A Study on the Effect of Source Collimator Hole Size on theReconstruction Accuracy in 90° Compton Scattering Inspection System

摘要

A new X-ray inspection method, which uses 90° Compton scattered and transmission signal, has been being developedmainly for the inspection of explosive materials. Since point-by-point scan of scattering samples is performed in the system,the beam size of source is closely related to the accuracy of inspection system. In this study, experimental assessment of theaccuracy of the reconstruction program was done according to the change of the source collimator hole diameters in the 90°Compton scattering inspection system. The hole diameters of source collimator employed were 2mm, 4mm, 6mm, and 8mm,and the voltage and current of the X-ray were 450 kVp and 2 mA, respectively. YAP(Ce) and CsI(Tl) detectors were used asthe transmission and scattering detectors, respectively. In this experiment, teflon surrounded by polyethylene blocks was usedas the scattering objects, and the reconstruction program predicted the linear attenuation coefficients of the object. As theresults of this work, for the collimator size of 6 mm, the calculation results were agreed with the reference values within theaccuracy of 14.0 % and 1.1 % for the total and Compton linear attenuation coefficients, respectively, which are the bestresults compared to the cases with other hole sizes. It is due to the fact that the ratio of scattered signal to backgroundincreases as the collimator hole size does. Even though the ratio is the highest for the 8mm hole case, the calculation resultsare not better than those for the 6mm hole case because of the large detection deadtime of about 30%. It is, therefore, notedthat several parameters such as signal-to-background ratio and detection deadtime, etc. are important and should beconsidered to determine the source collimator hole diameter in 90° Compton scattering inspection system.