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Encyclopedia of Physical Science and Technology EN001F-11 May 25, 2001 21:2

Actinide Elements

Siegfried H¨ubener
Forschungszentrum Rossendorf

I. Discovery, Occurrence, and
Synthesis of the Actinides
II. Radioactivity and Nuclear Reactions of Actinides
III. Applications of Actinides
IV. Actinide Metals
V. Actinide Ions
VI. Actinide Compounds and Complexes

GLOSSARY Speciation Characterization of physical and chemical
states of (actinide) species in a given (chemical)
2+
+
Actinyl ion Dioxo actinide cations MO and MO . environment.
2 2
Decay chain A series of nuclides in which each member Transactinide elements Artificial elements beyond the
transforms into the next through nuclear decay until a actinide elements, beginning with rutherfordium (Rf),
stable nuclide has been formed. element 104. The heaviest elements, synthesized until
Lanthanides Fourteen elements with atomic numbers 58 now, are the elements 114, 116, and 118. At present,
(cerium) to 71 (lutetium) that are a result of filling the bohrium (Bh), element 107, is the heaviest element
4 f orbitals with electrons. which has been characterized chemically; chemical
Nuclear fission The division of a nucleus into two or studies of element 108, hassium (Hs), and element 112
more parts, usually accompanied by the emission of are in preparation.
neutrons and γ radiation.
Nuclide A species of atom characterized by its mass num-
ber, atomic number, and nuclear energy state. A ra- THE ACTINIDE ELEMENTS (actinoids) comprise the
dionuclide is a radioactive nuclide. 14 elements with atomic numbers 90–103, which fol-
Primordial radionuclides Nuclides which were pro- low actinium in the periodic table: thorium (Th), pro-
duced during element evolution and which have tactinium (Pa), uranium (U), neptunium (Np), plutonium
partly survived since then due to their long half- (Pu), americium (Am), curium (Cm), berkelium (Bk), cal-
lives. ifornium (Cf), einsteinium (Es), fermium (Fm), mendele-
Radioactivity The property of certain nuclides of show- vium (Md), nobelium (No), and lawrencium (Lr). The ac-
ing radioactive decay in which particles or γ radia- tinides constitute a unique series of elements which are
tion are emitted or the nucleus undergoes spontaneous formed by the progressive filling of the 5 f electron shell.
fission. Although not formally an actinide element, actinium (Ac;

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