  Smuggling of special nuclear materials (SNM) and nuclear devices through
borders and ports of entry constitutes a major risk to global security.
Technologies are needed to reliably screen the flow of commerce for the
presence of high-$Z$ materials such as uranium and plutonium. Here we present
an experimental proof-of-concept of a technique which uses inelastic ($p,p'$)
nuclear reactions to generate monoenergetic photons, which provide means to
measure the areal density and the effective-$Z$ ($Z_{\text{eff}}$) of an object
with an accuracy which surpasses that achieved by current methods. We use an
ION-12$^{ \text{SC}}$ superconducting 12~MeV proton cyclotron to produce 4.4,
6.1, 6.9, and 7.1~MeV photons from a variety of nuclear reactions. Using these
photons in a transmission mode we show that we are able to accurately
reconstruct the areal densities and $Z_{\text{eff}}$ of a test object. This
methodology could enable mobile applications to screen commercial cargoes with
high material specificity, providing a means of distinguishing common cargo
materials from high-Z materials that include uranium and plutonium.
