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einsteinium ein·stein·i·um (īn-stī'nē-əm)
A radioactive transuranic element synthesized by neutron irradiation of plutonium or other elements. Its longest-lived isotope is Es 254 with a half-life of 275 days. Atomic number 99; melting point 860°C.
A synthetic, radioactive metallic element of the actinide series that is usually produced by bombarding plutonium or another element with neutrons. It was first isolated in a region near the explosion site of a hydrogen bomb. Its longest-lived isotope is Es 254 with a half-life of 276 days. Atomic number 99; melting point 860°C. See Periodic Table.
(Es), synthetic chemical element of the actinoid series of the periodic table, atomic number 99. Not occurring in nature, einsteinium (as the isotope einsteinium-253), produced by intense neutron irradiation of uranium-238, was identified in December 1952 by Albert Ghiorso and co-workers at Berkeley, Calif., in debris taken from the first thermonuclear or hydrogen-bomb explosion, in the South Pacific (November 1952).