The chemical element californium is classed as an actinide metal. It was discovered in 1950 by Stanley Thompson, Kenneth Street, Albert Ghiorso and Glenn Seaborg.
|Classification:||Californium is an actinide metal|
|Atomic weight:||(251), no stable isotopes|
|Melting point:||900 oC, 1173 K|
|Boiling point:||1472 oC, 1745 K (estimated)|
|Neutrons in most abundant isotope:||153|
|Electron configuration:||[Rn] 5f10 7s2|
|Density @ 20oC:||13.67 g/cm3|
|Atomic volume:||18.4 cm3/mol|
|Structure:||double hexagonal close-packed|
|Specific heat capacity||–|
|Heat of fusion||–|
|Heat of atomization||–|
|Heat of vaporization||–|
|1st ionization energy||608 kJ mol-1|
|2nd ionization energy||–|
|3rd ionization energy||–|
|Minimum oxidation number||0|
|Min. common oxidation no.||0|
|Maximum oxidation number||4|
|Max. common oxidation no.||3|
|Electronegativity (Pauling Scale)||1.3|
|Polarizability volume||20.5 Å3|
|Reaction with air|
|Reaction with 15 M HNO3|
|Reaction with 6 M HCl|
|Reaction with 6 M NaOH|
|Oxide(s)||CfO, Cf2O3, CfO2 , Cf7O12|
|Atomic radius||186 pm|
|Ionic radius (1+ ion)||–|
|Ionic radius (2+ ion)||–|
|Ionic radius (3+ ion)||109 pm|
|Ionic radius (1- ion)||–|
|Ionic radius (2- ion)||–|
|Ionic radius (3- ion)||–|
|Thermal conductivity||10 W m-1 K-1|
|Freezing/Melting point:||900 oC, 1173 K|
Discovery of Californium
Californium was the sixth synthetic transuranium element of the actinide series to be discovered.
It was first produced by Stanley Thompson, Kenneth Street, Albert Ghiorso and Glenn Seaborg in 1950 in California, USA.
The researchers bombarded curium-242 with alpha particles in the 60-inch cyclotron in Berkeley, California. Each nuclear reaction created californium-245 (half-life 44 minutes) and a neutron. Only about 700,000 atoms of californium-245 were produced in the experiment. This number of atoms is enough to make a cube with sides about 27 nanometers long. Chemical analysis proved that the new element had been made. (1)
Californium was isolated in macro quantities for the first time by Burris Cunningham and Stanley Thompson in 1958 at the Materials Testing Reactor in Arco, Idaho by prolonged (five years) neutron irradiation of plutonium-239. Approximately 1.2 micrograms of californium and 0.6 micrograms of berkelium were synthesized. (1a)
The element was named after the U.S. State of California and the University of California.
Appearance and Characteristics
Californium is harmful due to its radioactivity.
Californium is a synthetic radioactive silvery-white metal of moderate chemical reactivity.
It is a relatively soft, malleable metal and is easily cut with a razor-blade.
It slowly tarnishes in air to the oxide at room temperature. (2)
Californium-252 is a very strong neutron emitter.
Uses of Californium
Californium-252 (half-life of 2.645 years) is produced in nuclear reactors and has found a variety of uses.
It is used as a neutron emitter, providing neutrons for the start-up of nuclear reactors.
It has also been used as a target material for producing transcalifornium elements. Ununoctium, the heaviest of the elements, was produced when a californium target was bombarded with calcium ions. (2a)
Californium-252 is used in to treat cervical cancer. It is also used to analyze the sulfur content of petroleum and in neutron moisture gauges to measure the moisture content of soil. (3)
Abundance and Isotopes
Abundance earth’s crust: nil
Abundance solar system: negligible
Cost, pure: $ per g
Cost, bulk: per 100g
Source: Californium is a synthetic element and is not found naturally on Earth. The spectrum of californium-254 has been observed in supernovae. (4) Californium is produced in nuclear reactors by bombarding plutonium with neutrons and in particle accelerators.
Isotopes: Californium has 20 isotopes whose half-lives are known, with mass numbers 237 to 256. Californium has no naturally occurring isotopes. Its longest lived isotopes are 251Cf, with a half-life of 898 years, 249Cf with a half-life of 351 years and 250Cf with a half-life of 13.08 years.
1. B. B. Cunningham, Berkelium and Californium., Journal of Chemical Education, Vol 36.1 (1959) p32-33.
1a. B. B. Cunningham, Berkelium and Californium., Journal of Chemical Education, Vol 36.1 (1959) p35.
2. Richard G. Haire, The Chemistry of the Actinide and Transactinide Elements., Springer., Vol 3.12., p1526-1527.
2a. Richard G. Haire, The Chemistry of the Actinide and Transactinide Elements., Springer., Vol 3.12., p1503 – 1507.
3. United States Department of Energy., page 69 (pdf).
4. W. Baade, G. Burbidge, F Hoyle, E Burbidge, R Christy, W Fowler, Supernovae and Californium 254., Publications of the Astronomical Society of the Pacific, Vol 68.403 p.296- 297.
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