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Re: Luminescence & LSC



William G. Nabor wrote:
>
>     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.

Don't know if this is a common thing or a proprietary bit of technology, but
our Beckman LSC can be set to print a "lumex" value for each vial.  This is
supposed to give at least an estimate of the percentage of the raw CPM that
could be attributable to chemiluminescence.  The higher the lumex number,
the lower the reliability of your tritium-channel results.

We almost always just run our wipes immediately, even from the H-3 labs.  If
the H-3 numbers come out at background and the quench number is reasonably
low, a high lumex is irrelevant (if the sample's only 20 DPM above the
blank, who cares if 90% of it is chemilum?).  If the H-3 counts are higher
than our screening criteria, we run the sample again for confirmation,
regardless of the lumex result.  This procedure lets us get the vast
majority of the wipes out of the way quickly, so we can concentrate on the
small number of positive or questionable ones.

Eric Denison
denison.8@osu.edu