Source Composition, Sites of Origin and Acceleration of Cosmic Rays

The source composition of cosmic rays is deduced from the observed composition above the atmosphere by propagation (or nuclear transport) calculations. These calculations make corrections for the nuclear spallation reactions suffered by the cosmic-ray nuclei in the interstellar gas and clouds. To learn about the sites of origin, the source composition is compared with the general Galactic abundance of elements and isotopes, which is based on spectroscopic studies of the Sun and stars and composition of the C1 meteorites. (The composition of these meteorites is the least fractionated sampling of matter out of which the solar system condensed). While there are still alternative proposals on the sites and processes of cosmic-ray origin, we shall describe here our recent work which has yielded an agreement to 20% between the source composition derived from cosmic-ray observations, and those deduced from the general Galactic abundance of elements. It should be noted that the general Galactic abundances differ from the cosmic-ray source abundances by factors of up to 30. Hence, the agreement to 20% implies that the injection and nucleosynthetic processes we have postulated greatly improve the agreement between the source abundances derived from observations and those deduced from the general abundances.