Lesson Plan

• Describe the concept of radioactive decay and the meaning of half‑life.
• Explain the relationship λ = 0.693 / t½ and how it is derived.
• Apply the decay law N(t)=N₀e⁻ˡᵃᵐᵇ𝑑ᵃ t to calculate remaining nuclei and activity.
• Perform calculations using λ to solve typical A‑level problems involving half‑life and activity.

• Projector and screen
• Whiteboard and markers
• Scientific calculators (or calculator app)
• Worksheet with decay‑constant problems
• Half‑life data tables (printed)
• Graph paper for sketching exponential curves

Begin with a striking fact about the half‑life of carbon‑14 to capture interest. Ask students to recall what a half‑life represents and how it relates to decay probability. State that by the end of the lesson they will be able to calculate the decay constant λ and use it in real‑world problems.

1. Do‑now (5 min): Quick quiz on half‑life definitions and previous exponential decay work.
2. Mini‑lecture (10 min): Derive λ = 0.693 / t½ from N(t½)=½N₀ and introduce the decay law N(t)=N₀e⁻λt.
3. Guided example (15 min): Work through the ^60Co activity problem step‑by‑step on the board.
4. Paired practice (10 min): Students calculate λ and activity for a different radionuclide using the worksheet.
5. Concept check (5 min): Exit ticket – write the λ formula and one sentence explaining its significance.
6. Recap discussion (5 min): Highlight common mistakes and reinforce the link between half‑life and λ.

Summarise that the decay constant provides a convenient way to move between half‑life and exponential decay calculations. Collect exit tickets to gauge understanding, and assign homework: complete a set of problems converting half‑lives to λ and calculating activities for three different isotopes.