  Electron channeling in silicon crystals has brought forward the possibility
of having detected a particle's "internal clock", as an intrinsic oscillation
with de Broglie's frequency. The transmission probability along a major axial
direction is reduced with respect to neighboring angles, except for a sharp
peak at the atomic row direction. The pattern observed is a "W" instead of a
"U". This central peak is attributed to a process known as "rosette motion", in
which the crossing of successive atoms would be related to the de Broglie
frequency. A classical multiple scattering calculation found that, to represent
the experimental results, the interaction frequency had to be about twice the
de Broglie's clock frequency; that is, the "Zitterbewegung" frequency. In the
present paper, the observed characteristics of this process are shown to be
consistent with a free particle quantum mechanical motion described by Dirac's
Hamiltonian, albeit with an effective mass resulting from the interaction with
the crystal atoms. The introduction of a self-adjoint dynamic time operator
provides the connection with an internal "system time", the de Broglie clock.
