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

program achieving complete sample dissolution. The solutions of the residues were combined
with their supernatants, and then evaporated with three portions of 5 ml of 65% HNO3 to
remove HF and than dissolved in 30 ml of 2M HCl and 0.1 g H3BO3.
Radiochemical Separations
After sample digestion, polonium and lead were separated using the method proposed by
Vajda et. al [2]. The solution was loaded on Sr Resin column preconditioned in advance with
100 ml 2 M HCl. The column was rinsed with 100 ml of 2 M HCl and 25 ml 6 M HNO3 to
remove the non-retained ions. The effluent and washing solutions were combined and used
for analysis of uranium and thorium. Polonium was stripped with 60ml 6 M HNO3, and then
lead was eluted with 60 ml 6 M HCl. Polonium solution was carefully evaporated to dryness.
The residue was taken with 10 ml 0.5 M HCl transferred into a Teflon deposition cell, the pH
of the solution was adjusted to 1 using 6 M NaOH. Polonium was auto-deposited onto silver
disc at 90°C for 90 min with stirring the solution, and then Po-210 was determined by isotope
dilution alpha-spectrometry. The Pb fraction was evaporated 3 times with 2 mL of 65%
HNO3. The residue was dissolved in 20 ml 1 M HNO3, add 0.400 g oxalic acid to warm
solution and adjust the pH to 3-5 with NH3(aq) to precipitate Pb-oxalate. The Pb-oxalate
precipitate was filtered through a pre-weighed filter paper (∅ 24 mm). The filter was washed
with 3*1 mL water and 2 mL of ethanol, dried in oven at 40-50 o C, cooled in a dessicator and
weighted to determine the mass of lead-oxalate and the chemical recovery gravimetrically.
The lead-oxalate precipitate was transferred together with the filter into liquid scintillation
vial, dissolved in 1 mL 6 M HNO3 and mixed it with 14 mL ‘INSTA-GEL PLUS’ liquid
scintillation cocktail. Pb-210 was determined by liquid scintillation spectrometry. Figure 5
illustrates the LSC spectrum of Pb-210 in moss-soil.
Counts per channel
1000000
100000
10000
1000
100
32
36
46.503 Pb-210
59.537 Am-241
63.29 Th-234
Gamma-ray spectrum of the moss-soil reference material-IAEA 447
74.969 Pb Kα1
77.108 Bi Kα1
84.936 Pb Kβ1
87.343 Bi Kβ1
89.952 Th-231
92.80 Th-234
185.715 U-235
186.180 Ra-226
129.1 Ac-228
209.5 Ac-228
154.0 Ac-228
10 Detector:Broad Energy
Bottle: #943 (Moos-soil, IAEA-447)
Sample Amount: 45.42234 g
Real Time: 250012 sec
Live Time: 249816 sec
300.11 Pb-212
1
0 1000 2000 3000 4000 5000 6000 7000 8000
Channel number
238.626 Pb-212
240.981 Ra-224+241.924 Pb-214
277.4 Tl-208
270.2 Ac-228
295.217 Pb-214
351.992 Pb-214
338.7 Ac-228
328.3 Ac-228
Figure 4: Gamma spectrum of the moss-soil IAEA-447 in the channel range 0-8000
Final Darft, page 9