BZA READINGS -Reply

[FRAMEP@ORAU.GOV]

Alan Marchand wrote in part:

>The BZA filters are held for 24 hours for Radon decay. The
>detector counts the sample papers for 30 minutes. .... A 
>week later, they are counted again, 99% of the BZA
>filters now read zero. Calculations show a Thoron element. 
>... if we go by the 24 hour results the mask usage goes up. If
> we relyon the results from a week later some workers may 
>actually receive an uptake....Is  there any way to properly calculate for
>the Thoron or ....

Alan: There may well be a method available that will do just what you
want. The equation used is not easily sent via email. Get Herman
Cember's Introduction to Health Physics second edition p 405 or the third
edition page 574. Its the so-called two count method although I've heard
people refer to it as a Kovar factor method. In essence, you count about
4 hrs after sampling by which time the radon daughters have decayed
away. Then you count 10 to 20 hours later i.e. after 1 to 2 half lives of
the thoron daughters. The thoron daughters contribute to both the first
and second counts but the difference in counts gives you  all the
information you need to correct the first count. Its not a particulary good
method for very low activities and short count times but its the best I can
suggest.

Best wishes

Paul Frame
Professional Training Programs
ORISE
framep@orau.gov