[ RadSafe ] Any suggestions for a nuclear medicine wipe counter?

Cindy Bloom radbloom at comcast.net
Mon May 21 10:10:40 CDT 2007


It looks like I-131 emits a 192 keV beta 89.4% of the time (as well as 
various photons), so the efficiency for detection with a thin windowed GM 
detector will likely be much greater than that for Tc-99m, which is not 
associated with beta emissions (it's long-lived progeny Tc-99 is a beta 
emitter, but Tc-99's specific activity is so low that this beta emission 
would not typically be useful for detecting Tc-99m contamination in a 
nuclear medicine program).

Many of the programs I worked at used gas flow proportional counters (thin 
window or windowless) for detecting contamination; a sodium iodide or 
similar detector  might be a bit better for radionuclides with essentially 
only photon emissions like Tc-99m and I-125, but then you have the worry of 
how to set up the detector for different energies of interest, e.g., 
maximizing efficiency and minimizing background and hopefully not having to 
change settings for different radionuclides.

I think you will find that if you are only looking for I-131, a thin 
windowed GM counter will meet your needs.


At 08:59 AM 5/21/2007 -0500, garyi at trinityphysics.com wrote:
>Hi John,
>Thanks for your suggestion. I've never used that counter, but it seems 
>like it would be awfully
>close to or perhaps over the 1000 dpm/100 sq cm limit. You may have used 
>it with no
>problems, but I played with the numbers listed on the web page you kindly 
>sent me. At 6
>cpm/kdpm efficiency for Tc99m, and with the "Background Voltage" of up to 
>24 cpm, it can
>do better than 1000 dpm, but only if you count for the max count time of 
>20 minutes. And I
>wonder if "Background Voltage" refers to counts due to voltage/electronics 
>and not external
>field. The downloadable information is rather vague.
>Since I'm trying to help someone who is using mostly I131, which probably 
>counts less
>efficiently on this GM, I will probably keep looking. But like I said, I 
>haven't used it before
>myself so please let me know if you have tried it and liked it.
>Thanks again,
>On 20 May 2007 at 17:39, John Jacobus wrote:
>Date sent:  Sun, 20 May 2007 17:39:42 -0700 (PDT)
>From:  John Jacobus <crispy_bird at yahoo.com>
>Subject:  Re: [ RadSafe ] Any suggestions for a nuclear medicine wipe
>To:  garyi at trinityphysics.com, RADSAFE <radsafe at radlab.nl>
>Try this. The Wipe Counter (Model 1051). It uses a GM
>detector system, and is easy to operate, i.e.,
>pass/fail. I think that the NRC approved its use many
>years ago.
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