Isotopic Analysis of
Uranium Including
Uranium-233 in Soil Samples
By Alpha Spectrometry
R.Rosson,
J. Lahr and B. Kahn
Georgia
Institute of Technology
One gram soil samples with added U-232 tracer were
totally dissolved by a microwave-oven dissolution technique ( 1 ). Ten mg iron carrier was added to each of the
samples as a carrier in a hydroxide precipitation. The hydroxides were washed to remove excess ammonium hydroxide
and then dissolved with 8 M HCl. The solution containing the uranium was sorbed
on an anion exchange column, washed with 8M HCl + 0.05 M NH4I and 8 M HCl to remove interferences and
then eluted with 0.1M HCl ( 2 ). The separated
uranium solution was then converted to sulfates and electroplated ( 3 ). The electroplated samples were counted on an
alpha spectrometry system to determine each uranium isotope.
Upon viewing the alpha spectra, the U-234 region
appeared to have an extra peak but the resolution of the tracer was not as good
as possible. The samples were dissolved from the electroplated discs, sorbed on
UTEVA Eichrom columns ( 4 ), washed with 4M HNO3 then 6M HCl, eluted with 0.1M HCl and then re-electroplated. The resolution that was
achieved was now good enough to see a distinct U-233 peak at 4.82 MeV above the
U-234 peak at 4.76 MeV.
The resolution was 60 to 100 KeV prior to the second
column and 15 to 30 KeV full width half max of the tracer peak after second
column. The resolution problem could be related to the addition of the iron
carrier to the soil samples which already contain some iron.
To determine the amount of U-234 ( 73% 4.78, 27% 4.72
MeV alpha particles ) in the samples, we corrected for the 14.8 % of U-233 (
1.6% 4.73, 13.2 % 4.78, 84.4 % 4.82 MeV ) alpha particles that are in the U-234
region. The available software could calculate the amount of U-233 by using the
4.82 MeV alpha particle but for U-234 it could not subtract the U-233 alpha
particles in the U-234 region.
It is possible to determine
U-233 and U-234 in the same sample with the good resolution that is achievable
by electroplating samples and using currently available alpha particle pips.
Excess solids must be removed to achieve this resolution.
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(1) Garcia,
Ramon and Kahn, Bernd. Total Decomposition of Environmental Radionuclide
Samples with a Microwave Oven; Trans. Am. Nucl. Soc. 79: 55; 1998.
(2) Krieger H.L
and Whittaker, E.L. Radiochemical Method 908.0; Prescribed Procedures for
Measurement of Radionuclides in Drinking Water; U.S. Environmental Protection
Agency Report 600/4-80-032; pp. 96 - 102; Cincinnati OH; 1980.
(3) Talvitie,
N.A. Electrodeposition of Actinides for Alpha Spectrometric Determination;
Anal. Chem. 44: 280 - 283; 1972
(4) Gingell, T. The Determination of Uranium in Environmental Samples Using Extraction Chromatography. J. Radioanalytical Nuc. Chem. 226: 185-189; 1997.