Measurement of D-T branching ratio based on cross-calibration to D-3He

Summary form only given. Interest in the gamma-ray producing branch of D-T fusion has increased as the National Ignition Facility (NIF) is moving toward ICF D-T ignition. Measurements of the branching ratio for T(d,γ)5He relative to T(d,α)n are necessary if the gamma-rays are to be fully exploited as a fusion diagnostic. In the present experiment, gamma rays from T(d,γ)5He and D(3He,γ)5Li were measured using a Gas Cherenkov Detector (GCD) at Omega laser facility. The GCD is a high-energy gamma ray detector utilizing gamma-to-electron Compton scattering and electron-to-light Cherenkov principle. The high-bandwidth of the GCD allows for the detection of D-T fusion gamma rays before the 14.1 MeV neutrons arrive at the GCD, mitigating the neutron background issues that have plagued beam-target based measurements. The primary goal of the experiment was to cross-calibrate the D-T gamma/neutron branching ratio against the better known D-3He gamma/proton branching ratio. Accurate measurements of the neutron and proton fusion product yields are key components for this work. Initial experimental results show that D-T branching ratio is about 2.6 times less than the D-3He branching ratio, which is inconsistent with the assumption of charge independence of D-3He and D-T reactions. The refining of the exact branching ratio will be discussed at the conference.