RE: Swipe Testing

[vchase@bi-pharm.com]

I like to use Gelman Type A/E Glass Fiber Filters (37mm).  Isopropyl alcohol 
is sprayed on the filter before taking the swipe.  The filter is air dryed 
and Packard Ulitma Gold XR is added to a 7ml vial.  The filter doesn't 
dissolve but does become quite translucent (almost transparent) in Ultima 
Gold.  Also they don't float to the top of the vial like some dissolvable 
filters and are ready to count immediately after adding scintillation fluid. 
 I've observed a collection efficiency on the filters of between 10% to 20%. 
 The only problem I have with the filters is that they are somewhat flimsey. 
 They are not really made for rough surfaces (unpainted cinder block, 
concrete floors, etc).  It takes a little practice so that you don't apply 
too much pressure to the filter when swiping an area.  I've decided to live 
with the flimsy-ness(?) of the filter because I like the ability to count a 
sample right away and I found the counting efficiency to be better for this 
technique over paper filters and cotton swabs.

Speaking of cotton swabs,  I found that I lost some counting efficiency for 
low energy beta emitters (H-3 and C-14, particularly) over filter papers. 
 Didn't investigate the reason but a guess would be self absorption in the 
swap.  Also found some cotton swaps I was using as controls (blanks) to 
exhibit slighty more counts than filters in the lower energy regions. 
 However, the higher counts were not observed in all cases,  so I don't 
think it means anything.

Hope this helps.

Regards,
Vince Chase
vchase@bi-pharm.com
Radiation Safety Officer
Boehringer Ingelheim Pharmaceuticals
The opinions expressed here are those of the author and do not represent
the opinions policies or practices of Boehringer Ingelheim Pharmaceuticals.