[ RadSafe ] RE: Toxic Countertops

[Kai Kaletsch]

Hi Dan and all!

There are 2 different processes:

1) The escape of radon from the mineral grain (emanation fraction). This is 
driven by the recoil of the Rn nucleus after the decay of radium. I usually 
use 0.05 (5%) as a reasonable and conservative value for the emanation 
fraction in U ore. (In theory, considering the typical size of mineral 
grains and the recoil energy, it should be much less than 1%.)

2) Once the radon has escaped the mineral grain (through recoil) it travels 
by diffusion through the pore spaces. If the rock is dry, the radon can 
travel quite some distance before it decays. In U mines, I use 60 cm as a 
reasonable and conservative value (which is more than the thickness of a 
countertop).

This is how I understand the process as it relates to U ore. I don't have 
much experience with granite and would appreciate input on this. I was 
investigating elevated radon levels in a non-U mine last month and I used 
the same formulas for granite as I would use for U ore and got pretty good 
agreement with measured values.

So, lets look at the countertop example:

Assume 50 ppm (50e-4 %) U content (is that reasonable?) in a 100 kg 
countertop. Using 0.05 emanation fraction, we get a radon source term of 6.5 
e-3 Bq/s (using http://members.shaw.ca/eic/Tools/MassRadon.htm ).

In a 12 m3 room with 1 air change per hour, this results in 2 Bq/m3 (0.05 
pCi/L) Rn and 3e-4 WL (using 
http://members.shaw.ca/eic/Tools/RoomRadon.htm ).

Best Regards,
Kai

Kai Kaletsch
Environmental Instruments Canada Inc.

----- Original Message ----- 
From: "Dan W McCarn" <hotgreenchile at gmail.com>
To: "'radsafelist'" <radsafe at radlab.nl>
Sent: Thursday, July 24, 2008 1:24 PM
Subject: RE: [ RadSafe ] RE: Toxic Countertops


> Gentlemen:
>
> It all depends on the permeability of the granite!  Even relatively active
> granites usually have very low primary permeability so radon is retained
> within the mineral grains and rock itself to a great degree.  That's why
> granites are usually in secular equilibrium with all uranium daughters
> because they retain radon until it decays.  Most of the activity measured 
> by
> a scintillation counter comes from the Bi-214 decay at the end of the 
> chain.
> At a larger scale, where granites are fractured and faulted and develop
> significant secondary permeability, is there a good likelihood that radon 
> in
> significant quantities will be fluxed via changes in barometric pressure 
> to
> the surface, and these examples are noteworthy.
>
> But in countertops, chosen to avoid fractures, that is unlikely.  Most of
> the radon would be only from the very near surface.  The radon from deeper
> inside would have virtually no chance of diffusing to the surface.
>
> My opinion only!
>
> 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 Bob Cherry
> Sent: Thursday, July 24, 2008 1:30 PM
> To: 'Chris Cherry'
> Cc: 'radsafelist'
> Subject: [ RadSafe ] RE: Toxic Countertops
>
> Good point about the cemeteries! I will remember this and try to avoid
> spending a lot of time in one as long as I can.
>
> -----Original Message-----
> From: Chris Cherry [mailto:cpdcherry@]
> Sent: Thursday, July 24, 2008 1:24 PM
> To: Bob Cherry
> Subject: RE: Toxic Countertops
>
> I'm sure more people are harmed in quarrying the stone and installing it
> than get cancer from its radioactivity.
>
> Someone on the medphys list mentioned that cemeteries are full of both
> granite and dead people.  This may not be a coincidence.
>
> -CC
>
>
> --- On Thu, 7/24/08, Bob Cherry wrote:
>
>> From: Bob Cherry
>> Subject: RE: Toxic Countertops
>> To: "'Chris Cherry'"
>> Date: Thursday, July 24, 2008, 1:18 PM
>>
>> Old news. We almost got a
>> consulting job on this.
>>
>> -----Original Message-----
>> From: Chris Cherry
>> Sent: Thursday, July 24, 2008 1:15 PM
>> To: Bob Cherry
>> Subject: Toxic Countertops
>>
>> The article mentions the guy at Rice.
>>
>>
> <http://www.nytimes.com/2008/07/24/garden/24granite.html?pagewanted=2&_r=1&n
> o_interstitial>
>>
>> -CC
>
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