A beam of energy in a first form, such as electrons, is provided in a first direction. The beam may be pulsed or continuous. The beam is intercepted by a member, such as a converter target, to produce energy in a second form such as x-rays. The converter target may be formed from a heavy material such as tungsten or tantalum. The interaction of the electron beam with the converter target will produce energetic bremsstrahlung x-rays in an energy range including 10.6 Mev to approximately 13.0 Mev. This range is sufficient to excite the abundant nitrogen atoms in common explosives to induce the production of annihilation photons but is not sufficient to substantially excite atom of the most abundant elements of the earth's crust (e.g. oxygen, silicon, iron, aluminum, carbon, hydrogen, etc.), which comprise most common fabricated articles and soils. The converter target is disposed relative to an object (e.g. a suitcase in an airport) to obtain the production of energy in a third form, such as photons, from the object. The photons pass to a detector such as a scintillation counter which determines the concentration of the nitrogen in the object. The detector may be gated so as to be activated only when the photons are passing from the object to the detector. When the object is a suitcase which is moved along a conveyor, the detector may be downstream from the source in the direction of movement of the conveyor.