Einsteinium ( /aɪnˈstaɪniəm/ eyen-STYE-nee-əm) is a synthetic element with the symbol Es and atomic number 99. It is the seventh transuranic element, and an actinide.
Einsteinium was discovered in the debris of the first hydrogen bomb explosion in 1952, and named after Nobel laureate Albert Einstein. Its most common isotope einsteinium-253 is produced 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 from other actinides and products of their decay. Other, heavier isotopes are synthesized in various laboratories, but at much smaller amounts, by bombarding heavy actinide elements with light ions. Owing to the small amounts of produced einsteinium and its short half-life, there are currently no practical applications for it outside of basic scientific research. In particular, einsteinium was used to synthesize, for the first time, 17 atoms of the new element mendelevium in 1955.
Einsteinium is a soft, silvery, paramagnetic metal. Its chemistry is typical of the late actinides, with a preponderance of the +3 oxidation state but also an accessible +2 oxidation state, especially in solids. The high radioactivity of einsteinium produces a visible glow and rapidly damages its crystalline lattice, with released heat of about 1000 watts per gram. Another difficulty in studying its properties is conversion of einsteinium to berkelium and then californium at a rate of about 3% per day. Like all synthetic transuranic elements, isotopes of einsteinium are extremely radioactive and are considered highly dangerous to health on ingestion.
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