# Instructor guide: Reaction yield and detector-efficiency audit

Course: Introductory nuclear physics and reaction evidence

Suggested time: 50–60 minutes

## Learning target

Learners construct a reaction-yield ledger and separate modeled physical events from detector acceptance, backgrounds, and identification.

## Prepare

- Review scientific notation and area units.
- State the thin-target approximation.
- Prepare one background-only and one calibration run.

## Facilitation moves

- Ask what happens in the target before what appears in the detector.
- Require dimensional checks.
- Keep channel identification separate from total count excess.

## Misconception checks

- **Every detector count is a nuclear reaction.** Counts include backgrounds and acceptance effects; channel identification requires calibrated signatures and controls.
- **Cross section is the physical size of a nucleus.** It is an interaction-probability measure with area units, not usually a geometric silhouette.

## Accessibility and participation

- Translate powers of ten into factor language.
- Use a flow diagram from beam to target to detector.
- Provide unit cards and calculator support.

## Evidence of learning

- A dimensionally consistent yield ledger
- Correct efficiency separation
- A credible background-control plan

## Extension

Add target attenuation and compare the exact thick-target expression with the linear approximation.

## 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.