[ RadSafe ] Scintillation Counting Question

raymond.ilson at utoronto.ca raymond.ilson at utoronto.ca
Thu Aug 28 13:15:05 CDT 2008

Hi Elaine:

I had a similar problem with small samples taken from absorbent gels  
used to contain liquid rad waste. We were counting small samples to  
ensure that the disposal criteria were met and that the radioisotopes  
in the waste matched those indicated on the tag.

The counts often doubled by waiting 24 hours, so I agree with the  
previous comments about solubilization. Sonication, warming,  
shaking.... would all likely help, but could lead to residues on the  
outside of the vials and interfere with your counting as well. If  
there's no hurry, it may be simplest to determine when the counts  
peak, which appears to be about 24 hours, and start your counting at  
that point.


Raymond G. Ilson, Director
Office of Environmental Health and Safety,
Dalhousie University,
Halifax, Nova Scotia
Tel:   902-494-1241
Cell:  902-456-2541
Fax:  902-494-2996
raymond.ilson at dal.ca

  Quoting "Nielsen, Erik" <nielseec at nv.doe.gov>:

>  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
> Voice 702-295-8954
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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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