NASA researchers have found that a zone in the radiation belts surrounding Earth - which can offer reduced radiation exposure to spacecraft - moves to higher or lower altitudes and latitudes depending on the level of solar activity. "This new research brings us closer to understanding how a section of the radiation belt disappears," said lead researcher Shing Fung.

The Van Allen Belts, which were discovered by early satellite studies in the 1960s, resemble a pair of donuts around Earth, one inside the other with Earth in the hole of the innermost donut.

The safe zone, called the slot region, would appear as a gap between the inner and outer donut.


The maximum solar activity, the safe zone is raised due to the increased solar ultraviolet radiation heats Earth's upper atmosphere, called the ionosphere, causing it to expand. This increases the density of the plasma trapped in Earth's magnetic field.

More details,
http://www.space-travel.com/reports/Radiat...olar_Cycle.html

Rodolfo