WHAT IS YOUR RADIATION DOSE IN A POLAR ROUTE?

If you live in the USA you receive an annual radiation dose of about 3000 µSv or 3 mSv. This includes a dose of about 100 µSv (10 mrem) from every chest X-ray. (These estimates are from a table at the The Radiological Society of North America). About 10% of your total annual background radiation dose is due to GCRs. When looking at information about radiation doses you should remember that 1 mrem = 10 µSv, and that mrem and µSv combine the radiation dose with its effectiveness in a human body. Other measures of radiation effects, such as the rad and Gray (Gy), describe only the amount of radiation energy absorbed (not how it affects your body). Doses of X-rays, cosmic rays, and energetic protons can be easily compared by reporting the doses in µSv.

When you travel in a jet airliner at 37,000 ft you are flying above about 80% of our atmosphere. This means the shielding of the atmosphere is reduced and you will get a small dose of radiation from the galactic cosmic rays and energetic solar particles during your flight.

The CARI-6 program was developed by the FAA's Civil Aerospace Medical Institute to calculate the radiation dose from galactic cosmic rays for a passenger flying along a great circle between any two airports in the world. The program is available as a DOS .exe file and uses a menu driven user interface.

To help you use the program, we provide several examples below. You must specify the airports where you start and finish, the altitudes, and the time spent at each altitude. The CARI program identifies airports by their 4-letter ICAO codenames, not the 3-letter IATA airport codes used on your airline tickets, although the ICAO codes are becoming more common. Both abbreviations are listed in the table.

To make life simple the great circle distance was calculated and the time in flight found by assuming a constant velocity of 500 mi/hr. The ascent and descent times were one minute each, and the altitude was set to 37,000 ft. I looked at four flights, two that stay at mid-latitudes, one polar and one trans-equatorial. The GCR flux changes with solar activity, so I calculated doses for July 2000 (solar maximum) and July 2006 (solar minimum conditions). These dose calculations are somewhat crude as the flight profiles are very simple.

Airports Used to Create Doses

CARI-6 Doses for Several Flights

From the table we can see that doses during July 2006 (solar minimum) are greater than during July 2000 (solar maximum). This is because solar activity diverts the galactic cosmic rays away from our solar system. When solar activity is lower the GCR dose increases. Your dose is determined by your time aloft (look at ratios of Time Aloft and Dose). The largest dose is from the polar route. Even though the San Francisco-Sydney trip is longer, it crosses the equator, where the magnetic field screens the cosmic rays more effectively and reduces the dose.

In the polar regions energetic particles from the Sun can penetrate to the altitudes airplanes fly. The particles must be quite energetic and the Sun and Earth correctly aligned for this to happen. About one of these Ground Level Events (GLEs) happens each year (69 events since 1942), with more at solar maximum. A list GLEs from 1942-2005 is available at the Bartol Research Institute. No additional radiation dose due to the solar energetic particles was measured on a specially instrumented jet airplane flying polar routes.