Fine grained nuclear emulsion for higher resolution tracking detector

Fine grained nuclear emulsion with several 10 nm silver halide crystals can detect submicron tracks. This detector is expected to be worked as dark matter detector with directional sensitive. Now, nuclear emulsion became possible to be produced at Nagoya University, and extreme fine grained nuclear emulsion with 20 nm diameter was produced. Using this emulsion and new reading out technique with expansion technique, for optical selection and X-ray microscopy, recoiled tracks induced by dark matter can be detected automatically. Then, readout efficiency is larger than 80% at 120 nm, and angular resolution for final confirmation with X-ray microscopy is 20°. In addition, we started to construct the R&D underground facility in Gran Sasso.