0 radiation found naturally on earth that comes from some soil, rocks, etc., and from outer space -- 背景辐射（可在地球检测到的自然发生的辐射，来自外层空间以及土壤和岩石中）
An ideal environment would be a place that is naturally very cold and very dry, with low air pressure and background radiation.
These equations are coupled to a background radiation fluid, whose dynamics are determined by an acoustic wave equation.
The remainder of background radiation is time invariant by comparison.
For alfa-emitters the background radiation levels were reached after laser-based deactivation, and for beta-emitters initial activity was reduced by a factor of tens or more.
This hypothetical link between cosmic radiation and epigenetic changes may only be the tip of the iceberg regarding background radiation effects.
If the reactor is shut down, the gamma and neutron radiation falls to natural background radiation levels.
Water and seabed silt samples showed no increase in background radiation levels.
If we are to evaluate the effect of radiation doses on the population, we must compare them with naturally occurring background radiation.
