X-ray or gamma ray systems or devices – Specific application – Diffraction – reflection – or scattering analysis
Patent
1993-10-21
1995-05-30
Church, Craig E.
X-ray or gamma ray systems or devices
Specific application
Diffraction, reflection, or scattering analysis
378 86, G01N 23201
Patent
active
054209056
ABSTRACT:
A technique for detecting explosives and other materials using resonance fluorescence, resonance absorption, and other electromagnetic processes with a continuous spectrum of photons is disclosed. The method is particularly attractive as a way to detect explosives at airports and other transporation terminals. According to one aspect of the invention, bremsstrahlung or other continuous-spectrum photon radiation in the appropriate energy ranges is made incident on a target (e.g., a piece of luggage or other container) to resonantly excite the atoms of the target. In one embodiment, the energies of the photons scattered directly from the target are detected and measured. These energies are characteristic of the nuclear species excited in the target, and thus the concentrations of these elements in the target can be determined. A high concentration of nitrogen and oxygen with a low concentration of carbon indicates practically without fail an explosive material. In another embodiment, the energies of photons resonantly scattered from reference scatterers composed substantially of nuclear species of interest and located downstream from the target are detected and measured. The abundance of photons of energies corresponding to nuclear species of interest detected in this embodiment is inversely related to the abundance of the species in the target. In another aspect of the invention, electromagnetic processes occuring in the target as the photon beam passes through the target, in particular, Compton scattering and pair production, are detected to create three-dimensional images of the spatial distribution of the density and the atomic number or charge of the target. All four detection schemes of the invention are compatible and can be used individually or in combination to increase detectability of species in various situations.
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Church Craig E.
Massachusetts Institute of Technology
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