An accelerator-based, active, pulsed, interrogation system capable of non-destructive, elemental analysis from secondary gamma-ray emissions is being developed for various inspection applications. The system consists of a very narrow pulsed, electron accelerator (> 8 MeV) for photoneutron production and a multiple channel, gamma-ray detection system capable of ultra-fast detection. This system has applicability to cargo container inspections. Advantages of the system include use of highly penetrative, energetic, interrogating X-rays, compatibility with existing X-ray inspection systems, capability of large neutron production yield from the pulsed accelerator, ability to induce a volumetric, tailored neutron source spectrum within or very near the containers, and most importantly, the spectrometry capability of a ultra-fast, gamma-ray detection system. The portable detection system is described which has been designed to acquire multiple, single gamma-ray events (up to 40 MHz between each accelerator pulse) from neutron inelastic scattering (starting from within 100 ns after an accelerator pulse) and neutron capture interactions. The system and its overall operational requirements are described. Experimental results, using a 50 ps electron accelerator pulse and selected inspected objects, are presented along with numerical predictions and system characterizations.