Low-energy neutron resonances in erbium and gadolinium

The two neutron resonances in Er at 0.46 and 0.58 eV were measured using samples enriched in Er166, Er167 and Er168 It was found that both resonances occur in the target nucleus Er167. The isotopic cross-sections of Gd155 and Gd157 were measured from 0.02 to 0.30 eV and resonances were found in Gd155 at 0.0268 and in Gd157 at 0.0314 eV.

Parameters for these resonances were derived by fitting the data to single-level Breit-Wigner formulae. Isotopic assignments were made for fifteen Gd resonances between 1 and 25 eV from previously unpublished data using samples enriched in 155, 156, 157 and 158. The Breit-Wigner parameters for three of these were obtained.