From Big Medical Encyclopedia

ACTINOIDS (actinides) — family of relatives on the chemical properties of the elements of the 7th period of the Periodic Table of D. I. Mendeleyev following actinium.

This group includes 15 chemical elements (tab).

Characteristic oxidation level of the majority And. it is equal to three. The stable oxidation state of uranium is equal to six.

Actinium, thorium, protactinium, uranium, neptunium and plutonium meet in the nature. However crust contains in a little significant amounts only thorium (8×10-4%) and uranium (3×10-4%), the others in is insignificant trace amounts contain in uranium ores. All isotopes A. are radioactive (see Isotopes, radioactive).

And., (transuranic elements) located behind uranium, are open and synthesized in 1940 — 1961.

And. (hl. obr. some isotopes of uranium and plutonium) are used as powerful energy sources (nuclear power plants, nuclear weapon), and also for receiving isotopes. And., used in the industry (e.g., uranium, thorium, plutonium), have the high toxicity especially dangerous because of extremely slow terms of allocation And. from an organism. It demands strict observance of measures of protection (see. Antiactinic protection).

See also Periodic Table , Radioactivity .

Bibliography: Siborg. Artificial transuranic elements, the lane with English, M., 1965.

E. A. Maksimyuk.