radioactive dumping(Waste generated by the emission of particulate or electromagnetic radiation resulting from the decay of the nuclei of unstable elements)
radioactive tracer(A radioactive isotope which, when injected into a biological or physical system, can be traced by radiation detection devices, permitting determination of the distribution or location of the substance to which it is attached)
fallout(The descent of airborne solid or liquid particles to the ground, which occurs when the speed at which they fall due to gravity exceeds that of any upward motion of the air surrounding them)