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Americium (Am). Diagram of the nuclear composition and electron configuration of an atom of americium-243 (atomic number: 95), the most stable isotope of this element. The nucleus consists of 95 protons (red) and 148 neutrons (blue). Americium, named for the Americas and first synthesised in 1944, is an actinide and transuranic element in period 7, and the f-block of the periodic table. Actinides are soft radioactive metals. Americium-243 has a half-life of 7370 years, its nucleus emitting an alpha particle to form neptunium-239.
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