MULTIDIMENSIONAL NEUTRON-COMPUTED TOMOGRAPHY USING COOLED CHARGE-COUPLED-DEVICES

A prototype position-sensitive neutron detector was designed and built for two- and three-dimensional tomographic imaging of materials and complex assemblies. The detector system consists of an LiF-ZnS scintillator screen optically coupled to a cooled charge-coupled device (CCD). Practical resolution limits of the single screen system were calculated to be approximately 100-mu-m, determined by the neutron beam divergence and the resolution of the scintillator screen. Contrast resolution in a (200-mu-m)3 volume element was calculated to be 1% of the cross-section in small samples. The system included the MIT Research Reactor as a thermal neutron source (nominal flux approximately 2.4 x 10(8) n-degrees/cm2-sec), a rotating sample holder, and the two-dimensional position-sensitive detector. The effects of scatter were estimated and compared to data. Two- and three-dimensional tomograms were obtained of phantoms and several demonstration objects, including a control valve and an oil well dolomite core sample. The spatial resolution in the images compared favorably to predictions, and it is expected that the final system will improve resolution by at least a factor 10 over current technology.