The portion of tube 12 near its external walls is maintained at {TAIL ~ a temperature} at least 100 degrees C. below that of the alkali metal in tube 14 by {HEAD ~ means} such as thermal exchange with ambient temperature air or other coolant fluids 
The portion of tube 12 near its external walls is maintained at { TAIL ~ a temperature } at least 100 degrees C. below that of the alkali metal in tube 14 by { HEAD ~ means } such as thermal exchange with ambient temperature air or other coolant fluids
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH