Activation of115Inmby single pulses of intense bremsstrahlung

A new technique has been recently described for the absolute calibration of intense sources of pulsed radiation in the 0.2–1.5 MeV range of photon energies. An activation technique, it depended upon the storage of samples of the irradiating spectrum in the form of populations of nuclei excited to isomeric states with lifetimes of seconds to hours. Described here is the use of such a calibrated source to resolve severe conflicts in previous studies of the reaction ${}_{}{}^{115}{}_{}{}^{}\mathrm{In}$(γ,γ’ ${)}^{115}$ ${\mathrm{In}}^{\mathit{m}}$ through the 1078 keV ${\mathit{J}}^{\mathrm{\pi }}$=(5/$2^{+}$ level; this mode has traditionally served as the archetype for (γ,γ’) reactions. We report an integrated cross section of (18.7±2.7)×${10}^{\mathrm{-}2}$ ${\mathrm{cm}}^2$ keV with no evidence of any importance of nonresonant channels of excitation.