Poincare's Stepchild said: Most of the radioactives are very dense. As such, they sank to the core of the earth in its early life, when all was molten. They pretty much stay there, so that the upper mantle has radioactives in about the same porportion as the crust. Click to expand...

RADIOACTIVE ELEMENTS IN THE CORE

Those that have suggested the presence of radioactive elements in the Earth's core have usually done so in order to offer an alterative explanation for the power needed to run the geodynamo and/or as a way to explain where the volatile elements are in the Earth. ..............

Likewise it is not possible that U or Th or both are in the core. If U is in the core, there must also be Th there too and in chondritic Th/U proportions, since their chondritic ratio in the primitive mantle would dictate this. In the absence of experimental evidence showing similar solubility for U and Th in Fe-S and Fe-S-O liquids at high pressure and not other refractory lithophile elements, one must conclude that there is no U or Th in the core.