Editing Neutron source (section)

==Small devices==

===Spontaneous fission===
Some [[isotope]]s undergo [[spontaneous fission]] (SF) with [[Neutron emission|emission of neutrons]]. The most common spontaneous fission source is the isotope [[californium]]-252. <sup>252</sup>Cf and all other SF neutron sources are made by irradiating [[uranium]] or a [[Transuranium element|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. <sup>252</sup>Cf neutron sources are typically 1/4" to 1/2" in diameter and 1" to 2" in length. A typical <sup>252</sup>Cf neutron source emits 10<sup>7</sup> to 10<sup>9</sup> neutrons per second when new; but with a [[half-life]] of 2.6 years, neutron output drops by half in 2.6 years. 

===Alpha decay===
Neutrons are produced when [[alpha particle]]s hit any of several light isotopes including isotopes of [[beryllium]], [[carbon]], or [[oxygen]]. Thus, a neutron source can be fabricated 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 ~10<sup>6</sup>–10<sup>8</sup> neutrons per second. An alpha-beryllium neutron source may produce about 30 neutrons per 10<sup>6</sup> 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).

=== Photodisintegration ===
[[Gamma ray|Gamma radiation]] with an energy exceeding the neutron [[binding energy]] of a nucleus can eject a neutron, a process known as [[photodisintegration]]. Two example reactions are:
*<sup>9</sup>[[Beryllium|Be]] + >1.7 MeV photon → 1 neutron + 2 <sup>4</sup>He
*<sup>2</sup>[[Hydrogen|H]] ([[deuterium]]) + >2.26 MeV photon → 1 neutron + <sup>1</sup>H

===Sealed-tube neutron generators===
Some accelerator-based [[neutron generator]]s induce fusion between beams of [[deuterium]] and/or [[tritium]] ions and metal [[hydride]] targets which also contain these isotopes.