Recovery of the Point Pseudoresonance Structure of Cross Sections in the Region of Unresolved Resonances

Abstract

A model is proposed for recovering the point cross sections in the region of unresolved resonances. The approach consists in using probability tables P_i(σ) to construct the effective cross sections σ_i^′(E) on some choice of energy intervals [E_i, E_i+1]. In constructing the effective cross sections the densities P_i(σ′) and P_i(σ) are preserved. This makes it possible to preserve on the intervals [E_i, E_i+1] characteristics of the neutron–matter interactions such as the average cross section, average free path, transmission function, and others. The use of pseudoresonances in the field of unresolved resonances is not distinguished from the use of ordinary point cross sections in the region of resolved resonances. The proposed approach does not require modifications of the library formats and modeling schemes for the neutron trajectories in Monte Carlo programs. The calculations of two problems showed good agreement between the calculations of the change ΔK_eff using probability tables and the MCNP code and calculations using the PRIZMA code, in which pseudoresonances were used.