DENSITY: 8.8 +/− g/cc

Einsteinium, the tenth member of the actinide series, was discovered in 1952. Einsteinium and fermium (element 100) were most unexpectedly produced in the explosion of the first U.S. thermonuclear device, "Mike," tested at Eniwetok Atoll in the Pacific Ocean on November 1, 1952. Early analyses of debris from that explosion indicated that something unusual had occurred; the new, very neutron-rich isotope of plutonium, 244 Pu, was found during mass spectrometric analyses performed at the Argonne National Laboratory and another isotope of plutonium, 246 Pu, was detected at the Los Alamos Scientific Laboratory in the course of analyses of the Pu fractions. Scientists at the Radiation Laboratory at the University of California, Berkeley, using their previous experience with the separation of individual actinide elements, then joined in the search for trans-californium elements (elements of higher atomic number than californium). Tons of coral from the atoll were laboriously processed, and 253 99 (half-life 20 days) and 255 100 (half-life 20 hours) were positively identified based on the order of their elution (removal) from a cation-exchange resin column with an α -hydroxyisobutyrate solution. Because of the huge, nearly instantaneous neutron flux generated in the explosion, at least seventeen neutrons were successively captured by the 238 U in the thermonuclear device, producing uranium isotopes through 255 U, many of which β -decayed to higher atomic number elements, thus producing 253 Es and 255 Fm. After their declassification, these results were published jointly by the Berkeley Radiation Laboratory, the Argonne National Laboratory, and the Los Alamos Scientific Laboratory (Ghiorso et al., p. 1048[L], 1955).

The name einsteinium was chosen for element 99, in honor of the great scientist Albert Einstein. Einsteinium isotopes of masses 241 through 256 are known. All are radioactive, decaying by α -particle emission, electron capture, spontaneous fission , and β -decay. The mass 241 isotope has the shortest half-life (8 seconds), and the mass 252 isotope has the longest (1.29 years). The ground state electronic configuration of the gaseous einsteinium atom is [Rn]5f 11 7s 2 , analogous to that of its lanthanide homologue (holmium). The most stable ion in aqueous solution is Es 3+ , but Es 2+ and Es 4+ have been reported, and the metal is divalent.

SEE ALSO Actinium ; Berkelium ; Einstein, Albert ; Fermium ; Lawrencium ; Mendelevium ; Neptunium ; Nobelium ; Plutonium ; Protactinium ; Radioactivity ; Rutherfordium ; Thorium ; Transmutation ; Uranium .

Darleane C. Hoffman


Ghiorso, Albert; Thompson, S. G.; Higgins, G. H.; et al. (1955). "New Elements Einsteinium and Fermium, Atomic Numbers 99 and 100." Physical Review 99:1048[L].

Hoffman, Darleane C.; Ghiorso, Albert; and Seaborg, Glenn T. (2000). The Transuranium People: The Inside Story. Singapore: World Scientific Publishing.

Seaborg, Glenn T., and Loveland, Walter D. (1990). The Elements beyond Uranium. New York: Wiley.

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