Cosmic Rays

Cosmic rays originate in out in space.

They are produced by our Sun (when they are called the solar wind), stars, supernovae, neutron stars and black holes.

The most well-known source of cosmic rays is the Sun, with its solar wind. These particles have a characteristic energy limit and so we know that the super high energy ones are coming from something more powerful than our Sun.

In 1960 a scientist called suggested that lower-energy cosmic rays come mainly from inside our own galaxy (the Milky Way), whereas those of higher energy come from more distant sources. He expected to see different numbers of low energy cosmic rays coming from various directions at us from within our galaxy because the galaxy is not arranged symmetrically around us. He found that the lower-energy rays had directions are scattered in a similar pattern and his idea was right.

They travel at very fast speed indeed - very close to the speed of light.

Cosmic rays are made up from a stream of high-energy particles that are generally ionised atoms (ions), ranging from a single proton, up to an iron nucleus and sometimes an even heavier one!

When charged particles move they create a magnetic field (you should know this from your GCSE electricity work) and because there is a small magnetic field permeating the Galaxy (and an even smaller field permeating inter-galactic space) they travel in curved paths as their field interacts with that around them.

The earth's atmosphere protects us from being exposed to many of these particles. As a cosmic ray enters the atmosphere, it will collide with a particle in the atmosphere (usually a nitrogen or oxygen molecule) and cause ionisation of that. The collision produces matter out of the energy of the cosmic particle (you've heard of Einstein's equation E = mc² haven't you? .. but this is way beyond the scope of GCSE!) and the ramifications of that are studied to tell us more about the origins of the particles.

If you live at a high altitude or go up in an aeroplane your radiation dose increases because you are hit by more cosmic rays!

If you live nearer the poles you will receive a higher dose of cosmic radiation because the earth surface rotates more quickly at the equator than at the poles. also the atmosphere is deeper at the equator than at the poles.

As these particles travel through the atmosphere, they interact with nitrogen molecules in the atmosphere, exciting the electrons in them and causing them to emit light (rather like the way a fluorescent light works).

Cosmic rays have been detected with very high energies, we believe that they originate from quasars and active galactic nuclei. We do not know where these particles are coming from but a lot of exciting research is going on in that area. We have not got detectors that are able to detect cosmic rays of even higher energy but scientists are sure that super-energy Cosmic rays exist.. we just can't 'see' them with any instrument we have devised yet.