[ RadSafe ] Scintillation Counting

[H. Westenbrink]

Elaine,

May be the fotons will be absorbed by the tubes
Try a blanc tube with scintillation fluid and the 
external standard, so you will see the quench factor of the tube.

best regards,
Henk Westenbrink
h.westenbrink at amc.nl # 020-56 65752
Endocrinology & Radiochemestry
RSO
Central B-laboratory (F1-149)
AMC  Amsterdam  Holland

----- Original Message -----
From: "Marshall, Elaine" <emarshall at lrri.org>
Date: Monday, November 3, 2008 10:42 pm
Subject: [ RadSafe ] Scintillation Counting
To: radsafe at radlab.nl


> Does anyone have any insight so that I can get back to my researcher?
>  
>   
>  
>  The contract specified a "6 ml polypropylene vials" for counting the 
> 3H
>  samples. When I couldn't find those, and enquired, it turned out the
>  ones recommended were actually high density polyethylene.  There was 
> a
>  specific recommendation from a particular vendor.  However, since we 
> got
>  a much better deal on Vendor #2 HDPE 6 ml scintillation vials, we bought
>  those. 
>  
>   
>  
>  The first samples we tried to count in those vials, with 1 ml of Scint
>  fluid (as recommended in the protocol), gave us < 10% of the expected
>  counts (925 instead of 12,000 DPM).  We were using the racks for the
>  mini-vials.  The technician then tried counting these in another
>  scintillation counter (the one used by Rad Safety), and they wouldn't
>  count at all:  this instrument gave error messages.  After determining
>  it wasn't a matter of bad pipetting or something, I had the technician
>  transfer that sample and its scintillation fluid to a HDPE 20 ml vial,
>  add 9 ml more scint. fluid, and he got the expected counts (just under
>  12,000).  I then had him take 5 ml of that mixture and put it back in 
> a
>  clean 6 ml vial, and again, he got less than 10% of the counts expected
>  for the half of the volume counted (~500, instead of ~6000), so it
>  wasn't just the low volume of scintillation fluid suggested in the
>  protocol.  So it appears these vials don't count tritium well.   Do you
>  have any insight into this bizarre problem?  Vendor #2 has none, and
>  apparently has no data to actually support the use of these vials for
>  scintillation counting (at least for tritium, I didn't ask about other
>  isotopes).  They have offered to send me another type of vial, but that
>  doesn't entirely easy my mind.  
>  
>   
>  
>  Any comments/experience with this sort of issue would be greatly
>  appreciated!!  Like, is it something that "everybody knows" (except me
>  and apparently the people that developed the protocol for the contract)
>  that one always has to count 3H in glass???   Have you ever heard of
>  HDPE vials contaminated with something that quenches the heck out of
>  tritium? 
>  
>   
>  
>   
>  
>  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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