Neutron Cross Sections and Resonance Parameters of Yb Isotopes

Neutron transmission measurements have been carried out for Yb¹⁷⁰, Yb¹⁷¹, Yb¹⁷², Yb¹⁷³, Yb¹⁷⁴, and Yb¹⁷⁶ over a large energy region to determine the s-wave strength functions, level densities, scattering-radius parameters, and thermal cross sections. The values of the latter are found to be 17.0±1.0, 57±3, 10.2±1.5, 28±2, 142±5, and 14.9±1.0 b, respectively. From these, a paramagnetic scattering cross section of 5.2±0.9 b is extracted for Yb⁺⁺⁺ at 0.0253 eV. By comparing the level densities of Yb¹⁷¹ and Yb¹⁷³, a spin cutoff factor σ=2.8±0.8 b is derived. Average total cross sections are analyzed to determine the strength functions in the 5-15-keV region, which are compared with values derived in the low-energy region.