Airline crew are exposed primarily to cosmic radiation rather than radiation from the aircraft itself. At cruising altitude, the atmosphere provides much less shielding than it does at ground level.
The main contributors are:
1. Neutrons (largest contributor to dose)
High-energy neutrons produced when cosmic rays strike the atmosphere are typically the biggest single source of radiation dose to flight crew. Although neutrons are electrically neutral, they can interact strongly with tissue and contribute significantly to the effective dose.
2. Muons
Muons are the most numerous charged particles at cruising altitude. They pass easily through the aircraft and through the human body, but because they interact only weakly with matter, they contribute a smaller fraction of the total radiation dose than their abundance might suggest.
3. Gamma rays
Gamma rays are produced in cosmic-ray interactions and also contribute to the overall dose.
4. Electrons and positrons
These are part of the secondary cosmic-ray shower. They contribute to the dose but are less important than neutrons and muons.
5. Protons and heavier charged particles
These are present in smaller numbers at normal cruising altitudes. During rare solar particle events, their contribution can increase significantly, especially on high-latitude flights.
Approximate contributions on a typical long-haul flight are:
Neutrons: ~40-60%
Gamma rays: ~20-30%
Muons: ~10-20%
Electrons/positrons: ~5-15%
Other particles (including protons): a few percent
A typical radiation dose is:
Sea level (cosmic radiation): about 0.03-0.05 microsieverts per hour.
Cruising altitude (35,000-40,000 ft): typically 3-8 microsieverts per hour, depending on latitude, altitude, and solar activity.
A 10-hour long-haul flight therefore commonly results in a dose of 30-80 microsieverts.
Because of this occupational exposure, flight crew are among the most highly exposed groups of workers to natural radiation. In many countries, airlines monitor or estimate the annual cosmic-radiation doses received by pilots and cabin crew, particularly those flying long-haul and polar routes.