G
GSF - National Research Center
for Environment and Health
Institute of Radiation Protection
Determining radiation exposure of airline staff
As early as 1990 the International Commission on Radiological Protection (ICRP) found from
estimates that the professional group of pilots and other flight personnel are exposed to a level of cosmic
radiation that is comparable to or in the average, even higher than that of people who deal with artificial
radiation in medicine and technology. Therefore the same radiation protection criteria ought to apply to this
group of workers, too.
As a result, the ICRP worked out recommendations regarding annual dose limit, for example, and
these were adopted into European Law in 1996 and German legislation in August 2001. Like in other
European countries, in Germany in the radiological protection regulations, corresponding rules are laid down
for individual dose calculation in order to conform to the set limits.
As an immediate consequence of the ICRP recommendations, a number of European institutes had
issued research programmes, the aim of which was the theoretical and experimental recording of natural
exposure to ionising radiation in aircraft. The GSF has also been involved in both approaches and, with
support from the EU Commission, eventually developed the EPCARD program (European Program
Package for the Calculation of Aviation Route Doses) jointly with scientists from Siegen University. This
makes it possible to calculate the dose exposure from all the components of penetrating cosmic radiation on
any aviation route and for any flight profiles you wish. This program is, herewith, now available to interested
persons.
To explain the background physics: the very high-energy, galactic primary radiation from interstellar
space – predominantly protons – enters our solar system and strikes the earth’s atmosphere where it
discharges an avalanche of secondary particles: neutrons, pions, mesons, electrons, photons and again
protons. Depending on their energy and charge, the particles interact to varying degrees with the molecules
of the earth’s atmosphere, thereby losing energy, and they are ultimately absorbed in the earth’s
atmosphere or solid earth. Apart from this shielding effect of the earth’s atmosphere, there are two other
effects that shield against primary radiation, namely the sun and the earth’s magnetic field. The sun emits a
huge flow of matter known as solar wind, the effect of which is felt around a hundred astronomical units
away (1 AU = distance from the sun to the earth, approximately 150 million km) and which has to be
overcome by the primary particles. The intensity of the solar wind fluctuates depending on solar activity,
which can be deduced from the number of sunspots, with a cycle of 11 or 22 years. By contrast, the earth’s
magnetic field is almost constant in time; it is easiest to overcome at the poles because the particle
pathways there run roughly parallel to the magnetic field lines. At the geomagnetic equator, however, the
particles need to have an energy of over 15 GeV (=15 billion electronvolts) to advance perpendicular to the
field lines and get as far as the earth’s atmosphere. Since the far more frequent lower-energy particles are
deflected away from the earth, radiation exposure is far lower at the equator than at the poles.
All these effects were calculated using a “Monte-Carlo (MC) computer program” and the best NASA
models for galactic radiation and solar modulation at the time. The MC program FLUKA used for describing
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the interactions of particles (developed over many years by INFN and CERN ) runs through all the physical
processes using records from experiments on high-energy accelerators. The results were then used as the
fundamental data for EPCARD.
Why can we not simply use measurements taken in aircraft to do the dose measuring required by
law? This question is often asked and can be answered as follows:
1. Measurements with different, suitable experimental devices have been done and are done at
different times, at different geographical locations and at different flight altitudes so that as accurate a
physical model as possible is required which will find an adjustment of these measurements. In any case,
the whole “world dose matrix” at all locations and at all times cannot be covered by measuring flights.
2. The law requires the “effective dose” to be determined. This is a quantity used for estimating the
radiological risk, which involves not only physical but also radiobiological and other information. This
includes, for instance, the fact that neutrons have a far higher biological effect than photons and that the
radiation sensitivity of individual organs differs widely. The effective dose is thus not directly measurable
and either has to be fully calculated or be converted from measurements that represent an initial
approximation to actual doses. The latter method requires what are known as particle spectra, i.e. the
number of particles found in one of the many energy intervals. This information can only be obtained from
MC calculations in the particular energy range that is significant in terms of dosimetry. In the case of
neutrons, for example, this range is roughly between 0.001 electronvolts and 500 mega electronvolts.
Aviation doses can be estimated from the figure below, but these can alter considerably depending on
the route and flight profile. It clearly shows that, for a similar flight time, far lower doses accumulate on
flights over the equator (e.g. from Munich to Sao Paulo) than on the North Atlantic routes (e.g. en route to
San Francisco). For comparison: if one were to stay at our latitudes at sea level, the effective dose from
natural cosmic radiation in one year would be about 300 µSv (millisievert) and that from total natural
penetrating radiation (not considering radon radiation, etc.) about 1000 µSv.
More detailed calculations for specific flights may be done on-line with EPCARD presented here. For
airlines and other air undertakings, a full version is available, which permits the calculations for the daily
record keeping.
INFN=Istituto Nazionale di Fisica Nucleare, Italy. CERN=European Laboratory for High-energy Physics, Geneva,
Switzerland.
15
80
effective dose (µSv)
70
60
50
effective dose (left scale)
flight time (right scale)
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EPCARD V3.2
40
30
5
flight time (hours)
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10
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Figure: Comparison of flight time and effective dose for flights from Munich and Frankfurt (*) to selected
destinations by the shortest route, ranked by increasing flight time. The doses were calculated using
EPCARDv3.2 for January 2002 for the following conditions: ascent and descent 30 minutes each, assumed
flight altitude 37,000 ft (approx. 11 km).
Dr.-Ing. Hans Schraube