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Exposure to flight crew and frequent
flyers
Cosmic radiation contributes about 13% of
the natural background radiation level. It
is believed to come from Milky Way galaxy
but its’ origin is unclear. Cosmic radiation
consists primarily of charged and neutral
particles (protons, alpha particles, heavier
ions, and electrons) and secondary particles
generated by interaction of cosmic radiation
with atmosphere’s air (ions, neutrons, gamma
rays, electrons, etc). Along with solar
radiation it constantly bombards Earth’s
atmosphere.
The Earth’s magnetic field deflects many
charged particles that would otherwise reach
ground level but at jet aircraft attitudes
cosmic radiation can contribute
significantly to doses accumulated over
hundreds flight-hours by flight crew and
frequent flyers.
Flight crew is now recognized as
occupationally exposed to radiation
professional category and radiation
protection limits for flight crew are
similar to those in nuclear workers.
Short-haul vs.
Long-haul
Short-haul flights are flown at lower
altitudes than long-haul flights.
Consequently, there is more radiation
shielding provided by atmospheric air at
lower altitudes and lower dose received from
cosmic radiation. The latitude of the flight
route also makes a difference in the level
of cosmic radiation exposure. If two
same-distance flights are flown at different
geographic latitudes but at the same
altitude, the cosmic radiation level on the
lower-latitude flight will be usually lower
of the two because of the greater shielding
factor provided by earth's magnetic filed.
This shielding is maximum at the equator and
gradually decreases to zero at the south and
north poles.
For example, in 1958-200, at an altitude
of 10,000 m the average galactic cosmic
radiation level over Reykjavik, Iceland
(64°N, 22°W), was approximately twice that
over Lima, Peru (12°S, 77°W)
WHO is in the process of developing a
Fact Sheet on Cosmic Radiation and Exposure,
as well as producing occupational safety
information for civil aviation workers. |
