# Einsteinium
**Einsteinium** is a synthetic radioactive chemical element with the symbol Es and atomic number 99, classified as an actinide and solid at room temperature[1](https://pubchem.ncbi.nlm.nih.gov/element/99). It was discovered in December 1952 in the debris of the first thermonuclear explosion, the [Ivy Mike](https://www.edgepedia.org/ivy-mike) test on a Pacific atoll on 1 November 1952, and was named after [Albert Einstein](https://www.edgepedia.org/albert-einstein)[2](https://periodic-table.rsc.org/element/99/einsteinium). Because it is hard to create and exceptionally radioactive, only small amounts have ever been made, and it has no uses outside basic scientific research[3](https://newscenter.lbl.gov/2021/02/03/discoveries-at-the-edge-of-the-periodic-table-first-ever-measurements-of-einsteinium/) • [1](https://pubchem.ncbi.nlm.nih.gov/element/99).
| Key fact | Detail |
|---|---|
| Identity | Symbol Es, atomic number 99, actinide, period 7, electron configuration [Rn] 5f117s2 • [1](https://pubchem.ncbi.nlm.nih.gov/element/99) • [2](https://periodic-table.rsc.org/element/99/einsteinium) |
| Discovery | December 1952, in debris from the Ivy Mike thermonuclear test of 1 November 1952; announced in 1955[2](https://periodic-table.rsc.org/element/99/einsteinium) |
| First isotope | Es-253, half-life 20.47 days, formed by 15 neutron captures on uranium-238 followed by seven beta decays[1](https://pubchem.ncbi.nlm.nih.gov/element/99) |
| Longest-lived isotope | Es-252, half-life 471.7 ± 1.9 days; decays by alpha emission to berkelium-248 or electron capture to californium-252[4](https://www.sciencedirect.com/science/article/pii/0022190277800894) |
| Production | Bombarding curium targets with neutrons at Oak Ridge National Laboratory's High Flux Isotope Reactor; annual output only a few tens of micrograms[3](https://newscenter.lbl.gov/2021/02/03/discoveries-at-the-edge-of-the-periodic-table-first-ever-measurements-of-einsteinium/) • [5](https://www.nature.com/articles/s42004-021-00529-8) |
| Chemistry | Common oxidation state +3; oxidation states II and III reported, IV postulated but not established[1](https://pubchem.ncbi.nlm.nih.gov/element/99) |
| Melting point | 860 °C (1133 K)[2](https://periodic-table.rsc.org/element/99/einsteinium) |
| Uses | None outside basic research on actinide science and production of heavier transuranic elements[1](https://pubchem.ncbi.nlm.nih.gov/element/99) |
## Discovery
Einsteinium and fermium (element 100) were found unexpectedly in the debris of the "Mike" thermonuclear explosion in the [Pacific Ocean](https://www.edgepedia.org/pacific-ocean) in 1952. Fallout material gathered from a neighboring atoll was sent to [Berkeley, California](https://www.edgepedia.org/berkeley-california), where Gregory Choppin, Stanley Thompson, Albert Ghiorso, and Bernard Harvey examined it; within a month they had discovered and identified 200 atoms of the new element[2](https://periodic-table.rsc.org/element/99/einsteinium). Scientists explained the production through multiple neutron captures by the uranium used in the thermonuclear device followed by successive beta decays, resulting in atoms with atomic numbers 99 and 100[6](https://www2.lbl.gov/abc/wallchart/chapters/08/0.html). The specific isotope first identified, Es-253, was produced by combining 15 neutrons with uranium-238, which then underwent seven beta decays[1](https://pubchem.ncbi.nlm.nih.gov/element/99).
Cold War secrecy delayed publication: the discovery was not made public for three years, and the name einsteinium was first suggested in *Physical Review* on 1 August 1955 by [Albert Ghiorso](https://www.edgepedia.org/albert-ghiorso) and his colleagues[2](https://periodic-table.rsc.org/element/99/einsteinium). The formal paper "New Elements Einsteinium and Fermium, Atomic Numbers 99 and 100" appeared in *Physical Review* 99, 1048 (1955)[7](https://journals.aps.org/prl/transuranium-elements-and-the-physical-review).
## Production and availability
Einsteinium does not occur naturally in the [Earth's crust](https://www.edgepedia.org/earths-crust)[1](https://pubchem.ncbi.nlm.nih.gov/element/99). Today it is made by bombarding curium targets with neutrons to trigger a long chain of nuclear reactions, work done at [Oak Ridge National Laboratory](https://www.edgepedia.org/oak-ridge-national-laboratory)'s High Flux Isotope Reactor, one of only a few places in the world capable of making the element[3](https://newscenter.lbl.gov/2021/02/03/discoveries-at-the-edge-of-the-periodic-table-first-ever-measurements-of-einsteinium/). The heaviest actinides rely on long-term irradiations with intense thermal neutron fluxes in dedicated facilities such as HFIR or the SM-3 reactor in Dimitrovgrad, Russia[5](https://www.nature.com/articles/s42004-021-00529-8).
Quantities are minute. Annual production yields only a few tens of micrograms of a radioisotope with a half-life of less than 300 days, about 300 times less than what a typical target for superheavy-element synthesis requires[5](https://www.nature.com/articles/s42004-021-00529-8). In californium-252 production campaigns at Oak Ridge, einsteinium-253/254 is recovered as a byproduct in microgram amounts, alongside milligrams of berkelium-249 and picograms of fermium-257; a recent campaign recovered 95 percent of the Es-253/254 per column run[8](https://www.ornl.gov/news/tiny-amounts-rare-radioisotopes-recovered-during-californium-252-production-high-demand/). By 1961, enough einsteinium had been collected to be visible to the naked eye and weighed, though it amounted to only 10 millionths of a gram[2](https://periodic-table.rsc.org/element/99/einsteinium).
## Isotopes
Einsteinium has no stable isotopes[1](https://pubchem.ncbi.nlm.nih.gov/element/99). Sixteen isotopes with three isomers, ranging in atomic mass from 241 to 256, are recognized[1](https://pubchem.ncbi.nlm.nih.gov/element/99). The longest-lived is Es-252, whose half-life was measured as 471.7 ± 1.9 days by following the decay of its 785.1 keV gamma ray over three years[4](https://www.sciencedirect.com/science/article/pii/0022190277800894); it decays into berkelium-248 through alpha decay or into californium-252 through electron capture[1](https://pubchem.ncbi.nlm.nih.gov/element/99). The isotopes Es-253 and Es-254 are the ones of choice for physicochemical studies because of their availability and reasonable half-lives, and usually only a few micrograms are used in experiments to reduce worker exposure and minimize intense self-irradiation effects[1](https://pubchem.ncbi.nlm.nih.gov/element/99). Es-254 has a half-life of 276 days[3](https://newscenter.lbl.gov/2021/02/03/discoveries-at-the-edge-of-the-periodic-table-first-ever-measurements-of-einsteinium/).
## Chemical properties
Tracer studies using Es-253 show that einsteinium has chemical properties typical of a heavy trivalent actinide element[1](https://pubchem.ncbi.nlm.nih.gov/element/99). Oxidation states II and III have been reported, and state IV has been postulated from vapor transport studies but not established unequivocally[1](https://pubchem.ncbi.nlm.nih.gov/element/99). The element is a solid metal at room temperature with a melting point of 860 °C[2](https://periodic-table.rsc.org/element/99/einsteinium), and its ground-state electron configuration is [Rn] 5f117s2 • [2](https://periodic-table.rsc.org/element/99/einsteinium). The radiation and heat given off by einsteinium isotopes make experiments difficult[1](https://pubchem.ncbi.nlm.nih.gov/element/99).
## First bond-distance measurements, 2021
For nearly seven decades after discovery, very few experiments had been performed with einsteinium. In 2021 a team co-led by Berkeley Lab scientist Rebecca Abergel, who leads Berkeley Lab's Heavy Element Chemistry group and is an assistant professor in UC Berkeley's Nuclear Engineering department, and [Los Alamos National Laboratory](https://www.edgepedia.org/los-alamos-national-laboratory) scientist Stosh Kozimor published the first study characterizing some of its properties, in *Nature*[3](https://newscenter.lbl.gov/2021/02/03/discoveries-at-the-edge-of-the-periodic-table-first-ever-measurements-of-einsteinium/).
The sample, made at Oak Ridge's High Flux Isotope Reactor, was contaminated with a significant amount of californium, so the team abandoned [X-ray crystallography](https://www.edgepedia.org/x-ray-crystallography), which requires a pure sample, and instead used luminescence spectroscopy and X-ray absorption spectroscopy at the Molecular Foundry and the [Stanford Synchrotron Radiation Lightsource](https://www.edgepedia.org/stanford-synchrotron-radiation-lightsource)[3](https://newscenter.lbl.gov/2021/02/03/discoveries-at-the-edge-of-the-periodic-table-first-ever-measurements-of-einsteinium/). With less than 250 nanograms of Es-254, they measured the first-ever einsteinium bond distance and confirmed the +3 oxidation state; photophysical measurements also revealed a hypsochromic shift upon metal complexation, opposite from what had been previously observed with other f-elements[3](https://newscenter.lbl.gov/2021/02/03/discoveries-at-the-edge-of-the-periodic-table-first-ever-measurements-of-einsteinium/) • [9](https://foundry.lbl.gov/2021/03/09/first-ever-measurements-of-einsteinium/).
## Role in heavier-element research
Einsteinium has served as a stepping stone to heavier elements. Mendelevium (element 101) was produced in 1955 by bombarding Es-253 with helium ions, with production estimated at only a few atoms per experiment[6](https://www2.lbl.gov/abc/wallchart/chapters/08/0.html). As the next logical target element for synthesizing element 119, einsteinium's scarcity is now the limiting factor: annual production of a few tens of micrograms is about 300 times lower than what a typical target requires, so physicists have turned to heavier projectile isotopes such as titanium-50 instead[5](https://www.nature.com/articles/s42004-021-00529-8).
## References
1. [Einsteinium | Es (Element), PubChem](https://pubchem.ncbi.nlm.nih.gov/element/99)
2. [Einsteinium, Element information, properties and uses, Royal Society of Chemistry](https://periodic-table.rsc.org/element/99/einsteinium)
3. [Discoveries at the Edge of the Periodic Table: First Ever Measurements of Einsteinium, Berkeley Lab News Center](https://newscenter.lbl.gov/2021/02/03/discoveries-at-the-edge-of-the-periodic-table-first-ever-measurements-of-einsteinium/)
4. [Half-life of the longest-lived einsteinium isotope 252Es, Journal of Inorganic and Nuclear Chemistry](https://www.sciencedirect.com/science/article/pii/0022190277800894)
5. [Open questions on chemistry in the synthesis and characterization of superheavy elements, Communications Chemistry](https://www.nature.com/articles/s42004-021-00529-8)
6. [The Search for "Heavy" Elements, Lawrence Berkeley Lab](https://www2.lbl.gov/abc/wallchart/chapters/08/0.html)
7. [Transuranium Elements and the Physical Review, Physical Review Letters](https://journals.aps.org/prl/transuranium-elements-and-the-physical-review)
8. [Tiny amounts of rare radioisotopes, recovered during californium-252 production, in high demand for research, Oak Ridge National Laboratory](https://www.ornl.gov/news/tiny-amounts-rare-radioisotopes-recovered-during-californium-252-production-high-demand/)
9. [First Ever Measurements of Einsteinium, Molecular Foundry, Berkeley Lab](https://foundry.lbl.gov/2021/03/09/first-ever-measurements-of-einsteinium/)
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*Topic: Encyclopedia › Physical world and mathematics › Chemistry › Elements and inorganic substances › Element classifications and synthetic elements › Extended, synthetic, and hypothetical elements › Overview of synthetic and superheavy elements*
*Initially written Sep 17, 2026 · Reviewed: Oct 15, 2026 · Edited: Oct 15, 2026 · Last review: Oct 15, 2026*
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License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license