1. n. [Formation Evaluation]

Phenomena resulting from the transfer of energy from a gamma ray to matter, usually to an electron. The probability of a specific interaction occurring depends on the atomic number of the material and the energy of the gamma ray. In formation evaluation, there are two types of interactions of interest: the photoelectric effect, which indicates lithology, and Compton scattering, which depends on formation density. The third type of interaction, pair production, occurs at energies above those used for logging.

See related terms: Compton scattering,  pair production,  photoelectric effect,  scintillation detector