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. It was named after Alfred Einstein.
In 1961, enough einsteinium was produced to separate a macroscopic amount of 253Es. This sample weighted about 0.01µg and was measured using a special magnetic-type balance. 253Es so produced was used to produce mendelevium (Element 101) by neutron bombardment.
About 3 µg of einsteinium has been produced in the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratories by:
Sixteen isotopes with three isomers ranging in atomic mass from 241 to 256 are now recognized for einsteinium. 252Es has the longest half-life (472 days) but is only available in minute quantities. The isotopes 253Es and 254Es are the isotopes of choice for physicochemical studies because of their availability and reasonable half-lives. However, usually only a few micrograms of einsteinium isotopes are used in experiments to reduce worker exposure and to minimize the intense self-irradiation effects.