The nuclear emulsion is known as a solid detector which consists of gelatins and AgBr crystals containing several mol% iodine (hereinafter, refer as AgBr・I), and records traces of charged particles as lines of silver grains with high spatial resolution of submicron. This mechanism is that electrons generated by ionization loss when a charged particle penetrates a crystal react with interstitial silver ions in that crystal. On the other hand, it is thought that iodine contained in the AgBr・I crystal work as hole trap, and holes and electrons recombine with emitting photons. There are several reports that such a photon emission process of silver halide crystals is enhanced at cryogenic temperature. In those studies, they usually use light source or rubbing to excite electrons, but we can expect the same phenomenon even when using charged particles. Thus, we start basic research to use the nuclear emulsion as a scintillation detector.
In this paper, we will report about the result of detecting photons caused by β-ray with photo detector at cryogenic temperature (77K) for the first time.