γ -to-neutron branching ratio for deuterium-tritium fusion determined using high-energy-density plasmas and a fused silica Cherenkov detector

A fused silica Cherenkov detector was used to measure deuterium-tritium (DT) gammas during a set of 52 direct-drive cryogenic experiments performed at OMEGA. The detector was calibrated using the 4.4 MeV gamma from the first excited state of carbon, which is produced when 14-MeV DT neutrons impinge upon a carbon puck. An approximate DT gamma spectrum as well as neutron yields from a standard neutron time-of-flight detector at OMEGA were used to calculate a DT gamma to neutron branching ratio of (8.42 ± 2.84) × 10−5. Assuming an excited state to ground state ratio of 2.1:1, the measurement detailed in this work results in an approximate ground state only gamma-to-neutron branching ratio of 2.72 × 10−5. This value is somewhat lower than accelerator-based measurements of the ground state DT gamma only.