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

garyi at trinityphysics.com garyi at trinityphysics.com
Mon May 21 12:20:08 CDT 2007

Ha! you're right, I'm wrong (sorry John). 

Thanks for taking time to point out my error. 


On 21 May 2007 at 11:10, Cindy Bloom wrote: 

Date sent:  Mon, 21 May 2007 11:10:40 -0400 
To:  garyi at trinityphysics.com, rADSAFE <radsafe at radlab.nl> 
From:  Cindy Bloom <radbloom at comcast.net> 
Subject:  Re: [ RadSafe ] Any suggestions for a nuclear medicine wipe 


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 

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, 

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