In 1961, enough einsteinium was synthesized to prepare a microscopic amount of 253Es.
Einsteinium (chemical symbol Es, atomic number 99) is a synthetic element in the periodic table.
The isotopes of einsteinium range in atomic mass from 240.069 amu (240Es) to 258.100 amu (258Es).
Einsteinium is an inner transition metal of the actinide series, located in period seven of the periodic table, between californium and fermium.
A metallic, highly radioactive, transuranic element (seventh in the series) in the actinides, einsteinium is produced by bombarding plutonium with neutrons and was discovered in the debris of the first hydrogen bomb test.
Tracer studies using the isotope 253Es show that einsteinium has chemical properties typical of a heavy trivalent, actinide element.