The document describes a Standoff Explosive Detection System (SEDS) that can detect explosives from up to 20 meters away using thermal neutron activation analysis. SEDS uses a pulsed beam of neutrons to induce gamma ray emissions from nitrogen, chlorine, and copper in explosives. A large gamma ray detector then senses these gamma rays to detect and locate explosives within 10 seconds while penetrating materials like concrete and steel. The system is designed to be low cost, safe for operators, and deployable within 12 months of adequate funding.