Comparison of Several Methods for the Photographic Detection of Thermal Neutron Images

Abstract

Several methods of photographic detection of thermal neutron images have been studied and compared with regard to photographic speed, relative neutron‐gamma response, and image sharpness qualities. All these comparisons have been made using a low gamma content, monochromatic neutron beam (1.05 A) having an intensity of 3×10⁵ neutrons/cm²‐sec. The fastest speed, best neutron‐gamma response of the direct exposure methods, and good image sharpness have been obtained by using a direct exposure method employing a B‐10 loaded scintillator and type F x‐ray film. Gadolinium and rhodium intensifier screens with type KK film have also yielded good results by the direct exposure method (film and intensifier screens exposed to the neutron beam together). Results are also reported for the use of indium, cadmium, silver, and gold screens. The transfer method, in which the photographic film is exposed only to the radioactive decay radiation of an image‐carrying metallic screen, and not to the neutron beam itself, has been found useful not only because no effect on the image is produced by gamma radiation in the neutron beam, but also because improved image sharpness has been obtained. In the cases of indium and gold (the two materials which have been found useful for the transfer method in the neutron flux available for this study), the improved image resolution obtained with the transfer method has been shown to result from the fact that the high energy prompt (n,γ) radiation is not detected on the film.