Selective Detection of Low-Velocity Ions Using Nuclear Emulsion Films

We focused on the difference between the photographic sensitivities of nuclear emulsion films by the electronic stopping power (ESP) and nuclear stopping power (NSP) of charged particles. The effects of high-velocity particles, in which ESP was dominant, and of low-velocity particles, where both ESP and NSP were effective, were compared. Low-velocity Kr ions formed internal latent images by the interaction with NSP. This may be due to the formation of crystal defects by atomic collisions along the route of these ions in silver halide crystals, and such defects are detected only by internal development. On the other hand, high-velocity ions like $\alpha$-rays did not form internal latent images in the emulsion with Au+S sensitization, because sensitization centers on the surface of crystals accumulated excited electrons by ESP and only surface latent images were formed. It is demonstrated that internal latent images are characteristic signals by NSP. Low-velocity ions are selectively detectable by the internal development, even in high background fields like $\gamma$-rays, $\beta$-rays, or other high-velocity ions.