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NSRL User Guide

II. Operations

Solar Particle Event Simulation

General Considerations

Solar Particle Events are bursts of intense cosmic ray radiation produced by the sun during a magnetic storm on the surface of the sun.  They come in a variety of kinds, as exemplified by the August 1972 storm, March 1989, or the Carrington Event of 1859.  Each storm has its own individual spectrum of proton energies, and development over time.  The model for the NSRL SPE is based on the fluence of the August 1972 event, with an energy spectrum similar to the March 1989 event.   The majority of the protons are at very low energies, below 1 MeV, and pose little to no risk to astronauts in a space craft or space suit.  The SPESim begins with 50 MeV protons, which amounts to 91.66% of the total dose.  Then the beam energy increments in steps of 10 MeV up to 150 MeV where 0.14% of the total dose is delivered.  Higher energy protons represent a negligible fraction of the total fluence, and lower energy protons do not have sufficient penetration to be a concern to astronauts.  

Energy (MeV) Fraction
50 91.66%
60 2.93%
70 2.03%
80 1.51%
90 1.06%
100 0.81%
110 0.55%
120 0.37%
130 0.28%
140 0.20%
150 0.14%