from
The Collaborative International Dictionary of English v.0.48
Es \Es\ n.
the chemical symbol for {einsteinium}, a transuranic element
with atomic number 99. The atomic weight of the longest-lived
isotope, with a half-life of 276 days, is 254. The first
isotope discovered, having atomic weight 253 and a half-life
of 20 days, was recognized in 1952 in the debris from a
hydrogen bomb test. As much as 3 micrograms of einsteinium
were produced by a complex process involving long irradiation
of plutonium isotopes in nuclear reactors. Its chemical
properties are those of a trivalent actinide element. --HCP61
Syn: einsteinium, atomic number 99.
[WordNet 1.5 +PJC]
from
The Elements (07Nov00)
einsteinium
Symbol: Es
Atomic number: 99
Atomic weight: (254)
Appearance is unknown, however it is most probably metallic and silver
or gray in color. Radioactive metallic transuranic element belonging to
the
actinoids. Es-254 has the longest half-life of the eleven known isotopes
at
270 days. First identified by Albert Ghiorso and associates in the
debris of
the 1952 hydrogen bomb explosion. In 1961 the first microgram quantities
of
Es-232 were separated. While einsteinium never exists naturally, if a
sufficient amount was assembled, it would pose a radiation hazard.