Secondary photon-atom contributions to nonresonant excitation of 115In isomeric level

A 60Co source has been used to study the photoactivation of the 336 keV (T1/2=4.3 h) isomeric level of 115In in the indium-lead alloys. We have investigated the contribution to the nonresonant excitation from photon-atom interactions, involving Compton scattering, photoelectric effect and pair production. Our results show very clearly that the nonresonant excitations of the isomeric level are due to direct interactions between the photons and 115In atoms.