[ RadSafe ] Re: Fallout "preserved" in concrete
Arvic.Harms at npl.co.uk
Mon Feb 23 04:06:20 CST 2009
Neutron-irradiated concrete at 10-20 years post shutdown may contain:
H-3, C-14, Cl-36, Ca-41, Fe-55, Co-60, Ni-63, Ba-133, Eu-152 and Eu-154 (and natural occuring radionuclides). H-3 and Eu-152 will be the dominating activities.
More information on an NPL intercomparison we organised on neutron-activated concrete powder samples can be found on http://www.npl.co.uk/server.php?show=ConWebDoc.3031 (under "concrete results").
National Physical Laboratory
> -----Original Message-----
> From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl]On
> Behalf Of Dale Boyce
> Sent: 23 February 2009 00:01
> To: radsafe at radlab.nl
> Subject: Re: [ RadSafe ] Re: Fallout "preserved" in concrete
> 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.
> > Keith
> >> ------------------------------
> >> 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>
> >> Message-ID:
> >> <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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