An optical ionizing radiation detector, based on the attenuation of 850-nm light in 50/125- mu m multimode fibers, is described. The detection element consists of a section of coiled fibers that has been designed to strip higher-order optical modes. Cylindrical radiation shields with atomic numbers ranging from Z=13 (aluminium) to Z=82 (lead) are placed around the ionizing radiation detector so that the effectiveness of the detector can be measured. By exposing the shields and the detector to 1.25-MeV cobalt 60 radiation, the mass attenuation coefficients of the shields are measured. Electron spin resonance spectroscopy performed on the 50/125- mu m fibers shows the presence of germanium oxide and phosphorus-based color centers. The intensity of these centers is directly related to the accumulated gamma radiation.
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