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The D-T gamma-to-neutron branching ratio (3 H(d,γ) 5 He/ 3 H(d,n) 4 He) has been determined at inertial confinement fusion (ICF) conditions, where the center-of-mass energy of 14-24 keV is lower than in previous accelerator-based experiments. A D-T branching ratio value of (4.2 ± 2.0)×10-5 was determined by averaging the results of two methods: 1) a direct measurement of ICF D-T γ-ray and neutron emissions using absolutely-calibrated detectors, and 2) a separate cross-calibration against the D-3 He gamma-to-proton branching ratio (3 He(d,γ) 5 Li/ 3 He(d,p) 4 He). Neutron-induced backgrounds are significantly reduced as compared to traditional beam-target accelerator-based experiments due to the short pulse nature of ICF implosions and the use of gas Cherenkov γ-ray detectors with fast temporal responses and inherent energy thresholds. These measurements of the D-T branching ratio in an ICF environment test several theoretical assumptions about the nature of A = 5 systems, including the dominance of the 3/2 + resonance at low energies, the presence of the broad first excited state of 5 He in the spectra, and the charge-symmetric nature of the capture processes in the mirror systems 5 He and 5 Li.

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The National Ignition Facility (NIF), currently under construction at the Lawrence Livermore National Laboratory, will provide unprecedented opportunities for the use of nuclear diagnostics in inertial confinement fusion experiments. The completed facility will provide 2 MJ of laser energy for driving targets, compared to the approximately 40 kJ that was available on Nova and the approximately 30 kJ available on Omega. Ignited NIF targets are anticipated to produce up to 1019 DT neutrons. In addition to a basic set of nuclear diagnostics based on previous experience, these higher NIF yields are expected to allow innovative nuclear diagnostic techniques to be utilized, such as neutron imaging, recoil proton techniques, and gamma-ray-based reaction history measurements.