Nuclear radiation (AQA GCSE Physics): Revision Notes
Nuclear radiation
Nuclear radiation happens when unstable atoms break down. This process is called radioactive decay. It's completely random - we can't predict exactly when any particular atom will decay.
What is nuclear radiation?
Nuclear radiation is energy or particles that come from unstable nuclei. Some atoms have too many protons or neutrons, making them unstable. To become stable, they give off radiation and change into different elements.
When atoms become unstable due to having too many protons or neutrons, they must release energy to reach a stable state. This energy release is what we observe as nuclear radiation.
There are four main types of nuclear radiation:
- Alpha particles (α)
- Beta particles (β)
- Gamma rays (γ)
- Neutron radiation
Types of nuclear radiation
Alpha particles (α)
Alpha particles are the biggest and heaviest type of radiation. They are actually helium nuclei.
Alpha Particle Composition:
An alpha particle consists of:
- 2 protons (+2 charge)
- 2 neutrons (no charge)
- Total charge: +2
- Mass: approximately 4 atomic mass units
Key facts about alpha particles:
- Made of 2 protons and 2 neutrons
- Have a positive charge of +2
- Travel about 5 cm in air
- Very good at ionising atoms (knocking electrons off)
- Easily stopped by a sheet of paper or a few cm of air
Beta particles (β)
Beta particles are high-speed electrons shot out from the nucleus.
Despite being called "particles," beta radiation consists of electrons that originate from nuclear processes, not from the electron shells around the nucleus.
Key facts about beta particles:
- They are electrons with a negative charge of -1
- Much lighter than alpha particles
- Travel a few metres in air
- Moderately good at ionising atoms
- Stopped by a few millimetres of aluminium
Gamma rays (γ)
Gamma rays are electromagnetic radiation, like very powerful X-rays.
Key facts about gamma rays:
- Have no mass and no electric charge
- Travel at the speed of light
- Travel many kilometres in air
- Weakly ionising compared to alpha and beta
- Need thick lead or concrete to stop them
Neutron radiation
Neutrons are particles with no electric charge.
Key facts about neutron radiation:
- Have no electric charge (neutral)
- Don't directly ionise atoms
- Very good at penetrating materials
- Can travel long distances through buildings and people
- Difficult to stop
Properties of radiation
The different types of radiation have very different properties when it comes to their ability to ionise atoms and penetrate materials.
Ionising power
This is how good radiation is at removing electrons from atoms.
Ionising power is inversely related to penetrating power - radiation that ionises strongly doesn't travel far because it loses energy quickly through interactions with atoms.
- Alpha: Very high ionising power
- Beta: Medium ionising power
- Gamma: Low ionising power
- Neutron: Not directly ionising
Penetrating power
This is how far radiation can travel through materials.
- Alpha: Very low - stopped by paper
- Beta: Medium - stopped by thin aluminium
- Gamma: Very high - needs thick lead to stop
- Neutron: Very high - travels through most materials easily
Key Radiation Properties:
- Ionising power: Alpha > Beta > Gamma > Neutron
- Penetrating power: Neutron ≈ Gamma > Beta > Alpha
- Stopping materials: Paper stops α, thin Al stops β, thick Pb stops γ, neutrons are hardest to stop
Why does this matter?
Understanding radiation properties helps us stay safe around radioactive materials.
Critical Safety Information:
- Alpha particles are dangerous if swallowed but can't penetrate skin
- Beta particles can cause burns but are stopped by thin metal
- Gamma rays can pass through the body and cause damage inside
- Neutrons are very penetrating and hard to protect against
The key principle is that external exposure requires different protection than internal contamination. Alpha particles are harmless outside the body but extremely dangerous if ingested, while gamma rays pose risks from both external and internal sources.
Remember These Key Points:
- Nuclear radiation comes from unstable atoms that decay randomly
- Alpha particles are heavy, charged, and easily stopped by paper
- Beta particles are electrons that need thin metal to stop them
- Gamma rays have no mass or charge and need thick lead to stop them
- Neutron radiation has no charge and is very penetrating
- The more ionising the radiation, the less it can penetrate materials