[ RadSafe ] Radon travel in granite
webmaster at solidsurfacealliance.org
Sat Jul 26 16:30:08 CDT 2008
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.
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