Re: Fe-55

["schoenho" <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: William Lorenzen <LORENZEN_W@A1.TCH.HARVARD.EDU>
> An: Multiple recipients of list <radsafe@romulus.ehs.uiuc.edu>
> Betreff: Re: Fe-55
> Datum: Mittwoch, 20. August 1997 16:06
> 
> Franz,
> 
> Are you indicating that chemiluminesence is more prevelent with lsc
counting od 
> Fe-55 or just a general statement about LSC counting?
> 
> Regards,
> 
> William Lorenzen
> Children's Hospital
> Boston, MA
> 
> lorenzen_w@a1.tch.harvard.edu
> -----------------------------------------------------------------

William,

I wrote this warning, because in the course of measuring smearsamples for
Fe-55 we found out only after carefully looking at the results and the
chemiluminescense spectra that what we in the beginning mistook for Fe-55
was in fact chemiluminescense. This occured though the samples were kept in
the dark for hours and our Quantulus counters are cooled down to about 14
degree Celsius. The smear samples had been taken from the vicinity of a
Fe-55 source at a machine. We still do not know, what caused the
chemiluminescence, it might have been some dirt or oil on the surface where
the smear samples were taken. Something similar might occur when taking
smear samples in a laboratory. We had a similar experience when we tried to
measure distilled spirits directly for a rough estimation of C-14, but in
this case the chemiluminescence could be easily distinguished from the C-14
spectrum. 
It cannot be distinguished so easily from the much lower energetic tritium
betas. An indication of chemiluminescence would be the occurrance of
significantly lower values when remeasuring the same sample after some time
(hours or days). 

Modern liquid scintillation cocktails are relatively insensitive to
chemiluminescence, however I wanted to point out that one should be
cautious. Whenever one measures by LSC a radionuclide with higher energetic
betas like C-14, Sr-90 or alphas from radon or radium there is no problem
with chemiluminescence, because even if it would occur the spectral window
can be set easily to cut off the chemiluminescense.

To all LSC-users: I wish you happy counting without chemiluminescence and
quench!

Franz