[ RadSafe ] Re: Radon Travel in Granite and concrete
Peter Bossew
peter.bossew at jrc.it
Wed Jul 30 02:57:17 CDT 2008
Kai Kaletsch wrote:
> Peter's numbers for emanation from soil are much higher than my
> numbers for U ore. I have seen some higher emanation fractions on U
> ore , but the samples were either very weathered, unrepresentative of
> normal ore (airborne dust collected on a filter, emanation determined
> by alpha spectrum), the methodology was questionable or the grade was
> very low. So, the question becomes which emanation fraction one would
> expect from granite.
>
> The measured emanation fractions in both U ore and soil are much
> higher than what one would predict from a theoretical calculation,
> assuming the radium is evenly distributed in the ore grain. As Peter
> mentions, the range of the recoiling 222Rn nucleus is about 60 um in
> air. If we scale that by density to get an estimate of the range in
> the rock grain, we get about 0.02 um, which is a lot smaller than the
> size of the rock grain.
That seems to be a reasonable estimate. I have heard of about 0.05 um
within the grain.
> So, it would be physically impossible for any significant fraction of
> 222Rn to escape. One explanation is that the host rock normally gets
> there first and the U (which is pretty mobile) gets there later and
> just coats the outside of the grain. So at low U concentrations,
> almost all of the U would be in range of the pore space. Once you get
> to a few percent U, the layer of Uranium (and other late coming
> materials) becomes thicker and less of the Rn has a chance of getting
> out.
I have also heard about this theory. A way to check is measuring U conc.
in dep. of grain size. If it rises with decreasing size, it points to U
sitting on the surface, because the surface / volume ratio increases
with decreasing grain size. (This is btw. a common observation for 137Cs
and other fallout r.n. in sediments, which are normally attached on or
near the surface.)
>
> In granite, do we expect the U to by inside the rock grain or on the
> outside?
>
> While we are talking about radon movement, I have a few questions and
> hope someone on the list can help me out.
>
> What is a reasonable diffusion length to use for Rn in concrete? Does
> concrete have air-filled pore spaces like rock? (Peter is correct that
> the convective transport is probably more important for getting radon
> into your basement than diffusion. In my application, however, I do
> need to know the diffusion transport.)
diffusion lengths, 222Rn:
L = sqrt(D/lam) (lam= decay constant)
soil typically 1.5 m (0.1-3), building material: 0.5 (0.005-1).
(Porstendörfer J. (1991): Properties and Behaviour of Radon and Thoron
and Their Decay Products in the Air. 5th International Symposion on the
Natural Radiation Environment (NRE V), Salzburg 22-28 Sept. 1991,
Tutorial Session.)
Folkerts et al.: 0.06 and 0.8 m for two kinds of concrete. (Gives also
figures for other materials, and a list of useful material constants.)
Folkerts K. H., G. Keller, H. Muth (1984): Experimental Investigations
on Diffusion and Exhalation of 222Rn and 220Rn from Building Materials.
Radiat. Prot. Dosimetry 7 (1-4), 41-44.
UNSCEAR 1988: concrete 0.15 m (0.04-0.26)
For relation of porosity with diffusion constant and hence diffusion
length, and with water content: Nazaroff & Nero 1988, ch. 1.
diffusion constants:
Martinelli G. (1998): Gas Geochemistry and 222Rn Migration Processes.
Radiat. Prot. Dosimetry 78 (1),77-82.
air: 0.1 cm^2/s, water: 1.13e-5 at normal temperature.
See also Folkerts et al. (1984) and Porstendörfer (1991).
solid bodies: 10^-20 cm^2/s, within crystal lattice: 10^-22 ... 10^-70
(!), Morawska L., C. R. Phillips (1993): Dependence of the radon
emanation coefficient on radium distribution and internal structure of
the material. Geochimica and Cosmochimica Acta 57, 1783-1797 (Therefore
one thinks that the main mechanism for Rn to be set free is ejection by
recoil, rather than diffusion out of the grain.)
I think there is much more literature about the subject. As it isn't my
field of work, I can quote only these.
regards,
Peter
>
> If anyone has experience with cemented tailings backfill in a U mine
> and is willing to share, please contact me off list.
>
> Thanks,
> Kai
>
> Kai Kaletsch
> Environmental Instruments Canada Inc.
>
>
>
> points out that
> ----- Original Message ----- From: "Peter Bossew" <peter.bossew at jrc.it>
> To: "al gerhart" <webmaster at solidsurfacealliance.org>
> Cc: <radsafe at radlab.nl>
> Sent: Tuesday, July 29, 2008 7:31 AM
> Subject: Re: [ RadSafe ] Radon Travel in Granite
>
>
>> Rn transport, emanation power, etc.: I suggest consulting the
>> standard textbook,
>> Nazaroff, W. W., A. V. Nero (1988): Radon and its Decay Products in
>> Indoor Air. John Wiley & Sons.
>>
>> 0.2 eman. power = 20% set free of a "piece" (depending on
>> experimental setup, but not too much; once out of the grain, the Rn
>> is practically free.)
>> Interstitial water content: the model is, that water in the pore
>> space (as long as it is not too much) slows down the ejected recoil
>> nuclei to an extent that they are not captured by the neighbouring
>> grain. The kinetic energy of the recoil 222Rn nucleus is 86 keV,
>> their mean range in air is ca. 60 um. Experimentally, eman power in
>> soil (!) increases up to ca. 10% water, then remains approx. const.
>> up to ca. 20-30%. After that, experimentally difficult.
>>
>> U series assay by gamma spectrometry is not trivial.
>> - 238U : Via 234Th (63.3, 93 keV), 231mPa (1001), consult literature
>> about these lines first !!
>> - 226Ra: Via progenies 214Pb,Bi (295, 352, 609, 1120, 1764,...).
>> Container must be kept isolated ca. 3 weeks in order to establish sec
>> eq of 226Ra - 222Rn - progenies. For accurate measurement, sum/coinc
>> of some lines must be corrected for, if eff cal. done with standard
>> composed of single line radionuclides (as commonly done)(otherwise up
>> to a few % syst. error, depending on geom.). Validation with
>> certified U samples is advised. - Avoid the 186 line, possible, but
>> complicated.
>> - 210Pb: 46.6 keV. Density correction is crucial.
>> - 235U ff: not easy by g-spec., but possible. 144 keV line: sec. eq.
>> within 235U series required, due to contribution of 223Ra. Also
>> interference by 230Th must be accounted for.
>> - 232Th series: 228Ac (338, 911), 224Ra ff (239, 583, 2615).
>> Different caveats apply.
>>
>> As a summary, 226Ra ff, 228Ac and 224Ra ff are relatively easy and
>> straight forward, but 238U, 235U, 210Pb require a bit of experience
>> and good QA.
>>
>> regards,
>> Peter
>>
>>
>> al gerhart wrote:
>>> Okay, let me ask some questions in carpenter terms, math challenged
>>> Carpenter terms.
>>> "1) In "ordinary" dry soils, the emanation power is 0.2-0.3, and
>>> if one wants to be really conservative, one should set as much as 0.5."
>>> So that would be 2% to 5% of the Radon getting out of the grain,
>>> or out of the rock itself?
>>> "In wet soil (10% water m/m) the emanation power can be doubled."
>>> Radon transferred by dissolving in water? Fluid movement? On the
>>> lab samples, I have no idea how they were prepared, sorry. There is
>>> a phone number on the report and they are quite friendly and
>>> helpful, would be very interested in hearing any info on this
>>> matter, good or bad. Well, that doesn't sound right, how about
>>> supportive or non supportive of the report.
>>> I have purchased a Gamma Spectrometer, older model. Looking
>>> forward to learning how to use it correctly, interesting that so
>>> much info can be determined with Gamma Spectrometry. I got the
>>> shortcomings of the handheld meters, especially those that we are
>>> using. Thanks though for making sure we got it.
>>> Now here is something I can't figure out. No doubt it will show a
>>> wide gap in my understanding of decay chains. I see Radium, I see
>>> daughters except for Radon. If much of the Radon produced is trapped
>>> inside, or even if some of it is trapped inside, why is there no
>>> data for Radon?
>>> I think I am following Dan's info, he is using the equilibrium
>>> that should be present in the decay products, using the U-253 known
>>> value, one can deduct a possible value for u-238. Then that value is
>>> checked against what the lab report gives for Ra-226 as a method of
>>> verifying the method and result?
>>> And the end to all this is one quarter of one percent uranium in
>>> the granite? 1 in 400? 2,000 ppm = 1 in 500? And 80 ppm could be
>>> profitably mined?
>>> This is Juparana Bordeaux, pretty costly.
>>> This report was on a hot spot that was cored, does not represent
>>> the entire slab. Sometimes only one or two hot spots, sometimes all
>>> medium high like Niagara Gold, with the occasional hotter spot.
>>> But, that spot was about 36 times higher than an average Rossing
>>> mine granite?
>>> Geezzzz, I just want to sell countertops without setting myself up
>>> for being sued years later. Looks like a Physics degree, advanced
>>> math, and a Geologist degree needs to be completed first :)
>>> By the way, who was looking into toxic countertops?
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>>
>>
>> --
>>
>>
>> -----------------------------------------------------
>> Peter Bossew
>> European Commission (EC) Joint Research Centre (JRC) Institute for
>> Environment and Sustainability (IES)
>> TP 441, Via Fermi 1 21020 Ispra (VA) ITALY Tel. +39 0332 78 9109 Fax.
>> +39 0332 78 5466 Email: peter.bossew at jrc.it
>> http://rem.jrc.ec.europa.eu/
>> "The views expressed are purely those of the writer and may not in any
>> circumstances be regarded as stating an official position of the
>> European
>> Commission."
>>
>>
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>
>
--
-----------------------------------------------------
Peter Bossew
European Commission (EC)
Joint Research Centre (JRC)
Institute for Environment and Sustainability (IES)
TP 441, Via Fermi 1
21020 Ispra (VA)
ITALY
Tel. +39 0332 78 9109
Fax. +39 0332 78 5466
Email: peter.bossew at jrc.it
http://rem.jrc.ec.europa.eu/
"The views expressed are purely those of the writer and may not in any
circumstances be regarded as stating an official position of the European
Commission."
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