$\gamma$-ray emission from ${}^{12}\mathrm{C}$ and ${}^{13}\mathrm{C}$ samples irradiated with deuterium-tritium fusion neutrons was experimentally measured at the Omega Laser Facility and at the Ohio University Edwards Accelerator Laboratory. The intent of these measurements was to determine the feasibility of using ${}^{13}\mathrm{C}$-based plastic ablators with embedded ${}^{12}\mathrm{C}$ layers for “dark mix” diagnosis of inertial confinement fusion implosions. Spectrally resolved measurements at Ohio University identified significant 4.44-MeV $\gamma$-ray emission from the ${}^{13}\mathrm{C}(n,2n\gamma ){}^{12}\mathrm{C}$-L1 reaction channel. The recorded 4.44-MeV ${}^{13}\mathrm{C}$ signal was compared against emission from an identically irradiated ${}^{12}\mathrm{C}$ target with known ${}^{12}\mathrm{C}$($n,n^{\prime }\gamma ){}^{12}\mathrm{C}$-L1 cross section, which resulted in an average ${}^{13}\mathrm{C}(n,2n\gamma ){}^{12}\mathrm{C}$-L1 cross section of 117 $\pm$ 17 mb over the incident neutron energy distribution range from 14.4 to 15.8 MeV. Integrated ${}^{13}\mathrm{C}$ $\gamma$-ray signals above 2.9 MeV recorded with the Gas Cherenkov Detector at Omega exceeded MCNP6.1 predictions by a factor of 3. The additional signal was attributed to 4.44-MeV $\gamma \mathrm{s}$ resulting in an inferred ${}^{13}\mathrm{C}(n,2n\gamma ){}^{12}\mathrm{C}$-L1 cross section of $95\pm 11$ mb at 14.1-MeV average incident neutron energy. As a result, the ${}^{13}\mathrm{C}$-based “dark mix” diagnostic concept was deemed infeasible.

• Received 21 September 2020
• Accepted 12 April 2021

DOI:https://doi.org/10.1103/PhysRevC.103.064607