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Evaluation of exposure to cosmic radiation of flight crews of Lithuanian airlines.

BACKGROUND
In Lithuania the average annual effective dose due to cosmic radiation at the sea level is 0.38 mSv. The dose rate caused by cosmic radiation increases with altitude due to the decrease in attenuation of cosmic radiation by atmosphere. Dose rates at altitudes of commercial flights are tens times higher than those at the sea level. For this reason people who frequently fly receive higher doses which might even be subject to legal regulations. The European Council Directive (96/29/Euratom) on basic radiation safety standards requires that doses of aircrews members be assessed and the appropriate measures taken, depending on the assessment results.


OBJECTIVES
The aim of this study was to evaluate potential doses, which can be received by members of aircrews of Lithuanian Airlines. The assessment was done by performing measurements and calculations.


METHODS
Measurements were performed in flying aircrafts by thermoluminescent detectors, Geiger Muller counters and neutron rem counter. Such an approach lead to evaluation of doses due to directly ionizing particles and neutrons. Calculations were done with the help of the code CARI-6M. Such parameters as flight route, solar activity, duration and altitudes of flight were taken into account. Doses received during different flights and in different aircrafts were assessed. The results of measurements and calculations were compared and differences discussed. The results were also compared with the data obtained in other similar studies.


RESULTS
It was found that the highest doses are received in flights to Paris, London, Amsterdam, and Frankfurt by aircraft B737. A number of flights causing annual doses higher than 1 mSv was estimated.


CONCLUSIONS
Despite the fact that only European flights are operated by Lithuanian Airlines the dose of 1 mSv may be exceeded under some circumstances. If it happens some radiation protection measures shall be taken. These measures are also discussed.