the radioactive isotope content of a rock means the amount of elemental isotopes of the parent isotopes
radioactive_substance is nuclear_material. uranium is radioactive_substance. radioactive_isotope is radioactive_substance. radioactive_isotope is isotope. radioactive_waste is radioactive_material. plutonium is radioactive_substance. radioactive_dating is measurement. rutherfordium is radioactive_substance. nuclear_waste is radioactive_substance. rock is natural_material_consisting_of_minerals.