Radioactivity and the Nucleus: Question 6

Worked solution

Step 1: Recall what background radiation is

Background radiation is the ionising radiation that is present in the environment all the time, from both natural and man-made sources, regardless of whether a specific radioactive source has been deliberately placed nearby.

Step 2: Check each option against known sources of background radiation

• Radon gas seeps out of certain rocks and soils and, in many places, is the single largest natural contributor to background radiation.
• Cosmic rays are high-energy particles and radiation reaching the Earth from space; they are a well-established natural source of background radiation.
• Medical X-ray examinations are a recognised man-made source that adds to a person’s overall exposure to background radiation.
• Microwave signals from a mobile phone network are non-ionising electromagnetic radiation. Their photons do not carry enough energy to ionise atoms, so they are not counted as a source of (ionising) background radiation at all.

Step 3: Match to the correct option

Radon gas, cosmic rays and medical X-rays are all genuine, well-documented sources of background radiation. Microwave signals are a different, non-ionising kind of radiation altogether, so option D is the one that is NOT a source of background radiation.

Why the other options are wrong

Final answers

• Microwave signals from a mobile phone network are NOT a source of background radiation, option D.