HIGH-ENERGY X-RAY COMPUTED-TOMOGRAPHY FOR INDUSTRIAL APPLICATIONS

A high energy X-ray computed tomography (CT) system with an electron linear accelerator was developed to image cross-sections of large scale and high density materials. An electron linear accelerator is used for the X-ray source. The maximum X-ray energy is 12 MeV and average energy is around 4 MeV. The intensity of an X-ray fan beam passing through the test object is measured by a 15 channel detector array. CWO scintillators (CdWO4) and photodiodes are used for the X-ray detectors. The crosstalk noise due to scattering of X-ray photons by adjacent detectors is reduced to less than 1.6% by installing a tungsten shields between the scintillators. Extra channels are used to compensate for base line shift of the circuits. These techniques allowed attainment of a dynamic range of more than 85 dB and a noise level comparable to the signal amplitude of X-rays transmitted in a 420-mm thick iron block. Spatial resolution of 0.8 mm was confirmed with an iron test piece 200 mm in diameter.