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The equivalence between the neutron source and flux spectra is often implicitly used in practice although many times the users are not even aware of this. This work identifies two conditions under which the equivalence holds. Namely, if the neutron interaction between the source region and the volume where flux is observed is negligible, and the neutron mean track length in the observed volume does not depend on their energy, source and flux spectra are equivalent. Consequently, a flux determined on a closed surface from a full system calculation can be replaced by an equivalent source for a simplified model including only the region contained by the surface.
225. Summary and conclusions
In this work it was shown that under certain conditions, the neutron source and flux spectra are proportional. Two important assumptions were identified: no neutron scattering in the system and neutrons mean track length in the selected volume not depending on their energy. This equivalence can and already is used in different scenarios, for example using the neutron source spectrum in study of reaction rates or self-shielding of the target, where flux spectrum should be used otherwise. Or inversely, volume- or surface-averaged flux calculated by a Monte Carlo simulation can be used as an effective source spectrum for accelerating localized calculations.