Reliability of cross sections of the photoneutron reactions on ⁵¹V and ⁵⁹Co in the bremsstrahlung beam experiments

Using the experimental-theoretical method for evaluation of partial photoneutron reaction cross sections basing on objective physical criteria the reliability of data on the (γ, 1n) and (γ, 2n) reaction cross sections of 51V and 59Co nuclei obtained on bremsstrahlung γ-rays was investigated. It is found that partial reaction cross sections obtained by adding corrections to neutron yield cross sections σ(γ, xn) = σ(γ, 1n) + 2σ(γ, 2n) calculated within statistical theory do not satisfy the reliability criteria. Cross sections of the (γ, 1n) reaction are significantly underestimated in the considered experiments, while those of the (γ, 2n) reaction are overestimated, due obviously to the way information is obtained on the partial reaction cross sections by applying statistical theory corrections to the yield cross section of the σ(γ, xn). When describing the (γ, 1n) reaction cross section at photon energies below threshold B2n of the (γ, 2n) reaction, such corrections produce substantial systematic uncertainties in the ranges of energy where both partial reactions compete.