 Radon is produced by a solution of radium-226 (half-life of 1,600 years).Radium-226 decays by alpha-particle emission, producing radon that collects over samples of radium-226 at a rate of about 1 mm3/day per gram of radium; equilibrium is quickly achieved and radon is produced in a steady flow, with an activity equal to that of the radium (50 Bq).Gaseous 222Rn (half-life of about four days) escapes from the capsule through diffusion.