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Radioluminescence from rare earth oxide materials was measured in the visible wavelength range and the range from 1000 to 3000 nm in an ion beam accelerator and a fission reactor of Japan Materials Testing Reactor (JMTR). In erbium oxide, peaks at 560, 660, and 1540 nm were observed by the proton beam irradiation, and the complicated luminescence peaks around 1800 and 2000 nm were observed by the proton beam irradiation and at the reactor full power operation of 50 MW. The peaks at 560, 660, and 1540 nm are attributed to the electron transition between the energy levels of Er3+ ions. The complicated luminescences observed in JMTR were quenched with the irradiation time elapsed, though the intensity was not changed by the irradiation of the proton beam of 2.6 x 1013 p/cm2s. It was considered that the precursors for the complicated luminescent peaks around 1800 and 2000 nm disappeared under the neutrons irradiation.

To promote development of radiation-resistant core optical fibers, the ITER-EDA (International Thermonuclear Experimental Reactor-Engineering Design Activity) recommended carrying out international round-robin irradiation tests of optical fibers to establish a reliable database for their applications in the ITER plasma diagnostics. Ten developed optical fibers were irradiation-tested in a Co-60 gamma cell, a Japan Materials Testing Reactor (JMTR). Also, some of them were irradiation tested in a fast neutron irradiation facility of FNS (Fast Neutron Source), especially to study temperature dependence of neutron-associated irradiation effects. Included were several Japanese fluorine doped fibers and one Japanese standard fiber (purified and undoped silica core), as well as seven Russian fibers. Some of Russian fibers were drawn by Japanese manufactures from Russian made pre-form rods to study effects of manufacturing processes to radiation resistant properties. The present paper will describe behaviors of growth of radiation-induced optical transmission loss in the wavelength range of 350-1750nm. Results indicate that role of displacement damages by fast neutrons are very important in introducing permanent optical transmission loss. Spectra of optical transmission loss in visible range will depend on irradiation temperatures and material parameters of optical fibers.

Strong radioluminescence band and peaks were observed in fused silica core optical fibers under irradiation in fission reactors of Japan Materials Testing Reactor (JMTR) and in gamma-irradiation facility. A broad band in 400-1700 nm could be attributed to Cerenkov radiation, whose intensity was proportional to inverse of the third power of wavelength. The optical intensity of the peak at 450 nm, that was considered to be generated by oxygen vacancies, was proportional to the reactor power under the electronic excitation dose rate up to 5.0 x 10 3 Gy/s, and the dynamic range was at least more than five orders of magnitude. The peak intensity depends on details of silica microstructures and became twice after annealing at 773K. By using these radioluminescence peak and band, wide range dosimetry could be actualized in heavy radiation environments.

An experimental demonstration of fiber optic temperature sensing in the in-core region of Japan Materials Testing Reactor from 250 to 750 degrees C is described. Temperature data could be obtained for two full-power weeks with neutron fluxes of approximately 1014 n/cm2/s and gamma dose rates of approximately 5 X 103 Gy/s. The measurements were based on thermally generated IR light within the optical fiber itself. The fiber thus served as both signal generator and signal transmitter to the out-of-core region. The fibers utilized in the experiments where of high OH pure-silica-core type and showed good radiation resistance. In the IR region the transmission of the fibers was only weakly affected by the incident radiation. Radiation induced luminescence and Cerenkov radiation in the optical fibers were found to have small influence on the signal in the IR window. The high OH content of the fibers used in the present experiment precluded the use of the spectral regions at 945, 1245, and 1390 nm, due to the high intrinsic and radiation induced absorption at these wavelengths. The use of silica fibers limited the maximum temperature to < 1000 degrees C. The present experiments show that optical sensors based on IR emission can be used to monitor temperature in the in-core region of nuclear reactors for extended periods of time.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.