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nuclear power plants.
Unit of measurement
The effect of both electrons, α-particles and γ-radiation on living tissue is to cause ionization. The amount
of radiation energy absorbed is measured in gray (Gy)3, but as the biological effect depends not only on
energy but also on the composition of the radiation (different particles etc.), it is necessary to weight the
absorbed dose to obtain a dose equivalent, a unit of “harmful effect”, called sievert (Sv).4
Background Radiation
Everybody on earth is exposed to radiation. The total normal radiation (background radiation) per person
is virtually constant with a yearly dose equivalent estimated to be about 2 mSv in most countries. But due
to natural radioactivity in soil and rocks, in parts of Brazil the yearly average is as high as 5-10 mSv, and
in Kerala (India) a yearly dose of 28 mSv has been measured. In the industrial countries radiation from
other sources, mainly medical X-rays, is estimated to around 1 mSv. On top of this exposure, totalling
3 mSv/year, may be added “occupational exposure”.
Occupational Exposure
In recent years world-wide attention has been given to the problem of air crew being exposed to ionizing
radiation. In the European Union, following the recommendations of the International Commission on
Radiological Protection (ICRP), specific provisions on the health protection of air crew against dangers
arising from exposure to cosmic radiation have been laid down in legislation since May 2000. There is,
however, still some disagreement about the effects and even the amount of radiation to which air crew are
exposed while on duty.
A substantial part of the cosmic radiation is absorbed by the upper part of the atmosphere or deflected
by the earth’s magnetic shield, but some penetrates to ground level and thus forms part of our natural
environment. The intensity of cosmic radiation increases with height above sea level because the
atmosphere becomes thinner and absorbs less of the radiation (e.g. the intensity of cosmic radiation is
doubled by an increase in altitude from sea level to about 5000 feet and this doubling continues up to
about 70 000 feet). High altitude flight therefore increases the degree of exposure to cosmic radiation. The
polar regions have a greater radiation intensity than the equatorial regions, owing to flattening of the
atmosphere over the poles and the shape of the earth’s magnetic field.
Many studies have been conducted aboard airliners, mainly flying on North Atlantic routes, to
establish the amount of radiation to which the air crew are exposed. Based on these studies, it is possible
to calculate a radiation exposure of approximately 5 mSv per year for air crew flying 600 hours per year
north of N50 at altitudes above 39 000’, and approximately 3.3 mSv per year if the flight level is reduced
to altitudes around 33 000’. If the annual flying hours are calculated for cruising only (with deduction for
start, climb, descent, and landing) to 400 hours per year, the radiation exposure will be around 2 mSv.
Flying south of N50 will entail a further reduction in exposure.
31 Gy = 1 joule/kg = 100 rad (absorbed radiation).
41 Sv = 1 joule/kg = 100 rem
(dose equivalent = 1 Gy for β-radiation).
ICAO Preliminary Unedited Version — October 2008 II-1-13
In a recent study conducted by the national airline in a Contracting State, situated between N60 and
N70, the maximum radiation exposure in full-time air crew measured during ordinary scheduled flying
over one year was 2.8 mSv.
Maximum Exposure
The maximum radiation exposure, recommended by ICRP, for individual members of the public is 1 mSv
per year or, in particular cases, 5 mSv per 5 years. For workers exposed to radiation (and therefore under
special surveillance which may include annual health examinations) the recommended limit is 100 mSv
per five years or an average of 20 mSv per year with a maximum of 50 mSv in any one year. For pregnant
workers the recommended limit is 1 mSv per year or the same for the foetus as for any other individual
member of the general public.
Use of Computer Programmes to Estimate Dose
It is possible to estimate the radiation dose for a certain route by using a computer programme developed
for this purpose. The data to be input are the date and location of departure, the flight profile, detailing the
time in climb, cruise and descent, and the time and location of arrival.
One such programme, which is simple to use and has been validated, is produced by the Civil
Aeromedical Institute (CAMI) in the United States. CAMI was previously known as the Civil
Aeromedical Research Institute (CARI). The latest version of this computer programme is called CARI-6
　
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本文鏈接地址：Manual of Civil Aviation Medicine 1(62)