Exposure to cosmic               radiation in the plane

	Influence factors

Exposure increases with altitude, since the atmosphere absorbs part of the cosmic radiation. It also depends on the plane's route. As to the dose received, this of course varies with the duration of the flight. Members of flight crews are therefore more subject to exposure than occasional travellers.

Exposure increases with altitude

As we gain altitude, the protective atmospheric layer grows thinner, increasing our exposure to cosmic radiation.
At the cruising altitude of commercial aircraft, i.e. from 10,000 to 12,000 metres, the cosmic radiation is approximately 100 to 300 times more intense than at sea level. On board the Concorde, which flies at 18,000 metres, the rate of exposure is almost twice as high as on subsonic planes.

Exposure varies with latitude

Because of the barrier provided by the earth's magnetic field, there are more particles of cosmic radiation at higher latitudes, closer to the poles, than there are at the equator. Depending on the latitudes of the plane's route, we will therefore be more or less exposed to radiation.

Exposure depends on the flight's duration

For a given flight, the total dose of cosmic radiation received is directly proportional with the duration of exposure, and thus with the duration of the flight.

Measurements taken on board aircraft during the 1990s showed that flight personnel (on long haul flights) receive an average dose of approximately the same magnitude as the one due to exposure to natural radioactivity in France.

	To receive a dose of one millisievert
	17 months in Paris
	9 months in the Limousin region
	7 round-trip Paris-Tokyo or San Francisco flights
	13 round-trip Paris-New York Concorde flights
	1 1/2 days on board MIR (altitude 400 km)

Protection of flight personnel

Due to their professional activities, flight crews can receive an equivalent dose of a few mSv per year. European regulations adopted in 1996 therefore oblige companies operating aircraft to monitor the exposure of their flight crews. In France, the public authorities made the S.I.E.V.E.R.T. (Computerized System For Assessing the Exposure to Cosmic Radiation during Air Transportation) available to employers. This dose assessment tool was developed by the Civil Aviation Department (DGAC) and its partners: the Nuclear Protection and Safety Institute (IRSN),the Paris Observatory and the French Polar Research and Techniques Institute (IPEV).

European regulations

The 13 May 1996 European EURATOM directive n° 96-29 significantly modified the standards for protecting the health of the population and of workers against the dangers resulting from ionising radiation. It was transposed into French law by the decree n° 2001-270 of 28 March 2001.

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One of the innovations of the European directive is that it takes into account the exposure to natural radiation. With regard to the protection of flight crews, article 42 provides the following measures:
"Each Member State shall take the necessary measures so that companies operating aircraft take into account the exposure to cosmic radiation of flight crews who are likely to be exposed to more than 1 mSv per year. The company shall take the necessary measures in order to
- assess the exposure of the relevant personnel,
- take the assessed exposure into account when organising work programmes such as to reduce the doses of highly exposed flight personnel,
- inform the employees in questions of the possible dangers to their health resulting from their work,
- apply article 10 to female flight personnel.”

Article 10 of the directive relates to special protective measures during pregnancy. Upon informing her employer of her condition, a pregnant woman must no longer be assigned to in-flight duties if the equivalent dose received by the unborn child, until the end of the pregnancy, is likely to exceed 1mSV.

Assessment of radiation doses received during flights

In France, the Computerized System for Assessing the Exposure to Cosmic Radiation during Air Transportation - acronym: "S.I.E.V.E.R.T." - has been made available to airline companies in order to help them apply article 42 of the European directive. The service, of a professional nature, is available through an Internet server which is accessible to companies which have applied for access to the Department of Civil Aviation (DGAC). However, a public part allows a passenger to estimate the dose received during a trip.
The system provides exposure values which take into account the routes used by aircraft. These values are calculated on the basis of models which have been verified during many flights, and which offer a satisfactory margin of uncertainty. Moreover, in the event of a solar flare, the S.I.E.V.E.R.T. system makes it possible to assess the impact on the received dose.

S.I.E.V.E.R.T. is a tool which is adapted to the dosimetry of the exposure to cosmic radiation experienced by flight personnel. It does not require particular knowledge in the area of radiation protection within the airline company. It does not result in usage constraints amongst the personnel, as is the case with individual dosimeters.

S.I.E.V.E.R.T. must allow proper application of the regulations for at least three reasons. First of all, the results obtained are sufficiently close to reality so that the doses received by flight personnel are not underestimated. Secondly, the method for assessing radiation doses is the same for all airline companies. And finally, should further verifications prove necessary in the future, retrospective dose calculations would still be possible.

The S.I.E.V.E.R.T. usage principle is quite simple. The company prepares a record of completed or planned flights, and leaves it at the S.I.E.V.E.R.T. Internet address. The system then completes the record by adding the dose received during each flight. The doses are calculated according to the flight characteristics, using the dosimetric data validated by the Radiation Protection and Nuclear Safety Institute (IRSN).
The more information is provided above the intended route, the greater the accuracy of the dose. If the information is minimal, the dose is assessed using a standard route. At this stage, the data is anonymous and the dose file for flights can be retained for subsequent verifications. It is then up to employers to add up the doses received during flights carried out by each member of the flight crews. This information is made available to the person in question, and provided to the occupational doctor and to the Radiation Protection and Nuclear Safety Institute (IRSN).

At the heart of S.I.E.V.E.R.T., airspace is divided into altitude zones, with longitude and latitude, forming a map of 265,000 links. For each link, the Radiation Protection and Nuclear Safety Institute (IRSN) has assigned a value for the dose flow. The S.I.E.V.E.R.T. calculator assesses the time which the plane spends in each link, thus deducing the received dose. The total of the doses received in each link gives the total dose received during the flight.

Every month, the map of dose flows is validated by the Radiation Protection and Nuclear Safety institute (IRSN). This organsation has several means to carry out this validation. First of all, the calculation makes it possible to provide an overall forecasted value for each link in the airspace, while taking into account the cycles of solar activity. Radiation measurements, using dosimeters installed on the ground and in aircraft, are then used to confirm and, if necessary, correct the obtained values. In the event of a significant solar flare, a specific mapping is created and validated. The astrophysicists at the Paris Observatory are also asked to assess the impact of the solar flare. The time needed to carry out this complex study is rather long. One must therefore wait several weeks before being able to calculate the doses received on flights during a solar flare.