Francium-224

Main isotopes of francium

Iso­tope Decay abun­dance half-life (t1/2) mode pro­duct 221Fr syn 4.8 min α 217At 222Fr syn 14.2 min β− 222Ra 223Fr trace 22.00 min β− 223Ra α 219At

Francium (₈₇Fr) 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 greater than or equal to 106 (seaborgium) have most-stable-known isotopes shorter than that of francium, but those elements have only a relatively small number of isotopes discovered, thus, there is the possibility of a yet-unknown isotope having a longer half-life.

...
Wikipedia