Facebook Instagram Youtube Twitter

Galactic Cosmic Radiation – GCR

Cosmic Radiation - Natural Source of Radiation
Source: nasa.gov License: Public Domain

Galactic cosmic radiation, GCR, refers to sources of radiation in the form of high-energy particles originating outside the solar system. GCR are high-energy nuclei from which all surrounding electrons have been stripped away during their high-speed passage through the galaxy. The GCR incident in the upper atmosphere consists of a nucleonic component, which aggregate accounts for 98% of the total (2% are electrons). The nucleonic component then consists of a mixture of high-energy protons (~86%), alpha particles (~12%), and a trace of heavier nuclei (~1%). GCR is trapped by the galactic magnetic field. Therefore they have probably been accelerated within the last few million years and have traveled many times across the galaxy. Their acceleration mechanism is uncertain, but one possible mechanism is that the particle is accelerated by shock waves expanding from supernovas. The energy of these particles ranges between 108 eV and 1020 eV. A very small fraction are stable particles of antimatter, such as positrons or antiprotons.

The precise nature of this remaining fraction is an area of active research. The GCR fluence rate varies with solar activity, being lower when solar activity is higher. At solar minimums, due to lower solar magnetic field shielding, the fluence is significantly higher than at solar maximums.

Shielding of Cosmic Radiation

magnetosphere - earth magnetic field
An artist’s rendering of the structure of a magnetosphere: 1) Bow shock. 2) Magnetosheath. 3) Magnetopause. 4) Magnetosphere. 5) Northern tail lobe. 6) Southern tail lobe. 7) Plasmasphere. Source: nasa.gov License: Public Domain

Earth’s magnetic field provides a vital radiation shield from cosmic radiation. In addition to a protective atmosphere, we are lucky that Earth has a magnetic field. The magnetic field extends several tens of thousands of kilometers into space, protecting the Earth from the charged particles of the solar wind and cosmic rays that would otherwise strip away the upper atmosphere, including the ozone layer that protects the Earth from harmful ultraviolet radiation. It shields us from the full effects of solar wind and GCR. Without this protection, Earth’s biosphere might not exist as it does today or would be at least limited to the subsurface. Earth’s magnetic field also provides a radiation shield for astronauts and the ISS because it is in low Earth orbit.

Calculations of the loss of carbon dioxide from the atmosphere of Mars, resulting from the scavenging of ions by the solar wind, indicate that the dissipation of the magnetic field of Mars caused a near-total loss of its atmosphere.


Radiation Protection:

  1. Knoll, Glenn F., Radiation Detection and Measurement 4th Edition, Wiley, 8/2010. ISBN-13: 978-0470131480.
  2. Stabin, Michael G., Radiation Protection and Dosimetry: An Introduction to Health Physics, Springer, 10/2010. ISBN-13: 978-1441923912.
  3. Martin, James E., Physics for Radiation Protection 3rd Edition, Wiley-VCH, 4/2013. ISBN-13: 978-3527411764.
  5. U.S. Department of Energy, Nuclear Physics and Reactor Theory. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.

Nuclear and Reactor Physics:

  1. J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading, MA (1983).
  2. J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.
  3. W. M. Stacey, Nuclear Reactor Physics, John Wiley & Sons, 2001, ISBN: 0- 471-39127-1.
  4. Glasstone, Sesonske. Nuclear Reactor Engineering: Reactor Systems Engineering, Springer; 4th edition, 1994, ISBN: 978-0412985317
  5. W.S.C. Williams. Nuclear and Particle Physics. Clarendon Press; 1 edition, 1991, ISBN: 978-0198520467
  6. G.R.Keepin. Physics of Nuclear Kinetics. Addison-Wesley Pub. Co; 1st edition, 1965
  7. Robert Reed Burn, Introduction to Nuclear Reactor Operation, 1988.
  8. U.S. Department of Energy, Nuclear Physics and Reactor Theory. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.
  9. Paul Reuss, Neutron Physics. EDP Sciences, 2008. ISBN: 978-2759800414.

See above:

Cosmic Radiation