Gamma-Ray Resonant Absorption (GRA) is an automatic-decision radiographic screening technique that combines high radiation penetration with very good sensitivity and specificity to nitrogenous explosives. The method is particularly well-suited to inspection of large, massive objects (since the resonant γ-ray probe is at 9.17 MeV) such as aviation and marine containers, heavy vehicles and railroad cars. Two kinds of γ-ray detectors have been employed to date in GRA systems: 1) Resonant-response nitrogen-rich liquid scintillators and 2) BGO detectors. This paper analyses and compares
the response of these detector-types to the resonant radiation, in terms of single-pixel figures of merit. The latter are sensitive not only to detector response, but also to accelerator-beam quality, via the properties of the nuclear reaction that produces the resonant-γ-rays. Generally, resonant detectors give rise to much higher nitrogen-contrast sensitivity in the radiographic image than their non-resonant detector counterparts and furthermore, do not require proton beams of high energy-resolution. By comparison, the non-resonant detectors have higher γ-detection efficiency, but their contrast sensitivity is very sensitive to the quality of the accelerator beam. Implications of these detector/accelerator
characteristics for eventual GRA field systems are discussed.
KEYWORDS: Monte Carlo methods, Sensors, Detection and tracking algorithms, Optical spheres, Spherical lenses, Computer simulations, Gamma radiation, Satellites, Signal detection, Computing systems
The development of a rotating detection system in space is proposed to assist in locating typical isotropicaly distributed burst-events. The system is based on several small angular openings (for example, 5 degrees opening each), bundled into a rotating detection system array, using a controlled stepper motor. A transmission device in the system will transmit the detected signals to an analyzing computer. In this work we simulated the response of rotating monitoring systems, using three different monitoring algorithms, in order to compare each system's efficiency according to its monitoring pattern. Burst-events counting on a spherical surface were simulated as a system, with a one or more detectors located on the center of a sphere. The burst-events monitoring was simulated in Monte Carlo calculations in three separate modules, describing several courses for the detectors’ angular translations. The burst-events position was randomly changed at steps analogous to the monitoring period. The scored events resulting from each of the three algorithms were very similar, for 106 steps as well as for 107 steps. Enhancing the results statistics, by a factor of ten increase of the number of burst-events in the simulations, showed that the random monitoring algorithm is a three fold more efficient scoring compare to the other two patterned monitoring algorithms.
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