Re: Back-ground Determination for Thyroid Bioassay

[Doug Turner <turners@earthlink.net>]

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)?
>
>