What is the main source of ionizing radiation aircrew receive at altitude?

• A. Galactic cosmic radiation.
• B. Solar ultraviolet radiation.
• C. Terrestrial radiation.
• D. Radioactive cabin materials.

Answer: (A)

At flight altitude, the main ionizing radiation aircrew receive comes from galactic cosmic radiation. These high-energy particles from space penetrate the thinner atmosphere encountered at cruising heights, delivering dose directly and also generating secondary radiation as they interact with air molecules. While the Sun can emit particles during occasional solar events, the steady, baseline exposure aircrew experience is dominated by galactic cosmic rays. Terrestrial radiation is largely shielded by the atmosphere at altitude, and radioactive cabin materials contribute only a small, negligible amount compared to cosmic rays. Solar ultraviolet radiation is not a significant contributor to ionizing dose in this aviation context.