(n.) One who, or that which, traces.

alpha radiator atom atomic cocktail atomic model ball bar shot beta radiator bird shot buckshot bullet cannon shot cannonball case shot cobalt crossbar shot duck shot dumdum bullet expanding bullet fission products fluorescent paint gamma radiator grape grapeshot ion langrel shot manstopping bullet nuclear atom nuclide pellet planetary shell radiator radioactive waste radiocalcium radiocarbon radiocopper radioelement radioiodine radioisotope radiosodium radiothorium radium radium dial radium paint rifle ball round shot shell shot shrapnel slug split shot subshell tagged atom tagged element tracer atom tracer element valence shell