Isotopes of roentgenium

Roentgenium (₁₁₁Rg) 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 ²⁷²Rg in 1994, which is also the only directly synthesized isotope; all others are decay products of heavier elements. There are seven known radioisotopes, having mass numbers of 272, 274, and 278–282. The longest-lived isotope is ²⁸²Rg with a half-life of about 2 minutes, although the unconfirmed ²⁸³Rg and ²⁸⁶Rg may have longer half-lives of about 5.1 minutes and 10.7 minutes respectively.