[ RadSafe ] Re: Fallout "preserved" in concrete
daleboyce at charter.net
Sun Feb 22 18:01:06 CST 2009
A couple of things to think about. Concrete from accelerator shielding tends
to have europium neutron activation to Eu152 and Eu154. I don't have a chart
handy, but either 152 or 154 will dominate the activation products in gamma
spectra at 10-20 years post shutdown.
If you are doing liquid scintillation spectroscopy of concrete dust without
first fully chemically dissolving it, naturally occuring alpha emitters can
mimic tritium. Alpha's in solution will show up as a peak that is down
shifted in the spectrum by a factor of 6 or 7 from the alpha energy. If they
are in a fine powder they can get further down shifted due to energy
straggling. Concrete frequently has a fair amount of Th232.
----- Original Message -----
From: <welch at jlab.org>
To: <radsafe at radlab.nl>
Sent: Sunday, February 22, 2009 10:23 AM
Subject: [ RadSafe ] Re: Fallout "preserved" in concrete
> Thanks for the response, Mike.
> We are indeed sampling and counting the concrete. Our early results
> indicated the presence of tritium, which I did not expect to be uniformly
> distributed in the material (this is a collection of large shield blocks
> from an old cyclotron). We are scratching our heads a little and trying
> to come up with possible explanations. One idea is that the activity is
> really from Sr-90. But, we don't see any Cs137, so it's a bit puzzling.
> Other possible interference could be from naturally occuring activity (as
> you mentioned), but we haven't put all the pieces together yet. With
> respect to the fallout, I'm mainly wondering if there have been any
> attempts to benchmark such a thing, similar as has been done with the
> naturally occuring nuclides. If would be nice to have a reference to help
> substantiate or refute the idea.
> Thanks again.
>> Message: 2
>> Date: Fri, 20 Feb 2009 14:38:43 -0800
>> From: "Brennan, Mike (DOH)" <Mike.Brennan at DOH.WA.GOV>
>> Subject: RE: [ RadSafe ] Fallout "preserved" in concrete
>> To: <radsafe at radlab.nl>
>> <37C41083D3480E4BBB478317773B845D0148EE62 at dohmxtum31.doh.wa.lcl>
>> Content-Type: text/plain; charset="us-ascii"
>> I would expect it to differ from location to location, due to different
>> amounts of fallout. Any fallout that was cast in concrete in the 60s
>> has decayed to a little bit of Cs-137, a little Sr-90, and so few
>> plutonium atoms that you could name each one. I would expect that in
>> almost all cases it would be insignificant in comparison to the
>> naturally occurring radioactivity, which would also vary depending on
>> where the materials came from. Without knowing the particulars of the
>> gravel, sand, etc., I would guess that most of the activity comes from
>> K-40 and isotopes in the U-238 and Th-232 decay chains (probably in
>> secular equilibrium). For newer concrete, I suspect that the
>> controlling factor would be how much fly ash was used in it, as I
>> understand that radium and thorium is concentrated in the ash when the
>> coal is burned (I have no direct experience with this, however).
>> In the end, I suspect that if you want to know the activity from a given
>> piece of concrete, you will just have to sample and count it.
>> -----Original Message-----
>> From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On
>> Behalf Of Keith Welch
>> Sent: Friday, February 20, 2009 1:34 PM
>> To: radsafe at radlab.nl
>> Subject: [ RadSafe ] Fallout "preserved" in concrete
>> Hello Radsafers,
>> I'm looking for data regarding levels of radioactivity in concrete as a
>> result of weapons fallout. I'm evaluating some concrete that was cast
>> in the early to mid 1960s, and trying to determine if there might be
>> elevated levels of Sr-90 or other nuclides in the concrete due to the
>> prevailing levels in the environment at the time. I've searched the
>> on-line literature pretty thoroughly, and have not come up with
>> anything. Existing documentation that I can find only speaks to natural
>> radioactivity in concrete (NCRP etc.).
>> Thanks for anything you can suggest.
>> Keith Welch
>> Jefferson Lab
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