United States Department of Transportation
i
Ionizing Radiation in Earth’s Atmosphere and in Space Near Earth
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2011-05-01
[PDF-799.99 KB]
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Abstract:The Civil Aerospace Medical Institute of the FAA is charged with identifying health hazards in air travel and in
commercial human space travel. This report addresses one of these hazards – ionizing radiation.
Ionizing radiation is a subatomic particle of matter or packet of energy (photon) with sufficient energy to eject an
orbital electron from an atom. Charged subatomic particles from exploding stars (supernovae) are a constant
source of ionizing radiation in the atmosphere and in space. In space another constant source of ionizing
radiation is the solar wind from the Sun. The solar wind consists mostly of electrons and protons with energies
between 10 and 100 keV. The Sun undergoes an approximately 11-year cycle of rise and decline in activity and
during its active phase there is an increased emission of the solar wind and occasional eruptions of high-energy
particles (coronal mass ejections). Other sources of ionizing radiation during air travel include radioactive cargo,
radioactive substances released into the atmosphere as a result of a nuclear reactor accident or terrorist activity,
lightning, and terrestrial gamma-ray flashes.
A health effect following exposure to ionizing radiation for which the severity is radiation dose related is called a
deterministic effect (non-stochastic effect, tissue reaction). Deterministic effects may occur soon after radiation
exposure. For example, nausea and vomiting might be experienced by a space traveler a few hours after receiving
a large dose of ionizing radiation while outside a space vehicle during a coronal mass ejection.
If the probability (risk) of a health effect after exposure to ionizing radiation is dose related, it is called a
stochastic effect. Such effects seldom occur until years after the radiation exposure. Examples of stochastic effects
are cancer and genetic disorders. If one or both parents are irradiated prior to conceiving a child, there is a risk of
genetic disorders in the child and in its progeny.
The report can be used as a source book for instruction on ionizing radiation exposure of air and space travelers.
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