Re: Liquid scint counting of urine

[Schoenhofer <schoenho@via.at>]

At 15:13 1996-07-15 -0500, you wrote:
>Good Afternoon,
>
>I have access to a Beckman LS7000 LSC.  I counted my urine by the
>following method:
>
>1 ml of urine to 10 ml of Ecolite cocktail; dark dampened for approx. 5
>hrs;  counted on prg 4, channel 1 (lower limit - 0 and upper limit -
>655) for 10 min.  Used 10 ml of cocktail for background.
>
>Results: Background 25 cpm; sample 175 cpm/ml, H# 139 and efficiency of
>89% or 166 dpm/ml.  If there is 1400 ml/day of urine voided - then
>166dpm/ml x 1400ml/day = 235955dpm/day (0.11 micro curies per day) of
>activity in my urine? 
>
>Is there documentation anywhere that would tell me what gross beta would
>be for urine? I'm looking for baseline data to subtract from samples
>counted using the stated mini-procedure.
>
>the reason I'm asking this is to see if it is worthwhile to collect and
>count bioassays (urine) via a liquid scint counter as a quick go no-go
>test for further investigation (ie sending samples (spending money) to a
>lab certified to do bioassays for different isotopes).
>
>thanks for any and all assistance in this (possibly futile) matter
>
>Denny
>RSO, Carnegie Mellon University
>dr4i@andrew.cmu.edu
>412-268-3221
>412-268-3206 fax 
>
>=============================================================================

Denny,

I came home only yesterday after a four weeks sampling mission to the
Pacific, so I read your e-mail only yesterday. 

I do not know the counter you use, so I cannot comment on the settings you
use and on the H#. But your information of an efficiency of 89% is so
unrealistic that I cannot believe it. How did you find this efficiency? One
clear mistake in your procedure is that you use 10 ml of your cocktail as a
background. This is wrong, because this "background sample" has completely
different quench properties - much less quench - and therefore the countrate
will be much higher in the tritium range than of a urine sample containing
no tritium. On the other hand you should be aware that urine contains large
and varying amounts of potassium-40, which contribute to the countrate even
in the low-energy region. In the case of high contamination of urine with
tritium these two factors will of course not play a decisive role, but the
question of the 89% efficiency will lead to a clear underestimation.

We have done extensive work on the contamination of the human body by
tritium from watches with tritium containing luminous dials. Our procedure
was to minimize quench by diluting 1 ml of urine with 7 ml of tritium free
water and then mixing with a gelforming cocktail (12 ml of Quickszint 400,
Zinsser). Background was prepared by mixing urine from a person who were not
contaminated by tritium the same way. Efficiency was determined by
preparation of a sample from the same urine and dissolving a tritium
standard (from Wallac OY, Turku, Finland) in the prepared sample as an
internal standard. Measurement was then performed on one of our four ultra
low-level liquid scintillation spectrometers of the type "Quantulus" (Wallac
OY, Turku, Finland). Background is less than 0.5 cpm in the optimized
tritium window.  

To distil the urine sample is not a pleasant task and moreover wrong,
because tritium is present in urine not only as HTO, but also partly as
organically bound tritium (OBT). After distillation (why azeotropic???) the
OBT will remain in the residue and the water distilled will not contain all
tritium, thus yielding a wrong result. 

Finally I do not understand your question concerning a gross-beta-value. I
do not know whether your settings are optimized for tritium or cover the
whole range of beta particles up to high energetic nuclides like Sr-90 and
Y-90. If you suspect that your urine is contaminated by such higher
energetic radionuclides, then you should be very cautious, because the
maximum permissible concentration of tritium in urine is higher by orders of
magnitude than for other radionuclides. We have successfully applied LSC to
this problem and to the surveillance of effluents from nuclear research
facilities, but this can only be done with our ultra low-level liquid
scintillation spectrometers. 

A  c o r r e c t  done analysis for tritium in urine by LSC is not a go
no-go test, but a very reliable, simple analysis, which is at least equal to
any other analytical method, but much simpler, less time-consuming and less
costly.

We have published a paper on the tritium transfer from watches to the body
and another one on the surveillance of effluencts from a nuclear research
facility - any inquiries from you or fellow radsafers are welcome.

Franz Schoenhofer
Federal Institute for Food Control and Research
Vienna, AUSTRIA
Schoenhofer
Habichergasse 31/7
A-1160 WIEN
AUSTRIA/EUROPE
Tel./Fax:	+43-1-4955308
Tel.:		+43-664-3380333
e-mail:		schoenho@via.at