  We present the first three-dimensional MHD radio galaxy simulations that
explicitly model transport of relativistic electrons, including diffusive
acceleration at shocks as well as radiative and adiabatic cooling in smooth
flows. We discuss three simulations of light Mach 8 jets, designed to explore
the effects of shock acceleration and radiative aging on the nonthermal
particle populations that give rise to synchrotron and inverse-Compton
radiations. We also conduct detailed synthetic radio observations of our
simulated objects. We have gained several key insights from this approach: 1.
The jet head in these multidimensional simulations is extremely complex. The
classical jet termination shock is often absent, but motions of the jet
terminus spin a ``shock-web complex'' within the backflowing jet material of
the head. 2. Understanding the spectral distribution of energetic electrons in
these simulations relies partly upon understanding the shock-web complex, for
it can give rise to distributions that confound interpretation in terms of the
standard model for radiative aging of radio galaxies. 3. The magnetic field
outside of the jet itself becomes very intermittent and filamentary in these
simulations, yet adiabatic expansion causes most of the cocoon volume to be
occupied by field strengths considerably diminished below the nominal jet
value. Thus population aging rates vary considerably from point to point.
