Gamma Irradiation Studies of Some Borate Glasses

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.