Material identification using x-rays
First Claim
1. A method of detecting the mean atomic number of a mass of material within a container comprising the steps of:
- (a) subjecting the material to high energy X-rays and determining the mean number NA of X-rays transmitted through a region thereof,(b) separately and simultaneously subjecting the same region of the material to X-rays having a significantly higher energy than the first mentioned X-rays and determining the mean number NB of the higher energy X-rays transmitted therethrough,(c) computing the value of the ratio NA to NB, and(d) determining from a look-up table and delivering as an output the average atomic number corresponding to the computed value of the NA /NB ratio.
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Accused Products
Abstract
A method and apparatus for detecting the mean atomic number of a mass of material, for example freight in a vehicle comprises: subjecting the mass to X-rays and determining the mean number NA passing therethrough; subjecting the mass to higher energy X-rays and determining the new mean number NB ; and determining the mean atomic number of the mass from look-up tables against the computed ratio NA /NB. The mass, such as a railway wagon, may be scanned by two linear accelerators arranged perpendicular to each other, detector arrays being disposed respectively opposite the accelerators, so that a three dimensional image can be built up of the mass.
277 Citations
32 Claims
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1. A method of detecting the mean atomic number of a mass of material within a container comprising the steps of:
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(a) subjecting the material to high energy X-rays and determining the mean number NA of X-rays transmitted through a region thereof, (b) separately and simultaneously subjecting the same region of the material to X-rays having a significantly higher energy than the first mentioned X-rays and determining the mean number NB of the higher energy X-rays transmitted therethrough, (c) computing the value of the ratio NA to NB, and (d) determining from a look-up table and delivering as an output the average atomic number corresponding to the computed value of the NA /NB ratio. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. An x-ray analysis device for determining the mean atomic number of an object by locating a broad band X-ray source on one side of a testing station and a detector on the other side, comprising:
- a target having X-ray detectors positioned adjacent thereto, one of the detectors being positioned and adapted to receive X-rays scattered by the detector target in a generally rearward direction back towards the source and up to 45°
off the rearward axis and the other detector being positioned and adapted to detect forwardly propagating X-rays scattered off axis typically by more than 30° and
by less than 60°
thereto, due to so-called Compton scatter, each of the X-ray detectors providing signals proportional to the number of X-ray photons incident thereon;
means responsive to the two detector outputs forming a ratio of the number of photons detected by the two detectors and forming a numerical value thereof;
a look-up table containing information pertaining to given numerical ratios for different materials;
means for determining from the look-up table the information corresponding to the numerical ratio obtained from the outputs of the two detectors; and
means for delivering the said information as an output signal. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31)
- a target having X-ray detectors positioned adjacent thereto, one of the detectors being positioned and adapted to receive X-rays scattered by the detector target in a generally rearward direction back towards the source and up to 45°
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32. A method of detecting the mean atomic number of a mass of material within a container comprising the steps of:
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(a) subjecting the material to high energy X-rays on the order of 1 MeV and determining the mean number NA of X-rays transmitted through a region thereof, (b) subjecting the same region of the material to X-rays having a significantly higher energy than the first mentioned X-rays, said higher energy being at least about 5 MeV, and determining the mean number NB of the higher energy X-rays transmitted therethrough, (c) computing the value of the ratio NA to NB, and (d) determining from a look-up table and delivering as an output the average atomic number corresponding to the computed value of the NA /NB ratio.
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Specification