Background: Neutron activation cross sections for energies around 14 MeV are required for various applications. Because cross-section data for the rare-earth elements are too scarce, there is a need for their accurate measurement and refinement. The accuracy of the evaluation and cross-section trend studies can be improved with reliable experimental data too.

Purpose: The purpose of the paper is to provide measurements of new cross-section data and earlier published cross-section data with much better accuracy for lanthanide elements—Dy, Er, and Yb—and the re-evaluation of available systematics for (n,x) reactions.

Methods: The cross sections for (n,x) reactions were measured at (d-t) neutron energies with the activation technique. Theoretical calculations of cross-section values have been performed with the talys-1.2 code.

Results: The sets of cross sections for (n,p), (n,2n), and (n,α) reactions were analyzed and the systematics were tested over the 156 ≤ $A$ ≤ 176 mass region. The ${}^{156}$Dy(n,p)${}^{156}$Tb and ${}^{162}$Er(n,p)${}^{162}$Ho${}^{(m+g)}$ cross-section values at 14.7 MeV neutron energy are reported for the first time. The ${}^{176}$Yb(n,d+pn)${}^{175}$Tm, ${}^{176}$Yb(n,n’α)${}^{172}$Er, ${}^{162,163}$Dy(n,x)${}^{162}$Tb, and ${}^{163,164}$Dy(n,x)${}^{163}$Tb cross sections are obtained with much better accuracy. The reevaluation of systematics for (n,p) cross sections and the reexamination of a presence of isotopic effect in the target nuclei mass range was performed. It was done based on original and earlier available data.

Conclusions: Obtained experimental results can be used for nuclear reaction model testing and could be considered as supplementary ones for nuclear data evaluation. The straight-line systematic dependence for (n,α) cross section was confirmed. For Er isotopes, a clear isotopic effect was observed in case of ($n$,$p$) reactions and pointed out the necessity of reconsidering the systematics.

• Received 24 March 2012

DOI:https://doi.org/10.1103/PhysRevC.86.034609