  A detailed theoretical analysis of the 1s photoionization of neon is
presented. It is found that the most significant many-electron correlation in
computing photoionization of inner shells is the rearrangement of the outer
shells caused by the inner vacancy. Further noticeable effects are: (i) the
polarization of the ion core by the outgoing photoelectron and (ii) the
coherent effect of double excitation/ionization. The core polarization
increases the photoionization cross section by about 10% at the 1s threshold,
and the coherent excitation results in further increases by about 5%.
Incoherent excitation of the satellite channel leads to an additional 10%
increase in the photoabsorption cross section in the double-ionization
threshold region.
