[ RadSafe ] TFP - next questions

[Bradshaw, Keith]

Thanks for finding this again James.  This came up on RADSAFE a couple (?)
of years ago.

I doubt I'm alone in thinking simply precipiting carbonates is not specific
enough for Sr-90 analysis.  A whole range of natural (and artificial)
radionuclides would carry through the procedure.  Radium for example, but
there's more.

The counting procedure also seems a bit odd.  The Quantulus can be set to
alternate blank-sample-blank-sample, many times over, to iron out background
variation over long count times.  Here, they seem to have opted for 4 repeat
counts of 100 minutes for the sample, but a single long 5000 minute count
for the background.  Probably would have been better to divide the total
time into 20 or so equal blank-sample cycles.

To be fair, it wouldn't be the first time that the reported procedure is not
actually what has been done.  Perhaps in reality there was more.  But on the
basis of what's written I have doubts, as explained above.  It's a pity,
because these are hard won valuable samples.

>P.S. What is "secular equibrium"?  It sounds like something that 
>might happen on Dick Cheney's secret energy task force.

I've always thought it's an odd phrase too.  In this context it means Sr-90
decays to Y-90, which is itself radioactive.  Because the Y-90 half life is
very short compared to the Sr-90 half-life, the Y-90 activity will "grow in"
any separated Sr-90, and eventually the activities of the two will become
essentially equal.  After 7 Y-90 half-lives (or about 19 days) the Y-90
activity will be within 1% of the Sr-90 activity.

Personal views only

keith.bradshaw at niras.co.uk

web:  www.niras.co.uk


-----Original Message-----
From: James Salsman [mailto:james at bovik.org]
Sent: 04 January 2006 19:39
To: radsafe at radlab.nl
Subject: Re: [ RadSafe ] TFP - next questions


> At some point several years ago, there was a semi-detailed
> description of the method being used by the tooth fairy
> project to analyze teeth for Sr.  Can anyone point me to this post?

The following is quoted from pp. 23-24 and 49 of:
  http://mtafund.org/prodlib/radiation_health/final_report.pdf


<CUT>

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