Determination+of+the+238-U+234-U+Ratio

Back to Main 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/ 238 U activity ratio. The sample solution has been obtained by dissolution of uranophane mineral (Ca[(UO 2 )SiO 3 (OH)] 2 ×6H 2 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 CeF 3 coprecipitation and the uranium alpha spectrum is measured by alpha spectrometry.

Performance of the work

 * 1) Take 2 ml of the uranophane solution into a beaker and add 4.5 dpm of 232 U tracer.
 * 2) Evaporate to dryness
 * 3) Prepare the anion exchange column (instructions below)
 * 4) Dissolve the evaporation residue in 3 ml of 9 M HCl
 * 5) 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
 * 6) Rinse the column with 30 ml of 9 M HCl
 * 7) Elute uranium with 20 ml of 0.1 M HCl (Po is still retained in the ion exchanger)
 * 8) Evaporate the solution into dryness
 * 9) Dissolve the residue in 2.5 ml of 1 M HCl by warming on a hot plate
 * 10) Transfer the solution with a disposable pipette into a Daniel tube
 * 11) Rinse the beaker with 2 ml of 1 M HCl and add to Daniel tube
 * 12) Add 200 μl of Ce carrier (Ce 3+ concentration 100 μg/ml, prepared by dissolving Ce 2 O 3 or CeCl 3 ×7H 2 O in 1 M HCl)
 * 13) Add four drops of 15 % TiCl 3 solution to reduce all uranium to +IV state
 * 14) Add 0.5 ml of concentrated (40%) HF to precipitate Ce(U)F 3 . Close the tube, shake gently and let it stay for one hour in refrigerator.
 * 15) Wet the 0.1 μm filter with an ethanol/water mixture and place the filter into a syringe filter.
 * 16) Filter 5 ml of deionized water through the filter and check that the filter system does not leak.
 * 17) Filter 5 ml of Ce-substrate solution (prepared from Ce-stock solution containing 860 μg CeCl 3 ×7H 2 O 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.
 * 18) Filter the CeF 3 precipitate on the filter.
 * 19) Rinse the Daniel tube with 5 ml of deionized water and filter the solution through the syringe filter.
 * 20) Let the filter dry and glue it on plastic holder
 * 21) Determine the alpha spectrum from the source

Preparation of the ion exchange column

 * 1) Test the column with deionized water to check possible leakages
 * 2) 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
 * 3) Add three bed volumes of deionized water
 * 4) Pretreat the column with three bed volumes of 9 M HCl