Nuclear emulsions for dark matter detection

On silver halide (AgX) emulsion grains (∼200 nm in diameter) for neutrino detection in OPERA project, a latent image center composed of a cluster of ≧4 Ag atoms is formed with ∼18 electron-hole pairs by current photographic process in each grain. According to the analysis in this paper, AgX emulsion grains (∼40 nm) for dark matter detection should behave quite differently, forming a latent image center under such extraordinary condition that as many as ∼1000 electrons and surplus positive holes are created for ∼10 femtoseconds (fs) in each grain, causing violent recombination and re-halogenation of Ag clusters. Therefore, it is necessary to strongly reduce the recombination and re-halogenation of Ag clusters in the nuclear emulsions for dark matter detection. Further proposals are made on the design of nuclear emulsions for dark matter detection.