Hi Jan,

you can probably find a place to buy well characterized soil, however, I suggest that you pick soil that is relevant to the site you want to investigate radiocesium mobility in and then get it characterized by your regional soil testing laboratory. In this way you will get more meaningful data and its not too hard to characterize the basic soil properties (CEC, pH, P, N, C, etc. and clay composition (using XRD). Cheers, Thomas

 Dear Sir,

As suggested Thomas sir, it is the best  option. 

I agree with Thomas.  I would add that the 'charactrrisation' should be targeted to your application.  You need to know what controls Cs mobility and measure that or a proxy.

Dear Ján,

I can recommend LUFA Speyer from Germany, have a look at the English version of their website where they sell a variety of standard and characterized soils: http://www.lufa-speyer.de/index.php/dienstleistungen/standardboeden/8-dienstleistungen/artikel/57-standard-soils 

In addition, you could think about creating your own artifical soil (depending on if this is suitable for your experiments). Do you know the OECD Guidelines for the testing of chemicals? Have a look at the OECD 207 test guideline: http://www.oecd-ilibrary.org/environment/test-no-207-earthworm-acute-toxicity-tests_9789264070042-en

The guideline describes an artificial soil test for the testing of chemicals to earthworms. For their toxicity tests they suggest an artificial soil test substrate, for example, as follows: 

• 10 % sphagnum peat
• 20 % kaolin clay
• 70 % industrial sand

All these ingredients can be easily purchased at a variety of national and international stores and catalog companies (or at your local department store). Depending on the composition it will only be an approximation to a real soil, but you can standardize your test soil and vary the ingredients one by one to have defined and reproducible test conditions.

Thank you all. I need organic free soil - pure clay. I will test the absorption in the system humic acids (prepared) - Cs - clay, therefore I prefer to  use "synthetic" clay (or very well defined clay/loam without organic)  to avoid any interferences. Anyway, thanks for advices.

If you're interested in Cs-137 or Cs-134, here's a good option from the radioanalytical side: https://nucleus.iaea.org/rpst/referenceproducts/referencematerials/radionuclides/IAEA-444.htm

I think suggestion of Andre Patrick Heinrich is the best.

I think the proposal of Andre  is the best