Fusion gamma rays were measured in D-3He experiments using negative ion-based neutral beam injection (N-NBI) in reverse shear plasmas of the JT-60 tokamak. 3He gas was puffed at plasma initiation and just before N-NB injection. The D-3He reaction produces 3.6 MeV alphas and 14.7 MeV protons, but there is also a small branch which provides 5Li and 16.7 MeV gamma rays. The total D-3He reaction rate can be evaluated from measurement of gamma rays of the 3He (d, γ) 5Li reactions using a 3 in. diam by 3 in. long Bi4Ge3O12 scintillator. The gamma-ray detector was located 17 m below the plasma center and measured the gamma-rays in a vertical line of sight. The detector was mounted inside a heavy collimator with polyethylene and lead shielding. The floor penetration, a 4 × 8 cm2 hole, was used as a precollimator. Energy calibration of the detector was done with photopeaks for neutron capture gamma rays from the structural materials in D-D discharges. The detection efficiency was calculated with Monte Carlo code MCNP-4B for 16.7 MeV gammas. The pulse height analysis of the gamma rays resulted in the D-3He fusion power of 110±30kW in this experiment.
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