Re: Radon in water by LSC (EPA Proposed Method)

[Franz Schoenhofer <schoenho@via.at>]

At 20:33 07.01.2000 -0600, you wrote:
>Franz,
>
>I think Paul was asking if anyone has experience specifically with APHA 
>Standard Method
>7500-Rn. 

Well, I thought that the question was more generally meant, but you might
be right. Sorry I do not know this APHA method, but it seems from your
reply that a water miscible gelforming cocktail is used. I have always used
the extraction method with a water immiscible cocktail introduced by
Prichard and Gesell a long time ago. With a water miscible cocktail any
other radionuclide present would interfere, whereas radon is the only
radionuclide to be extracted into the water immiscible cocktail. (Rn220
will decay fast enough not to interfere.) This prevents also quenching by
for instance iron and manganese, because they will not be extracted. 

Furthermore we always record the pulse-height spectra on our
"Quantulus"-counters automatically and check the spectra before evaluation
visually - any wrong sample preparation could be detected. Even in the case
of the extraction we have found small quench effects, but we always
optimize the window using the spectra. We always run with each batch a
background and a similarily treated Ra-226-standard in equilibrium. We
adjust the window to maximize the figure of merit. We do not used fixed
windows. Alphas are very little affected by quench and as I have confirmed
the close-to-100% efficiency is practically not changed. When we use the
alpha-beta-discrimination feature of the "Quantulus" we do not even have
any theoretical interference by betas. Therefore any error introduced by
this negligible changes is by far lower than the error from sample taking,
pipetting etc. 

>interested in others thoughts on the specific procedure Paul referred to.

If you could tell me where I can find this method I would be interested
myself in it and could comment more easily.

I have some years ago worked on an ISO standard for radon and radium in
water, but since I am just now changing my working place I have at the
moment no access to my papers.

Best regards,

Franz
Franz Schoenhofer
Habicherg. 31/7
A-1160 Vienna
Austria
Tel.: +43-1-495 53 08
Fax.: same number
mobile phone: +43-664-338 0 333
e-mail: schoenho@via.at

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