Chemical equation carbon dating
The major radionuclides of concern are potassium, uranium, and thorium and their decay products.Some of these decay products, like radium and radon, are intensely radioactive but occur in low concentrations.In addition to this internal exposure, humans also receive external exposure from radioactive materials that remain outside the body and from cosmic radiation from space.The worldwide average natural dose to humans is about 2.4 millisieverts (m Sv) per year.An airline crew typically gets an extra dose on the order of 2.2 m Sv (220 mrem) per year.
This radiation interacts with atoms in the atmosphere to create an air shower of secondary radiation, including x-rays, muons, protons, alpha particles, pions, electrons, and neutrons.
This is because humans evolved too recently for the difference in activity over a fraction of a half-life to be significant.
Put another way, human history is so short in comparison to a half-life of a billion years that the activity of these long-lived isotopes has been effectively constant throughout our time on this planet.
In these areas it can represent a significant health hazard.
Concentrations over 500 times higher than the world average have been found inside buildings in Scandinavia, the United States, Iran, and the Czech Republic.
In Europe, the average natural background exposure by country ranges from under 2 m Sv annually in the United Kingdom to more than 7 m Sv annually in Finland, as shown in.