Einsteinium-256

Main isotopes of einsteinium

iso NA half-life DM DE (MeV) DP 252Es syn 471.7 d α 6.760 248Bk ε 1.260 252Cf β− 0.480 252Fm 253Es syn 20.47 d SF – – α 6.739 249Bk 254Es syn 275.7 d ε 0.654 254Cf β− 1.090 254Fm α 6.628 250Bk 255Es syn 39.8 d β− 0.288 255Fm α 6.436 251Bk SF – –

Einsteinium (₉₉Es) is a synthetic element, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no stable isotopes. The first isotope to be discovered (in nuclear fallout from an H-bomb test) was ²⁵³Es in 1952. There are 19 known radioisotopes from ²⁴⁰Es to ²⁵⁸Es, and 3 nuclear isomers (^250mEs, ^254mEs, and ^256mEs). The longest-lived isotope is ²⁵²Es with a half-life of 471.7 days, or around 1.293 years.

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