Lesson Plan

• Describe the relationship between decay constant, half‑life, and activity.
• Explain how radiation type and half‑life affect the suitability of an isotope for a specific application.
• Compare Americium‑241, Cobalt‑60 and Iodine‑131 for smoke alarms, food irradiation and equipment sterilisation.
• Apply selection criteria to choose an appropriate isotope for a given practical scenario.

• Projector and screen
• PowerPoint slides with isotope tables and decay curves
• Student handout summarising isotopes and applications
• Interactive clicker/quiz app for quick checks
• Diagram of a smoke alarm chamber (or a disassembled unit)
• Radiation‑safety poster

Begin with a striking fact: the tiny amount of Americium‑241 in a smoke alarm can save lives every day. Review students’ prior knowledge of half‑life and basic radiation types. State that by the end of the lesson they will be able to justify the choice of an isotope for three real‑world applications.

1. Do‑now (5'): Students write the half‑life formula and give one example of a short‑half‑life isotope.
2. Mini‑lecture (10'): Review alpha, beta, gamma radiation and the decay constant‑half‑life relationship.
3. Guided analysis (15'): Examine the provided isotope table; discuss how radiation type and half‑life match each application.
4. Group activity (10'): Teams match isotopes to the three target applications and justify their choices.
5. Whole‑class discussion (10'): Highlight safety, regulatory, and logistical factors influencing isotope selection.
6. Exit ticket (5'): Each student writes a one‑sentence rationale for the best isotope to use in a new scenario (e.g., sterilising medical syringes).

Recap how radiation type and half‑life together dictate an isotope’s suitability for specific uses. Collect the exit tickets to gauge understanding and clarify any misconceptions. Assign homework: research another isotope (e.g., Strontium‑90) and propose a novel application, citing its radiation type and half‑life.