a special radioactivity log for open-hole surveying that responds to variations in the specific gravity of formations. It is a contact log (i.e., held against the wall of the hole). It emits neutrons and then measures the secondary gamma radiation that is scattered back to the detector in the instrument. The density log is an excellent porosity-measuring device, especially for shaly sands. Some trade names for it are Gamma-Gamma Density Log, Formation Density Log, and Densilog.
