Factors affecting cosmic ray exposures in civil aviation

Cosmic rays come from the Sun and other sources in our galaxy and beyond. Primary cosmic rays undergo nuclear reactions when they strike atoms in the atmosphere, generating a complex variety of secondary particles. These can give radiation doses to people on the ground but also in aeroplanes where dose rates are higher. Doses from cosmic rays depend on duration of exposure, altitude, latitude, and calendar period. The first of these is self-evident: at a given dose rate, the dose increases with duration of exposure. At ground level, the atmosphere provides considerable shielding, but during flight we leave part of this shielding below us. Latitude (distance from the equator) is also important. The Earth's magnetic field helps to deflect cosmic rays away. This protection is greatest at the equator and least at the poles so that the intensity of cosmic rays in the atmosphere increases as one moves to higher latitude. The magnetic field generated by the solar wind also affects the number of cosmic ray particles reaching the earth. The higher the flux of particles from the Sun, the lower the cosmic ray doses at aircraft altitudes. The intensity of this solar wind varies with calendar period. © 2005.