A method for detecting nitrogenous materials within an object by means of Gamma-Resonance Absorption (GRA), including placing on one side of an object a target containing 13C for bombardment with a proton beam of approximately 1.75 MeV energy, to produce a source of 9.172 MeV gamma-rays for scanning the object, reading from the gamma-ray detector the total and the non-resonant attenuations of the incident photon flux, and deriving from the attenuations the net resonant attenuation and the spatial distribution thereof; wherein scanning the object includes: I. performing a rapid pre-scan to classify the overall gamma-ray-attenuation regime and locate regions of high physical density, in which longer scanning times might be required; II. performing a full scan to identify and locate regions that contain nitrogenous materials; and III. performing a plurality of scans in same or different segments to establish presence of explosives.