1. n. [Formation Evaluation]

A device for measuring the number and energy of gamma rays. The device consists of a crystal and a photomultiplier. In the crystal, an incident gamma ray imparts energy to electrons through Compton scattering, photoelectric absorption and pair production. The electrons excite the detector crystal lattice. Crystal de-excitation emits visible or near-visible light, the scintillation, which is detected by the photomultiplier and transformed into an electrical pulse. The frequency and amplitude of the electric pulse are related to the number of gamma rays and their respective energy levels, and are recorded in a log. Scintillation detectors are used in all natural gamma ray, induced gamma ray and density logging devices.

See: activation log,  density measurement,  gamma ray log,  natural gamma ray spectroscopy,  photoelectric effect