Radon

In nature, radon is found in the Earth's atmosphere, 6 · 10⁻¹⁴ ppm (v/v), and in igneous rocks, 1.7 · 10⁻¹⁰ ppm (w/w) [4]. The isotope found in nature is ²²²Rn (T_½ = 3.825 days) [4].