[ RadSafe ] Advection / Diffusion of Radon through Media

Dan W McCarn hotgreenchile at gmail.com
Wed Aug 20 19:18:12 CDT 2008


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

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

More information about the RadSafe mailing list