Applications of Radioactivity

Radioactive materials give out nuclear radiation. The three main types are alpha ($\alpha$), beta ($\beta$) and gamma ($\gamma$). They have different penetrating abilities, so we choose the type to match the job.

Choosing the right source

• Alpha ($\alpha$): very ionising, stopped by air or paper; useful when you need radiation to be blocked easily.
• Beta ($\beta$): medium penetration; passes through paper but is reduced by thin metal.
• Gamma ($\gamma$): very penetrating; needs thick lead or concrete to reduce it.

Half-life $t_{1/2}$ is the time for the activity to fall to half its starting value. Short half-life means it becomes safe more quickly; long half-life means a steady output over time.

$$\text{After one half-life: activity} = \tfrac{1}{2} \times \text{original}$$

Key applications

• Smoke alarms (household): A tiny $\alpha$-source ionises the air to allow a small current. Smoke blocks the $\alpha$, the current drops, and the alarm sounds. Alpha is chosen because smoke easily stops it.
• Irradiating food: $\gamma$-rays kill bacteria and moulds so food lasts longer. The food is irradiated but does not become radioactive.
• Sterilising medical equipment: Sealed, wrapped tools are exposed to $\gamma$-rays to kill microbes without heating them.
• Measuring thickness (industry): A $\beta$-source and detector sit on either side of a sheet (paper or metal foil). If the sheet is too thick, fewer $\beta$-particles get through, so rollers adjust. Alpha would not penetrate; gamma would penetrate too easily.
• Medical diagnosis (tracers): A patient swallows or is injected with a $\gamma$-emitting tracer. $\gamma$-rays leave the body and are detected to build an image. Tracers have short $t_{1/2}$ so they do not stay radioactive for long.
• Cancer treatment (radiotherapy): Strong, focused $\gamma$ (or $\beta$) radiation is aimed at tumours to damage cancer cells more than healthy cells. Sessions are carefully planned to limit dose to healthy tissue.

Safety and risk

Ionising radiation can kill cells or damage DNA, causing mutations and possibly cancer. Safe use follows three rules: reduce time exposed, increase distance from the source, and use shielding (lead, concrete). Sources are moved and stored in sealed, labelled containers.