Dynamic gamma-ray monitoring at radioprotection levels with extrinsic polymer optical fiber sensors

Abstract

The dynamic performance of extrinsic gamma-ray sensors at radioprotection levels is studied. The sensors have been fabricated with chemically etched polymer optical fibers covered with an inorganic scintillator powder (Terbium doped Gadolinium Oxysulfide). This scintillator shows a maximum emission peak at 543 nm, therefore only the signal amplitude at this wavelength has been measured with a commercial grade CCD spectrometer. The transducers have been done at the end of both short (1 m) and large fiber patchcords (27 m). Short patchcords are further mechanically spliced to a fiber link 25 m length through an industrial grade connector-less mating sleeve, and therefore can be easily replaced if needed.All tests were run under gamma irradiation from a 137Cs source, the reference isotope for environmental protection. The measured response of the devices is very repeatable and stable, with a percentage standard deviation below 2% when the air kerma rate is above 1 Gy/h. This deviation increases for lower rates. A Limit of Detection of 0.2 Gy/h, with an integration time at the detection stage of 10 s, has been achieved for transducers done in the 1 m length patchcords spliced to the 25 m length fiber link. This integration time can be further reduced when no splice is included between transducer and detection unit. The behavior of the devices is linear with the delivered air kerma rate, and can provide reliable measurements under repeated radiation exposures. This behavior makes the sensors useful to quickly detect the presence of hazardous radioactive materials in accidental leakage scenarios.