Worldwide Open Proficiency Test: Determination of ... - Nucleus - IAEA

2.3.4.3. Determination of U-234, U-238, Pu-239+240, Pu-238, Am-241 and Sr-90 using the
conventional sequential separation method
Preparation of the samples
The samples were ashed at 600 o C. Ten g weighed ash replicates were taken from the different
bottles. Sample decomposition was carried out using the conventional wet digestion
procedure, after addition of Sr carrier, Pu-242 and Am-243 tracers. Nine samples were spiked
with U-232 tracer too, for the determination of U-238 and U-234.
Radiochemical Separations
For the separation of uranium, the supernatant obtained from Ca-oxalate precipitation was
evaporated to dryness, the oxalate was decomposed by digestion and repeated evaporation
with 65% HNO3. The residues were dissolved in 15-30 ml 3 M HNO3, and then loaded on
UTEVA resin column (Bed volume; 1.4 ml, column length: 26 mm) pre-conditioned with 20
ml 3M HNO3. The column was washed with 30 ml 3 M HNO3, followed by 20 ml 6 M HCl.
Uranium fraction was eluted with 6 ml of H2O eluted with 6 ml of H2O, and then evaporated
with 2 ml 65% HNO3. After electro-deposition onto stainless steel discs, uranium was
determined by alpha-spectrometry.
2.3.4.4. Determination of U-234, U-238, Pu-239+240, Pu-238, Am-241 using the rapid
method
Preparation of the samples
The samples were ashed at 600 o C. Half g weighed ash replicates were taken from the
different bottles. Sample decomposition was carried out by molten salt fusion with 2 g LiBO2,
0.2 g NaCO3 and 0.1 g KI after addition of Pu-242 and Am-243 and U-232 tracers.
The melt was pured into 100 ml 1MHCl and then dissolved.
Radiochemical Separations
The actinides were preconcentrated after reduction with N2H4 by co-precipitation with
calcium fluoride in acidic solution [3]. After dissolution of the precipitate the actinides were
separated by selective extraction chromatography using a single column filled with TRU
resin. Am, Pu and Th were stripped separately, while U and Np were stripped together. U
fraction was purified by extraction chromatography using UTEVA resin.
Alpha sources were prepared from the chromatographic strip solutions directly by micro-coprecipitation
with neodymium fluoride. Activities were determined by isotope dilution alpha
spectrometry. Figures 6, 7, 8 and 9 shows the alpha spectra obtained from the moss-soil
sample.
2.3.4.5. Instrumentation
Alpha-spectrometer system Canbrerra Alpha Analyst
Alpha-spectrometer system: EG & G ORTEC OCTETE, with EG & G Ultra BU-020-450-AS
PIPS detectors, Canberra AMX 884 multiplexer, RPI 554, ADC 8701,and AIM556
modules.The alpha spectra were collected and evaluated using Canberra Genie 2000 software.
WALLAC QUANTULUS 1220 Liquide Scintillation Spectrometer. Liquid Scintillation
Spectra were collected and evaluated using Wallac WINQ v. 1.1 and EASYview v.1.0.3.4.
Claisse Fluxer and Milestone MLS-Ethos plus microwave.
Final Darft, page 11