Fast Neutron Radiography at reactor YAYOI

Abstract

Fast Neutron Radiography (FNR) has been studied with use of the fast neutron source reactor YAYOI of the University of Tokyo. Three kinds of imaging techniques have been applied to the FNR. A CR39 nuclear track detector has been used successfully in the first FNR experiments at YAYOI. This is called as a CR39 track-etch method. The etched out images on the CR39 sheet usually have a low optical density. In order to perform an imaging technique with high resolving power and high contrast, a combination method of a thin type of luminescent converter and X-ray film (a film method) has been developed for the FNR. The converter is made of mixture of PMMA and ZnS(Ag), the thickness of which is 40 μ m. The system could observe the gap of 100 μ m. In the procedure with use of the CR39, it took long time, about 24 hours, to get images. And it took about 3 hours to get imaging results by the film method. A fast neutron television method (FNR-TV) was proposed for shortening the time of taking the images and for taking real time images. The same technique as a current thermal neutron television system was applied to the system while different luminescent converter was used. The prototype converter was made of mixture of polypropylene resin and ZnS(Ag). Static images and real time images were obtained successfully by the fast neutron television method.