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Einsteinium (Template:PronEng) is a synthetic element. On the periodic table, it is represented by the symbol Es and atomic number 99. It is the seventh transuranic element, and seventh in the series of Actinides. It was named in honor of Albert Einstein.
Its position on the periodic table indicates that its chemical and physical properties are similar to other metals. Though only small amounts have ever been made, it has been determined to be silver-colored. According to tracer studies conducted at Los Alamos National Laboratory using the isotope 253Es, this element has chemical properties typical of a heavy trivalent, actinide element.
Like many of the synthetic elements, many of einsteinium's isotopes are radioactive.
Einsteinium does not occur naturally in any measurable quantities. The modern process of creating the element starts with the irradiation of Plutonium-239 in a nuclear reactor for several years. The resulting Plutonium-242 isotope (in the form of the compound Plutonium(IV) oxide) is mixed with aluminum and formed into pellets. The pellets are then further irradiated for approximately one year in a nuclear reactor. Another four months of irradition is required in a different reactor. The result is a mixture of californium and einsteinium, which can then be separated.
Aside from being the byproduct of creating other elements, or a step in the production of other elements, einsteinium has no known uses.
Einsteinium was first identified in December 1952 by Albert Ghiorso at the University of California, Berkeley. He was examining debris from the first hydrogen bomb test of November 1952 (see Operation Ivy). He discovered the isotope 253Es (half-life 20.5 days) that was made by the nuclear fusion of 15 neutrons with 238U (which then went through seven beta decays). These findings were kept secret until 1955 due to Cold War tensions.
In 1961, enough einsteinium was synthesized to prepare a microscopic amount of 253Es. This sample weighed 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's High Flux Isotope Reactor in Tennessee by bombarding 239Pu with neutrons. Around 3 milligrams were created over a four year program of irradiation and then chemical separation from a starting 1 kg of plutonium isotope.
Nineteen radioisotopes of einsteinium have been characterized, with the most stable being 252Es with a half-life of 471.7 days, 254Es with a half-life of 275.7 days, 255Es with a half-life of 39.8 days, and 253Es with a half-life of 20.47 days. All of the remaining radioactive isotopes have half-lives that are less than 40 hours, and the majority of these have half-lives that are less than 30 minutes. This element also has three meta states, with the most stable being 254mEs (t½ 39.3 hours). The isotopes of einsteinium range in atomic mass from 240.069 u (240Es) to 258.100 u (258Es). The most original isotope is the 252Es.
The following is a list of all known compounds of einsteinium: