Apparatus and method for detecting and locating hidden explosive substances. The detection apparatus includes a thermal neutron beam generator, a gamma ray detector, data collection module and sensors, and a detection processing module. The thermal neutron beam generator includes a fast neutron source, a neutron moderator to slow the fast neutrons to thermal neutrons, and a rotatable neutron shield enclosing the generated thermal neutrons. The rotatable neutron shield has an aperture through which a thermal neutron beam is projected at a remote target. Gamma rays radiating from hidden explosives in the remote target are detected by the gamma ray detector, while the associated detection processing module spatially locates the target based at least in part on the position of the aperture in the rotatable neutron shield.