es 99

Isotopes of einsteinium. Einsteinium ( 99 Es) is a synthetic element, and thus a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotope to be discovered (in nuclear fallout from the Ivy Mike H-bomb test) was 253 Es in 1952. There are 18 known radioisotopes from 240 Es to 257 Es, and 3 ... pmk 99 tahun 2015