Rate of Carbon Contamination on Al Targets in a High Vacuum Electron Excitation X-Ray Tube

Abstract

The rates of carbon contamination on Al targets caused by electron bombardments in two vacuum systems, one evacuated by a diffusion pump (∼5×10-6 mmHg) and the other by an ion pump (∼5×10-7 mmHg), have been obtained by detecting C K-emission spectra with a grazing incidence concave grating spectrograph. Simultaneously Al L-emission spectra were photographed. Intensity estimates for C K-emission were photographically made in reference to the intensity of graphite C K-emission using a characteristic curve of photographic plates. The rates of carbon contamination are about 1.1×10-5% per sec in the vacuum system of the ion pump and about 6.0×10-4% per sec in the vacuum system of the diffusion pump (oil: Santo Vac 5), expressed as fractions of the intensity of graphite C K-emission. The decrease of Al L-emission intensity was not detected in the ion pump system, but was observed remarkably in the diffusion pump system.