  Processes of K-shell ionization and accompanying characteristic x-ray
radiation (CXR) by high-energy electrons moving through a multifoil copper
target are considered. Expressions describing the main characteristics of these
processes are derived. It is shown that the average K-shell ionization cross
section in the target is not defined just by the target material and the
electron energy, but also depends on the number of foils in the target, their
thickness and separation between them. The corresponding CXR yield is therefore
not unambiguously defined by the aggregated target thickness, but depends on
the above parameters as well. It is demonstrated that the average K-shell
ionization cross section in a multifoil target can be several times larger than
the conventional cross section of this process without the density effect
impact. This results in a considerable enhancement of CXR yield from the
multifoil target compared to the case of electron incidence upon a single foil
of the same aggregated thickness. Comparison of CXR yield in the considered
case with the yields of some other types of x-ray emission in multifoil targets
is made.
