Fajans-Paneth Rule

a rule established empirically in 1913 by K. Fajans and F. Paneth holding that a radioisotope present in solution in microscopic quantities as a cation is more strongly adsorbed on a precipitate that is separating or already deposited the lower the solubility of the compound that this cation forms with an anion of the precipitate. The Fajans-Paneth rule is used in radiochemical coprecipitation.