Optical phenomena in KU-1 silica core fiber waveguides under pulsed reactor irradiation

The light emission intensity and transient optical absorption (TOA) have been measured in the wavelength range 400–750 nm in KU-1 silica core fibers under irradiation of the BARS-6 pulsed fission reactor (pulse duration 80 μs, fluence per pulse up to 5×1012 n/cm2 (E>0.5 eV), dose rate up to 105 Gy/s). The fast light emission component attributed to Cherenkov radiation is followed by a weak emission tail with the characteristic time (150±50) μs. The transient absorption reaches 2.5×10−4 cm−1 (relaxation time 600–1200 μs). The sub-linear dependence of Cherenkov radiation on the dose rate and the occurrence of both the tail of light emission and transient absorption are ascribed to the appearance of optical inhomogeneities of the silica glass under intense pulsed reactor irradiation.