Dictionary:Induced gamma-ray spectroscopy log

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Bombardment by high-energy neutrons causes elements to emit gamma rays of characteristic energy. Borehole logging of the gamma energy spectrum resulting from a 14 MeV pulsed neutron source allows identification and analysis (as ratios) of the formation fluid and rock elements. A log for carbon/oxygen distinguishes hydrocarbon from water and hence determines saturation independent of salinity. Silicon/calcium discriminates sandstones from carbonates. Measurement may include spectra of both inelastic (fast-neutron) and capture-gamma (thermal-neutron) reactions. Also called neutron activation log. See gamma-ray spectroscopy log.