Device for looking at a foil irradiated in the context of neutron radiography

In such devices, the foils must be irradiated for an undesirably long time, in order to obtain a satisfactory picture to look at. In order to achieve results with good contrast, even with small densities of etched traces, a case closed on all sides has an opening on the front to accommodate an unetched foil. The side opposite the opening is coverd with a black coating. Against this black background, unetched surfaces appear dark, so that there is no reflection of light beams. However, if there are etched traces on the film, different brightnesses will appear on the film foil, depending on the diameters and depth of these traces. (orig./PW)