Gamma ray radiation induced visible light absorption in P-doped silica fibers at low dose levels

A CCD Fiber Optic Spectrometer has been used to monitor the gamma ray radia tion induced loss in P-doped fibers at different dopant concentrations (1, 5 and 10 mol%) with a light source tan incandescent bulb with a temperature of 2800-3000 K). The range of dose rates is limited to that used in medica l applications (cancer treatments), that is 0.1 to 1.0 Gray per minute (Gy/ min). At low integral dose level (<2.0 Gy) four absorption peaks were obser ved (470, 502, 540 and 600 nm) within the visible region. It has been obser ved that the radiation induced loss at 470 and 600 nm depends strongly on d ose rate. At dose rates of 0.2 and 0.5 Gy/min the induced loss shows nonlin ear relation to the total dose. However, at high dose rate (1.0 Gy/min) and low dose rate (0.1 Gy/min) it seems to have a linear dependence with total dose. The conversion from NBOHCs to GeX centers was observed during gamma radiation at low dose rates (0.1-0.5 Gy/min). At the wavelength of 502 and 540 nm, the radiation induced losses show excellent linear relations with t otal dose (<2.0 Cy) with little dose rate dependence. Experimental results show that the sensitivity (induced loss (dB) per meter fiber per Gy) of 5 m ol% P-doped silica fiber is more than 30 times greater than that of a stand ard multi-mode (MM) communication fiber. The results suggest that P-doped s ilica fiber is a good candidate as a sensing component in fiber optic dosim etry, especially for radiation therapy applications. (C) 1999 Elsevier Scie nce Ltd. All rights reserved.