Gamma Ray Diagnostics in Large Helical Device

Gamma ray diagnostics have been developed and installed in Large Helical Device (LHD) to study plasma physics, as well as to measure neutron fluence and spectrum in the LHD torus hall. LaBr3:Ce scintillation and high purity Germanium (HPGe) detectors have been installed. LaBr₃:Ce scintillation detectors were used to measure gamma rays emitted from the plasma. Radiation shielding, composed of borated polyethylene and lead, was designed for the LaBr₃:Ce scintillation detector based on Monte Carlo radiation transport calculations. A gamma ray peak around 480 keV, believed to correspond to the 6Li(d, p’γ)7Li reaction, was observed. HPGe detectors were utilized for measuring the activity of metal foils. Using the activation analysis method, the thermal and epithermal neutron fluence distribution inside the LHD torus hall, the neutron spectrum, and the relationship between radioactivity and total neutron emission yield were determined.