Theoretical Assessment of Aircrew Exposure to Galactic Cosmic Radiation Using the FLUKA Monte Carlo Code

Following the publication of the ICRP 1990 recommendations, the need to assess the dose received by aircrew and frequent flyers during air travel has arisen. The ICRP stated that exposure of aircrew to cosmic radiation should be considered as occupational exposure. Several countries have already implemented the ICRP recommendations. Due to the wide range of particles and energies at aircraft flight altitudes, dose measurement is complex and the use of an appropriate computer program for dose calculation is therefore essential. Calculations of cosmic rays propagation through the atmosphere are carried out using the FLUKA Monte Carlo code, based on the latest atmospheric and primary spectra data. In order to assess the effective dose for a specific flight route, a computer routine, FlyRad, links the different segments of the route with the corresponding particles fluence values, taken from the database calculated with FLUKA, and a set of conversion coefficients (fluence to effective dose). Calculations performed for the flight routes of the Israeli airlines show that aircrew members are exposed to occupational annual doses above 1 mSv. Their classification as radiation workers should therefore be considered. Introduction In 1991 the ICRP stated that exposure of aircrew to cosmic radiation should be considered as occupational exposure [1]. In 1996 the European Basic Safety Standards Directive also included the exposure of aircrew to cosmic radiation as occupational exposure [2]. Article 42 in the European Directive, which deals with the protection of aircrew, states that measures should be taken "when organizing working schedules with a view to reducing the doses of highly exposed aircrew". According to Article 10 in the Directive, as soon as a pregnant aircrew member informs her employer of her pregnancy, "the protection of the child to be born should be comparable with that provided for members of the public" (the dose to the child to be born should not exceed 1 mSv during the rest of the pregnancy). Several countries have already implemented the ICRP recommendations or the European BSS Directive. Due to the wide range of particles and energies at aircraft flight altitudes, dose measurement is complex and the use of an appropriate computer program for dose calculation is therefore essential. Galactic cosmic radiation bombards continuously the earth and consists of about 85% protons, 12% helium nuclei, 2% electrons and 1% heavier nuclei with atomic numbers from 3 to ~90 at energies up to 10 eV (but mostly in the range of 10-10 eV). The primary cosmic rays interact with air nuclei and generate a cascade of secondary particles such as neutrons, protons, pions, muons, electrons and photons. Cosmic radiation increases with altitude causing aircrew members to be exposed to enhanced levels of radiation. Methods The Atmospheric Model The atmosphere characteristics (composition and magnetic field) were calculated using NASA’s MSISE model [3] and the IGRF magnetic field model [4]. The atmosphere was simulated up to 100 km using 56 layers of homogeneous density. The data for density and chemical composition were taken from the Mass Spectrometer Incoherent Scatter Extended (MSISE) model. Infinite planes represented the atmosphere geometry, one on top of each other with different thickness, and different nitrogen, oxygen, argon and hydrogen content. The flight altitude range was represented by relatively more layers than other parts of the atmosphere model.