Radiation doses during extreme solar energetic particle events

TL;DR

This paper examines radiation doses from extreme solar energetic particle events, focusing on risks to aviation and space missions, and provides estimates based on recent and historical data.

Contribution

It offers first estimates of radiation exposure during extreme SEP events, incorporating radionuclide data and modeling assumptions.

Findings

Extreme SEP events can significantly increase radiation doses at aviation and space altitudes.

Parameters like fluence and spectrum critically influence radiation risk assessments.

Historical radionuclide data can be used to estimate past extreme SEP event impacts.

Abstract

Ions and electrons accelerated to high energies during flares and coronal mass ejections at the Sun may escape the solar atmosphere and, guided by the interplanetary magnetic fields, propagate through space to near-Earth locations. These Solar Energetic Particles (SEPs) can be detected directly by spacecraft instrumentation. The highest energy SEPs may also propagate through the geomagnetic field and precipitate to low atmospheric heights, producing secondary particles including neutrons and protons that trigger the formation of cosmogenic radionuclides. The space weather effects associated with the SEP ion population (for the most part protons) consist principally of radiation risk to aviation, humans in space and spacecraft. This paper focusses on the risks to aviation and astronauts and emphasizes how the parameters of the SEP event, including fluence and spectrum, affect radiation doses. Space weather effects for events that took place in recent decades, for which a large body of measurements and models exist, are discussed. SEP events of extreme magnitudes, such as those extrapolated from radionuclide data from the distant past are then considered and first estimates of the associated radiation at aviation altitudes and in space presented. These are worst-case estimates derived within the assumption that the radionuclide spike was caused by a single SEP event and that the particle spectrum and geomagnetic conditions were the same during all events.