Radiation from Natural and Human Sources We have the ability to measure very small amounts of radiation - we can actually detect single atoms as they disintegrate. So when we hear the clatter of a radiation detector, we feel that we are in danger. But the numbers we encounter from various human-made sources are quite trivial compared with the natural bath of radiation that the galaxies pour down on us as cosmic rays, and the earth and all its lovely vegetation produce, and even our water, food, and our bodies themselves are naturally radioactive. This situation has existed since life first evolved, eons ago. In fact, the earth was much more radioactive then than now.
The figure above shows the average radiation dose we get each year from various sources. We get so little from nuclear power and its associated operations (including the meltdown at Three Mile Island), that it hardly shows up on this graph. The fallout from the reactor accident at Chernobyl produced a measurable peak that is now quite low. The fallout from testing nuclear weapons made a much larger peak, but it too has largely subsided. But all these radiation doses are dwarfed by the average radiation dose we get from medical diagnostics: dental and other x-rays, radioisotope