Radioactive Decay & Half-Life Simulator
Watch hundreds of unstable atoms decay at random and compare the count with the half-life curve.
Each atom decays at random, but half of them are gone after every half-life. Press Start, change the half-life, and watch the measured count follow the theory curve. Click an atom to make it decay now.
About the Radioactive Decay & Half-Life Simulator
Free radioactive decay & half-life simulator. Watch hundreds of unstable atoms decay at random and compare the count with the half-life curve. Drag, change the sliders and see the result live. No sign-up, works on phone and computer. Built for atomic & quantum, the radioactive decay & half-life simulator runs instantly in your browser: change a setting or drag an object and the result updates at once, so you learn by trying things out rather than only reading about them.
Watch hundreds of unstable atoms decay at random and compare the count with the half-life curve. Use it to explore atomic & quantum ideas at your own pace, then check what you found against the key ideas further down this page.
How to use the Radioactive Decay & Half-Life Simulator
- Use the controls to change Half-life, Number of atoms, Samples. The simulation reacts instantly.
- Pick an option such as Custom, Fast (Ba-137m), Slow (long-lived) to switch modes or load an example.
- Press "Start", "Reset atoms" to start, reset or change what is happening.
- Where you see a glowing handle, object, weight or atom, drag it with your mouse or finger. Everything responds in real time.
- Watch the readouts and graphs update as you experiment, and compare what you see with the key ideas below.
Things to try
- Press Start and check the atoms left at 1, 2 and 3 half-lives.
- Use only 50 atoms and see how noisy the graph is.
- Use 600 atoms and compare with the theory line.
- Change the half-life while it runs and see the curve change.
Key ideas you can learn
- Each atom decays at random, but a large group decays predictably.
- After one half-life half of the atoms are left, after two a quarter, and so on.
- The half-life does not depend on how many atoms you have.
- Small samples are noisy, large samples follow the curve closely.
Where this is used in the real world
Carbon dating, medical imaging and cancer treatment, smoke detectors, nuclear power and dating rocks all use radioactive decay.
Who is this simulation for?
Advanced high-school and university students in chemistry and physics, and curious learners who want to see how the atomic world behaves.
For teachers: project it on the board, let students predict what will happen, then run it together. For students: change one thing at a time and write down what changes.
Frequently asked questions
What is a half-life?
The time it takes for half of a sample of unstable atoms to decay. It is a fixed property of each isotope.
Can you predict when one atom will decay?
No. Each atom decays at random. Only the behaviour of a large group is predictable.
Is the Radioactive Decay & Half-Life Simulator free to use?
Yes. It is completely free, with no signup, no download and no ads inside the simulation. It runs in your web browser.
Does the Radioactive Decay & Half-Life Simulator work on a phone or tablet?
Yes. It uses touch as well as the mouse, so you can drag objects with your finger. A larger screen makes the controls easier to see.