In today’s cross section data processing process, asymptotic scattering model is employed by NJOY for the neutron/nucleus elastic scattering interactions in the epithermal energy region, which means that the energy of a scattered neutron is always lower than its incident energy and it falls evenly within the interval of [αE, E]. This model has recently been proved to have non-ignorable errors at some resonances of heavy nuclides. In this study, to investigate the impact of heavy nuclides resonance elastic scattering models to the resonance integrals, exact scattering kernel is employed and a deterministic code Estuary is developed to efficiently solve the neutron slowing down problem. Numerical results demonstrate that with the use of Estuary, results given in the literature obtained by the Monte Carlo method can be reproduced. With the resonance cross section approximately represented by the single-level Breit-Wigner formulation, investigations are made for different resonance parameters for both asymptotic and exact scattering models. Relations between errors and these related parameters are summarized.

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