Calculation of Radiation Exposure at Aviation Altitudes in Case of Solar Particle Events

Cosmic rays, i.e., protons and atomic nuclei with high energy from astrophysical origin, are the dominant producers of enhanced radiation doses at aircraft altitudes. While the assessment of dose rates produced by the permanent galactic cosmic ray (GCR) component is well-established and operational, the evaluation of the sporadic solar cosmic ray (SCR) contribution during so-called Ground-Level Enhancements (GLEs) is an issue of current research. Several institutions developed codes for the assessment of solar radiation doses at flight altitudes. EURADOS Working Group WG11 conducted a study comparing route doses and dose rates at flight altitudes during two selected GLEs as calculated by means of nine computer codes. For GLE42 (29 September 1989) pre-defined solar particle characteristics were provided to the participants of the study. In contrast, for GLE69 (20 January 2005) the participants were asked to define the proton characteristics on their own based on published information made available to them.

In the study it was found that GCR route doses show a standard deviation from the median consistent with the results published in the earlier EURADOS report on GCR exposure. For GLE42 a standard deviation from the median of about 30% is obtained for the SCR route doses, while for GLE69 the standard deviation from the respective median amounts to 50%. The lowest and the highest SCR route doses obtained by the different codes for a given flight may differ by up to a factor of 10. One of the main reasons for the differences in the computed results is found to be the unequal identification and handling of the GLE characteristics, such as energy spectrum and directional distribution. Therefore, we strongly suggest developing a traceable method to identify and handle the solar particle characteristics during GLEs. Furthermore, we see an urgent need to validate codes used for dose assessment of radiation exposure due to solar particle events by in-flight measurements.

The results of this study and further detailed information were published in an EURADOS report which is available under https://eurados.sckcen.be/sites/eurados/files/uploads/Publications/2021/EURADOS-Report-2021-03.pdf.