Most primaries that reach the earth's atmosphere have traveled through the Milky Way for millions of years. Anomalous component means peculiar part of a group. Physicists gave anomalous component primaries this name when they were discovered in the early 1970's. The composition and behavior of these particles differed greatly from those of galactic and solar primaries, which had been identified by the late 1950's. Galactic cosmic rays come from outside the solar system.
Most primaries are galactic cosmic rays.
About 98 percent of galactic cosmic rays are atomic nuclei, which carry a positive electric charge. Roughly 12 percent are helium nuclei, each consisting of two protons and two electrically neutral particles called neutrons. The remainder include nuclei of all chemical elements heavier than helium. The 2 percent of primaries that are not nuclei are electrons, which are negatively charged, and positrons. A positron is the antiparticle of an electron.