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Re: Back-ground Determination for Thyroid Bioassay



The background increase could be due to radioactive iodine contamination of
the crystal.  Iodine sublimes from the gaseous to the solid form and is
expelled in the breathe as a gas.  When the iodine come in contact with the
cooler surface of the detector it returns to a solid.  An easy way to
prevent this contamination is to wrap the detector with a plastic film such
as Saran Wrap which is easily removed if it becomes contaminated.  You might
a one hour background count and then clean the detector thoroughly with an
alcohol solution to see if there is contamination present.  

Good Luck,

Doug Turner <turners@earthlink.net>

 At 04:29 PM 9/29/96 -0500, you wrote:
>Is the increase in background associated with a drift in gain, or
>peak-broadening (increase in FWHM) that might be indicative of a yellowing of
>the crystal (I assume that you're using an NaI probe)?
>
>