In the directly heated oxide cathode, the core metal wire comprises {TAIL ~ a tungsten core wire} or {HEAD ~ a rhenium tungsten core wire} 
In the directly heated oxide cathode , the core metal wire comprises { TAIL ~ a tungsten core wire } or { HEAD ~ a rhenium tungsten core wire }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD