Atomic Number: 99 Atomic Radius: 245 pm (Van der Waals)
Atomic Symbol: Es Melting Point: 860 °C
Atomic Mass: 252 Boiling Point:
Electron Configuration:
[Rn] 7s2 5f11
Oxidation States: 3, 2
Albert Ghiorso
Einsteinium was identified by Albert Ghiorso in 1952.


(Albert Einstein) Einsteinium, the seventh transuranic element of the actinide series to be discovered, was identified by Ghiorso and co-workers at Berkeley in December 1952 in debris from the first large thermonuclear explosion, which took place in the Pacific in November, 1952. The 20-day 253Es isotope was produced.

In 1961, enough einsteinium was produced to separate a macroscopic amount of 253Es. This sample weighted about 0.01Mg and was measured using a special magnetic-type balance. 253Es so produced was used to produce mendelevium (Element 101).

About 3Mg of einsteinium has been produced at Oak Ridge National Laboratories by

  1. irradiating kilogram quantities of 239Pu in a reactor for several years to produce 242Pu,
  2. fabricating the 242Pu into pellets of plutonium oxide and aluminum powder,
  3. loading the pellets into target rods for an initial 1-year irradiation at the Savannah River Plant, and
  4. irradiating the targets for another 4 months in a HFIR (High Flux Isotopic Reactor).

The targets were then removed for chemical separation of the einsteinium from californium.


Sixteen isotopes of einsteinium are now recognized. 252Es has the longest half-life (472 days).


Tracer studies using 253Es show that einsteinium has chemical properties typical of a heavy trivalent, actinide element.


Los Alamos National Laboratory, Periodic Table of Elements, http://periodic.lanl.gov/list.shtml.