Study on luminescence of fine-grained nuclear emulsion by charged particles

Abstract Silver bromide, which is an indirect transition-type semiconductor, has been used as a photographic film and a charged particle tracking detector since the 19th century because it is sensitive to absorption of light or energy loss by charged particles. At cryogenic temperatures, it is known that the luminescence occurs in silver bromide with high quantum efficiency via impurities such as iodide ions. It was studied only by photo-excitation and tribo-excitation in the previous studies, and in this paper, for the first time, we observed the luminescence produced by charged-particle excitation by using a fine-grained nuclear emulsion consisting of 40 nm silver iodobromide crystals. The ratios of the contribution to luminescence among the electron–hole pairs expected by the energy deposition of charged particles were (5.7 ± 0.8)% with 5.48 MeV α -rays and (22.5 ± 3.5)% with 10 to 60 keV γ -rays at 88 K. The luminescence wavelength produced by α -rays had a peak at 540 nm and was shorter than that produced by photo-excitation having a peak at 575 nm.