[ RadSafe ] Radon travel in granite Radiation levls from granite known over 50 years ago.
Bernard L. Cohen
blc+ at pitt.edu
Fri Aug 1 11:08:24 CDT 2008
With all the discussion about radiation from granite, I am surprised
that no one has brought up the radiation in the Congressional office
buildings and Grand Central Station (New York). As I recall, regular
users of these buildings (including Congressmen and Senators) get
several hundred mrem per year of gamma radiation from the granite. Have
there been radon measurements there?
parthasarathy k s wrote:
> Dan,
>
> I am happy to see that every one is keen to know more about natural radioactivity.
>
> I am somewhat late in responding to the "radioactive" granite story.
> Overall very informative thread! I remember it was in the mid fifties Prof
> Bill Spiers (Leeds University, UK) and his friends discovered
> increased levels of radiation from granitic areas. Some one living in a building in granitic areas gets more dose
> than another who lives in a wooden house.Then it was a novel
> idea.
>
> The present excitement is
> because people who are not familiar with natural radioactivity do not
> expect radiation over a granite countertop. Next story may be on
> radioactivity in Brazil nut! ( It was interesting news in the 50s; may be now as well for those who are radio-phobic!). It will be shocking to them if we calculate the dose to the tender cell lining in the mouth as we eat Brazil nuts. The tissue tract of a micrometer diameter and a few tens of micrometer length will receive mega rads! The story may get top billing!
>
> I am pleased to see the flurry of "activity" around the NYT story. Any
> professor who starts using a radiation detector for the first time may
> be thrilled to test every thing that comes in the way. I am not sure whether such routine measurements will be appealing to any peer reviewed journal.
>
> Another related matter. I recall that the staff of a British Museum
> which exhibited some geological samples(some of them can be pretty
> radioactive) was convicted for exposing people to undesirable levels of
> radiation! I do not remember the details. Our colleagues from UK may be
> able to tell us more about it.
>
> The best way to spice up a news story is to add some radioactivity in it!
>
> Regards
> Parthasarathy
>
>
>
> ----- Original Message ----
> From: Dan W McCarn <hotgreenchile at gmail.com>
> To: radsafe at radlab.nl
> Cc: "Emer, Dudley" <EMERDF at nv.doe.gov>; al gerhart <webmaster at solidsurfacealliance.org>
> Sent: Tuesday, 29 July, 2008 3:32:46 AM
> Subject: RE: [ RadSafe ] Radon travel in granite
>
> Elmer:
>
> On my calculation, I get 2.97 ug per pCi U-238 as you do.
>
> Assuming secular equilibrium between U-238 and U-234 (age of granite > 2
> million years)
>
> ug : U-238 = 2.9752E+00, U-235 = 2.1316E-02, U-234 = 1.6072E-04 ug ; Summed
> = 2.9967 ug U-Natural
> pCi: U-238 = 1.0000 , U-235 = 0.0461 , U-234 = 1.0000 pCi; Summed
> = 2.0461 pCi U-Natural
>
> Total activity is 2.0461 pCi per 2.9967 ug U-Nat uranium in secular
> equilibrium or
>
> 0.6828 pCi / ug U-Nat total activity
>
> Your comments related to ingrowth are essential to understand in order to
> interpret the meaning of the analyses. The sample would need to be canned
> for 30 days or so if crushed.
>
> But, if I assume that the U-235 activity is 37.83 pCi / g given Al's lab
> report,
>
> Then:
>
> 1) the activity of U-238 should be 821.2363 pCi/g, which is
> in rough equilibrium with Ra-226 (986.95 pCi/g) in Al's report;
>
> 2) the total U-natural should be 2460.96 ug / g or about 0.25% U-Nat for the
> rock.
>
> That would be enough to mine if commercial quantities actually showed this
> endowment, which I strongly doubt for a "plain" granite.
>
> When granitic batholiths are intruded, the last remaining watery portions of
> the magma, having gone through differential precipitation (Bowen Reaction
> Series), is enriched in uranium and sometimes other metals e.g. gold. These
> quartz-rich remainders can form intra-batholithic intrusions or
> peri-batholithic intrusions enriched in uranium.. I suspect that Al's rock
> may, in fact, be something of this nature.
>
> I'd say that the only way would be in a vein within a granite, or a
> pegmatite, but not a granite itself, and the samples were "high-graded" to
> show a hot-spot, not representative of the overall composition of the
> granite. Of course what I'd call a pegmatite, and someone else may call
> granite from the dimension stone business, may be something of an issue!
>
> For an "average" granite composed of 10 ppm U (e.g. Wyoming),
> the average activity would be 6.828 pCi/g.
>
> For the Rossing anatectic granite of 100 ppm U (0.01% U) in Namibia (active
> uranium mine):
> The average activity would be 68.28 pCi/g
>
> I hope my numbers are correct!
>
> Dan ii
>
> Dan W. McCarn, Geologist; 3118 Pebble Lake Drive; Sugar Land, TX 77479; USA
> HotGreenChile at gmail.com UConcentrate at gmail.com
>
>
> -----Original Message-----
> From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On Behalf
> Of Emer, Dudley
> Sent: Monday, July 28, 2008 3:00 PM
> To: al gerhart; radsafe at radlab.nl
> Subject: RE: [ RadSafe ] Radon travel in granite
>
> Al,
> I'm kind of curious about the lab report and how was it done. How was
> the sample prepared? Was it a crushed sample or in-situ? Was the sample
> sealed and allowed to have the radon chain in-grow before measuring?
>
> For a sample with this much thorium and uranium the report is missing
> some expected nuclides and apparently misreporting others..
>
> Considering the half life of Sc-46 is 83 days it is most likely being
> misreported due to the Bi-214 photo peak at 1120.3 keV with a 15% yield.
> While Cs-137 and Co-60 have photo peaks close to Bi-214, these Bi-214
> yields are very low (<0.05%) and unless the count times were very long
> it's unlikely these are due to Bi-214. While one may find fallout Cs in
> a field sample the Co is problematic; perhaps a lab contamination
> problem or maybe check sources near the detector. Did they run a blank?
>
> I would expect that other uranium chain daughters would have been
> detected and reported; specifically the Th-234, Pa-234m and Th-230 which
> can help establish the degree of equilibrium in the U-238 chain.
>
> For conversions:
> 1 pCi/g U-238 = 2.97 ppm
> 1 pCi/g Th-232 = 9.1 ppm
> 1 pCi/g K-40 = 1224 ppm
>
> 1 pCi = 0.37 Bq
>
> You will not be able to convert a Geiger counter reading into isotopic
> activity - that will require a calibrated spectrometer.
>
> Dudley Emer
> Geophysicist
> National Security Technologies
> 702-295-7808 office
> 702-794-5824 pager
> 702-521-8577 cell
>
>
> -----Original Message-----
> From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On
> Behalf Of al gerhart
> Sent: Saturday, July 26, 2008 2:30 PM
> To: radsafe at radlab.nl
> Subject: [ RadSafe ] Radon travel in granite
>
> Hi all,
> First post, long time lurker. Finally something I can contribute to,
> some facts on radioisotope content, countertop size, porosity of
> granite, and Radon/radiation levels.
>
> Countertop granite is pretty porous. We cut and polish wet, it soaks
> up the water, turns darker. Water will soak through the center of the
> slab in a few hours.
>
> We have to use a torch to dry out places that need epoxy, seams,
> rodding grooves, lamination edges. It takes a while to dry it out,
> heat and let cool, heat again, and so on.
>
> There has been an explosion of newer stones that were less likely to
> be used years ago, but these days they resin the back, apply fiberglass
> mesh, so it doesn't break up during polishing. Some stones get a coat
> of polyester resin, which is then ground off during polishing. The
> resined slabs still soak up the water anyway, and they stain from oil or
> even hard water, so there is still some amount of porosity present.
>
> As to emanation rates, I know several leading Radon techs and a few
> Radon scientists (Kitto and Steck). The Radon emission range will run
> from 4 pCi/SF/Hr to over 500 pCi/SF/Hr (that would be Niagara Gold, it
> was featured in both the NY Times story and the CBS Morning show). The
> Niagara Gold sample was from my sample collection, part of a 72" x 18"
> remnant that I bought off a competitor here in Oklahoma.
>
> That particular sample measured over 200 uR/hr Gamma (PM 1703 on
> contact, yes, I need a better meter) but the hottest spot on that
> remnant was as high as 250 uR/hr Gamma, or 5300 to 6300 cpm with one of
> George's LENi Geiger counters (pancake probe, about 9 mm standoff).
> 10.5 mR/Hr supposedly.
>
> As to 50 ppm being reasonable, not sure, we aren't smart enough to
> convert ppm into pCi/g or cpm. :) I can say that I have seen reports
> much higher, 200 to 4,000 cpm.
>
> I have a lab report on the countertop in Houston Texas that lead to
> this flurry of reports. It gave two Radium isotope contents as 1,130
> pCi/g or so.
>
> Potassium 40, 53.9 .
> Scandium 46 , 31.65
> Cobalt 60 , .13
> Cesium137 , .189
> Thallium 208, 37.8
> Lead 210 , 415.5
> Bismuth 212 , 85.46
> Bismuth 214 , 410.77
> Lead 214, 484.99
> Radium 226 , 986.95
> Radium 228 , 128.34
> Thorium 228 , 144.76
> Uranium 235 , 37.83
>
> ARS Houston Granite Countertop report
>
> We use US units here, darn it, but I'll figure out how to convert the
> example in Kai's example.
>
> Can anyone tell me if it is possible to convert a Geiger counter
> reading into PPM of Isotopes? Sure it must have a lot to do with the
> isotope rad level, but are there any rules of thumbs for a quick and
> dirty guess?
>
> Thanks for the excellent site. I am learning so much here.
>
> Al Gerhart
>
>
>
>
>
>
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--
Bernard L. Cohen
Physics Dept., University of Pittsburgh
Pittsburgh, PA 15260
Tel: (412)624-9245 Fax: (412)624-9163
e-mail: blc at pitt.edu web site: http://www.phyast.pitt.edu/~blc
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