Re: Th-232/Ra-228

["Ralph E. Wild" <rewild@ATTGLOBAL.NET>]

I thought this kind of separation was fairly common when ores, tailings, 

or soils containing U or Th are exposed to repeated wetting and drying 

cycles.  In the Florida phosphate region, many ore bodies are overlain 

by soil with elevated Ra-226 concentrations.  In Florida, I believe 

water table fluctuations were the driver.  I recall a paper from a few 

decades ago that discussed the same sort of process in tailings piles in 

arid regions where precipitation/evaporation events were the driver.



Ralph E. Wild, Ph.D.

rewild@attglobal.net

Employed by but not speaking for:

URS Corporation

DOE Programs and Nuclear Services





Erik Nielsen wrote:



> I have found that thorium mill tailings of an intermediate age 20-40 

> years have a higher concentration of Th-228 than Th-232.  My 

> supposition is that removal of the Th-232 concentrated Ra-228 in the 

> spoils above the Th-232 concentration.  As the Ra-228 in the spoils 

> decayed the Th-228 would build up to an equilibrium that would be 

> above the Th-232 concentration.

> 

> Fresh thorium mill tailings would not have this effect as the Ra-228 

> would not have had a chance to ingrow to the Th-228 and the Th-228 

> would decay away until supported by the Ra-228 present.  Much older 

> tailings would have the Th-228 close to equilibrium with the Th-232 as 

> the Ra-228 that had been concentrated had dropped back to the 

> equilibrium value supported by the Th-232 and thus the Th-228 value 

> would decay to the supported equilibrium level.

> 

> 

> Erik C. Nielsen

> Senior Radiochemist

> 

> Antech Ltd Waltz Mill Laboratory

> P.O. Box 158, Bldg G, M/S 62

> Madison, PA 15663

> 

> mailto:enielsen@antechltd.net

> 

> (V) 724-722-5214

> (F) 724-722-5208

> 

> 

> 

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