- Californium (Cf) is a silvery-white, dense, radioactive metal with atomic number 98, belonging to the actinide series.
- Its electron configuration is [Rn] 5f¹⁰ 7s², and it commonly exhibits oxidation states of +3 and +2, with +3 being the most stable in compounds. The atomic structure contains ninety-eight protons, most often one hundred and fifty-three neutrons in californium-251 (²⁵¹Cf), and ninety-eight electrons arranged in seven shells.
- Californium does not occur naturally and is synthesized in specialized high-flux nuclear reactors through prolonged neutron irradiation of lighter actinides such as curium or berkelium. The most significant isotopes are californium-252 (²⁵²Cf), with a half-life of 2.645 years and exceptional neutron emission properties, and californium-251 (²⁵¹Cf), with a half-life of 898 years.
- Californium was first synthesized in 1950 by Stanley G. Thompson, Kenneth Street Jr., Albert Ghiorso, and Glenn T. Seaborg at the University of California, Berkeley. It was produced by bombarding curium-242 (²⁴²Cm) with alpha particles in a cyclotron, yielding californium-245 (²⁴⁵Cf) and a neutron. The element was named after the state of California and the University of California, following the tradition of naming newly discovered elements after their place of discovery.
- Californium-252 is renowned for being one of the most powerful neutron sources known. It emits about 2.3 million neutrons per second per microgram through spontaneous fission, making it invaluable for initiating nuclear reactors, in neutron radiography, in oil well logging, and for detecting trace amounts of metals in mining and geology. It is also used in neutron therapy for certain types of cancer, where its high neutron flux can target tumors resistant to gamma or X-ray radiation.
- Chemically, californium behaves similarly to other trivalent actinides and rare earth metals. In air, it tarnishes slowly, forming a thin oxide layer. Californium(III) oxide (Cf₂O₃) is its most stable compound, while californium(II) compounds can be formed under reducing conditions. Californium halides, such as CfF₃ and CfCl₃, are well-characterized, and Cf³⁺ ions in aqueous solution form complexes with ligands such as nitrates and sulfates.
- Biologically, californium has no natural role and is highly radiotoxic due to its alpha emissions and, in the case of ²⁵²Cf, strong neutron radiation. Inhalation or ingestion can cause severe damage to bone marrow, liver, and other organs, and neutron exposure requires extensive biological shielding.
- Environmentally, californium is produced only in minute quantities in specialized nuclear facilities, such as the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory. Its high radioactivity and neutron output require rigorous containment to prevent environmental contamination.
