  The determination of hydrogenous content in commercial cargoes is an
important challenge in cargo security. Prior work has shown the feasibility of
hydrogenous cargo classification in radiographic applications. This result was
achieved by using the significant material to material differences in the
energy dependence of their neutron scattering cross-sections. The work
presented here details the application of this technique to
multiple-monoenergetic neutron transmission measurements of several
heterogeneous cargo mock-ups with the goal of quantifying hydrogenous content.
It demonstrates the ability to determine the hydrogenous content of a cargo
container by performing analysis of pulse-height data of transmitted neutrons.
The set-up used for these feasibility studies was able to detect and quantify
areal densities of up to 30 g/cm$^2$ of high density polyethylene (HDPE), even
when mixed with metallic materials. Accurate determination of the hydrogenous
content of the cargo has two important uses: it can allow for better imaging
and discrimination of conventional contraband during cargo screening; it may
also allow the unfolding of the individual elemental contributions from an
effective atomic number, $Z_{\mathrm{eff}}$, as determined from multiple
monoenergetic gamma radiography (MMGR). This combination of capabilities could
make multiple monoenergetic neutron radiography applications a significant
contribution to cargo security.
