actinium

ac·tin·i·um

A0068700 (ăk-tĭn′ē-əm)n. Symbol Ac A radioactive element found in uranium ores, used in equilibrium with its decay products as a source of alpha rays. Its longest lived isotope is Ac-227 with a half-life of 21.77 years. Atomic number 89; melting point 1,050°C; boiling point 3,198°C; specific gravity (calculated) 10.07; valence 3. See Periodic Table.

[From Greek aktīs, aktīn-, ray (from its radioactivity); see nek^w-t- in Indo-European roots.]

actinium

(ækˈtɪnɪəm) n (Elements & Compounds) a radioactive element of the actinide series, occurring as a decay product of uranium. It is used as an alpha-particle source and in neutron production. Symbol: Ac; atomic no: 89; half-life of most stable isotope,²²⁷Ac: 21.6 years; relative density: 10.07; melting pt: 1051°C; boiling pt: 3200 ± 300°C[C19: New Latin, from actino- + -ium]

ac•tin•i•um

(ækˈtɪn i əm)

n. a radioactive, silver-white, metallic element that glows blue in the dark, resembling the rare earths in chemical behavior and valence. Symbol: Ac; at. no.: 89; at. wt.: 227. [< French (1900); see actino-, -ium²]

ac·tin·i·um

(ăk-tĭn′ē-əm) Symbol Ac A silvery-white, highly radioactive metallic element of the actinide series that is found in uranium ores. It is about 150 times more radioactive than radium and is used as a source of alpha rays. Its most stable isotope has a half-life of about 22 years. Atomic number 89. See Periodic Table.

Thesaurus

Noun

actinium - a radioactive element of the actinide series; found in uranium oresAc, atomic number 89chemical element, element - any of the more than 100 known substances (of which 92 occur naturally) that cannot be separated into simpler substances and that singly or in combination constitute all matteruranium ore - any ore from which uranium can be extracted

Translations

actinium

(ăktĭn`ēəm) [Gr.,=like a ray], radioactive chemical element; symbol Ac; at. no. 89; mass number of most stable isotopeisotope
, in chemistry and physics, one of two or more atoms having the same atomic number but differing in atomic weight and mass number. The concept of isotope was introduced by F.
..... Click the link for more information. 227; m.p. about 1,050&degC;; b.p. 3,200&degC;±300&degC;; sp. gr. 10.07; valence +3. Actinium is a silver-white metal with a cubic crystalline structure. It is found with uranium minerals in pitchblendepitchblende
, dark, lustrous, heavy mineral, a source of radium and uranium. Largely natural uranium oxides, triuranium octaoxide (U₃O₈) and uranium dioxide (UO₂
..... Click the link for more information. . The pure metal can be prepared by reducing its fluoride with lithium vapor at about 1,200&degC;. Actinium-227, the most stable isotope, has a half-lifehalf-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.
..... Click the link for more information. of 21.77 years. The other seven isotopes of actinium have very short half-lives ranging from 10 days to less than 1 min.

Actinium is 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
..... Click the link for more information. . 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&degC;; b.p. about 3,460&degC;; sp. gr. 6.19 at 25&degC;; valence +3.
..... Click the link for more information. and of members 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.
..... Click the link for more information. , of which it is usually considered the first member. It reacts with water to form an insoluble hydroxide; with halides to form a trifluoride, trichloride, bromide, or iodide; with oxalic acid to form the oxalate; with oxygen or sulfur to form the sesquioxide or sesquisulfide.

Actinium was first recognized in 1899 by André Debierne in uranium residues from pitchblende after the radium was extracted by Pierre and Marie CurieCurie
, family of French scientists. Pierre Curie, 1859–1906, scientist, and his wife, Marie Sklodowska Curie, 1867–1934, chemist and physicist, b. Warsaw, are known for their work on radioactivity and on radium.
..... Click the link for more information. . It was later found to be identical with an element discovered in 1902 by Fritz Giesel and which he called emanium.

Actinium

Ac, a radioactive chemical element in the Group III of the Mendeleev periodic table, atomic number 89. No stable isotopes.

Actinium was discovered in 1899 by the French chemist A. Debierne while he was studying uranium ore tailings. The ten known radioactive isotopes of actinium have mass numbers ranging from 221 to 230. The longest-lived actinium isotope, ²²⁷Ac (half-life T_½=21.8 years), emits beta particles (98.8 percent) and alpha particles (1.2 percent). The isotopes ²²⁷Ac and ²²⁸Ac (T_½=6.13 h; also known as mesothorium II, MsThll) occur naturally in uraniferous and thoriferous ores as members of the naturally occurring radioactive families. The surface layer of the earth’s crust (thickness 1.6 km) contains 11,300 tons of ²²⁷Ac, but the actinium content in the earth’s crust is very small compared to that of other elements (6.10^-10 percent by mass).

The element actinium is a silvery white metal with a face-centered cubic lattice (T_m=1050° ± 50°C, T_b probably about 3300°C); it glows faintly in the dark because of its high radioactivity. In moist air it becomes coated with a white film of oxide which prevents further oxidation of the metal. Actinium is trivalent in chemical compounds. Almost all actinium salts are white and are colorless in solution. Most of them (except AcP0₄) are isomorphic with the corresponding lanthanum compounds. Actinium forms the same insoluble compounds as does La (hydroxide, phosphate, oxalate, carbonate, fluosilicate). Actinium hydroxide Ac(OH)₃ is more basic than lanthanum hydroxide La(OH)₃. Because of the extraordinary similarities between the chemical properties of actinium and lanthanum, isolation of actinium in pure form from its natural hosts (containing La and other rare earths) involves great difficulties, and therefore milligram amounts of actinium (²²⁷Ac) are obtained artificially through neutron bombardment of radium ²²⁶Ra. Since probability of ²²⁷Ac decay with alpha emission is low, and the energy of beta particles emitted by this isotope is very small (46 keV), any emission accompanying the radioactive decay of ²²⁷Ac went undetected for a long time; until 1935 it was assumed that radioactive decay of ²²⁷Ac occurred without emission. Modern instruments are capable of identifying such soft beta radiation, but it is still quite difficult to make quantitative measurements; therefore, the behavior of ²²⁷Ac is usually monitored in terms of the activity of its daughters, in experiments involving trace amounts of the radionuclide. Mixed with beryllium, ²²⁷Ac is used in the preparation of neutron sources, in which neutrons are formed by irradiating ⁹Be nuclei with alpha particles emitted by ²²⁷Ac daughters.

REFERENCES

Seaborg, G., and J. Katz. Khimiia aktinidnykh elementov. Moscow, 1960. (Translated from English.)
Bagnall, K. Khimiia redkikh radioaktivnykh elementov, poloniiaktinii. Moscow, 1960. (Translated from English.)

S. S. BERDONOSOV

actinium

[ak′tin·ē·əm] (chemistry) A radioactive element, symbol Ac, atomic number 89; its longest-lived isotope is ²²⁷Ac with a half-life of 21.7 years; the element is trivalent; chief use is, in equilibrium with its decay products, as a source of alpha rays.

actinium

a radioactive element of the actinide series, occurring as a decay product of uranium. It is used as an alpha-particle source and in neutron production. Symbol: Ac; atomic no.: 89; half-life of most stable isotope,²²⁷Ac: 21.6 years; relative density: 10.07; melting pt.: 1051°C; boiling pt.: 3200 ± 300°C

actinium

ac·tin·i·um

actinium

ac•tin•i•um

ac·tin·i·um

actinium

actinium

Actinium

REFERENCES

actinium

actinium

actinium

actinium

ac·tin·i·um (Ac),

ac·tin·i·um

actinium

Synonyms for actinium

noun a radioactive element of the actinide series

Synonyms

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