B. Tsuchiya

K. Okamoto

S. Nagata

T. Muraga

T. Nishitani

T. Shikama

T. Suzuki

T. Tanaka

T.K. Toh

National Institute for Fusion Science (NIFS-Repository)

§9. 14MeV Neutron Detection System Utilizing Radioluminescence and Optical Fiber Shikama, T., Toh, T.K., Nagata, S., Tsuchiya, B., Suzuki, T., Okamoto, K. (IMR, Tohoku University) Nishitani, T. (FNS, Tokai, JAERI) Tanaka, T., Muraga, T. A possibility of applying a compact optical system to diagnostics of high energy neutrons from a fusion nuclear fusion reaction has been studied, utilizing radiation resistant optical fibers and radio luminescent (radiation-induced luminescent) materials sensitive to a fast neutron. Several materials, which were expected to radiate luminescence, were attached at an end of a synthesized fused silica (Si02) made radiation resistant optical fiber whose core-diameter was O.2mm and were exposed to high energy neutrons generated by the deuterium-tritium (D-T) reaction in the Fast Neutron Source (FNS) of Japan Atomic Energy Research Establishment (JAERJ) in Tokai, and to gamma-rays from cobalt-60 sources in the lAERJ-Takasaki, at room temperature. The fast neutron flux was in the range of I 0"·l2n/m2s in the FNS and the gamma-ray dose rate was about 5Gy/s for the water in JAERI-Takasaki gamma-ray facility. An optical signal was guided through a 30 m long radiation resistant optical fiber, which was developed in the ITER-EDA (ITER Engineering Design Activity) framework for the purpose of applying optical fibers to in-vessel components in the ITER, to a measuring instrument composed of an optical grating and a CCD, the PMA-II made by Hamaphoto Co. Ltd. Silver activated zinc sulfide (ZnS-Ag), copper activated zinc sulfide (ZnS-Cu), and a strontium aluminate doped with europium and dysprosium (Sr,AI,Oy-EuDy), were found to be radioluminescent, being sensitive to high energy neutrons with a peak position at 450nm, 570nm, and 500nm, respcctively, having a half width of75-150nm. Figure I shows a luminescent spectrum from the ZnS-Ag under a fast neutron flux of about I0 12n/m2s. The ZnS-Ag had the strongest luminescence among three but its intensity decreased with the increase of neutron fluence, in the meantime, the other two, the ZnS-Cu and the Sr,AI,Oy-EuDy had relatively weak luminescent intensity but their peak intensity did not change substantially with the fast neutron fluence up to f020n/m2. Changes of the luminescent peak intensities are shown in Fig 2 as a function of irradiation time. For a high sensitivity, the ZnS-Ag is the best among three, but for a long-term stability and being free from frequent re-calibration or replacement, the ZnS- Cu and the SrAI,04-EuDy arc preferable. Behaviors of radioluminescence were different in between the fast neutrons and the gamma-rays, indicating that the discrimination of the neutrons from the gamma-rays is possible. The present results clearly shows that a simple fast-neutron-detection system can be composed for a burning plasma machine. 438 3500 3000 -;;;-.B: - 2500 -J .5 ... o . , 0-o 2000 1500 1000 50: ~I' ,~i,.~~I~~ .''''~d. 200 300 400 500 600 700 800 900 Wavelength (nm) Fgure 1 Radioluminescent spectrum from ZnS-Ag under 14MeV fusion neutron irradiation in FNS. :i 3500 • 3000 ....... " SrAl20,:Eu,Dy • ZnS:Ag o ZoS:Cu ~ 2500 ·························0··· .~ E 2000 . 5 • .....• o ······0··· o o ... . ~ 1500 . .................................................... .. 0 8' • .. ~ ....................... ~A .. ................... ZI. ••••••..•••••••••••••• .j).. " ~" 1000 • " . ~ .... ~ .............. t:: 500 .......... 0. ..... 6 6 o~~~~~~~~~~~ o 10 20 30 40 50 60 70 80 Irradiation Time (,) Figure 2 Change of optical intensity of radioluminescence by 14MeV neutron in the course of irradiation. 14MeV neutron flux is about 10' '·l2n/m2s in FNS of JAERJ 

14MeV Neutron Detection System Utilizing Radioluminescence and Optical Fiber

14MeV Neutron Detection System Utilizing Radioluminescence and Optical Fiber

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