shells and subshells [7] is presented in the form of a periodic table of

L2(2p) subshells) for Be, B, C, N, O, F, and Ne respectively (Fig.

The subshells 3s and 3p of the shell of M for Ar and K (Fig.

The shell of N (subshells 4s and 4p) for Ga is the same as in Fig.

The shell of N (subshells 4s and 4p) for Kr is the same as in Fig.

17 (a, b, c, and d) shows the shell of M (subshells 3s, 3p,

where I(E, r) is the distribution of electrons in the specimen as a function of energy E and position r, [[sigma].sub.x](E) is the ionization cross section for the relevant subshell, [f.sub.x] is the fraction of ionization events producing x rays in the line of interest and [[sigma].sub.x] is the absorption coefficient for the x rays on their path to the detector at position [r.sub.0].

where [n.sub.x] is the number of electrons in the subshell and [b.sub.x] and [c.sub.x] are parameters to be determined by fitting to experimental data or other calculation.

To calculate the ionization cross section for the subshell Eq.

I have now completed systematic calculations of the electron ionization cross sections from all subshells that might be relevant for microanalysis.

Since this is the first time that M cross sections have been explicitly calculated it is interesting to compare them with K and L cross sections for subshells with comparable binding energy.

Rez, Electron ionization cross sections for atomic subshells, Microc.