{TAIL ~ A directly heated oxide cathode} 1, wherein said core metal wire comprises {HEAD ~ a tungsten core wire} or a rhenium tungsten core wire 
{ TAIL ~ A directly heated oxide cathode } 1 , wherein said core metal wire comprises { HEAD ~ a tungsten core wire } or a rhenium tungsten core wire
TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH