Method of determining object characteristics

FIELD: physics.

SUBSTANCE: characteristics of an object are determined based on mean free path length of penetrating radiation. An incident beam of penetrating radiation is generated, said beam being characterised by direction of propagation and energy distribution. Groups of detector elements are placed in the zone of the penetrating radiation beam in which each detector element is characterised by a field of view. The field of view of each detector element is collimated. Radiation scattered by the group of voxels of the object under investigation is detected, where each voxel is the intersection the field of view of at least one detector element with the direction of propagation of the incident penetrating radiation beam. Attenuation of the scattered penetrating radiation between pairs of voxels is calculated, where each voxel from the said pair corresponds to at least one of two directions of propagation of the incident penetrating radiation beam.

EFFECT: more accurate determination of characteristics of a monitored object.

14 cl, 11 dwg

The technical field to which the invention relates.

This invention relates to methods and systems research object with penetrating radiation, in particular for the inspection of objects using a simultaneous detection of penetrating radiation scattered in different, possibly opposite, directions.

The level of technology

In the period from September 2001 is widely used x-ray computed tomography (CT) for the detection of explosives, hidden in the Luggage of passengers. This method consists in the definition of "CT number" of the objects in the suitcase. The number of CT is essentially a measure of the attenuation of radiation per unit length of x-rays (with a given energy distribution in the material comprising each object. The number of CT can then be used to identify the material. The number of CT scans used in this description and appended claims, refers to the measure x-ray attenuation, conventionally adopted in relation to the attenuation of radiation in the water.

For organic materials, the number of CT is essentially a measure of the density of electrons in the material, which in turn is proportional to the mass density. Thus, the system x-ray computed tomography is capable of measuring bulk density improvement is ü hidden materials. Mass density of explosives is approximately in the range of 1.2 to 1.7 grams per cubic centimeter (g/cm³). As systems are x-ray computed tomography reproduce the contents of the container in three dimensions, we also determined the volume of each of the hidden object. Combining this information with the density obtained the mass of each object. By screening a minimum size bulk density of 1.2-1.7 g/cm³threats to the transportation of explosives can be automatically detected and powered audible alarm.

The disadvantages of systems x-ray computed tomography are size and cost. Both the size and the cost mainly due to the presence of a rapidly rotating platforms on which place the x-ray source and the detector matrix.

In U.S. patent No. 5930326 called "tomography System based on side-scattered radiation" describes a method of detecting radiation scanning of acute x-ray beam scattered at 90 degrees, one or more array segment collimated detector arrays. The distribution of radiation intensity of side scatter is then used to display (three-dimensional) organic objects that are hidden in the container. The above patent is included in Yes is a great description as a reference.

Disclosure of inventions

The preferred implementation of the present invention includes methods and systems determine the characteristics of objects based on the determination of the average free path length of the penetrating radiation based on the pairwise analysis of voxels.

This method in various embodiments of the invention may include:

the formation of the incident beam of penetrating radiation characterized by the direction of propagation and distribution of energy;

the placement of groups of detector elements near the beam of penetrating radiation, each of the detector elements is characterized by a field of view;

callmerobbie field of view of each detector element;

changing the direction of propagation of the incident beam of penetrating radiation so that it is sequentially irradiated test object at the point of falling;

detection of radiation scattered by the voxels of the scanned object, and the voxels are defined as the intersection of the direction of propagation of the incident beam with a field of view of the detector element;

the calculation of the attenuation of penetrating radiation between pairs of voxels, the fall of the incident beam.

According to further variants of implementation of the present invention, the detection of radiation may include dete the aims of the individual components of the energy scattered penetrating radiation incident beam. In addition to changing the direction of propagation of the incident beam can scan the incident beam in generally perpendicular to the propagation direction so that the incident beam is irradiated test object at the point of incidence. The attenuation of penetrating radiation can be represented as a function of position within the inspected object.

According to another possible alternative embodiment of the invention the placement of the sensors next to the incident beam of penetrating radiation may include the placement of detector arrays for detecting scattered radiation in directions component of the vector which is mainly parallel to the direction of propagation of the incident beam of penetrating radiation, or to enable the placement of the sensors on the plane, generally perpendicular to the beam of penetrating radiation.

The calculation of the attenuation of penetrating radiation may include determination of the average free path length of the scattered emission as a function of position within the inspected object. Callmerobbie may include limiting the field of view of each detector direction, including a specific range of angles relative to the direction of propagation of the incident beam.

According to further variants of the implementation of izopet is of the above-described method may further include changing the energy distribution of the incident beam of penetrating radiation. In addition, the scanning may include the scanning aperture in the x-ray tube, as well as the activation of the discrete elements of the source matrix. The material can be identified as a threat substance based on a comparison of the average free path length calculated in accordance with the above ideas, table of measured values. The correctness of the calculated attenuation of radiation can be confirmed by re-probing bills detector elements with opposite fields of view.

Brief description of drawings

Figure 1 presents the principle of operation of the system tomography-based determination of the attenuation of the scattered radiation according to the options of implementing the present invention.

Figure 2 presents the geometry in which the obstructing object is blocking one of the incident beam system shown in figure 1.

Figure 3 schematically shows the preferred implementation of the present invention, in which the detector elements opposite detector arrays detects the lateral scattering of the penetrating radiation of the scanned object.

Figure 4 schematically presents a scenario in which two surrounding an object located between the monitored object and the upper and lower elements of the detector matrix for the detective who by side scatter.

Figure 5 and 6 present system scan baggage and small packets according to the options of implementing the present invention.

Figure 7 presents a system in which the scattered radiation detectors are located on one side of the scanned object as in the movable monitoring device.

On Fig shows a variant embodiment of the invention, in which the radiation source is located above the inspected object, and a detector matrix for detecting scattered radiation from each side of the inspected object.

Figure 9 and 10 shows embodiments of the present invention to inspect passengers, in which the source of penetrating radiation is respectively above (or below) the scanned object in the horizontal attitude of the plane.

Figure 11 presents a handheld device to scan, including two collimated x-ray detector and the source, emitting a lot of scanning of x-rays, according to a variant implementation of the present invention.

The implementation of the invention

The present invention is based on the ideas set forth in U.S. patent No. 5930326 describing a simple and effective method is more accurate measurements of density hidden organic objects. According to a preferred variant implementation of this is about the invention of the two detector matrix detects the distribution of lateral scattering. This method provides full three-dimensional reproduction of organic objects in the container, and a more accurate determination of density than could be obtained using the methods described in U.S. patent No. 5930326.

With reference to Figure 1 below describes the tomography-based determination of the attenuation of the scattered radiation, which consists mainly in the analysis of lateral attenuation of the scattered radiation of the scanning beam of x-rays as it is deepening in the test object.

It should be noted that although in the present description as the incident beam 10 of penetrating radiation is an x-ray beam, it should be understood that any beam of penetrating radiation covered by the invention, i.e. a beam of x-rays, gamma rays, etc.

Figure 1 is a scanning x-ray beam 10 is emitted to the left and passes through the block 12 of the organic material. At time t₁and t₂the beam 10 of x-rays is characterized respectively by the intensity of I₁and I₂and the actual position are indicated by the numerals 10 and 11 in figure 1. Segment the detector array 14 for detecting scattering is placed over the organic material and each detector element 15 of the detector matrix 14 collimated thus, th is would be his field of view 16 for detecting the scattered radiation is directly under him or perpendicular to the direction of propagation of the incident beam 10. One of the detector elements 15 are selected. At time t₁and t₂it detects scattered radiation, respectively, of the volume elements 17 and 18 contained in the organic material 12. The intensity ratio S₁and S₂scattered radiation that is defined in the i-th detector element at time t₁and t₂, is defined by the following equation:

where A(Λ) is the attenuation coefficient, characterizing the scattered radiation in organic material at a distance ΔI between the two beams;

Λ is the average free path length of the scattered radiation in organic material.

The attenuation coefficient A(Λ) is defined:

Thanks to its simple geometry presented in figure 1, you can see that the intensity of the incident beam of x-rays in two voxels equal to (I₁=I₂). In this case, equation (1) has the form

and, thus, weakening (and, consequently, the average free path length of the radiation in organic material) can be determined from the relationship S₂/S₁. Since the average free path length for organic materials is proportional to the mass density can be calculated density of the material.

However, in practice, integration is zywnosci I ₁and I₂generally not equal. They could be equal, if, for example, organic material 12 is rotated relative to the beams 10 and 11 or interfering object 20 blocked one of the incident beams, as shown in figure 2.

Consider the case presented in figure 2. Because I₁≠I₂then equation (1) indicates that A(Λ)≠S₂/S₁. In fact, as I₁and I₂unknown, the attenuation cannot be determined from the equation (1).

The present invention provides a previously missing solution to this problem, as described below, with reference to Figure 3. Preferred embodiments of the present invention include two matrices for the detection of side-scattered radiation: upper matrix U for the detection of side-scattered radiation and the lower matrix L for the detection of side-scattered radiation. It should, of course, be understood that the indication on the upper and lower direction is randomly selected and the detector matrix can be placed in any covered by this invention directions component of the vector which is mainly parallel to the direction of propagation of the incident beam of penetrating radiation. Thus, the upper detector matrix U and the lower detector matrix L, shown in Figure 3, can the same USP is Hom to be called, for example, the left and right matrices.

The intensity ratio of scattered radiation in the selected detector element of the upper detector matrix at time t₁and t₂is given by the following equation:

Similarly, the ratio of the signals at the bottom of the detector matrix is given by the equation:

Multiply equations 4 and 5, we obtain

You can see that now the expression for the attenuation coefficient in equation (6) is free from unknown intensities I₁and I₂beam and does not depend on the provisions of the organic material 12 in a suitcase or on the number of surrounding objects 20, which may impede the passage of the incident beam. The only requirement is that a sufficient intensity of the two incident beams and enough free path for the passage of scattered radiation for each of the two detector arrays.

Another important aspect of this invention is the fact that you use only the relationship of the intensities of the scattered radiation (for example, only the relationship of L₁/L₂and U₂/U₁present in equation (6) and hence the method of calculating the attenuation coefficient, presented in equation (6), does not depend on any surrounding object is 20, which can reduce scattered radiation before it reaches one or both detector arrays. This is shown schematically in figure 4, where two of the surrounding object 40 and 42 are located between the monitored organic material 12 and the upper detector matrix U and the lower detector matrix L. In this scenario, the attenuation of radiation in the organic unit 12 (and therefore density) can be determined regardless of the surrounding noise, obstructing the path as the incident beam and scattered radiation.

Equations (4) and (5) based on the assumption that voxels on the beams 1 and 2, which is the source of scattered radiation, are basically the same distance from each of the detector arrays. In fact, in the General case, the voxel beam 1 will be at a different distance from each of the detector arrays than the voxel beam 2. In order to correct these differences, equations (4) and (5) are the following:

where, for example, dΩ_L1- the solid angle of the detector element of the lower matrix for the bill on the beam 1.

Amended by the solid angle of equation (6) is reduced to the following form:

Basically, the coefficient dΩ_L2dΩ_U1/(dΩ_{L1 /dΩU2)that corrects for the solid angle, is quite small and its value is usually close to one.}

Measurement of attenuation (and hence density) hidden organic materials on the basis of the equation (9) can be performed in any system using a sharp x-ray beams and comprising two segmental matrix for detection of scattered radiation. Figure 5 and 6 present two systems for baggage scanning and small packets in which the source of penetrating radiation includes, respectively, the ring 50 with aperture scanning near the x-ray tube 51 and the x-ray source 52 on the basis of carbon nanotubes, comprising discrete elements that can be selectively activated, as described, for example, in pending application U.S. No. 11/737,317, filed on April 19, 2007, and incorporated into this description by reference. And in fact, in another case, one uses the left detector matrix 54 and the right detector matrix 56, as described above. In addition, between the source of the study and the scanned object can be accommodated matrix inverse scattering 58, to provide additional pictures or information about the characteristics of the material.

Alternatively, the method of the invention can also be used to test hidden in the container Mat is rials, when difficult access to the container (because of the location of detector arrays). Such a scheme is presented on Fig.7, where the collimated detector matrix 60 is placed at an angle in the direction opposite the x-ray source 61. In the embodiment of the invention, presented in Fig.7, as an example, the x-ray source 61 and detector matrix 60 are fixed on the movable system for forming the image of the backscattered x-ray radiation, for example on the platform 62 that is used to control vehicles 64.

On Fig presents an alternative embodiment of the invention for scanning vehicles or containers on top. In this case, the detectors 70 and 72 are placed on the sides of the system (which can be, for example, on the portal 74 or platform), while the x-ray source 76 is placed over the controlled object 78.

In figures 9 and 10 presents two alternatives for implementing the invention for the detection of contraband organic materials carried by passengers in suitcases or backpacks, or hidden under clothing. Figure 9 shows a variant embodiment of the invention, in which the passenger 80 is scanned by a beam of x-rays 82, falling from above. The x-ray beam 82 can also be set in p is the situation, provides scanning of the passenger from the bottom. Figure 10 schematically shows a variant, in top view, scanning the passenger 80 x-ray beam 82, which remains mainly in the horizontal plane. In each case, the detector matrix 72 are placed on both sides of the passenger 80.

Figure 11 presents an alternative embodiment of the invention, which uses a handheld device to check. In this embodiment of the invention, the device 90 includes two separate collimated detector element 94 x-ray radiation, each of which includes a detector 92 and 93. In addition, the device 90 includes 95 source emitting the scanning beams 96 and 97 of x-rays, as described above, or, alternatively, it can emit, as shown in the figure, two fixed beam, and only one of them can be active at a given point in time. The beams 96 and 97 can be activated sequentially by using, for example, valves. The emitted beams are interleaved in time, allowing you to determine the attenuation coefficient hidden organic materials 98, in accordance with equation (6).

The expression for the attenuation coefficient shown in equation (6)

,

allows you to measure the average length Λ of the free mileage the scattered radiation a separate part of the hidden organic material. By changing the energy scan sharp beam average length of Λ mean free path in the material can be measured for several different ranges of energies of x-rays. Based on the analysis of changes in mean length Λ mean free path in the material, depending on the energy of x-rays in addition to measuring the density of the material to determine the approximate effective atomic number Z of the material. For example, compared to materials with a lower Z-average free path length for materials with a higher Z will decrease faster with decreasing photon energy, due to the strong dependence of the photoelectric effect (absorbs x-rays) from the effective atomic number of the material. Cross section of photoelectric absorption increases rapidly with the increase of the effective atomic number of the material and with decreasing energy x-ray photons.

Alternatively, instead of changing energy scanning x-ray beam can be used are sensitive to changes in energy detector elements in the detector matrix. As an example of the use of CdZnTe detectors that measure the energy of each x-ray detector beam. Then energy x-ray detector Lou who she can be excluded and the calculated attenuation coefficient, asked by equation (6), for several different ranges of energies of x-rays, which allows to measure both the density and effective atomic number. Using these two measurements, you can more accurately identify the material constituting the organic object, to increase the speed of detection and reduce false alarm rate. It should be noted that each of the above alternative embodiments of the invention may optionally include deenergizes mode.

According to further variants of the invention, the material can be identified as a threat substance based on a comparison of the average free path length calculated in accordance with the above ideas, table of measured values. The correctness of the calculated attenuation of radiation can be confirmed by re-probing bills detector elements with opposite fields of view.

All of the above options should be considered only as examples of the invention. Specialist ordinary skill in the relevant field of technology it is obvious that various variations and modifications without leaving the scope of the present invention according to the attached claims.

1. The way to determine the population characteristics of the object on the basis of the average free path length of the penetrating radiation, including the formation of the incident beam of penetrating radiation characterized by the direction of propagation and distribution of energy, placing a group of detector elements in the area of the beam of penetrating radiation, in which each of the detector elements is characterized by a field of view, callmerobbie field of view of each detector element, detection of radiation scattered by a group of voxels of the scanned object, in which each voxel is the intersection of the field of view of at least one of the detector elements with the direction of propagation of the incident beam of penetrating radiation, and calculating the attenuation of the scattered penetrating radiation between pairs of voxels, where each voxel from the specified pair corresponds to at least one of the two directions of propagation of the incident beam of penetrating radiation.

2. The method according to claim 1, which further changes the propagation direction of the incident beam of penetrating radiation, sequentially irradiating the test object at the point of falling.

3. The method according to claim 1, in which the radiation detection includes detection of the individual components of the energy scattered penetrating radiation incident beam.

4. The method according to claim 1, which further scan of the incident beam in the direction perpendicular to the direction of its propagation through the irradiation of the incident beam of the inspected object at the point of falling.

5. The method according to claim 1, which further represent the attenuation of penetrating radiation through the provisions of the inspected object.

6. The method according to claim 1, in which the placement of the sensors in the area of the incident beam of penetrating radiation includes the placement of detector arrays scattered radiation in directions component of the vector which is parallel to the direction of propagation of the incident beam.

7. The method according to claim 1, in which the placement of the sensors next to the incident beam of penetrating radiation includes the placement of the sensors on the plane perpendicular to the beam of penetrating radiation.

8. The method according to claim 1, in which the calculation of the attenuation of penetrating radiation includes determining the average free path length of the scattered radiation by the position of the inspected object.

9. The method according to claim 1, in which callmerobbie involves limiting the field of view of each detector element in a direction that includes a specific range of angles relative to the direction of propagation of the incident beam.

10. The method according to claim 1, which further modify the energy distribution of the incident beam of penetrating radiation.

11. The method according to claim 1, which includes the scanning aperture relative to the x-ray tube.

12. The method according to claim 1, wherein the scanning includes Akti is Italy discrete elements of the matrix of emitters.

13. The method according to claim 1, which further identify the material as a threat substance by comparing the average free path length with the table of measured values.

14. The method according to claim 1, which further confirm the correctness of the calculation of attenuation through re-sensing waxes detector elements with opposite fields of view.