• Quick retrieval from earlier learning (Alpha, beta and gamma radiation). Students answer on mini whiteboards.
• Show answers together and note who needs support in the main task.

1. Which type of radiation: stopped by a few mm of aluminium? (alpha (α) / beta (β) / gamma (γ)) → beta (β)Prompt: The more ionising the radiation, the less penetrating it is.
2. Why are gamma rays used to sterilise medical equipment in sealed packs? (They pass through the packaging and kill microbes / They are stopped by plastic / They make the equipment radioactive / They heat the equipment to 1000 °C) → They pass through the packaging and kill microbesPrompt: Gamma is very penetrating.
3. Nuclear radiation: which statement is NOT true? (Background radiation comes from natural and man-made sources. / Gamma radiation is stopped by a sheet of paper. / Gamma rays are part of the electromagnetic spectrum. / Radioactive decay is random.) → Gamma radiation is stopped by a sheet of paper.Prompt: Which radiation needs lead to stop it?

• Show the periodic table and ask what patterns students can see before anything is explained.
• Share the objective: Half-life calculations. Read the success criteria together.

• Work through the example out loud, saying why you do each step, not just what you do.
• Example: A sample has an activity of 1600 Bq. Its half-life is 6 days. What is its activity after 24 days, in Bq?
• Step 1: 24 ÷ 6 = 4
• Step 2: 1600 ÷ 2^4 = 100
• Step 3: So the answer is: 100 Bq
• Answer: 100 Bq
• Pause after each step and ask a student to say what comes next.

• Do these together. Students try each step on whiteboards before you reveal it.
• Use the hints as prompts rather than giving the answer.

1. A sample has an activity of 1200 Bq. Its half-life is 30 hours. What is its activity after 90 hours, in Bq? → 150 BqPrompt: How many half-lives have passed?
2. The count rate of a radioactive source falls from 1200 counts/min to 600 counts/min in 4 minutes. What is its half-life, in minutes? → 4 minPrompt: Count how many times the rate halved.

• Students work on the student sheet. Circulate and check the first two answers of every student early.
• Students who finish: write a question of their own for a partner, with the answer.

The 8 questions are on the student sheet below, with answers in the key.

• Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.

1. A sample contains 1600 undecayed nuclei. How many remain undecayed after 4 half-lives? → 100Prompt: After each half-life, half of the remaining nuclei are left.
2. The count rate of a radioactive source falls from 960 counts/min to 120 counts/min in 15 minutes. What is its half-life, in minutes? → 5 minPrompt: Count how many times the rate halved.

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-10.