SPWLA Glossary

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An [[activation logging|activation log]] wherein the [[formation|formations]] have been bombarded by high-energy [[neutron|neutrons]]. Specific atoms upon [[irradiation]] transform into [[isotopes]] which emit [[gamma ray|gamma rays]] exhibiting specific energy levels within the energy spectrum. Identification of the energy levels of the induced gamma [[radiation]] is a means of identifying the original atoms in place in the formation. The quantity of material containing the original atoms is deduced from the amount of gamma radiation at specific energy levels. Downhole instruments may use encapsulated [[source|sources]], which emit neutrons continuously as the tool is moved along the formation wall, or [[neutron generator|neutron generators]], which emit neutrons in cyclic pulses with measurements made between pulses. The type of source used depends on the substances searched for. Compare [[spectral gamma ray log|spectral gamma-ray log]]. Also see [[neutron activation]].