The radiation shield 7 including a plurality of {HEAD ~ said metal foils} stacked in {TAIL ~ layers} with orifices in adjacent layers being offset from one another such that said radiation shield is substantially opaque to infrared radiation while permitting the passage of said alkali metal vapor 
stacked in
The radiation shield 7 including a plurality of { HEAD ~ said metal foils } stacked in { TAIL ~ layers } with orifices in adjacent layers being offset from one another such that said radiation shield is substantially opaque to infrared radiation while permitting the passage of said alkali metal vapor
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL 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 OTH OTH