[ RadSafe ] Scintillation Counting Question

[Nielsen, Erik]

 To expand on Cary's comment.

I would recommend vigorous shaking of your sample/cocktail mixture and
degassing it by setting it in an ultrasonic cleaning bath for a few
minutes.  The ultrasound will degas the sample as well as contribute to
the homogenization of the sample/cocktail mixture.

Erik C. Nielsen 
Senior Scientist 
Remote Sensing Laboratory 
P.O. Box 98521, M/S RSL-47 
Las Vegas, NV 89193-8521 

http://www.nv.doe.gov/nationalsecurity/homelandsecurity/frmac/default.ht
m 

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Message: 8
Date: Tue, 26 Aug 2008 17:41:38 -0700
From: "Cary Renquist" <cary.renquist at ezag.com>
Subject: RE: [ RadSafe ] 
To: "Marshall, Elaine" <emarshall at lrri.org>,	<radsafe at radlab.nl>

Just a thought...  
Perhaps it is a physical phenomenon.
Since the tritium compound is moderately soluble, perhaps it initially
forms 
small (microscopic) globules in the aqueous solution that eventually
"dissolve"
in the cocktail -- the globules might not be large enough to see, but
large enough 
to keep the tritium beta from interacting with the cocktail.

Cary

-----Original Message-----
From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On
Behalf Of Marshall, Elaine
Sent: Monday, 25 August, 2008 14:47
To: radsafe at radlab.nl
Subject: [ RadSafe ] Scintillation Counting Question

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
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