Radioactive decay and nuclear radiation.pptx

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Radioactive decay and nuclear radiation

Atomic structure

Lesson 4 of 10

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Warm-up

Atomic structure

Lesson 4 of 10

Answer each one, then check.

1

What is an unstable nucleus?

2

What is an ion?

3

What is a Geiger-Müller tube used for?

4

What is a helium nucleus made of?

5

What is the unit of activity?

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Warm-up - Answers

Atomic structure

Lesson 4 of 10

1

What is an unstable nucleus?

A nucleus that will change to become more stable

2

What is an ion?

A charged atom

3

What is a Geiger-Müller tube used for?

Detecting radiation

4

What is a helium nucleus made of?

Two protons and two neutrons

5

What is the unit of activity?

The becquerel (Bq)

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Learning Objectives

Atomic structure

Lesson 4 of 10

1

Describe radioactive decay as a random process.

2

Define activity and count rate.

3

Name the types of nuclear radiation and describe them.

4

Compare alpha, beta and gamma in penetration, range in air and ionising power, and apply this to uses.

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Atomic structure

Lesson 4 of 10

RADIOACTIVE DECAY

Some atomic nuclei are unstable. The nucleus gives out radiation as it changes to become more stable: this is radioactive decay, and it is a random process.

Activity is the rate at which a source decays, measured in becquerel (Bq). Count rate is the number of decays recorded each second by a detector.

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Penetrating Power

Atomic structure

Lesson 4 of 10

The more ionising, the less penetrating.

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Types of Radiation

Atomic structure

Lesson 4 of 10

Learn the properties.

Radiation

What it is

Stopped by

Range in air

Ionising power

Alpha (α)

Two protons and two neutrons (a helium nucleus)

A sheet of paper or a few cm of air

A few cm

Strongly ionising

Beta (β)

A high-speed electron from a neutron changing into a proton

A few mm of aluminium

About 1 m

Moderately ionising

Gamma (γ)

Electromagnetic radiation from the nucleus

Thick lead or several metres of concrete

Very long

Weakly ionising

Neutron (n)

A neutron from the nucleus

Thick concrete or water

Long

Indirectly ionising

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Choosing a Source

Atomic structure

Lesson 4 of 10

Which radiation would you use for a smoke detector, and why?

1

Detector

Uses alpha radiation ionising the air between two plates to make a small current

2

Why alpha

It is strongly ionising but stopped by paper, so is safe outside the detector

3

Smoke

Absorbs the alpha particles, the current falls and the alarm sounds

ANSWER

Alpha: it ionises air strongly (to give a current) but cannot escape the device.

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Monitoring Thickness

Atomic structure

Lesson 4 of 10

Which radiation could be used to monitor the thickness of aluminium foil? Explain.

1

Alpha

Absorbed completely by the foil: no use

2

Gamma

Passes through almost unchanged, so the thickness has little effect

3

Beta

Partly absorbed: the count on the other side changes with thickness

ANSWER

Beta radiation: it is partly absorbed by thin foil, so changes in the count rate show changes in thickness.

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Key Ideas

Atomic structure

Lesson 4 of 10

Getting the exam points.

Random

It is not possible to predict when a particular nucleus will decay.

Activity or count rate

Activity in becquerel (Bq); count rate is the number of counts per second on a detector.

Ionising

Radiation that removes electrons from atoms to make ions can damage living cells.

Choose the radiation

Match penetration and ionising power to the job, and think about safety.

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Key Terms

Atomic structure

Lesson 4 of 10

Radioactive decay

The random process in which an unstable nucleus emits radiation.

Activity

The rate at which a source decays, in becquerel.

Count rate

Number of decays detected each second.

Ionising

Able to knock electrons off atoms.

Alpha particle

Two protons and two neutrons.

Gamma ray

Electromagnetic radiation from the nucleus.

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Atomic structure

Lesson 4 of 10

YOUR TASK

Which Radiation?

12 minutes

For each use, choose alpha, beta or gamma and explain: (a) a smoke detector, (b) checking for a leak in an underground pipe using a tracer, (c) monitoring the thickness of paper in a factory.

1

Match penetration to the job.

2

Consider safety.

WHAT A GOOD ANSWER SHOWS

(a) Alpha: strongly ionising, stopped by paper. (b) Gamma: penetrates soil and can be detected above ground. (c) Beta: partly absorbed by paper so the count changes with thickness.

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Can I...?

Atomic structure

Lesson 4 of 10

Define radioactive decay.

Say decay is random.

Define activity and count rate.

Describe alpha, beta and gamma.

State what stops each.

Compare ionising powers.

Choose a source for a use.

Explain a choice.

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Summary & Exam Focus

Alpha: helium nucleus; beta: fast electron; gamma: EM wave.

Penetration: alpha < beta < gamma.

Ionising power: alpha > beta > gamma.

Activity in Bq; count rate per second.

EXAM FOCUS

Describe what an alpha particle is. (1 mark)

Two protons and two neutrons.

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