{HEAD ~ 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 means such as thermal exchange with ambient temperature air or other coolant fluids 
{ HEAD ~ 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 means such as thermal exchange with ambient temperature air or other coolant fluids
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH REL REL REL 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 OTH OTH OTH