In a filament cathode, {HEAD ~ an alkaline earth oxide} having {TAIL ~ an average grain size} of 0.1 μm to 2.0 μm is coated in a thickness of 0.5 μm to 4.0 μm on the surface of a core metal wire 
having
In a filament cathode , { HEAD ~ an alkaline earth oxide } having { TAIL ~ an average grain size } of 0.1 μm to 2.0 μm is coated in a thickness of 0.5 μm to 4.0 μm on the surface of a core metal wire
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH