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Comment by moring

12 hours ago

Wikipedia says that potassium-40 has the largest contribution to background radiation, about 10x as much as thorium: https://en.wikipedia.org/wiki/Environmental_radioactivity

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moring

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austin-cheney  8 hours ago

This article says it’s all about the thorium and radon. https://en.wikipedia.org/wiki/Background_radiation

I have no idea which of these articles is more correct.

  • adrian_b  8 hours ago

    Potassium is everywhere, including in every living cell.

    So the exposure to potassium radiation is constant for any living being on Earth.

    Exposure to thorium and radon varies greatly depending on the location, i.e. it can be significant in places with granitic rocks or with sediments whose origin is in the erosion of granitic rocks.

    So some people, animals etc. may be exposed to more thorium/radon radiation than from other sources, especially if inhaling dust or radon gas, but for most the greatest exposure is from the content of potassium 40 and carbon 14 that is inside their bodies (which produce only weak beta radiation).

    • austin-cheney  2 hours ago

      Yes that is true, but most of potassium and carbon are not radio isotopes. All of thorium is radioactive. As such it is likely true that all life carries some quantity of radioactive potassium and radioactive carbon but that does not mean radioactive carbon or potassium are more abundant or available than thorium everywhere life exists.

geysersam  11 hours ago

Where does the potassium come from?

  • adrian_b  8 hours ago

    Potassium is an element absolutely essential for any life form on Earth.

    Any cell of any living being, including humans, contains potassium ions, which are required to neutralize the excess negative charge of proteins, otherwise the interior of the cells would become acidic and it would self-destroy.

    No other positive ion can replace potassium, because any other abundant positive ion has a much greater tendency of forming solid precipitates, which would also destroy the cell. That is why any living cell expels the abundant ions of sodium and calcium outside it, while pumping inside any potassium ions from the environment. The moment when a living cell stops pumping potassium and magnesium inside and sodium and calcium outside, is when the cell dies.

    Among the primordial chemical elements, which already existed at the formation of the Solar System, there are many which are weakly radioactive, i.e. they have some isotopes with half lives that are of at least many hundred million years, but of many billion years for most of them.

    Among these weakly radioactive elements, the human body contains not only potassium 40, but also calcium 48, but the latter is much more weakly radioactive than potassium. Besides primordial radioactive isotopes, there are also radioactive isotopes that are formed continuously by the cosmic radiation, like carbon 14, which is also present in the body of any living being.

    Among the primordial radioactive isotopes, the most radioactive are uranium 235 and potassium 40, followed by uranium 238, thorium 232 and platinum 190. The existence of weakly radioactive isotopes is not random, but it is determined by a set of rules of nuclear stability. For instance, potassium 40 is radioactive because any isotope with an even atomic mass of a chemical element with an odd atomic number and heavier than nitrogen is radioactive. Potassium 40 just happens to have an unusually long half life, so it has not decayed yet (the long half life is because potassium 40, like Buridan's ass, cannot decide whether it should decay into argon or into calcium, so it stays in limbo).

    All living beings have mechanisms for repairing damages caused by radiation to their nucleic acids, so the very low levels of ubiquitous natural radiation are not worrisome, except in certain locations where they are much higher than normal.