What is "skyshine"

(Radiation) skyshine describes the ionizing radiation emitted by a nuclear technical or medical facility, reaching the facility's surroundings not directly, but indirectly through reflection and scattering at the atmosphere back to earth's surface. This effect can happen, when the shielding barrier around the source of radiation is open at the top. In a wider sense, skyshine also describes radiation reflected off the ceiling inside a nuclear facility.

The intensity of radiation measured at the surface immediately surrounding the facility increases with growing distance from the shielding barrier to reach a maximum and then fall again continuously with further increasing distance. Depending on the type of radiation the maximum is reached at different distances from the source of radiation. For example, x-rays emitted from linear accelerators reached maxima of 18 MeV at a distance of 13.6 m and 6 MeV at 4.6 m in studies.

thumb |Schematic of AVR reactor originally without top shielding Between 1967 and 1975 significant radiation damage of the surroundings was caused by radiation skyshine at and near the AVR reactor in Jülich, Germany, which, in its original BBC construction, lacked a top shielding barrier.

In 2011, the skyshine effect reached media attention in the controversy around the radioactive waste repository after higher levels of radiation were measured outside the facility, despite it being shielded by a shielding wall.