New Evaluated Data on Photoneutron Reaction Cross Sections for Ni Nuclei

The reliability of the cross sections obtained for ( ) and ( ) partial photoneutron reactions on Ni nuclei in experiments with beams of both bremsstrahlung gamma radiation and quasimonoenergetic annihilation photons was studied by means of objective physical criteria. It is found that data obtained using bremsstrahlung gamma radiation do not satisfy these physical criteria and are obviously unreliable. At the same time, the reliability of data obtained using quasimonoenergetic photons is questionable. Partial reaction cross sections for Ni that satisfy the above physical criteria were evaluated by means of the experimental–theoretical method within which one employs experimental data only on the neutron yield cross section and the results obtained by calculating partial reaction cross sections on the basis of the combined photonuclear reaction model, which are independent of the problems of experimentally determining neutron multiplicities. It is shown that the discrepancies between the evaluated and experimental cross sections are due to systematic uncertainties appearing in experimental data because of determining the multiplicities of neutrons by their measured energies. It is also found that the competitions of evaluated and experimental data for the neighboring nuclei Ni and Ni differ significantly, which is caused by special features of the processes of their photodisintegration—first of all, by significant distinctions between the energy thresholds and absolute values of the cross sections of ( ) and ( ) reactions on these nuclei.