| Atomic Number: | 99 | Atomic Symbol: | Es |
| Atomic Weight: | 254 | Electron Configuration: | 2-8-18-32-29-8-2 |
| Shells: | 2,8,18,32,29,8,2 | Filling Orbital: | 5f11 |
| Melting Point: | oC | Boiling Point: | oC |
| Description: | Man made radioactive metal. |
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 isotope produced was the 20-day 253Es isotope. In 1961, a sufficient
amount of einsteinium was produced to permit separation of a macroscopic amount
of 253Es. This sample weighted about 0.01Mg. A special magnetic-type balance was
used to make this determination.
253Es so produced was used to produce mendelevium (Element 101). About 3Mg of
einsteinium has been produced at Oak Ridge National Laboratories by irradiating
for several years kilogram quantities of 239Pu in a reactor to produce 242Pu.
This was then fabricated into pellets of plutonium oxide and aluminum powder,
and loaded into target rods for an initial 1-year irradiation at the Savannah
River Plant, followed by irradiation in a HFIR (High Flux Isotopic Reactor).
After 4 months in the HFIR the targets were 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.