6.28P Describe uses of radioactivity, including: a household fire (smoke)…

The idea

This Physics-only content requires description of five uses of radioactivity. In smoke alarms, alpha particles ionise air so a current flows; smoke absorbs the ions and the alarm sounds. Food is irradiated with gamma rays to kill microorganisms and extend shelf life. Medical equipment is sterilised by gamma radiation, which kills microbes without opening sealed packaging. Tracers use a gamma-emitting isotope taken into the body so its movement can be detected outside; thickness gauges use the absorption of beta or gamma radiation to monitor and control the thickness of paper, plastic or metal sheet. In medicine, gamma sources are used to diagnose by imaging and to treat cancer by directing radiation at tumours. Each use exploits a property such as ionising power, penetration or absorption.

What earns the marks

• Explains that alpha particles ionise air in a smoke alarm and smoke interrupts the current.
• States that gamma radiation kills microorganisms in food irradiation to extend shelf life.
• Describes gamma sterilisation of equipment as killing microbes on sealed items.
• Explains that a gamma-emitting tracer is detected outside the body to follow its movement.
• Describes a thickness gauge as using absorption of beta or gamma radiation to monitor sheet thickness.
• Identifies diagnosis by imaging and treatment by directing radiation at tumours.

Common mistakes and how to put them right

• Uses an alpha emitter as a medical tracer.

  Put it right: Choose a gamma emitter so radiation escapes the body for detection.

• Claims food irradiation makes the food radioactive.

  Put it right: State that it kills microorganisms instead.

• Describes a thickness gauge as measuring emitted radiation only.

  Put it right: Explain that absorption of transmitted radiation varies with thickness.

Exam tips

• Link each use to the penetrating or ionising property that makes it suitable.
• Name the type of radiation for each use rather than saying only 'radiation'.
• Keep each description to one clear sentence covering what the source does and why it works.