Atomic#099-Einsteinium - Einsteinium [1] is a synthetic radioactive isotope, first discovered by Albert Ghiorso and co-workers in debris from a 1952 thermonuclear explosion in the South Pacific. It is produced by intense neutron irradiation of Uranium-238 (U-238). There are 11 known isotopes.

Properties of Einsteinium
Symbol: Es Atomic number: 99 Atomic weight: 254.0881 Periodic Table group: IIIb [2] [3]
Atomic#099-Einsteinium Properties

Einsteinium [4]
Pronounced As: instinm, insti- [named for Albert Einstein [5]], artificially produced radioactive chemical element; symbol: Es; Atomic#99; mass of most stable Atomic# isotope252; The Melting Point is about 860?C; The Boiling Point is unknown; The Specific Gravity (density) is unknown; valence +2, +3. Einsteinium [6], is a member of group IIIb of the Periodic Table; its chemical properties are believed to be similar to those of the other members of the actinide series. The seventh transuranium element to be discovered, Einsteinium was isolated in Dec., 1952, by Albert Ghiorso and his co-workers at the Univ. of California at Berkeley in residue from the first thermonuclear test explosion in the South Pacific. They identified Einsteinium-253, which has a half-life of 20.5 days. It was not until 1961 that a weighable quantity (about 0.01 microgram) of the element was separated; it was used to prepare the element mendelevium. Weighable quantities of einsteinium have since been prepared by neutron bombardment of plutonium. Seventeen isotopes, all of which are radioactive, are known. Einsteinium-252, the most stable isotope, has a half-life of 472 days.

Atomic#099-Einsteinium Chart

[1] [2] [4] [6] Encyclopedia.com: Periodic Table of the Elements: Einsteinium
[3] From Compton's InteractiveEncyclopedia ?1999 The Learning Company, Inc.
[5] Encyclopedia.com: general link to Einsteinium