Neutron-induced luminescence of insulators

We have tried to make in-situ observations of ion- and neutron-induced luminescence and/or fluorescence of various kinds of silica glass and crystal. Experiments were carried out using the YAYOI nuclear reactor at the University of Tokyo. minescence from the specimen in the reactor core is transported to a monochromator away from the core by a light guiding tube, in order to avoid any influence of the background γ radiation on the photon-detecting system. The observed in-reactor luminescence spectra of SiO2 show two broad bands peaked at around 470 and 800 nm. The 470 nm band is very similar to that observed in previous ion-induced luminescence as well as electroluminescence. Ion-induced luminescence exhibits two bands centered at 340 and 450 nm. The 450 nm band is consistent with the 470 nm measured for the in-reactor luminescence. From the incident energy dependence, the 450 nm luminescence is assigned to oxygen-vacancy-related or impurity-related color centers caused by an electron excitation effect of injected ions and neutrons. in-reactor luminescence measurements, the 800 nm band is more intense than the 470 nm band, although no appreciable emission has appeared near 800 nm in the ion-induced luminescence and electroluminescence. Therefore the 800 nm band is very probably due to the Cerenkov radiation caused by γ-rays in the reactor. However, the wavelength dependence of the emission intensity does not support the Cerenkov radiation; even the strong optical absorption at around 500 nm is taken into account.