This paper presents a radioisotope-based concept for determining whether an anomaly in the ground contains an explosive material or not. Nitrogen-based explosives, commonly used in landmines, are rich in carbon, nitrogen and oxygen. Hydrogen is also present in the explosive material, but can be found as well in the mine casing (if plastic or wood). Moreover, explosive materials have a density that is higher than that of most organic materials, but lower than that of metals. All these features are employed in a detection concept that relies on the use of an isotopic source of neutrons. The amount of slowing-down of the source's fast neutrons, as they scatter to the thermal energy, is indicative of the hydrogen content. The enhancement of the intensity of fast neutrons, due to resonance scattering by carbon, nitrogen and oxygen, is indicative of their combined presence. Moreover, the photons that accompany neutron production, are Compton-scattered, providing an indication of the electron-density of the anomaly. These three measurements, contrasted against those obtained from the surrounding soil, are indicative of the presence or absence of a mine, or a mine-like, target.
This paper identifies the unique characteristics of 252Cf as a neutron source and shows how they are utilized in nondestructive testing of industrial materials and monitoring of engineering processes. Conventional use of the source to produce the thermal neutrons needed in radiography and neutron activation analysis is reviewed. The ability to directly employ the fast neutrons emitted by 252Cf is demonstrated by a number of transmission, activation and scattering methods. Techniques that use this source to assay fissionable materials are also discussed.
KEYWORDS: Sensors, Scattering, Monte Carlo methods, Compton scattering, Inspection, Photoelectric effect, Gamma radiation, Photon transport, Target detection, Chemical species
This paper investigate, with the aid of Monte Carlo simulations and laboratory experiments, a technique for the detection of narcotics in large cargo containers using gamma-radiation. The transmission and back-scattering of photons, at different energies, is used to provide information useful for identifying the presence of bulk quantities of commonly encountered narcotics.
A fast-neutron technique that employs isotopic sources is proposed for the identification of explosive materials. The technique relies on analyzing the spectrum of transmitted neutrons. Identification methods are developed to enable discrimination between explosives and other materials. A threshold-value method and artificial neural networks are used. Monte Carlo simulations, as well as laboratory experiments, are utilized to demonstrate the feasibility of the proposed techniques.
Compton scattering and photoelectric absorption of gamma rays are used as indicators of material electron density and mean atomic number, respectively. These indicators are shown to be adequate for discriminating explosive materials from other organic or polymer materials of similar mass densities. A transmission-scattering map is shown, experimentally and by Monte Carlo simulation, to provide a useful and simple indicator for the presence or absence of explosives.
KEYWORDS: Sensors, Data modeling, Inverse problems, Medical imaging, Monte Carlo methods, Signal attenuation, Target detection, Tomography, Error analysis, Imaging systems
A tomographical imaging system capable of reproducing electron density distributions of an irradiated object plane via measurement of the Compton scattered radiation is presented as a potential contender for portal imaging. The method which imposes minimal constraints on the measurement apparatus unlike most scanning methods is capable of density reconstruction with limited projections of scattered photon energy spectra acquired under conditions of wide angle source and detector collimation. As such, density reconstruction becomes a nonlinear inverse problem. This problem is presented along with a discussion on potential solution strategies to confine the impact of solution instability.
A number of nuclear techniques have been utilized or considered for detecting concealed explosives. These techniques range from those utilizing multi-energetic x rays to those relying on high energy photons or neutrons. The physical principles behind these methods are reviewed. Each technique is critically examined, in view of its ability to distinguish explosive materials from other common materials of similar composition. The suitability of each method for use in airport security also is discussed.
A number of nuclear techniques have been utilized or considered for detecting concealed explosives. Theses technique range form those utilizing multi-energetic x-rays to those relying on high energy photons or neutrons. The physical principles behind these methods are reviewed. Each technique is critically examined, in view of its ability to distinguish explosive materials form other common materials of similar composition. The suitability of each method for use in airport security is also assessed.
A method for imaging a target with Compton scattered gamma radiation is presented. This method accepts simultaneously, in the detector energy spectrum, radiation scattered from the entire target in a single measurement. The energy spectrum provides the information necessary for reconstructing the electron density distribution within the target. Models on which the reconstruction process is based are presented and tested against Monte Carlo simulation and experimental data. Image reconstruction from simulations demonstrate the feasibility of the method. The problems encountered in reconstructing images from experimental spectra are addressed along with some workable solutions.
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