JP2006019205A - X-ray generator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray generator capable of accurately controlling X-ray. <P>SOLUTION: The X-ray generator is provided with a table. This table prestores the correlation between a lighting time which is a physical quantity relevant to a lighting condition and the amount of electron beams (emission current). An optimal emission current of this emission current is a value which optimizes electron beam characteristics, for example, a condition in which the diameter of a virtual light source becomes minimum. The optimal emission current I becomes lower as the lighting time becomes longer. The amount of the electron beams according to the lighting time at present is set by reading the correlation from the table. Accordingly, the amount of electron beams can always be accurately and optimally set regardless of the situation of lighting conditions, and an X-ray can be controlled accurately. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an X-ray generator used in an industrial field, a medical field, or the like, and more particularly, to a technique for controlling the amount of an electron beam from an electron source disposed in the X-ray generator.

  The X-ray generator generates X-rays by accelerating an electron beam generated from a cathode (electron source) constituting an electron gun and colliding with a target. The X-ray brightness (luminance) is conventionally controlled by controlling the amount of electron beam (also called “tube current” or “emission current”) generated from the electron gun. In order to control the electron beam amount, the following method is used.

  That is, the electron gun is composed of a cathode (cathode), a Wehnelt electrode, and an anode (anode). In the irradiation direction of the electron beam from the cathode to the target, the above-mentioned Wehnelt electrode and anode are placed between the cathode and the target. They are arranged in order. The anode extracts an electron beam generated from the cathode, and the electron beam is accelerated toward the target by the extraction by the anode. The Wehnelt electrode controls the electron beam quantity of the electron beam from the cathode drawn out by the anode, and the electron beam quantity can be changed by the potential of the Wehnelt electrode.

Conventionally, a filament made of tungsten was used as the cathode, but in recent years, a single crystal formed of lanthanum hexaboride (LaB ₆ ), cerium hexaboride (CeB ₆ ), etc., which has high brightness and is resistant to wear and cut. Or a chip | tip of a sintered compact may be used (for example, refer patent document 1). When the cathode is formed with these chips, an electron beam amount of about 10 times is obtained as compared with the case where the cathode is formed with tungsten. In either case of the filament or the chip, except for the difference in durability against wear and cutting, the life is extended if the cathode is kept on for a long time in order to generate the electron beam. Therefore, the physical quantity related to the lighting condition described above is utilized by utilizing the physical quantity related to the lighting condition, for example, the relation that the cathode is consumed depending on the lighting time, the cathode temperature (that is, the cathode temperature) and the degree of vacuum. Alternatively, the correlation with the material loss related to the lifetime is stored in advance, and the lifetime is assumed based on the actual physical quantity (see, for example, Patent Document 2).
Japanese Patent Laid-Open No. 02-204952 (page 1-3, FIG. 1 to FIG. 4) JP 2003-115398 A (page 3-6, FIGS. 2-4, 7)

  However, by controlling the emission current by operating the Wehnelt electrode, there are cases where X-rays having a desired resolution and brightness cannot be obtained even if the brightness of the X-rays is controlled.

  For example, in order to brighten the X-ray image, setting a large amount of electron beam near the Wehnelt electrode, that is, setting the emission current high, causes the problem that the virtual light source diameter becomes larger than necessary, and setting the emission current extremely low. As a result, there is a problem that the brightness of the original electron source cannot be obtained due to the space charge effect.

  The virtual light source diameter and space charge effect will be specifically described with reference to FIG. FIG. 2A is an explanatory diagram when the virtual light source diameter is small, and FIG. 2B is an explanatory diagram when the virtual light source diameter is large. In FIG. 2, reference numeral 11 denotes a cathode, reference numeral 16 denotes a Wehnelt electrode, reference numeral 17 denotes an anode, reference numeral B denotes an electron beam, and reference numeral φ denotes a virtual light source diameter. As described above, the extraction by the anode 17 accelerates the electron beam B toward the target (not shown in FIG. 2). At this time, if the electric potential of the Wehnelt electrode 16 is too low (the negative value of the electric potential is too large), charges are likely to be accumulated in the vicinity of the cathode 11, and the electron beam B is not drawn out to the anode 17 due to the space charge effect. Becomes lower. In other words, if the emission current is set low, the electron beam B is not extracted to the anode 17 due to the space charge effect. Increasing the electric potential of the Wehnelt electrode 16 (decreasing the negative value of the electric potential) facilitates the extraction of the electron beam B to the anode 17 and increases the emission current as the electric potential of the Wehnelt electrode 16 increases. . The electron beam B is focused by the potential of the Wehnelt electrode 16 and once forms an image near the anode 17. The imaging diameter at this time is referred to as “virtual light source diameter” in this specification.

  If the potential of the Wehnelt electrode 16 is increased so that the space charge effect does not occur, the virtual light source diameter φ is once reduced as shown in FIG. However, if the potential is increased too much, the virtual light source diameter φ increases as shown in FIG. As the virtual light source diameter φ increases, the X-ray source diameter also increases and the resolution of the apparatus decreases. Conversely, when the virtual light source diameter φ is small, the resolution is also improved.

  The behavior of extracting these electron beams greatly depends on the shape of the cathode. Therefore, even if the emission current value (Wernert electrode potential) that minimizes the virtual light source diameter at a certain point in time is set, the virtual light source diameter will not be minimum if the cathode shape changes over time due to lighting. It will end up.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an X-ray generator capable of accurately controlling X-rays.

  In order to solve the above problems, the inventors have obtained the following knowledge. The time-dependent change of the cathode shape due to lighting is estimated from lighting conditions, that is, lighting time, cathode temperature (electron source temperature), and degree of vacuum. Therefore, if the correlation between each cathode shape and the amount of electron beam with which the electron beam characteristics are optimized is stored in advance, the apparatus can always operate in an optimum state.

  In other words, if the electron beam amount is initially set to an optimum value, and the correlation between the physical quantity related to the lighting condition and the optimum electron beam amount is obtained and stored in advance, the optimum value of the electron beam amount can be obtained over time. The optimum value of the amount of electron beam corresponding to the lighting time can be assumed based on the above-described correlation. That is, the electron beam amount can be set to an optimum value over time.

  As an index for setting the electron beam amount to the optimum value, for example, the above-described virtual light source diameter is used. FIG. 3 is a graph schematically showing changes in the virtual light source diameter with respect to the emission current. If the electric potential of the Wehnelt electrode is too low, the space charge effect occurs as described above, resulting in a lower emission current. However, in the range where the space charge effect does not occur, the emission current increases as the electric potential of the Wehnelt electrode increases. Becomes higher. As shown in FIG. 3, the virtual light source diameter φ once decreases when the emission current I increases, and the virtual light source diameter φ increases when it further increases. The emission current I that minimizes the virtual light source diameter φ (or the potential of the Wehnelt electrode 16 corresponding thereto) corresponds to the optimum amount of electron beam. Further, the change of the virtual light source diameter φ with respect to the emission current I with the lighting time changes as shown by the dotted line.

  From the above, it has been found that if the correlation between the lighting conditions and the amount of electron beam that optimizes the device operation is obtained and stored in advance, the amount of electron beam can be set to an optimum value over time.

  The present invention based on such knowledge has the following configuration.

  That is, the invention described in claim 1 is an X-ray generator comprising an electron source that generates an electron beam and a target that generates X-rays by collision of the electron beam from the electron source, An electron beam amount setting means for setting a predetermined value, a lighting control means capable of generating an electron beam amount of a predetermined value by turning on the electron source, and a lighting condition for the electron source lighted by the lighting control means And storage means for storing a correlation between electron beam quantities for optimizing electron beam characteristics based on a history of lighting conditions, and the lighting control means includes a correlation stored in the storage means. Control is performed so that the amount of electron beam is changed to an optimum value over time based on the relationship.

  [Operation / Effect] According to the invention described in claim 1, the storage means stores the physical quantity related to the lighting condition of the electron source and the electron beam quantity that optimizes the electron beam characteristics based on the history of the lighting condition. The correlation is stored in advance. The lighting control means controls to change the electron beam amount to an optimal value with time based on the correlation stored in the storage means. That is, the lighting control unit sets the optimum electron beam amount according to the current lighting time by reading the above-described correlation from the storage unit. As a result, the electron beam amount can always be set accurately and optimally regardless of the lighting conditions, and X-rays can be accurately controlled.

  As an example of the above-described invention, the physical quantity related to the lighting condition is the lighting time, the temperature of the electron source, and the degree of vacuum, and the storage means includes at least one of the lighting time, the temperature of the electron source, and the degree of vacuum. The correlation between the physical quantity and the electron beam quantity is stored (the invention according to claim 2). Note that not all of these physical quantities are necessary, and it is only necessary to know the optimum electron beam quantity from the lighting conditions. Therefore, the electron beam amount may be set by a combination of the lighting time, the temperature of the electron source, and the degree of vacuum.

  In each invention, an example of the electron source is a single crystal or sintered chip formed of lanthanum hexaboride or cerium hexaboride (the invention according to claim 3). Another example of the electron source is a filament formed of tungsten.

  The present specification also discloses an invention relating to the following X-ray imaging apparatus.

  (1) X-ray imaging that includes an X-ray generation unit that generates and irradiates X-rays and an X-ray detection unit that detects the irradiated X-rays, and captures an X-ray image based on the detected X-rays In the apparatus, the X-ray generation means includes an electron source that generates an electron beam, a target that generates X-rays by collision of the electron beam from the electron source, and an electron beam amount that sets the electron beam amount to a predetermined value. Setting means, lighting control means capable of generating an electron beam amount of a predetermined value by turning on the electron source, physical quantities related to the lighting conditions of the electron source turned on by the lighting control means, and the lighting conditions Storage means for storing an electron beam quantity correlation for optimizing the electron beam characteristics based on the history of the light, and the lighting control means determines the electron beam quantity over time based on the correlation stored in the storage means. The best X-ray imaging apparatus and controls to change the value.

  According to the invention described in (1) above, the X-ray detection unit detects the X-rays emitted from the X-ray generation unit, so that an X-ray image is captured based on the detected X-rays. In this X-ray generation means, the storage means stores in advance the correlation between the physical quantity related to the lighting condition of the electron source and the electron beam quantity that optimizes the electron beam characteristics based on the history of the lighting condition. The lighting control means controls to change the electron beam amount to an optimal value with time based on the correlation stored in the storage means. That is, the lighting control unit sets the optimum electron beam amount according to the current lighting time by reading the above-described correlation from the storage unit. As a result, the electron beam amount can always be set accurately and optimally regardless of the lighting conditions, and X-rays can be accurately controlled. Then, a desired controlled X-ray image can be taken with high accuracy.

According to the X-ray generator of the present invention, the storage means stores in advance the correlation between the physical quantity related to the lighting condition of the electron source and the electron beam quantity that optimizes the electron beam characteristics based on the history of the lighting condition. I remember it. The lighting control means controls to change the electron beam amount to an optimal value with time based on the correlation stored in the storage means. That is, the lighting control unit sets the optimum electron beam amount according to the current lighting time by reading the above-described correlation from the storage unit. As a result, the electron beam amount can always be set accurately and optimally regardless of the lighting conditions, and X-rays can be accurately controlled.
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  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view illustrating a configuration of an X-ray tube according to an embodiment.

  An X-ray tube 1 shown in FIG. 1 is used in a representative X-ray imaging apparatus such as an X-ray nondestructive inspection device. The X-ray imaging apparatus uses the X-ray tube 1 and X-rays irradiated from the X-ray tube 1. And an X-ray detector 2 for detection. Examples of the X-ray detector 2 include an image intensifier (II) and a flat panel X-ray detector (FPD). When the X-ray detector 2 detects the X-rays emitted from the X-ray tube 1, an X-ray image is captured based on the detected X-rays. Each component around the controller 32 including the X-ray tube 1 and the controller 32 described later corresponds to the X-ray generator in the present invention, and also corresponds to the X-ray generating means in the present invention. The X-ray detector 2 corresponds to the X-ray detection means in this invention.

The X-ray tube 1 includes a cathode (cathode) 11 that generates an electron beam B, a target 12 that is opposed to the cathode 11 and generates X-rays by collision of the electron beam B from the cathode 11, and the cathode 11 and the target. 12 and two focusing coils 13 for focusing the electron beam B. That is, in this embodiment, the focusing coil 13 is provided in two stages. In the present specification, the focusing coil 13 on the cathode 11 side is referred to as “first focusing coil 13 ₁ ”, and the focusing coil 13 on the target 12 side is referred to as “second focusing coil 13 ₂ ”. If there is no notice in particular, the following explanation will be made by unifying “focusing coil 13”.

In this embodiment, a single crystal or sintered chip formed of lanthanum hexaboride (LaB ₆ ), cerium hexaboride (CeB ₆ ), or the like is used as the cathode 11. This chip is more resistant to wear and cut than a filament made of tungsten. The cathode 11 corresponds to the electron source in the present invention, and the target 12 corresponds to the target in the present invention.

The focusing coil 13 is formed in an annular shape, and an aperture 15 having a diaphragm hole 14 for focusing the electron beam B is disposed at the center thereof. Each focusing coil 13 is connected to a controller 32 via each lens power supply 31 outside the X-ray tube 1, and a current is passed from the lens power supply 31 to the focusing coil 13 to generate a magnetic field. Similar to the focusing lens, the focusing coil 13 focuses the electron beam B. The focusing coil 13 can freely change the focal length of the electron beam B by changing the current passed through it, that is, the excitation intensity. In the present specification, the lens power supply 31 for supplying current to the first focusing coil 13 ₁ is referred to as “first lens power supply 31 ₁ ”, and the lens power supply 31 for supplying current to the second focusing coil 13 ₂ is referred to as “second lens power supply 31. ₂ ”. If there is no notice, the following description will be unified with “lens power supply 31”.

Between the cathode 11 and the first focusing coil 13 ₁ , a Wehnelt electrode 16 and an anode (anode) 17 are arranged in this order in the irradiation direction of the electron beam B from the cathode 11 toward the first focusing coil 13 ₁ . . The anode 17 is normally at ground potential.

  The Wehnelt electrode 16 controls the amount of electron beam B (ie, emission current) of the electron beam B extracted from the cathode 11 by the anode 17, and the amount of electron beam varies depending on the potential of the Wehnelt electrode 16. The anode 17 extracts the electron beam B generated from the cathode 11. The extraction by the anode 17 accelerates the electron beam B toward the target 12. These cathode 11, Wehnelt electrode 16 and anode 17 constitute an electron gun 18. The Wehnelt electrode 16 corresponds to the electron beam amount setting means in this invention.

  An electron gun 18 composed of a cathode 11, a Wehnelt electrode 16 and an anode 17 is housed in a vacuum vessel, and a vacuum gauge 19 for measuring the degree of vacuum is disposed in this vacuum vessel. The degree of vacuum measured by the vacuum gauge 19 is sent to the controller 32.

In addition, between the cathode 11 and the second focusing coil 13 ₂ is provided with deflection coils not shown, for deflecting the electron beam irradiation B. Then, a current is passed through the deflection coil to generate a magnetic field and perform deflection. Distribution設箇plants and the deflection coils, is not particularly restricted but the distribution設個number, if between the cathode 11 and the second focusing coil 13 _2, can be changed according to the irradiation conditions of the electron beam B.

  Next, a specific configuration around the controller 32 will be described. In addition to the lens power source 31 described above, the controller 32 includes an input unit 33, a monitor 34, a memory unit 35, a high voltage power source 36, a cathode power source 37, a Wehnelt power source 38, and a lighting time measuring unit 39. .

  The controller 32 controls each component of the lens power source 31, monitor 34, memory unit 35, high voltage power source 36, cathode power source 37, Wehnelt power source 38 around the controller 32 and the X-ray tube 1. The inputted input data is given to each component around the controller 32 and the X-ray tube 1 via the controller 32. In the present embodiment, the controller 32 always calculates the electron beam amount from the degree of vacuum measured by the vacuum gauge 19 and the lighting time measured by the lighting time measuring unit 39 based on a table 35a of the memory unit 35 described later. An operation to obtain the optimum value is performed. The controller 32 includes a central processing unit (CPU) and the like, and corresponds to the lighting control means in the present invention.

  The input unit 33 includes a pointing device represented by a mouse, a keyboard, a joystick, a trackball, a touch panel, and the like. The monitor 34 displays input data input from the input unit 33 and data transmitted from each component around the controller 32.

The memory unit 35 has a function of writing and storing various data sent via the controller 32 and reading it out as necessary. The memory unit 35 is configured by a storage medium represented by ROM (Read-only Memory), RAM (Random-Access Memory), and the like. In addition, the memory unit 35 includes a table 35 a that stores a table (see the graph of FIG. 5) as a correlation between the lighting conditions and the amount of electron beam (emission current) in the vicinity of the Wehnelt electrode 16. The table indicating the correlation is established under the condition that the emission current becomes the optimum value. The condition for the emission current to be an optimum value is when the virtual light source diameter is at a virtual light source diameter φ _ms (see FIG. 3) at which φ (see FIG. 3) is minimum. The table 35a corresponds to the storage means in this invention.

  The high voltage power supply 36 supplies a high voltage to the cathode power supply 37 and also supplies a high voltage to the Wehnelt power supply 38. The cathode power source 37 applies a negative high voltage to the cathode 11. Then, a current flows through the cathode 11 by applying a voltage from the cathode power source 37, and the cathode 11 is heated and lit to generate the electron beam B. That is, the cathode power source 37 generates the electron beam B from the cathode 11 by turning on the cathode 11 as an electron source.

  The Wehnelt power source 38 applies a high voltage power source having a negative value as the potential of the Wehnelt electrode 16 to the Wehnelt electrode 16. The value of the electron beam amount (emission current) changes depending on the potential of the Wehnelt electrode 16 applied to the Wehnelt electrode 16.

  The controller 32 controls ON / OFF of the lighting of the cathode 11 and setting of the value of the emission current by operating the high voltage power source 36, the cathode power source 37, and the Wehnelt power source 38. The lighting time is determined by turning on / off the cathode 11, and the lighting time is measured by the lighting time measuring unit 39 and sent to the controller 32. Note that the lighting time is obtained by accumulating the lighting time from the start of use of the cathode 11, and the lighting time is measured while being accumulated in the final lighting time that was lighted last time.

  Further, the cathode temperature and the degree of vacuum at the time of lighting are also stored in the table 35a, and the degree of cathode consumption can be estimated from the lighting history. That is, since the cathode shape can be estimated, it is possible to set the electron beam amount at the optimum value at the next lighting.

  Next, the specific contents of the table 35a will be described with reference to the explanatory diagram of FIG. 2 and the graphs of FIGS. FIG. 2A is an explanatory diagram when the virtual light source diameter is small, and FIG. 2B is an explanatory diagram when the virtual light source diameter is large. FIG. 3 is a graph schematically showing a change in the virtual light source diameter with respect to the emission current, FIG. 4 is a graph schematically showing a change in the virtual light source diameter with respect to the lighting time, and FIG. 6 is a graph schematically showing a change in emission current with respect to lighting time.

As described above, if the potential of the Wehnelt electrode 16 is too low, the electron beam B is not extracted to the anode 17 due to the space charge effect, and if the potential of the Wehnelt electrode 16 is increased, the emission current increases accordingly. As shown in FIGS. 2 and 3, if the virtual light source diameter φ is once reduced and the potential of the Wehnelt electrode 16 is further increased, the emission current I increases accordingly. 2 and 3, the virtual light source diameter φ is increased. The emission current I at the virtual light source diameter φ _ms that minimizes the virtual light source diameter φ is the optimum amount of electron beam.

  Specifically, for example, the electron beam spread (emission pattern) when the emission current is changed is obtained in advance, and the electron beam amount when the pattern is not blurred by the space charge effect and the virtual light source diameter φ is minimum is calculated. The optimum value is stored in the memory unit 35. A graph in which the virtual light source diameter φ in the emission pattern is associated with the emission current is the graph of FIG.

  When the cathode 11 is lit for a long time, the tip of the cathode 11 is consumed depending on the lighting time of the cathode 11, the temperature of the cathode 11 (that is, the cathode temperature), and the degree of vacuum, and the shape of the tip changes. As a result, as shown in FIG. 3, the change in the virtual light source diameter φ with respect to the emission current I also changes as shown by the dotted line.

  Therefore, the operation of obtaining the emission pattern when the emission current is changed and storing it in the memory unit 35 is repeated while increasing the lighting time. The graph at this time is the graph of FIG. 4 and FIG. Further, the data obtained at this time is stored in the table 35a as a correlation.

  Note that the virtual light source diameter and emission pattern may be measured for all devices, but data acquired in advance by a specific device may be stored in the table 35a.

  FIG. 4 is a graph in which the lighting time is plotted on the horizontal axis and the virtual light source diameter φ is plotted on the vertical axis in a state where the emission current value that is the optimum value when the lighting time is 0 is fixed. As the lighting time becomes longer, as shown in FIG. 3, the emission current I that is the optimum value shifts to a lower value. However, in the graph of FIG. 4, the value of the emission current I which is the optimum value when the lighting time is set to 0 is fixed, so that the value of the emission current I deviates from the optimum value and can be seen from the optimum emission current. For example, the emission current I having a fixed value is shifted to the higher one. As a result, the virtual light source diameter φ, which is the minimum when the lighting time is 0, becomes larger as the lighting time becomes longer as shown in FIG.

  On the other hand, FIG. 5 is a graph in which the lighting time is plotted on the horizontal axis and the optimum emission current I is plotted on the vertical axis under the conditions when the virtual light source diameter φ is minimized. As described above, when the lighting time becomes longer, the emission current I that is the optimum value shifts to a lower value. Since the value of the emission current I becomes the optimum value is synonymous with the fact that the virtual light source diameter φ is minimized, as shown in FIG. 5, when the virtual light source diameter φ is fixed to the minimum and the lighting time becomes long. The emission current is low. The lighting time in FIG. 5 corresponds to the physical quantity related to the lighting conditions in the present invention, and the emission current I in FIG. 5 corresponds to the electron beam quantity in the present invention. Further, the condition for minimizing the virtual light source diameter φ corresponds to the condition for optimizing the electron beam characteristics in the present invention. 5 is established under the condition that the virtual light source diameter φ is minimum, the relationship between the lighting time and the emission current I shown in the graph of FIG. 5 is a physical quantity related to the lighting condition in the present invention. , And the electron beam quantity correlation that optimizes the electron beam characteristics based on the lighting condition history.

  Thus, since the graph shown in FIG. 5 is stored in the table 35a in advance, the emission current corresponding to the current lighting time measured by the lighting time measuring unit 39 is set using this table. More specifically, the current lighting time is applied to the graph of FIG. 5, and the value I intersected on the graph is the optimum emission current I. Even if the lighting time changes, the controller 32 operates the Wehnelt electrode 16 so as to change the emission current to the solid line on the graph in FIG. 5, that is, to change the electron beam amount to an optimum value with time. .

  The graph of FIG. 5 is a graph under a constant degree of vacuum, but the characteristics of the graph of FIG. 5 change as the degree of vacuum changes. The graph when the degree of vacuum is changed is as shown in FIG. FIG. 6 is a graph schematically showing changes in the optimum emission current with respect to the lighting time when the degree of vacuum is changed.

As shown in FIG. 6, when the degree of vacuum is P ₁ , P ₂ , P ₃ and P ₁ <P ₂ <P ₃ , the emission current I shifts to the lower side as the degree of vacuum increases. The graph of FIG. 6 is also stored in advance in the table 35a. By using this table, the emission current according to the degree of vacuum measured by the vacuum gauge 19 and the current lighting time measured by the lighting time measuring unit 39 is set.

  According to the X-ray generation apparatus including the components around the X-ray tube 1 and the controller 32 configured as described above, the table 35a of the memory unit 35 includes the lighting time, which is a physical quantity related to the lighting conditions, and the electron beam. The correlation of quantity (emission current) is stored in advance (see the graph of FIG. 5). Among these emission currents, the optimum emission current is a value that optimizes the electron beam characteristics, and is obtained based on a history of lighting conditions. Based on the correlation stored in the table 35a, the controller 32 controls to change the electron beam amount to an optimal value over time. That is, the controller 32 sets the optimum electron beam amount according to the current lighting time by reading the above-described correlation from the table 35a. As a result, the amount of electron beam can always be set accurately and optimally regardless of the lighting conditions, and X-rays can be accurately controlled so that, for example, X-rays having a desired luminance can be obtained. be able to.

  In the graph of FIG. 6, the degree of vacuum is listed in addition to the lighting time as a physical quantity related to the lighting condition, and the electron beam amount is set by a combination of the lighting time and the degree of vacuum.

  Further, according to the X-ray imaging apparatus provided with the X-ray tube 1, the X-ray dose can be accurately controlled in the X-ray generation apparatus, and as a result, a desired controlled X-ray image can be accurately captured. it can.

  The present invention is not limited to the above-described embodiment, and can be modified as follows.

  (1) In the above-described embodiments, the X-ray imaging apparatus has been described by taking an industrial apparatus such as a non-destructive inspection apparatus as an example. However, the present invention can also be applied to a medical apparatus such as an X-ray diagnostic apparatus. it can.

  (2) In the embodiment described above, a single crystal or sintered chip that is resistant to wear and cut is used as the electron source, but a filament formed of tungsten may be used.

  (3) In the embodiment described above, the focusing coil 13 is a so-called two-stage type, but it may be three or more stages. Only one stage may be used.

  (4) In the above-described embodiment, there is a correlation between the lighting time and the emission current as shown in the graph of FIG. 5, and a correlation between the lighting time and the degree of vacuum and the emission current as shown in the graph of FIG. However, the present invention is not limited to the correlation shown in FIGS. For example, as shown in FIG. 7, there may be a correlation between the lighting time and the temperature of the cathode 11 (cathode temperature) and the emission current, or a combination of the lighting time, the cathode temperature, and the degree of vacuum. It may be a correlation with the emission current. The temperature of the cathode 11 corresponds to the temperature of the electron source in the present invention.

The cathode temperature may be directly measured by, for example, a pyrometer (radiation thermometer), but may be indirectly converted from the amount of current flowing through the cathode 11. As shown in FIG. 7, assuming that the cathode temperatures are T ₁ , T ₂ , T ₃ and T ₁ <T ₂ <T ₃ , the optimum emission current I shifts to the lower side as the cathode temperature increases. The graph of FIG. 6 may be stored in the table 35a in advance.

  Further, the physical quantity related to the lighting condition is not only the lighting time, cathode temperature and vacuum degree, but also, for example, the diameter L of the front surface of the chip as shown in FIG. 8 and the consumption rate consumed per unit time (material loss related to life). And the like, as long as they are physical quantities related to lighting conditions that are normally used. When the cathode 11 is a chip, the entire chip becomes small as shown by the dotted line when consumed. In the case where the surface irradiated with the electron beam B is the front surface, as shown in FIG. 9, the diameter L of the front surface is also shortened according to the lighting time. FIG. 9 is a graph schematically showing a change in the diameter L of the front surface of the chip with respect to the lighting time.

  (5) The measurement of the lighting time is not limited to the measurement as in the embodiment. For example, a means (for example, an optical sensor) for monitoring the presence / absence of the electron beam B, that is, lighting ON / OFF may be provided, and the lighting time may be set as the lighting time. In this case, since the actual lighting time is measured as the lighting time, the controller 32 gives a lighting command to the high voltage power source 36, but the lighting is not actually performed. The error of the lighting time which arises can be prevented.

  (6) In the above-described embodiment, the setting has been described in which the virtual light source diameter is minimized as the optimum electron beam characteristics. However, the present invention is not limited to this, and may be a condition setting that maximizes the X-ray dose. Regardless, even if the emission current is reduced if the time simply passes, the same result can be obtained as a result.

It is a schematic sectional drawing which shows the structure of the X-ray tube which concerns on an Example. It is explanatory drawing which represented typically the electron beam of a Wehnelt electrode vicinity, (a) is explanatory drawing when a virtual light source diameter is small, (b) is explanatory drawing when a virtual light source diameter is large. . It is the graph which represented typically the change of the virtual light source diameter with respect to emission current. It is the graph which represented typically the change of the virtual light source diameter with respect to lighting time. 6 is a graph schematically showing a change in emission current with respect to lighting time. It is the graph which represented typically the change of the emission current with respect to the lighting time when each degree of vacuum was changed. It is the graph which represented typically the change of the emission current with respect to lighting time when each cathode temperature was changed. It is explanatory drawing which represented typically the change of the chip | tip which comprises a cathode. It is the graph which represented typically the diameter change of the chip front surface with respect to lighting time.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... X-ray tube 2 ... X-ray detector 11 ... Cathode 12 ... Target 16 ... Wehnelt electrode 32 ... Controller 35a ... Table B ... Electron beam

Claims (3)

  An X-ray generator comprising an electron source for generating an electron beam and a target for generating X-rays by collision of the electron beam from the electron source, and an electron beam amount setting means for setting the electron beam amount to a predetermined value Lighting control means capable of turning on the electron source to generate a predetermined amount of electron beam, physical quantities related to the lighting conditions of the electron source turned on by the lighting control means, and history of the lighting conditions Storage means for storing an electron beam amount correlation for optimizing the electron beam characteristics based on the above, and the lighting control means determines the electron beam amount over time based on the correlation stored in the storage means. An X-ray generator characterized by controlling to change to an optimum value.   2. The X-ray generator according to claim 1, wherein the physical quantity related to the lighting condition is the lighting time, the temperature of the electron source, and the degree of vacuum, and the storage means includes the lighting time, the temperature of the electron source, An X-ray generator characterized by storing a correlation between a physical quantity including at least one of the degrees of vacuum and the electron beam quantity. 3. The X-ray generator according to claim 1, wherein the electron source is a single crystal or sintered chip formed of lanthanum hexaboride or cerium hexaboride. Line generator.

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