4.4.2.1 - Radioactive decay and nuclear radiation

What is radioactive decay?

Radioactive decay is when unstable nuclei give out radiation as they change (decay) to become more stable

What type of process Is radioactive decay?

Radioactive decay is a random process

What is meant by ‘Activity’?

Activity - refers to the rate at which a source of unstable nuclei decays

What is activity measured in?

Measured in Becquerel (Bq)

1 Bq is how many decays per second?

1 Bq = 1 decay per sec

Define ‘count rate’

Count rate - refers to the number of decays recorded each second by a detector

E.g. the number of radiation reaching a Geiger-muller tube

What are the four types of nuclear radiation that can be emitted?

• Alpha particles (a)

• Beta particles (B)

• Gamma rays (Y)

• A neutron (n)

Describe the alpha particles that are released as radiation.

Alpha particles contain two neutrons and two protons

What element’s nucleus are alpha particles like?

Helium nuclei

Describe the properties of alpha particles.

• Don’t penetrate for into materials

• Strongly ionising

What is a beta particle and when is it released?

Beta particles are high speed electrons ejected from the nucleus as a neutron turns into a proton

Describe the properties of beta radiation.

• Moderately ionising

• Penetrate materials also moderately

What is gamma radiation?

Gamma radiation is short wavelength, electromagnetic radiation emitted from the nucleus

Describe the properties of gamma radiation.

• Penetrate far into materials

• Weakly ionising

Why do atoms release neutrons?

The release of a neutron helps rebalance their atomic and mass numbers

What is meant by ionising radiation?

• Radiation that knocks electrons off atoms (creating positive ions)

• Ionising power of a radiation source is how easily it can create positive ions

List the properties of alpha radiation.

• Don’t penetrate far and are stopped quickly

• Can only travel a few cm in the air

• Absorbed by a sheet of paper

• Strongly ionising

How far can alpha radiation travel in the air?

A few cm only

Where is alpha radiation most commonly used?

In smoke detectors

Describe how smoke detectors use alpha radiation.

The alpha radiation ionises air particles allowing a current to flow

However, if there is smoke in the air, the smoke binds with the ions (in the air)

This means that the current can no longer flow - causing the alarm to sound

List the properties of beta radiation.

• moderatley ionising

• Moderately penetrating - travel far in materials before colliding

• Absorbed by a sheet of aluminium (roughly 5 mm)

How far can beta radiation travel in air?

Have a range in the air of a few metres

By what material is beta radiation absorbed by?

A sheet of aluminium - roughly 5mm thick

What is beta radiation mainly used for?

Used to test the thickness of sheets of metal

Describe why beta radiation is used to test the thickness of metal sheets.

The particles are not immediately absorbed by the material like alpha radiation and would not penetrate as far as gamma rays.

List the properties of gamma rays.

• Penetrate far into materials

• Travel long distances in the air

• weakly ionising

Why are gamma rays weakly ionising?

Gamma rays are weakly ionising as they tend to pass through rather than collide with atoms (although they do eventually hit something)

What are gamma rays absorbed by?

Can be absorbed by thick sheets of lead or metres of concrete