Major mechanism of photoactivation for theIn115(γ,γ’)Inm115process byCo60γ-ray irradiation

The ${}_{}{}^{115}{}_{}{}^{}\mathrm{In}$(γ,γ’ ${)\mathrm{}}^{115}$ ${\mathrm{In}}^{\mathrm{m}}$ photoactivation process was studied by γ-ray irradiation with an intense ${}_{}{}^{60}{}_{}{}^{}\mathrm{Co}$ source. The nonresonant activation of ${}_{}{}^{115}{}_{}{}^{}\mathrm{In}$ to the 1078 keV level proposed was reinvestigated. No evidence was obtained for such a direct process but an indirect process of resonance absorption of Compton-scattered γ rays offered a reasonable explanation for the experimental results. Hot atom chemical studies using tris(acetylacetonato) indium(III) as a target material indicated that the excitation of the isomeric level via nonresonant process must be less than 3.3% of the resonance effect.