Long-term bleaching of optical glasses darkened by Co60 ionizing radiation

Typical camera designs include optical glass elements that ma be affected by the ionizing radiation present in the natuml space environment. Ordinary optical glasses darken at low (10 mcI) dose levels when exposed to ionizing radiation. This darkening decreases the sensitivity ofoptical sensors. Optical glass flats ofFK 51, LaK 9, PK 51A, and ZK N7 were exposed to a 10.6 krad dose of ionizing mdiation. Spectrophotometer tmces determined the transmittance of the samples as a function ofwavelength in the range 350 to 850 nm befoie and at various time inteivals after the irradiation. These measured values were then used to evaluate the rate of recovery or "bleaching" of the exposed samples. To prevent celemted bleaching, the samples were kept at room temperature and away fmm light, except during measurement. Tables of the measuied data and plots of the tmnsmissivity vs. wavelength at various times after irradiation are presented.