Determination of the deuterium-tritium branching ratio based on inertial confinement fusion implosions

Abstract

The deuterium-tritium (D-T) γ-to-neutron branching ratio [[superscript 3]H(d,γ)[superscript 5]He/[superscript 3]H(d,n)[superscript 4]He] was determined under inertial confinement fusion (ICF) conditions, where the center-of-mass energy of 14–24 keV is lower than that in previous accelerator-based experiments. A D-T branching ratio value of (4.2 ± 2.0) × 10[superscript −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-[superscript 3]He γ-to-proton branching ratio [[superscript 3]He(d,γ)[superscript 5]Li/[superscript 3]He(d,p)[superscript 4]He]. Neutron-induced backgrounds were 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[superscript +] resonance at low energies, the presence of the broad first excited state of [superscript 5]He in the spectra, and the charge-symmetric nature of the capture processes in the mirror systems [superscript 5]He and [superscript 5]Li.