[ RadSafe ] RE: Gross Alpha

[Bob Shannon]

Short answer:  Liquid scintillation counting is more sensitive to lower
energy emissions (e.g., Tc-99, C-14, H-3) and is therefore less likely to
underreport gross activity when results compared to summed isotopic values. 

Longer answer (I won't go into detail but there is plenty): Beware of GROSS
activity measurements. They are probably the most AB-used and misunderstood
of radioanalytical techniques.  The effect you describe is not always the
case - especially in many cases where gross measurements are most
applicable. You should figure out specifically why your measurements are
divergent.  Screening measurements should be conservative - i.e. if there is
any bias they should exhibit a high bias relative to the nuclide(s) of
concern. 

You don't want to miss seeing the problem.  


Bob Shannon
KAMS
303-432-1137

-----Original Message-----
From: owner-radsafe at list.vanderbilt.edu
[mailto:owner-radsafe at list.vanderbilt.edu] On Behalf Of Khalid Aleissa
Sent: Friday, February 04, 2005 10:42 PM
Cc: radsafe at list.vanderbilt.edu
Subject: Gross Alpha

Gross alpha and beta counting using LSC show much higher values than
proportional counter measurements, does anyone have a rational explanation
for the reason? One more thing, the detection limit for proportional counter
is higher (better sensitivity) than that for LSC, for gross alpha and gross
beta counting and it is believed this is due to the difference in sample
size, BKG, and efficiency difference, are there any other factors?

Khalid

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