Background radiation and hazards
Background radiation (Separate Physics only)
is around us all the time. It comes from:
- Natural sources: rocks (especially gas, which seeps out of the ground), from space, and food and drink.
- Man-made sources: fallout from nuclear weapons tests and nuclear accidents, and medical procedures.
How much you receive depends on where you live (areas with granite rock, such as Cornwall, have more radon) and your job (airline pilots get more cosmic rays).
When you measure a source's count rate, measure the background count too and subtract it.
Key terms
Radiation dose (Separate Physics only)
measures the risk of harm to the body from radiation. It is measured in . A sievert is a big dose, so millisieverts (mSv) are often used:
1000 mSv = 1 Sv
In the UK, a person gets about 2.7 mSv a year on average, mostly from background radiation. A chest X-ray adds only a tiny dose. The higher the dose, the greater the risk of cells being damaged or turning cancerous.
Key terms
Half-life and hazard (Separate Physics only)
How dangerous a radioactive material is depends on its and the type of radiation it gives out.
- An isotope with a short half-life is very active at first, so it is dangerous in the short term, but its activity drops quickly.
- An isotope with a long half-life is less active, but stays radioactive for a very long time. This is why nuclear waste has to be stored safely for thousands of years.