1. n. [Formation Evaluation]
A wireline log of the concentration by weight of aluminum in the formation, based on the principle of neutron activation. Aluminum (27Al) can be activated by capturing relatively low-energy neutrons from a chemical source to produce the isotope 28Al, which decays with a half-life of 2.3 minutes and emits a relatively easily detected 1.78 MeV gamma ray. A natural gamma ray spectrometer will detect this gamma ray along with the other natural gamma rays. If the natural gamma spectrum has been measured before activation, it can be subtracted from the spectrum after activation to give an estimate of Al content. Al is a relatively direct indicator of the volume of clay, since clay minerals are alumino-silicates.
See: activation log, chemical neutron source, geochemical log, induced gamma ray spectroscopy, natural gamma ray spectroscopy
