Cross Sections for the ${\mathrm{Ni}}^{58}(\alpha ,p)$, ${\mathrm{Ni}}^{58}(\alpha ,\gamma )$, and ${\mathrm{Co}}^{59}(\alpha ,n)$ Reactions

Thick-target yields have been measured for the ${\mathrm{Ni}}^{58}(\alpha ,\gamma )$ reaction from 4.9 to 6.1 MeV, the ${\mathrm{Ni}}^{58}(\alpha ,p)$ reaction from 4.9 to 11 MeV and the ${\mathrm{Co}}^{59}(\alpha ,n)$ reaction from 5.8 to 10 MeV. The reactions were identified by measuring the coincident annihilation radiation from the induced ${\beta }^{+}$ activities. The absolute thick-target positron yields, which were measured at approximately 100-keV energy intervals, have an accuracy of ±6%. The reaction cross sections were obtained to an accuracy of 15 to 20% by the differentiation of the smooth thick-target yield curves. Over the measured energy range, the cross sections increase from 1 to 12 μb for the ${\mathrm{Ni}}^{58}(\alpha ,\gamma )$ reaction, 0.6 μb to 316 mb for the ${\mathrm{Ni}}^{58}(\alpha ,p)$ reaction, and 0.06 to 228 mb for the ${\mathrm{Co}}^{59}(\alpha ,n)$ reaction. The total reaction cross section for ${\mathrm{Ni}}^{58}$ is compared to some values predicted by optical models. The ${\mathrm{Co}}^{59}(\alpha ,n)$ yields are compared to those obtained by measuring the neutrons directly with the graphite sphere detector.