Swipe Testing

[ABELQUIE@ORAU.GOV]

Sorry to get in on this one a bit late, but you can imagine the number of
emails that accumulate when out of the office for 3 days!

Anyway, let me add my two cents worth.  While Reg Guide 1.86 (and
similar NRC and DOE regs) state that smears should be performed using
"dry filter or soft absorbent paper", the removable limits are not
dose-based (neither are the total contamination limits for that matter). 
Further, the collection efficiency depends on the contaminant, surface
conditions, swipe material, and many other factors - yet most people
assume it is 100% (there is usually no collection efficiency term in the
denominator).  For these very reasons, swipe testing should be
considered as a qualitative check on the level of removable
contamination.    

The argument that dry smears reflect real conditions (people's hands are
dry, etc.) and thus detect removable contamination that could lead to
internal exposure is misleading.  Many times I have smeared a surface
with a dry filter paper and the net effect was to push the dust/dirt
around (very little was collected by the smear) -yet it was apparent that
the smear certainly did not reflect the amount that could become airborne
and inhaled.  The case is even more extreme for tritium - using dry
smears collects very little tritium, while the "real" level of tritium on a
surface that exchanges with the ambient atmosphere would be many
times that determined by a dry smear.  

My point - swipe surveys should be considered as semi-quantitative data
at best, and an estimate of the collection efficiency should be considered
in the determination of removable level.  So if you wish to continue
smearing for tritium and C-14 with dry smears determine your collection
efficiency (I'd bet less than 10%), others will moisten their smears and
increase CE to over 70%.  

Finally, ISO-7503 provides some interesting points on smears and
calculation of removable activity.  It recommends a default CE of 10% in
absence of any better data.  Very finally, while I'm not certain, I do not
believe that the guidelines associated with NRC's new decommissioning
rule with have separate limits for removable - it will say something like
use ALARA to justify the presence of any removable contamination.

Have a nice weekend.

Eric Abelquist
abelquie@orau.gov