Re: Counting Wet Smears

[James G. Barnes <mail15077@pop.net>]

Good afternoon,

    If it were critical to count the wet smears, I think the approach I would 
take would be to characterize several dry smears to get a very accurate 
determination of the activity.  Then I would measure the activity with my field 
equipment to establish a "dry" reading.  Then, I would moisten the smears and 
re-read them.  The difference between the wet and dry readings would give me a 
correction factor for the instrument.

    When checking them in the field, I'd read the wet smears and apply the 
correction factor to get field results.  I'd then take the smears back to the 
lab, dry them out, and count them at my leisure.

    One could also think about using NaI (maybe a 3" X 3"), but I would be 
afraid that the background would obliterate any chance of seeing low levels of 
contamination on smears.


Jim Barnes, CHP
Radiation Safety Officer
Rocketdyne Division; Rockwell Aerospace

    >      I am looking for information on methods to count wet smears.  Much 
    > of 
    >      the work performed at Hanford is out-of-doors and can't necessarily 
    >      stop just because of a little rain or dew.  Currently, smears are 
    >      dried before counting.  However, if there is a justifiable technique 
    >      for counting a wet smear, I would like to hear about it.
    >      
    >      In addition, are there any definitions of "how wet is wet"?  At what 
    >      point is a smear considered a wet smear?
    >      
    >      The isotopes of concern are Co-60, Eu-152, and Cs-137.  The smear 
    >      media is masslin and cloth technical smears.
    >      
    >      Please send replies to me directly at ml_johnson@ccmail.pnl.gov.
    >