# OCR AS/A Level Physics A

# Nuclear and particles physics

Navigate to resources by choosing units within one of the unit groups shown below.

## Introduction

### Overview

Delivery guides are designed to represent a body of knowledge about teaching a particular topic and contain:

- Curriculum Content: A clear outline of the content covered by the delivery guide
- Thinking Conceptually: Expert guidance on the key concepts involved, common difficulties students may have, approaches to teaching that can help students understand these concepts and how this topic links conceptually to other areas of the subject
- Thinking Contextually: A range of suggested teaching activities using a variety of themes so that different activities can be selected which best suit particular classes, learning styles or teaching approaches.

## Curriculum Content

### Overview

**Content (from A Level)**

**6.4 Nuclear and particle physics**

This section provides knowledge and understanding of the atom, nucleus, fundamental particles, radioactivity, fission and fusion.

Nuclear power stations provide a significant fraction of the energy needs of our country. They are expensive; governments have to make difficult decisions when building new ones. The building of nuclear power stations can be used to evaluate the benefits and risks to society (HSW9). Ethical, environmental and decision making issues may also be discussed (HSW10 and HSW12). The development of the atomic model also addresses issues of scientific development and validation (HSW7,11).

**6.4.1 The nuclear atom**

(a) alpha-particle scattering experiment; evidence of a small charged nucleus

(b) simple nuclear model of the atom; protons, neutrons and electrons

(c) relative sizes of atom and nucleus

(d) proton number; nucleon number; isotopes; notation \(\displaystyle ^A_ZX\) for the representation of nuclei

(e) strong nuclear force; short-range nature of the force; attractive to about 3 fm and repulsive below about 0.5 fm

(f) radius of nuclei; \(\displaystyle R=r_0A^{1/3}\) where \(\displaystyle r_0\) is a constant and A is the nucleon number

(g) mean densities of atoms and nuclei.

**6.4.2 Fundamental particles**

(a) particles and antiparticles; electron–positron, proton–antiproton, neutron–antineutron and neutrino–antineutrino

(b) particle and its corresponding antiparticle have same mass; electron and positron have opposite charge; proton and antiproton have opposite charge

(c) classification of hadrons; proton and neutron as examples of hadrons; all hadrons are subject to both the strong nuclear force and the weak nuclear force

(d) classification of leptons; electron and neutrino as examples of leptons; all leptons are subject to the weak nuclear force but not the strong nuclear force

(e) simple quark model of hadrons in terms of up (u), down (d) and strange (s) quarks and their respective anti-quarks

(f) quark model of the proton (uud) and the neutron (udd)

(g) charges of the up (u), down (d), strange (s), anti-up (\(\displaystyle \bar u\)), anti-down (\(\displaystyle \bar d\)) and the anti-strange (\(\displaystyle \bar s\)) quarks as fractions of the elementary charge \(\displaystyle e\)

(h) beta-minus (\(\displaystyle \beta^-\)) decay; beta-plus (\(\displaystyle \beta^+\)) decay

(i) \(\displaystyle \beta^-\) decay in terms of a quark model;

\(\displaystyle d\rightarrow u+_{-1}^0e + \bar v\)

(j) \(\displaystyle \beta^+\) decay in terms of a quark model;

\(\displaystyle u\rightarrow d+_{-1}^0e + v\)

(k) balancing of quark transformation equations in terms of charge

(l) decay of particles in terms of the quark model.

**6.4.3 Radioactivity**

(a) radioactive decay; spontaneous and random nature of decay

(b) (i) \(\displaystyle \alpha\)-particles, \(\displaystyle \beta\)-particles and \(\displaystyle \gamma\)-rays; nature, penetration and range of these radiations

(ii) techniques and procedures used to investigate the absorption of \(\displaystyle \lambda\)-particles, \(\displaystyle \beta\)-particles and \(\displaystyle \gamma\)-rays by appropriate materials

(c) nuclear decay equations for alpha, beta-minus and beta-plus decays; balancing nuclear transformation equations

(d) activity of a source; decay constant \(\displaystyle \lambda\)of an isotope; \(\displaystyle A=\lambda N\)

(e) (i) half-life of an isotope; \(\displaystyle \lambda t_{1/2} =\text {In(2)}\)

(ii) techniques and procedures used to determine the half-life of an isotope such as protactinium.

(f) (i) the equations \(\displaystyle A=A_0e^{-\lambda t}\) and \(\displaystyle N=N_0e^{-\lambda t}\), where A is the activity and N is the number of undecayed nuclei

(ii) simulation of radioactive decay using dice

(g) graphical methods and spreadsheet modelling of the equation \(\displaystyle \frac {\Delta N}{\Delta t} = -\lambda N\) for radioactive decay

(h) radioactive dating, e.g. carbon-dating.

**6.4.4 Nuclear fission and fusion**

(a) Einstein’s mass–energy equation; \(\displaystyle \Delta E = \Delta mc^2\)

(b) energy released (or absorbed) in simple nuclear reactions

(c) creation and annihilation of particle–antiparticle pairs

(d) mass defect; binding energy; binding energy per nucleon

(e) binding energy per nucleon against nucleon number curve; energy changes in reactions

(f) binding energy of nuclei using \(\displaystyle \Delta E = \Delta mc^2\) and masses of nuclei

(g) induced nuclear fission; chain reaction

(h) basic structure of a fission reactor; components – fuel rods, control rods and moderator

(i) environmental impact of nuclear waste

(j) nuclear fusion; fusion reactions and temperature

(k) balancing nuclear transformation equations.

### Classifying the atom

The revision of atomic number, nucleon number and the structure of the atom provides a useful link to the GCSE course. Learner resource 1 provides a summary of the key information and a few easy questions. The NZ curve indicates interesting trends in the number of neutrons and protons in the nucleus. The cyberphysics website has some interesting question on the topic (see 'A Level: Radioactivity questions').

Learner resource 2 gets students to plot the curve and mark on the three common types of decay.

### Size of the atom

The Rayleigh Oil Drop experiment detailed by the Institute of Physics provides a neat way of illustrating just how small the distances being measured are. Whilst also reinforcing some of the numerical skills form the AS course (see 'Estimating the size of a molecule using oil').

The School Physics website also provides details of a similar experiment (see 'The oil drop experiment').

The Physbot site has some nice detail about calculating the atomic radius (see 'Nuclear physics').

### Particle physics

There are a variety of introductions and particle physics summaries. This one on PhysicsNet provides a good overall summary (see 'Particle interactions').

There are a range of interesting resources on the Institute of Physics website this provides an introduction to particle physics (see 'Preparation for particle physics topic').

These activities from the Institute of Physics help with classification of particles into the Hadrons, Meson, Leptons and Baryons (see 'The particle zoo').

There are also some interesting particle physics apps available two of the popular ones are the A-Z of Particles and the Particle Zoo both free to download from the app store and provide another route into understanding particle classification.

### Nuclear decay

There are a variety of online resources to help students learn and understand the equations involved in exponential decay. The University of Georgia has a simple factual summary on its Hyperphysics site (see 'Radioactive half-life').

The PhysicsNet site has a similar offering (see 'Radioactive decay').

The schoolphysics site has a good treatment of logarithmic graphs (see 'Mathematical consideration of radioactive decay').

Antoine Education has quite a detail section on nuclear decay (see 'Exponential law of decay').

The s-cool site is a more straightforward explanation with less detail (see 'Activity and the decay constant').

## Thinking Conceptually

### Overview

**Approaches to teaching the content**

This theme introduces student to the study of nuclear and particle physics. It builds upon their study of radioactivity from GCSE. The study of particle physics enables students to discuss the cutting edge of physics and where will the next ten years lead us in terms of our understanding of matter. Students should be given the opportunity to see how radioactive sources are handled and how ionising radiation is measured. They should also experience a variety of analogies to radioactive decay to help cement the mathematical principles. The ethical and safety debate with regards to nuclear power is an opportunity to put the subject matter in a wider context.

**Common misconceptions or difficulties students may have**

Whilst students may well be familiar with the structure of the atom from their previous studies they may not have considered the wider implications of this. The concept of reducing the various forces they have encountered in physics down to four fundamental forces often proves to be challenging as does the array of new particles they are exposed to in the particle physics section. Often a strong historical timeline can help the students appreciate that the particle were discovered over time and theories had to evolve to explain the observations. Nuclear decay can also provide challenges for students and it is important to try and install the concept that the exponential decay is caused by the rate of decaying being proportional to the quantity remaining. Calculations involving mass and energy can be challenging and students need to be extremely careful about the layout of their work.

**Conceptual links to other areas of the specification – useful ways to approach this topic to set students up for topics later in the course.
e.g. links to radioactivity, fields and particles**

This theme links to a wide variety of areas within physics. The mathematical links between nuclear decay and the discharge of a capacitor are obvious and essential in order to develop a broader understanding of the physical world. The particle physics and antimatter links back to some of the ideas discussed with regards to quantum theory and photon energy. The electric and magnetic fields used to accelerate and study particles also provides useful opportunities for reinforcing content. Logarithmic graphs used to interpret decay help reinforce concepts learners will have encountered in materials, fields and astrophysics.

### Alpha particle scattering experiment

The students need to understand how the results were gathered and the interpretation of them and how this led Rutherford to formulate his model of the atom. The results can be conceptually challenging for students who view their world as solid rather than mostly empty space.

These activities from the Institute of Physics are helpful particularly the use of the 1/r hill to show the scattering (see 'Rutherford's experiment).

This YouTube video produced by Perimeter classroom shows the same thing using a wine glass if you don’t have a 1/r hill (see 'Rutherford scattering with marbles').

Georgia State University’s Hyper Physics website has some nice detail and graphical explanations of the experiment and its results (see 'Rutherford scattering').

This link provides some nice historical background information on the experiment:

Rutherford's alpha scattering experiment.

### Half-Life

The water flow model from the Institute of Physics provides an interesting link between contexts and helps reinforce the idea of the rate of decay being proportional to the quantity. The experiments help students pin their practical understanding to the mathematical concepts (see 'Modelling radioactive decay').

This experiment from the Exploratorium is similar to the dice experiment listed on the Institute of Physics page but can be used more visually (see 'Radioactive decay model').

### Binding energy per nucleon

The University of Georgia provides a simple summary of nuclear binding energy (see 'Nuclear binding energy').

Learner resource 3 provides a worked example of calculating nuclear binding energy and Learner resource 4 provides the data for first calculating nuclear binding energy per nucleon and the plotting the graph.

The students can then mark on the areas where nuclear fission will happen and where nuclear fusion occurs.

### Balanced nuclear transformations

The students frequently need to practise these in order to gain an appreciation of how the conservation rules are applied to real decays or nuclear transformations. The sparknotes site provides a simple summary of the majority of the work they have covered (see 'Nuclear reactions').

The cyberphysics site focuses on some of the particle transformations and could help students struggling with the wider range of interactions and decays that they encounter at A-level (see 'Balancing the equations').

The s-cool site also has a different focus and explanation (see 'Decay equations').

The Antonine Education web site has a detailed summary and a wide variety of examples plus a little extension work on metastable states and gamma decay (see 'Nuclear instability').

## Thinking Contextually

### Overview

The theme has a links to an incredibly wide range of contexts and novel applications. Particle physics linking with medical scanning in the form of Positron Emission Tomography and prospects of antimatter drives or energy sources. The applications of ionising radiation are numerous and to name but a few:

- Sterilisation of medical instruments
- Checking welds
- Measuring the density of new road
- Medical tracers
- Radiotherapy
- CT scans
- Measuring the thickness of paper or aluminium foil
- Smoke Detectors
- Chemical tagging

The work on Nuclear binding energy also has key applications from nuclear fission and fusion including:

- Nuclear power
- Atomic bombs
- Tokamak
- PP cycle in stars

The vast array of context in which this material can be set is impressive but the opportunities for practical study are more limited.

### Uses of ionising radiation

The number of applications of radioactive isotopes is seemingly endless but some common ones are discussed here.

Medical Tracers

The University of Georgia hyperphysics website provides a nice summary (see 'Radioactive tracers').

The How Stuff Works site has more on medical tracers (see 'How nuclear medicine works').

Other uses of tracers are discussed on the New Zealand Science Learn site (see 'Using isotopes as tracers').

The Institute of Physics has some nice resources like this one on gamma cameras (see 'Gamma cameras').

Further applications are discussed on the cyberphysics site (see 'Uses of nuclear radiation').

### PET scans

Studying these conveniently links the properties of antimatter with those of ionising radiation. The Institute of Physics site has a variety of resources available including a video file and a PowerPoint presentation (see 'PET').

The University of Georgia’s Hyperphysics website has a good explanation here (see 'Nuclear medicine').

The Cyberphysics site has some interesting detail on the procedure as well as an animated tomograph (see 'PET (cyberphysics)').

### Nuclear fusion and Tokamaks

The How Stuff Works site explains how the magnetic confinement fusion reactors work and how the incredibly high temperatures area achieved (see 'How nuclear fusion reactors work').

The Georgia State University hyperphysics site shows how the magnetic confinement works and links to the study of circular motion and F=qvB (see 'Magnetic confinement fusion').

'ITER: the world's largest Tokomak' shows a schematic of the new International Tokomak project ITER.

Inside stars nuclear fusion occurs through the pp cycle.

The university of Surrey website provides a good summary of the theme here (see 'Energy generation in stars').

The Georgia State University hyperphysics site provides a detailed summary of the pp cycle here (see 'Proton-proton fusion').

### Nuclear reactor demonstration

There are some useful animations on the University of Colorado’s PhET site (see 'Nuclear fission').

This site has an excellent simulation of the workings of a nuclear reactor with students able to click on the relevant parts to see their location and function (see 'Nuclear reactor simulator').

This animation is less detailed but does look at different types of reactor which can provoke interesting discussions on safety and nuclear power (see 'Nuclear power plant illustrations').

### Investigating the random nature of radioactive decay

### Investigating the absorption of α-particles, β-particles and γ-rays by appropriate materials

### Investigating the half-life of radioactive materials

## Acknowledgements

### Overview

OCR’s resources are provided to support the teaching of OCR specifications, but in no way constitute an endorsed teaching method that is required by the Board and the decision to use them lies with the individual teacher. Whilst every effort is made to ensure the accuracy of the content, OCR cannot be held responsible for any errors or omissions within these resources. We update our resources on a regular basis, so please check the OCR website to ensure you have the most up to date version.

© OCR 2015 - This resource may be freely copied and distributed, as long as the OCR logo and this message remain intact and OCR is acknowledged as the originator of this work.