{HEAD ~ The radiation shield} acts to reflect infrared radiation emanating from the reaction zone back toward {TAIL ~ the reaction zone} while permitting the passage of the alkali metal vapor to the condensing means 
{ HEAD ~ The radiation shield } acts to reflect infrared radiation emanating from the reaction zone back toward { TAIL ~ the reaction zone } while permitting the passage of the alkali metal vapor to the condensing means
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH