The shape of the lesson
By the end of the lesson, learners can
- Test each radiation: Put paper, aluminium and lead in the path and see which radiation gets through.
- Ionising and penetrating, opposite orders: The most ionising is the most easily stopped; the most penetrating ionises least.
- Nature: alpha = helium nucleus, beta = electron, gamma = EM wave.
- Stops: paper (alpha), a few mm aluminium (beta), thick lead (reduces gamma).
- Order: ionising alpha > beta > gamma; penetration gamma > beta > alpha.
One picture every idea returns to
Alpha is a helium nucleus, beta is a fast electron, and gamma is electromagnetic radiation. Alpha is the most ionising but most easily stopped (by paper). Gamma is the least ionising but most penetrating (needs thick lead). Beta is in between, stopped by a few millimetres of aluminium.
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, Three kinds of decay.. An unstable nucleus can throw out three very different things: a heavy charged chunk, a tiny fast particle, or a burst of pure energy. | Whole class, then pairs |
| 5 to 17 min | Teach and check: Test each radiation | Put paper, aluminium and lead in the path and see which radiation gets through. Project tab 2 of the lab (Alpha, beta, gamma) and let a student drive it while the class predicts. | Whole class, then pairs |
| 17 to 30 min | Teach and check: Ionising and penetrating, opposite orders | The most ionising is the most easily stopped; the most penetrating ionises least. | Think-Pair-Share |
| 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, 15 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 Ionising and penetrating, opposite orders, 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.
Think-Pair-Share
Pose the question, give thirty seconds of silent thinking, then a minute to compare with a partner before a few pairs share with the class. The silent minute is the part that cannot be cut.
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 |
|---|---|
| Ionising power and penetrating power run in opposite orders. | Alpha ionises most but is stopped by paper, while gamma ionises least but passes through everything except thick lead. The most penetrating radiation is the least ionising. |
Alpha, beta and gamma radiation: worksheet
6 questions, 15 marks. Written in the style of the papers; no past paper question is reproduced.
State the nature of alpha, beta and gamma radiation.
State the charge on each of the three types of radiation.
State what material is needed to stop, or greatly reduce, each type of radiation.
A source is unaffected by paper but is completely stopped by 3 mm of aluminium. Identify the radiation and give your reason.
Put the three radiations in order of ionising power, and in order of penetrating power. State the link between the two.
Explain why alpha radiation is fairly harmless outside the body but very dangerous if a source is breathed in.
Answer key and marking notes
- Alpha is a helium nucleus (two protons and two neutrons). ✓
- Beta is a fast-moving electron from the nucleus. ✓
- Gamma is a high-frequency electromagnetic wave. ✓
- Alpha: charge +2. ✓
- Beta: charge -1. ✓
- Gamma: no charge. ✓
- Alpha is stopped by a sheet of paper (or a few cm of air). ✓
- Beta is stopped by a few millimetres of aluminium. ✓
- Gamma is only greatly reduced by thick lead or concrete. ✓
- It is beta. ✓
- Paper does not stop it (so not alpha), but aluminium does stop it completely (so not gamma). ✓
- Ionising: alpha > beta > gamma. Penetration: gamma > beta > alpha. ✓
- The more strongly ionising a radiation is, the less it penetrates. ✓
- Outside the body it is stopped by skin (or air), so it does little harm. ✓
- Inside the body it is very strongly ionising, damaging cells directly. ✓
4 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.
What is an alpha (α) particle?
- Aa helium nucleus (2 protons and 2 neutrons)
- Ba fast-moving electron
- Ca high-frequency electromagnetic wave
- Da single proton
What is a beta (β) particle?
- Aa fast-moving electron emitted from the nucleus
- Ba helium nucleus
- Can electromagnetic wave
- Da neutron
What is gamma (γ) radiation?
- Aa high-frequency electromagnetic wave with no charge and no mass
- Ba stream of helium nuclei
- Ca stream of electrons
- Da stream of protons
Which type of nuclear radiation is stopped by a single sheet of paper?
- Aalpha
- Bbeta
- Cgamma
- Dnone of them
Quiz key
An alpha particle is a helium nucleus: 2 protons and 2 neutrons, with a charge of +2. A fast electron is a beta particle and an electromagnetic wave is gamma radiation.
A beta particle is a fast-moving electron created and emitted when a neutron in the nucleus changes into a proton. It is much lighter than an alpha particle and has a charge of −1.
Gamma radiation is a high-frequency electromagnetic wave, so it has no charge and effectively no mass. This is why it is the most penetrating and the least ionising of the three.
Alpha is the least penetrating and is stopped by a sheet of paper. Beta is stopped by a few millimetres of aluminium, while gamma needs thick lead or concrete to reduce it.
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.