Preparation of Relatively Clean Carbon Backings Used in Charged Particle Induced X-Ray Studies for X Rays below 4 keV

In a recent series of studies of M-shell ionization induced by protons, alpha particles, and fluorine ions, an unmanageable background of low energy contaminant x rays was observed. These K-shell x rays were primarily from Ca, K, Cl, S, P, Si and Na. The energy range of these contaminants is from 3.691 to 1.041 keV. The M-shell x rays being studied were for various elements from U (~ 3.5 keV) down to Eu (1.5 keV). In order to evaluate and reduce the problem, the contaminants for carbon foils from a number of different manufacturers and a wide variety of foil float-off procedures have been studied. Carbon foils have been produced in our laboratory using carbon rods from several different manufacturers. In this paper, techniques will be described that are most appropriate to reduce the above contaminants to a reasonable level. These techniques should be useful in trace element analysis (PIXE) studies and fundamental ionization measurements for low x-ray energies.