A [[well log]] that records formation [[density]]. The logging tool consists of a [[gamma ray source|gamma-ray source]] (e.g., Cs<sup>137</sup>) and a [[detector]] shielded from the [[source]] so that it records backscattered [[gamma ray|gamma rays]] from the [[formation]]. The backscattering depends on the electron density of the formation, which is roughly proportional to the bulk density. The source and detector usually are mounted on a skid which is pressed against the borehole wall. The compensated density logging tool includes a secondary detector which responds more to the mud cake and small, borehole irregularities. The response of the second detector is used to correct the measurements of the primary detector. The density log applies primarily to uncased holes. Sometimes called a gamma-gamma log. See also [[Compton scattering]], [[ZA effect|Z/A effect]], and [[compensated formation density log]]. Compare [[nuclear cement log]].

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