 The 220Rn isotope is a natural decay product of the most stable thorium isotope (232Th), and is commonly referred to as thoron.It has a half-life of 55.6 seconds and also emits alpha radiation.Similarly, 219Rn is derived from the most stable isotope of actinium (227Ac)—named "actinon"—and is an alpha emitter with a half-life of 3.96 seconds.