JP5459145B2 - X-ray generator - Google Patents

Description

  The present invention relates to an X-ray generator capable of scanning an electron beam.

  In a general X-ray generator, an electron beam generated from a cathode (electron gun) passes through a diaphragm (aperture) through a deflection coil group and a focusing lens, which are electron optical systems, and then collides with a target. X-rays are generated. Usually, in an X-ray generator, an electron beam is deflected by passing a constant current through a deflection coil to align the optical axis of the electron optical system.

  When the optical axis adjustment of the electron optical system is incomplete in the X-ray generator, changing the lens power of the focusing lens moves the focus (electron beam spot) position reduced and focused by the focusing lens. In some cases, the electron beam does not reach the target at all. In particular, in an apparatus for reducing and focusing an electron beam with two or more focusing lenses in order to reduce the X-ray focal spot size, there are as many optical axes as the number of focusing lenses, and the electron beam is all light. It needs to be adjusted to match the axis.

  Usually, unlike an electron microscope, an X-ray generator does not have a means for directly observing an electron beam, and an electron optical system based on an X-ray dose measured by an X-ray detector such as an X-ray imaging device. Optical axis alignment is performed. However, such a method cannot know the direction in which the optical axis is shifted and the magnitude of the shift of the optical axis. For this reason, it is difficult to grasp the sense of the optical axis alignment of the electron optical system, and it takes time for the optical axis alignment work.

Japanese Patent Laid-Open No. 2003-344596

  The problem to be solved by the present invention is to provide an X-ray generator capable of easily and quickly performing an optical axis alignment operation.

The present invention made to solve the above problems
a) an electron source that generates an electron beam;
b) a target disposed opposite to the electron source and generating X-rays by collision of an electron beam;
c) A diaphragm member that is disposed between the electron source and the target and has a diaphragm hole that limits an electron beam passage range;
d) a deflecting means disposed between the electron source and the aperture member for deflecting the electron beam;
e) X-ray detection means for detecting the X-ray dose generated at the target;
f) an X-ray generator having control means for controlling the deflection means by forming a deflection signal of an electron beam based on the X-ray detection data obtained by the X-ray detection means,
The control means performs scanning control of the deflection means by superimposing a scanning signal on the deflection signal so that the electron beam is irradiated to a region including the diaphragm hole in the diaphragm member,
The apparatus further comprises display means for displaying an electron beam profile based on X-ray detection data obtained by the X-ray detection means during scanning control of the deflection means.

  In this case, an external scan signal generator for generating an electron beam scan signal is connectable, and the control means superimposes and adds the scan signal generated by the scan signal generator to the deflection signal. It is preferable to provide an adder circuit.

  In the present invention, the control means performs scanning control of the deflection means by superimposing the scanning signal on the deflection signal so that the electron beam is irradiated onto the area of the diaphragm member including the aperture hole. An electron beam profile is displayed on the display means based on the detected X-ray detection data. That is, the X-ray dose generated by the electron beam that has passed through the aperture hole among the electron beams irradiated to the aperture member colliding with the target is detected by the X-ray detection means, and the electron beam profile is displayed on the display means. . Therefore, the amount of deflection of the electron beam can be set so that the electron beam passes through the center position of the aperture hole while observing the electron beam profile, and the optical axis can be adjusted easily and quickly.

  Further, if an external scan signal generator is connectable and a scan signal is acquired from the scan signal generator, the configuration of the conventional X-ray generator can be used as it is.

The optical system conceptual diagram of the micro focus X-ray tube of the X-ray generator which concerns on one Example of this invention. The figure which shows the principal part structure of a X-ray generator. The block diagram which shows the flow of a process from the scanning signal generation in a control part to emission pattern acquisition. The figure which shows an example of the emission pattern drawn on the screen of a personal computer. The conceptual diagram of optical axis alignment.

  An embodiment of the present invention will be described below with reference to the drawings.

As shown in FIGS. 1 and 2, the X-ray generator according to this embodiment includes a microfocus X-ray tube 10 that generates X-rays and an X-ray for detecting X-rays emitted from the X-ray tube. A line detector (scintillation detector) 20 is provided. FIG. 1 shows a conceptual diagram of an optical system of the microfocus X-ray tube 10, and FIG. 2 shows a main configuration of the X-ray generator.
The cathode (cathode) 1 of the microfocus X-ray tube 10 is a known cathode such as tungsten, lanthanum hexaboride (LaB ₆ ), cerium hexaboride (CeB ₆ ), and an electron beam generated from the cathode 1 is The trajectory is deflected by the deflection coil group 2 which is an electron optical system. Then, the image is reduced and focused by the focusing lens 3 and collides with the target 4 to generate X-rays from a micro focus. An aperture 7 having an aperture 7a is disposed in the gap portion of the focusing lens 3 to limit the electron beam passing range.

  The deflection coil group 2 includes a coil (coil 2a, coil 2b) for deflecting an electron beam in the Y direction perpendicular to the optical axis (indicated by a broken line L in FIG. 2) and a coil (not shown) for deflecting in the X direction. Has been. By passing a constant current through each coil, the electron beam is deflected and the optical axis is adjusted. The X-ray generator according to this embodiment includes a control unit 21 that controls the deflection coil group 2 based on X-ray detection data from the X-ray detector 20. The control unit 21 controls the deflection coil group 2 so that the electron beam is scanned in the X direction and the Y direction (raster scan). At this time, the X-ray detection data of the X-ray detector 20 and the deflection coil group 2 are controlled. The optical axis of the electron beam is adjusted based on the amount of deflection of the optical axis of the electron beam.

  Specifically, the control unit 21 superimposes a sawtooth current having an arbitrary amplitude or frequency as a scan signal on the current flowing through each coil of the deflection coil group 2. As a result, the electron beam is scanned in two directions, ie, the X direction and the Y direction perpendicular to the optical axis (raster scan), and the X-ray detector 20 acquires an emission pattern that is a current angular density distribution of the electron beam.

  Next, the principle of emission pattern acquisition will be described with reference to FIGS. The electron beam emitted from the cathode 1 is raster scanned in two directions perpendicular to the optical axis by a deflection coil group 2 in which a sawtooth current flows. At this time, only an electron beam in a specific angular direction passes through the aperture 7a of the aperture 7 and collides with the target 4, so that X-rays proportional to the current angular density in that direction are generated. The generated X-rays are detected by the X-ray detector 20 in synchronization with the raster scan, and a current angular density distribution in each angular direction, that is, an emission pattern (corresponding to the electron beam profile of the present invention) is obtained.

FIG. 3 shows the flow of processing in the control unit 21 from generation of a scan signal to acquisition of an emission pattern. In this embodiment, the control unit 21 includes a personal computer 22, a scan signal generation circuit 23, a scan signal control circuit 24, an optical axis alignment signal generation circuit 25, and an addition circuit 26. The optical axis alignment signal generation circuit 25 generates a constant potential used for optical axis alignment of the original electron beam.
By operating the personal computer 22, a sawtooth scan potential is generated from the scan signal generation circuit 23. After the amplitude and period are modulated in the scan signal control circuit 24 and the scan signal generation circuit 23 controlled by the personal computer 22, this signal is added to the signal from the axis alignment signal generation circuit 25 by the addition circuit 26. , Converted into current. As a result, a sawtooth scan current flows through each coil of the deflection coil group 2, and the electron beam is raster scanned with a specific amplitude and period. Note that FIG. 3 shows scan potentials for horizontal scanning in the X direction and vertical scanning in the Y direction, but they may be reversed.

  The X-ray detection signal generated by the X-ray detector (scintillation detector) 20 is enhanced by a photomultiplier tube (not shown) and then transmitted to the scan signal generation circuit 23. At this time, the scan signal generation circuit 23 can visualize the signal by acquiring the signal in synchronization with the raster scan, and the visualization signal is transmitted to the personal computer 22. Thereby, an emission pattern is drawn on the screen of the personal computer 22. That is, in this embodiment, the scan signal generation circuit 23 and the personal computer 22 function as display means. FIG. 4 shows an example of an emission pattern drawn on the screen of the personal computer 22. As shown in FIG. 4, when the emission pattern is located at the center of the screen (position indicated by a cross in FIG. 4), the optical axis of the electron beam is located at the center of the aperture.

  Therefore, for example, as shown in FIG. 5A, when the emission pattern is shifted from the center of the screen, the optical axis alignment signal generated by the optical axis alignment signal generation circuit 25 so as to move the emission pattern to the center. By adjusting (FIG. 3), optical axis alignment can be performed accurately and easily.

The present invention is not limited to the above embodiment, and the following modifications are possible.
(1) In the above-described embodiment, the deflection coil group 2 is a so-called one-stage type, but it may be two or more stages.
(2) In the above-described embodiment, the X-ray generator and the X-ray detector are separate bodies, but the X-ray detector may be incorporated in the X-ray generator.
(3) In the above-described embodiment, the deflection coil is used as the deflection means, but a deflection electrode may be used.
(4) A scan signal generator may be provided separately from the X-ray generator and externally attached to the X-ray generator. In this case, the scan signal generator is connected to the X-ray generator only when the optical axis of the electron beam is aligned, and the scan signal generated by the scan signal generator is superimposed on the deflection coil via the addition circuit of the control circuit. You can make it.

DESCRIPTION OF SYMBOLS 1 ... Cathode 2 ... Deflection coil group 3 ... Condensing lens 4 ... Target 7 ... Aperture 7a ... Diaphragm hole 10 ... Micro focus X-ray tube 20 ... X-ray detector 21 ... Control part 22 ... Personal computer 23 ... Scan signal generation circuit 24 ... Scan signal control circuit 25 ... Optical axis alignment signal generation circuit 26 ... Adder circuit

Claims (2)

a) an electron source that generates an electron beam;
b) a target disposed opposite to the electron source and generating X-rays by collision of an electron beam;
c) A diaphragm member that is disposed between the electron source and the target and has a diaphragm hole that limits an electron beam passage range;
d) a deflecting means disposed between the electron source and the aperture means and deflecting the electron beam;
e) X-ray detection means for detecting the X-ray dose generated at the target;
f) an X-ray generator having control means for controlling the deflection means by forming a deflection signal of an electron beam based on the X-ray detection data obtained by the X-ray detection means,
The control means scans the deflection means by superimposing a scanning signal on the deflection signal so as to irradiate the electron beam to a region including the diaphragm hole in the diaphragm member,
An X-ray generation apparatus comprising: display means for displaying an electron beam profile based on X-ray detection data obtained by the X-ray detection means during scanning control of the deflection means. An external scan signal generator that generates an electron beam scan signal can be connected,
The X-ray generator according to claim 1, wherein the control unit includes an adder circuit that superimposes and adds a scan signal generated by the scan signal generator to the deflection signal.

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