Galactic cosmic ray

Galactic cosmic ray

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Galactic cosmic rays are cosmic rays that have their origin inside our Galaxy. GCRs are high-energy charged particles, and are usually protons, electrons, and fully ionized nuclei of light elements. They are a strong source for cosmic ray spallation
Cosmic ray spallation
Cosmic ray spallation is a form of naturally occurring nuclear fission and nucleosynthesis. It refers to the formation of elements from the impact of cosmic rays on an object. Cosmic rays are highly energetic charged particles from outside of Earth ranging from protons, alpha particles, and nuclei...

 in the atmosphere of the Earth.


The magnetic fields of the Earth
Earth's magnetic field
Earth's magnetic field is the magnetic field that extends from the Earth's inner core to where it meets the solar wind, a stream of energetic particles emanating from the Sun...

, the sun
Stellar magnetic field
A stellar magnetic field is a magnetic field generated by the motion of conductive plasma inside a star. This motion is created through convection, which is a form of energy transport involving the physical movement of material. A localized magnetic field exerts a force on the plasma, effectively...

, and the galaxy itself bend the paths of the galactic cosmic rays.

Some of the isotopes have half-lives that are comparable to the time interval since their formation, and isotopic ratios can therefore carry some information about the amount of time that has passed since they were formed. In a few cases, there are isotopes are unstable with respect to electron capture
Electron capture
Electron capture is a process in which a proton-rich nuclide absorbs an inner atomic electron and simultaneously emits a neutrino...

, but because they are fully stripped, they have not decayed in flight.


Most galactic cosmic rays have energies too low to penetrate the Earth's atmosphere, and the radii of their helical trajectories in the Earth's magnetic field tends to channel them to the poles. When they strike the atmosphere, they can create large showers
Particle shower
In particle physics, a shower is a cascade of secondary particles produced as the result of a high-energy particle interacting with dense matter. The incoming particle interacts, producing multiple new particles with lesser energy; each of these then interacts in the same way, a process that...

of secondary particles that are detected on Earth's surface.

As a radiation hazard

Galactic cosmic rays are one of the most important barriers standing in the way of plans for interplanetary travel by crewed spacecraft.

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