Innershell ionization by 150 MeV electron impact

The innershell ionization by electron impact has been investigated over many years. In the present paper, the K-shell X-ray for Al, Si, Cu, Zn, In and Sn, the L-shell X-ray for In, Sn, Au, Pb and Bi, and the M-shell X-ray for Au, Pb and Bi by 150 MeV electron impact were measured. Accelerated electron beam impinged on the thin targets kept inside a large scattering chamber, and arrived at a beam dump located at about 15 m from the targets. A Si(Li) detector and a flow-mode proportional counter were used for the measurement of produced X-ray. The cross-section (sigma x) for X-ray production was determined from the obtained X-ray spectra. The ionization cross-section (sigma) was determined by the equation sigma = sigma x/w, where w is the fluorescence yield of the shell concerned. The results on the K-shell ionization cross-section is shown as a function of the atomic number of targets. The agreement between experimental data and the prediction by Kolbenstvedt and by Pessa-Newell was generally good in cases of the elements 13 <= Z <= 50. The intensity ratio for K-shell X-ray (Kα/Kβ) was in reasonable agreement with recent calculation. It should be noted that the data at low energy for low and medium Z elements are well described with the scaling law expected from the Bethe formula (sigma U2 - ln(E/U)). It was also found empirically that experimental data gathered more closely on a single curve in the sigma U-(E/U)/U plot. At the present stage, the theoretical background for this scaling law was not found. (Kato, T.)