Einsteinium is a synthetic element with the symbol Es and atomic number 99. It is the seventh transuranic element, and an actinide.
Einsteinium was discovered as a component of the debris of the first hydrogen bomb explosion in 1952, and named after Albert Einstein. Its most common isotope einsteinium-253 (half life 20.47 days) is produced artificially from decay of californium-253 in a few dedicated high-power nuclear reactors with a total yield on the order of one milligram per year. The reactor synthesis is followed by a complex procedure of separating einsteinium-253 from other actinides and products of their decay. Other isotopes are synthesized in various laboratories, but at much smaller amounts, by bombarding heavy actinide elements with light ions. Symbol: Es
Electron configuration: Rn 5f11 7s2
Discovered: 1952
Melting point: 860 °C
Discoverer: Albert Ghiorso
Atomic mass: 252 u