New interpretation of the 232Th unresolved resonance self-shielding effect

The resonance self-shielding effect of 232Th has been investigated in the energy range (4–100) keV. The self-shielding factors are computed with the average resonance parameters from various Evaluated Nuclear Data Files (ENDF/B, JENDL, BROND and JEFF) and from recent evaluation for this nucleus [Koyumdjieva, N., Janeva, N., Lukyanov, A.A., 2010. Cross section structure of 232Th in the URR (4–150) keV. J. Phys. G: Nucl. Part. Phys. 37, 075101.] characterized by energy dependent fluctuating neutron strength functions for s- and p-wave.A new statistical model combined with an analytical scheme for calculation and analysis of shielded cross sections functional is utilized in the computational work. Its main advantage toward conventional procedures used in the Unresolved Resonance Region is the capacity for reconstruction of neutron cross section structure including resonance dependence of neutron flux in a reactor medium.The obtained results for self-shielding factors are compared with the corresponding experimental data and the accuracy and sufficiency of various evaluations of 232Th for a reliable description of the resonant cross section structure in the URR is tested.

► An examination of the self-shielding effect of 232Th in the URR is performed.
► A new procedure for analytical calculation of the self-shielding factors is applied.
► The resonance dependence of neutron flux in a reactor medium is accounted for.
► The computational results are compared with corresponding experimental data.
► The validity of various evaluations for 232Th in the URR is tested.