Direct measurement of Ni-59(n, p) Co-59 and Ni-59(n, alpha) Fe-56 at fast-neutron energies from 500 keV to 10 MeV

Nuclear reaction data for neutron induced reactions on unstable nuclei are critical for a wide range of applications spanning studies of nuclear astrophysics, nuclear reactor designs, and radiochemistry diagnostics. However, nuclear data evaluations of the reaction cross sections are largely based on calculations due to the difficulty in performing this class of measurements and the resulting lack of experimental data. For neutron induced charged particle reactions at fast neutron energies, at the MeV scale, these cross section predictions are predominately driven by statistical Hauser-Feshbach calculations. In this work, we present partial and total Ni-59(n, p) and Ni-59(n, alpha) cross sections, measured directly with a radioactive Ni-59 target, and compare the results to the present nuclear data evaluations. In addition, the results from this work are compared to a recent study of the (59) Ni(n, xp) reaction cross section that was performed via an indirect surrogate ratio method. The expected energy trend of the cross section, based on the current work, is inconsistent with that of the surrogate work. This calls into question the reliability of that application of the surrogate ratio method and highlights the need for direct measurements on unstable nuclei, when feasible.