Thorium isotope fractionation in the dissolution of inorganic samples by amicrowave method

Several procedures of general application for the total dissolution of inor ganic samples using a microwave oven were studied in detail. They were appl ied to the determination of thorium isotopes by alpha spectrometry. This st udy revealed the existence of various stages during the process of digestio n that led to an apparent differential behaviour of the isotopes of thorium , so that the original isotopic composition of the sample was completely lo st. We introduced changes in the dissolution procedures which resulted in g ood agreement between the experimentally determined and the true isotopic r atios.