Investigation of Radiation Fields at Aircraft Altitudes

Cosmic rays are believed to originate from several possible sources and recent research suggests that the bulk originate from the gas and dust of the interstellar medium and are accelerated by strong shock waves driven by supernova explosions. Cosmic ray particles are made up of ∼98.5% hydrogen and helium and only 1.5% have charges greater than 2. Their average energy is about 1 GeV/nucleon and they lose energy through ionisation interactions and nuclear interactions with atoms of air as they penetrate deeply into the Earth's atmosphere. A very complicated radiation field develops as particles are generated by successive interactions of primary and secondary nuclei and a cascade of hadrons is produced in the atmosphere. The intensity of particles reaches a maximum at about 20 km above sea level (∼60 g.cm -2 ). The relative abundances of different particles change with depth within the atmosphere and mainly muons which are the decay products of charged mesons, reach sea level because of their weak interaction. The radiation field produced and consequently its effect on aircrew and frequent travellers is a matter of some concern. This paper outlines the results of investigations carried out to determine the characteristics of this radiation field and assess its impact on aircrew.