[ RadSafe ] Calculations of Radionuclide Activity Concentrations - Reference Request

[Dan McCarn]

Dear Shane:

Keep in mind that for soils, the concentration of U-234 will be often
depleted relative to U-238 and U-235 because of dislocation of U-234
following alpha decay of U-238 to Th-234.  There is about 100 KeV of
kinetic energy imparted to the nucleus that dislocates it from the
original mineral lattice, thus making it far more leachable in mildly
or stronglyoxidizing soil environments.  This dislocation will likely
cause the resulting nucleus to end-up in the pore space between soil
grains.

The published values that I've seen assume "equilibrium"
concentrations of U-238 and U-234 e.g. "Nuclear Wallet Card", 6th
Edition, July 2000, Jagdish K. Tuli National Nuclear Data Center,
Brookhaven National Laboratory.  These values are appropriate for well
mineralized, reducing uranium ores of > 2 million years of age.
Younger ores, and especially soils, deviate strongly from these
values.

Soils are typically oxidizing, at least to some extent.  Because
uranium is very soluble in oxidizing environments, any
easily-leachable fraction will be mobilized. If the soil column
contains a highly reduced fraction (humus layer), it may show and
increased amount of U-234 wrt U-238 since it will act as a trap for
uranium mobilized above that zone.  Desert soils will differ from
humus-rich soils in moister climates.  These mechanisms for
re-concentration are important to understand.

Now, if you are asking about published "corrected" elemental abundance
fractions for a soil, that would have to be determined EMPIRICALLY for
each soil, and probably for each layer in the soil. So if you are
looking for references, I don't think you can "hang your hat" on any
published value per se.  Go with the data and how they differ from
"standard, equilibrium values". Please note that I do not mention
"weight" abundance, but rather isotopic abundance...

Equilibrium U-238 isotopic abundance is 99.274%; U-238 weight
abundance is 99.283%;
Equilibrium U-234 isotopic abundance is 0.00545% U-234 weight
abundance is 0.00536%

Best!

Dan ii

Dan W McCarn, Geologist
108 Sherwood Blvd
Los Alamos, NM 87544-3425
+1-505-672-2014 (Home – New Mexico)
+1-505-670-8123 (Mobile - New Mexico)
HotGreenChile at gmail.com (Private email) HotGreenChile at gmail dot com


On Thu, Mar 22, 2012 at 12:23 PM,  <ProRadCon at aol.com> wrote:
> Greetings,
>
> I am researching the variations in calculations of activity  concentrations
> for NORM radionuclides based on their isotopic weight  fraction in the
> element, and elemental weight fraction in a solid  media.  For example, the
> calculation of U-238 activity concentration in  soil based on known or dictated
> elemental weight fraction.  I am  seeing some potential variation in the
> parameters provided by professional  colleagues that might lead to percent
> variations in the conversions, and I want  to find any resource(s) that might
> address them, such as a publication  (preferably peer-reviewed).
>
> I have performed the conversion calculations for U-238, U-235, U-234,  and
> Th-232 numerous times over the years and have always used the same
> reference.  So I'm not looking for someone to provide  the conversions, I'm looking
> for references showing variations in the  values due to differing references.
>
>
> Thank you in advance,
>
> Shane  Brightwell, MS, CHP
> President
> Professional Radiation Consulting,  Inc.
> 7 Balmoral Drive
> Pittstown, NJ 08867
> Office: (908) 730-9224
> Fax: (720) 294-1153
> Mobile: (631) 278-0610
> E-mail:  proradcon at aol.com
>
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