All through our lives, we inhale and ingest radioactive elements that are naturally present in the Earth crust or produced by cosmic radiation. These elements then start irradiating our bodies from the inside.
More than half of internal radiations comes from potassium 40, which enters the human body by food ingesting it. Along with the radioactive carbon 14 isotope , eight thousand atoms decay in our bodies every second: human beings are radioactive creatures !
Atoms of potassium 40 and carbon 14 are emitters of beta electrons, particles which are immediately absorbed by the body. 11% of the decay products of a potassium 40 atom take the form of gamma rays, particles which are penetrative enough to be detected outside the body.
The primordial radioisotopes which exist (alongside their descendants) within rocks on Earth can also be found in trace quantities in drinking water, vegetation and food. These can then result in internal irradiation, in conjunction with the radioactive dust inhaled with the air.
Unfortunately, these regulation processes do not exist for radionuclei originating from uranium or thorium, which means that the doses we feel are directly related to the quantities we absorb.
Of all the heavy elements which are formed by the decay of uranium or thorium, the ingestion or inhalation of lead 210 is responsible for the most important internal exposure. Uranium 238, along with its two descendants thorium 234 and protactinium 234, and uranium 234 are primarily ingested and form high concentrations around the kidneys and on the bones. Thorium 230 and thorium 232 attach themselves to the lungs, and their descendants (radium 226 and radium 228) can often be found in food.
The presence of these natural radioisotopes in our bodies on average makes up an annual dose of 0.25 mSv per year.
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