Californium
Element 98 · Actinide
Californium is one of the most expensive substances on Earth, produced only in microgram amounts per year. Its isotope californium-252 is an extraordinarily strong neutron source: one microgram emits over two million neutrons per second. This makes it valuable for starting nuclear reactors, scanning for metals and water underground, and analyzing materials. Like other heavy actinides it is intensely radioactive and hazardous.
Key facts
| Atomic number | 98 |
|---|---|
| Atomic weight | [251] |
| Category | Actinide |
| Group / Period | — / 7 |
| Block | f |
| Electron configuration | [Rn] 5f10 7s2 |
| Common oxidation states | +3 |
| State at STP | Solid |
| Electronegativity | 1.3 |
| Density | 15.1 g/cm3 |
| Melting point | 900 °C |
| Boiling point | 1470 °C (estimated) |
Occurrence
Californium is entirely synthetic, made by long neutron irradiation of plutonium and curium targets in specialized high-flux reactors.
Applications
Californium-252 neutron sources for reactor startup
Neutron scanners for detecting metals, water, and explosives
Research in nuclear physics
Common compounds
- Californium(III) oxide (Cf2O3)
- Californium oxychloride (CfOCl)
- Californium(III) fluoride (CfF3)
Californium was discovered in 1950 by the Berkeley team and named after the state of California; it remains one of the costliest elements to produce.
Data source: IUPAC standard atomic weights 2021