Einsteinium

Einsteinium, chemical element, symbol Es; for physical constants see Periodic Table. Einsteinium was discovered in 1952 in the debris of the first thermonuclear explosion by Albert Ghiorso and co-workers at Berkeley, Calif. A special magnetic-type balance was used to weigh the amount of einsteinium-253 obtained, about 0.01 g. The element is prepared by irradiation of plutonium isotopes in a high flux reactor. It is a metallic element and a member of the actinide series. All of its 14 known isotopes are radioactive.