Gamma-induced attenuation in normal single-mode and multimode, Ge-doped and P-doped optical fibers: A fiber optic dosimeter for low dose levels

Ge-doped, P-doped, normal single-mode (SM) and multimode (MM) optical fiber s were exposed to Cobalt-60 gamma radiation at dose rates of 0.5 and 3.0 Gy /min, typical radiotherapy dose rates. A CCD-based fiber optic spectrometer was used to measure the real-time absorption spectra of these fibers in th e visible region. Experimental results have shown that P-doped fiber is the most radiation-sensitive of the fibers tested. At the wavelength of 502 nm , the radiation-induced loss in P-doped fiber shows a linear relationship w ith the total dose with no dose-rate dependence. This indicates that dose r ates have no influence on a fiber optic dosimeter operating at this wavelen gth. The radiation-induced losses in normal MM fibers, Ge-doped MM fibers, and Ge-doped SM fibers are shown to be dose-rate dependent.