Remote sensing device to detect materials of varying atomic numbers

A method for identifying fissile material within an interrogated vessel, comprising:

• casting an incident photon beam from an electron beam accelerator through the interrogated vessel on the fissile material;
• detecting an emerging photon beam within an energy range from about 1 MeV to about 50 MeV from the fissile material with an array of fission-fragment detectors, a first set of scintillator paddles, and a second set of scintillator paddles, wherein the array of fission-fragment detectors, the first set of scintillator paddles, and the second set of scintillator paddles (a) are arranged sequentially in a direct path of the emerging photon beam such that each receives the emerging photon beam, and (b) are sensitive to different ranges of photon beam energy;
• obtaining a first signal from the array of fission-fragment detectors, a second signal from the first set of scintillator paddles, and a third signal from the second set of scintillator paddles, each signal indicative of photon yield within the different ranges of photon beam energy;
• and
• determining a photon energy regime of the emerging photon beam through identification of a drop in photon yield in at least one of the three signals, the determined photon energy regime identifying the fissile material within the interrogated vessel.