the radioactive isotope content of a rock means the amount of elemental isotopes of the parent isotopes
radioactive_substance is not nuclear_material. radioactive_isotope is not radioactive_substance. radioactive_isotope is radioactive_substance. radioactive_substance is nuclear_material. rutherfordium is radioactive_substance. plutonium is radioactive_substance. radioactive_isotope is not isotope. radioactive_dating is measurement. radioactive_isotope is isotope. rock is natural_material_consisting_of_minerals.