A novel fiber optic sensor responds with a supra-linear relationship between optical density readout and absorbed dose, when irradiated with high doses of x and gamma radiation (10$+$MIN@2$/ to 10$+4$/ Gy). The radiation sensor medium is a radiochromic gel core filling a flexible fluorinated polyethylene plastic tubing that is fitted with either Suprasil quartz plugs as radiation-insensitive end windows or Pyrex glass beads that serve as lenses. Readings are made with a specially designed spectrophotometer enabling efficient propagation of interrogating light with a narrow band-pass filter at the optical wavelength of the radiation-induced color absorption band maximum (600 nm). The absorption at 600 nm is related to the formation of a highly conjugated carbocationic dye. The formation of the conjugation proceeds through very fast kinetics (approximately 1 ns) followed by relatively slower kinetics (2 ms). The shortest selective fiber optic sensor length is 5 cm and outer diameter is 0.27 cm, allowing selective placement of the sensor portion into remote irradiated components. Fiber optic sensor lengths up to 150 cm allow dose measurements as low as 10 $+$MIN@2$/ Gy. Extraction of radiation dosimetry data to the external reader is carried out either in real-time or on demand following irradiation, and is made possible by connecting the sensor length to ancillary fiber optic access loop.
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