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(kăl`ĭfôr'nēəm) [from CaliforniaCalifornia
, most populous state in the United States, located in the Far West; bordered by Oregon (N), Nevada and, across the Colorado River, Arizona (E), Mexico (S), and the Pacific Ocean (W). Facts and Figures

Area, 158,693 sq mi (411,015 sq km). Pop.
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], 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 seriesactinide series,
a series of radioactive metallic elements in Group 3 of the periodic table. Members of the series are often called actinides, although actinium (at. no. 89) is not always considered a member of the series.
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 of chemical elements, found in Group 3 of the periodic tableperiodic table,
chart of the elements arranged according to the periodic law discovered by Dmitri I. Mendeleev and revised by Henry G. J. Moseley. In the periodic table the elements are arranged in columns and rows according to increasing atomic number (see the table entitled
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. Its chemical properties are similar to those of lanthanumlanthanum
[Gr.,=to lie hidden], metallic chemical element; symbol La; at. no. 57; at. wt. 138.90547; m.p. about 920°C;; b.p. about 3,460°C;; sp. gr. 6.19 at 25°C;; valence +3.
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. Eighteen isotopes of californium are known, with half-liveshalf-life,
measure of the average lifetime of a radioactive substance (see radioactivity) or an unstable subatomic particle. One half-life is the time required for one half of any given quantity of the substance to decay.
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 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 elementtransuranium elements,
in chemistry, radioactive elements with atomic numbers greater than that of uranium (at. no. 92). All the transuranium elements of the actinide series were discovered as synthetic radioactive isotopes at the Univ.
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 to be synthesized, californium has yet to be found in the earth's crust. Californium was first produced in 1950 by Glenn T. SeaborgSeaborg, Glenn Theodore
, 1912–99, American chemist, b. Ishpeming, Mich., grad. Univ. of California at Los Angeles, 1934, Ph.D. Univ. of California at Berkeley, 1937.
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, 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).



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 (T1/2 = 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.


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



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


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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16, 1974 PHYSICAL REVIEW LETTERS Berkeley chemist Albert Ghiorso and his colleagues described bombarding an isotope of the heavy element californium with oxygen ions.