  The elemental energy spectra of cosmic rays play an important role in
understanding their acceleration and propagation. Most current results are
obtained either from direct measurements by balloon or satellite detectors, or
from indirect measurements by air shower detector arrays on the Earth's
surface. Imaging Air Cherenkov Telescopes (IACTs), used primarily for gamma-ray
astronomy, can also be used for cosmic-ray physics. They are able to measure
Cherenkov light emitted both by heavy nuclei and by secondary particles
produced in their air showers, and are thus sensitive to the charge and energy
of cosmic ray particles with energies of tens to hundreds of TeV.
  A measurement of the energy spectrum of iron nuclei, based on 71 hours of
data taken by the VERITAS array of IACTs between 2009 and 2012, will be
presented. The energy and other properties of the primary particle are
reconstructed using a template-based likelihood fit. The event selection makes
use of direct Cherenkov light, which is emitted by the primary particle before
starting the air shower. A multivariate method is used to estimate the
remaining background. Using these methods, the iron spectrum was measured in
the energy range from 20 TeV to 500 TeV.
