Unit Planner: Atomic, nuclear and particle physics Unit 11: Atomic and nuclear

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End date:

Diploma assessment

When will the content be assessed?

xPaper 1
xPaper 2
Paper 3
Investigation

Text book reference

Hamper SL 229 - 263

Inquiry: Establishing the purpose of the unit

Transfer Goals
List here one to three big, overarching, long-term goals for this unit. Transfer goals are the major goals that ask students to “transfer”, or apply, their knowledge, skills, and concepts at the end of the unit under new/different circumstances, and on their own without scaffolding from the teacher.

• Electron energy levels
• Binding energy is energy released
• Interpretting the BE curve

Content
List here the key content that students will know by the end of the unit

• Why Thomson's experiment led to the discovery of the electron and the plum pudding model.
• The Geiger - Marsden experiment and its results.
• Light has wave like characteristics.
• Different colours of light have different wavelengths.
• A spectrum can be obtained using a diffraction grating.
• Distinguish between a line spectrum and a continuous spectrum.
• The size of the nucleus is 10-15m.
• Definitions of nuclear quantities Z, A and N.
•  E=mc2.
• The electron Volt as a unit of energy.
• The scale of difference between energy associated with chemical and nuclear reactions.
• Distinguish between α, β and γ radiation
• Identify and α particle as a Helium nucleus.
• Write the nuclear equation for α decay and calculate the amount of energy released.
• β particles are electrons and understand why there can't be electrons inside the nucleus.
• Unlike α's, β's are not mono-energetic.
• Introduce the idea of antimatter and the positron.
• Define gamma radiation as high energy EM.
• Nuclear decay is a random process and that the probability of decay is related to the amount of energy that will be released when it happens.
• If dN/dt ∝ N then the decay is exponential.
• Classify proton, neutron and electron into lepton and hadron.
• State the fundamental forces of nature and their relative strengths.
• Electromagnetic interactions are the result of the exchange of virtual photons.
• Baryons and mesons as subdivisions of hadrons.
• All hadrons are made of combinations of 6 different flavoured quarks.
• Introduce the standard model and how to use it to predict interactions

Skills
List here the key skills that students will develop by the end of the unit.

• Explain why Thomson's experiment led to the discovery of the electron and the plum pudding model.
• Write the nuclear equation for α decay and calculate the amount of energy released.
• Interpret the isotope chart to understand why fission fragments are neutron rich.
• Interpret the BE curve to understand why small nuclei joining together will release energy.
• Calculate the energy released in a simple fission reaction.
• Interpret the BE curve to understand why a large nucleus will release energy if it splits into two small ones.
• Construct simple Feynman diagrams to represent electromagnetic interactions.
• Construct simple Feynman diagrams involving quarks.
• Use conservation of baryon number, lepton number and charge to determine if certain processes are possible.

Concepts
List here the key concepts that students will understand by the end of the unit

• Understand why the GM results could not be explained by the plum pudding model.
• Understand why the Rutherford model explains the GM results.
• Understand that light is a form of energy and that it comes from matter which is made of atoms
• Understand why solids don't give line spectra.
• Understand that the experimental fact that all nuclei have a mass that is a multiple of some fundamental mass implies that the nucleus is made of a number of smaller particles.
• Understand that the fact that nuclear charge (also quantized) is less than the number of mass particles implies that there are is another particle, the neutron, in the nucleus.
• Understand why we conclude that the nuclear force is very strong and short range.
• Understand that binding energy is not in the nucleus but has been released.
• Introduce the Unified mass unit.
• Understand how to calculate binding energy from tables of mass and plot the BE/nucl curve.
• Understand that if a nucleus can change into one with higher BE then it will as this will release energy.
• Understand why α particles are so ionising and see how this property enables them to be easily detected by ionisation and cloud chambers but means they have short range.
• Understand that since there is no change in the nucleus there will be no change in BE when γ is emitted so this implies that the nucleus was in an excited state.
• Understand that the number of decays per second in a sample of material is directly proportional to the number of nuclei.
• Understand how half life gives a measure of the rate of decay of a sample.
• Understand why the activity is also exponential and that the activity is more useful to us than the number of particles.
• Interpret the BE curve to understand why a large nucleus will release energy if it splits into two small ones.
• Understand that two pull a nucleus apart requires energy to be put in and this can be achieved by adding a neutron to 235U.
• Understand why high temperatures are required to fuse two light nuclei.
• Understand how a force can be caused by the exchange of a particle.
• Understand that the strong force must involve a massive particle.
• Understand why mesons are made of 2 quarks and baryons 3.

Applications
Examples of real world practical applications of knowledge.

• Apply knowledge of EM to understand why the mini solar system model can't be right.
• Deduce from knowledge of mechanics that physical systems will tend to a state of lowest energy.
• Apply the conservation of momentum and energy to predict that α radiation is mono-energetic.
• Apply the conservation of energy and momentum to deduce that if β particles are not mono-energetic then there must be a third invisible particle, the neutrino.
• Apply the conservation of energy and momentum to understand why two small nuclei can't simply join to form one big one.
• Discuss the health risks involved with exposure to radiation.

Action: teaching and learning through Inquiry

Approaches to teaching
Tick boxes to indicate pedagogical approaches used.

xLecture
xSimulation
xSmall group work (pairs)
xHands on practical
xVideo

TOK
Examples of how TOK can be introduced in this unit

• Thomson's discovery of the electron is another interesting point, Thomson wasn't the first person to find an electron he was the first person to realise that the blue line could be described in terms of particles.
• Another interesting knowledge issue is the way that we tell the history leaving out any experiments that don't lead to the result we want. Is this history or chronology?
• What is the point of learning about models that turn out to be wrong?
• The way particle physicists use high energy projectiles to gain knowledge about the very small is also interesting. I use the example of 4 boxes containing a glass, steel ball, sponge and a cat. A bullet is fired into each and the sound tells us what was inside. Spare the cat by saving it for last.
• Visible light is just one part of the EM spectrum why do we use this region for vision? was it by design or did it have to be this way? The fact that we use chemical reaction to detect EM radiation means we have to use visible light as its the wavelength that excites electrons.
• When atoms are drawn they are never drawn to scale since if the electrons were on the page the nucleus would be too small to see. This can cause some misconceptions.

• In this section we often talk about pulling nuclei apart and how much work we would have to do but we can't actually grab the nucleons and pull them. How can we base the model on a thought experiment?
• Why don't we drop the idea about energy and simply use mass.
• The names α, β and γ have stuck even though we now know what they are.
• One interesting aspect of neutrinos is the fact that they are so unreactive, able to pass through light years of matter. Could there be other particles (maybe millions) that simply don't interact with our matter? If these did exist what would be the point in making theories about them?
• The whole idea about antimatter and symmetry is interesting.
• Physics in literature e.g. Angels and Demons, how the facts are manipulated to make a good story.
• When dealing with the random nature of radioactive decay one could bring up Schroedinger's cat but I tend to leave him out at this stage, preferring not to let the cat out of the bag too early. I do have one of these T shirts though.
• When discussing health risks of radiation it is worth mentioning that a lot of data about the effect of radiation on the human body came from the aftermath of Hiroshima and Nagasaki. Is it ethically acceptable to use this data? It is said that more lives have been saved by these events than were ended.
• How can there be a safe limit to radiation?
• Why do astronauts have a higher acceptable limit than other people?
• When CERN increased the energy of the proton beam to energies approaching the time just after the big bang people were worried that this could lead to a massive explosion.
Daily mail
Telegraph
Time
CERN press release
Who should you believe?
Has the Large Hadron Collider destroyed the world yet?
• Might be worth introducing the man behind the diagrams, Richard Feynman. Loads of good video clips of his lectures on youtube.
This is the way nature works
and some documentaries
The world from another point of view
The fantastic Mr Feynman
• Naming of particles and their properties is interesting. Spin makes you think the particles are spinning but do they really? Are quarks charming and strange? Do quarks have flavour?
• Who decides whether the meaning of a word can be changed to fit some physical property?
• Positive and negative numbers isn't enough to represent the properties of quarks so colour is used.
• Can you have an anticolour?
• Can you something really exist that can never be found on it own?

NOS
Examples of how NOS can be introduced in this unit.

• This is the best example of the scientific method in the syllabus. Observation - Hypothesis - Experiment- Theory. Use the plum pudding model to predict the results from the GM experiment and show that the results falsified the theory leading to a modification.
• Another example of scientific method (its hardly surprising that there are so many examples of the scientific method in science) how the observation of line spectra leads to the energy level model.
• Occam's razor crops up again here. It could be that different nuclei have different mass and charge because they are different, however this would give many different particles, it would be simpler if they were all made of the same 2 particles.
• The idea that mass and energy were equivalent was a paradigm shift.
• Scientific research needs to be financed and this often means there has to be some way of taking advantage of the potential discoveries. The race to make the first atom bomb provided the finance for early nuclear research.
• Sometimes discoveries are made almost by accident and this might have been the case with Becquerel and the discovery of radioactivity. Apparently he left a sample of Uranium salts in a drawer with some photographic plates. When the plates were developed they were found to be fogged, he concluded that the Uranium was giving out radiation that affected the plates. This may not be true but its a good story
• The conservation laws developed in mechanics also apply to these particles that we can't see.
• The development of new technologies to accelerate and detect particles led to the discovery of more particles.
• The neutrino is an interesting beast. The fact that betas have a spread of energy means that either the law of conservation of energy and Newtons laws of motion are wrong (unthinkable) or their exists an invisible particle (better). Why is the "invisible man" a better option than the laws of physics being wrong?
• The neutrino was eventually discovered due to an event that was predicted. This is often the way that particle physics works. A particle is predicted based on the known interactions between known particles, predictions of interactions are made based on the particle properties. When these interactions are observed then the particle is discovered.
• Scientific literacy and the public understanding of science: Scientific arguments can be used for and against nuclear power stations.
• Feynman diagrams are a useful tool in particle physics. If the diagram is possible then so is the interaction.
• Classification of particles into different groups helps predict interactions.
• At times it may not seem like it but this is an example of Occam's razor. It would be much more complicated if each meson and baryon were different fundamental particles

Resources
Video clips, simulations demonstrations etc.

Reflections

What went well
List the portions of the unit (content, assessment, planning) that were successful

What didn’t work well
List the portions of the unit (content, assessment, planning) that were not as successful as hoped

Notes/changes/suggestions:
List any notes, suggestions, or considerations for the future teaching of this unit

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