Characterization of nuclear emulsions in overview of photographic emulsions

Nuclear emulsions for OPERA and WIMPs detection are characterized in the overview of photographic emulsions with respect to the grain size dependence of their sensitivities. The emulsions are classified into three groups. The grains in Class I, which are larger than 0.5 μm in diameter, are highly sensitive owing to their large light absorbance, and used for color films. The grains in Class II, which are 0.1 ∼ 0.5 μm in diameter and include those for OPERA films, are principally defect-free and therefore afford efficient latent image formation. The grains in Class III, which are smaller than 0.1 eV and expected to be available for WIMPs detection, are still poorly understood and interesting to study from the viewpoints of the formation and characterization of quantum-sized grains. Discussions are also made on the mechanism of the reset function brought about by the “refresh” treatment for OPERA films and its applicability to those for WIMPs detection.