|MadSci Network: Astronomy|
Cosmic rays are basically charged particles traveling with very high energies (high velocity) through the Galaxy. These are either atomic nuclei (protons and neutrons) or electrons. The most common type of nuclear cosmic ray is the proton (hydrogen nucleus). High-energy gamma rays (photons) are also grouped with cosmic rays, though they carry no charge. Sometimes cosmic rays enter the Earth's atmosphere and interact with air molecules to create what are called secondary cosmic rays. These can be charged particles, neutral particles (no net charge), or photons (particles of light). These in turn interact with more air molecules, making more secondary cosmic rays, so that by the time the "cosmic ray shower" reaches the ground, one primary cosmic ray particle could have produced millions of secondaries.
As for "what are they used for mainly?", that is a tricky question. Usually when someone asks what something is used for, they mean what kind of device can be built to use the phenomenon to *do* something. Well, cosmic rays will never help make a Star Trek phaser or cook a better meatloaf, since they come from space and it is rather difficult and inefficient to try to harness their energy. However, I think you may mean "what about cosmic rays makes them worth studying?" That question has many answers, and the field of cosmic ray astrophysics is very large.
A big question in cosmic ray astrophysics is where cosmic rays get such high energies, and how they are formed. By studying the energy distribution and elemental abundances of primary cosmic rays, we can gain great insight into the conditions and physics of other astrophysical sources, such as supernovae. Other fields also benefit by studying cosmic rays. By studying secondary cosmic rays on the ground, we can study the nuclear physics of the interactions of the primaries and secondaries with atoms and molecules in the air.
There are a number of kinds of cosmic ray detectors, which I won't get into right now but you can read up on it later if you are interested. There are ground-based detectors for secondary cosmic rays. There are also high-altitude balloons and spacecraft designed to study primary cosmic rays before they interact with the atmosphere. The balloons are usually flown near the arctic or antarctic, where the Earth's magnetic field helps guide the cosmic rays in. Even the Voyager spacecraft were being used to study cosmic rays throughout the solar system.
Cosmic rays pass through your body all throughout the day, even indoors! Here is a simple experiment you can try. First, get a Geiger counter. (You science teacher may have one. Otherwise, the local college physics department may have one.) Place it in a room away from the walls. (There may be some natural radiation emitted by the walls. Don't worry -- it's only a tiny amount and isn't dangerous, but it may mess up the experiment.) It helps to set the counter for audio, so that when it picks up radiation it clicks or beeps. You should hear a click every few seconds. Those clicks are secondary cosmic rays passing through your Geiger counter!
I hope this answers your question!
BCNU Interesting Web Sites: Cosmic Ray Group (Balloon- and space-based experiments) Naval Research Laboratory Voyager Cosmic Ray Subsystem IUPAP Cosmic Ray Commission (Contains links to other cosmic ray sites)
Try the links in the MadSci Library for more information on Astronomy.