A Review of Methods to Prepare Self-Supporting Carbon Targets and of Their Importance in Accelerator Experiments

Abstract

Carbon occupies a special position compared to all other elements. Without carbon, the basis for life would be impossible. Organic chemistry or carbon chemistry is an independent part of chemistry. Just so the element carbon occupies an exceptional position in target preparation for nuclear measurements due to its melting point, the highest of all elements, the very low vapor pressure and the chemical stability which is comparable to that of the noble metals. Carbon has only two stable isotopes and one radioactive isotope the half-life of which is long enough to prepare targets. The natural abundance of carbon-12 is nearly 99% which means a natural carbon target can be used in most cases as isotopic ¹²C-target. But this is only one part of the story, the other one is given by the excellent properties of the self-supporting foils. The good tensile strength of an amorphous carbon layer can be estimated by the minimum thickness of a self-supporting foil. Carbon foils can be prepared even below 1 μg/cm² (≈ 60 Å), they are one order of magnitude thinner than foils of any other element.