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Cambridge IGCSE Physics · 0625

Chapter 5: Nuclear physics — Part 3

Topic 5.2.1 · Detection of radioactivity

Background radiation

Background radiation is the ionising radiation that is always present around us.

Significant sources include:

  • radon gas in the air
  • rocks and buildings
  • food and drink
  • cosmic rays
Background radiation sources: radon in air, rocks and buildings, food and drink, and cosmic rays.
Diagram 1: Background radiation sources: radon in air, rocks and buildings, food and drink, and cosmic rays.

Detectors and count rate

Ionising nuclear radiation can be measured with a detector connected to a counter (for example a Geiger–Müller tube).

Count rate is measured in counts per second or counts per minute.

Corrected count rate = measured count rate − background count rate. Always take a background reading with no source present.

Detector connected to a counter; measured count rate minus background count rate giving a corrected count rate.
Diagram 2: Detector connected to a counter; measured count rate minus background count rate giving a corrected count rate.

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