I would like to suggest reading the following paper: Chapter 2: Fundamentals of Isotope Geochemistry (usgs.gov)

A standard of radioactivity in aqueous solution can never be considered a stable in the long term. The provider should specify the limits of use. The solution will be prepared in a way that limits adsorption, precipitation, and other phenomena that may affect the homogeneity and the concentration of the solution, e.g. adequate pH, adding a carrier, ...but these phenomena can never be totally avoided. The decay of the radionuclide may also have an effect on the chemistry of the solution.

Dear sir,

You can look to this paper.

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.scielosp.org/pdf/aiss/2012.v48n4/362-373&ved=2ahUKEwipvePOh9TxAhWV5OAKHSGDCnYQFjAJegQIIxAC&usg=AOvVaw0UnzeO6XJdwgaQh3rA1zlW