CRaTER Science


LET Spectra

Galactic Cosmic Rays

Solar Proton Events

Biological Effects of


Estimate Your Annual
Radiation Exposure

Radiation dose chart
  (interactive & print versions)

Reading Room

Cancer risk from GCR
  (pdf, 2006)
Cell damage detection
  (pdf, 2005)
One-Two Particle Punch
  (website, 2006)
Cosmic Radiation and Bones
  (text, 2005)
Are We Trapped on Earth?
  (website, 2006)
2006 Space Weather Week
  Presentation by H.Spence
  (pdf, 2006)
  describing instrument
  (pdf, 2006)
Radioactive Moon
  (website, 2005)
Proton Inelastic Processes
  (pdf, 2004)
Monte Carlo Simulation
  to Assess True Risk
  (pdf, 2002)
Response of Silicon-based
  LET Spectrometers
  (pdf, 2005)

nasa logo

Solar Proton Events

Solar Proton Events (or SPEs) occur when protons emitted by the Sun become accelerated to very high velocities by the release of extreme energy from a solar flare or a shockwave from a Coronal Mass Ejection (or CME).

SPEs are defined as a flux (of protons with energies higher than 10MeV) greater than 10 particles cm-2 s-1 ster-1 (per centimeter-squared per second per steradian) for more than fifteen minutes.

The protons travel along the extended magnetic field lines of the Sun, some making their way to the Earth. Once caught in the Earth's magnetic field, the solar protons travel to weaker regions of the field lines and enter the ionospheric region of the atmosphere, producing further ionization. This may cause significant radiation increase, leading to the disturbance of electronic systems.

The Earth's atmosphere and extensive magnetosphere protect humans on the Earth's surface from the radiation increase that happens during an SPE. However, astronauts in space (for example, on the Moon or orbiting Earth) are extremely vulnerable to this radiation. In the interest of future space exploration, it is important to learn as much as possible about SPEs—both their short- and long-term effects.