(1) An encapsulated radioactive material which produces neutrons for neutron logging. The neutrons usually are produced in alpha-berillium reactions. The alpha particle producing element may be americium, plutonium, or sometimes radium. Californium-252. which is sometimes used in special applications, is an intense source of 2.3-MeV neutrons but has a short half life of 2.65 years.

(2) A neutron generator. An electromechanical device which emits high-energy (14-MeV) neutrons in controlled cyclic pulses. Pulsed neutron radiation is required in Thermal Decay Time Logging, Neutron Lifetime Logging, carbon-oxygen logging, and activation logging instruments.