Editing Californium (section)

=== Isotopes ===
{{main|Isotopes of californium}}
Twenty [[isotope]]s of californium are known ([[mass number]] ranging from 237 to 256<ref name="NNDC2008" />); the most stable are {{sup|251}}Cf with [[half-life]] 898 years, {{sup|249}}Cf with half-life 351 years, {{sup|250}}Cf at 13.08 years, and {{sup|252}}Cf at 2.645 years.<ref name="NNDC2008" /> All other isotopes have half-life shorter than a year, and most of these have half-lives less than 20 minutes.<ref name="NNDC2008" />

{{sup|249}}Cf is formed by [[beta decay]] of berkelium-249, and most other californium isotopes are made by subjecting berkelium to intense neutron radiation in a [[nuclear reactor]].{{sfn|CRC|2006|p=4.8}} Though californium-251 has the longest half-life, its production yield is only 10% due to its tendency to collect neutrons (high [[neutron capture]]) and its tendency to interact with other particles (high [[neutron cross section]]).{{sfn|Haire|2006|p=1504}}

{{sup|252}}Cf is a very strong [[neutron]] emitter, which makes it extremely [[radioactive]] and harmful.<ref>{{cite journal|author = Hicks, D. A. |title = Multiplicity of Neutrons from the Spontaneous Fission of Californium-252|journal = Physical Review|date = 1955|volume = 97|issue = 2|pages = 564–565|doi = 10.1103/PhysRev.97.564|last2 = Ise|first2 = John|last3 = Pyle|first3 = Robert V.|bibcode = 1955PhRv...97..564H |url = http://www.escholarship.org/uc/item/6031k6m2}}</ref><ref>{{cite journal|author = Hicks, D. A. |title = Spontaneous-Fission Neutrons of Californium-252 and Curium-244|journal = Physical Review |date = 1955|volume = 98|issue = 5|pages = 1521–1523|doi = 10.1103/PhysRev.98.1521|last2 = Ise|first2 = John|last3 = Pyle|first3 = Robert V.|bibcode = 1955PhRv...98.1521H }}</ref><ref>{{cite journal|author =Hjalmar, E.|author2 =Slätis, H.|author3 =Thompson, S.G. |title = Energy Spectrum of Neutrons from Spontaneous Fission of Californium-252| journal = Physical Review| date = 1955| volume = 100|issue =5|pages = 1542–1543| doi = 10.1103/PhysRev.100.1542|bibcode = 1955PhRv..100.1542H }}</ref> {{sup|252}}Cf, 96.9% of the time, [[alpha decay]]s to [[curium]]-248; the other 3.1% of decays are [[spontaneous fission]].<ref name="NNDC2008" /> One [[microgram]] (μg) of {{sup|252}}Cf emits 2.3&nbsp;million neutrons per second, an average of 3.7 neutrons per spontaneous fission.<ref name="osti">{{cite journal|author = Martin, R. C.|author2 = Knauer, J. B.|author3 = Balo, P. A.| title = Production, Distribution, and Applications of Californium-252 Neutron Sources| date = 1999|url = http://www.osti.gov/bridge/purl.cover.jsp?purl=/15053-AE6cnN/native/ |doi = 10.1016/S0969-8043(00)00214-1|journal = Applied Radiation and Isotopes |volume = 53|issue = 4–5|pages = 785–92|pmid = 11003521 }}</ref> Most other isotopes of californium, alpha decay to curium ([[atomic number]] 96).<ref name="NNDC2008" />