Level 1 · Foundations teaching kit · Grades 8–9
Atoms, nuclei, and radiation
Use the learner record during the live investigation, then use the instructor guide to facilitate comparison, address misconceptions, and assess evidence-bounded reasoning.
Learner lab record
Isotope decay and detection record
How do elapsed half-lives change remaining nuclei, present activity, total transformations, and expected detector counts?
Setup
Use only the simulated isotope ledger. Do not handle radiation sources. Change elapsed half-lives first, then test mass defect and detector efficiency separately.
Predict first
- 1. Predict the remaining fraction after three half-lives.
- 2. Predict whether 50% efficiency changes the physical decay count.
| Variable | Role | Unit |
|---|---|---|
| Starting nuclei and half-life | model inputs | count and s |
| Elapsed half-lives | independent | half-lives |
| Remaining nuclei and activity | dependent | count and Bq |
| Detector efficiency | measurement input | % |
Observation columns
Analyze
- 1. Does each half-life remove half of the original or half of what remains?
- 2. Why does present activity fall while total transformations rise?
- 3. Which quantity changes when efficiency changes?
- 4. Why is emitted energy not absorbed dose?
Conclusion frame
After ___ half-lives, ___ of the original nuclei remained; detector efficiency changed ___ but did not change ___.
Instructor guide · 40–50 minutes
Teach the investigation, not the interface
Learning target: Learners distinguish exponential population decay, present activity, integrated transformations, detector counts, emitted energy, and dose.
Prepare
- • Confirm the activity uses transformations per second.
- • Prepare a repeated-halving visual.
- • Use simulated or public data only.
Facilitation moves
- • Ask for fractions before scientific notation.
- • Separate what the nucleus does from what the detector records.
- • Require the dose boundary in every energy discussion.
Accessibility and participation
- • Pair exponential notation with fractions and percentages.
- • Use a 100-token physical model without any source material.
- • Allow calculator or spreadsheet support for repeated halving.
Evidence of learning
- • Correct repeated-halving table
- • Separation of activity and cumulative transformations
- • Accurate detector-efficiency explanation
Misconception checks
After two half-lives nothing remains.
Repeated halving approaches zero without reaching it in the ideal continuous model.
Detector counts equal dose.
Dose also requires deposited energy per mass, radiation type, geometry, and biological weighting.
Extension
Add a daughter isotope and sketch the coupled parent-daughter population history.