Cosmic Rays

Cosmic rays are high energy charged particles. They are produced by the sun and the stars. Before entering into the atmosphere, the cosmic rays consist of 89% protons, 9% helium nuclei and the remaining 3% heavy nuclei. These are called as primary cosmic rays. When these rays collide with the nuclei of the air, they produce nuclear fragments.

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These nuclear fragments then carry on splitting process on further collision producing more such fragments. These are called secondary cosmic rays.

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The Energy of Cosmic Rays

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Cosmic rays arrive with a variety of energies. At the lowest energies, cosmic radiation is very common. These particles originate from sources close to Earth such as the Sun. We are shielded from most of the low energy particles by their interaction with the Earth's atmosphere and magnetic field.

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The basic unit of measurement used in discussing the energy of a cosmic ray is the electronvolt, or eV. One eV is the amount of energy gained by a single electron when passing through an electric potential of one volt. Common batteries (such as a D-cell) have a potential of 1.5 volts, so a single electron through a regular battery will gain 1.5 eV.

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As the energy of the cosmic rays increases, the frequency of the particles decreases steeply. On arrival at the Earth, their path experiences less bending in the magnetic field and they penetrate deeper into the atmosphere. Particles with intermediate energy levels, around what is called the "Knee" of the spectrum, are called Very High Energy cosmic rays and they occur with a frequency of one per square meter per year. For the highest energy cosmic rays, above 1016 eV or what is called the "Ankle," the rate of events falls to one per square kilometer per century.

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Health threat from cosmic rays

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The health threat from cosmic rays is the danger posed by galactic cosmic rays (GCR) and solar energetic particles to astronauts on interplanetary missions or any missions that venture through the Van-Allen Belts or outside the Earth's magnetosphere. Space radiation health risks also occur for mission in low Earth orbit such as the International Space Station (ISS) where GCR dominate organ dose equivalents, while radiation exposure limits can be reached for cumulative times on ISS of about 2 years (with variable maximum duration dependent on crew age at mission and sex).

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Galactic cosmic rays (GCRs) consist of high energy protons (85%), helium (14%) and other high energy nuclei (HZE ions). Solar energetic particles consist primarily of protons accelerated by the Sun to high energies via proximity to solar flares and coronal mass ejections. They are one of the most important barriers standing in the way of plans for interplanetary travel by crewed spacecraft.

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References

http://www.telescopearray.org/index.php/about/what-are-cosmic-rays

https://en.wikipedia.org/wiki/Health__threat__from__cosmic__rays

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