Thermal neutron flux evaluation using a single crystal diamond detector (SDD) was carried out in the core region of the UTR-KINKI reactor where a mixed radiation field by thermal and fast neutrons and gamma-ray exists. The pulse shape discrimination method to extract pulses with a rectangular shape as well as a wide pulse-width was established to exclude pulses induced by gamma-rays. The SDD, using a 6 LiF thermal neutron converter, is able to detect pulse events caused not only by fast neutrons but also by thermal neutrons through energy depositions into the diamond by energetic alpha and triton particles induced by thermal neutrons. Additionally, the SDD without the thermal neutron converter was used for the measurement of the energy deposition events only by fast neutrons. A comparison of the pulse counts of the SDD with or without the thermal neutron convertor deduced the energy deposition spectra by thermal neutrons. The thermal neutron flux in the core region of the UTR-KINKI reactor was evaluated to be 7.6 × 10 6 n cm −2 s −1 W −1 up to a reactor power of 1 W.

A large volume and fast response gamma ray diagnostic based on the LaBr 3 (Ce) scintillator was installed to obtain the gamma ray spectrum in the Large Helical Device (LHD) for understanding energetic ion confinement. The advantages of the LaBr 3 (Ce) scintillator are relatively sensitive to gamma rays due to its relatively heavy weight density of 5.3 g/cc, high counting operation because of a relatively short pulse width of ∼ 100 ns, and relatively better energy resolution of ∼3%. The gamma ray diagnostic was installed at the outboard side of LHD. The radiation shielding for the LaBr 3 (Ce) detector was designed to avoid unwanted signals due to stray neutrons and gamma rays using the three-dimensional radiation transport calculation MCNP6. In-situ energy calibration of the LaBr 3 (Ce) detector was performed using 60 Co and 137 Cs gamma ray sources. We surveyed a neutron effect on the LaBr 3 (Ce) detector in an electron-cyclotron-heated deuterium plasma discharge. The pulse counting rate of LaBr 3 (Ce) detector under the total neutron emission rate of 2×10 11 n/s was 110 kcps. Therefore, the LaBr 3 (Ce) detector is expected to be utilized in most of ion cyclotron resonance frequency (ICRF) discharges, where the total neutron emission rate of ∼10 11 n/s. We plan to measure the gamma ray spectrum in deuterium ICRF discharges.