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Gamma-Ray Resonant Absorption (GRA) is an automatic-decision radiographicscreening technique that combines high radiation penetration with very goodsensitivity and specificity to nitrogenous explosives. The method isparticularly well-suited to inspection of large, massive objects (since theincident gamma-ray probe is at 9.17 MeV) such as aviation and marinecontainers, heavy vehicles and railroad cars. Two kinds of gamma-ray detectorshave been employed to date in GRA systems: 1) Resonant-response nitrogen-richliquid scintillators and 2) BGO detectors. This paper analyses and compares theresponse of these detector-types to the resonant radiation, in terms ofsingle-pixel figures of merit. The latter are sensitive not only to detectorresponse, but also to accelerator-beam quality, via the properties of thenuclear reaction that produces the resonant gamma-rays. Generally, resonantdetectors give rise to much higher nitrogen-contrast sensitivity in theradiographic image than their non-resonant detector counterparts andfurthermore, do not require proton beams of high energy-resolution. Bycomparison, the non-resonant detectors have higher gamma-detection efficiency,but their contrast sensitivity is very sensitive to the quality of theaccelerator beam. Implications of these detector/accelerator characteristicsfor eventual GRA field systems are discussed.Comment: 11 page

Detectors for the gamma-ray resonant absorption (GRA) method of explosives detection in cargo: a comparative study