Background radiation is around us all of the time. It comes from: • natural sources such as rocks and cosmic rays from space • man-made sources such as the fallout from nuclear weapons testing and nuclear accidents. • The level of background radiation and radiation dose may be affected by occupation and/or location. • Radiation dose is measured in sieverts (Sv) • 1000 millisieverts (mSv) = 1 sievert (Sv)