We don’t directly feel nuclear radiation, but it is present all around us — and even within us! Potassium ions are vital for the functioning of all living cells, vegetables and fruits are good potassium sources. So if you are eating a healthy diet, you probably carry around 140 g of potassium. While most of the potassium atoms are stable, 0.012% is the active 40K isotope with a half-life of 1.24 billion years.
Challenge
How many radio active potassium ions are in your body?
How many of decays pers second does this amount produce?
What energy dose (in J/kg = Gy) is deposited in a 70 kg person? (Assume 1.3 MeV per decay)
More on Potassium
Potassium in its metallic form is so soft, that you can cut it with a knife!
It reacts instantly with oxygen and water, often bursting into flames. It must therefore be stored under oil or vacuum.
The name comes from potash – the ash of plants from which it is first isolated.
Stay curious
Is there a link between the high flammability and the radioactivity of potassium?
What is the average annual radiation dose we are exposed to (not only 40K)?
Links
Wikipedia: Potassium
Government of Canada: Radiation Doses
A great intro, sources of doses and numbers for yearly dose
Wikipedia: Sievert
About the equivalent dosis Sievert and how it relates to the absorbed dose Grey.
UK Government: Ionising radiation – dose comparisions
A great table of doeses for different exposures