Radon Isotopes

There are 39 known isotopes of radon (86Rn), from 193Rn to 231Rn; all are radioactive. The most stable isotope is 222Rn with a half-life of 3.8215 days, which decays into 218Po. Six isotopes of radon, 217-222Rn, occur in trace quantities in nature as decay products of, respectively, 217At, 218At, 223Ra, 224Ra, 225Ra, and 226Ra. 217Rn and 221Rn are produced in rare branches in the decay chain of trace quantities of 237Np; 222Rn (and also 218Rn in a rare branch) is an intermediate step in the decay chain of 238U; 219Rn is an intermediate step in the decay chain of 235U; and 220Rn occurs in the decay chain of 232Th.