Einsteinium

Einsteinium was not created deliberately — it was found. When the United States detonated the first thermonuclear device, Ivy Mike, on November 1, 1952, in the Marshall Islands, an unprecedented cascade of neutron captures and beta decays occurred inside the fireball. Scientists from Los Alamos, Argonne, and Lawrence Berkeley National Laboratories collected coral and filter paper samples from the blast site and detected two new elements in the fallout. One was einsteinium, element 99, found as einsteinium-253 embedded in the vaporized debris.

Einsteinium is produced in such vanishingly small quantities — typically nanograms to micrograms — that practical applications are impossible. Its scientific value lies in nuclear research and as a precursor for synthesizing even heavier elements. Bombardment of einsteinium targets with helium ions was used to produce mendelevium (element 101) in 1955. In 2021, researchers at Lawrence Berkeley National Laboratory studied einsteinium's chemistry directly for the first time using just 200 nanograms, measuring its bond length and exploring its coordination chemistry in a landmark experiment.

Albert Ghiorso, Bernard Harvey, Gregory Choppin, Stanley Thompson, and Glenn Seaborg identified einsteinium in early 1953 while analyzing coral and filter paper collected from the Ivy Mike test site. The discovery was immediately classified by the U.S. government and kept secret for nearly three years. The existence of einsteinium (and fermium) was finally declassified and announced publicly in 1955. The element was named in honor of Albert Einstein, who had died in April 1955 just months before the announcement. The first deliberate laboratory synthesis via neutron irradiation of plutonium was accomplished in 1961, producing 3 nanograms — at the time, the largest quantity ever created.

Einsteinium does not occur naturally on Earth under normal conditions. It was first found in thermonuclear detonation debris, where extreme neutron fluxes briefly produced heavy actinides through rapid neutron capture. Today it is synthesized in small quantities by prolonged neutron bombardment of lighter actinides in high-flux nuclear reactors, primarily at Oak Ridge National Laboratory. Even under the best conditions, only microgram quantities can be accumulated.

Einsteinium chemistry is extraordinarily difficult to study due to severe scarcity and intense radioactivity. The element is believed to adopt a +3 oxidation state in most compounds, with some evidence for +2 and +4 states. In 2021, scientists directly measured einsteinium's covalent radius and studied its interactions with organic ligands for the first time, finding that its chemical behavior differed subtly from predictions based on neighboring actinides. Oxide, fluoride, and chloride species have been tentatively characterized at the tracer level.

• Einsteinium was discovered not in a laboratory but in the radioactive fallout of a nuclear weapons test — making it the only element whose discovery was triggered by a thermonuclear explosion.
• The discovery was classified top secret for nearly three years; the scientists who found it could not publish their results until 1955.
• Albert Einstein died on April 18, 1955, just months before the public announcement of element 99 bearing his name — he never knew an element had been named in his honor.
• A 2021 study using just 200 nanograms of einsteinium — about one-millionth the mass of a grain of sand — represented one of the most challenging chemical experiments ever attempted.
• Einsteinium-253 has a half-life of only 20.5 days, which means the samples collected from the Ivy Mike test were decaying rapidly even as scientists raced to identify them.