Scintillation Counting

[Susan Radosevich <Susan.Radosevich@ehs.ucsb.edu>]

One of our researchers is experiencing problems when counting carbon-14 
radiolabeled inorganic bicarbonate samples.  I was hoping someone may 
have had a similar experience and could offer suggestions...

The researcher prepared two sets of vials for counting in a liquid 
scintillation counter.  The first set consisted of radiolabeled 
carbon-14 organic matter deposited on membrane filters.  The second 
set of vials contained 4 micro liters of carbon-14 labeled inorganic 
bicarbonate (aqueous).  Four milliliters of scintillation fluid was used 
in 20 ml glass vials for both sets.  They found that the number of 
counts degraded over time for the inorganic bicarbonate upon storage of 
the vials for approximately a week, while the counts for organic 
bicarbonate set remained constant over time.

Does anybody know the cause for the reduction in counts?  One possible 
cause is out-gassing of bicarbonate through a reaction to carbon 
dioxide which didn't mix with the scintillation fluid.  

Any suggestions would be appreciated!

Susan.Radosevich@ehs.ucsb.edu

----------------------
Susan R. Radosevich
Radiation Safety Office
University of California, Santa Barbara
phone: (805) 893-7255
page:  (805) 957-0293
Susan.Radosevich@ehs.ucsb.edu