Improving the image contrast and resolution in the phase-contrast neutron radiography

The phase-contrast radiography is an edge-enhancement technique which allows to visualize objects providing very low contrast with the conventional absorption radiography technique. The image formation in this case is based on the phase variations transformed to intensity variations in a beam with a high lateral coherence by its transmission of the object. Due to the fact that neutrons could not be easily focused in a spot with a micrometric size like X-rays we need a small diaphragm and a large distance between the diaphragm and the sample in order to achieve a good lateral coherence length for the neutron phase-contrast radiographic experiments. The main beam parameters which generate some differences between the different beam facilities and influence the phase-contrast effect are the beam divergences and the beam spectra of each beam lines. Various examples of phase-contrast imaging performed at neutron beam lines with different beam parameters will be shown. The combination of the phase-contrast effect with the effect of image magnification due to the beam divergence which leads to an improvement in the image contrast and resolution will be presented in detail.