Loading...
An unstable nucleus can decay randomly and emit radiation. Alpha is a helium nucleus, beta-minus an electron produced in a nuclear change, and gamma an electromagnetic wave. Alpha is strongly ionising but weakly penetrating, while gamma penetrates further. Balance mass number and atomic number in nuclear equations. Beta emission is not simply an ordinary orbital electron leaving an unchanged nucleus.
Video by Cognito. The video’s own board label is retained; follow the specification reference and scope notes on this lesson for assessed content.
Viewing focus: Compare alpha, beta and gamma radiation
After watching, attempt these questions before opening the answers. You can also use the written lesson below.
After watching 1: Which radiation is an electromagnetic wave?
Gamma. Gamma has no mass number or electric charge.
After watching 2: Can the next individual radioactive decay be timed exactly?
No. Decay is random at the individual-nucleus level.
What you'll be able to do
An unstable nucleus can decay randomly and emit radiation. Alpha is a helium nucleus, beta-minus an electron produced in a nuclear change, and gamma an electromagnetic wave. Alpha is strongly ionising but weakly penetrating, while gamma penetrates further. Balance mass number and atomic number in nuclear equations. Beta emission is not simply an ordinary orbital electron leaving an unchanged nucleus.
Half-life is the time for the number of undecayed nuclei, or activity, to halve on average. The next individual decay cannot be predicted, but large populations follow a reliable statistical pattern. Subtract background count rate before interpreting source counts. After n half-lives, the fraction remaining is (1/2)ⁿ. Activity and count rate are related, but detector geometry and efficiency affect the measured count.
Irradiation is exposure to radiation; contamination places radioactive material on or inside something. An alpha source can be especially hazardous inside the body despite low external penetration. Tracers, sterilisation and radiotherapy use different properties and require exposure control. Fission splits heavy nuclei and may sustain a controlled chain reaction; fusion combines light nuclei under demanding conditions. Both release energy through nuclear changes, unlike chemical combustion.
Attempt these problems on paper before opening the worked reasoning. Explain your steps as well as giving a final answer.
Common mistakes to avoid
Key takeaways
Question 1: How much remains after three half-lives?
1/8, or 12.5%.
Check the assessed scope and practical or mathematical requirements.
An external explanation or interactive activity to use alongside the lesson. It may include extension material.
Close the notes and answer from memory. Revisit any explanation you cannot yet reconstruct.
Test yourself
Answer a few questions, then review anything you missed.
Start with the quiz above to check the key ideas. You can also choose another topic from the practice library.