Cosmic Rays

Cosmic rays are high energy particles, originating from outer space, that strike the earth. An increase in altitude means an increase in radiation from cosmic rays. A move from a coastal location to the mountains increases cosmic radiation levels.

Flying on an airplane also increases the radiation levels. Although the particles responsible for cosmic radiation can affect the cells in our body, they are difficult to detect. At typical flight altitudes of 20 000 – 40 000 feet (6 - 12 km) the cosmic radiation contains a soup of neutrons, protons, electrons, photons, muons and pions. These particles will not be measured accurately with the type of simple radiation detectors that are commonly found in nuclear power stations or in army surplus stores.

Cosmic radiation levels are never constant. If you take today the same flight you took six months ago, the dose you receive will be different. The largest variations of cosmic ray intensity occur over an 11-year cycle, which is influenced by the sun’s activity (see figure below).

Galactic cosmic radiation is at a minimum during solar maximum, but during solar minimum, more of that radiation can reach the Earth. The most recent solar minimum occurred in early 1997, and solar maximum occurred ahead of schedule in May 2000. The next solar minimum will occur in late 2007 and it is already apparent that cosmic radiation levels are increasing.

PCAire updates its table of solar activity as soon as the data becomes available

(1) Some of the information shown here is summarized from an article by Susan Baily, published in the January 2000 issue of Nuclear News.