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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.

The changes in gamma-ray induced optical absorption in phosphate glasses resulting from changes in composition, conditions during melting, and additions of small amounts of some oxides are discussed. A resolution of the induced spectra showed that the observed absorption is due to the superposition of three bands at 2.3, 2.9, and 5.5 e.v. (540, 425, and 225 mu) and to a fourth band whose absorption peak is beyond 6 e.v. The ultraviolet induced absorption increases, whereas the visible absorption decreases in glasses melted under reducing conditions as opposed to those melted under normal conditions in air and on replacement of K+ by Na+ or Li+. A similar effect is produced on replacement of Ba++ by Pb++ and on the addition of T12O to a CaO-P2O5 glass or the addition of As2O3 to a CaOP2O5, GeO2 glass. Additions of large amounts of GeO2 are accompanied by a decrease in the number of nonbridging oxygens and a decrease in the visible induced absorption. Replacement of Ca ++ by Ba++ ions showed an over-all decrease in the induced absorption. The addition of small amounts of the oxides of germanium, titanium, iron, thallium, niobium, and arsenic showed an appreciable effect in inhibiting the visible induced coloration.

The role of cerium in the suppression of gamma-ray induced coloration in glass has been found to depend on the relative concentration of Ce3+ to Ce4+ ions as well as on the total cerium content. In a borate glass having high ultraviolet transmission, it has been found that both Ce3+ and Ce4+ ions are necessary to suppress the optical absorption bands induced in the visible region. The role of cerium can be explained on the basis of a change in its oxidation state as a result of gamma irradiation. It is postulated that the cerous ions, by the reaction Ce3+→ Ce4++e, suppress the induced visible band at 2.36 ev (525 mμ), which may result from positive hole centers. High cerous ion concentration results, however, in an induced center (Ce3++e) which absorbs in the visible at about 1.9 ev (650 mμ). The presence of Ce4+ ions near Ce3+ prevents the formation of this center possibly by the reaction Ce4++e→ Ce3+. These induced opposite changes in the oxidation state of cerium tend to maintain a balance in the ratio of Ce3+ to Ce4+ ions in the glass during irradiation, and the suppression of the visible bands depends on this ratio.

Observations made on some lead borate, lead aluminoberate, and lead beroaluminosilicate glasses showed that an absorption band is induced at 1.5 ev (825 m mu ) by gamma irradiation. Experimental evidence indicates that this band is associated with Pb/sup 2+/ ions and beron in the structure of these glasses. On replacing PbO by Tl/sub 2/O in a borate glass, two strong bands were observed; one band corresponds to the 1.5 ev band induced in lead bcrate glasses and a completely new band at 1.0 ev (1235 m mu ). A postulate for the center responsible for the absorption band at 1.5 ev is proposed. (auth)

A glass scintillator which can be used as one of the main components of a slow-neutron time-of-flight spectrometer was developed. Sodium aluminoborate glass containing 73 mole% B/sub 2/O/sub 3/ and 8.0 mole% Ce was melted under highly reducing conditions in a series of ceriumactivated very high boron- containing glasses. The glass is water white with very high light transmittance for wave lengths greater than 3800 A. It has a neutron-detection efficiency which is 25 to 30% greater than any other known glass scintillator in the energy range 10/sup 2/ to 10/sup 4/ ev, and is considerably better than any other type of detector. It was found that the neutron pulse height increases with increasing cerium content up to a maximum and then decreases with further increases in the cerium content. The molar content of cerium required to obtain a maximum pulse height for each B/sub 2/O/sub 3/ concentration increases linearly with the increase in the B/sub 2/O/sub 3/ content. However, the maximum pulse height decreases gradually with the B/sub 2/O/sub 3/ content from 17.0 arbitrary units at 54.5 mole% to 6.7 at 73.4 mole%. This lower pulse height is still considerably above the photomultiplier noise at room temperature. (auth)