The changes produced by ionizing radiation in the absorption spectrum of NaNO3crystals are in the main caused by two effects: the conversion of NO3mdash;ions into NO2mdash;ions with an absorption band, which has its peak at 345 mmgr; 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 mmgr;. The formation of the color centers is assumed to be connected with the presence in the lattice of NO2mdash;ions, although no precise model can be proposed for these centers. The color center band can be bleached by ultraviolet light even at mdash; 190deg;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 NO2mdash;ions. Therefore the NO2mdash;band is relatively much stronger in crystals exposed to the ionizing radiation at higher temperatures, for instance in the pile, while in crystals xhyphen;rayed at mdash; 190deg;C the color center band prevails.
展开▼
