Question: @Sam, How long will it take for radiation to clear?

Samantha Watson answered on 9 Nov 2016:

For xray radiation once the machine that generates the xrays has stopped, the radiation is gone. A bit like when you turn the switch off, the lamp stops giving out light.

But for radioactive material which give out radiation, you can’t turn it off. But as the atoms in the material give out energy those atoms stop being radioactive or just to be complicated, sometimes they change into another type of radioactive material. To keep it simple let’s assume that the atoms stop being radioactive once they have given off energy in the form of radiation. This is what’s called radioactive decay. Over time the material becomes less radioactive as fewer of the atoms remain radioactive. For any given material the length of time for the amount of radioactivity to half will always be the same, no matter how much radioactive material you start with. Radioactivity is measured in Bequerels (or Bq) and the time for 10,000 Bq to decay to 5,000 Bq will be the same as the time for 50 Bq to decay to 25 Bq. This time is known as the half life. Depending on the type of material the length of the half life will vary. For some materials it will be a few seconds, and for others it can be thousands of years. So the time for an amount of radiation to “clear” or decay away will depend on the type of material.