An estimation of Canadian population exposure to cosmic rays from air travel
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ORIGINAL PAPER
An estimation of Canadian population exposure to cosmic rays from air travel Jing Chen • Dustin Newton
Received: 8 August 2012 / Accepted: 28 October 2012 / Published online: 9 November 2012 Ó Her majesty the Queen in Right of Canada 2012
Abstract Based on air travel statistics in 1984, it was estimated that less than 4 % of the population dose from cosmic ray exposure would result from air travel. In the present study, cosmic ray doses were calculated for more than 3,000 flights departing from more than 200 Canadian airports using actual flight profiles. Based on currently available air travel statistics, the annual per capita effective dose from air transportation is estimated to be 32 lSv for Canadians, about 10 % of the average cosmic ray dose received at ground level (310 lSv per year). Keywords Cosmic rays Annual effective dose Population exposure
Introduction Everyone is exposed to ionizing radiation from natural sources. There are two main contributors to natural radiation exposures: high-energy cosmic ray particles incident on the Earth’s atmosphere and radioactive nuclides that originate in the Earth’s crust and are present everywhere in the environment. Background radiation levels in the atmosphere are generated primarily by galactic cosmic rays. There are two major effects that shield against primary cosmic radiation, namely the Sun’s and the Earth’s magnetic fields. Entering the solar system, the fluence of cosmic rays is modulated by the periodic solar activity: The Sun emits a huge flow of matter known as solar wind which has to be overcome by the primary particles (predominantly J. Chen (&) D. Newton Radiation Protection Bureau, Health Canada, 2720 Riverside Drive, Ottawa K1A 0K9, Canada e-mail: [email protected]; [email protected]
protons). 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 years. The shielding effect of the Sun is smaller during the period of solar minimum activity. When approaching the Earth, the cosmic rays are deflected by Earth’s magnetic field acting as cutoff in their energy spectra. It is easiest to overcome this field at the magnetic poles because the particles there run roughly parallel to the magnetic field lines. In contrast, at the geomagnetic equator, the particles need to have much higher energy (over 15 GeV) to cross perpendicularly the magnetic field lines and enter the Earth’s atmosphere. Since the far more frequent lower-energy particles are deflected away from the Earth, radiation exposure is lower at the equator than at the poles. Thus, the fluence of the primary particles is a function of the time in the solar cycle and of the location in the geomagnetic field. Interaction of these primary particles with the atoms in the atmosphere results in a complex field of secondary cosmic radiation which for example includes neutrons, protons, pions, photons, electrons, and muons. A comprehensive review of worldwide exposure from natural sources was g
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