Replies

"Cosmic rays are high energy charged particles, originating in outer space, that travel at nearly the speed of light and strike the Earth from all directions. Most cosmic rays are the nuclei of atoms, ranging from the lightest to the heaviest elements in the periodic table. Cosmic rays also include high energy electrons, positrons, and other subatomic particles. The term "cosmic rays" usually refers to galactic cosmic rays, which originate in sources outside the solar system, distributed throughout our Milky Way galaxy. However, this term has also come to include other classes of energetic particles in space, including nuclei and electrons accelerated in association with energetic events on the Sun (called solar energetic particles), and particles accelerated in interplanetary space." http://www.srl.caltech.edu/personnel/dick/cos_encyc.html Cosmic rays may broadly be divided into two categories, primary and secondary. The cosmic rays that arise in extrasolar astrophysical sources are primary cosmic rays; these primary cosmic rays can interact with interstellar matter to create secondary cosmic rays. The sun also emits low energy cosmic rays associated with solar flares. The exact composition of primary cosmic rays, outside the Earth's atmosphere, is dependent on which part of the energy spectrum is observed. However, in general, almost 90% of all the incoming cosmic rays are protons, about 9% are helium nuclei (alpha particles) and nearly 1% are electrons. The ratio of hydrogen to helium nuclei (28% helium by mass) is about the same as the primordial elemental abundance ratio of these elements (24% by mass He) in the universe. The remaining fraction is made up of the other heavier nuclei which are abundant end products of stars' nuclear synthesis. Secondary cosmic rays consist of the other nuclei which are not abundant nuclear synthesis end products, or products of the Big Bang, primarily lithium, beryllium, and boron. These light nuclei appear in cosmic rays in much greater abundance (about 1:100 particles) than in solar atmospheres, where their abundance is about 10−7 that of helium. http://en.wikipedia.org/wiki/Cosmic_ray __________________________________________________________________________________________________________________________________________________ Man! After all these years I still can't get a straight answer!