Uranium in the Earth's core

Abstract

That there is no radioactivity in the earth's core is a concept that has long been held. The reason is that the major radioactive elements, potassium and uranium, exist as siderophobic compounds, such as silicates and oxides, in the earth's mantle and thus were thought to be immiscible with the metal core. An experimental measurement of the binary system of steel and UO 2 , however, shows that above 3120 K the system is a two‐phase liquid, the one rich in UO 2 and the other poor in UO 2 . The phase diagram predicts that there must be a temperature above which there is total miscibility between UO 2 and steel. This temperature may be above the boiling point of UO 2 , estimated as 3750 K. The temperature at the core‐mantle interface of the earth's interior is estimated most recently as 3130 K. Thus there is a strong likelihood that uranium exists in the earth's metal core. Hence the natural alpha radioactivity of uranium offers a power source for the earth's magnetic dynamo.