Einsteinium is an artificially created radioactive element . Its chemical symbol is Es, and its atomic number (number of protons in its nucleus) is 99.
Chemists place einsteinium in the actinide group of transuranium elements . For information on the position of einsteinium on the periodic table, see the article Periodic table .
Einsteinium has 17 known isotopes, forms with the same number of protons but different numbers of neutrons. The most stable isotope has an atomic mass number (total number of protons and neutrons) of 252. That isotope has a half-life of 472 days—that is, due to radioactive decay, only half the atoms in a sample of isotope 252 would still be atoms of that isotope after 472 days.
Scientists at the University of California, the Argonne National Laboratory, and the Los Alamos National Laboratory named this element in honor of the famous scientist Albert Einstein . Einsteinium was first discovered in 1952 in the debris from a hydrogen bomb explosion. Scientists collected this debris on filter papers carried by radio-controlled airplanes and from fallout on a nearby coral atoll. This new element formed when a great number of neutrons from the explosion collided with atoms of uranium 238 and were captured by their nuclei. Fermium , element 100, was formed at the same time.
Scientists first produced einsteinium in laboratory experiments in 1954. Today, one isotope of einsteinium, with mass number 253 and a half-life of 20 days, is produced in small amounts in nuclear reactors. Einsteinium compounds have also been prepared.
