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Trapped Radiation and the South Atlantic Anomaly

The South Atlantic Anomaly

For low altitude spacecraft (e.g. less than 1,000 km altitude), there is one region where the a significant population of trapped protons is encountered - known as the South Atlantic Anomaly (SAA). The reason for this particular region of high concentrations of particles is complex - due to the tilt and offset of the magnetic dipole with respect to the geographic axis. This results in significant populations of particles located in a relatively close trapped radiation belt being brought down to low altitudes in an area over the South Atlantic ocean centred just to the East of Brazil.

The SAA region is relatively stable and gives rise to significant proton fluxes for low altitude spacecraft. The protons are very penetrating and give rise to relatively high doses inside the spacecraft. They also contribute indirectly to single-event effects through proton-induced nuclear reactions (PINRs).

Surrey satellites have flown a number of experiments to measure and map the SAA region, including the Cosmic Radiation Environment and Dosimetry (CREDO) experiment onboard UoSat-3. This experiment was followed by the more sophisticated Cosmic Ray Experiment (CRE) which was flown on both KITSAT-1 PoSAT-1.

The images shown on the right illustrate some of the data acquired from CREDO and CRE, clearly showing the high concentration of particles located in the SAA region during periods of normal solar activity.

Acknowledgement:
This topic is based on original material written by Dr Craig Underwood

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