Absorption Spectrum of NaNO3 Exposed to Ionizing Radiation

Abstract

The changes produced by ionizing radiation in the absorption spectrum of NaNO3 crystals are in the main caused by two effects: the conversion of NO3— ions into NO2— ions with an absorption band, which has its peak at 345 mμ and shows a characteristic structure when observed at low temperature; and the production of color centers with a continuous absorption band with peak at 335 mμ. The formation of the color centers is assumed to be connected with the presence in the lattice of NO2— ions, although no precise model can be proposed for these centers. The color center band can be bleached by ultraviolet light even at — 190°C; at room temperature it is partially destroyed by the ionizing radiation which is able to produce the centers, while this is not the case with respect to the NO2— ions. Therefore the NO2— band is relatively much stronger in crystals exposed to the ionizing radiation at higher temperatures, for instance in the pile, while in crystals x-rayed at — 190°C the color center band prevails.