Cosmic Rays

1. Cosmic Rays Not part of the EM spectrum like UV and IR

2. Gamma-rays have the smallest wavelengths and the most energy of any other wave in the electromagnetic spectrum. • These waves are generated by radioactive atoms and in nuclear explosions. • Gamma-rays can kill living cells, a fact which medicine uses to its advantage, using gamma-rays to kill cancerous cells.

3. Gamma-rays travel to us across vast distances of the universe, only to be absorbed by the Earth's atmosphere. • Instruments aboard high-altitude balloons and satellites like the Compton Observatory provide our only view of the gamma-ray sky.

4. Cosmic rays are energetic particles that are found in space and filter through our atmosphere. • Cosmic rays have interested scientists for many different reasons. • They come from all directions in space, and the origination of many of these cosmic rays is mostly unknown.

5. Galactic Cosmic rays are mostly pieces of atoms, protons electrons and atomic nuclei which have had all of the surrounding electrons stripped during their high speed passage through the galaxy.

6. Most galactic cosmic rays are probably accelerated in the blast waves of supernova remnants. • The remnants of the explosions expanding clouds of gas and magnetic field can last for thousands of years and this is where cosmic rays are accelerated. • Bouncing back and forth in the magnetic field of the remnant randomly lets some of the particles gain energy, and become cosmic rays. • Eventually they build up enough speed that the remnant can no longer contain them and they escape into the galaxy.

7. Cosmic rays were originally discovered because of the ionozation they produce in our atmosphere. • Cosmic rays also have an extreme energy range of incident particles, which have allowed physicists to study aspects of their field that can not be studied in any other way.

8. In the past, we have often referred to cosmic rays as "galactic cosmic rays", because we did not know where they originated. • Now scientists have determined that the sun discharges a significant amount of these high-energy particles.

9. "Solar cosmic rays" (cosmic rays from the sun) originate in the sun's chromosphere. • Most solar cosmic ray events correlate relatively well with solar flares.

10. Cosmic Rays at the Energy Frontier • These particles carry more energy than any others in the universe. • Their origin is unknown but may be relatively nearby

11. Roughly once a second, a subatomic particle enters the earth's atmosphere carrying as much energy as a well-thrown rock. • Somewhere in the universe, that fact implies, there are forces that can impart to a single proton 100 million times the energy achievable by the most powerful earthbound accelerators. • Where and how?

12. Those questions have occupied physicists since cosmic rays were first discovered in 1912 (although the entities in question are now known to be particles, the name "ray" persists). • The interstellar medium contains atomic nuclei of every element in the periodic table, all moving under the influence of electrical and magnetic fields.

13. Without the screening effect of the earth's atmosphere, cosmic rays would pose a significant health threat; indeed, people living in mountainous regions or making frequent airplane trips pick up a measurable extra radiation dose.

14. Perhaps the most remarkable feature of this radiation is that investigators have not yet found a natural end to the cosmic-ray spectrum. • Most well-known sources of charged particles--such as the sun, with its solar wind--have a characteristic energy limit;

15. they simply do not produce particles with energies above this limit. • In contrast, cosmic rays appear, albeit in decreasing numbers, at energies as high as astrophysicists can measure. • The data run out at levels around 300 billion times the rest-mass energy of a proton because there is at present no detector large enough to sample the very low number of incoming particles predicted.

16. Nevertheless, evidence of ultrahigh-energy cosmic rays has been seen at intervals of several years as particles hitting the atmosphere create myriad secondary particles (which are easier to detect). • On October 15, 1991, for example, a cosmic-ray observatory in the Utah desert registered a shower of secondary particles from a 50-joule (3 x 1020 electron volts) cosmic ray.

17. Although the cosmic-ray flux decreases with higher energy, this decline levels off somewhat above about 1016 eV, suggesting that the mechanisms responsible for ultrahigh-energy cosmic rays are different from those for rays of more moderate energy.

18. In 1960 Bernard Peters of the Tata Institute in Bombay suggested that lower-energy cosmic rays are produced predominantly inside our own galaxy, whereas those of higher energy come from more distant sources. • One reason to think so is that a cosmic-ray proton carrying more than 1019 eV, for example, would not be deflected significantly by any of the magnetic fields typically generated by a galaxy, so it would travel more or less straight.

19. If such particles came from inside our galaxy, we might expect to see different numbers coming from various directions because the galaxy is not arranged symmetrically around us. • Instead the distribution is essentially isotropic, as is that of the lower-energy rays, whose directions are scattered.

20. Supernova Pumps • Such tenuous inferences reveal how little is known for certain about the origin of cosmic rays. • Astrophysicists have plausible models for how they might be produced but no definitive answers.

21. This state of affairs may be the result of the almost unimaginable difference between conditions on the earth and in the regions where cosmic rays are born. • The space between the stars contains only about one atom per cubic centimeter, a far lower density than the best artificial vacuums we can create.

22. http://www.sciam.com/0197issue/0197swordy.html • http://helios.gsfc.nasa.gov/cosmic.html • http://zebu.uoregon.edu/~js/glossary/cosmic_rays.html • http://www.geocities.com/SunsetStrip/1483/ozone.html • http://science.msfc.nasa.gov/newhome/headlines/ast26mar99_1.htm

23. http://www.mpihttp://helios.izmiran.troitsk.ru/cosray/main.htmhttp://www.mpihttp://helios.izmiran.troitsk.ru/cosray/main.htm • hd.mpg.de/hfm/CosmicRay/CosmicRaySites.html

24. Galactic Cosmic rays are high energy particles that flow into our solar system from far away in the galaxy. Galactic Cosmic rays are mostly pieces of atoms, protons electrons and atomic nuclei which have had all of the surrounding electrons stripped during their high speed passage through the galaxy. • Most galactic cosmic rays are probably accelerated in the blast waves of supernova remnants. The remnants of the explosions expanding clouds of gas and magnetic field can last for thousands of years and this is where cosmic rays are accelerated. Bouncing back and forth in the magnetic field of the remnant randomly lets some of the particles gain energy, and become cosmic rays. Eventually they build up enough speed that the remnant can no longer contain them and they escape into the galaxy. • http://helios.gsfc.nasa.gov/cosmic.html#cractys • http://www.geocities.com/SunsetStrip/1483/ozone.html • http://science.msfc.nasa.gov/newhome/headlines/ast26mar99_1.htm

25. http://www.sciam.com/0197issue/0197swordy.htmlhttp://www.mpihttp://helios.izmiran.troitsk.ru/cosray/main.htm-hd.mpg.de/hfm/CosmicRay/CosmicRaySites.htmlhttp://www.sciam.com/0197issue/0197swordy.htmlhttp://www.mpihttp://helios.izmiran.troitsk.ru/cosray/main.htm-hd.mpg.de/hfm/CosmicRay/CosmicRaySites.html