Californium

Californium

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melting point: 900°C
boiling point: Unknown
density: Unknown
most common ions: Cf²⁺, Cf³⁺

Element 98, named after the state of California, was first synthesized by the research group of Glenn Seaborg in 1950 at the University of California at

Berkeley. A target of microgram amounts of an isotope of curium (²⁴²Cm) was bombarded with accelerated helium ions in a cyclotron, to produce approximately 5,000 atoms of a californium isotope of mass 245 and a half-life of 44 minutes.

Californium, like all the actinide elements heavier than plutonium, exists in a stable trivalent oxidation state in aqueous solutions . It has also been found to exist in the (less stable) tetravalent oxidation state in solution. The ground state electronic configuration for the atom is 5f¹⁰7s². Metallic californium has a face-centered cubic structure near its melting point and a double hexagonal close-packed structure at temperatures below its melting point. Californium has eighteen isotopes, all of which are radioactive. The longest-lived isotope has a mass number of 251 and a half-life of 900 years. The isotope having mass number 252 and a half-life of 2.65 years undergoes radioactive decay , a fraction of which (3%) is via spontaneous nuclear fission ; it releases neutrons in the fission event. Californium-252 has been used as a neutron source in a variety of analytical techniques, in medical diagnostic tests that require activation analysis , and in the production of short-lived nuclides. Californium neutron sources are used to image low density materials (especially hydrogenous materials). The compactness and portability of ²⁵²Cf neutron sources has resulted in their use in such areas as the detection of metals in deep wells, lunar exploration, and nuclear weapons monitoring.

see also Actinium; Berkelium; Einsteinium; Fermium; Lawrencium; Mendelevium; Neptunium; Nobelium; Plutonium; Protactinium; Rutherfordium; Seaborg, Glenn theodore; Thorium; Uranium.

Gregory R. Choppin

Bibliography

Choppin, Gregory R.; Liljenzin, Jan-Olov; and Rydberg, Jan (2001). Radiochemistry and Nuclear Chemistry, 3rd edition. Woburn, MA: Butterworth-Heinemann.

Seaborg, Glenn T., and Loveland, Walter D. (1990). The Elements beyond Uranium. New York: Wiley-Interscience.