The shape of the lesson
By the end of the lesson, learners can
- Share the energy: Watch a neutron decay: an electron and an antineutrino fly out, sharing the available energy.
- Particles and their antiparticles: Same mass, opposite charge.
- Why the neutrino was needed: The continuous beta spectrum looked like a violation of conservation.
- Antiparticle: same mass, opposite charge.
- Beta-minus: electron + antineutrino.
- u: from carbon-12.
One picture every idea returns to
Every particle has an antiparticle with the same mass but opposite charge; the positron is the electron antiparticle. Beta-minus decay emits an electron and an antineutrino; beta-plus decay emits a positron and a neutrino. Alpha particles leave with discrete energies, but beta particles have a continuous range, because the energy is shared with the (anti)neutrino. The unified atomic mass unit u is one twelfth of the mass of a carbon-12 atom.
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, The missing energy.. Beta particles come out with a puzzling spread of energies, unlike the sharp lines of alpha decay. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 13 min | Teach and check: Share the energy | Watch a neutron decay: an electron and an antineutrino fly out, sharing the available energy. Project tab 3 of the lab (Beta decay and neutrinos) and let a student drive it while the class predicts. | Whole class, then pairs |
| 13 to 21 min | Teach and check: Particles and their antiparticles | Same mass, opposite charge. | Pairs |
| 21 to 30 min | Teach and check: Why the neutrino was needed | The continuous beta spectrum looked like a violation of conservation. | 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, 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 Why the neutrino was needed, 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 |
|---|---|
| An antiparticle has the same mass as its particle, only the charge is reversed; do not say it is lighter or heavier. | Beta-minus decay emits an antineutrino (with the electron), while beta-plus emits a neutrino (with the positron); keep the pairing right. The unified atomic mass unit is defined from carbon-12, as one twelfth of that atom mass. |
Antiparticles and neutrinos: worksheet
6 questions, 12 marks. Written in the style of the papers; no past paper question is reproduced.
State what is meant by an antiparticle, giving one example.
State the two particles emitted in beta-minus decay.
Explain why beta particles are emitted with a continuous range of energies.
Define the unified atomic mass unit (u).
State the two particles emitted in beta-plus decay.
State two ways in which a positron is related to, and differs from, an electron.
Answer key and marking notes
- An antiparticle has the same mass as its particle but the opposite charge ✓
- For example, the positron is the antiparticle of the electron ✓
- An electron (the beta-minus particle) ✓
- and an electron antineutrino ✓
- The available energy is shared between the beta particle and the (anti)neutrino ✓
- and the share varies from decay to decay, so the beta energy ranges up to a maximum ✓
One unified atomic mass unit is one twelfth of the mass of a carbon-12 atom ✓
- A positron (the beta-plus particle) ✓
- and a neutrino ✓
- It has the same mass as the electron ✓
- but it carries the opposite (positive) charge ✓
14 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.
The antiparticle of the electron is the:
- Aproton
- Bpositron
- Cneutron
- Dneutrino
An antiparticle has the same mass as its particle but the opposite:
- Aspeed
- Bsize
- Cspin only
- Dcharge
Beta-minus decay emits an electron together with:
- Aan antineutrino
- Ba neutrino
- Ca positron
- Da proton
Beta particles have a continuous range of energies because the energy is shared with:
- Aa gamma photon only
- Banother electron
- Ca neutrino or antineutrino
- Dthe nucleus equally
The unified atomic mass unit is defined as:
- Athe mass of a proton
- Bone twelfth of the mass of a carbon-12 atom
- Cthe mass of a hydrogen atom
- Done twelfth of an oxygen-16 atom
The neutrino was originally proposed to preserve the conservation of:
- Acharge only
- Bnucleon number
- Cmass only
- Denergy and momentum in beta decay
Beta-plus decay emits a positron together with:
- Aa neutrino
- Ban antineutrino
- Can electron
- Dan alpha particle
The charge on a positron is:
- A−e
- B0
- C+e
- D+2e
Compared with the continuous beta spectrum, alpha particles are emitted with energies that are:
- Acontinuous
- Bdiscrete
- Calways zero
- Dalways larger
An antineutrino is emitted in:
- Abeta-plus decay
- Balpha decay
- Cgamma decay
- Dbeta-minus decay
The mass of a positron compared with that of an electron is:
- Aequal
- Bmuch larger
- Cmuch smaller
- Dzero
The strongest evidence for the existence of the neutrino is the:
- Adiscrete spectrum of alpha decay
- Bcharge of the electron
- Ccontinuous energy spectrum of beta decay
- Dpenetration of gamma rays
Gamma radiation is often emitted after alpha or beta decay because the daughter nucleus:
- Agains a proton
- Bis left in an excited state and releases energy
- Closes a neutron
- Dbecomes an isotope
In beta-plus decay, a proton in the nucleus changes into a:
- Aneutron and electron
- Bproton and photon
- Cneutron and antineutrino
- Dneutron, positron and neutrino
Quiz key
The positron is the electron antiparticle.
Same mass, opposite charge.
Beta-minus emits an electron and an electron antineutrino.
The (anti)neutrino carries a variable share, giving a continuous spectrum.
1 u = (1/12) of the mass of a carbon-12 atom.
The unseen neutrino carries the missing energy and momentum.
Beta-plus emits a positron and a neutrino.
The positron carries charge +e.
Alpha energies are discrete and characteristic of the decay.
Beta-minus emits an electron and an antineutrino.
A particle and antiparticle have equal mass.
The continuous beta spectrum implied an unseen particle sharing the energy.
A gamma photon carries away energy as the nucleus drops to a lower state.
A proton becomes a neutron, emitting a positron and a neutrino.
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.