Radioactive decay and nuclear radiation

Some atomic nuclei are unstable. To become more stable, they emit radiation in a process known as radioactive decay. This process is entirely random, meaning it is impossible to predict exactly when a nucleus will decay.

Key terms

1. Activity:

   • The rate at which a source of unstable nuclei decays.

   • Measured in becquerels (Bq), where 1 Bq equals one decay per second.

2. Count-Rate:

   • The number of decays detected per second by a radiation detector, such as a Geiger-Müller tube.

Types of nuclear radiation

Alpha, beta and gamma radiation

Unstable nuclei can emit different types of radiation during radioactive decay. These include:

1. Alpha Particles (α):

   • Composed of two protons and two neutrons, making it the same as a helium nucleus.

   • Properties:

     • Large and heavy.

     • Strongly ionising, meaning they can easily knock electrons off atoms.

     • Low penetration power: stopped by a sheet of paper or a few centimetres of air.

2. Beta Particles (β):

   • A high-speed electron emitted when a neutron in the nucleus turns into a proton.

   • Properties:

     • Smaller and faster than alpha particles.

     • Moderately ionising.

     • Medium penetration power: stopped by a few millimetres of aluminium.

3. Gamma Rays (γ):

   • High-energy electromagnetic radiation emitted from the nucleus.

   • Properties:

     • No mass and no charge.

     • Weakly ionising but very penetrating.

     • Requires several centimetres of lead or metres of concrete to be stopped effectively.

The penetration power of alpha, beta and gamma radiation

4. Neutrons (n):

1. • Occasionally emitted during radioactive decay. Neutrons have no charge but can penetrate materials deeply and cause further nuclear reactions.

Applications of radiation

You should understand the practical uses of radiation and evaluate which type is best suited for specific applications. Here are some examples:

1. Alpha Radiation:

   • Used in smoke detectors. Alpha particles ionise air, creating a small electric current. Smoke disrupts this current, triggering an alarm.

   • Not harmful outside the body due to low penetration.

2. Beta Radiation:

   • Used for thickness control in manufacturing (e.g., paper or foil production). Beta particles pass through the material, and the detector measures how much radiation gets through to adjust thickness.

   • Can penetrate light materials but stopped by denser barriers.

3. Gamma Radiation:

   • Used for sterilising medical equipment and killing cancer cells in radiotherapy.

   • High penetration makes it ideal for deep tissue treatments and passing through sealed containers to sterilise contents.

Safety considerations