It is found in many foodstuffs (bananas for example), and indeed fills an important dietary requirement, ending up in our bones.(Humans have about 65 Bq/kg of K-40 and along with those foods are therefore correspondingly radioactive to a small degree.
The two most important chains providing nuclides of significance in NORM are the thorium series and the uranium series: Another major source of terrestrial NORM is potassium 40 (K-40).
The long half-life of K-40 (1.25 billion years) means that it still exists in measurable quantities today.
Terrestrial NORM consists of radioactive material that comes out of the Earth’s crust and mantle, and where human activity results in increased radiological exposure.
The materials may be original (such as uranium and thorium) or decay products thereof, forming part of characteristic decay chain series, or potassium-40.
It beta decays, mostly to calcium-40, and forms 0.012% of natural potassium which is otherwise made up of stable K-39 and K-41.
Potassium is the seventh most abundant element in the Earth’s crust, and K-40 averages 850 Bq/kg there.
A 70 kg person has 4400 Bq of K-40 – and 3000 Bq of carbon-14.) Cosmogenic NORM is formed as a result of interactions between certain gases in the Earth’s atmosphere and cosmic rays, and is only relevant to this paper due to flying being a common mode of transport.
Since most cosmic radiation is deflected by the Earth’s magnetic field or absorbed by the atmosphere, very little reaches the Earth’s surface and cosmogenic radionuclides contribute more to dose at low altitudes than cosmic rays as such.
For most human activities involving minerals and raw materials, the levels of exposure to these radionuclides are not significantly greater than normal background levels and are not of concern for radiation protection.