How to use nucfilm’s actinides adsorbing sheets

PRELIMINARY

Warning : The method described is recommended only for untreated waters having drinking water quality. For waste waters the method may be used, but requires special precaution.

Nucfilm ’s actinides adsorbing sheets are polymethylmetacrylate sheets covered on one side with a binder holding a finely ground cation exchanger (Diphonix ,Eichrom Industries).

Sampling

There is no need to acidify waters having drinking water quality. Simply avoid glass containers. Use polyethylene bottles and fill them completely.

Exposition to the water sample

Fill 80 ml of your untreated water sample into a 100 ml FEP beaker. Don't use glass beakers. FEP (Fluor-Ethylene-Propylene) showed negligible adsorption. Add 0.5 ml concentrated formic acid (85%) to reduce pH to 2 to 3 . If your sample is already at low pH, e.g. a nitric acid solution, adjust pH to around 2 and just try if it works.
Rinse the sheet with distilled or deionized water and fix the sheet with a stainless steel clamp or glue it to a plastic (e.g. Plexiglass) holder (“Pattex” works well as a glue). Place it in your sample as shown in the figure . Stir at approx. 200 rpm using a teflon covered stirring rod. After 20 to 24 h remove the sheet from your sample, rinse it with distilled or deionized water and dry it with not too hot air (hair drier). Don’t touch the surface.

For some samples containing high CO ₂ concentrations gas bubbles may form on the film surface. In this case just lift the sheet shortly out of the sample and put it back. This removes the bubbles. This prodcedure may be necessary several times during the first hour of exposition.
It is not known if these gas bubbles hinder adsorption. Any data would be welcome .

Measurement

With the sheet at a distance of about 10 mm from the surface of a 900 mm ² alpha detector you have a detection efficiency around 20% . Assuming a 100% adsorption efficiency 1 count/1000s thus corresponds to around 65 mBq/l in your sample.

Adsorption efficiency and calibration

For drinking waters you can expect to have adsorption efficiencies > 80% for 20 mm x 20 mm sheets exposed as given above. To verify adsorption efficiency you can expose successively several sheets in the same 80 ml sample. Assuming that every sheet takes up the same fraction of the uranium that remained in the sample, adsorption efficiency will be 1- (U activity on sheet n+1)/ (U activity on sheet n).
U standard solutions can be prepared with uranylnitrate.


Energy resolution

Film thickness is several µm making energy resolution far worse than for the Ra adorbing films. However even when measured in air you still have ²³⁴ U and ²³⁸ U separated. There is an interference of the ²³⁴ U lines with the ²²⁶ Ra lines.
Actually Ra adsorbtion efficiency of these films seems to be far lower than U adsorbtion efficiency. So far there has been no systematic tests on Ra adsorbtion. Thus any data would be welcome .


December 24, 2000 Heinz Surbeck