{HEAD ~ The improvement} 9, wherein {TAIL ~ said at least one element} capable of attenuating x rays is selected from the group consisting of lead oxide, bismuth oxide, tantalum oxide, and uranium oxide 
{ HEAD ~ The improvement } 9 , wherein { TAIL ~ said at least one element } capable of attenuating x rays is selected from the group consisting of lead oxide , bismuth oxide , tantalum oxide , and uranium oxide
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