Gas release from Al2O3 and stainless-steel surfaces under x-ray irradiation

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Abstract
Measurements have been made on the amount and type of gas species released under x-ray irradiation from Al2O3 and stainless-steel surfaces in an ultrahigh vacuum environment. These surfaces had not been degassed but had been held more than 24 h at a background pressure of 1×10−9 Torr prior to irradiation. The energy spectrum of the x rays was characteristic for a tungsten-target bremsstrahlung spectrum for electron energies varying from 15 to 50 keV. The predominant gas species observed mass spectrometrically were CO2 from Al2O3 and O2, CO2, and CO from stainless steel. Mean quantum yields for the release of the species have been determined and are in the range from 3×10−5 to 2×10−3 molecules per number of photons in the bremsstrahlung spectrum. Mean quantum yields were observed to decrease with increasing mean photon energy. The mean photon energy dependence of the mean quantum yield for gas release was correlated with the photon energy dependence of the photon absorption coefficient of the substrate material. The amount of CO2 released was found to be independent of CO partial pressure.

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