The Kinetics of Gamma‐Ray Induced Coloring of Glass

When glasses are colored by ionizing radiation the induced optical absorption increases as the radiation progresses and appears to be due to the superposition of a number of individual absorption bands. A detailed study of this process has been made using a specimen of Corning boro-silicate glass colored by exposure to 60Co gamma rays. This particular sample was chosen because only four bands are formed. If it is assumed that each band is Gaussian shaped the spectrum may be separated into four absorption bands. The peak energy E0 and full width U of these bands are, in electron volts: E0= 4.85, U= 1.19; E0= 3.95, U= 1.30; Eo= 2.58, U= 0.58; E0= 2.02, U= 0.52. For each band growth curves may be constructed showing how the density of absorption centers increases as a function of dose. These growth curves have been fitted with theoretical curves based on the following considerations: the radiation field creates ionization electrons in the glass; for each ionization electron one electron deficient region or hole is formed; absorption bands observed are due to centers formed by electron trapping although the possibility that some of the bands are due to hole trapping is not ruled out; and competition for ionization electrons exists between holes and the various kinds of electron traps. Satisfactory agreement between the observed and calculated curves is obtained. The theory indicates that the “radiation protection” imparted to glass by materials such as CeO2 may arise in several different ways and that it would be possible to decide between them from rather simple experiments.