[ RadSafe ] Scintillation Counting Question

[Marshall, Elaine]

I have a researcher who posed the following question to me.  I have not
experienced this yet and was wondering if anyone else might have an
idea.

 

"For this study counting tritium (as estradiol), we are using Ultima
Gold cocktail, 10-12 ml for 40 microliter samples.  We are seeing
something that seems odd to me:  after holding for at least half an hour
in the dark, we get counts that seem low, and if re-counted a day or so
later, the counts go UP, by about 50%, and reach the expected levels.  I
know of a number of reasons for counts to go DOWN, but don't understand
how they can go up.  We do make a point of mixing well, without shaking
so much as to cause bubbles.  Any clue???"

 

The researcher wanted me to add that these are aqueous samples, although
the actual tritiated compound is only moderately aqueous-soluble.

 

Thanks!!

 

 

Elaine T. Marshall, CHP

Radiation Safety Officer

Lovelace Respiratory Research Institute

2425 Ridgecrest Drive SE

Albuquerque, NM  87108

(505) 348-9578

emarshall at lrri.org