Performance Evaluation in Transmission Neutron Tomography using Geant4

Thermal neutron tomography is a non-destructive technique used for the investigation of the internal structure of objects. This technique provides complementary information to X-ray tomography for a wide range of applications in science and engineering. High spatial resolution of a neutron tomography system can be achieved with a thinner scintillator and a well collimated neutron beam. In this work, Geant4 is used to model and study the performance of a thermal neutron tomography system which includes a thermal neutron source, a scintillation screen and a pixilated imaging detector. The thermal neutron source is assumed to be a beam extracted from the PULSTAR research reactor at North Carolina State University (NCSU). The 6LiF:ZnS(Ag) scintillator is modelled along with the pixelated detector to record the projection data. The projection data is obtained by simulating 25 μm, 50 μm and 250 μm thick scintillators at two positions from the beam aperture yielding different L/D ratio. The filtered back projection (FBP) algorithm is used for the reconstruction of the projection data. Several FBP filters are evaluated with the Hanning filter giving the best reconstruction performance. Further simulations are carried out for the measurement of the spatial resolution of the radiographs and the scintillator screen separately. The results show that as the scintillator screen thickness decreases and/or as the object and detector distance from the beam aperture increases, the spatial resolution improves. Estimation of the contribution of tomographic image reconstruction is performed and found to be of similar magnitude to other components.