Average dose due to natural radioactivity deposited internally

isotope radioactivity

in millibecquerel (mBq)* radiation dose in mSv (per year) critical organ

carbon-14 2.2(10⁻⁷)

per kilogram beta rays 0.016 gonads

potassium-40 3.9(10⁻⁷)

per kilogram beta rays 0.165 gonads

potassium-40 5.6(10⁻⁸)

per kilogram gamma rays 0.023 gonads

radium and daughters 3.7(10⁻⁹)

in body alpha, beta, gamma rays 7.6 bones

radon and daughters 1.2(10⁻²)

per 1 in inhaled air alpha, beta, gamma rays 20 lungs

*Millibecquerel is a unit of radioactive disintegration rate; it corresponds to that quantity of a radioactive element in which there is one disintegration every 1,000 seconds.