Californium

californium (kăl`ĭfôr'nēəm) [from California], artificially produced, radioactive metallic chemical element; symbol Cf; at. no. 98; mass no. of most stable isotope 251; m.p. about 900°C;; b.p. about 1,470°C;; density unknown; valence +3. Californium is a member of the actinide series of chemical elements, found in Group 3 of the periodic table. Its chemical properties are similar to those of lanthanum. Eighteen isotopes of californium are known, with half-lives ranging from about 40 sec for californium-239 to about 900 years for californium-251, the most stable isotope. Californium-249 (half-life 351 years) is most useful for chemical investigations; it is obtained by the decay of berkelium-249. Four solid compounds of californium have been prepared; they are the trichloride, oxychloride, oxyfluoride, and oxide. Californium-252 (half-life 2.6 years) is produced in nuclear reactors for use as a source of neutrons for counters and electronic systems in industrial and medical applications. The sixth transuranium element to be synthesized, californium has yet to be found in the earth's crust. Californium was first produced in 1950 by Glenn T. Seaborg, Stanley G. Thompson, Albert Ghiorso, and Kenneth Street, Jr., in a cyclotron at the Univ. of California at Berkeley by bombarding curium-242 with alpha particles, resulting in californium-245 (half-life 45 min).

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californium

a metallic transuranic element artificially produced from curium. Symbol: Cf; atomic no.: 98; half-life of most stable isotope, ²⁵¹Cf: 800 years (approx.)

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californium [‚kal·ə′fȯr·nē·əm]

(chemistry)

A chemical element, symbol Cf, atomic number 98; all isotopes are radioactive.

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Californium 

Cf, an artificial radioactive chemical element of the actinide series, atomic number 98. It has no stable isotopes. It was originally produced in 1950 by the American scientists S. Thompson, A. Ghiorso, K. Street, and G. Seaborg using the nuclear reaction ²⁴²Cm(d, n)²⁴⁵Cf. The element was named after the location of its discovery (the state of California).

The known isotopes of californium have mass numbers 242 to 256. The following isotopes are relatively stable and may be prepared in macroquantities by prolonged irradiation of uranium or plutonium with neutrons: ²⁴⁹Cf (T_1/2 = 360 years), ²⁵⁰Cf (13.2 years), ²⁵¹Cf (more than 800 years), and ²⁵²Cf (2.65 years). The first solid compounds of californium, ²⁴⁹Cf₂O₃ and ²⁴⁹CFOCl, were produced in 1958. The most typical state of oxidation of californium, like the other heavy actinides, is +3; a less typical state is +2. Californium may be separated from the other actinides using extraction and chromatographic methods. Compounds of ²⁵²Cf may be used as powerful small-scale neutron sources.

REFERENCES

Gol’danskii, V. I., and S. M. Polikanov. Tiazhelee urana. Moscow, 1969. Vdovenko, V. M. Sovremennaia radiokhimiia. Moscow, 1969.

S. S. BERDONOSOV