Where a metal foil construction is utilized, a plurality of such metal foils may be stacked in layers with orifices in {HEAD ~ adjacent layers} being offset from one another such that {TAIL ~ the radiation shield} is substantially opaque to infrared radiation while permitting the passage of the alkali metal vapor 
Where a metal foil construction is utilized , a plurality of such metal foils may be stacked in layers with orifices in { HEAD ~ adjacent layers } being offset from one another such that { TAIL ~ the radiation shield } is substantially opaque to infrared radiation while permitting the passage of the alkali metal vapor
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD 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 OTH OTH