High resolution measurements of double differential (n, α) cross sections of ⁵⁸Ni and ^natNi between 4.2 and 6.5 MeV neutrons

Double differential (n, α) reaction cross sections of ⁵⁸Ni and ^natNi were measured for 4.2-6.5 MeV neutrons with energy resolution good enough to separate α-particles from the low-lying levels of residual nuclei by using a gridded ionization chamber. Angular distribution and excitation functions were derived for α₀, α₁ and α_i≥2 components (α-particles to the ground level, the 1st level and levels higher than the 2nd level, respectively). The experimental results were compared with these obtained from calculation based on Hauser-Feshbach model employing the optical potential and the level density parameters derived to reproduce the experimental values of total, (n, p) and (n,α)cross sections. The calculation showed fair agreement with the experimental data while it underestimated the (n,α)cross section above 6 MeV.