K-IONIZATION CROSS SECTION OF ALUMINIUM BY ELECTRON IMPACT (3KEV-30-KEV)

The K-ionization cross section of Aluminium by electron impact was measured detecting quantitatively the Al-K X-rays emitted by thin targets of known mass thickness. The apparatus and the measurements are briefly described. The experimental results are considerably higher than the values of the theories using the Born approximation. The discrepancy increases with increasing energy of the incoming electron. At twenty-fold threshold energy for example, the measurements are higher than Burhop's calculations by a factor of 1.7. It is shown that considering the process of K-ionization the influence of the nuclear field on the impact electron increases with decreasing atomic number. Thus, the calculations of Rudge and Schwartz using coulomb wave functions for the impact electron, are closest to the measurements (maximum deviation 16%). The formula of Gryzinski based on classical calculations is a good approximation to the experimental results if multiplied by a factor 1.23. © 1969 Springer-Verlag.