description
This work focuses on optimizing the properties of photon counting imaging detectors of Timepix family with Silicon, CdTe and GaAs sensors.
The optimization addresses two distinct goals:
a) Achieving the best energy resolution for specific target applications such as X-ray diffraction, X-ray fluorescence imaging or absorption K-edge imaging. The energy resolution of 130 eV (Gaussian fit sigma, i.e. 300 eV FWHM) for 8 keV Cu Kα XRF line was achieved with Silicon sensors (300 µm thick), and 0.45 keV (Gaussian fit sigma, i.e., 1 keV FWHM) for 23.1 keV Cd Kα XRF with CdTe sensors (1 mm thick).
b) Achieving the best detector stability measured as signal to noise ratio (SNR) for applications in X-ray radiography. The detector stability directly affects the maximal reachable contrast in the radiographic images. The noise of ideal photon counting detector follows Poissonian statistics. Its SNR should be equal to sqrt(N) where N is the number of counted photons. Therefore, the maximal SNR of such detector should theoretically reach any value for sufficiently high N. The real photon counting detectors are affected by various influences causing the SNR value to saturate (e.g. sensor polarization, threshold fluctuations, temperature influence etc.). The results of optimizations proved the SNR>2000 under normal X-ray flux conditions or SNR>1000 under very high flux of 360 Mcounts/mm2/s (achieved with GaAs sensor by AdvaFAB Oy). The corresponding contrast in images allows to recognize 5 µm thick defects in 7 mm thick Aluminum block after 1 s exposure time.
