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Re: LSC OF Fe55 SAMPLES



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

----------
> Von: Ryanchp@aol.com
> An: Multiple recipients of list <radsafe@romulus.ehs.uiuc.edu>
> Betreff: LSC OF Fe55 SAMPLES
> Datum: Dienstag, 29. Juli 1997 03:29
> 
> RADSAFERS
> 
> DOES ANYONE HAVE ANY DATA ON LSC OF Fe55 SAMPLES I NEED EFFICIENCY, TYPE
OF
> SCINTILLATION LIQUID, AND COUNTER.
> BEST INFO I HAVE FROM PACKARD THAT THE EFFICIENCY IS SIMILAR TO H3.
> 
> PLEASE "E" MAIL ME AT 
> RYANCHP@AOL.COM
> 
> THANK YOU
> BOB RYAN
> -----------------------------------------------------------------

Bob,

Efficiency for a given radionuclide depends on the type of samples you have
(organic, aqueous, mixing ratio .....), on the scintillation cocktail you
use, the quench, the window you use on your instrument etc. This is also
true for tritium of course. To determine it for a given system I recommend
that you use standards - by the way the only practical method to have
acceptable and reliable results and to fulfill the requirements of quality
assurance. For low-level measurements you would even have to determine
background with the same system without the radionuclide and then you
should determine the optimum window setting by maximizing the figure of
merit.

Specifically for Fe-55 I have a warning: At the moment we try to develop a
reliable method for the measurement of smear samples for Fe-55. The samples
collegues collected were from a measurement device for thickness. The smear
sample contained oil from the machine and we obtained readings which rose
in cpm in the beginning. We use the ultra low-level counters Quantulus
(Wallac Oy, Finland) on which we can check also for chemiluminescence by
recording the delayed coincidence spectrum. It seems that what could be
attributed to the low energetic Fe-55 betas is in reality
chemiluminescence, which might be very persistent. (Smearsamples from the
shutter which is not easily accessible, but contains no oil, showed no
counts.) We are working to verify whether the counts really come from
chemiluminescence. 

Work on determination of Fe-55 was done by a group of the University of
Regensburg. I think that a contribution must have been published in the
proceedings of the MARC III conference, held in Kona, Hawaii in April 1994.
Sorry, I use for radsafe my home computer, so I do not have it at hand. I
know for sure, that they have a web site on the internet, I think you could
easily find it using University (or in German Universitaet) Regensburg for
your search. They also used Quantulus for their work. 

Hope this is a little help.

Franz