Radium vs Radon

For a few decades in the early twentieth century, radium was the most glamorous substance on Earth. It glowed in the dark, it seemed to cure cancer, and it cost more per gram than anything ever sold. It was put into watch dials, toothpaste, face cream and drinking water. Then the people who worked with it began to sicken and die, and radium became the first great lesson in the dangers of radioactivity.

• The paint on old radium watch dials has stopped glowing not because the radium is gone, only about five per cent has decayed in a century, but because the zinc sulfide phosphor has been worn out by the radiation.
• Marie Curie's laboratory notebooks are still radioactive and are stored in lead lined boxes; readers must sign a waiver to handle them.

Radon is the noble gas nobody wants in the house. It is colourless, odourless and chemically almost inert, so you would never notice it. But it is radioactive, and it rises continuously out of the ground wherever rocks contain traces of uranium. In poorly ventilated buildings it collects, and breathing it over years is the second biggest cause of lung cancer after smoking.

• Radon is the densest gas among the elements, about eight times heavier than air.
• For the average person in the UK, radon accounts for roughly half of all the radiation dose they receive in a year.