Regarding natural background ionising radiation received by the world population, which statement is correct?
- A Average annual effective dose from all natural sources is about 0.24 millisievert, dominated by cosmic rays
- B Average annual effective dose from all natural sources is about 2.4 millisieverts, dominated by inhalation of radon ✓
- C Average annual effective dose from all natural sources is about 24 millisieverts, dominated by terrestrial gamma rays
- D Average annual effective dose from all natural sources is about 2.4 millisieverts, dominated by internal potassium-40
Correct answer: B. Average annual effective dose from all natural sources is about 2.4 millisieverts, dominated by inhalation of radon
Explanation
UNSCEAR estimates the global average annual effective dose from natural background at approximately 2.4 millisievert, and inhalation of radon and its decay products is the single largest contributor, accounting for roughly half of this dose. Cosmic rays, terrestrial gamma rays and ingested radionuclides including potassium-40 contribute smaller shares. Option A is off by a factor of ten, option C inflates the dose by tenfold, and option D names the wrong dominant contributor, making it the most tempting distractor.
Reference: Park's Textbook of Preventive and Social Medicine, 26th ed.
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