The shape of the lesson
By the end of the lesson, learners can
- Lower the dose: Adjust distance, time and shielding and see how each lowers the radiation dose.
- Three defences, and good handling: Distance, time and shielding cut the dose; careful storage and handling keep it that way.
- Time: spend less time near the source.
- Distance: stay further away (use tongs).
- Shielding: lead or concrete between you and the source.
One picture every idea returns to
Ionising radiation damages living cells, so exposure must be kept as low as possible. The dose is reduced by keeping your distance, limiting the time of exposure, and shielding with dense materials such as lead. Sources are stored in lead-lined containers and handled with tongs.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Distance, time, shielding.. Ionising radiation does its damage quietly, cell by cell, with no warning you can feel. | Whole class, then pairs |
| 5 to 17 min | Teach and check: Lower the dose | Adjust distance, time and shielding and see how each lowers the radiation dose. Project tab 7 of the lab (Safety) and let a student drive it while the class predicts. | Whole class, then pairs |
| 17 to 30 min | Teach and check: Three defences, and good handling | Distance, time and shielding cut the dose; careful storage and handling keep it that way. | Connect-Extend-Challenge |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 12 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Three defences, and good handling, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Connect-Extend-Challenge
After the new idea, each student writes three lines: how it connects to what they knew, how it extends their thinking, and what still challenges them. Pairs compare, then the challenges become the plenary.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| The three ways to cut your radiation dose are distance, time and shielding: stay further away, spend less time near the source, and put dense material such as lead between you and it. | Return to Three defences, and good handling: ask a pair to state the correct version and show it on the lab before moving on. |
Safety with ionising radiation: worksheet
6 questions, 12 marks. Written in the style of the papers; no past paper question is reproduced.
State why ionising radiation can be harmful to people.
State the three main ways a worker can reduce the dose they receive from a radioactive source.
Explain why a radioactive source is picked up with long tongs rather than with bare hands.
State how radioactive sources should be stored when not in use, and why.
People who work with radiation often wear a small badge. State what this badge is for.
A radiographer takes X-ray images of patients all day. Describe three precautions they should take to keep their own dose low.
Answer key and marking notes
It can damage or kill living cells (and can cause cancer). ✓
- Spend less time near the source. ✓
- Stay a greater distance away. ✓
- Use shielding such as lead or concrete. ✓
- The tongs keep the source further from the body. ✓
- The dose falls with distance, so the hands receive much less radiation. ✓
- In a clearly labelled lead-lined box. ✓
- The lead absorbs the radiation, so people nearby receive a low dose. ✓
To monitor (measure) the total dose of radiation they have received. ✓
- Stand behind a shielded screen or wall during the exposure. ✓
- Keep a distance from the beam and the patient when the X-ray is taken. ✓
- Limit the time of exposure, and wear a monitoring badge. ✓
1 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
Which is a sensible safety precaution when handling a radioactive source in the laboratory?
- Ahold the source with tongs and keep it at arm's length, pointing away from people
- Bhold it tightly in your bare hand to keep it steady
- Ckeep it in your pocket between experiments
- Dlook closely along the line of the source to aim it
Quiz key
Using tongs and keeping the source at a distance, pointing away from people, reduces the dose received. Bare-hand contact, carrying it in a pocket, or pointing it toward yourself all increase exposure.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.