TRACING AND ELIMINATION OF PROCESS-INDUCED CONTAMINATIONS IN SPUTTER-DEPOSITED TARGETS BY ELASTIC RECOIL DETECTION ANALYSIS

Target foils for nuclear physics experiments have been prepared by hig h vacuum sputter deposition and analyzed for preparation induced conta minations using ERDA (elastic recoil detection analysis) with heavy io ns. Sputter deposition has been shown to be a very effective method fo r the production of thin self-supporting targets, in particular those which cannot be made in certain cases by other techniques. Its low mat erial consumption is of special importance for targets from expensive isotopes. During the development of this sputter deposition technique, contaminants introduced by the preparation method were traced by ERDA and eliminated by appropriate countermeasures. ERDA has proven to be a useful tool for quantitative thin film analysis. Its sensitivity of about 10(-2) at.% is sufficient for nuclear target analysis and roughl y equal for all elements. If highly energetic ions, e.g. 170 MeV I-127 , are used, elements from H up to the heaviest ones can be detected si multaneously, and therefore the relative content can be determined pre cisely. Light elements in thin foils have been simply identified by th eir energy signals in solid state detectors, as for instance H in V fo ils. For thicker targets or heavier components, an ionization detector with particle identification has been used. In self-supporting test f oils of suitable elements the origin of every contaminant could be tra ced back by systematic analyses and reduced to a tolerable level. Base d on this experience, the sputter setup was optimized to allow the pre paration of targets of many elements with a minimum of contamination.