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At Kyoto University Research Reactor Institute(KURRI), we installed a Cyclotron-Based Epithermal Neutron Source(C-BENS) for Boron Neutron Capture Therapy(BNCT). C-BENS consists of a cyclotron accelerator that can provide a ~ 1000 μA, 30 MeV proton beam, a neutron production beryllium target and the moderator that can reduce the energy of fast neutrons to an effective energy range. C-BENS can provide epithermal neutron flux of 1.2 × 10 9 (cm-2 s-1) larger than that of conventional reactor-based neutron sources which have been using for clinical trials of BNCT. During irradiation of BNCT, it is important to detect neutron flux up to 109 (cm-2 s-1). Now we have been developing the real-time neutron flux monitor with the characteristics such as the resistance of radiation damage and low attenuation rate in optical fiber. To evaluate detection system, the thermal neutron irradiation field using C-BENS in water phantom with the thermal neutron flux from 108 to 109 was used. The good linearity between the detector counts and thermal neutron flux was obtained.