Exposure to Cosmic Radiation during Air Travel
When we travel by airplane at high altitude, we are generally exposed to higher cosmic radiation, compared to the amount we receive on the ground. Between 6km and 12km altitude where the commercial airplanes usually fly, we receive an elevated level of cosmic radiation, mainly from galactic and solar origins.
Sources of galactic cosmic radiation originate from the deep space. Galactic cosmic radiation consists of high-energy electromagnetic component (gamma radiation) and nucleonic component. Radiation enters our atmosphere and interacts with the air molecules, producing cascades of secondary galactic cosmic radiation (Figure 1). They attenuate when travelling through the atmosphere where their energies are absorbed by the surrounding air molecules. The primary and secondary galactic cosmic radiations share the largest portion of the radiation dose we receive during air travel at high altitude.
Solar cosmic radiation is generated near the surface of the Sun by magnetic disturbances. Solar cosmic radiation is composed primarily of protons. Similarly, they enter the atmosphere, weakening on the course due to attenuation by the air molecules. Solar cosmic radiation also contributes to the radiation dose we receive at high altitude during air travel.
The atmospheric shielding effect against cosmic radiation primarily depends on the Earth's magnetic field and air molecules which vary with time and location. Thus, the amount of radiation dose we receive during air travel will be affected by a number of factors, including flight period, flight altitude and flight path. If you would like to have a rough estimate on how much radiation dose you receive, including information on doses corresponding to flights from Hong Kong to some popular destinations, please try the dose calculator available online at http://www.dbcp.gov.hk/eng/edu/cal.htm.