The structure of the atom and isotopes, alpha, beta and gamma radiation and their properties, half-life and decay calculations, the uses and dangers of radiation, and nuclear fission and fusion.

What this dot point is asking

CCEA Double Award wants you to describe the atom and isotopes, the three types of radiation (alpha, beta, gamma) and their properties, half-life and decay calculations, the uses and dangers of radiation, and nuclear fission and fusion. The half-life calculation and the radiation-properties comparison appear in most P1 papers.

Atoms and isotopes

Some isotopes have unstable nuclei; these are radioactive and decay, giving out radiation at random.

Types of radiation

Radioactive decay is random (you cannot predict when one nucleus decays) and spontaneous (unaffected by temperature or chemical change).

Half-life

To find the remaining activity, divide the time by the half-life to get the number of halvings, then halve the starting value that many times.

Uses, dangers, fission and fusion

Uses of radiation include medical tracers and treating cancer (gamma), sterilising equipment, and smoke alarms (alpha). Dangers are that ionising radiation can damage or kill cells and cause cancer, so exposure must be kept low using shielding, distance and time.

Examples in context

Example 1. Carbon dating. Carbon-14 has a half-life of about 5700 years, so measuring how much is left dates ancient remains.

Example 2. Smoke alarms. A smoke alarm uses an alpha source: smoke particles absorb the alpha radiation, the current drops, and the alarm sounds. Alpha is safe here because it cannot penetrate the casing.

Try this

Q1. Which radiation is stopped by a sheet of paper? [1 mark]

• Cue. Alpha.

Q2. A source of activity $240\ \text{Bq}$ has a half-life of $2$ hours. Find its activity after $6$ hours. [2 marks]

• Cue. Three half-lives: $240 \rightarrow 120 \rightarrow 60 \rightarrow 30\ \text{Bq}$.

Q3. State the difference between nuclear fission and nuclear fusion. [2 marks]

• Cue. Fission splits a large nucleus; fusion joins small nuclei. Both release energy.