Einsteinium

Einsteinium is the actinide element with atomic number 99, first isolated and identified in 1952 by teams from Berkeley and Argonne Laboratories within the radioactive fallout of the first U.S. hydrogen bomb test. All of its isotopes have very short half-lives, it does not occur in nature, and it can only be produced atom by atom in high-flux reactors or accelerators, in vanishingly small amounts at a time. It therefore has no industrial or civilian uses and is currently studied only as a research object for the nuclear physics and chemistry of transuranium elements.

Einsteinium compounds such as einsteinium(III) oxide (Es2O3) and einsteinium(III) chloride (EsCl3) have only ever been prepared in the laboratory on the scale of single atoms to microgram quantities, to determine their oxidation states and actinide periodic behavior; they have never been produced on any scale nor appear in any civilian product.