Science lesson plan · 10th grade (Year 11 in England) · 45 minutes
Half-life calculations
Atoms, elements and the periodic table
CCSS NGSS.HS-PS1-8CCSS NGSS.SEP 5England: GCSE Combined Science: Atomic structure (radioactivity) (half-lives)
Objective and success criteria
Students will: Half-life calculations.
- I can answer questions on today's skill on my own, without help.
- I can explain each step and say why it works.
- I can check my answer and spot a mistake.
Before and after
Needs first: Alpha, beta and gamma radiation
Leads to: Date rocks and fossils with radioactive decay
Materials: Periodic tables, Atom model kits, Mini whiteboards, A diagram or short video clip of the idea, Printed student sheet (below).
Warm-up · 5 min
- 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.
- Which type of radiation: a fast-moving electron from the nucleus? (alpha (α) / beta (β) / gamma (γ)) → beta (β)Prompt: The more ionising the radiation, the less penetrating it is.
- 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 heat the equipment to 1000 °C / They make the equipment radioactive) → They pass through the packaging and kill microbesPrompt: Gamma is very penetrating.
- Nuclear radiation: which statement is NOT true? (Alpha radiation is the most dangerous if the source is inside the body. / Gamma rays are part of the electromagnetic spectrum. / Gamma radiation is stopped by a sheet of paper. / Background radiation comes from natural and man-made sources.) → Gamma radiation is stopped by a sheet of paper.Prompt: Which radiation needs lead to stop it?
Hook · 5 min
- 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.
I do: model it · 10 min
- 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.
We do: guided practice · 10 min
- Do these together. Students try each step on whiteboards before you reveal it.
- Use the hints as prompts rather than giving the answer.
- A sample has an activity of 3200 Bq. Its half-life is 30 hours. What is its activity after 120 hours, in Bq? → 200 BqPrompt: How many half-lives have passed?
- The count rate of a radioactive source falls from 640 counts/min to 320 counts/min in 8 minutes. What is its half-life, in minutes? → 8 minPrompt: Count how many times the rate halved.
You do: independent practice · 10 min
- 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.
Exit ticket · 5 min
- Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
- A sample has an activity of 800 Bq. Its half-life is 12 hours. What is its activity after 12 hours, in Bq? → 400 BqPrompt: How many half-lives have passed?
- The count rate of a radioactive source falls from 800 counts/min to 100 counts/min in 45 minutes. What is its half-life, in minutes? → 15 minPrompt: Count how many times the rate halved.
Watch out for
- Everyday meanings of words getting in the way of the science meaning: define key words explicitly.
- Remembering facts without the reason: ask "why?" and "what is the evidence?"
Support and stretch
Support
- Review first: Alpha, beta and gamma radiation.
- Use concrete materials: periodic tables.
- Give the first step of each question, or a partly worked example to finish.
- Pair with a confident partner for the guided practice.
Stretch
- Move on to: Date rocks and fossils with radioactive decay.
- Explain a common mistake in writing and how to fix it.
- Write a word problem that uses today's skill, then solve a partner's.
Homework and more practice
Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-10.
Free lesson plan from eurekami.com/lesson-plan-builder