Editing Wireline (cabling) (section)

===Nuclear tools===
[[File:Putting the radioactive charge in the wireline string.JPG|thumb|Putting the radioactive charge in the wireline string]]
[[File:Locked case for Radioactive Source for Logging Job.JPG|thumb|Locked case for radioactive source for logging job]]
Nuclear tools measure formation properties through the interaction of reservoir molecules with radiation emitted from the logging tool. The two most common properties measured by nuclear tools are formation porosity and rock density:

Formation porosity is determined by installing a [[neutron source|radiation source capable of emitting fast neutrons]] into the downhole environment. Any pore spaces in the rock are filled with fluid containing hydrogen atoms, which slow the neutrons down to an epithermal or thermal state. This atomic interaction creates gamma rays which are then measured in the tool through dedicated detectors, and interpreted through a calibration to a porosity. A higher number of gamma rays collected at the tool sensor would indicate a larger number of interactions with hydrogen atoms, and thus a larger porosity.<ref>{{Cite web|url=http://www.slb.com/content/services/evaluation/petrophysics/porosity/cnl.asp|archiveurl=https://web.archive.org/web/20080508160819/http://www.slb.com/content/services/evaluation/petrophysics/porosity/cnl.asp|url-status=dead|title=Schlumberger, Compensated Neutron Log<!-- Bot generated title -->|archivedate=May 8, 2008}}</ref>

Most open hole nuclear tools utilize double-encapsulated chemical sources.

Density tools use gamma ray radiation to determine the lithology and density of the rock in the downhole environment.  Modern density tools utilize a Cs-137 radioactive source to generate gamma rays which interact with the rock strata. Since higher density materials absorb gamma rays much better than lower density materials, a gamma ray detector in the wire line tool is able to accurately determine formation density by measuring the number and associated energy level of returning gamma rays that have interacted with the rock matrix.  Density tools usually incorporate an extendable caliper arm, which is used both to press the radioactive source and detectors against the side of the bore and also to measure the exact width of the bore in order to remove the effect of varying bore diameter on the readings.

Some modern nuclear tools use an electronically powered source controlled from the surface to generate neutrons. By emitting neutrons of varying energies, the logging engineer is able to determine formation lithology in fractional percentages.