Core Content

1. What is background radiation?

Background radiation is the low level of radiation that is always present in our surroundings. It comes from natural and artificial sources.

2. Main sources of background radiation:

Natural Radiation Sources (85%):

• (a) Radon gas (in the air):
  A radioactive gas released from rocks underground. It mixes with the air and contributes to about half of the natural background radiation.
• (b) Rocks and buildings:
  Some rocks contain radioactive materials. These are used in construction, exposing us to small amounts of radiation.
• (c) Food and drink:
  Plants absorb radioactive materials from the soil, and animals eat these plants. So food and drink contain tiny amounts of radiation.
• (d) Cosmic rays (from space):
  High-energy radiation from the Sun and outer space. More exposure occurs at higher altitudes (e.g., mountains or flying in airplanes).

Artificial Radiation Sources (15%)

• Medical use (X-rays, cancer treatment) – 14%
• Other sources (nuclear industry, past weapon tests, flying) – 1%

3. Measuring radiation

Radiation is measured using a Geiger-Müller (GM) tube connected to a counter.

• The GM tube detects the radiation.
• The counter shows the count rate – how often radiation is detected.

4. Count rate units:

• Count rate is measured in:
  counts per second (count/s) or
  counts per minute (count/min)