Methods to reduce contamination in targets prepared by vacuum deposition

Target makers have been concerned about the source of impurities which were found from experimental data obtained using targets prepared by vacuum vapor deposition. These impurities may arise from the process of producing the target, the separated isotope used in the evaporation, or contaminants introduced during the experiment. This study is an attempt to determine the source of impurities found in the targets. Impurities in the targets can make it difficult for experimenters to analyze their data. For targets such as magnesium, aluminum, calcium and other readily oxidized materials, the following points are important: a clean system is needed, the best possible vacuum attainable, and as short an evaporation time as the desired uniformity of a target will permit. Developmental work with the cryopump system has shown the potential for reducing many contaminants, particularly carbon. There are several problems associated with these systems, but they are not insurmountable