Radiative Capture Cross Sections of ^155,157Gd for Thermal Neutrons

Thermal neutron radiative capture cross sections σ_0γ of ^155,157Gd are determined by summing the transition cross sections feeding the ground states of the respective product nuclei. The transition cross sections feeding the ground states from the discrete states in the low-excitation region, where the decay schemes are known completely, were measured using a guided cold neutron beam at the Budapest Research Reactor. Transitions from the states at the higher excitation, the so-called quasi-continuum levels, are determined from simulations with the extreme statistical model normalized to the intensity balance through the low-lying discrete levels. A significant non-1/v correction was applied to ^155,157Gd, leading to σ_0γ(¹⁵⁵Gd) = 56 700(2100) b and σ_0γ(¹⁵⁷Gd) = 239 000(6000) b.