P6 Module Introduction - WikispacesRadioactive+Materials+SOW… · The model begins by reviewing what we know about the atom, ... P6 Module Introduction ... ask the students to mark

OCR 21st Century Science: P6 Radioactive materials

COLLINS NEW GCSE SCIENCE © HarperCollinsPublishers Ltd 2011

P6 Module Introduction

Pages 256−257 in the Student Book provide an introduction to this module.

When and how to use these pages

These pages summarise what students should already know from KS3 or from previous GCSE units and provide

an overview of the content that they will learn in this module.

o Use these pages as a revision lesson before you start the first new topic.

o Brainstorm everything that students remember about the different topics using the headings as a starting point. Compare your list with the points on page 256.

o Use the questions on page 256 as a starting point for class discussions.

o Ask students if they can tell you anything about the topics on the right-hand page.

o Make a note of any unfamiliar / difficult terms and return to these in the relevant lessons.

Suitable answers to the questions on page 256 are:

o Gamma rays, X-rays and some ultraviolet rays.

o Ionisation is the process by which high-energy radiation knocks electrons out of atoms and molecules in material it passes through. It can be dangerous because it can damage or even kill living cells. Damage to cells can increase the risk of developing cancer.

o Nuclear power stations and coal fired power stations both use steam to turn their turbines. In nuclear power stations the heat to produce steam comes from nuclear fission reactions; in a coal fired power station coal is burnt. Nuclear power stations don’t emit polluting gases or greenhouse gases as coal fired power stations do. But they produce radioactive waste products which need to be disposed of in a way that prevents damage to the environment and to people from ionising radiation that they emit. The cost of producing electricity and the energy efficiency of the process is similar in nuclear and coal fired power stations. Accidents at nuclear power stations can have devastating effects on the environment.

You could revisit these pages at the following points:

o before lesson p6_06 on the hazards of ionising radiation, pages 270−271

o before lesson p5 _09 on obtaining energy from the nucleus, pages 276−277.

Overview of module

The model begins by reviewing what we know about the atom, its structure and its nucleus, and how we know this.

It moves on to explain that radioactive elements have unstable nuclei that emit ionising radiation. Sources of

background radiation are covered. Then the three types of nuclear radiation are considered in more detail.

Students learn about their nature, their ionising ability and their penetrating ability.

Radioactive decay from one element to another is covered next, and nuclear decay equations are introduced for

Higher-tier students. This leads on to the concept of half-life.

The effects of ionising radiation on living cells is considered next, and the use of the ‘equivalent dose’ as a

measure of biological effect. Then the benefits of making use of radiation are covered, followed by discussion of

assessing the risks posed to people working with radioactive materials.

The module moves on to an explanation of how nuclear fission produces energy and how the resulting chain

reaction is controlled in a nuclear power station. It ends with a discussion of energy from fusion and the problems

that need to be overcome if we are to make use of this reaction for our energy on Earth.

Obstacles to learning

Students may need extra guidance with the following terms and concepts:

The atom

Students may find it challenging to understand the scale of the sizes and masses of atoms and their constituent

particles. They may not necessarily appreciate the provisional nature of models of the atom.

Radioactive decay

Students may believe that radioactive decay occurs entirely as a result of human activity. They may find it difficult

to appreciate that decay is a random process and yet follows a predictable overall pattern.

Some students may confuse radioactive decay with biological decay.

Higher-tier students need to be able to deal with nuclear decay equations; some may find these complex and

confusing.

P6 Module Introduction continued


Half-life

Students may find it difficult to understand that each half-life is the time for the radioactivity to drop to half its

previous value, but since the rate at which the activity decreases becomes less, two half-lives don’t add up to the

total period of time for which the material is radioactive.

Ionising radiation

Students may find it difficult to understand that ionising radiation comes from the nucleus.

They may not appreciate that there is no such thing as a safe level of ionising radiation.

They may have some misconceptions, such as thinking that anything exposed to ionising radiation becomes

radioactive. This is confusion between irradiation and contamination.

Fission and fusion

Students may confuse the terms fission and fusion.

Practicals in this module

This module provides the following practical work:

o demonstrating background radiation

o demonstrating detection of alpha radiation

o demonstrating the range and penetration of alpha, beta and gamma radiation

o modelling the random nature of radioactive decay

o making models of the fission and fusion processes

o demonstrating disposal of radioactive waste items

Key vocabulary covered in this module

electron isotope neutron nucleus proton strong nuclear force

background radiation ionising radiation radioactive

alpha radiation beta radiation gamma radiation nucleon number

activity radioactive decay daughter product half-life decay chain

equivalent dose ion mutation sievert

radioactive tracer radiotherapy sterile

contamination hazard irradiation risk

binding energy chain reaction nuclear fission nuclear fuel nuclear fusion

coolant control rod fuel rod high-level waste intermediate-level waste low-level waste



P6 Analysing, evaluating and reviewing

Pages 266−267 in the Student Book prepare students for controlled assessment.


This activity provides an opportunity to build and assess the skills that students will use when analysing data and

evaluating an investigation.

Ask students to:

o read through the context and tasks, listing any terms that they do not understand

o as a whole class or in small groups, discuss the tasks to ensure that all students understand the terminology used and to clarify what is required

o work individually or in small groups to answer the questions for each task.

If time allows, ask the students to mark one another’s work using the mark scheme provided.

Notes

The purpose of this activity is for students to consider how an investigation should be analysed so that it can be

evaluated. The context provided is that of investigating radioactive decay. It is not assumed that students will see

this practical activity being carried out (though there are a number of learning outcomes that would be achieved by

so doing) but the focus of the activity is to reflect and comment upon how the class in the Student Book text

responded. This is an effective way of making key points about the development of these skills on the approach to

carrying out centre-marked assignments.

The tasks are progressively more challenging and give access to higher-grade outcomes as students proceed

through them.

Answers Task 1

We would expect that the results would not be identical but would follow the same general trend.

The data follows a clear trend and the general pattern is as would be expected, so the experiment appears to

be producing accurate data.

The count of 14 at 270 s seems to be rather low, as do the readings of 1 and 0 at 370 s and 390 s. The value of

12 at 410 s seems rather high.

Task 2

The best-fit curve should show the shape of those on p. 269 of the Student Book.

Task 3

The experiment could be repeated to confirm the general trend and the mean count reading for each period of

time calculated. The more samples for a particular period of time are taken, the more the random errors will

cancel one another out. However, the overall pattern is as would be expected. If the graph was used to

calculate the half-life of protactinium and this was compared with accepted values this would be a further check.

Task 4

The graph shows the curve typical of a radioactive decay curve. The outliers are more apparent later in the

experiment, when the readings are smaller and a slight fluctuation has a significant impact.

The repeatability of the data is generally good, bearing in mind that radioactive decay is a random process.

The variation in the readings is generally characteristic of radioactive decay curves, because of the random

nature of decay.

P6 Analysing, evaluating and reviewing continued


Mark scheme

For grade E, students need to:

o Comment on how the students collected the data and its accuracy or repeatability.

o Comment on the limitations to accuracy or range of data due to their techniques and equipment.

o Identify individual results which are outliers, or justify a claim that there are no outliers.

For grades D, C, in addition they need to:

o Suggest improvements to their apparatus or techniques, or alternative ways to collect data.

o Use the general pattern of their results as a basis for assessing accuracy and repeatability.

For grades B, A, in addition they need to:

o Describe and justify improvements to their apparatus or techniques, or alternative ways to collect the data.

o Consider critically the repeatability of their evidence, accounting for any outliers.



P6 Exam-style questions

Pages 284–285 in the Student Book are exam-style questions.


These questions are based on the whole of Module P6 and cover a range of different types of questions that

students will meet in their written exams.

o The questions could be used as a revision test once you’ve completed the module.

o Work through the questions as a class as part of a revision lesson.

o Ask students to mark each other’s work, using the mark scheme provided.

o As a class, make a list of the questions that most students did not get right. Work through these as a class.

Notes on the worked examples

The first question shows how ideas about properties of radioactive emissions can be used to explain how a smoke

detector works; the answers and comments indicate the key points that should be covered. The second question

relates to irradiation and contamination of materials from a nuclear power station. It shows that in this type of

question the key terms need to be understood, their distinctive meaning explained and the implications described.

Assessment Objectives

These exam-style questions cover the Assessment Objectives as described below.

Assessment Objectives Questions

AO1 Recall, select and communicate their knowledge and understanding of science

1c, 1d, 2, 3, 4a, 5a, 6a

worked example 1a, 2a, 2b, 2c

AO2 Apply skills, knowledge and understanding of science in practical and other contexts

5b, 6b, 7

worked example1b, 1c, 1d

AO3 Analyse and evaluate evidence, make reasoned judgements and draw conclusions based on evidence

1a, 1b, 4b, 4c

worked example 2d

Answers

These answers are also supplied on the Teacher Pack CD so that students can mark their own or their peer’s work.

Question

number

Answer Additional notes Mark

1a Alpha

Tracing paper reduces count to100 cpm; only

alpha is stopped by tracing paper

1

1

2

1b The count is still above background radiation of

50 cpm

1

1c Background radiation is around all the time 1

1d One of: rocks, buildings, cosmic rays, medical

and industrial use of radioactive sources

1

2a Wear protective clothing such as lead aprons

Deal with radioactive sources remotely

Shield the sources

1

1

1

3

2b Two of: miner, airline pilot, radiographer, nuclear

reactor engineer, etc.

2

3 Relevant points include:

Things to be dealt with: spent fuel rods, reactor

components, and clothing

For 5 – 6 marks:

Answer correctly describes nature of

materials and explains methods of

6

P6 Exam-style questions continued


Materials with high levels of radiation will be

stored under water for a period of time until the

level of activity has reduced sufficiently for ti to

be processed. It is then processed into glass

discs which are stored underground in stainless

steel drums

Intermediate level waste: short half life materials

are buried in shallow landfill sites. Intermediate

waste with a longer half life, which will therefore

be radioactive for a longer period of time, is

stored deep underground

Low level waste is burned or placed in closed

containers before being buried in landfill sites

disposal according to classification. All

information is relevant, clear,

organised and presented in a

structured and coherent format.

Specialist terms are used

appropriately. Few, if any, errors in

grammar, punctuation and spelling

For 3 – 4 marks:

A complete description and a full

explanation of the disposal of one type

of material. For the most part the

information is relevant and presented

in a structured and coherent format.

Specialist terms are used for the most

part appropriately. Occasional errors in

grammar, punctuation and spelling

For 1 – 2 marks:

A complete description but no effective

explanation of disposal OR a partial

explanation but many details omitted.

Answer may be simplistic. Limited use

of specialist terms. Errors of grammar,

punctuation and spelling

4a Radioactive source is injected into the blood

stream of the patient

A detector is used to find out where the radiation

goes, how much it is diminished and so to detect

any obstructions

1

1

2

4b As it has a short half-life it will not last long

enough to cause damage

2

4c It may not last long enough to reach the affected

part of the body in sufficient quantities to obtain

a good image

2

5a Isotopes have the same number of protons but

different numbers of neutrons in the nucleus

1

5b It will be sufficiently radioactive for thousands of

years to be detected in archaeological remains

The date can be determined by measuring the

current activity level and therefore the fraction of

current amount of C-14 present compared with

the original level. From this data the number of

half lives which have elapsed can be calculated

1

1

2

6a Alpha 42He

Beta 0-1e

1

1

2

6b

23892U →

23490Th +

42He the atomic numbers balance

the mass numbers balance

2

7a

Graph plotted correctly:

time as the independent variable on x-axis and

count rate per minute on y-axis

axes labelled and calibration started at zero

points should be plotted accurately

and a line of best fit drawn

1

1

1

1

4

7b At least three constructions made correctly on

graph to see how long count rate takes to drop

to half its value; for example 160 to 80, 120 to

60 and 80 to 40 give respective values of 3.1,

3.2 and 3.1 minutes. Within the accuracy of the

graph a value of 3.1 minutes is acceptable

3



P6 Module Checklist

Pages 282–283 in the Student Book provide a student-friendly checklist for revision.


This checklist is presented in three columns showing progression, based on the grading criteria. Bold italic means

Higher tier only.

Remind students that they need to be able to use these ideas in various ways, such as:

o interpreting pictures, diagrams and graphs

o applying ideas to new situations

o explaining ethical implications

o suggesting some benefits and risks to society

o drawing conclusions from evidence they have been given.

These pages can be used for individual or class revision using any combination of the suggestions below.

o Ask students to construct a mind map linking the points on this checklist.

o Work through the checklist as a class and note the points that need further class discussion.

o Ask students to tick the boxes on the checklist worksheet (on the Teacher Pack CD) if they feel confident that they are well prepared for the topics. Students should refer back to the relevant Student Book pages to revise the points that they feel less confident about.

o Ask students to use the search terms at the foot of the relevant Student Book pages to do further research on the different points in the checklist.

o Students could work in pairs, and ask each other what points they think they can do, and why they think that they can do those, and not others.

P6 Module Checklist continued


Module summary

In the introduction to this module, students were presented with a number of new ideas. Work through the list

below as part of their revision. Ask students to write their own summaries and mind maps, using this list as a

starting point.

Radioactive emissions and decay

o Evidence for the nuclear model of the atom comes from alpha particle scattering experiments

o Ionising radiation is emitted from radioactive elements, which have unstable nuclei

o Alpha particles are positively charged and have high ionising ability; they can be stopped by skin or a sheet of paper

o Beta particles have negative charge; they are lighter and faster than alpha particles and not such good ionisers; they are stopped by a 3mm sheet of aluminium

o Gamma rays are high-energy electromagnetic radiation; they are weak ionisers and penetrate well; they need thick blocks of dense material such as lead to stop them

o Radioactive decay is a random process

o The activity of a sample of radioactive material decreases with time; each element has a specific half-life: the time for half the sample to decay, or the time for the activity to fall to a half

Uses and risks of ionisation

o Ionisation produces ion pairs by knocking electrons out of atoms

o Ionising radiation has a harmful effect on cells of living organisms

o The biological effect depends on the ‘equivalent dose’ of the radiation

o There are beneficial uses of ionising radiation in medicine and in industry

o Risks to those working with radiation need to be evaluated, protective measures put in place and exposure regulated

Fission and fusion

o Large amounts of energy are produced by nuclear fission

o Fission in a nuclear reactor is carefully controlled

o Low-level, intermediate-level and high-level radioactive waste have different levels of activity and need to be need to be dealt with in certain ways to minimise risk

o Nuclear fusion of hydrogen nuclei to helium nuclei is the main energy-producing reaction in the Sun; great technical problems need to be overcome to generate power in this way on Earth



Checklist P6 Aiming for C

Use this checklist to see what you can do now. Refer back to pages 257–281 if you’re not sure. Look across the rows to see how you could progress – bold italic means Higher tier only.

Remember you’ll need to be able to use these ideas in many ways:

interpreting pictures, diagrams and graphs applying ideas to new situations explaining ethical implications suggesting some benefits and risks to society drawing conclusions from evidence you’ve been given.

Look at pages 300–306 for information about how you’ll be assessed.

Working towards a C grade

Aiming for Grade E Aiming for Grade C describe how the Rutherford−Geiger−Marsden scattering experiment gave evidence for the atomic nucleus

recall that protons and neutrons make up the nucleus of an atom and that electrons orbit the nucleus

recall that the strong force holds the nucleus together

understand that isotopes of an element have the same number of protons but different number of neutrons

recall that radioactive elements give off ionising radiation

recall that background radiation is everywhere and describe the different sources

recall that the three types of nuclear radiation are alpha, beta and gamma; recall their penetration properties and describe how to distinguish between them

understand that alpha is a helium nucleus, beta is an electron and gamma is an electromagnetic wave

understand that radioactivity is a random process, unaffected by physical or chemical conditions

describe how unstable nuclei decay to form new nuclei by alpha or beta and gamma radiation

represent isotopes using nuclear symbols

understand that over time the activity of radioactive sources decreases

recall that the half-life of a radioactive element is the time taken for half of the nuclei in a sample to decay

calculate half-life from data or graphs

OCR 21st Century Science: P6 Checklist


Aiming for Grade E Aiming for Grade C recall that ionising radiation can damage living cells: higher levels may kill the cells and lower levels can cause mutations

understand that when certain atoms in the body are ionised the resulting charged ion can break apart DNA in a cell and cause damage

use data to compare the radiation dose from different sources, interpret data on risk related to dose, and describe measures taken for the safety of people who work with radioactive sources

recall that there is a wide range of half-life values, and understand that how long a radioactive source will be considered a danger is related to its half-life

describe how ionising radiation can be used to kill cancer cells

explain the advantages of sterilising medical instruments and food

describe the beneficial uses of ionising radiation, including how tracers are used to diagnose medical conditions

understand that the best sources for various uses are selected based on their nature and half-life

understand that a nuclear fuel releases energy; recall that the energy released by nuclear fission is much greater than that released in chemical reactions

describe the fission reaction

explain the conditions for a chain reaction

understand the functions of fuel rods, control rods and coolant in a nuclear reactor

recall that all nuclear power stations produce radioactive waste, and describe how low-, intermediate- and high-level wastes are dealt with

describe nuclear fusion of hydrogen nuclei

use E = mc2 to explain that the mass lost in nuclear fission and nuclear fusion results in the release of energy



Checklist P6 Aiming for A

Use this checklist to see what you can do now. Refer back to pages 257–281 if you’re not sure. Look across the rows to see how you could progress – bold italic means Higher tier only.

Remember you’ll need to be able to use these ideas in many ways:

interpreting pictures, diagrams and graphs applying ideas to new situations explaining ethical implications suggesting some benefits and risks to society drawing conclusions from evidence you’ve been given.

Look at pages 300–306 for information about how you’ll be assessed.

Working towards an A grade

Aiming for Grade C Aiming for Grade A describe how the Rutherford−Geiger−Marsden scattering experiment gave evidence for the atomic nucleus

recall that the strong force holds the nucleus together

understand that isotopes of an element have the same number of protons but different number of neutrons

recall that radioactive elements give off ionising radiation

recall that background radiation is everywhere and describe the different sources

understand that alpha is a helium nucleus, beta is an electron and gamma is an electromagnetic wave

describe how unstable nuclei decay to form new nuclei by alpha or beta and gamma radiation

represent isotopes using nuclear symbols

write complete nuclear equations for alpha and beta decay

calculate half-life from data or graphs

understand that when certain atoms in the body are ionised the resulting charged ion can break apart DNA in a cell and cause damage

use data to compare the radiation dose from different sources, interpret data on risk related to dose, and describe measures taken for the safety of people who work with radioactive sources

recall that there is a wide range of half-life values, and understand that how long a radioactive source will be considered a danger is related to its half-life

describe the beneficial uses of ionising radiation, including how tracers are used to diagnose medical conditions

OCR 21st Century Science: P6 Checklist


Aiming for Grade C Aiming for Grade A understand that the best radioactive sources for various beneficial uses are selected based on their nature and half-life

describe the fission reaction

explain the conditions for a chain reaction

understand the functions of fuel rods, control rods and coolant in a nuclear reactor

write a complete nuclear equation for a fission reaction

recall that all nuclear power stations produce radioactive waste, and describe how low-, intermediate- and high-level wastes are dealt with

use E = mc2 to explain that the mass lost in nuclear fission and nuclear fusion results in the release of energy



p6_01 The nuclear atom

Resources

Student Book pages 258−259 Interactive Book: Matching pairs activity ‘Isotopes’ Homework pack p6_01

Files on Teacher Pack CD: p6_01_worksheet

Video about the scale of the Universe; presentation or animation about atomic structure; video about the discovery of the nucleus; scissors and paper

Learning outcomes P6.1.3 understand that an atom has a nucleus, made of protons and neutrons, which is surrounded by electrons

P6.1.4 understand that the results of the Rutherford–Geiger–Marsden alpha particle scattering experiment

provided evidence that a gold atom contains a small, massive, positive region (the nucleus)

P6.1.5 understand that protons and neutrons are held together in the nucleus by a strong force which

balances the repulsive electrostatic force between the protons

P6.1.8 understand that every atom of any element has the same number of protons but the number of

neutrons may differ, and that forms of the same element with different numbers of neutrons are called

isotopes

Ideas about Science IaS 1.1 data are crucial to science. The search for explanations starts from data; and data are collected to test

proposed explanations

IaS 2.7 even when there is evidence that a factor is correlated with an outcome, scientists are unlikely to accept

that it is a cause of the outcome, unless they can think of a plausible mechanism linking the two

Numeracy focus: Developing a sense of scale of the size of the atom.

In this lesson students are learning to:

understand the structure of the atom

explain how experimental evidence supports ideas about the structure of the atom

Key vocabulary

electron isotope neutron nucleus proton strong nuclear force


Students may find it challenging to understand the scale of the sizes and masses of atoms and their constituent

particles. They may not necessarily appreciate the provisional nature of models of the atom.

Stimuli and starter suggestions

Show the video (available on YouTube) ‘The Universe from macro to micro scales’ or the well known video

‘Powers of ten’.

Discuss size, orders of magnitude, the very big and the very small. Tell students that in this module we will be

focusing on what happens in the nucleus of an atom.

Learning activities worksheet p6_01 Low demand Explain to students that a model can help to explain various phenomena. Show how we can use

the idea of positively charged protons, neutral neutrons and negatively charged electrons to explain how atoms

behave. Emphasise the scale of the model and say that we can’t see these particles. However, it is a useful model.

Use an animation or a presentation (such as the PowerPoint ‘Building Blocks of Matter: Atoms’, slides 1–19,

available from the Chemistry section of the ‘Science with Mr Jones’ website), to show the structure of the atom.

Discuss the size and charge of each particle as you ‘build up’ the atom.

Students can do activity 1 on the worksheet.

Teaching and learning notes: Students need to know the components of an atom and their properties; that atoms

are neutral; and that most of the mass of the atom is in the nucleus.

Standard demand Ask students how we could know that the atom has a massive, positive nucleus, given that it

is so small. Use p. 259 in the Student Book to describe the Rutherford–Geiger-Marsden alpha particle scattering

experiment. Tell students about the results and ask them for possible explanations. Discuss in pairs first and then

with the whole group. This might be supported by using a video, such as ‘The Discovery of the Atomic Nucleus (3

p6_01 The nuclear atom continued


of 15)’, available on YouTube, which shows Brian Cox at the Rutherford Laboratory in Cambridge explaining the

discovery of the nuclear atom.

Students can do activity 2 on the worksheet. In taking feedback, emphasise the point that what Rutherford with his

team did was not only to observe the effects and record the data but then to devise an explanation that would fit.

Teaching and learning notes: Students will need to know the setup, results and conclusions from the alpha

particle scattering experiment.

High demand Ask Higher tier students if they see any problems that might exist in a nucleus with many positive

particles and draw out the idea that these particles will repel each other. Tell them that there is a ‘strong nuclear

force’ between all nucleons (protons and neutrons) that is very strongly attractive, but only acts over very small

distances, which holds these particles together.

Use p. 259 in the Student Book and questions 5 and 6 to teach students about isotopes (which are not in the

Chemistry specification). Isotopes have the same number of protons, and therefore are the same element, but

have different numbers of neutrons. Isotopes of an element all have the same electronic structure.

Students can do activity 3 on the worksheet.

Plenary suggestions Challenge the students: ‘How many times can you cut a piece of A4 paper in half?’ Start off the process by cutting

a sheet of paper in half, in half again, and so on (it will quickly become very small indeed!). Tell them that you

would need to cut it 32 times to get to the size of an atom.

Student Book answers Q1

Particle Mass Charge

electron 0 –1

proton 1 +1

neutron 1 0

Q2 92 (there must be the same number of electrons as protons in a neutral atom)

Q3 No neutrons would be deflected through a small angle. Because they are neutral, they will be unaffected by any

charges in the gold foil.

Q4 The positive charges on both the gold nucleus and the alpha particle will create a repulsive electrostatic force

between the particles.

Q5 Neutron. O-16, 8 neutrons; O-17, 9 neutrons; O-18, 10 neutrons

Q6 Masses will be different. Chemical properties will be the same.

Worksheet answers Activity 1 (Low demand)

Q1 Similar to Figure 2 on p. 258 of the Student Book.

Q2 a) Neutron

b) Proton

c) Electron

d) Protons and electrons

e) 6 f) 6 g) 6

Activity 2 (Standard demand)

Q1 a) Line labelled A passing straight through.

b) Line labelled B showing beam reflected back.

c) Line labelled C showing a slight deviation through an acute angle.

Activity 3 (High demand)

Q1 Particles in a nucleus – approximately equal numbers of protons and neutrons. Protons shown with + charge

and arrows showing the electrical force of repulsion. Larger arrows showing strong nuclear force, attractive

between all particles, holding the nucleus together inside a spherical outline.

Q2 Chemical reactions depend on the electrons and their arrangement in the atom. For an element all isotopes

have the same electronic structure, and so the same chemical behaviour.



p6_01 The nuclear atom

1 Parts of the atom

1 Label the parts of the atom below, using these words:

protons neutrons electrons nucleus

2 a) What part of the atom has no charge? ………………………………………..

b) What part of the atom has a positive charge? ………………………………..

c) What part of the atom has a negative charge? ……………………………….

d) There are the same number of these two particles in an atom. What are they?

……………………………………………………………………………………..

e) How many protons does the atom have? ……………….

f) How many neutrons does the atom have? ……………...

g) How many electrons does the atom have? ……………...

p6_01 The nuclear atom continued


2 The Rutherford–Geiger–Marsden alpha scattering experiment

The diagram shows the setup for the Rutherford–Geiger–Marsden alpha particle scattering experiment.

1 a) Draw in a path that shows that the atoms were mostly empty space. Label this path A.

b) Draw in a path that shows that the atom has a small massive nucleus. Label this path B.

c) Draw in a path that shows that this nucleus is positive. Label this path C.

3 Understanding the nucleus

1 Imagine that a friend of yours had missed the lesson in which the concept of the strong nuclear force was explained. They’ve asked you to go over it. What diagrams and words could you use to summarise it?

2 Although isotopes have different masses, they have the same chemical properties. Why do you think this is? (Think about which part of the atom is involved in chemical reactions.)



p6_02 Radioactive elements

Resources

Student Book pages 260−261 Interactive Book: Quick Starter ‘Background radiation dose’; Naked Scientist animation ‘Where does radiation come from? Homework pack p6_02

Files on Teacher Pack CD: p6_02_worksheet; p6_02_technician

Equipment for demonstration; Health Protection Agency presentation ‘What is radiation?’ (useful throughout lesson)

Learning outcomes P6.1.1 recall that some elements emit ionising radiation all the time and are called radioactive

P6.1.2 understand that radioactive elements are naturally found in the environment, contributing to background

radiation

P6.1.9 understand that the behaviour of radioactive materials cannot be changed by chemical or physical

processes

Ideas about Science IaS 1.2 we can never be sure that a measurement tells us the true value of the quantity being measured

IaS 1.3 if we make several measurements of any quantity, these are likely to vary




describe how some elements are radioactive and emit ionising radiation

describe how radiation is around us all the time

explain what contributes most to background radiation

Key vocabulary

background radiation ionising radiation radioactive


Students may believe that radioactive decay occurs entirely as a result of human activity. They may find it difficult

to appreciate that decay is a random process and yet follows a predictable overall pattern.


At the beginning of this lesson start the Geiger–Muller tube and counter (see technician sheet p6_02) but have

no radioactive sources out. Note the time when you started the counter going. Do not point this out to students

until the relevant point in the lesson.

Ask the class ‘What is radiation?’ Remind them of their work on electromagnetic radiation in module P2.

Emphasise that radiation is energy that travels through space and that it can be in the form of electromagnetic

waves, or of energetic particles.

Learning activities worksheet p6_02 Low demand Divide students into groups. Ask them to model an atom, with students themselves representing

the sub-atomic particles. Have a commentator for each group explain the relative numbers of protons, neutrons,

and electrons. Then ask them to demonstrate the effects of ionising radiation. One student should be the ionising

radiation, which collides with an electron. The electron moves away from the atom.

Discuss the ion pair that results from ionisation – a positive ion and a negative electron. Both can move off to

interact with something else. Discuss the properties of something that causes ionisation. Explain that ionising

radiation is emitted from radioactive elements. Refer to the Student Book p. 260.

Standard demand Point out the Geiger–Muller tube and counter that you set up earlier. Explain that it is a

detector of ionising radiation. It is counting even though there is no radioactive source out in the lab. Allow the

students to watch it count for a while. Explain that it is detecting background radiation – low-level radiation which is

around us all the time. Ask where this might be coming from.

Ask students to look at Figure 5 on p. 261 of the Student Book. Discuss:

different sources

which sources contribute the most

places where you may get higher background radiation count.

p6_02 Radioactive elements continued


Measure the background count in the lab.

Note the time and stop the counter.

Note the number of counts and the number of minutes the counter has been counting.

Background count (in counts per minute) = count / time in minutes.

Teaching and learning notes: Students will need to know what contributes to background radiation.

High demand Start the counter counting again. Ask students to watch the count increasing and, if there is an

audio output, ask students to listen. They will see (and hear) that the counts do not come regularly. Each is a

radioactive decay but it’s impossible to predict when a particular atom is going to decay.

Explain that the amount of radiation is dependent only on the radioactive element and the amount of it present. It

results from changes in the nucleus of an atom and is unaffected by temperature or other surrounding conditions.

Emphasise the importance in science of making observations and then developing supporting explanations. A lot of

science is not ‘just common sense’ and has involved creative thought and argument to develop ideas.

Plenary suggestions Divide students into groups. Ask them to think of people who may experience a greater level of background

radiation. Ask them to role-play the person and explain who they are and why they are experiencing more

background radiation, e.g. an airline pilot (cosmic rays), someone who lives on Dartmoor (radon from granite), a

radiographer (X-rays), etc.

Student Book answers Q1 (secondary) electron – labelled negative; ion, with nucleus and one fewer orbiting electron – labelled positive.

Q2 Uranium, radium, polonium – these are mentioned in the text, but accept any other correct element.

Q3 Airline pilot, miner, radiographer – and any other correct response.

Q4 Improve ventilation.

Q5 Background levels remain fairly even. These scientists detected a sudden increase in background radiation.

Q6 The random nature of radioactivity means that you need to take any reading over a period of time and then get

an average of counts/min.


Suitable responses might be:

Most background radiation comes from natural sources, such as cosmic radiation and rocks, not man-made

sources.

Although background radiation doesn’t reach harmful levels, radiation can be hazardous and some of the things

that contribute to background radiation, such as weapons testing, certainly are hazardous.

Most isotopes are stable. Furthermore, unstable isotopes eventually reach a stable form.


Q1 Low-level radiation that is around us all the time.

Q2 It is random in that it is impossible to predict when a particular atom will decay or precisely when the next

emission will be detected. However over a period of time these random events will be at a fairly steady level

because there are so many atoms involved.

Q3 Granite rock

Q4 It has been around since the Earth was formed and was present when life evolved, so our bodies can cope with

it.

Q5 14%


Q1 Outer space

Q2 a) Increased it.

b) It has been decreasing.

Q3 Radioactive decay can be accurately measured and it is a property of the material and not the conditions it is

kept in.




Technician sheet

Equipment and materials

GM tube and counter

webcam or visualiser (optional)

Method

The GM counter is left running in the room to record and display the background count. This is to demonstrate that the background radiation is present, is a random process but has a fairly steady level. No sources are needed.

Notes

If the counter has an audible output this will be useful, although not essential. Having a clearly visible display is important though, so a webcam or visualiser may be useful.




1 The things people say

Three students are talking about the lessons they’ve been doing on radioactivity. These are the things they said. Explain what you think about their ideas.

A: ……………………………………………………………………………………………………..

…………………………………………………………………………………………………………

…………………………………………………………………………………………………………

…………………………………………………………………………………………………………

B: ……………………………………………………………………………………………………..

…………………………………………………………………………………………………………

…………………………………………………………………………………………………………

…………………………………………………………………………………………………………

C: ……………………………………………………………………………………………………..

…………………………………………………………………………………………………………

…………………………………………………………………………………………………………

…………………………………………………………………………………………………………

This radiation is creepy – it just shows what scientists get up to. If they hadn’t been building nuclear power stations and bombs, we wouldn’t have any of this.

I think it’s worrying – all these atoms decaying. If this is true everything’s just falling apart. We’ll end up with no proper materials, just loads of atomic particles.

I don’t know why we’re spending time on this – you can’t see any of this radiation so it’s not going to hurt us.

A

B

C

p6_02 Radioactive elements continued


2 Background radiation

1 Explain what is meant by ‘background radiation’.

2 Alice notices that when the GM counter is monitoring background radiation the count per minute rises and falls a little, but doesn’t vary much. She doesn’t understand why the teacher describes it as a random process. Explain why it is random.

3 The dark spots on this map show very high levels of background radiation in Britain. What is there to cause this higher background count?

Background radiation in Britain

4 Why are we not too concerned about background radiation?

5 We use radioactive sources in medicine. How much does this contribute to background radiation?

3 Radioactivity

1 Cosmic rays contribute about 12% to background radiation. Find out where cosmic rays come from.

2 In the 1950s test explosions of atomic bombs were carried out above ground.

a) What will that have done to background radiation at the time?

b) How has that contribution changed over the years since then?

3 Marie Curie said:

My experiments proved that the radiation of uranium compounds can be measured with precision under determined conditions, and that this radiation is an atomic property of the element of uranium. Its intensity is proportional to the quantity of uranium contained in the compound, and depends neither on conditions of chemical combination, nor on external circumstances, such as light or temperature.

Identify the key ideas in this text about radioactive materials.



p6_03 Three types of ionising radiation

Resources

Student Book pages 262−263 Interactive Book: Quick Starter ‘Alpha particles’; Quick Starter ‘Gamma rays’; Matching pairs activity ‘Alpha’ Homework pack p6_03

Files on Teacher Pack CD: p6_03_worksheet; p6_03_technician

Equipment for demonstrations

Learning outcomes P6.1.10 recall that three types of ionising radiation (alpha, beta and gamma) are emitted by radioactive materials

and that alpha particles consist of two protons and two neutrons, and that beta particles are identical to

electrons

P6.1.11 recall the penetration properties of each type of radiation

Ideas about Science IaS 1.6 if a measurement lies well outside the range within which the others in a set of repeats lie, or is off a graph

line on which the others lie, this is a sign that it may be incorrect. If possible, it should be checked. If not, it should

be used unless there is a specific reason to doubt its accuracy


recall the three types of ionising radiation emitted by radioactive materials

distinguish between alpha, beta and gamma radiation by their properties

Key vocabulary

alpha radiation beta radiation gamma radiation nucleon number


Students may find it difficult to understand that ionising radiation comes from the nucleus.


Explain to students about safety procedures when dealing with radioactive sources and that the procedures are

given by responsible organisations. Be sure to follow the guidance for using radioactive sources in schools given

by CLEAPSS or the Institute of Physics.

Use a spark counter to demonstrate alpha radiation and explain that this shows how these particles are capable

of ionising other materials but that their range is limited. See the technician sheet p6_03.

Learning activities worksheet p6_03 Low demand Tell students that we have just used and detected one type of ionising radiation, but Ernest

Rutherford in his experiment with a magnet found that there were three different types. Use p. 262 in the Student

Book to illustrate and discuss Rutherford’s experiment.

Explain to students that since only charged particles are detected by a magnetic field, two of the rays must consist

of charged particles. They must be oppositely charged because they are deflected in different directions. Alpha

radiation is positively charged and beta radiation is negatively charged. Gamma radiation is not deflected by the

magnetic field, so it is not charged. Remind students that they have already met gamma radiation as a high-

frequency electromagnetic wave.

Explain that the three types of radiation have different ionising abilities. Alpha is a good ioniser as it is a relatively

massive particle.

Standard demand Explain that only alpha radiation, a good ioniser, produces sparks on the spark counter

demonstrated at the start of the lesson, but all types of radioactive radiation can be detected with a GM tube. Tell

them that we are now going to investigate the properties of alpha, beta and gamma radiation. Students can use the

worksheet to record observations.

Demonstrate the range of alpha, beta and gamma in air (see technician sheet p6_03). Set up the GM tube in a

clamp and connect it to a counter. Take a background count. Fix the source in its holder and clamp it next to the

GM tube (record this distance as 0 cm). Record 30-second counts at several increasing distances from the GM

tube, as described on the technician sheet, either until the count rate falls to the background count rate (giving you

the range in air of the alpha and beta), or you reach the end of the bench (gamma). Note that alpha particles travel

about 3 cm in air, beta can still be detected about a metre away and gamma is not stopped by air at all. It is worth

p6_03 Three types of ionising radiation continued


telling students that the particles are stopped by air because they collide with air molecules and lose energy. They

just stop; they do not leave the air radioactive. Ask students to summarise the key points in their notes.

Then demonstrate what will stop the ionising radiation (again see the technician sheet). Move the source and GM

tube so that a reasonable count rate is achieved (about 2–5 cm, depending on the source) and place paper,

cardboard, thin aluminium sheet and lead sheet in turn between the source and the GM tube. Note when the count

falls to near background count. Note that alpha is stopped by paper, beta by about 3 mm aluminium and gamma by

3 cm lead. Point out the increasing densities of the barriers.

Discuss consequences of these different penetrating abilities. For example, alpha cannot get through skin but if you

breathe it in, say with radon gas, it will cause damage by ionisation inside the body. Ask students to summarise the

key points in their notes. Discuss safety procedures in school labs in the light of these results.

Teaching and learning notes: Students will need to know the ionising and penetrating properties of alpha, beta

and gamma radiation.

High demand Ask Higher tier students ‘What are alpha and beta radiation?’. Explain that Henri Becquerel is

credited with the discovery of beta particles. In 1900, he showed that beta particles were identical to electrons. In

1907, Ernest Rutherford and Thomas Royds finally proved that alpha particles were helium ions. If there is time, or

for homework, students could research these discoveries.

Use p. 263 in the Student Book and questions 5 and 6 to make the points that:

mass number is the number of protons and neutrons in the nucleus

proton number is the number of protons in the nucleus.

Explain nuclear symbol notation and emphasise that radioactivity relates to the nucleus and particles found within

in the nucleus –the nucleons. Beta particles are not orbital electrons, but come from the nucleus when a neutron

changes into a proton.

Plenary suggestions Ask students to write some safety rules for school based on what they have met this lesson.

Student Book answers Q1 Charged particles are deflected by magnetic fields. Alpha and beta have opposite charges so will be deflected

in opposite directions. Gamma has no charge and will not be deflected by the magnetic field.

Q2 Alpha particles are by far the most massive; the heavier the particle the better the ioniser.

Q4 It has been lost in collisions with air molecules.

Q5 The beta particle has zero mass and a charge of –1; the e is the symbol for an electron.

Q6 C86 C126 C14

6 C226


Alpha Beta Gamma

What particle or wave? particle (helium nucleus) particle (electron) electromagnetic wave

Mass? 4 0 0

Charge? +2 –1 0

Range in air? 3 cm 1 m not stopped in air

Stopped by? paper 3 mm aluminium 3 cm lead or 3 m concrete

Ionising ability? good not as good as alpha poor

Deflected by a magnetic field? yes yes no

Deflected by an electric field? yes yes no


Q1 Lead. All ionising radiation is stopped by lead.

Q2 Positioned class at least 1 m away; never directed the source towards the class.


Q1 Alpha particles are 2 protons and 2 neutrons: a helium nucleus. Beta particles are electrons and are very light

(massless compared with protons and neutrons).

Q2 A neutron decays to form a proton and an electron. The electron is ejected.




Technician sheet


Starter demonstration: Spark counter detection of alpha radiation

EHT supply 0–5 kV

spark counter

forceps

sealed pure alpha source: plutonium-239 (239Pu), 5 µCi (if available) or sealed (semi-pure) alpha source: americium-241 (241Am), 5 µCi

Main demonstration: Investigating the range and penetration of alpha, beta and gamma radiation

GM tube and counter/scaler

metre rule

sealed pure alpha source: plutonium-239 (239Pu), 5 µCi (if available) or sealed (semi-pure) alpha source: americium-241 (241Am), 5 µCi

sealed pure beta source: strontium-90 (90Sr), 5 µCi

sealed gamma source: radium-226 (226Ra), 5 µCi

set of absorbers (e.g. paper, cardboard, thin aluminium and lead sheet of varying thickness)

holder for radioactive sources

Method

Starter demonstration: Spark counter detection of alpha radiation

1 Connect the positive, high-voltage terminal of the spark counter (joined to the wire that runs under the gauze) to the positive terminal of the EHT supply (without its 50 MΩ safety resistor).

2 Connect the other terminal on the spark counter to the negative terminal of the power supply and connect this terminal to earth.

3 Turn the voltage up slowly until it is just below the point of spontaneous discharge. This is usually between 3000 V and 4500 V.

p6_03 Technician sheet continued


4 Use forceps to hold a radioactive source over the gauze. You should see and hear sparks jumping between the gauze and the high voltage wire underneath.

5 Move the source slowly away from the gauze and note the distance at which it stops causing sparks.

6 The alpha particles are ionising the air. The strong electric field causes an avalanche of ions and the subsequent sparks.

Notes

Health and Safety

Read the school’s guidance for using radioactive sources. Free guidance is available from CLEAPSS: refer to Guide L93 on the safe use of radioactive sources, at www.cleapss.org.uk.

Beware the high voltage.

A school EHT supply is limited to a maximum current of 5 mA, which is regarded as safe. For use with a spark counter, a 50 MΩ safety resistor should be included in the circuit. This reduces the maximum shock current to less than 0.1 mA.

Although the school EHT supply is safe, shocks can make the demonstrator jump. It is therefore wise to see that there are no bare high voltage conductors. Use female 4 mm connectors where required.

Other notes

The spark counter consists of a metal gauze with a wire running underneath. Philip Harris calls it a ‘spark discharge apparatus’.

Any kink or bend in the wire in the counter is liable to cause a spark discharge at that point. If that happens, the wire should be replaced.

A continuous spark (which will very soon damage the wire) shows the voltage is too high.

The spark counter should be dust-free. Dust around the stretched wire can usually be blown away.

The gauze on top is connected to the earth on the EHT supply as a safety precaution.

Method

Main demonstration: Investigating the range and penetration of alpha, beta and gamma radiation

Range

1 Set up the GM tube in a clamp and connect it to a counter. Lay a metre rule on the bench for measuring the distance between source and GM tube. Leave at least 1 m of bench available. Take a background count.

2 Fix the source in its holder and clamp it next to the GM tube (record this distance as 0 cm). Record 30-second counts at several increasing distances from the GM tube.

3 For alpha radiation, record the 30-second count at 0 cm, 1 cm, 2 cm, 3 cm and 4 cm from the source.

4 For beta radiation, record the 30-second count at 20 cm intervals, i.e. 0 cm, 20 cm, 40 cm, etc. from the source.

5 For gamma radiation, record as for beta.

Penetration

1 Set up the source 2–5 cm from the GM tube so a reasonable count rate is recorded. This distance will depend on which source you are using.

2 Starting with paper, place the different absorbers between the source and the counter and observe the effect.

3 Note when the count falls to background levels – this is where the radiation from the source has been stopped by the absorber.

p6_03 Technician sheet continued


Notes

Health and Safety

Read the school’s guidance for using radioactive sources. Free guidance is available from CLEAPSS: refer to Guide L93 on the safe use of radioactive sources, at www.cleapss.org.uk.

Students should be out of the line of the radiation path and should remain at least one metre away from the source.

Notes

Note that 5 µCi is equivalent to 185 kBq.

GM tubes are very delicate, especially if they are designed to measure alpha particles. The thin, mica window needs a protective cover so that it is not accidentally damaged by being touched.

Some education suppliers now stock all-in-one GM tubes with a counter.

Education suppliers stock a set of absorbers that range from tissue paper to thick lead. This is a useful piece of equipment to have in your prep room. You can make up your own set. This should include: tissue paper, plain paper, some thin metal foil (e.g. cigarette paper, wrapping from a chocolate from an assortment box and a small piece of gold leaf).




1 Properties of ionising radiation

Your teacher will conduct some demonstrations showing you some of the properties of ionising radiation.

Use pages 262–263 in your Student Book and your observations from the demonstrations to complete the table below.

Nature and properties of ionising radiation

Alpha Beta Gamma

What particle or wave?

Mass?

Charge?

Range in air?

Stopped by?

Ionising ability?

Deflected by a magnetic field?

Deflected by an electric field?

p6_03 Three types of ionising radiation continued


2 Demonstrating properties of ionising radiation

1 Suggest a material to line the box we keep the radioactive sources in schools. Give a reason for your choice.

2 How did the teacher ensure that no radiation reached the class during the demonstrations?

3 Were there any results that didn’t fit the expected pattern?

4 How were they dealt with?

3 What are alpha and beta radiation? (Higher tier)

1 What makes alpha particles so much heavier than beta particles?

2 Electrons do not exist in the nucleus. Explain what happens in the nucleus to emit an electron in beta emission.



p6_04 Radioactive decay

Resources

Student Book pages 264−265 Interactive Book: Naked Scientist animation ‘What happens when radioactive elements decay?’

Homework pack p6_04


Equipment for starter demonstration: bucket of water and sponge

Learning outcomes P6.1.12 describe radioactive materials in terms of the instability of the nucleus, radiation emitted and the

element left behind

P6.1.13 complete nuclear equations for alpha and beta decay

P6.1.14 understand that, over time, the activity of radioactive sources decreases

Numeracy focus: Understanding nuclear decay equations (Higher tier).

ICT focus: Accessing a computer simulation of radioactive decay.


understand that the activity of radioactive sources decreases with time

describe how unstable nuclei decay to form new nuclei

Key vocabulary

activity radioactive decay decay chain


Some students may confuse radioactive decay with biological decay.

Higher-tier students need to be able to deal with nuclear equations; some may find these complex and confusing.


Show students a bucket of water and a sponge. Immerse the sponge in the water and squeeze the air out of it.

Raise the sponge above the water so that water runs out of it. Ask students to consider what will happen to the

rate of flow of water over the next 10 minutes. Point out that we can describe the trend with much more

confidence than we can predict when the last drop of water will have dropped out of it.

Learning activities worksheet p6_04 Low demand Ask students how they think that scientists can use radioactive decay to, for example, put a date on

the remains of a Viking longship. Explain that, being made of wood and therefore containing carbon, it is possible

to measure the amount of the radioactive isotope carbon-14 still present.

Explain that the carbon is decaying into another element and that by measuring how much of the carbon is still

radioactive and comparing it with the proportion in a living tree, the age can be estimated.

The key points to get across here are that:

Radioactive elements decay into other elements.

The more radioactive element present, the greater the amount of radiation given off.

‘Activity’ is a scientific word for the amount of radiation emitted. It is usually measured in the lab in counts per

second or per minute.

Activity decreases with time.

Teaching and learning notes: Emphasise that the radioactive isotope hasn’t been introduced by scientists but is

naturally present. Explain that this process isn’t always of use – dating a 1000-year-old ship with carbon is possible

but using the same isotope with, say, dinosaur remains, wouldn’t work. The time involved is too great, and that

isotope would have already decayed.

Standard demand Discuss what happens to the nucleus when alpha, beta or gamma radiations are emitted,

giving examples. Use p. 265 of the Student Book to help the discussion.

Point out that alpha and beta decay both result in another element being formed (the proton number changes) but

gamma emission will just reduce the energy in the atom and not change its element. It often accompanies alpha

and beta decay as they leave the atom in an excited (i.e. energetic) state.

p6_04 Radioactive decay continued


High demand (Higher tier) Explain that radioactive decay often continues to form a chain, as the nucleus formed

from one decay is also unstable, so decays to another nucleus, and so on. Students can do question 1 of the third

worksheet activity on the uranium decay chain.

Introduce nuclear decay equations using Figures 4 and 5 on p. 265 of the Student Book. Students should do

Questions 5 and 6 on p. 265 and question 2 of activity 3 on the worksheet for practice.

Teaching and learning notes: Emphasise from the decay chain that at any one time all the radioactive isotopes

will be decaying, although they are present in very different amounts. However, the chain eventually ends with a

stable element.

Plenary suggestions Ask students to look at the picture of the alchemist’s laboratory on p. 264 of the Student Book. How does the

alchemist’s dream compare with radioactive decay? Ask for suggestions and discuss.

Student Book answers Q1 The activity of the spent fuel rods has decreased enough so it is safe to move them.

Q2 There is no change in proton number.

Q3 Alpha; the mass has decreased by 4.

Q4 Decreases the energy in the new nucleus.

Q5 Rn He Ra 22286

42

22688 +→

Q6 Xe e Ra 13154

01-

13153 +→


Q1 alpha; 2; neutrons; 4

Q2 beta; electron; the same

Q3 particles; new


Q1 Alpha and beta decay both involve changing the number of protons in the nucleus, which changes the element

from one to another (though gamma decay does not).

Q2 There appears to be evidence of chemicals being heated strongly, being blasted with air, being mixed with

other chemicals and being made into solutions.

Q3 Radioactive decay occurs due to changes in the nucleus; none of the alchemist’s processes would do that.


Q1 Uranium-238 (alpha) → thorium-234 (beta) → protactinium-234 (beta) → uranium-234 (alpha) → thorium-230

(alpha) → radium-226 (alpha) → radon-222 (alpha) → polonium-218 (alpha) → lead-214 (beta) → bismuth-214

(beta) → polonium-214 (alpha) → lead-210 (beta) → bismuth-210 (beta) → polonium-210 (alpha) → lead-206

Q2 a) He Th U 42

23490

23892 +→

b) e N C 01

147

146 −

+→

c) e Pa Th 01

23491

23490 −

+→

d) e CmAm 01

24496

24495 −

+→

e) He Bi At 42

20983

21385 +→



p6_04 Radioactive decay

1 Alpha and beta decay

The diagrams show how the masses of elements change when they decay by emitting an alpha particle or a beta particle.

Complete these sentences.

1 In …………… decay, the radioactive nucleus gives out an alpha particle, which is

made up from ….... protons and 2 ……………

The new element has a mass which is ……….. less than the original nucleus.

2 In …………. decay, the radioactive nucleus gives out a beta particle, which is an

………………… from the nucleus.

The new element has ………………………… mass as the original nucleus.

3 Both alpha and beta decay release ……………………..

Both alpha and beta decay result in the formation of a …………. element.



2 The alchemist’s dream

1 Is it true to say that radioactive decay involves one element changing into a completely different one?

2 Study Figure 1 on page 264 of the Student Book and look at the processes that the alchemists are using to try to change the materials. Make a list of these.

3 Suggest whether any of these processes are likely to bring about the changes that take place in radioactive decay.

3 Radioactive decay chains

When an alpha particle is emitted the mass number decreases by 4 and the proton number decreases by 2.

When a beta particle is emitted the mass number stays the same but the proton number increases by 1.

The diagram on the next sheet shows the uranium-238 decay chain. It represents all the changes from element to element when uranium-238 decays, finally forming stable lead.

1 Between each change of element on the diagram, write whether an alpha or a beta particle was emitted.

2 Write nuclear decay equations to show these reactions:

a) the alpha decay of uranium-238 to produce thorium-234

b) the beta decay of carbon-14 to produce nitrogen-14

c) the beta decay of thorium-234

d) the beta decay of americium-244

e) the alpha decay of astatine-213.

You will need to consult a Periodic Table (page 309 of the Student Book).





p6_05 Half-life

Resources

Student Book pages 268−269 Interactive Book: Drag and drop activity ‘Half-lives’ Homework pack p6_05

Files on Teacher Pack CD: p6_05_worksheet; p6_05_practical

Scissors; large sheets of plain paper; plastic cups; about 50 dice

Learning outcomes P6.1.15 understand the meaning of the term half-life

P6.1.16 understand that radioactive elements have a wide range of half-life values

P6.1.17 carry out simple calculations involving half-life

Ideas about Science IaS 1.4 the mean of several repeat measurements is a good estimate of the true value of the quantity being

measured

IaS 1.5 from a set of repeated measurements of a quantity, it is possible to estimate a range within which the true

value probably lies

IaS 2.1 it is often useful to think about processes in terms of factors which may affect an outcome (or input

variables which may affect an outcome variable)

IaS 2.6 to investigate a claim that a factor increases the chance (or probability) of an outcome, scientists compare

samples (e.g. groups of people) that are matched on as many other factors as possible, or are chosen randomly so

that other factors are equally likely in both samples. The larger the samples, the more confident we can be about

any conclusions drawn

Numeracy focus: Plotting, drawing and interpreting graphs from own and secondary data.


understand the meaning of half-life in radioactive decay

understand that radioactive elements have a wide range of half-lives

Key vocabulary

activity daughter product decay chain half-life


Students may find it difficult to understand that each half-life is the time for the radioactivity to drop to half its

previous value, but since the rate at which the activity decreases becomes less, two half-lives don’t add up to the

total period of time for which the material is radioactive.


Draw a picture on the board of a pond and, some way from the pond, draw a frog. Tell students that the frog is

dying, but wishes to do so in the water. It summons up its remaining energy and manages to jump half the way to

the pond in one leap. Its next leap is weaker and it only covers half the remaining distance; the next leap is

shorter again, and only covers half the remaining distance again. Ask the students to work out how many jumps it

will take, if the pattern continues, to reach the pond. Explain, after discussion, that, theoretically, it will never

reach the edge, even though it gets closer and closer (accept that in practice it would be so close it would tumble

in).

Say that radioactive decay is rather like this. Explain that the decay emissions from a source become less and

less as time goes by, but never completely finish.

Learning activities worksheet p6_05 + practical p6_05 Low demand To simulate how the number of radioactive atoms decreases with time, ask students to do activity 1

on the worksheet. Discuss the half-life of a radioactive material by going through the section on p. 268 of the

Student Book. Students can do Q1 and Q2 on p. 268.

Teaching and learning notes: Students need to understand that the number of radioactive nuclei present and the

activity both decrease with time, and the meaning of half-life.

Standard demand Give out the practical sheet. This allows students to model the random nature of radioactive

decay with dice, and to draw a decay graph that illustrates half-life. As this needs about 50 dice it may need to be

done as a demonstration. Throw the dice, remove the sixes, count and record the remaining dice and repeat. Ask

p6_05 Half-life continued


students to describe the trend in the number of remaining dice each time. They should analyse the results

graphically as outlined on the practical sheet.

Explain that the sixes represent atoms that have decayed. Draw out through questioning that this is why the activity

becomes less – there are fewer remaining atoms of the original material left to decay.

There can then be a useful discussion about repeating experiments; students can be challenged to explain whether

repeating this would give results that were the same, similar, or quite different, and how they could try to get to a

‘true value’.

Remind students that this is, of course, only a model but one that can be used to emphasise particular features of

radioactive decay. Point out that the way scientists have developed ideas about half-life and rates of decay is to

conduct large numbers of experiments with different radioactive materials. The more experiments with the more

different materials used to produce data, the more confident we can be about the underlying patterns.

Students can do Q3 and Q4 on p. 269.

High demand Higher-tier students need to be able to do calculations involving half-life. Q5 and Q6 on Student

Book p. 269 and activity 3 on the worksheet provide practice. It is worthwhile emphasising that the half-life is a

fundamental characteristic of an element. It isn’t dependent upon the conditions under which the material is kept,

nor (and this may be harder for some students to accept) upon the quantity. Emphasise that the quantity of the

material present will affect the count rate, but not the half-life.

Teaching and learning notes: Students need to be able to calculate activity after a given length of time.

Plenary suggestions Show students a smoke detector and explain that it has in it an americium source. Americium-241 has a half-life of

432 years. Say that if they were to be injected with a radioactive tracer, such as carbon-11 this would enable

images of functions in their body to be displayed. It has a half-life of around 20 minutes. Ask students to suggest

why each of these half-lives makes that material suitable for its intended purpose.

Student Book answers Q1 Iron as it has a much shorter half-life.

Q2 Radioactive isotopes decay into another element so after a time there will be a mixture of the original element

and its daughter products.

Q3 The half-life is long enough (5730 years) so that enough is present in archaeological samples for it to be

measured.

Q4 In 60 minutes the sample will have gone through 4 half-lives. The count rate will be reduced by ½ × ½ × ½ × ½

= 1/16 so the activity now is 16 000/16 = 1000 counts per second.

Q5 400 → 200 → 100 → 50 represents 3 half-lives, in a time of 75 minutes. The half-life is 15 minutes.

Q6 Start at 160 counts/minute. Same half-life, so after 2 days the count will be 80 counts/min. After 4 days the

count rate will be 40 counts/min, and so on.

Worksheet answers Activity 2 (Standard demand)

Uranium-235 … will remain radioactive for a very long time to come.

Carbon-14 … can be used to put an accurate age on organic remains in archaeological sites.

Fluorine-18 … can be made without the body having radioactive materials inside for longer than is necessary.

Strontium-90 … can continue to be used by schools for a reasonably long period of time.


Q2 2.5 min

Q3 3 half-lives

Q4 1/8

Q5 4.5 counts/second



p6_05 Half-life simulation

P Modelling radioactive decay with dice

Objectives

In this activity you will:

model the process of radioactive decay.


about 50 dice • plastic cup • plastic tray

Method

1 Shake the dice into the tray.

2 Count the number of dice showing a six. These represent decayed nuclei. Put them to one side.

3 Count the number of dice remaining and record in the table.

4 Repeat until you have around eight sets of data.

Results

Number of throw Number of dice remaining

0

1

Analysis

1 Draw a graph of x = number of throw against y = number of dice remaining.

2 Draw a smooth curve through the points.

Questions

1 How many throws does it take to halve the number of dice?

2 How many throws does it take to go from half to a quarter the number of dice?

3 What do you notice about these two values?



p6_05 Half-life

1 Simulating radioactive decay

1 Cut out the rectangle of dots on the third page of this worksheet. Then cut the dotted rectangle in half.

2 Take one of the halves and count the number of spots.

3 Write the number on this half and stick this half piece of dotted paper at the top left-hand edge of a large piece of plain paper.

4 Cut the remaining dotted paper in half, count the spots, write the number on this piece and stick it next to the first portion on the plain paper.

5 Repeat until only one spot remains.

This is a model of radioactive decay. The number of spots represents the number of decayed nuclei and so the level of emission from the radioactive source, or its activity.

Write two or three sentences about how the activity of a radioactive source changes over time.

…………………………………………………………………………………………………………

…………………………………………………………………………………………………………

…………………………………………………………………………………………………………

…………………………………………………………………………………………………………

…………………………………………………………………………………………………………

2 Comparing half-lives

Match up these half sentences.

Uranium-235 has a half-life of 700 000 000 years. This means that some of the waste from some types of nuclear power station …

… can continue to be used by schools for a reasonably long period of time.

Carbon-14 has a half-life of 5760 years. This means it …

… can be made without the body having radioactive materials inside for longer than is necessary.

Fluorine-18 has a half-life of 109 minutes. It is injected into the body to allow scanning of internal organs. The short half-life means that scans …

.… can be used to put an accurate age on organic remains in archaeological sites.

Strontium-90 is used in school science laboratories to demonstrate beta emissions. It has a half-life of 28 years, which means that the same source …

… will remain radioactive for a very long time to come.



3 Half-life of barium-137 (Higher tier)

This graph was obtained when the activity of a sample of barium-137 was monitored for 30 minutes.

1 Draw a smooth curve through the points.

2 Calculate the half-life of barium-137.

3 How many half-lives will have passed after 7.5 minutes?

4 What is the fraction of the original sample is now left?

5 Use your graph to determine the activity after 7.5 minutes.





p6_06 Hazards of ionising radiation

Resources

Student Book pages 270−271 Homework pack p6_06


Learning outcomes P6.2.1 understand that ionising radiation can damage living cells and these may be killed or may become

cancerous

P6.2.2 understand that ionising radiation is able to break molecules into bits (called ions), which can then take

part in other chemical reactions

P6.2.4 recall that radiation dose (in sieverts) (based on both amount and type of radiation) is a measure of the

possible harm done to your body

P6.2.5 interpret given data on risk related to radiation dose

Ideas about Science IaS 2.3 if an outcome occurs when a specific factor is present, but does not when it is absent, or if an outcome

variable increases (or decreases) steadily as an input variable increases, we say that there is a correlation between

the two


samples (eg groups of people) that are matched on as many other factors as possible, or are chosen randomly so





IaS 5.1 everything we do carries a certain risk of accident or harm. Nothing is risk free. New technologies and

processes based on scientific advances often introduce new risks

IaS 5.2 we can sometimes assess the size of a risk by measuring its chance of occurring in a large sample, over a

given period of time

IaS 5.3 to make a decision about a particular risk, we need to take account both of the chance of it happening and

the consequences if it did

Numeracy focus: Using ideas about probability in the context of risk.

Literacy focus: Completing cloze passages, conducting and summarising research and writing explanations.

ICT focus: Using the internet to research information about the nuclear disaster in Japan in 2011.


describe how ionising radiation can damage living cells

understand the unit of radiation dose

assess the risks of ionising radiation

Key vocabulary

equivalent dose ion mutation sievert


Students may not appreciate that there is no such thing as a safe level of ionising radiation.


Show a news item on the whiteboard about the Fukushima disaster. Discuss why people living within 20 km had

to be moved from their houses.

Assess how much students already know about the effects of increased radiation.

Learning activities worksheet p6_06 Low demand Discuss the various possible effects on the body when a person is exposed to radiation. Make use

of Figure 2 on p. 270 of the Student Book. Ask students to identify what the various outcomes are of a cell being

irradiated. Draw together key ideas and jointly draft a summary for recording in notes.

Then ask students to do activity 1 from the worksheet, which involves working independently on a cloze passage to

reinforce these ideas.

p6_06 Hazards of ionising radiation continued


Teaching and learning notes: Students need to be able to describe how ionising radiation can damage living

cells. They need to know what the hazards are and then be able to assess the risk level before making an informed

decision.

Standard demand A common question is, what is the most damaging type of radiation? Ask students for their

opinions. Use Student Book p. 271 to guide answers this question. People working with ionising radiation need to

be able to quantify exposure to radiation in order to assess the level of risk. It is also important for all people to be

able to make an informed decision about where to live, whether nuclear power stations pose a risk, how medical

procedures involving radiation may affect us.

Introduce the sievert (Sv) and equivalent dose (see p. 271 for definitions). Discuss the relative doses from

background, airline travel, etc. and how much higher the dose is that will cause harm.

Emphasise that exposure to ionising radiation is all about assessing the risk. People are not destined to get cancer

but with information about the hazard, which involves intensity of radiation and length of exposure, then informed

estimates of the risk can be made. Emphasise that changing factors affects the probability. Deciding on what is an

acceptable risk is something that scientific evidence can inform. It should be informed by both the likelihood and

the seriousness of the possible harm.

Explain that students are going to be finding out more about the disaster at the Japanese nuclear power station

and researching key points. Give students worksheet activity 2. Explain how they are to conduct the research, draw

attention to the key features to cover, and suggest how they could summarise their findings.

Teaching and learning notes: Have a feedback session after about 15 minutes of research to ensure students

are on the right track.

High demand (Higher tier) Explore with students the idea that ions formed by the actions of ionising radiation are

then available to take part in other chemical reactions. Draw attention to Figure 3 in the Student Book p. 271 and

point out that a number of elements present in the body in large proportions (oxygen, hydrogen, nitrogen and

carbon) are particularly susceptible to ionisation. Explain how a charged ion can disrupt the chemistry of a

molecule. Ask students to answer Q5 and Q6 on p. 271.

Activity 3 on the worksheet asks students to construct an explanation of key points on this topic; it is designed to

provide an opportunity to develop the skills of extended writing.

Teaching and learning notes: Encourage students to peer-assess their work and provide each other with positive

feedback.

Plenary suggestions Refer to the ‘teaser’ introduction on p. 270 of the Student Book. In the 1950s and 1960s it was commonplace for

shoe shops to have X-ray machines so that customers could see if shoes fitted them. Allowing for 0.005 mSv per

X-ray, ask students to estimate the typical annual dose. Draw attention to the assumptions used, such as how

many feet X-rayed, how many shoes tried, how many purchases per year. Point out that even though the dosage is

small, for some people the exposure could become quite high.

Student Book answers Q1 An electron and a positive ion.

Q2 Not inevitable. The cells can sometimes repair the damage if it is not too great.

Q3 Background radiation is 2 mSv per year. The dose at the perimeter was much higher at 11.9 mSv per hour. It

would not take many hours for the exposure at Fukushima to cause death.

Q4 It can be breathed into the body. Alpha radiation is a good ioniser and would produce many electron–ion pairs

that would interfere with the cell’s molecules.

Q5 Higher; CT scan dose equivalent 10 mSv per hour much greater than air crew dose equivalent 9 mSv per year.

Q6 When the cells have mutated the effects may not become evident for many years.


Ionising radiation is radiation which, when it makes contact with a molecule, breaks it into bits called ions. Ions are

charged. If the radiation hits a living cell it can damage or even kill it. Sometimes the damage can be repaired, but

sometimes the damage causes the cell to mutate. This can cause cancer.

The greater the intensity of the radiation, the more likely it is that there will be some damage to living tissues. The

radiation may come from man-made sources, such as medical X-rays, or from natural sources such as cosmic

radiation.



p6_06 Hazards of ionising radiation

1 How ionising radiation affects living cells

Use words from the word box to complete this passage.

………………. radiation is radiation which, when it makes …………. with a molecule,

breaks it into ………. called ions. …….. are charged. If the radiation hits a …………. cell

it can damage or even ……... it. Sometimes the ……… can be repaired, but …..………

the damage causes the cell to mutate. This can cause ………..

The ………….. the ................... of the radiation, the more likely it is that there will be some

damage to living …………...... The radiation may come from man-made ………….., such

as …………………………………….., or from natural sources such as …………. radiation.

2 Nuclear disaster

In March 2011 there was a disaster at the nuclear power station at Fukushima in Japan, causing widespread damage, contamination, illness and death. Research the story and assemble a summary of the key points, including responses to these questions.

What were the causes of the disaster?

What were the effects of the disaster?

What role did ionising radiation have in this incident?

3 Ionisation in the body

Plan and write a short account of the effect of ionising radiation on living cells. Your account should include:

a brief explanation of what ionising radiation is

a description of the effect of the radiation

identification of the possible outcomes of radiation exposure.

When you have drafted your account, ask another student to review it and provide feedback.

bits cancer contact cosmic damage greater

ionising ion kill living sometimes

sources tissues medical X-rays intensity



p6_07 Useful radiation

Resources

Student Book pages 272−273 Interactive Book: icould career video ‘Applications of radioactivity: How useful is radioactivity?’

Homework pack p6_07


Learning outcomes P6.2.3 recall and explain how ionising radiation can be used:

a. to treat cancer

b. to sterilise surgical instruments

c. to sterilise food

d. as a tracer in the body

Ideas about Science IaS 5.4 to make a decision about a course of action, we need to take account of both its risks and benefits, to the

different individuals or groups involved

IaS 5.5 people are generally more willing to accept the risk associated with something they choose to do than

something that is imposed, and to accept risks that have short-lived effects rather than long-lasting ones

Literacy focus: Reading text and interrogating it to extract information.

ICT focus: Accessing relevant information from the internet to support research.


recall how ionising radiation can be used to our benefit

Key vocabulary

radioactive tracer radiotherapy sterile


Students may have some misconceptions about ionising radiation, such as thinking that anything exposed to

radiation then becomes radioactive.


Tell students about the way in which in the past radium was used in clock faces to make the hands and numbers

visible in the dark. Explain that radium is radioactive and that bombardment of the paint by the emissions caused

a glow.

Ask students to suggest why this was done and why it was discontinued. This could be enhanced with images of

typical clock faces (search on ‘radium clock face’) and of the women who were affected (search on ‘radium girls’).

Learning activities worksheet p6_07 Low and standard demand Introduce some applications of radioactive materials and ask students to read the

section on destroying cells on Student Book p. 272, and then, move on to the section on detecting brain tumours.

Depending on the literacy level of the students this may need some mediation and explanation. Bring in some

discussion of the IaS listed above when talking about treating or diagnosing cancer using ionising radiation.

Ask students to identify key points from this and to suggest an effective way of summarising the key points

(possibly using simple sketches) for recording.

The main part of this lesson is taken up with structured research. Worksheet activities 1 and 2 can be used to guide

students. The following are some suggested websites, but check them first.

www.cancer.gov and search for radiation therapy

www.physlink.com go to Education and search for sterilising food

www.radiologyinfo.org and search for nuclear medicine

Students should take notes of their findings and, if time allows, prepare a poster illustrating the uses they have

found out about.

Teaching and learning notes: Have a feedback session after 15 minutes of internet research to ensure students

are on the right track.

p6_07 Useful radiation continued


High demand Higher-attaining students could be asked to prepare a presentation on one or more uses of

radiation. The presentation should make it quite clear:

what the scientific ideas are that are being applied

the particular advantage that it offers

how the risks are assessed and managed.

Note that Higher-tier student need to be able to explain the use of the different ionising radiations for different uses

– see the final section of Student Book p. 273.

Plenary suggestions Ask students to work in pairs to summarise three key points about what they have learned during this lesson that

they didn’t know previously. Collate points to produce a summary and allow opportunity for the recording of key

points.

Student Book answers Q1 a) So that they do not kill healthy cells as well as the cancer cells.

b) It would not penetrate the skin.

Q2 Quicker, instruments stay sterile until the packet is opened, can sterilise plastics and heat-sensitive materials.

Q3 When it is a fresh food that has a short shelf-life, or a fresh food that is transported a long way between grower

and shop.

Q4 Inject tracer; allow time for the tracer to accumulate in the brain; use a gamma camera and computer to build

up a 3D picture of the brain and tumour.

Q5 A gamma emitter as it will be able to get out of the body to be detected and will do little damage while in the

body. A short half-life is needed so that it does not stay radioactive for long (a few hours).



p6_07 Useful radiation

1 Research on uses of ionising radiation

Research the following uses of radiation and prepare a summary of the key points to feed back to the rest of the class

Treating cancer

1 Find out about the effect of the treatment:

a) What does the ionising radiation do to the tumour?

b) What precautions are taken to avoid damage to anything other than the tumour?

2 Find out about the radioactive sources used:

a) What sources are used?

b) What radiation do they emit?

c) What are the half-lives of these sources?

3 Find out about how the treatment is organised:

a) Who is the person who deals with this procedure?

b) Where are these procedures done?

Sterilising surgical instruments

1 Find out about the procedure:

a) What is sterilisation?

b) What are the advantages of sterilising with radiation rather than by chemical or heat methods?


a) What will the ionising radiation do?

b) What sources are used?

c) What radiation do they emit?

d) What are the half-lives of these sources?

Sterilising food

1 Find out about the procedure:

a) What happens when food is irradiated?

b) What are the advantages of sterilising food?

c) What are the disadvantages of sterilising food?


a) What sources are used?

b) What type of radiation do they emit?

p6_07 Useful radiation continued


2 Radioactive tracers in medicine

Research the uses of radioactive elements as tracers in the body. Use these questions as guidelines to focus your research.

1 What is a tracer?

2 When do doctors need to use tracers in the body?

3 What sources are used?

4 What type of radiation do they emit?

5 What are their half-lives?

6 What are the advantages of being able to use a tracer for diagnosis?

3 Presentation

Use your research findings to produce an informative presentation. This may be a PowerPoint, a printed leaflet, or other type of presentation of your choice.

The presentation should include ideas and information about:

what the scientific ideas are that are being applied

the particular advantage that it offers

how the risks are assessed and managed.



p6_08 Keeping people safe

Resources

Student Book pages 274−275 Homework pack p6_08


Learning outcomes P6.2.6 understand that radioactive materials expose people to risk by irradiation and contamination

P6.2.7 understand that we are irradiated and contaminated by radioactive materials all the time and recall the

main sources of this background radiation

P6.2.8 relate ideas about half-life and background radiation to the time taken for a radioactive source to become

safe

P6.2.9 recall categories of people who are regularly exposed to risk of radiation and that their exposure is

carefully monitored, including radiographers and workers in nuclear power stations

Ideas about Science IaS 2.4 a correlation between a factor and an outcome does not necessarily mean that the factor causes the

outcome; both might, for example, be caused by some other factor

IaS 2.5 in some situations, a factor alters the chance (or probability) of an outcome, but does not invariably lead to

it. We also call this a correlation


samples (e.g. groups of people) that are matched on as many other factors as possible, or are chosen randomly so



IaS 5.5 people are generally more willing to accept the risk associated with something they choose to do than

something that is imposed, and to accept risks that have short-lived effects rather than long-lasting ones

IaS 5.6 people’s perception of the size of a particular risk may be different from the statistically estimated

risk. People tend to over-estimate the risk of unfamiliar things (like flying as compared with cycling), and of

things whose effect is invisible or long-term (like ionising radiation)

IaS 5.7 governments and public bodies may have to assess what level of risk is acceptable in a particular

situation. This decision may be controversial, especially if those most at risk are not those who benefit

IaS 6.3 in many areas of scientific work, the development and application of scientific knowledge are subject to

official regulations

IaS 6.4 some questions, such as those involving values, cannot be answered by science

Literacy focus: Reading articles about the job of a radiographer, and about contamination and irradiation.


understand that risks need to be evaluated by assessing the level of risk and the consequences of harm

describe the risks to people from irradiation and contamination

explain how the time taken for a radioactive source to become safe depends on its half-life

recall that exposure is regulated in certain occupations

Key vocabulary

contamination hazard irradiation risk


There may be confusion between contamination and irradiation.


This lesson is about hazard and risk, so to begin ask students to think of risky jobs, and list them in order of risk.

Where does a worker in the nuclear industry figure on this list?

Learning activities worksheet p6_08 Low demand Display the definitions of hazard and risk from p. 274 in the Student Book. Discuss what

radiographers do. The website of the Society of Radiographers is www.radiographycareers.co.uk and has

information on it about what radiographers do. Better still, ask a radiographer from your local hospital to come in

and talk to the class about their job and the hazards they encounter.

p6_08 Keeping people safe continued


Worksheet activity 1 asks students to identify risks facing a radiographer at work. They can then determine if

something needs to be done about it and, if action needs to be taken, indicate what that action should be. Students

need to draw on what they learned in earlier lessons about how radiation can be stopped – remind students that X-

rays are electromagnetic radiation, like gamma rays, but can be stopped by a lesser thickness of lead.

Teaching and learning notes: Students need to understand how to list hazards and evaluate risk.

Standard demand Discuss contamination and irradiation (see Student Book p. 275). Make sure that students are

clear about the distinction. Then ask them to read the text on activity 2 on the worksheet. This is based on an

article published by the Washington State Department of Health Office of Radiation Protection. In it an analogy is

used to explain the difference between contamination and irradiation. Make sure students can access the ideas in

the text; discuss key points as appropriate, ask students to answer the questions. Have a feedback session.

Explain that ideas about contamination are based on evidence and they attempt to explain the correlation between

contaminants and effects on the body.

High demand Ask students to read the text in activity 3, which is based on a blog article from a firm which sells

radiation detection meters about the effects of contamination in tap water and food from the damaged reactors of

the Fukushima power plant. It includes ideas about how contamination can enter the body, what may have been

causing the higher levels of radiation in Tokyo’s tap water and why it has now returned to safe levels.

Looking at the risk assessment done at the beginning of this lesson, review the list of possible actions. Discuss the

need for shielding and for strict guidelines and monitoring, e.g. by film badges. Refer to the final section on p. 275

of the Student Book. Students should add to their risk assessment if necessary.

Ideas about contamination are based on large-scale studies in the past; explain that because the evidence base is

large scientists can be confident about the conclusions they have drawn.

Plenary suggestions Have a discussion about how robots could be used in the nuclear industry.

Student Book answers Q1 Dead or damaged cells, mutations, cancer

Q2 No as the background equivalent dose is not high enough to cause lasting damage to living cells.

Q3 5 × 8 days = 40 days

Q4 Radiation from fallout to the earth – plants grow in radioactive soil, animals eat the plants, humans eat the

plants/animals.

Q5 There is an increased risk of cancer but it may not happen as the cells may repair themselves.


Imaging technology Risk represented? How is the risk managed?

X-ray Ionising radiation can cause burns, mutation

and death

Safe distance, shielding, restrict

exposure time

CT scan Ionising radiation can cause burns, mutation

and death

Safe distance, shielding, restrict

exposure time

MRI None

Ultrasound None


Q1 Contamination Q2 Irradiation

Q3 Contamination Q4 There is no radioactive material on the person or object.

Q5 Anything sensible from the article. Q6 Shielding; removal of the person from the site.


Q1 a) Radioactive b) Relatively short half-life

Q2 Because radioactive dust can get trapped in the lungs, whereas radioactive food passes through the body.

Q3 Because cell division is taking place at a greater rate in children and this process is particularly susceptible to

damage from radiation.

Q4 People may not be aware of the short-lived nature of some of the radiation and continue to be suspicious.



p6_08 Keeping people safe

1 Risk assessment for a radiographer

Diagnostic radiographers provide images to help find out what is going on inside patient’s body. They produce images for most departments in a hospital, including accident and emergency, outpatients, operating theatres and wards.

Some of the imaging technologies that a diagnostic radiographer may use are:

X-ray – looks through tissues to examine bones, cavities and foreign objects

CT (computed tomography) – uses X-rays to provide cross-sectional views (slices) of the body

MRI (magnetic resonance imaging) – builds a 2D or 3D map of the different tissue types within the body. MRI uses a magnetic field to make molecules in the body oscillate

ultrasound – uses high-frequency sound to produce an image. It is well known for its use in obstetrics and gynaecology. Ultrasound is also used to check circulation and examine the heart.

Look at the imaging technologies used. Which of these represent a risk to the radiographer? How do you think a radiographer minimises the risk? Complete the table to show your answers.

Imaging technology Risk represented? How is the risk managed?

X-ray

CT scan

MRI

Ultrasound

2 Contamination versus irradiation

Read this description of contamination and irradiation, adapted from an article published by the Office of Radiation Protection, Washington State Department of Health. Then answer the questions that follow.

Contamination

Contamination is the process by which radioactive material is deposited where it is not wanted, in particular where its presence may be harmful. Contamination could be thought of as a cup of coffee that has spilled. If the coffee cup is not securely covered with a lid, some of the coffee could spill on your clothes. Facilities using radioactive materials regularly monitor for contamination. Workers are trained to work safely with radiation and use special handling techniques so as not to create or spread contamination.

Irradiation

When an unstable atom decays it emits energy in the form of radiation. When this is ionising radiation, this process is called irradiation. Once the person or object is removed from the pathway of the radiation, or is outside the range of the radiation, they are no longer being irradiated. Medical or dental X-rays are an example of irradiation.

p6_08 Keeping people safe continued


When someone or something is irradiated it does not become ‘radioactive’. Since the person, or object, did not come in actual physical contact with the radioactive material, the person or object could not be contaminated. Irradiation can be thought of as the aroma from a cup of coffee as you pass by. As you walk further away from the coffee, the smell becomes fainter and fainter. Since you did not come in physical contact with the coffee, there is no way the coffee could be on you or your clothes.

1 Some radioactive material leaked from the damaged nuclear power station into the sea. Is this irradiation or contamination?

2 The fallout from the accident at the nuclear power station increased background radiation. Is this irradiation or contamination?

3 Workers leaving nuclear laboratories or power stations sometimes have to shower. Is this to remove the effects of contamination or irradiation?

4 Explain why irradiation does not lead to an object or person being radioactive.

5 Discuss how well the coffee analogy explains the difference between contamination and irradiation.

6 Contamination can be cleaned up. What can be done to limit irradiation to safe levels?

3 Contaminated food

Read this article about contamination due to the Fukushima nuclear disaster.

Wednesday 4 May 2011

As Japanese emergency workers continue to pump out thousands of gallons of contaminated water from the damaged reactors of the Fukushima Power Plant, radiation contamination in food and water has emerged as a new focus of the international media.

There are many ways that radiation can enter the body for contamination to occur. Radioactive materials that enter into digestive tract can do damage while they reside in the body, but most of these materials pass through quickly. Radiation that gets trapped in other areas of the body, such as radioactive dust being breathed in and lodged in the lungs, can pose a serious threat because the longer the radiation resides in the body, the more harm it can do.

Recently Japan reported dangerously high levels of radiation in Tokyo’s tap water, leading to widespread fear and government advice against giving tap water to children (who are more susceptible to radiation and have lower exposure limits). Since this incident, the radiation in Tokyo’s tap water has returned to safe limits. Radiation in food has also been a problem. Widespread bans have gone into place on the sale and consumption of crops from affected areas, as well as seafood caught in the ocean near the plant. Much of the radiation present in the contaminated food and water is iodine-131, which has a half-life of only 8 days. This type of radiation won’t be around for long, but the fear of radiation is more likely to hurt the Japanese economy as buyers shy away from food that they think might still have some contamination.

(Adapted from: dtectsystemsblog.blogspot.com)

1 Iodine-131 is a contaminant.

a) What makes it dangerous?

b) Why is it not dangerous for long?

2 Why might breathing contaminated air pose a greater hazard than eating contaminated food?

3 Why are children more susceptible to radiation than adults?

4 Why might people continue to be wary of food from the area even after the contamination has ceased?



p6_09 Energy from the nucleus

Resources

Student Book pages 276−277 Interactive Book: Naked Scientist animation ‘What’s the difference between a nuclear reactor and an atomic bomb?’ Homework pack p6_09


Ping-pong balls or modelling clay to make nuclear models; images/videos of fires and of atomic bomb tests; animations of fission and fusion

Learning outcomes P6.2.10 understand that a nuclear fuel is one in which energy is released by changes in the nucleus

P6.2.11 know that in nuclear fission a neutron splits a large and unstable nucleus (limited to uranium and

plutonium) into two smaller parts, roughly equal in size, releasing more neutrons

P6.2.12 recall that the amount of energy released during nuclear fission is much greater than that released in a

chemical reaction involving a similar mass of material

ICT focus: Accessing animations of fission and fusion.


understand that nuclear reactions produce energy

explain the difference between nuclear fusion and nuclear fission

recall that nuclear reactions release much more energy that chemical ones

Key vocabulary

binding energy chain reaction nuclear fission nuclear fuel nuclear fusion


Students may confuse the terms fission and fusion.


Explain that this lesson is about using nuclear fuels to produce energy. Show students images of large scale

combustion, such as a forest fire or oil refinery fire, and then ask them to compare it with a nuclear reaction, such

as archive clips of atom bomb tests. Ask for ideas about the difference between these and draw out that nuclear

reactions involve changes in the nucleus of the atom; such changes can release huge amounts of energy.

Learning activities worksheet p6_09 Low demand Tell students they are going to learn about nuclear reactions that release energy. Define nuclear

fission and nuclear fusion. See Student Book p. 276, especially Figure 2. If possible, supplement with online

animations (basic ones can be found on the ‘Schoolphysics’ website). Emphasise that in fission a heavy unstable

nucleus splits into two lighter ones, and that in fusion two light nuclei join.

Students can work in groups to do activity 1 on the worksheet, for which they will need materials to make nuclear

models, such as ping-pong balls and sticky tack or modelling clay. They should show how a large nucleus

disintegrates into two products for fission, and use small groups of balls coalescing for fusion. Ask groups to

demonstrate their action models. Students can then answer Q1 on Student Book p. 276.

Teaching and learning notes: Students need to know that energy is released in nuclear fission and fusion, and be

able to give a simple description of both processes.

Standard demand Discuss the energy released in nuclear fission and fusion. Use the data at the top of Student

Book p. 277 to point out the massive amounts of energy per kilogram available from nuclear fission and fusion

compared with the energy per kilogram available from fossil fuels.

Bring out these teaching points:

The energy released per fission or per fusion reaction is small, but these are nuclear reactions and there are

many many nuclei per kilogram, so the energy available per kilogram is enormous.

Students may appreciate a little better the enormous energy released if you tell them that the energy from the

Sun comes from fusion reactions. This energy is released about 150 million km from Earth but provides Earth

with heat, light and sustains life on Earth.

Refer to lesson p6_01, where students learned that the strong nuclear force binds protons and neutrons together

in the nucleus. If you change the nuclear configuration then will be a change in energy. In the case of fission and

p6_09 Energy from the nucleus continued


fusion less energy is needed to bind the resulting nucleons together, so energy is released. Ask students in what

form this energy is released.

Refer to online animations if possible (as described in Low demand above). What are the resulting particles doing?

They are moving – therefore the energy released is in the form of kinetic energy. This may be transferred to heat

when the resultant particles collide with other particles.

Students can do Q2–4 in the Student Book and activity 2 on the worksheet.

Teaching and learning notes: Students will need to be clear that nuclear reactions release more energy than

chemical ones.

High demand (Higher tier) look more closely at fission. Put the equation for the fission of uranium-235 (Student

Book p. 277) on the board. Point out that the total mass number is the same each side of the equation. Ask

students to put the equation into words that will tell the story of nuclear fission reaction. Starting with ‘A neutron …’

You are looking for an answer such as:

‘A neutron penetrates the U-235 nucleus and makes it unstable. The unstable nucleus splits into barium and

krypton and also releases three neutrons and energy in the form of KE.’

If possible show the interactive simulation of fission at phet.colorado.edu (search the site for nuclear fission

simulation). Ask: ‘How can we keep this process going?’. The answer is in the neutrons produced. If there are more

U-235 nuclei available these neutrons can go on to split more U nuclei. This is called a chain reaction. Use the

‘chain reaction’ facility on the website to show this. Use the controls to add more U-235 nuclei. Note that there is a

minimum number below which a chain reaction is not sustained. This is called the critical mass. Notice the very

speedy release of energy. If this is not controlled you have an explosive situation. This is what happens in an

atomic bomb.

Students can do Q5 and Q6 in the Student Book and activity 3 on the worksheet. It is worth mentioning that Figures

3 (and 4), Q5, and worksheet activity 3 all give different fission products for U-235. There is no fixed set of products

from this fission – a variety of daughter nuclei can be produced, but the mass numbers must be conserved.

Plenary suggestions Show a video clip of a domino rally (or the Honda TV advert ‘The Cog’) and discuss with students the extent to

which this represents the concept of a chain reaction.

Student Book answers Q1 They are both nuclear reactions that produce energy. Fission is splitting of heavy nuclei. Fusion is joining light

nuclei.

Q2 About 174 000×

Q3 Binding energy that holds the nucleus together is much greater than the electrostatic energy that is involved in

chemical reactions.

Q4 It can release a huge amount of energy but this can be difficult to control.

Q5 3

Q6 27


Key features of a successful model are given on the worksheet.


Q1 The energy binding the protons and neutrons into the nucleus.

Q2 KE of the particles

Q3 More energy is produced per kg of fuel. (Students may suggest that less greenhouse gases are produced from

nuclear fuels; they are in less danger of running out in the foreseeable future; or another valid suggestion.)


Q1 It is neutral and will not be affected by the charged particles of the atom. It has enough KE to penetrate the

nucleus.

Q2 88

Q3 a) 57 protons

b) 88 neutrons

Q4 Neutrons given off by the fissions. Enough uranium nuclei to sustain it (critical mass).



p6_09 Energy from the nucleus

1 Fission and fusion

Figure 2 on page 276 in the Student Book shows how fusion and fission are different processes.

Decide how you can use the materials provided to make action models to show these processes and emphasise the difference between them. Your models should clearly indicate:

what happens in fission

what happens in fusion

the difference between the processes

the energy transfer that occurs.

2 Nuclear fuels and energy

1 Where does the energy come from in fission and fusion reactions?

2 How is it released?

3 Suggest one advantage of using nuclear fission rather than fossil fuels to produce energy.

3 Fission and the chain reaction

In this equation the two products of fission of uranium-235 are lanthanum and bromine.

U + n → La + Br + 3 n

1 Suggest a reason why a neutron is able to penetrate the nucleus.

2 What is the mass number for bromine?

3 a) How many protons are there in the nucleus of lanthanum-145?

b) How many neutrons are there in the nucleus of lanthanum-145?

4 What are the necessary conditions to set up a chain reaction?

235 92

1 0

145 57

? 35

1 0



p6_10 Harnessing fission energy

Resources

Student Book pages 278−279 Interactive Book: Quick Starter ‘Are you a NIMBY?’; News video clip ‘Nuclear power’

Homework pack p6_10


Examples of objects to represent waste from a nuclear power station, e.g. overalls, paper notices, a flask with a sludgy substance, bits of machinery, a metal tube to represent spent fuel rods (labelled), etc.; three cardboard boxes

Learning outcomes P6.2.13 understand how the nuclear fission process in nuclear power stations is controlled, and use the

terms chain reaction, fuel rod, control rod and coolant

P6.2.14 understand that nuclear power stations produce radioactive waste

P6.2.15 understand that nuclear wastes are categorised as high level, intermediate level and low level, and relate

this to disposal methods

Ideas about Science IaS 6.1 science-based technology provides people with many things that they value, and which enhance the

quality of life. Some applications of science can, however, have unintended and undesirable impacts on the quality

of life or the environment. Benefits need to be weighed against costs

Literacy focus: Discussing, debating and explaining points of view.


understand that nuclear fission produces radioactive waste that needs to be dealt with appropriately

describe how the fission process is controlled in nuclear reactors

Key vocabulary

chain reaction coolant control rod fuel rod

high-level waste intermediate-level waste low-level waste


Ask students to consider and record, as individuals, what their attitude is towards nuclear power.

Point out that during the lesson we are going to be considering how to deal with radioactive waste from nuclear

power stations and how to control the fission process in a reactor. We will have a debate about nuclear power

and at the end of the lesson we will see if anyone has changed their mind.

Learning activities worksheet p6_10 Low demand Discuss the siting of nuclear power stations, referring to Figure 2 on p. 278 of the Student Book.

Students answer Q1 and Q2.

Go through activity 1 on the worksheet with students.

Standard demand Use pp. 278–279 of the Student Book as a basis for a discussion of the waste from nuclear

power stations, and how the different levels of waste are dealt with.

Hold up some examples of typical objects that might be waste from a power station – see the resources list above,

and add anything else you can think of. Have three boxes labelled low, intermediate, high. Hold up the items one

by one and ask the class what level of waste is it. After discussion, put it in the correct box. Then ask the class to

write a label for each box to say how the waste should be dealt with. Draw out key points and ask students to

answer Q3 and Q4 on p. 279.

Teaching and learning notes: Students need to know how waste is dealt with.

High demand Discuss control of the fission process. Remind students about the chain reaction (Student Book p.

277). Explain that an uncontrolled chain reaction leads to a bomb. Ask for ideas about how the chain reaction can

be controlled. Explain that there only needs to be one neutron per fission going on to initiate another fission. The

others need to be absorbed.

Refer to Figure 5 on Student Book p. 279 and explain about the use of control rods to absorb neutrons. Point out

that the fail-safe position for these rods is fully into the reactor, so if anything goes wrong the rods are dropped into

the reactor immediately and all the neutrons are absorbed. The reaction stops and the reactor will then shut down.

p6_10 Harnessing fission energy continued


Also point out the other features of the reactor:

the fuel rods

the coolant, which takes the heat generated away to heat water to make steam, which then drive turbines as in a

fossil fuel power station.

The British Energy website has a slide show about nuclear fission and controlling fission in a power station; clicking

on ‘How power stations work’ gives an animation of how an AGR or a PWR reactor works.

Teaching and learning notes: Students need to know the purpose of fuel rods, coolant and control rods.

Plenary suggestions Have a debate about whether nuclear power is a good thing or a bad thing. See if anyone has changed their mind

since the start of the lesson. Ask them to explain why.

If you are a subscriber, there are good Upd8 activities on the nuclear power debate and dealing with waste.

Student Book answers Q1 They are all by the sea.

Q2 1

Q3 Mixed with molten glass in stainless steel drum; drums stored in concrete.

Q4 Paper, clothing and rags. Burned, placed in closed containers and buried in shallow landfill.

Q5 The coolant absorbs the heat around the reactor core and transfers it to the steam generator.

Q6 Control rods absorb neutrons and so control the speed of the chain reaction.


A good response might indicate that an ideal site would be away from centres of population to reduce the number

of people affected, be near the coast to provide access to cooling water and have good rail links to allow easy

transport of materials. Good road links and connections to the National Grid might be lesser considerations, as they

would be easier to arrange.


A Much of the material isn’t flammable. That which is would still be radioactive even if burned and would, in the

process, be spread over a wider area.

B The procedures described have been developed with careful consideration of the risks and have enabled most

power stations to run safely for many years. However, they don’t completely eradicate all risks.

C This is true. However, there is still a risk associated with nuclear power. These procedures are designed to

cope with waste produced in the normal course of operation.


This depends on the personal response. A good response will cover the criteria indicated on the worksheet and IaS

6.1 (above).



p6_10 Harnessing fission energy

1 Location of power stations

Imagine that you are working with a team of people to recommend the location of a site for a new nuclear power station. There are a number of factors you have been thinking about, including:

how close to towns and cities

how close to the National Grid

how close to the coast

how close to rail services

how close to good roads.

Thinking about those factors, describe what you think would be an ideal location, and explain why.

…………………………………………………………………………………………………………

…………………………………………………………………………………………………………

…………………………………………………………………………………………………………

…………………………………………………………………………………………………………

…………………………………………………………………………………………………………

…………………………………………………………………………………………………………

…………………………………………………………………………………………………………

…………………………………………………………………………………………………………

…………………………………………………………………………………………………………

2 Dealing with waste

Three students have been in a lesson where they are thinking about the disposal of nuclear waste. This is what they say:

For each of the comments suggest a response, supported by reasons.

A They’ve really thought clearly about how dangerous material is. As long as the regulations are followed no-one’s going to get hurt.

Nuclear waste is such a big problem; all this waste it produces means that nuclear power stations can’t be run safely.

I think we should just burn it all. If it goes up in smoke it can’t be a problem any more.

B

C

p6_10 Harnessing fission energy continued


3 Acceptable risk

A visiting speaker comes to your school and talks about nuclear power. She gets some tough questions. At the end, she says:

‘Look, you have to accept that there will always be risks with producing electricity. People want electricity; they want it to be cheap, reliable and plentiful. Any method of producing it has problems. If you burn fossil fuels you increase global warming. Renewables can help but the energy they harvest is too dilute to be the entire solution. Nuclear has risks. We can manage those risks but there will always be a chance that something will go wrong and that people will get hurt.

The challenge isn’t to find a perfect energy source; there isn’t one. The challenge is to educate people into realising that everything has a risk and that they have to accept that as part of the package.’

She also says that it’s really important for young people to be involved with this debate and encourages you to respond.

Your teacher asks you to compose an e-mail saying what you think about this. In your reply:

1 Say whether you think the speaker’s perspective was a valid one.

2 Explain what your point of view is.

3 Make it clear whether you think that nuclear power represents an acceptable risk and why.



p6_11 Harnessing fusion energy

Resources

Student Book pages 280−281 Interactive Book: Drag and drop activity ‘Fusion’ Homework pack p6_11


Video of Sun’s energy production; video of fusion power research

Learning outcomes P6.1.6 understand that, if brought close enough together, hydrogen nuclei can fuse into helium nuclei releasing

energy, and that this is called nuclear fusion

P6.1.7 understand that Einstein’s equation E = mc2 is used to calculate the energy released during

nuclear fusion and fission (where E is the energy produced, m is the mass lost and c is the speed of light

in a vacuum)

Ideas about Science IaS 6.1 science-based technology provides people with many things that they value, and which enhance the

quality of life. Some applications of science can, however, have unintended and undesirable impacts on the quality

of life or the environment. Benefits need to be weighed against costs

Numeracy focus: Calculating mass loss and energy released.


describe the nuclear fusion of hydrogen to helium

identify the advantages and problems of producing usable energy from nuclear fusion


Have a video clip of the Sun’s energy production in action playing as students enter the lab (such as ‘The Sun in

Action’ on YouTube). Explain that the topic for this lesson is nuclear fusion and that the Sun is powered by

nuclear fusion; it is the energy released in this process that provides our Earth with heat and light.

Learning activities worksheet p6_11 Low demand Remind students that fusion is the joining of light nuclei to form a heavier one (lesson p6_09). You

may find it useful to use diagrams and animations from that lesson.

Talk about the particular fusion reaction given on Student Book p. 280. Write the reaction in words. Note that

hydrogen-2 and hydrogen-3 are isotopes of hydrogen. Hydrogen-2 (deuterium) has 1 proton and 1 neutron.

Hydrogen-3 (tritium) has 1 proton and 2 neutrons. If you are teaching Higher tier students, note that the symbol

equation is on p. 281.

Ask students to represent the stages in the fusion process by means of a simple storyboard (worksheet activity 1);

this encourages the breaking down of a process into steps and the graphics make it easy to share and compare.

Standard demand The website of the Culham Centre for Fusion Education (www.ccfe.ac.uk) has much useful

information, including a video giving an overview of fusion energy and the JET project. Show this if possible, and

ask the students, working in groups, to come up with advantages and disadvantages of harnessing fusion energy

on Earth. Use Student Book pp. 280 and 281 to discuss a full list of advantage and disadvantages. You could hold

a class debate on the use of fusion reactors. The JET project is a good example of an international team of

scientists working at the cutting edge of science research to solve a problem that is high on most agendas at

present.

Then ask students to do activity 2, which encourages them to identify and summarise key points for and against

fusion reactors.

High demand (Higher tier) Introduce E = mc2 as an equation which defines the interchangeabilty of mass and

energy. Using E = mc2 we can calculate the amount of energy released in both fission and fusion reactions. Use

the example on p. 281 to go through these calculations with the students. Worksheet activity 3 provides another

calculation based on fission.

If you have time and the right audience this may interest your students: Have you heard of a black hole

containment device? It is an idea in science fiction time travel where the mass of the black hole can be changed to

energy according to Einstein’s equation E = mc2 and used to power a space ship.

Teaching and learning notes: Students need to know that fusion produces a vast amount of energy, and Higher

tier students will need to be able to calculate energy released from the Einstein equation.

p6_11 Harnessing fusion energy continued


Plenary suggestions The Culham Centre for Fusion Education also has an interview with Brian Cox at the Culham JET project talking

about fusion, energy and the role of scientists. It is 13 minutes long, so you may well want to take bits from it.

Student Book answers Q1 Hydrogen-1: 1 proton and 0 neutron

Hydrogen-2: 1 proton and1 neutron

Hydrogen-3: 1 proton and 2 neutron

Q2 Any three of:

the by-products of fusion are not radioactive

fusion does not contribute more CO2 to the atmosphere

produces a lot more energy per kilogram than fossil fuels

fuel supplies will last for millions of years. Deuterium comes from water and tritium from the Earth’s crust.

the small amount of fuel needed makes this a relatively safe process.

Q3 By using containment in doughnut-shaped magnetic fields of huge strength.

Q4 The mass decreases.

Q5 Kinetic energy of the neutron. Use Einstein’s equation E = mc2.


A good response will use suitable sketches and display the reaction, covering the criteria on the worksheet.


Key points to include are:

For: products not radioactive, doesn’t contribute to global warming, huge energy output, small amounts of fuel.

Against: incredibly high temperatures needed, technologically difficult, potential safety issues, hugely

expensive, current prototypes use more energy than they generate.


Q1 n3 Kr Ban U 10

9236

14156

10

23592 ++→+

Q2 Uranium-235 + neutron = 390.300 × 10–27

+ 1.675 × 10–27

= 391.975 × 10–27

kg

Q3 Barium-141 + krypton-92 + 3 × neutrons = 233.993 × 10–27

+ 152.600 × 10–27

+ 5.025 × 10–27

= 391.618 × 10–27

kg

Q4 Loss in mass = 0.357 × 10–27

kg

Q5 Energy released per atom = change in mass × (3 × 108)2 = 3.57 × 10

–28 × (3 × 10

8)2 = 3.213 × 10

–11 J

Q6 3.213 × 10–11

× 2.529 × 1024

= 8.126 × 1013

J



p6_11 Harnessing fusion energy

1 Fusion storyboard

One of the ways of showing a sequence of events is by using a storyboard. This consists of a number of sketches to show various stages, like a comic strip or animation.

Devise a way of representing the fusion reaction shown in Figure 2 on page 280 of the Student Book with a storyboard. You should think clearly about what each step should show. A good representation will clearly indicate:

the nature of the reactants

the nature of the products

the transfer of energy.

2 Power generation

Imagine that two of your friends have been asked to lead a debate in the class on the use of fusion reactors, one leading the case for and the other one against. Write clear notes using bullet points for each, summarising the key points they should make in leading their arguments. Refer to pages 280–281 of the Student Book and consider your answers to Q2 and Q3 on page 281.

3 Calculating energy released in nuclear reactions

Follow the steps below to calculate the energy released when a nucleus of uranium-235 absorbs a neutron and undergoes fission to form barium-141, krypton-92 and three neutrons.

Particle Mass (kg)

neutron 1.675 × 10–27

uranium-235 390.300 × 10–27

krypton-92 152.600 × 10–27

barium-141 233.993 × 10–27

1 Write the equation of this reaction.

2 Calculate the initial mass of the uranium nucleus and one neutron.

3 Calculate the final mass of the products – the barium, krypton and three neutrons.

4 Calculate the loss in mass

5 Use E = mc2 to calculate the energy released.

6 There are 2.529 × 1024 atoms of uranium in a kilogram. How much energy will be released per kilogram?

Documents

P6 Module Introduction - WikispacesRadioactive+Materials+SOW… · The model begins by reviewing what we know about the atom, ... P6 Module Introduction ... ask the students to mark