Analysis using neutrons

A tool suitable for borehole logging, including production oilwell borehole logging, contains a radioisotope neutron source, a fast neutron detector and a gamma-ray detector. The fast neutron detector is positioned to detect neutrons as they leave the source and before they enter the material to be analysed. Subsequent interactions with the material of neutrons scattered by the fast neutron detector give rise to gamma-rays which are detected. Information is registered as to the time delay between detection of a neutron and detection of a gamma-ray. This may be presented simply as an energy spectrum of gamma-ray detection events selected by coincidence or anticoincidence with detection of a neutron, or a time spectrum at selected energy levels. (author)