Q: help with scintillation counting

[Doug Easton]

wgallin at gpu.srv.ualberta.ca (Warren Gallin) wrote:

>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.

The 40% efficiency is not all that bad. Depends on the type oc sample.

-Doug Easton



>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