Energy dispersive x-ray diffraction system: A response function for the CZT detector and an analysis of noise at low momentum transfer arguments

A cadmium zinc tellurium (CZT) detector is employed in a custom made energy dispersive x-ray diffraction (EDXD) system to investigate the potential of identifying breast cancer. An analytical model for the response of the CZT detector in the diagnostic energy range was formulated. Hole tailing and fluorescence escape are two major problems of the CZT detector that were characterized in the model. The generated response functions and the full energy peak efficiencies for energies ranging from 0.2 to 100 keV agree well with the results obtained via Monte Carlo (GEANT4 simulation package) methods. The response functions were applied to extract the mean free paths of electrons lambdae) and holes (lambdah) of the CZT detector. An 241Am spectrum was unfolded and fitted with the model to yield lambdae = 200 cm and lambdah = 0.04 cm. The response functions were used to correct 50 kV x-ray spectra measured with the CZT detector. The extra counts at lower energies caused by fluorescence escape and hole tailing were removed and put back to higher energy bins. Corrections were also applied to diffraction data and it was found that a correction for the response has minor impact on the diffraction data. Since there exist problems with the diffraction data at low momentum transfer arguments (x) a preliminary analysis of noise at low x was conducted. The scatter from the 3 mm diameter pinhole used to define the beam area on the target samples was 6% of the primary beam. A new CdTe detector has been recently purchased for the diffraction system. This detector has less problems with hole tailing and noise. The analytical model was applied to calculate the response functions of the CdTe detector.