Puzzler

[Bates.Estabrooks@rfets.gov (Bates Estabrooks)]

          Here's a "Puzzler" for the RADSAFE community.  Unlike Click 
          and Clack I don't know the answer, nor can I offer fuzzy dice 
          to the winner, but this may be of interest to all of you and 
          help us out a bit.
          
          Here at Rocky Flats we have a long history of working with 
          "the most dangerous substance known to man."  As such, as we 
          tear this place down, we need to screen everything that leaves 
          the site for disposal, for "DOE radionuclides"; i.e., 
          239/240Pu, 241Am, 233/234U, 235U, and 238U.
          
          Recently we have surveyed several metallic items like trailer 
          roofs, and chain link fence posts, using smears, and direct 
          surveys with NE Electra instruments.  Often we have seen 
          effectively no removeable activity (<20 dpm/100 cm2 alpha) but 
          high direct alpha readings (~200 to 240 dpm/100cm2).
          
          Subsequently, we have covered these high spots with plastic 
          and resurveyed days later to allow the short-lived activity to 
          decay away.  In one case, with chain link fence posts, we 
          covered eight spots, and allowed them to sit for 28 days (I'm 
          not sure why that particular duration).
          
          The resultant surveys showed direct alpha activity still 
          running in the range of 60-150 dpm/100cm2.
          
          In another similar instance (a trailer roof) we had a piece of 
          the metal lab analyzed by radiochem. and alpha spec. for DOE 
          nuclides and they all came back extremely low (Am: 0.0427 
          pCi/g, Pu: 0.0177 pCi/g, 234U: 0.0338, and 235U: 0.0216).  We 
          are having the fence posts analyzed now.
          
          So, the question:  what alpha-emitters are we seeing? And, 
          what mechanism is fixing them to these metal surface so they 
          are not seen on smears?
          
          Any ideas would be appreciated to help corraborate/refute our 
          own.
          
          Bates Estabrooks
          RFETS
          bates.estabrooks@rfets.gov