Determination of 55-Fe in Nuclear Waste

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Laboratory of Radiochemistry

Department of Chemistry

University of Helsinki

Finland

Learning Goals

- Solvent-extraction
- Liquid Scintillation Counting with electron capture
- Using Quench Correction

Theory

Production and Creation of ^{55}Fe (read)

Theory behind Extraction of ^{55}Fe (read)

Experimental Procedure

Separation of ^{55}Fe

- Elute 2 g of ion exchange resin with 8 mL of 8 M HNO
_{3}overnight. Separate the resin by filtration. - Take 1 mL of the solution into a centrifuge tube and add 10 mg Fe-carrier (FeCl
_{3}) and dilute with water to total volume of 10 mL. Take a 100 µL sample for AAS/ICP-MS/ICP-OES measurement. - Add drop by drop concentrated ammonia until Fe(OH)
_{3}precipitates (pH 8-9 ). Centrifuge the sample for a couple of minutes and discharge the supernatant. - Dissolve the precipitate in 8 M HCl and transfer the solution into 100 mL extraction funnel. Extract the sample two times with 25 mL di-isopropyl ether. Discharge the aqueous phase.
- Combine the ether fractions and back-extract the iron into aqueous phase by extracting it twice with 15 mL of distilled water. Transfer the water solution into a centrifuge tube and discharge the ether fraction.
- Add ammonia to precipitate the iron (pH 8-9). Use a warm water bath to facilitate the precipitation. Centrifuge and discharge the supernatant. Wash the precipitate with small amount of water, centrifuge and discharge the rinse water.
- Dissolve the precipitate in 5 mL 0.2 M HCl in a warm water bath.
- Pour the solution into an ion exchange column (Dowex 50 w x 4; 50/100, pretreated with 20 mL of 0.2 M HCl). Wash the column with 10-20 mL of 0.2 M HCl.
- Elute the iron from the column with 40 mL of 0.5 % oxalic acid into a centrifuge tube.
- Add a drop of 30 % hydrogen peroxide. Precipitate the iron with concentrated ammonia on a warm water bath. Centrifuge and discharge the solution.
- Dissolve the residue into a small amount of strong HF. Transfer the sample into a liquid scintillation vial (weighed before addition). Add 1 mL of distilled water, weigh the sample.
- Take a 100 µL sample for the iron measurement with AAS/ICP-MS/ICP-OES.
- Measure the activity of
^{55}Fe from the rest of the sample by liquid scintillation counting.

Measurement of ^{55}Fe by Liquid-Scintillation Counting

Add 9.5 mL of scintillation cocktail Optiphase ’Hisafe’3 (LKB, Wallac). Shake well. Measure after ½ hour with a liquid scintillation counter.

To be able to calculate ^{55}Fe radioactivity, counting efficiency need to be determined (efficiency calibration). Counting efficiency is determined from a ^{55}Fe standard series using Fluorescein (C_{20}H_{12}O_{5}) as a quenching agent.

A quenching standard series

Add reagents into plastic scintillation vials as follows:

Shake well. After ½ hour measure the samples in a liquid scintillation counter.

Draw a quenching standard quenching curve. Determine the counting efficiency for ^{55}Fe from the curve.

Determination of Chemical Yield

Chemical yield of the analysis is determined by iron measurement of the 100 μL aliquot with AAS/ICP-MS/ICP-OES. Prepare iron standard (1, 2, 3, 5, 10 ppm) and measure them. Draw a standard curve. Measure your unknown sample and determine its iron content (ppm) from your standard curve. Calculate the yield (%). Take into account the dilution of the samples.

Other

Describe in detail the whole separation procedure and explain why each step was made. Draw a separation procedure scheme.

Calculate the chemical yield of ^{55}Fe separation.

Calculate the activity concentration of ^{55}Fe in the resin and its uncertainty.

Equipment

| MQ-H | HF | Fluorescein | Scintallation cocktail | |

1 | 0.5 mL | 2 mL | 1 drop | 0 mL | 9.5 mL |

2 | 0.5 mL | 1.9 mL | 1 drop | 0.1 mL | 9.5 mL |

3 | 0.5 mL | 1.8 mL | 1 drop | 0.2 mL | 9.5 mL |

4 | 0.5 mL | 1.6 mL | 1 drop | 0.4 mL | 9.5 mL |

5 | 0.5 mL | 1.0 mL | 1 drop | 1.0 mL | 9.5 mL |

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