Preparation of large-area sources with uniform layers for the spectrometryof alpha-emitting nuclides

A procedure for the preparation of large-area sources with uniform layers f or cr-spectrometry for the large-area grid ionization chamber has been deve loped. It is based on the direct evaporation of a sample solution in the co unting dish in the presence of an excess of a sublimable chemical compound like ammonium nitrate. In the course of evaporation this excess compound pr ecipitates and thus avoids the formation of clusters during the further eva poration process. After dryness, the excess compound is removed from the so urce by sublimation. Samarium nitrate is added as an internal standard and the alpha-activity of the isotope Sm-147 is chosen to measure the counting efficiency due to self-absorption. Examples are presented of the applicatio n of large-area sources for a-spectrometry for the large-area grid ionizati on chamber.