Low-velocity ion tracks in fine grain emulsion

We have studied low-velocity Kr ion responses of nuclear emulsions for the possibility of tracking Ag and Br recoils from galactic dark matter particles. Tracks of 680–1180 km/s Kr ions have been observed in a 40 nm-sized AgBr grain emulsion with scanning electron microscopy. The tracks have a linear energy-dependency in range, angles biased along the incident direction, and a high developed-grain number density with respect to expected electronic stopping. We find that the fine grain emulsion is sensitive enough to low-velocity heavy ions whose energy losses are mainly governed by nuclear stopping.