  The motion of charged particles in a crystal in the axial channeling regime
can be both regular and chaotic. The chaos in quantum case manifests itself in
the statistical properties of the energy levels set. These properties have been
studied previously for the electrons channeling along [110] direction of the
silicon crystal, in the case when the classical motion was completely chaotic.
The case of channeling along [100] direction is of special interest because the
classical motion here can be both regular and chaotic for the same energy
depending on the initial conditions. The semiclassical energy level density (as
well as its part that corresponds to the regular motion domains in the phase
space) is computed for the 10 GeV channeling electrons and positrons. It is
demonstrated that the level spacing distribution for both electrons and
positrons can be better described by Berry--Robnik distribution than by both
Wigner (completely chaotic case) or Poisson (completely regular case)
distributions.
