actinium series


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actinium series,

natural radioactive decay series beginning with uraniumuranium
, radioactive metallic chemical element; symbol U; at. no. 92; mass number of most stable isotope 238; m.p. 1,132°C;; b.p. 3,818°C;; sp. gr. 19.1 at 25°C;; valence +3, +4, +5, or +6.
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-235 (also called actinouranium) and ending with leadlead,
metallic chemical element; symbol Pb [Lat. plumbum]; at. no. 82; at. wt. 207.2; m.p. 327.502°C;; b.p. about 1,740°C;; sp. gr. 11.35 at 20°C;; valence +2 or +4.
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-207. See radioactivityradioactivity,
spontaneous disintegration or decay of the nucleus of an atom by emission of particles, usually accompanied by electromagnetic radiation. The energy produced by radioactivity has important military and industrial applications.
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