Cosmic ray research began in 1912 when Victor Hess and two assistants flew in a balloon to an altitude of about 16,000 ft. and discovered evidence of a very penetrating radiation coming from outside our atmosphere. This was the first observation of what we now call cosmic rays, high-energy charged particles that constantly bombard the earth.
You can imagine that, in 1912, it could have been alarming to discover that we are all constantly subjected to a powerful radiation coming from an unknown source in space. At first, Hess' ideas were largely dismissed in favor of less radical explanations. Other researchers soon found similar results, though, and it became clear that radiation was actually coming from outer space. Cosmic ray physicists now seek to understand everything they can about this omnipresent phenomenon.
We now know more about what cosmic rays are. The cosmic radiation is primarily protons, but also includes nuclei, antiprotons, electrons and positrons. We still do not know exactly where cosmic rays come from, how they are accelerated, or how they propagate through space, but there are many theories. Many of the cosmic rays we observe were probably formed at the beginning of the universe. It is presently believed that supernovae are also an important source of cosmic rays. As cosmic rays travel through space, they undergo a number of transformations due to their interaction with matter, magnetic fields and radiation. In reconstructing the history of cosmic rays, we are actually investigating events and processes in the far reaches of space.
The Particle Astrophysics Lab (PAL) studies cosmic rays using a magnetic spectrometer which is carried by helium balloon (unmanned) to an altitude of 120,000 ft. This allows PAL to observe cosmic rays before they interact with the earth's atmosphere. Under optimum conditions, 400 cosmic rays per second pass through the detectors in the PAL magnetic spectrometer.
Each flight of the PAL instrument now yields approximately 8 gigabytes of data. Each recorded particle is identified by its charge, velocity, magnetic rigidity and the nature of its interaction with matter. Researchers can then compare the spectra observed (the number of particles at each energy) with the spectra predicted by different theoretical models. Many observations have revealed antiproton spectra above values predicted by the most prominent cosmic ray propagation model. This suggests an additional source of antiprotons or a failure of the standard model.
PAL has focused its efforts on observing the spectra of protons, helium nuclei, positrons and antiprotons. Observing these spectra will provide information on the sources of primary cosmic rays, the methods of cosmic ray acceleration, the size and location of confinement regions of cosmic rays, and the propagation of cosmic rays in interplanetary space.
For more information about cosmic ray research in general, see the following sources:
This is an informative 120-page book with index. It seems to be the best cosmic ray primer available for people who do not have a scientific background. It also has great 60's style drawings.
Rossi's book gives a more advanced scientific account while remaining highly readable.
This is the book to read if you have a strong physics background.
