(1) An encapsulated radioactive material which produces [[neutron|neutrons]] for [[neutron log|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 Log|Thermal Decay Time Logging]], [[Neutron Lifetime Log|Neutron Lifetime Logging]], [[carbon oxygen log|carbon-oxygen logging]], and [[activation logging]] instruments.

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