  A method was developed for measuring photonuclear reactions concurrently at
several discrete photon beam energies on a stack of different target materials
via a single irradiation. Concentric ring targets of the materials (in order
from front to back targets: Au, TiO$_2$, Zn, Os, and Au) were irradiated at the
High Intensity Gamma-ray Source (HI$\gamma$S). As a proof of principle, we
report the result of the cross section measurements from the front Au target.
The excitation functions of the $^{197}$Au($\gamma$,n)$^{196}$Au and
$^{197}$Au($\gamma$,3n)$^{194}$Au reactions were determined in the incident
photon energy range of 13-31 MeV using quasi-monoenergetic photon beams
provided at HI$\gamma$S. The cross sections of the combined ground state
(2$^{-}$) and short-lived first isomeric state (m1, 5$^{+}$), and of the second
isomeric state (m2, 12$^{-}$) in the $^{196}$Au production are obtained
separately by subtracting the $\gamma$ rays from the internal conversion of the
second isomeric state. The excitation function of the second isomeric state via
the photon-induced reaction $^{197}$Au($\gamma$,n)$^{196m2}$Au was measured for
the first time. By using the activation method rather than direct neutron
counting, the exclusive cross sections for the ($\gamma$,n) and ($\gamma$,3n)
reactions were determined. Comparing the yields from the front and back gold
targets validates our ability to simulate the effect of photon scattering in
the target stack and provides a method for assessing the systematic uncertainty
of our technique.
