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The purpose of the work is to determine the activities of 238
U and 234
U in a water sample and calculate the 234
U activity ratio. The sample solution has been obtained by dissolution of uranophane mineral (Ca[(UO2
O]) originating from Zaire. First, the 233
U tracer is added to an aliquot of the stock solution and the solution is evaporated to dryness. After dissolution into 9 M HCl interfering radionuclides are separated by anion exchange chromatography. Finally, a uranium alpha counting source is prepared by CeF3
coprecipitation and the uranium alpha spectrum is measured by alpha spectrometry.
Performance of the work
- Take 2 ml of the uranophane solution into a beaker and add 4.5 dpm of 232U tracer.
- Evaporate to dryness
- Prepare the anion exchange column (instructions below)
- Dissolve the evaporation residue in 3 ml of 9 M HCl
- Pour the solution into the ion exchange column. Uranium is retained, Th and Ra are eluted, Po is retained here but will be separated from uranium in step 7
- Rinse the column with 30 ml of 9 M HCl
- Elute uranium with 20 ml of 0.1 M HCl (Po is still retained in the ion exchanger)
- Evaporate the solution into dryness
- Dissolve the residue in 2.5 ml of 1 M HCl by warming on a hot plate
- Transfer the solution with a disposable pipette into a Daniel tube
- Rinse the beaker with 2 ml of 1 M HCl and add to Daniel tube
- Add 200 μl of Ce carrier (Ce3+ concentration 100 μg/ml, prepared by dissolving Ce2O3 or CeCl3×7H2O in 1 M HCl)
- Add four drops of 15 % TiCl3 solution to reduce all uranium to +IV state
- Add 0.5 ml of concentrated (40%) HF to precipitate Ce(U)F3. Close the tube, shake gently and let it stay for one hour in refrigerator.
- Wet the 0.1 μm filter with an ethanol/water mixture and place the filter into a syringe filter.
- Filter 5 ml of deionized water through the filter and check that the filter system does not leak.
- Filter 5 ml of Ce-substrate solution (prepared from Ce-stock solution containing 860 μg CeCl3×7H2O in1 ml of 1 M HCl by pipetting 10 ml stock solution to 908 ml of 1 M HCl + 82 ml 40% HF) through the filter.
- Filter the CeF3 precipitate on the filter.
- Rinse the Daniel tube with 5 ml of deionized water and filter the solution through the syringe filter.
- Let the filter dry and glue it on plastic holder
- Determine the alpha spectrum from the source
Preparation of the ion exchange column
- Test the column with deionized water to check possible leakages
- Fill the column with Dowex 1×4 anion exchange resin (stored in MilliQ water) with the help of deionized water and check that there are no air bubbles in the column
- Add three bed volumes of deionized water
- Pretreat the column with three bed volumes of 9 M HCl