Re: airfilters and radon daughters - Thoron vs. radon

[AndrewsJP@AOL.COM]

In a message dated 11/29/2001 9:15:02 PM Eastern Standard Time, SAFarberMSPH@CS.COM writes:



> In a message dated 11/29/01 3:14:06 PM Pacific Standard Time, idias@interchange.ubc.ca writes: 
>
>
> > 24 hours of decay is fine if the Ra-220 concentration is low, but the thoron progeny are longer lived that the radon progeny. 
>
> Radsafe: 
>
>
> Thoron [Rn-220] has a half life of only 56  seconds vs. Rn-222 at 3.8 days. Thoron airborne levels are accordingly usually quite negligible [often thoron does not even escape to any degree from the soil, or thorium bearing rock,  or building materials due to its very short half life vs. Rn-222] so the thoron progeny in air would almost always be very low as well. 
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>
> Stewart Farber 
>
> email: SAFarberMSPH@cs.com 


Yes, as far as it goes.  The fuel for the Peach Bottom and Fort St. Vrain reactors in the US used thorium as a part of the fuel.  In the processing of the coated particles and the formation of thorium carbide, substantial amounts of Rn-220 were released and plate out of the daughters was a significant problem in the fuel fabrication process.  The worst problem occured in the plate out of the Pb-212 on the internals of the glove boxes used for making the particles.  The boxes became rather intense radiation sources after thorium particles were produced for a while.  The 10.64 hour half life makes it quite persistent in this kind of process. In this environment, our air sample counting protocol used decays of 4 hours after end of sampling, 24 hours, and 72 hours to determine the long lived alpha components in the presence of the Pb-212.


Best wishes for the holidays.


John Andrews

Knoxville, Tennessee