RU2497104C1 - X-ray inspection system - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: X-ray inspection system employs one source of fan-shaped X-ray beams, which can move on an arc whose length is equal to a quarter circle, with a varying step in the range of 0°…90°. Said beam irradiates an inspected object moving at constant speed. After irradiation, radiation passing through the inspected object is detected, followed by conversion of said signals to digital codes which are equivalent to flat images of the inspected object obtained at different angles, storing said images, computer processing and displaying flat or three-dimensional images of the inspected object on a monitor screen. Radiation passing through the inspected object is detected using a detector line in form of part of a circle with radius equal to the radius of the arc on which the radiation source moves.

EFFECT: reduced distortion of shadow X-ray images of inspected objects.

3 dwg

Description

The invention relates to the field of technical means of non-contact x-ray monitoring of objects and can be used to detect illegal hidden investments in them, for example, drugs, weapons, etc., at customs and police checkpoints.

A known method of scanning controlled objects with a fan-shaped beam of x-rays [1, p. 43-48]. This method has a very high control performance, provides a simple way to record X-ray images in digital form, provides maximum radiation safety for people and controlled objects, allows you to inspect bulky goods and vehicles, and also has high resolution and contrast sensitivity.

Devices that implement this method [1, p.142-147] and [2, 3, 4] include a conveyor system that provides uniform movement of the control object (OK) relative to one radiation source, a special diaphragm (collimator) for forming a fan-shaped beam, a detector line for recording the X-ray transmitted through the object, as well as electronic equipment for converting the X-ray image into a digital code and for presenting the image of the object on the monitor screen. Such complexes are called single-projection and their significant drawback is the receipt of a two-dimensional (flat) x-ray image of the controlled object. This drawback does not allow the operator with a high probability of detecting (recognizing) illegal hidden investments in OK, which can lead to the passage of contraband.

The device [1, p. 48-50], which also implements a scanning method, includes two sources of x-ray radiation with corresponding detector arrays. The radiation sources for the greatest effect are located relative to each other at an angle of 90 °. This arrangement of radiation sources increases the probability of recognition of objects located in controlled objects, up to 60%, which is an important advantage. The main disadvantage of this two-projection device is the possibility of obtaining although two, but still flat X-ray images of the OK and its contents.

The closest in technical solution to the proposed invention is an X-ray inspection complex, made by the method of obtaining a three-dimensional image in an X-ray inspection complexes [5].

In the prototype, instead of two, one X-ray source is used, moving inside the inspection tunnel along a rigid arc with a variable fixed pitch from 0 ° to 90 °. The control object in the inspection tunnel moves uniformly, linearly and reversely relative to the x-ray source. The relative position of the arc and the control object provides an image of objects from the side at 0 ° and from above - at 90 °. The complex control equipment makes it possible to generate in digital codes a series of N flat images taken at different angles of the radiation source relative to the OK through a step selected by the operator. The received digital codes of a series of images are programmed to obtain on the monitor screen a three-dimensional (three-dimensional) image of the OK itself and the objects in it. In the inspection complex opposite the arc, a detector line in the form of a right angle is fixed on the bottom and one side wall of the tunnel. In the center of the arc (circle) is a conveyor system with an OK located on it. The arc length is a quarter of a circle, which allows the x-ray source to move from 0 ° to 90 °. The length of the sides of the detector line and its location in the inspection tunnel are such that it fixes a fan X-ray beam in any position of the radiation source on the arc.

The disadvantage of the prototype is that on the generated x-ray images in some cases there may be image distortion, which can lead to incorrect operator analysis of the obtained x-ray information.

This is due to the fact that the angles of incidence of X-rays β on the receiving detectors of the “L” -shaped line at different positions of the radiation source on the arc will differ from each other and, in some cases, will be significantly less than 90 °. If the angle β≈90 °, then almost all the radiation falls on the detectors of the line and their output signals will be maximum. As angle β decreases, the intensity of the x-ray incident on the detector and, accordingly, the number of photon particles reaching the detectors will decrease, as a result of which the detector output signal will also become less than the maximum value. A decrease in the radiation intensity is also possible when the X-ray beam is attenuated by corresponding objects with an increased density of the material. It is obvious that at β << 90 ° the output signal of individual detectors will be deliberately false and false shaded points will appear on the screen. As a result, some false region of the x-ray image may be formed from such false points on the monitor screen. And this, in turn, will somewhat distort the real shadow picture of the X-ray image of the control object, which can lead to incorrect analysis by the operator of the received image and to the omission of hidden illegal investments by him.

The aforesaid can be illustrated in FIG. 1, which shows a fragment of the prototype complex scheme (digital notation taken from [5]). Indeed, in positions 1, i and n of the radiation source 5, the angles of incidence of the rays β ₁ , β ₂ , and β _3, respectively, will differ significantly from each other.

In single-projection and two-projection complexes, the radiation sources are always stationary and therefore the influence of the angles of incidence of the rays on the value of the output signal of the detectors is taken into account by software.

Let us consider in more detail the question of the influence of the angle at which x-ray radiation falls on the surface of the detector line on the value of its output signal.

It is known that at high energies, electromagnetic radiation should be considered as a combination of particles - quanta of the electromagnetic field or photons [6, p.24]. The total amount of energy transferred by radiation is determined by the energy of individual photons, as well as their quantity.

It is assumed that the characteristics of the radiation source during operation remain fixed. Therefore, the energy of x-rays, on average, remains constant. This means that the number and energy of photons also remain approximately the same.

Currently, inspection installations use mainly semiconductor detectors. The main mechanisms of the interaction of photons with the semiconductor material of the detector are the photoelectric effect and the Compton effect.

As a result of the photoelectric effect, the photon is completely absorbed, transferring its energy to the electron released from the atom of the substance. In Compton scattering of photons, weakly bound electrons of atoms of the substance of the detector are released from the atoms, while the energy of the scattered photons decreases. One quantum of x-ray radiation (photon) is able to produce a large number of electrons. In both cases, the formation of free electrons occurs, which are "carried away" from the detection region under the action of a voltage applied to this region. The current of released electrons is the response of the detector to x-rays, i.e. output signal.

From the above X-ray detection mechanism, it becomes clear that the value of the detector output signal directly depends on the number of photons incident on the detector [7, p.372], as well as on their energy, which affects the number of electrons released in the semiconductor material of the detector by a single quantum radiation during Compton interaction. When x-ray radiation passes through the scanned control object, its scattering and partial absorption occur. In this case, the number of photons of a given radiation reaching the detector surface will be less, and their energy will be lower. Accordingly, the number of free electrons formed in the detector will also be less, and the detector response (output signal) will be weaker.

For clarity of further discussion, we consider the propagation of x-ray radiation in the absence of an object of control. This excludes the effect of OK on the photon energies reaching the detector. The constancy of the average self-energy of photons eliminates significant deviations in the value of the detector output signal associated with the transfer of energy to electrons. We neglect the attenuation of x-rays in the air. Then the magnitude of the detector output signal will depend only on the number of photons reaching its surface. Therefore, when considering issues related to energy transfer, one can go from the radiation intensity to the flux of photon particles. Given the invariance of the characteristics of the radiation source, we assume that the average value of the flux density of x-ray radiation at a fixed distance from the detector line will also be constant.

The density of this emitted flux φ is equal to the number of photon particles dN passing through a unit area dS located perpendicular to the direction of propagation of these particles per unit time dt and is determined by the characteristics of the radiation source:

, $$\varphi =\frac{dN}{dSdt}$$

,

where from

dN = φdSdt.

The number of photons arriving at the detector will be equal to:

dN '= φdS'dt,

where dS 'is the projection of a single site dS on the surface of the detector (figure 2).

The figure shows that

dS '= dS cosα,

и $$\overrightarrow{n}\text{'}$$

, проведенными к единичным поверхностям dS и dS' соответственно.where α is the angle between normals $$\overrightarrow{n}$$

and $$\overrightarrow{n}\text{'}\text{'}$$

drawn to unit surfaces dS and dS ', respectively.

The angles α and β shown in figures 1 and 2 are interconnected by the simplest expression: α = 90 ° -β.

From here, we can estimate the ratio of the number of photon particles reaching the detector when the beam propagation direction is different from the detector perpendicular to the surface of the detector to the number of photons reaching the detector when the beam is normally incident on its surface:

. $$\frac{dN\text{'}\text{'}}{dN}=\frac{\varphi dS\cos \alpha }{\varphi dS}=\cos \alpha$$

.

Finally, you can write:

dN '= cosαdN.

The last expression determines the dependence of the number of photons reaching the detector surface on the angle at which x-ray radiation comes to the surface of this detector.

This dependence shows that the value of the detector output signal decreases with increasing angle α (or decreasing angle β), which is equivalent to the presence of some object of control in the scanning zone. In addition, the presence of such a dependence complicates the possible computer processing of the resulting image due to the need to take into account the above distortions.

In known designs of X-ray installations, two reasons can be distinguished for which the direction of the radiation coming to the detector differs from normal to the detector surface:

- fan-shaped divergence of the x-ray beam at the exit of the collimator;

- “L” -shaped form of the detector line.

Fan-shaped x-ray beam is a generally accepted technical solution for scanning large-sized OKs. One reason remains - the “L” -shaped form of the detector line.

The aim of the invention is to reduce the distortion of shadow x-ray images of objects of control, which significantly increases the likelihood of the operator conducting the correct analysis of the resulting visual

information.

This goal is achieved by the fact that, along with an inspection tunnel, inside of which there is an x-ray source with a collimator, moving with a reversible electric drive along a rigid guide in the form of an arc with a length of a quarter of a circle with a fixed variable pitch, a conveyor system with an object of control and two restrictive light barriers located in the center of the arc, a detector ruler located opposite the arc on the other side of the conveyor system and allowing reg X-ray radiation in any position of the source, control unit, analog-to-digital converter, program information processing unit, control panel and operator, in the inspection X-ray complex, the rigid guide is made in the form of a circle, on the inside of which there is a detector ruler, repeating the shape of a circle, opposite a quarter of the arc along which the radiation source with the collimator moves, on the other hand from the conveyor system, and allowing to register X-ray radiation source at any position.

The principle of operation of the inspection x-ray complex is illustrated in figure 3, which presents its electrical structural diagram.

The complex consists of a security tunnel 1 of a rectangular shape. Inside the tunnel is a rigid guide 2 in the shape of a circle. A detector line 3 is fixed on the inner side of the guide in the shape of a repeating part of a circle. Opposite the detector line, an X-ray source with a collimator (slotted diaphragm) 4 is installed on the guide, which, with the help of a reversible electric drive 5, can move along an arc in the range from 0 ° to 90 ° with a fixed varying step. In the center of the guide (circle) is a conveyor system 6 with a control object 7 located on it. The conveyor system is driven by an electric reversible drive, which is not shown separately in the figure. The radiation source moves in an arc so that at an angle of 0 ° it is located strictly on the side of the control object, and at an angle of 90 ° it is strictly on top of the controlled object. The length of the detector line and its location on the rail is such that it should fix the x-ray fan in any position of the radiation source 4 on the rail 2. The conveyor system with the control object is limited by two light barriers 8 from two sides of the OK, the signal from which comes to the control unit (BU) 9 and to turn on (off) the x-ray source 4. The control unit also receives commands from the control panel (PU) (computer keyboard) 10, with which the operator interacts p 11. In turn, the control unit 9 is connected with a reversible electric drive 5 of the radiation source and an electric reversible drive of the conveyor system 6. The final positions of the drive 5 on the guide 2 are recorded, for example, by means of end contacts, and information about this also goes to the control unit 9 . In addition, block 9 gives commands to start and end the operation of the analog-to-digital converter (ADC) 12 and the program information processing unit (BPOI) 13. Analog signals are sent to the ADC 12 from detector line 3 for converting them into a digital code, and the ADC output is connected to the BPOI information input. The results of the BPOI are displayed on the screen of the monitor 14, with which the operator 11 analyzes the received images.

The detector line 3 consists of many elementary x-ray detectors and serves to register the x-ray radiation transmitted through the monitoring object and convert it into an analog electrical signal.

The X-ray source is turned on only with direct transmission of OK 7. The signals for switching the source on and off come from the light barrier system 8. They are mounted slightly above the conveyor belt. When the tape moves, an OK installed on it sequentially crosses the rays of light barriers, thus ensuring the "logic of work" of the inspection complex: turning on and off the radiation source, beginning and end of reading the detector line, reverse conveyor, etc.

In the initial position, the x-ray source with the slit diaphragm 4 is in position "1", i.e. strictly on the side of OK. The control object itself is located on one side of the plane of distribution of fan beams behind the rays of light barriers 8.

The complex works as follows.

At the command of the operator with the PU 10 through the control unit 9, a command is received for the electric drive of the conveyor 6 to start the uniform movement of the object with a low constant speed. When the control object crosses the first beam of the light barrier 8, the x-ray source 4 is turned on and the scanning process begins. A fan-shaped beam hits the control object and crosses it along the line. A beam passing through an object, carrying information about the absorption of x-rays by the object along this line, falls on the detector line. The width of the fan-shaped beam incident on the detector line is usually 2 ... 3 mm. The conversion of the x-ray image into an analog electrical signal at all detectors occurs simultaneously. On command from the control unit, the analog signals are subsequently converted by the ADC 12 into digital codes, which are received by the BPOI 13. The received codes are adequate to the intensity of the fan-shaped x-ray radiation after it crosses the object of control, i.e. in BPOI, one column of the shadow image of the object is formed in the codes.

With further movement of the OK, the following sections (lines) are similarly scanned and a two-dimensional matrix is formed in the BPOI corresponding to the image of the entire illuminated object. This image in codes, obtained at an angle of 0 °, is stored in the BPOI memory.

After the OK leaves the zone of action of the second beam of the light barrier 8, they generate commands to turn off the radiation source 4 and to the control unit 9. Unit 9 sends a command to the electric drive 5 and the conveyor electric drive 6. In this case: the drive 5 moves the radiation source 4 upward along the guide 2 to some step preselected by the operator (Ш ₁ ), and the conveyor electric drive is switched on to reverse, as a result of which the OK starts moving in the opposite direction.

When the OK crosses the first (but on the other hand) beam of the light barrier, the radiation source 4 is switched back on and the scanning process begins, but already at the angle of the radiation source with respect to the OK (0 ° + W ₁ ). Everything goes the same as described above. As a result in memory

BPOI is recorded in codes the second flat image OK, obtained at an angle (0 ° + W ₁ ).

After the OK leaves the zone of action of the second beam of the light barrier 8, they similarly generate commands to turn off the source 4 and to the control unit 9. In this case, the drive 5 moves the source 4 along the arc by one more step Ш ₁ , and the conveyor electric drive is switched back on. The object of control begins to move in the other direction.

When OK crosses the first beam of the light barrier, the X-ray source is switched on again and the scanning process begins, but already at an angle (0 ° + 2Sh ₁ ). As a result, the third OK image obtained at an angle (0 ° + 2SH ₁ ) is recorded in the codes of the BPOI.

Then everything happens the same way up to the angle of the radiation source, equal to 90 °; each time a new angle differs from the previous one step Ш ₁ . The signal in the control unit about the radiation source reaching its highest position (angle 90 °) can be formed by the corresponding end contact.

After all N flat OK images are written to the memory of the BPOI, the process of converting all flat images into one three-dimensional one begins with a command from the control unit. After receiving this three-dimensional image, information from the BPOI is displayed on the monitor screen 14 and the operator begins to analyze it. It is known that in this case, a three-dimensional image of an object can be rotated on the screen and a convenient angle for analysis can be chosen.

When scanning the second control object, everything happens the same way. The difference is that the radiation source is now moving from top to bottom. That is why the electric drive 5 is reversible. Flat images in codes will be obtained:

- the first at an angle of 90 °;

- the second at an angle (90 ° -W ₁ );

- the third at an angle (90 ° -2Sh ₁ ) and so on to an angle of 0 °.

Scanning of the third object of control is similar to scanning of the first object, etc.

When scanning OK at different angles (in such a wide range), x-ray radiation must pass not only through the object itself, but also through the conveyor structure elements in order to get to the line detectors. The conveyor in these places should not have metal parts that will noticeably absorb x-rays. In places of intersection with the conveyor beam, theoretically, there should only be a conveyor belt, which will not introduce distortions into the x-ray image. In reality, metal elements of the conveyor structure may occur on the path of the x-ray beam. However, in this case, the background from the structural elements for each fixed position of the radiation source will be constant; it can be converted and written in digital form into memory without being on the conveyor belt OK. When scanning an object, the background recorded for each position can be subtracted from digitally obtained real OK images. This will lead to the fact that finally digital flat images of OK will be recorded in the memory of the BPOI without any background.

It is known that the performance of the inspection complex depends on the time the image of the control object is taken and the time the operator analyzes the information. With the described algorithm, the time for obtaining a three-dimensional image of objects will, of course, be longer than the time for obtaining their flat images in known search complexes. However, to speed up the overall process of monitoring objects, i.e. To increase the productivity of this complex, the following ways can be suggested:

1. Initially, the radiation source is set to its initial position (the angle is 0 °), one-projection scanning is performed, and the first flat side image OK is displayed on the monitor screen. If the operator does not have any suspicions, the image analysis process ends here.

2. If the operator had suspicions when analyzing the first lateral flat image, then he transfers the radiation source immediately to its highest position (angle 90 °) from the control panel 10 through the control unit 9, performs a one-projection scan again and the second flat image is displayed on the monitor screen OK image - top view. If in this case the operator has no suspicions, the analysis process also ends there.

3. If the operator has suspicions when analyzing the second flat image, then he can set any angle (convenient for analysis) from the control panel and get the corresponding flat image. If in this case the operator no longer has any suspicions, then the analysis process ends here.

4. If, however, the operator had suspicions during the analysis of the third flat image, then he can scan OK using the algorithm proposed above and get a three-dimensional image of objects in it on the monitor screen. Obviously, it is in this case that the operator is likely to be able to determine the presence (or absence) of illegal hidden investments.

5. You can immediately get a three-dimensional image of OK, using a large step of moving the radiation source. In case of suspicion, the step of moving the radiation source can be made smaller and then the scanning process can be repeated.

6. Modern control equipment can work according to an algorithm that allows to obtain a three-dimensional image of not the entire object of control, but only some part of it, which aroused suspicion among the operator, etc.

The proposed ways to reduce the time of the process of monitoring objects without reducing its quality can also be regarded as the broad functionality of the proposed complex, which allows revealing hidden illegal investments by any methods convenient for the operator.

Thus, using a detector ruler in the form of a part of a circle, the proposed inspection X-ray complex will reduce the distortion of shadow X-ray images and, thereby, increase the likelihood of the operator performing the correct analysis of the received visual information. This complex has great functionality, which generally increases the efficiency of the process of searching for illegal hidden investments in objects of control.

Information sources

1. Koshelev V.E. X-ray methods and technical means of customs control: a training manual. - M .: Binom-Press LLC, 2003.

2. Radiographic installation of the scanning type (options). RF patent for the invention No. 2257639, 2005.

3. Complex radiographic inspection. RF patent for the invention No. 2256905, 2005.

4. X-ray television device. RF patent for the invention No. 2204122, 2003.

5. A method of obtaining a volumetric x-ray image in x-ray inspection complexes. RF patent for the invention No. 2462101, 2011 (prototype).

6. Herod I.E. The quantum physics. Basic laws: textbook. - M.: Laboratory of Basic Knowledge, 2001. - 272 p.

7. Frisch S.E., Timoreva A.V. General Physics Course, Volume III: textbook; under the general. ed. L.I. Orlova, 6th ed. - M .: State. ed. Fizmat. literature, 1961. - 608 p.

Claims (1)

Inspection X-ray complex containing an inspection tunnel, inside of which there is an X-ray source with a collimator, moving with a reversible electric drive along a rigid guide in the form of an arc quarter-circle in length with a fixed variable pitch, a conveyor system with an object of control and two restrictive light barriers located in the center of the arc, and a detector line located opposite the arc on the other side of the conveyor system and allowing registration x-ray radiation in any position of the source, and outside the inspection tunnel there is a control unit associated with an electric drive, conveyor system and light barriers, the first output of the control unit is connected to the first input of the analog-to-digital converter, the second input of which is connected to the outputs of the line detectors, the second the output of the control unit is connected to the first input of the software information processing unit, the second input of which is connected to the output of the analog-to-digital converter, the output of the software The information processing is connected with the monitor input, and the operator interacts with the monitor and the control panel connected to the control unit, characterized in that the rigid guide is made in the form of a circle, on the inside of which there is a detector ruler that repeats the shape of a circle, opposite the quarter of the arc, along which moves the radiation source with a collimator, on the other hand from the conveyor system, and along the length allows you to register x-ray radiation in any position of the source.

Images