Re: Luminescence and LSCs

["Schoenhofer" <schoenho@via.at>]

Schoenhofer
Habichergasse 31/7
A-1160 Wien
AUSTRIA
Tel./Fax: +43-1-4955308
Mobiltel.: +43-664-3380333
e-mail: schoenho@via.at

----------
> Von: baumbaug@nosc.mil
> An: Multiple recipients of list <radsafe@romulus.ehs.uiuc.edu>
> Betreff: Luminescence and LSCs
> Datum: Mittwoch, 20. August 1997 23:44
> 
> Franz,
> 
>         As I understand/remember it (Liquid Scintillation Counters aren't
my
> expertise), when an energetic particle (let's use a beta as an example)
> interacts with a solvent/fluor molecule, light is emitted from the L.S.
> sample vial in all directions and is "directed" into two photomultiplier
> tubes which convert the light into a measurable electrical pulse.  As you
> noted, an energetic Beta particle like P-32 can give rise to more than
300
> photons.
> 
>         Luminescence from chemiluminescence or photoluminescence is
commonly
> referred to as "single events" since each reaction results in the
emission
> of a "single" photon. The coincidence Gate Circuit was introduced to
reduce
> noise level in L.S. counters.  Up to a certain number of single events,
the
> coincidence circuit can discriminate between single events and true
> gamma/x-ray photons or beta particles.  
>         Except in "rare" cases, luminescence is not a problem with "state
of
> the art" LSC's because they "tell you" if you have a problem!  I have a
> LS-6000 series Beckman and I feel "very" comfortable with the data
received.
> I don't want to start a technology (or any other type of) war here
because I
> respect your opinion, but in my "personal" opinion, Quantulus' are
re-warmed
> 50's technology.  Having said that, however, you can count a dirty soil
> sample a LOT easier than I can...(grin).
> 
>         Joel
>  
------------------------------------------------------------------------

Joel, 
You did not start a war, though it seems something like a "religious war"
with different LS counters. For me it is quite problematic to understand
your statement that "Quantulus is rewarmed 50`s technology". I always
thought that there is "one" Quantulus available, but you seem to have
something else than I have. I do not know where you got the information
about the rewarmed 50`s technology - maybe it was from a certain
US-competitor? The first Quantulus I purchased (serial number 1) was in
1983 revolutionary, because it was the first commercially available counter
with MCA technique, software controlled, with storage of the pulse height
spectra on computer and software to evaluate the results from the spectra
stored to optimize counting conditions and results according to optimum
figure of merit. It was the first commercially available counter with an
effective anticoincidence shielding. I am proud of having contributed to
the development of this counter by putting forward my idea of an "ideal LS
counter". Later electronics have been modernised. An effective
Alpha-Beta-Discrimination has been introduced some time later. 

I wonder again, where you got the information about the rewarmed 50`s
technology. I have not tested your Beckman counter, so I for sure will not
comment on it. I wonder what you have tested under the name of "Quantulus".
But I want to inform you, that the four Quantulus I have do not  give me a
warning, but they  m e a s u r e  the contribution of chemoluminescense.
Since we are doing low-level counting I take this only as an indication of
the presence of chemoluminescence, because deducing the count rate from the
normal count rate will give quite large errors due to the error propagation
laws. 

The counter one purchases should clearly depend on the purpose of the
measurements to be performed. If you have only to verify that the tritium
concentration of waste water is below 37 000 Bq/l then no low-level counter
is needed and any reading of tritium plus chemoluminescence below this
value will indicate compliance. But if you really want to do ultra
low-level measurements then your decision for purchase will sure not depend
on the technology used, but on the lower limits of detection to be achieved
by the counter. And in this respect I find from a lot of intercomparison
exercises, that our results are always among the best ones achieved. Only
in the case of tritium measurements there is a better counter - the high
volume counter ALOKA - which is obviously not suited at all for the
determination of other radionuclides.

I am not a salesman for this counter, but I have not purchased until now
altogether five of these counters just for fun, but because of their
superior performance. We have developed quite a few methods for this
counter, which save us money and time - including tritium, Sr-90, radon in
air, radon in water, radium in water, Kr-85 in air, gross alpha and beta
activity in water etc. Any radsafer interested is invited to contact me on
my private e-mail address for further information

Regards,

Franz