Explore radioactivity in everyday objects, use a detector to find a hidden source in a mock medical scan, and see evidence of radiation in a cloud chamber. Discover how radioactivity is a natural part of our world and a carefully controlled tool that helps scientists and doctors understand and diagnose disease.
What is radioactivity
The term ‘radiation’ is often used to mean ionising radiation, but there are also non-ionising forms, including radio waves, microwaves and visible light.
Atoms are the tiny building blocks that make up everything around us. Most atoms are stable, but some have unstable nuclei. Radioactivity is the process by which these unstable atoms transform into more stable forms. As they do so, they release energy and particles, which we detect as radiation.
There are several types of ionising radiation, including alpha particles (α), beta particles (β) and gamma rays (γ). Gamma rays are a particularly energetic form of electromagnetic radiation, similar to visible light and X-rays but with much higher energy. Because gamma rays can travel through the body and be detected outside, they are especially useful for medical imaging.
Radioactivity is all around us
You might be surprised to learn that many everyday objects are naturally radioactive. Bananas contain a tiny amount of radioactive potassium. Brazil nuts absorb radioactive elements from the soil. Granite rocks and worktops contain traces of naturally occurring uranium and thorium. Even the air contains small amounts of radioactive radon gas that comes from rocks underground.
The average person in the UK receives around 2.6 mSv of radiation each year from natural and everyday sources. This background radiation is a normal part of life and has always been present on Earth.
A key idea in radiation science is that dose matters. Almost everything is radioactive to some extent, but the amount of radiation received is usually extremely small. Simply detecting radioactivity does not automatically mean something is dangerous.
Banana for scale?
Some radiation exposures can be compared using Banana Equivalent Doses (BEDs). This is not an official scientific unit, but a simple way of comparing very small radiation doses. Bananas naturally contain a tiny amount of radioactive potassium-40, so eating one banana gives a dose of about 0.1 microsieverts (µSv), defined as one Banana Equivalent Dose. This helps put radiation exposures into perspective and reminds us that low levels of natural radioactivity are a normal part of everyday life.
Note: Unlike radiation received from an X-ray or flight, the dose from eating bananas does not accumulate indefinitely.
Your body carefully controls the amount of potassium it contains, excreting excess via your kidneys. So the dose from eating extra bananas does not accumulate in the same way as many other radiation exposures.
How to detect radiation
Radiation cannot normally be seen by the human eye, but scientists have developed instruments that allow us to detect it.
A Geiger counter detects ionising radiation and converts it into sounds or readings that we can interpret. It counts ionising events, often displaying the result as counts per second and producing an audible sound.
In the apron activity, you become the scanner, using a detector to locate a hidden radioactive source inside a model body organ. This demonstrates the basic principle used in nuclear medicine imaging.
The cloud chamber provides another way to observe radiation. Although radiation itself remains invisible, charged particles moving through a supersaturated vapour leave tiny trails of droplets behind them. Some tracks appear short and thick, while others are long and thin, depending on the particle that created them. Scientists can use these patterns to learn about the particles passing through the chamber. Some tracks come from natural background radiation and cosmic rays arriving from space, revealing atomic processes taking place around us all the time.
Using radioactivity to diagnose disease
Radioactivity is not only found in nature. Carefully controlled radioactive materials can be powerful tools in medicine.
One important example is positron emission tomography (PET). In a PET scan, a small amount of a radioactive tracer is given to the patient. The tracer is often attached to a molecule similar to glucose, the body’s fuel source. Some tissues absorb the tracer more than others, and the radiation emitted is detected by specialised scanners.
Many cancers absorb more of certain tracers than surrounding healthy tissues, causing them to appear as bright regions on PET images. This helps doctors detect disease, monitor treatment and identify cancer recurrence. PET scans are also used to investigate heart disease and disorders of the brain.
Unlike X-rays or CT scans, which mainly show the body’s structure, PET scans show how tissues are functioning. This gives doctors a powerful, non-invasive way to study processes occurring inside the body and diagnose disease at an early stage. The radiation dose used in medical imaging is carefully chosen to provide valuable diagnostic information while minimising patient exposure.
Researchers at the University of Southampton are working with partners across academia and industry to develop the next generation of radiotracers for PET imaging. This work helps doctors see disease more clearly and diagnose patients earlier.