Re: Re[2]: Radon Question from Occ-Med-Env -Reply

[Schoenhofer <schoenho@via.at>]

At 12:49 1996-07-02 -0500, you wrote:
>I haven't followed this thread closely, but I think that what he means is
>that it would only take about three minutes for the first alpha-emitting
>daughter (Po-218) to be at 50% equilibrium with the radon inside the mask,
>assuming that none of it is returned outside the mask (clearly not the case).
>Is it taken for granted that we're talking only about "radon" as Rn-222, with
>a 4 day 1/2life, here? What about thoron, Rn220, with a 55 second 1/2life?
>
>============================================================================

Dear Ccja,

You mention, that Rn-220 has a half life of 55 seconds. How should it be
present in air in not negligible concentrations - except in a store house
for thorium ore? Only very few cases are known, where thoron and its
daughters contribute significantly to the dose from indoor air - these are
especially constructed traditional Japanese houses in some areas of Japan,
where thorium containing mud has been used for construction. 

The original question lacks all information about the circumstances of the
work and the workers to be protected.

I do not know much about the mechanism of breathers and filters, but the air
inside the mask containing only radon and no daughters will be expelled
within a very short time. There is no time for build up even of Po-218.
Therefore a filter removing the daughters will do it - in spite of a high
radon (222) concentration the dose will be close to zero. 

Franz Schoenhofer
Federal Institute for Food Control and Research
Vienna, Austria

Schoenhofer
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