Theory
For a gas mixture, the differential cross-section of Migdal effect from neutron–nucleus scattering in the soft limit is given by26,27,57
$$\frac{{{\rm{d}}}^{2}\sigma }{{\rm{d}}{E}_{{\rm{R}}}{\rm{d}}{E}_{{\rm{e}}}}=\sum _{i}\frac{{\rm{d}}{\sigma }_{{\rm{s}}}^{i}}{{\rm{d}}{E}_{{\rm{R}}}}\sum _{n\kappa }\frac{{\rm{d}}{p}_{\upsilon }^{i}(n\kappa \to {E}_{{\rm{e}}})}{{\rm{d}}{E}_{{\rm{e}}}}$$
(2)
where the summation over i accounts for each species in the gas mixture. \({\sigma }_{{\rm{s}}}^{i}\) denotes the scattering cross-section, which includes contributions from elastic (n, n), inelastic (n, n′), fission (n, 2n) and radiative capture (n, γ) processes and can be obtained from the ENDF database ENDF/B-VIII.0 (ref. 58)….