Background radiation (AQA GCSE Physics): Revision Notes
Background radiation
What is background radiation?
Background radiation is low-level radiation that exists around us all the time. This means we are constantly exposed to small amounts of ionising radiation from our environment.
Background radiation comes from two main types of sources:
- Natural sources - radiation that occurs naturally in our environment
- Man-made sources - radiation created by human activities
The levels of background radiation are very low and generally not harmful to our health. However, it's important to understand where this radiation comes from and how it affects us.
Sources of background radiation
Background radiation comes from several different sources. The biggest contributor is radon gas, which makes up about half of all background radiation we experience.
Natural sources include:
- Radon gas (50%) - the largest single source
- Cosmic rays (10%) - radiation from outer space that reaches Earth
- Ground and buildings (14%) - radioactive materials naturally present in rocks and building materials
- Food and drink (11.5%) - small amounts of radioactive materials in what we eat and drink
Man-made sources include:
- Medical procedures (14%) - X-rays, radiotherapy, and nuclear medicine
- Nuclear power stations (0.3%) - a very small contribution
- Other human activities (0.2%) - including nuclear weapons testing
It's worth noting that medical procedures actually contribute more background radiation than nuclear power stations do.
Radon gas
Radon is a radioactive gas that deserves special attention because it's the biggest source of background radiation. Here's what you need to know about radon:
Radon forms when uranium in rocks naturally breaks down (decays). During this process, radon gas is produced and can escape from the ground into the air around us.
Radon is dangerous because it emits alpha particles when it decays. Alpha particles can be particularly harmful if breathed into the lungs, where they can damage living cells.
The gas can build up inside houses and other buildings, especially in areas where the underlying rocks contain more uranium. This is why some parts of the country have higher levels of radon than others. Areas like Cornwall have higher natural radon levels due to the type of rock found there.
The amount of radon varies from place to place because it depends on the type of rock in the area. Granite rocks, for example, tend to produce more radon than other types of rock.
Radiation dose
Scientists measure radiation exposure using units called sieverts (Sv). For smaller doses, they use millisieverts (mSv), where 1000 mSv = 1 Sv.
The dose of background radiation we receive is very low - only about 0.003 mSv per hour. This means the radiation we're exposed to naturally is not immediately dangerous.
However, radiation can become harmful at higher doses. A radiation dose of 100 mSv (0.1 Sv) can be fatal, which shows how much stronger dangerous radiation is compared to background radiation.
This is why radioactive materials used in medicine and industry must be carefully controlled and handled with proper safety measures.
Summary
Key Points to Remember:
- Background radiation is low-level radiation that's always around us from natural and man-made sources
- Radon gas is the biggest source (50%) and comes from uranium decay in rocks
- Natural sources include radon, cosmic rays, rocks, and food - these make up most background radiation
- Man-made sources include medical X-rays and nuclear power, but contribute much less
- Radiation dose is measured in sieverts - background radiation levels are very low and generally safe