R-matrix analysis of T(T,2n)α neutron spectra from ensemble of OMEGA implosion experiments using nested sampling

A detailed analysis of historic neutron time-of-flight (nToF) data from OMEGA ICF experiments has been performed to fit T(T,2n)α neutron spectra with a R-matrix model [1]. These experiments used high purity tritium fills and span a wide range of ion temperatures. In ICF, the ion temperature serves as a proxy for the centre of mass energy, which directly governs the reaction physics. Previous studies have shown that the best fit feeding factors of the T(T,2n)α vary with reaction energy [2]. As T(T,2n)α is the mirror reaction of 3He(3He,2n)α, accurate fitting of the nuclear physics model is of astrophysical relevance. In this present study we include additional OMEGA nToF data to the analysis and use a fully Bayesian approach in inferred the varying feeding factors.

Fitting to the OMEGA nToF data, we ensure improved accuracy of the inference of the TT neutron spectral shape by using recent developments on detector models. A nested sampling method, PolyChord, was employed to robustly find posterior distributions of the feeding factors. Finally, we investigate making feeding factors a linear function of energy and fitting all OMEGA experiments simultaneously. As a separate point of comparison, a model-independent P spline method has been used to compare to the R-matrix fits in the energy domain.



[1] – Brune, C. et al. (2015), Phys. Rev. C 92, 014003

[2] – Gatu Johnson, M., et al. (2018). Physical review letters, 121(4), 042501.