Neutron source

A neutron source is any device that emits neutrons, irrespective of the mechanism used to produce the neutrons. Neutron sources are used in physics, engineering, medicine, nuclear weapons, petroleum exploration, biology, chemistry, and nuclear power. Neutron source variables include the energy of the neutrons emitted by the source, the rate of neutrons emitted by the source, the size of the source, the cost of owning and maintaining the source, and government regulations related to the source. Some isotopes undergo SF with emission of neutrons. The most common spontaneous fission source is the isotope californium-252. 252Cf and all other SF neutron sources are made by irradiating uranium or a transuranic element in a nuclear reactor, where neutrons are absorbed in the starting material and its subsequent reaction products, transmuting the starting material into the SF isotope. 252Cf neutron sources are typically 1/4" to 1/2" in diameter and 1" to 2" in length. A typical 252Cf neutron source emits 107 to 109 neutrons per second when new; but with a half-life of 2.6 years, neutron output drops by half in 2.6 years. A typical 252Cf neutron source costs $15,000 to$20,000. Neutrons are produced when alpha particles hit any of several light isotopes including isotopes of beryllium, carbon, or oxygen. Thus, one can make a neutron source by mixing an alpha-emitter such as radium, polonium, or americium with a low-atomic-weight isotope, usually by blending powders of the two materials. Alpha neutron sources typically produce ~106–108 neutrons per second. An alpha-beryllium neutron source may produce about 30 neutrons per 106 alpha particles. The useful lifetime for such sources depends on the half-life of the radioisotope. The size and cost of these neutron sources are comparable to spontaneous fission sources. Usual combinations of materials are plutonium-beryllium (PuBe), americium-beryllium (AmBe), or americium-lithium (AmLi). Gamma radiation with an energy exceeding the neutron binding energy of a nucleus can eject a neutron (photoneutron).