For radiation protection purposes, the approximate average annual effective dose received by every individual on earth from NATURAL background sources is about:
- A 0.02 mSv
- B 0.24 mSv
- C 2.4 mSv ✓
- D 24 mSv
Correct answer: C. 2.4 mSv
Explanation
Worldwide estimates place natural background radiation at roughly 2.4 mSv per year, contributed mainly by radon inhalation, cosmic rays, terrestrial gamma rays and internal radionuclides such as potassium-40. This baseline matters because occupational limits of 20 mSv per year are set relative to it. Values of 0.02 and 0.24 mSv underestimate background by one to two orders of magnitude.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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