MEASUREMENT OF COSMIC RADIATION EXPOSURE OF AIRCRAFT CREW AT COMMERCIAL AVIATION ALTITUDES by Vladimir M. VUJI^I] 1 , David R. SIMOVI] 2 , Novica M. STALETOVI] 1 , Milija ZE^EVI] 3 , Suzana A. BOGOJEVI] 4 , and Djordje R. LAZAREVI] 5* 1 Union – Nikola Tesla University, Belgrade, Serbia 2 Serbian Environmental Protection Agency, Belgrade, Serbia 3 European University, Belgrade, Serbia 4 Serbian Institute of Occupational Health “Dr Dragomir Karajovi}”, Belgrade, Serbia 5 Department of Radiation and Environmental Protection, Vin~a Institute of Nuclear Sciences, University of Belgrade, Belgrade, Serbia Scientific paper http://doi.org/10.2298/NTRP1701052V The measurement results of ambient dose equivalent rate in an aircraft, performed by a stan- dard portable dosimeter, at a non-commercial flight Belgrade – Podgorica at altitudes up to 9000 meters, are shown. By numerical interpolation of the measurement results, a functional dependency of the ambient dose equivalent rate on the altitude of the airplane flight is deter- mined, obtaining a good agreement with the reference values. For commercial airlines in the Balkan region, total ambient dose equivalent, regarding the aircraft crew occupationally ex- posed to radiation in the course of a flight, was calculated and the maximum permitted num- ber of flight hours per year, was estimated. Key words: cosmic radiation, ambient dose equivalent rate, portable dosimeter, air craft crew, Balcan region INTRODUCTION The aircraft crew and the passengers are exposed to high levels of radiation emitted from the sun and cosmic deep space, wherein the exposure to cosmic ra- diation approximately doubles for every 2000 meters of raising the flight altitude [1]. This exposure does not pose almost any health risk to an average air traffic passenger, travelling occasionally, but the health of the airplane crew and even business people may be af- fected depending on the altitude and the amount of time spent on flight. Hence, in 1991, the International Commission on Radiation Protection recommends that exposure to cosmic radiation of aircraft crews on commercial flights should be regarded as occupational exposure [2], which is supported by subsequent publi- cations on this subject [3, 4]. Also, the time of flight control measures and route selection regarding a crew, were proposed. At altitudes of commercial airline flights, cosmic rays in the air originate, to the greatest extent, from pro- ton and alpha particles coming from beyond the solar system which, on entering the earth's atmosphere, suc- cessively collide mainly with the atoms of nitrogen and oxygen, producing photons and other subatomic parti- cles. The Earth's magnetic field provides partial protec- tion from cosmic radiation – the protection is strongest at the equator and weakest at the poles. The reason for this is the direction of incoming cosmic radiation in relation to the direction of the Earth's magnetic field. At the equa- tor, the direction of cosmic radiation movement is per- pendicular relative to the direction of magnetic field lines, while at the poles, the angles between these lines are lesser [5]. Moreover, the level of cosmic radiation at a geographical position is never constant. Long-term stud- ies have demonstrated that there are solar cycles of about eleven years of solar activity that af fect the intensity of cosmic radiation in the Earth's atmosphere. In addition, solar storms (mainly emission of protons and electrons) can happen at any time, but more often occur during the peak of the solar cycle. As the cosmic radiation consists of charged, ionized particles, they are under the influence of highly ionized particles from a solar storm. Perturba- tions in the Earth's magnetic field, caused by solar storms, scatter low-energy particles of cosmic radiation that would otherwise have entered the Earth's atmo- sphere. For this reason, the intensity of cosmic radiation is at a minimum during solar maxima. V. M. Vuji~i}, et al.: Measurement of Cosmic Radiation Exposure of ... 52 Nuclear Technology & Radiation Protection: Year 2017, Vol. 32, No. 1, pp. 52-56 * Corresponding author; e-mail: djordje.lazarevic@vinca.rs