  Cosmic-ray muons are highly penetrative charged particles that are observed
at sea level with a flux of approximately one per square centimetre per minute.
They interact with matter primarily through Coulomb scattering, which is
exploited in the field of muon tomography to image shielded objects in a wide
range of applications. In this paper, simulation studies are presented that
assess the feasibility of a scintillating-fibre tracker system for use in the
identification and characterisation of nuclear materials stored within
industrial legacy waste containers. A system consisting of a pair of tracking
modules above and a pair below the volume to be assayed is simulated within the
GEANT4 framework using a range of potential fibre pitches and module
separations. Each module comprises two orthogonal planes of fibres that allow
the reconstruction of the initial and Coulomb-scattered muon trajectories. A
likelihood-based image reconstruction algorithm has been developed that allows
the container content to be determined with respect to the atomic number Z of
the scattering material. Images reconstructed from this simulation are
presented for a range of anticipated scenarios that highlight the expected
image resolution and the potential of this system for the identification of
high-Z materials within a shielded, concrete-filled container. First results
from a constructed prototype system are presented in comparison with those from
a detailed simulation. Excellent agreement between experimental data and
simulation is observed showing clear discrimination between the different
materials assayed throughout.
