Inertial-confinement fusion-plasma-based cross-calibration of the deuterium-tritium γ-to-neutron branching ratio
J. Jeet, A. B. Zylstra, M. S. Rubery, Y. Kim, K. D. Meaney, C. J. Forrest, V. Yu. Glebov, C. J. Horsfield, A. M. McEvoy, H. W. Herrmann
Abstract
The deuterium-tritium (D-T) $\ensuremath{\gamma}$-to-neutron branching ratio $[^{3}\mathrm{H}(d,\ensuremath{\gamma})^{5}\mathrm{He}/^{3}\mathrm{H}(d,n)^{4}\mathrm{He}]$ has been determined previously under inertial-confinement fusion (ICF) conditions and in beam-target based experiments. In the former case, neutron-induced backgrounds are mitigated compared to the latter due to the short pulse nature of ICF implosions and the use of gas Cherenkov $\ensuremath{\gamma}$-ray detectors. An added benefit of ICF based measurements is the ability to achieve lower center-of-mass energies as compared to accelerators. Previous ICF based experiments however report a large uncertainty in the D-T $\ensuremath{\gamma}$-to-neutron branching ratio of $\ensuremath{\approx}48%$, which arises from the necessity of an absolute detector calibration and/or a cross-calibration against the D-$^{3}\mathrm{He} \ensuremath{\gamma}$-to-proton branching ratio. A more precise value for the branching ratio based on data taken at the OMEGA laser facility is reported here, which relies on a cross-calibration against the better known $^{12}\mathrm{C}$ neutron inelastic scattering cross section. A D-T branching ratio value of $(4.6\ifmmode\pm\else\textpm\fi{}0.6)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ is determined by this method.