Editing Neutron source (section)

===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.