Research and development of a super high sensitive nuclear emulsion gel

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A research and development was performed on the nuclear emulsion gel, which has a long history and no new R&D trial was performed for a long period. With the help of Fuji film co., we applied' the newest technologies, i.e. controlled double jet production of AgBr and core-shell structure of the micro crystal, which were currently used in the photographic emulsion production, to the production of the nuclear emulsion gel.The developed nuclear emulsion gel can record 65 grains per 100 microns long trajectory of a minimum ionizing particle. The achieved sensitivity is about 1.8 times higher than Fuji ET7B used for a long time until today and about 1.4 times higher than the gel used in DONUT experiment.Also, we tried to create a fine resolution gel of 0.05 micron diameter. Though it has almost no sensitivity to a minimum ionizing particle, we can investigate the possibility of position resolution of nuclear emulsion by using electron-microscopes. The developed grains are normally larger than the original size of the micro crystal, because of a rapid growth of a filament like structure (diameter about 25 nm) from the grains. Further R&D is needed to suppress the filament growth and keep the position resolution as fine as the original size.