EFFECT OF IONIZING-RADIATION ON IN-SITU RAMAN-SCATTERING AND PHOTOLUMINESCENCE OF SILICA OPTICAL FIBERS

Raman fiber optic chemical sensors provide remote in situ characteriza tion capability. One application of Raman fiber optic chemical sensors is the characterization of the contents of nuclear waste tanks. In th ese tanks it is expected that approximately 20 meters of optical fiber will be exposed to radiation levels between 100 and 1000 rads/hour. I n support of this work two silica optical fiber types (one a communica tions grade fiber and the other nominally radiation resistant) have be en tested at the radiation levels expected in the tanks. Luminescence and Raman scattering measurements have been performed in situ with 488 -nm excitation on two types of silica optical fiber exposed to a const ant low to moderate dose rate of gamma radiation of 880 rads(Si)/hour from a Co-60 source for a total dose of greater than 45 krads. The nom inally radiation-resistant fiber was also excited with 514.5-nm and ne ar-infrared 830-nm laser radiation. The rate of the silica Raman signa l fdecrease is more than three times greater for the visible excitatio n wavelengths than for the 830-nm excitation for the radiation resista nt fiber. The behavior of the 650-nm photoluminescence line upon irrad iation was different for the two fibers studied, both in terms of the shift of the 650-nm line and rate of increase of the normalized photol uminescence intensity. In all cases the photoluminescence from the fib ers was less than the Raman intensity. No radioluminescence was observ ed in either fiber. The radiation resistant fiber exhibited photobleac hing effects on the Raman transmission when photoannealed with 488-nm laser light.