# Instructor guide: Isotope decay and detection record

Course: Atoms, nuclei, and radiation

Suggested time: 40–50 minutes

## 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.

## 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.

## 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

## Extension

Add a daughter isotope and sketch the coupled parent-daughter population history.

## Evidence boundary

Assess the learner's reasoning only within the declared model and recorded observations. Do not upgrade a simulation result into a claim about an unmodeled physical system.