Facts About Californium
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Atomic Number: 98
Atomic Symbol: Cf
Atomic Weight: 251
Melting Point: 1,580 F (860 C)
Boiling Point: Unknown

Word origin: Californium is named for the state of California, as well as the University of California system.

Discovery: Stanley G. Thompson, Glenn T. Seaborg, Kenneth Street and Albert Ghiorso at the University of California, Berkeley, first produced californium in 1950. They bombarded atoms of 242Cmwith helium ions using the 60-inch cyclotron, which yielded 244Cf.

Californium was the sixth transuranium element to be discovered.

Properties of californium

Californium is in the second half of the actinide series. As a metal, californium is fairly reactive. When standing in air or moisture, small pieces or foils of the metal quickly oxidize, but not violently. In high temperatures, a face-centered cubic structure has also been observed. The metal is trivalent and has a room-temperature, double-hexagonal close-packed structure.

The elements in the second half of the actinide series have f electrons that are removed or shielded from valence electrons. Because of this, californium resembles the behavior of lanthanide elements that exhibit divalent, trivalent, or tetravalent oxidation states in solid-state compounds. In solution, californium’s trivalent state is most stable.

Though not much californium exists, some alloys and numerous compounds have been made from it.

There are 20 reported isotopes of californium ranging in atomic mass from 237 to 256, though the isotopes with mass of 237 and 238 have not yet been confirmed. The element’s most stable isotope is 251Cf, which has a half-life of about 898 years. Either through alpha decay or spontaneous fission, 251Cf decays to 247Cm.

Sources of californium

Californium is artificially produced. There are two successful methods of preparing it. Both involve the reduction of californium trifluoride with lithium metal at an elevated temperature, then using thorium or lanthanum metal to reduce californium oxide. The largest amount of californium metal produced at one time was about 10 milligrams.

It has been suggested that californium may be produced in supernovae stellar explosions. These explosions have characteristic light curves that would agree with the radioactive decay of 254Cf. This suggestion, however, is questioned.

Uses of californium

252Cf is a very efficient source of neutrons, which makes it a useful element. Currently, it is used in the oil well industry. Californium can be used in devices called neutron moisture gauges that find oil-and water-bearing layers within the wells. Additionally, it used as a neutron source in a process called neutron activation that can find gold and silver ores through on-the-spot analysis. Many more uses for californium are expected.

(Sources: Los Alamos National Laboratory, Jefferson Lab)