Isotopes of francium
has no stable isotopes. A standard atomic weight cannot be given. Its most stable isotope is 223Fr with a half-life of 22 minutes, occurring in trace quantities as an intermediate decay product of 235U.
Of elements whose most stable isotopes have been identified with certainty, francium is the most unstable. All elements with atomic number of 106 or greater have most-stable-known isotopes shorter than that of francium, but those elements have only a relatively small number of isotopes discovered. The possibility remains that undiscovered isotopes of these elements may have longer half-lives.
