Gamma Irradiation Studies of Some Borate Glasses

Abstract

The gamma‐ray‐induced optical absorption in a series of cabal (calcium‐boron‐aluminum) glasses was studied and is interpreted, wherever possible, in terms of structural concepts. A resolution of the observed absorption spectra showed that three Gaussian‐shaped bands were induced with their maxima at about 2.3, 3.5, and 5.0 e.v. (550, 350, and 250 mμ). The 2.3‐e.v. band decreased in intensity with increasing CaO content, reaching a minimum intensity at a composition corresponding to the four‐coordination of about 20% of the boron. Further increase in CaO content was associated with an increase in the intensity of this band. The intensity of the 3.5‐e.v. band decreased gradually with increased mole per cent of CaO and increased with increased Al2O3. The 5.0‐e.v. band showed an abrupt increase in intensity which corresponded to the appearance of non‐bridging oxygens in the network. Replacing Ca2+ by Mg2+, Sr2+, or Ba2+ or replacing Li+ by Na+ or K+ showed that glasses containing large ions of low field strength give less induced absorption than glasses containing small ions of high field strength. A potassium alumina borate glass melted under reducing conditions gave a considerably higher ultraviolet transmission, before irradiation, as compared with the same glass melted under normal conditions. The gamma‐induced absorption of these two glasses showed that reducing conditions resulted in a decrease in the intensity of the 2.3‐ and 3.5‐e.v. bands, whereas it caused an increase in the far‐ultraviolet‐induced absorption. The effect of additions of arsenic, thallium, titanium, germanium, and some rare‐earth oxides is discussed.