Nuclear fission and fusion.pptx

AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Nuclear fission and fusion

Atomic structure

Lesson 10 of 10

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Warm-up

Atomic structure

Lesson 10 of 10

Answer each one, then check.

1

What is a nucleus?

2

What is an isotope?

3

What is energy conserved?

4

What happens to mass in E = mc²?

5

What is a chain reaction?

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Warm-up - Answers

Atomic structure

Lesson 10 of 10

1

What is a nucleus?

The centre of an atom, made of protons and neutrons

2

What is an isotope?

An atom with the same protons but different neutrons

3

What is energy conserved?

Energy cannot be created or destroyed

4

What happens to mass in E = mc²?

It can be converted to energy

5

What is a chain reaction?

A reaction that keeps itself going

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Learning Objectives

Atomic structure

Lesson 10 of 10

1

Describe nuclear fission and how a chain reaction occurs.

2

Explain how the chain reaction is controlled in a nuclear reactor and uncontrolled in a nuclear weapon.

3

Draw and interpret diagrams of fission and chain reactions.

4

Describe nuclear fusion.

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Atomic structure

Lesson 10 of 10

FISSION AND FUSION

Nuclear fission is the splitting of a large and unstable nucleus, such as uranium or plutonium. Nuclear fusion is the joining of two light nuclei to form a heavier nucleus.

In both, energy is released. In fusion some of the mass is converted into the energy of radiation.

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A Fission Chain Reaction

Atomic structure

Lesson 10 of 10

Each fission produces neutrons that cause more fission.

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Nuclear Fusion

Atomic structure

Lesson 10 of 10

Two light nuclei join to make a heavier one.

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Nuclear Fission

Atomic structure

Lesson 10 of 10

Follow the steps.

1

A neutron is absorbed

An unstable nucleus such as uranium-235 absorbs a neutron.

2

The nucleus splits

Into two smaller nuclei, roughly equal in size.

3

Two or three neutrons are released

Also gamma rays.

4

Energy is released

All the fission products have kinetic energy.

5

Chain reaction

The neutrons go on to cause further fission.

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Controlled or Uncontrolled?

Atomic structure

Lesson 10 of 10

IN A NUCLEAR REACTOR

• The chain reaction is controlled.

• Control rods absorb excess neutrons so only one neutron from each fission causes another.

• Energy is released steadily to heat water.

IN A NUCLEAR WEAPON

• The chain reaction is uncontrolled.

• Neutrons cause many more fissions each time.

• A huge amount of energy is released in an instant: an explosion.

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Describing a Chain Reaction

Atomic structure

Lesson 10 of 10

Explain how a chain reaction occurs in a fission reactor.

1

Start

A neutron is absorbed by a uranium-235 nucleus which splits

2

Neutrons released

2 or 3 neutrons are released

3

Continues

These neutrons are absorbed by more nuclei, which also split, so the reaction keeps going

ANSWER

The neutrons released in each fission cause further fissions, so the reaction sustains itself.

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Fusion

Atomic structure

Lesson 10 of 10

Describe what happens in nuclear fusion.

1

Two light nuclei

Join together to form a heavier nucleus

2

Mass

Some of the mass is converted to energy released as radiation

3

Conditions

Very high temperature and pressure are needed to overcome the repulsion between the positive nuclei

ANSWER

Light nuclei join to form a heavier nucleus, releasing energy.

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Comparing Them

Atomic structure

Lesson 10 of 10

Points to remember.

Fission

A large nucleus splits into two smaller ones; releases neutrons; chain reaction.

Fusion

Two small nuclei join; needs very high temperature; powers the Sun.

Both

Release energy; fusion releases more per kilogram of fuel than fission.

Waste

Fission produces radioactive waste; fusion products are largely not radioactive for long.

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Key Terms

Atomic structure

Lesson 10 of 10

Nuclear fission

The splitting of a large, unstable nucleus.

Nuclear fusion

The joining of two light nuclei to form a heavier nucleus.

Chain reaction

A reaction in which the products cause more of the same reaction.

Control rods

Rods that absorb neutrons to control a reactor.

Fission products

The smaller nuclei produced by fission.

Nuclear reactor

A device in which fission is controlled.

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Atomic structure

Lesson 10 of 10

YOUR TASK

Fission or Fusion?

10 minutes

State whether each is fission or fusion: (a) uranium-235 absorbs a neutron and splits (b) hydrogen nuclei join to make helium (c) a chain reaction in a reactor (d) the process in the Sun.

1

Decide if a nucleus splits or joins.

WHAT A GOOD ANSWER SHOWS

(a) Fission (b) Fusion (c) Fission (d) Fusion.

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Can I...?

Atomic structure

Lesson 10 of 10

Define fission.

Define fusion.

Describe a chain reaction.

Describe control in a reactor.

Describe uncontrolled fission.

Draw and interpret a fission diagram.

Describe fusion conditions.

Compare fission and fusion.

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Summary & Exam Focus

Fission: large nucleus splits into two smaller nuclei plus 2 to 3 neutrons and gamma.

Chain reaction: neutrons cause further fission.

Controlled in a reactor, uncontrolled in a weapon.

Fusion: two light nuclei join, releasing energy.

EXAM FOCUS

Describe what happens in nuclear fission. (3 marks)

Neutron absorbed, nucleus splits, neutrons and energy released.

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