Radioactivity
Unstable nuclei emit alpha, beta or gamma radiation.
About this topic
Radioactive nuclei are unstable and decay spontaneously, emitting radiation. Alpha particles (helium nuclei) are stopped by paper, beta particles (electrons) by thin aluminium, and gamma rays (EM waves) need thick lead or concrete to attenuate. Decay is random for each nucleus, but predictable for large samples.
In alpha decay the nucleus loses two protons and two neutrons; in beta decay a neutron turns into a proton and emits an electron; gamma emission follows when the nucleus settles to a lower energy. A Geiger counter clicks as radiation ionises gas in its tube. Background radiation comes from rocks, radon gas, cosmic rays and even bananas.
Radiation ionises atoms and can damage cells, so exposure should be limited by time, distance and shielding. It is used in medical imaging, cancer therapy, smoke detectors and dating ancient objects.
Being radioactive does not make a thing glow, and a person exposed to radiation does not become radioactive; contamination with radioactive material is a different matter.
Key ideas
- Alpha stopped by paper
- Beta stopped by aluminium
- Gamma needs lead
Quick check
Use cases: where Radioactivity helps
- Homework: review the key idea behind Radioactivity before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Radioactivity without notes.
- Visual learning: play with the interactive lab to see how Radioactivity changes when you adjust its inputs.
- Teaching a friend: explain Radioactivity in your own words, then compare your version with the key ideas.
The same laws describe car crashes, sports, satellites and everyday machines.
Frequently asked questions
What is Radioactivity?
Unstable nuclei emit alpha, beta or gamma radiation.
What will I learn in Radioactivity?
Alpha stopped by paper. Beta stopped by aluminium. Gamma needs lead.
Is Radioactivity part of Physics?
Yes. It is one of 150 Physics topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Radioactivity lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Radioactivity?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.