[ RadSafe ] RE: Toxic Countertops

Mon Jul 28 02:51:43 CDT 2008

Kai, Dan, and all interested:

about Rn generation and transport:

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. In wet 
soil (10% water m/m) the emanation power can be doubled. - There is 
abundant literature about this.

2) Often diffusion accounts only for the minor part of Rn transport in 
soil. More efficient is convective transport, driven by pressure 
differences. In particular buildings can produce a stack effect which 
literally sucks Rn out of the soil, into the basement or ground floor of 
the building. Also changes in ground water level can give rise to 
"bursts" of indoor Rn conc.

The main geologic factor is soil or rock permeability, even more 
important than U content. There are examples for very high soil gas and 
indoor air Rn concentrations, without any extravagant U activity in 
underlying soil or rock. Soil gas concentrations of a few 100 kBq/m^3, 
and indoor concentrations of up to a few  kBq/m^3 can be produced 
without much U in the ground. (I know of one example of almost 20 
kBq/m^3 indoor, without particularly high U). - Of course this requires 
particularly poor insulation of basements or ground floors, typically 
found in older buildings.

regards,
Peter

Kai Kaletsch wrote:
> 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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