The gamma spectometry tool (GST) measures both inelastic and capture [[gamma ray]] spectra, providing a detailed measurement of formation response to [[neutron]] bombardments. Eight essential elements are identified and their concentrations are determined. Measurements of carbon, oxygen, silicon, calcium, iron, chlorine, hydrogen, and sulfur are used to compute the hydrocarbon [[saturation]], salinity, [[lithology]], [[porosity]], and shaliness of the formation. See also [[carbon oxygen log|carbon-oxygen log]]. GST is a mark of Schlumberger.

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