Fundamental sources of uranium and thorium
Global Distribution of Uranium and Thorium
The three quantitatively significant natural radioéléments are, in order of decreasing abundance, potassium, thorium, and uranium. All the isotopes of thorium and uranium are radioactive, but K40 (0.0118% of all K) is the only radioactive isotope of potassium. The true average and specific lithologie abundances of radioéléments throughout the earth may never be learned from direct measurement, but these elements have been measured extensively at the surface and interpreted for the interior from indirect evidence. The three sources of data are:
Chemical and radiometric analysis of meteorites interpreted to be representative of different earth layers;
Chemical and radiometric analysis of surficial rocks; and
Estimation of values for the earth’s interior from heat-flow and rock-conductivity data.