Editing Wireline (cabling) (section)

===Natural gamma ray tools===
Natural gamma ray tools are designed to measure gamma radiation in the Earth caused by the disintegration of naturally occurring potassium, uranium, and thorium. Unlike nuclear tools, these natural gamma ray tools emit no radiation. The tools have a radiation sensor, which is usually a scintillation crystal that emits a light pulse proportional to the strength of the gamma ray striking it. This light pulse is then converted to a current pulse by means of a photomultiplier tube (PMT). From the photomultiplier tube, the current pulse goes to the tool's electronics for further processing and ultimately to the surface system for recording. The strength of the received gamma rays is dependent on the source emitting gamma rays, the density of the formation, and the distance between the source and the tool detector. The log recorded by this tool is used to identify [[lithology]], estimate shale content, and depth correlation of future logs.