Luminescence & LSC

["William G. Nabor" <wgnabor@uci.edu>]

Joel Baumbaugh recently posted a message about LSC chemiluminescence in
which he stated that such was a single photon event and not a problem with
newer LSC counters.  This has not been my experience.

I have never heard of this "single photon" bit, but I do know that chemo is
still a major concern, at least for environmental samples (e.g., lab wipes).
 Perhaps a vigorous reaction emits several photons from several foci that
seem to the LSC as a single real event.  In any case, we still see it even
with the latest cocktails and counters.  Several popular bench cleaners are
a real pain.  There are three things you can do to counter chemo:

     1) Chemo appears in the lower half of the H-3 window.  You can count in
the full window and then crank the upper level discriminator down to 50% and
count again.  A drop in the count rate of about 50% means H-3.  No change
means chemo

     2)  If your counter can print a spectrum, do that and see if all the
counts are in the lower half of the H-3 range (chemo).

     3) Chemo has a much shorter half-life than H-3.  If you have the time,
count your sample in the morning and again in the evening.  A significant
drop in the count rate means that it is chemo.  It has been our experience
that all chemo disappears after 3 days.  For our lab wipes of H-3 labs, we
simply fill the vials and then let them sit for 3 days and count then.
Whatever we see after that we assume to be H-3.
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William G. Nabor
University of California, Irvine
EH&S Office
Irvine, CA,  92697-2725
WGNABOR@UCI.EDU
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