[ RadSafe ] Radon travel in granite

Mon Jul 28 17:02:46 CDT 2008

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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