Ra-NucfilmDiscs and U-NucfilmDiscs are discs covered with a thin film selectively adsorbing radium or uranium. They make sample preparation for alpha spectrometry very easy and no toxic or radioactive substances are used. read more
... and an old frequently cited paper about NucfilmDiscs
Exclusive distributor for Nucfilm-Discs : Triskem International, links to product sheets and application notes on their homepage.
(comment concerning U-NucfilmDiscs application note : instead of formic acid, citric acid can be used (50 mg citric acid monohydrate / 100 ml).