A method and associated apparatus for detecting concealed fissile,
fissionable or special nuclear material in an article, such as a shipping
container, is provided. The article is irradiated with a source of fast
neutrons, and fast neutrons released by the fissile or fissionable
material, if present, are detected between source neutron pulses. The
method uses a neutron detector that can detect and discriminate fast
neutrons in the presence of thermal neutrons and gamma radiation. The
detector is able to process high count rates and is resistant to
radiation damage, and is preferably a solid state neutron detector
comprised of silicon carbide.