A well-logging technique in which the [[formation]] in the near environment of the irradiating tools is irradiated with [[neutron|neutrons]] which transform some nuclei into [[radioisotope|radioisotopes]]. The specific radioactive [[isotopes]] which are produced by activation of the nuclei can be detected by their characteristic induced [[radioactivity]] energy levels and [[decay time|decay-time]] schemes. This provides a means for identifying the elements originally present. See also [[induced spectral gamma ray log|induced spectral gamma-ray log]] and [[neutron activation]].