Forecasting the effect of neutron beam divergence on the quality of tomographic images

The impact of the divergence of a neutron beam emitted by a surface source on the quality of 2D tomographic images has been assessed through a computer code specially written for this purpose. It generates position spectra used as projections for the final image reconstruction, based on the geometric and physical properties of the sample and its positioning in the system, detector resolution, beam divergence expressed by the width of its rocking curve, and on the counting statistics. Such a forecast is important in order to evaluate whether measures to reduce the divergence are worthwhile at all, before efforts and investment to design and manufacture collimators or purchase them are done. It also helps to optimize parameters prior to performing the measurements with real imaging systems. Simulated images of some test objects obtained under different beam divergences have been compared with experimentally acquired ones, using an imaging system equipped with a position sensitive detector (PSD). Further simulations performed under a constant divergence, to evaluate the impact of the total rotation angle applied to the object, have also been done, showing that the developed simulator is an useful tool to plan experiments and to optimize parameters of imaging systems of this kind.