IONIZING-RADIATION DETECTOR USING MULTIMODE OPTICAL FIBERS

An optical ionizing radiation detector, based on the attenuation of 85 0-mn light in 50/125-mum multimode fibers, is described. The detector is especially well suited for application on spacecraft because of its small design. The detection element consists of a section of coiled f ibers that has been designed to strip higher-order optical modes. Cyli ndrical radiation shields with atomic numbers ranging from Z = 13 (alu minum) to Z = 82 (lead) were placed around the ionizing radiation dete ctor so that the effectiveness of the detector could be measured. By e xposing the shields and the detector to 1.25-MeV cobalt 60 radiation, the mass attenuation coefficients of the shields were measured. The de tector is based on the phenomenon that radiation creates optical color centers in glass fibers. Electron spin resonance spectroscopy perform ed on the 50/125-mum fibers showed the presence of germanium oxide and phosphorus-based color centers. The intensity of these centers is dir ectly related to the accumulated gamma radiation.