Experimental Validation of Gamma Reaction History (GRH) Response to Neutron Induced Gamma Rays

The Gamma Reaction History (GRH) diagnostic has provided a fusion reaction history at the National Ignition Facility (NIF) by detecting a 16.75 MeV gamma ray generated from deuterium-tritium (DT) fusion reactions. Two gas cells of the GRH detector typically operate at 10 MeV or 8 MeV energy thresholds to isolate the DT fusion gammas, however, the GRH signal may be contaminated by various neutron-induced gammas such as (1) imploding capsules (e.g., C or SiO2), (2) hohlraum (e.g., Au or U), and (3) thermo-mechanical package (e.g., Si or Al). Experimental validation of the GRH response to the neutron-induced gamma rays is necessary to reduce uncertainty in the measurement of the fusion reaction history. Elemental samples of C, Si, Al, and W were irradiated with 14 MeV DT fusion neutrons at the OMEGA Laser Facility and their resulting gamma emission was measured. The Geant4 Monte-Carlo simulation will be compared with experimental measurements to validate a neutron-induced gamma production and a GRH detector response.