[ RadSafe ] Advection / Diffusion of Radon through Media

Fri Aug 29 09:57:44 CDT 2008

Hi Dan,

Please take a look at 
http://members.shaw.ca/eic/RadonExhalationFromSurfaces.pdf (Be patient, it's 
a scanned pdf. So, it's kinda big: 5 Meg).

This is something that I wrote up at my first real job. It gives you the 
equations. The point of this paper is that you do not need to have a uniform 
source distribution in order to calculate the radon flux through a surface.

My experience with granite is fairly limited. I took measurements in a 
refuge station in granite and the measured Rn values corresponded well with 
the assumptions of 10% emanation and 60 cm diffusion length (which are my 
default values for low grade ore), when I used uranium concentrations 
derived from gamma measurements (30 - 50 ppm U).

Of course, other combinations of emanation and diffusion length would also 
work, like 20% emanation and 30 cm diffusion length. The point is, however, 
that you need a substantial diffusion length (tens of cm) to make the 
numbers work out. I'm pretty sure diffusion was the main transport 
mechanism, since the refuge station was in permafrost and therefore no water 
inflows. That means that a 10 cm slab would release almost 10 times the 
amount of radon as a 1 cm slab.

I'm not sure if I completely understand your question about advection. Radon 
definitely gets carried with flowing water. Water inflows in underground U 
mines usually carry radon. When you de-water an open pit mine, you will see 
radon reporting to the de-watering wells hundreds of meters away from the 
orebody. I am trying to convince exploration people to use this property 
when they are looking for orebodies. The trick is that you have to get the 
water flowing. It doesn't work if it is just sitting there. (Still water is 
actually a good radon barrier with a diffusion length ~ 2 cm.)

Regards,
Kai

Kai Kaletsch
Environmental Instruments Canada Inc.

----- Original Message ----- 
From: "Dan W McCarn" <hotgreenchile at gmail.com>
To: "'Radsafe'" <radsafe at radlab.nl>
Sent: Thursday, August 21, 2008 1:32 PM
Subject: RE: [ RadSafe ] Advection / Diffusion of Radon through Media

Hello Group:

What I'm really fishing for transport equations for diffusion / advection 
including
time and decay or some papers / pubs that describe the mechanisms.

Dan ii

Dan W. McCarn, Geologist; 3118 Pebble Lake Drive; Sugar Land, TX 77479; USA
Home: +1-281-903-7667; Austria-cell:  +43-676-725-6622
HotGreenChile at gmail.com   mccarn at unileoben.ac.at   UConcentrate at gmail.com

From: "Dan W McCarn" <hotgreenchile at gmail.com>
To: "'Radsafe'" <radsafe at radlab.nl>
Sent: Wednesday, August 20, 2008 7:18 PM
Subject: [ RadSafe ] Advection / Diffusion of Radon through Media

> Hello:
>
> Perhaps this has been done somewhere before:  How does one go about
> estimating that component of radon that emanates from a granite or other
> material? There are several factors that I can think of:
>
> 1 - Nature of uranium mineralization: a) contained within minerals e.g.
> zircon, monazite; biotite and b) epigenetic mineralization via solutions
> precipitating U minerals in pore spaces and fractures.  Most granites show
> secular equilibrium in the uranium series.  Is this a macroscopic or
> microscopic property?  Does the 5 MeV or so recoil dislodge the radon that
> far away from the origin in a mineral grain? Since granites are massive
> rock
> bodies, emanation of radon and subsequent decay would / could occur within
> the same granite, except near the margins.
>
> Does the accumulation of alpha decays e.g. U-238, Th-234, U-234, Th-230,
> Ra-226 ⇒ Rn-222 make it more accessible to mobilization? Because U-234 is
> more easily leachable than U-238 (Wyoming Basins, Kazakhstan), this
> suggests
> to me that the Ra-226 has been fairly well dislocated prior to decay to
> Rn-222.
>
> 2 - Dual porosity matrix - the nature of the permeability associated with
> fractures or porous fractions of a material vs. that portion that is
> contained within a mineral grain.  I can imagine that if the rock was
> porous
> / permeable enough to be an aquifer, that the radon would advect at the
> same
> rate as the water.  This is borne-out by borehole measurements in and near
> sandstone U deposits.
>
> 3 - Distance to a surface (e.g. fracture or actual surface of material)
>
> Empirically, does a 1 or 2 cm slab of uniform composition granite emanate
> at
> the same rate per unit surface area as a 10 cm slab?
>
> Dan ii
>
> Dan W. McCarn, Geologist; 3118 Pebble Lake Drive; Sugar Land, TX 77479;
> USA
> HotGreenChile at gmail.com   UConcentrate at gmail.com
>
>
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