Half-lives hazards and uses of nuclear radiation - Teacher Slides.pptx

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Half-lives, hazards and uses of nuclear radiation

Atomic structure

Lesson 9 of 10

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Warm-up

Atomic structure

Lesson 9 of 10

Answer each one, then check.

1

What is half-life?

2

What is a tracer?

3

Which radiation is most penetrating?

4

Give one danger of ionising radiation.

5

What is standard form?

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Warm-up - Answers

Atomic structure

Lesson 9 of 10

1

What is half-life?

The time for activity to halve

2

What is a tracer?

A substance that can be followed inside the body

3

Which radiation is most penetrating?

Gamma

4

Give one danger of ionising radiation.

It can damage or kill cells

5

What is standard form?

A number written as a × 10ⁿ

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Learning Objectives

Atomic structure

Lesson 9 of 10

1

Explain why the hazards of a radioactive material differ with its half-life.

2

Describe and evaluate the use of nuclear radiation in exploring internal organs and treating unwanted tissue.

3

Evaluate the perceived risks of nuclear radiation using data.

4

Use data given in standard form.

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Atomic structure

Lesson 9 of 10

HALF-LIFE AND HAZARD

Radioactive isotopes have a very wide range of half-lives. Short half-lives are very active but decay quickly; long half-lives stay radioactive for a very long time.

In medicine, nuclear radiations are used to explore internal organs and to control or destroy unwanted tissue.

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Nuclear Radiation in Medicine

Atomic structure

Lesson 9 of 10

The radiation is chosen for its penetration and half-life.

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Half-Life and Hazard

Atomic structure

Lesson 9 of 10

Data (approximate).

Isotope

Half-life

Comment

Technetium-99m

6 hours

Gamma emitter used as a medical tracer; gone from the body quickly

Iodine-131

8 days

Used to treat the thyroid; decays within weeks

Cobalt-60

5 years

Gamma source for radiotherapy

Uranium-238

4.5 × 10⁹ years

Stays radioactive for billions of years

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Why Half-Life Matters

Atomic structure

Lesson 9 of 10

Explain why a source with a very long half-life is a hazard for a long time, and why a source with a very short half-life is a hazard mainly at first.

1

Very long half-life

The activity falls extremely slowly, so it remains radioactive for a very long time

2

Very short half-life

It is very active at first but decays quickly, so it is a hazard for only a short time

ANSWER

Long half-life: long-term hazard, low activity. Short half-life: intense at first but soon gone.

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Choosing a Medical Tracer

Atomic structure

Lesson 9 of 10

Explain why technetium-99m is suitable as a tracer to explore organs in the body.

1

Gamma

Penetrating, so it passes out of the body to the detector, and weakly ionising, so it does little damage

2

Half-life 6 hours

Long enough to take the scan but decays quickly so the patient is not radioactive for long

ANSWER

It emits gamma rays, which pass out of the body and are weakly ionising, and its half-life is short.

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Evaluating Risk

Atomic structure

Lesson 9 of 10

Balance benefits and risks.

Benefits

Diagnose disease without surgery; destroy tumours.

Risks

Ionising radiation can damage healthy cells and cause cancer.

Reduce risk

Use small doses, short half-lives and beams from different directions.

Judging

Use the data on dose and consequences to say whether the risk is acceptable.

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Key Terms

Atomic structure

Lesson 9 of 10

Tracer

A radioactive substance used to follow a process in the body.

Radiotherapy

Treating cancer using nuclear radiation.

Half-life

The time for the activity to halve.

Gamma camera

A device that detects gamma rays from a tracer.

Unwanted tissue

Tissue such as a tumour.

Risk

The chance of harm.

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Atomic structure

Lesson 9 of 10

YOUR TASK

Evaluate the Scan

12 minutes

A doctor uses technetium-99m (half-life 6 hours, gamma) to scan a patient's kidneys. Give two reasons why it is suitable and one risk.

1

Consider penetration.

2

Consider half-life.

WHAT A GOOD ANSWER SHOWS

Reasons: gamma passes out of the body; short half-life. Risk: ionising radiation may damage cells (small).

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Can I...?

Atomic structure

Lesson 9 of 10

Explain hazard and half-life.

Explain why gamma tracers are used.

Explain why a short half-life suits a tracer.

Describe radiotherapy.

Explain beams from different directions.

Evaluate risks and benefits.

Read standard form data.

Use data in an answer.

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Summary & Exam Focus

Half-lives range from fractions of a second to billions of years.

Tracers: gamma, short half-life.

Radiotherapy: focus beams to destroy tumours.

Weigh benefits and risks.

EXAM FOCUS

Explain why a radioactive tracer used inside the body should emit gamma radiation and have a short half-life. (4 marks)

Gamma passes out of the body and short half-life means it does not remain long.

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Exam Practice: Half-lives, hazards and uses of nuclear radiation

Atomic structure

Lesson 9 of 10

Answer all questions. Use the mark allocation as a guide to how much to write. · 17 minutes

Question 1 · 3 marks · Explain

Different radioactive isotopes have different half-lives. Explain why radioactive waste with a very long half-life is a problem.

Question 2 · 4 marks · Explain

Technetium-99m is a radioactive isotope with a half-life of 6 hours. It emits gamma radiation. It is injected into a patient so that…

Question 3 · 3 marks · Explain

In radiotherapy, narrow beams of gamma radiation are directed at a tumour from several different directions. Explain why.

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Exam Practice: Half-lives, hazards and uses of nuclear radiation (cont.)

Atomic structure

Lesson 9 of 10

Question 4 · 2 marks · Compare

Uranium-238 has a half-life of 4.5 × 10⁹ years. Iodine-131 has a half-life of 8 days. State which isotope stays radioactive for longer and…

Question 5 · 4 marks · Evaluate

Some people are worried about using radioactive materials in medicine. Evaluate the risks and benefits of using a radioactive tracer.

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Question 1 · 3 marks · Explain

Atomic structure

Lesson 9 of 10

“

Different radioactive isotopes have different half-lives. Explain why radioactive waste with a very long half-life is a problem.

HOW TO ANSWER IT

Command word: Explain. Worth 3 marks, so plan before writing.

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Question 1 · mark scheme

Atomic structure

Lesson 9 of 10

3 marks available. Award a mark for each point made.

Long half-life means it stays radioactive

1 mark

For a very long time

1 mark

So it must be stored safely

1 mark

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Question 2 · 4 marks · Explain

Atomic structure

Lesson 9 of 10

“

Technetium-99m is a radioactive isotope with a half-life of 6 hours. It emits gamma radiation. It is injected into a patient so that internal organs can be explored. Explain why technetium-99m is suitable for this use.

HOW TO ANSWER IT

Command word: Explain. Worth 4 marks, so plan before writing.

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Question 2 · mark scheme

Atomic structure

Lesson 9 of 10

4 marks available. Award a mark for each point made.

Gamma passes out of the body

1 mark

Detected outside the body

1 mark

Weakly ionising: little damage

1 mark

Short half-life: decays quickly

1 mark

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Question 3 · 3 marks · Explain

Atomic structure

Lesson 9 of 10

“

In radiotherapy, narrow beams of gamma radiation are directed at a tumour from several different directions. Explain why.

HOW TO ANSWER IT

Command word: Explain. Worth 3 marks, so plan before writing.

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Question 3 · mark scheme

Atomic structure

Lesson 9 of 10

3 marks available. Award a mark for each point made.

High dose where the beams cross at the tumour

1 mark

Healthy tissue receives low dose

1 mark

Reduces damage to healthy cells

1 mark

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Question 4 · 2 marks · Compare

Atomic structure

Lesson 9 of 10

“

Uranium-238 has a half-life of 4.5 × 10⁹ years. Iodine-131 has a half-life of 8 days. State which isotope stays radioactive for longer and give a reason.

HOW TO ANSWER IT

Command word: Compare. Worth 2 marks, so plan before writing.

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Question 4 · mark scheme

Atomic structure

Lesson 9 of 10

2 marks available. Award a mark for each point made.

Uranium-238

1 mark

Much longer half-life

1 mark

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Question 5 · 4 marks · Evaluate

Atomic structure

Lesson 9 of 10

“

Some people are worried about using radioactive materials in medicine. Evaluate the risks and benefits of using a radioactive tracer.

HOW TO ANSWER IT

Command word: Evaluate. Worth 4 marks, so plan before writing.

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Question 5 · mark scheme

Atomic structure

Lesson 9 of 10

4 marks available. Award a mark for each point made.

Benefit described

1 mark

Risk described

1 mark

Small dose or short half-life reduces risk

1 mark

A conclusion

1 mark

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