History

(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.

Isotopes

Fourteen isotopes of einsteinium are now recognized. ²⁵⁴Es has the longest half-life (275 days).

Properties

Tracer studies using ²⁵³Es show that einsteinium has chemical properties typical of a heavy trivalent, actinide element. 
A Periodic Table of the Elements at Los Alamos National Laboratory