What else do we know? 
  1. Radon was discovered in the late 1800’s by Canadian scientists Harriet Brooks and Ernst Rutherford at McGill University. Its ability to cause cancer was discovered in the 1950-1970’s in Canadian uranium miners. Very high residential radon was 1st discovered in the 1980’s.
  2. Radon emits alpha particle radiation, which, as it has mass, is very different to the more commonly known (and less dangerous) x-ray radiation that is made up of photons (light). For a given dose, alpha particle radiation deposits much more energy per unit of distance (what is called higher ‘linear energy transfer’) compared to x-rays, making it more hazardous.
  3. Radon has a half-life of 3.8 days, meaning that, in that period of time, 50% of a given amount of radon will have emitted an alpha particle and transformed into the next element in the chain of radioactive decay – in this case, solid radioactive polonium-210.
What the science says:

In his 1904 book Radioactivity, Rutherford described the first experiments showing that radon – which he had called the ‘radium emanation’ – arose from the earth and accumulated in caves and cellars with undisturbed air.

Reference: Rutherford, E. Radioactivity of the Atmosphere and Ordinary Materials. Radioactivity. Cambridge University Press. 1904, Chapter 11, Section 212, pages 357-362.