What is the greatest source of natural background radiation exposure?

What is the greatest source of natural background radiation exposure?

• A. Cosmic rays
• B. Radioactive materials
• C. The body itself
• D. Radon gas

Answer: (D)

The main idea is understanding where natural background radiation comes from and which source contributes most. Radon gas stands out because it forms in soil from uranium decay and can seep into buildings through cracks and foundations. Once inside, it accumulates, and its short‑lived decay products attach to dust and are inhaled. Those decay products emit alpha particles that deliver a significant dose to lung tissue. People spend most of their time indoors, so indoor radon exposure tends to dominate the natural background radiation a person receives, more than cosmic rays or external radiation from surrounding rocks. The body’s own trace radionuclides provide a smaller, constant internal dose, and external exposure from the environment is present but typically less than the indoor radon contribution.

The main idea is understanding where natural background radiation comes from and which source contributes most. Radon gas stands out because it forms in soil from uranium decay and can seep into buildings through cracks and foundations. Once inside, it accumulates, and its short‑lived decay products attach to dust and are inhaled. Those decay products emit alpha particles that deliver a significant dose to lung tissue. People spend most of their time indoors, so indoor radon exposure tends to dominate the natural background radiation a person receives, more than cosmic rays or external radiation from surrounding rocks. The body’s own trace radionuclides provide a smaller, constant internal dose, and external exposure from the environment is present but typically less than the indoor radon contribution.