Einsteinium

Einsteinium is a chemical element, in the periodic table einsteinium has the
symbol Es and atomic number 99. It is a member of the actinide series, is
metallic and radioactive, with no known uses. It is named after Albert Einstein.

It was the seventh transuranic element to be discovered. It was first
identified in December 1952 by Albert Ghiorso at the University of
California, Berkeley and another team headed by G.R. Choppin at Los Alamos.
Both were examining debris from a nuclear weapon test of November, 1952.
They discovered the isotope 253, which has a half-life of 20.5 days.

In 1961, enough einsteinium was produced to separate a macroscopic amount of
isotope 253. This sample weighted about 0.01 mg and was measured using a
special balance. The material produced was used to produce mendelevium.

Further einsteinium has been produced at the Oak Ridge National Laboratory.
Around 3 mg was created over a four year program of irradiation and then
chemical separation from a starting 1 kg of plutonium isotope.

Fourteen isotopes of einsteinium are now recognized. They have half-lives
ranging from 2 seconds (257) up to 471 days (252).

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