Excitation functions and mean projected recoil-ion ranges of the isomeric nuclei produced in proton-, ${}_{}{}^3{}_{}{}^{}\mathrm{-}$, and α-particle-induced reactions on ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ were measured by an activation technique for bombarding energies ${\mathit{E}}_{\mathit{p}}$≲50 MeV, and E${\mathrm{}}^3$He, α≲40 MeV. Isomeric yield ratios (${\mathrm{\sigma }}_{\mathit{m}}$/${\mathrm{\sigma }}_{\mathit{g}}$) were determined as a function of the incident particle energy. The experimental excitation functions and isomeric yield ratios were compared with those from statistical model calculations based on the Hauser-Feshbach formalism. From the analysis of excitation functions, recoil-ion ranges, and isomeric yield ratios, the observed reactions were able to be grouped into three distinctly different ones in the energy region studied: (i) compoundlike reaction for (p,3n), ${(}^3$He,4n), (α,3n), and (p,pn${)}^{196}$${\mathrm{Au}}^{\mathit{m}}$, (ii) one-neutron stripping reaction for ${(}^3$He,2p), and (iii) nonequilibrium one-neutron knockout or pickup reactions with transfer of a small amount of angular momentum for the ${(}^3$He,α), (α,αn), and (p,pn${)}^{196}$${\mathrm{Au}}^{\mathit{g}}$ that are intermediate between (i) and (ii). We propose a semiempirical method which predicts isomeric yield ratios in the compoundlike reactions, within a factor of 0.7 to 1.4, from the spin distribution of the compound nucleus.

• Received 30 October 1989

DOI:https://doi.org/10.1103/PhysRevC.41.889