Q: help with scintillation counting

[Warren Gallin]

LSC depends on the weak tritium beta particle exciting the fluorescent
chemicals in the toluene-based scintillation fluid.  To do aqueous samples
you need a scintillation fluid that is designed for aqueous samples, usually
containing a detergent to get the water near enough the fluor to get
efficient energy transfer.
    Two possibilities for you: 1) you're not using a water-compatible
scintillation fluid or 2) the efficiency even in the appropriate scint fluid
may be lower because the water is tied up in a detergent micelle, which
could partially quench the signal.



In Article <otterpop-ya023180001911961804590001 at news.msu.edu>,
otterpop at pilot.msu.edu (Otter) wrote:
>I am doing some basic scintillation counting using tritium.  I checked the
>efficiency of the counter using a tritiated machine standard and it came
>out to be 64%.  I then counted a sample of tritiated water, which if I used
>it as the standard, would give me an efficiency of about 40%.  I then
>counted a sample of tritiated toluene, which correlated to a similar
>efficiency as the machine standard tritium (64%).  Both the samples (water
>and toluene) are 15 years old, but I took into consideration the decay
>factor.  Why would I see a difference in efficiency between the tritiated
>water sample and the tritiated toluene sample?  Is the water quenching more
>which would result in a lower count?  Could there be something such as
>evaporation that could have taken place over the last 15 years to the
>samples?  I know that the tritiated standard contains toluene.  Could this
>have some sort of effect because the tritiated water sample contains no
>toluene?  I know all of my calculations are correct and the problem lies
>some where between the water and toluene.  Or, maybe the problem might be
>that my tritiated water sample could be contaminated or dilluted somehow..
>
>Thanks again for your time and help,
>
>Otter
Warren Gallin
Department of Biological Sciences
University of Alberta
Edmonton,  Alberta     T6G 2E9
Canada
wgallin at gpu.srv.ualberta.ca