Isotopes of meitnerium

Meitnerium (₁₀₉Mt) 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 synthesized was ²⁶⁶Mt in 1982, and this is also the only isotope directly synthesized; all other isotopes are only known as decay products of heavier elements. There are eight known isotopes, from ²⁶⁶Mt to ²⁷⁸Mt. There may also be two isomers. The longest-lived of the known isotopes is ²⁷⁸Mt with a half-life of 8 seconds. The unconfirmed heavier ²⁸²Mt appears to have an even longer half-life of 67 seconds.