Isomeric cross-section ratio for the formation of ${}_{}{}^{58}{}_{}{}^{}\mathrm{Co}_{}^{\mathit{m},\mathit{g}}{}_{}{}^{}$ in neutron, proton, deuteron, and alpha-particle induced reactions in the energy region up to 25 MeV

Excitation functions were determined for ${}_{}{}^{58}{}_{}{}^{}\mathrm{Fe}$(p,n${)}^{58}$${\mathrm{Co}}^{\mathit{m}}$, ${}_{}{}^{\mathrm{nat}}{}_{}{}^{}\mathrm{Fe}$(d,xn${)}^{58}$${\mathrm{Co}}^{\mathit{m}}$, ${}_{}{}^{55}{}_{}{}^{}\mathrm{Mn}$(α,n${)}^{58}$${\mathrm{Co}}^{\mathit{m}}$, and ${}_{}{}^{59}{}_{}{}^{}\mathrm{Co}$(n,2n${)}^{58}$${\mathrm{Co}}^{\mathit{m}}$ reactions from the respective thresholds to 14.12 MeV in work with protons, 12.97 MeV with deuterons, 13 MeV with neutrons, and 25.52 MeV with alpha particles. The radioactivity of the activation product ${}_{}{}^{58}{}_{}{}^{}\mathrm{Co}_{}^{\mathit{m}}{}_{}{}^{}$(${\mathit{T}}_{1/2}$=9.15 h) was determined by high resolution γ-ray and x-ray spectrometry. Using the present ${\mathrm{\sigma }}_{\mathit{m}}$ results and the (${\mathrm{\sigma }}_{\mathit{m}}$+${\mathrm{\sigma }}_{\mathit{g}}$) data reported earlier, the isomeric cross-section ratio ${\mathrm{\sigma }}_{\mathit{m}}$/(${\mathrm{\sigma }}_{\mathit{m}}$+${\mathrm{\sigma }}_{\mathit{g}}$) was determined for each reaction. Statistical model calculations taking into account the precompound effects were performed for the above-mentioned four reactions as well as for the ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$(n,p${)}^{58}$${\mathrm{Co}}^{\mathit{m},\mathit{g}}$ process. A consistent set of model parameters was used. The isomeric cross-section ratio for the pair ${}_{}{}^{58}{}_{}{}^{}\mathrm{Co}_{}^{\mathit{m},\mathit{g}}{}_{}{}^{}$ strongly depends on the level scheme and branching ratios of the known levels of ${}_{}{}^{58}{}_{}{}^{}\mathrm{Co}$. Different reactions produced different angular momentum distributions of the compound nucleus, resulting in different isomeric cross-section ratio at the same excitation of the compound nucleus. The ratio was found to be relatively high for target nuclei with high spin values. © 1996 The American Physical Society.