Measurement of thermal neutron cross section and resonance integral for theEr170(n,γ)Er171reaction by using aMn55monitor

Abstract

The thermal neutron cross section and the resonance integral of the reaction $^{170}\mathrm{Er}$($n,\ensuremath{\gamma}$)$^{171}\mathrm{Er}$ were measured by the Cd-ratio method using a $^{55}\mathrm{Mn}$ monitor as single comparator. Analytical grade ${\mathrm{MnO}}_{2}$ and ${\mathrm{Er}}_{2}{\mathrm{O}}_{3}$ powder samples with and without a cylindrical 1 mm Cd shield box were irradiated in an isotropic neutron field obtained from three $^{241}\mathrm{Am}$-Be neutron sources. The induced activities in the samples were measured with a 120.8% relative efficiency $p$-type HPGe detector. The correction factors for gamma-ray attenuation (${F}_{g}$), thermal neutron self-shielding (${G}_{\mathit{th}}$), and resonance neutron self-shielding (${G}_{\mathit{epi}}$) effects, and the epithermal neutron spectrum shape factor ($\ensuremath{\alpha}$) were taken into account. The thermal neutron cross section for the ($n,\ensuremath{\gamma}$) reaction in $^{170}\mathrm{Er}$ has been determined to be 8.00 \ifmmode\pm\else\textpm\fi{} 0.56 b, relative to that of the $^{55}\mathrm{Mn}$ monitor. However, some previously reported experimental results compared to the present result show a large discrepancy ranging from 8.3 to 86%. The present result is, in general, in good agreement with the recently measured values by 9%. According to the definition of Cd cut-off energy at 0.55 eV, the resonance integral obtained is 44.5 \ifmmode\pm\else\textpm\fi{} 4.0 b, which is determined relative to the reference integral value of the $^{55}\mathrm{Mn}$ monitor by using cadmium ratios. The existing experimental data for the resonance integral are distributed between 18 and 43 b. The present resonance integral value agrees only with the measurement of 43 \ifmmode\pm\else\textpm\fi{} 5 b by Gillette [Thermal Cross Section and Resonance Integral Studies, ORNL-4155, 15 (1967)] within uncertainty limits.