[en] Estimates are given for half-lives of the radioactive decay of radium and radon isotopes by emission of /sup 14/C nuclei. The classical one-dimensional WKB approximation for penetration through a pure Coulomb barrier is used in the calculations. Results indicate that naturally occurring radon isotopes are /sup 14/C emitters like their parent radium isotopes, whose decay rates by emission of /sup 14/C nuclei have recently been measured. The predicted half-lives for decay of /sup 219/Rn, /sup 220/Rn, and /sup 222/Rn by emission of /sup 14/C nuclei are in the range 10/sup 11/--10/sup 14/ yr. For radium and radon isotopes the minimum half-life is obtained when the double-magic /sup 208/Pb and the semimagic /sup 206/Hg, respectively, are the daughter products of these new radioactive decay modes