Naturally Occuring Radon Isotopes -Reply

[FRAMEP@ORAU.GOV]

Bill Kolb wrote:

>Does anyone have figures for the natural ratio of atmospheric
>Radon-222 to Rn-220?  Thanks.

As Ron said, there is no natural ratio. I can give an idea as to what
common relative numbers might be though. Its a very different
situation indoors and outdoors and we are talking ballpark figures.

Outdoors:ICRP 50 "Lung Cancer Risk from indoor Exposures to Radon
Daughters" says"the available measurements indicate for areas with
normal natural soil activity, long-term mean concentrations of 1-10
and 0.5-20 Bq/cubic meter for Rn-222 and Rn-220 respectively in the
air 1-10 m above ground level".  Some other numbers I've seen seem to
agree with this estimate and put the Rn-220 numbers the same as or
somewhat higher (say twice) than the Rn-222 numbers.

Indoors: ICRP 50 and the limited other data I've seen suggest that
the indoor concentration of Rn-222 is often about 3 to 5 times that
of the Rn-220. 

Best of luck

Paul Frame
Professional Training Programs
ORISE
framep@orau.gov