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