Background Radiation

Background radiation is the ionising radiation that is always present around us, even when no obvious source is nearby. It comes from natural materials, space, and small amounts in what we eat and breathe. Because radioactive emission is spontaneous and random, the background count is never exactly the same each time.

Main sources

• Radon gas (in the air): A radioactive gas that seeps from certain rocks and soil. It can collect indoors and is a major contributor in many regions.
• Rocks and buildings: Materials like granite contain tiny amounts of radioactive elements. Homes and schools are built from these materials, so they add to background levels.
• Food and drink: Natural isotopes such as potassium-40 are found in foods (for example, bananas). The amounts are very small.
• Cosmic rays: High-energy particles from space. Background is higher at high altitude and during flights.

Measuring background radiation

Ionising radiation can be detected using a detector connected to a counter (for example, a Geiger–Müller tube with a counter). The counter shows a count rate in $\text{counts/s}$ or $\text{counts/min}$.

To measure a radioactive source correctly, first measure the background count rate, then measure source + background in the same position and time. Subtract background to get the corrected count rate.

Why results vary

• Background fluctuates randomly. Taking measurements for longer helps reduce the effect of random changes.
• Location matters: altitude, local rocks, and building materials can change the level.

Common misconceptions

• Background radiation is normal and usually low; it does not mean something is unsafe nearby.
• In this topic, we mean ionising radiation. Non-ionising waves like visible light and microwaves are not counted as background radiation here.