Abstract: A technique for assaying samples entails irradiating a sample with a beam of gamma rays of sufficient energy to excite the nuclei of the assay elements into their isomeric states, ceasing the irradiation, detecting the gamma rays resulting from the decay of the isomeric states to the ground state, and analyzing the detected gamma rays to determine the content of assay elements in the sample. In a preferred embodiment, the apparatus is configured such that the irradiated sample is rapidly moved to a shielded environment in which the gamma rays from the isomeric transitions are detected. The system is ideally suited for analyzing large samples of ore for gold, silver, barium and other assay elements, but can be embodied to detect any assay elements susceptible to photon activation analysis in any sample geometry.