CN104411081A - Linear array micro-nano focus X-ray source for micro-nano CT (computer tomography) system - Google Patents

Abstract

The invention discloses a line array micro-nano focus X-ray source for a micro-nano CT system, comprising a cathode 2, a grid 3, an anode 4, a focusing electrode 5, a magnetic solenoid 7, a deflection electrode 8 and a target 9; The cathode is used to generate electrons, the anode is used to accelerate the electrons, the grid is arranged between the anode and the cathode to adjust the intensity of the electron beam emitted by the cathode, and the focusing electrode is used to complete the acceleration. The first focusing of electrons, the magnetic solenoid is used to complete the second focusing of electrons, and the deflection electrode is used to control the position of electrons hitting the target. By using this line array micro-nano focus X-ray source, static CT scanning can be realized, that is, the ray source, the object under test, and the detector are all in a static state, and electronic beam scanning is used instead of mechanical scanning to avoid errors caused by mechanical scanning. Less external interference, high precision, small size, light weight, fast detection speed, can be applied to different types of CT systems.

Description

Line array micro-nano focus X-ray source for micro-nano CT system

technical field

The invention relates to a line array micro-nano focus X-ray source device, in particular to a line array micro-nano focus X-ray source for a micro-nano CT system

Background technique

The traditional micro-focus X-ray source generally has only one focal point. For the micro-nano-microsecond level fast dynamic digital imaging detection system required in the fields of biology and medicine, the performance of the traditional micro-focus X-ray source cannot meet its requirements. At present, the micro-focus X-ray source generally has only one focal point. When it is used in a micro-nano CT system, it has the following disadvantages: the scanning of all X-ray projections required for the high-resolution reconstruction of a general micro-nano CT system usually lasts for many Therefore, a large amount of heat will be generated at the same position of the target layer, which may cause the metal target to melt or even be burned; secondly, the micro-focus CT system with one focus uses mechanical scanning, which will inevitably introduce mechanical errors and affect CT System resolution and other performance indicators.

Contents of the invention

Technical problem: The object of the present invention is to provide a line array micro-nano focus X-ray source for a micro-nano CT system. This line array micro-nano focus X-ray source can be used in a micro-nano CT system, using electronic scanning technology , Use electrical signals to control the scanning of the electron beam to replace the mechanical scanning in the traditional CT system, reduce the scanning error and time, and improve the accuracy of system detection.

In order to solve the above technical problems, the present invention provides the following technical solutions:

The present invention provides a line array micro-nano focus X-ray source for a micro-nano CT system, which is characterized in that it includes a cathode 2, a grid 3, an anode 4, a focusing electrode 5, a magnetic solenoid 7, a deflection electrode 8 and Target 9; the cathode is used to generate electrons, and the anode is used to accelerate electrons; the grid is arranged between the anode and the cathode to adjust the intensity of the electron beam emitted by the cathode; the focusing electrode is used to complete The accelerated electrons are focused for the first time, the magnetic solenoid is used to complete the second focusing of the electrons, and the deflection electrode is used to control the position of the electrons hitting the target.

Further, the X-ray source is accommodated in the casing 1, and the casing is used to isolate air.

Further, the voltage applied to the deflection electrode is a saw-tooth wave voltage. By applying continuous deflection voltage to the electron beam, the electron beam is continuously scanned on the X-ray target, and the continuous scanning of the X-ray focus on the X-ray target is realized.

Further, the cathode uses a field electron emission material.

Further, the cathode emits electrons in a continuous emission manner.

Further, the voltage between the anode and the cathode is 20-160KV.

Compared with the prior art, the line array micro-nano focus X-ray source device provided by the present invention has the following advantages: The line array micro-nano focus X-ray source provided by the present invention adopts electronic scanning technology, and realizes X-ray through time-sharing scanning of electron beams. The scanning of the ray micro-focus on the ray target replaces the mechanical scanning in traditional CT and avoids the errors caused by mechanical scanning; when the high-intensity and high-density electron beam hits the ray target, it will generate a lot of heat. Control the time-sharing scanning of the electron beam, so that the electron beam hits different positions on the radiation target at different times, thereby improving the heat dissipation efficiency and preventing the temperature of the radiation target from being too high; by scanning the electron beam to control the focus on the metal target, the scanning can be reduced Time, reduce the radiation dose to the human body when used in medical, security and other fields; use field electron emission cathode, good controllability, no need to heat the cathode, instantaneous emission, by adjusting the grid voltage, the number of electrons emitted can be controlled, so that Control the size of the tube current.

Description of drawings

When reading the description in conjunction with the accompanying drawings, the structure and various features and advantages of the line array micro-nano focus X-ray source device will become easier to understand, wherein:

1 is an overall schematic diagram of a line array micro-nano focus X-ray source device according to a preferred embodiment of the present invention;

Figure 2 is a schematic diagram of the electronic scanning of the line array micro-nano focus X-ray source;

Figure 3 is a waveform diagram of the sawtooth voltage applied to the deflection electrodes;

Fig. 4 is a point-like tandem target structure diagram of the micro-nano focus ray source according to the present invention;

Fig. 5 is a schematic diagram of the generation of X-rays by the electron beam incident on the lattice target;

Figure 6 is a schematic diagram of the comparison of X-ray intensity generated by the target point and the target base;

Figure 7 is a schematic diagram of electron bremsstrahlung;

Figure 8 is a comparison chart of the X-ray conversion capabilities of tungsten, diamond, and beryllium materials.

Detailed ways

The technical solutions in the embodiments of the present invention will be described in detail below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

The invention relates to a line array micro-nano focus X-ray source device, in particular to a line array micro-nano focus X-ray source for a micro-nano CT system.

A line-array micro-nano focus X-ray source 13 for a micro-nano CT system. This X-ray source 13 includes a cathode 2 for generating electrons, an anode 4 for accelerating electrons, and an electron regulator between the cathode 2 and the anode 4. A large number of grids 3, focusing the electron beam into a small cross-section, a focusing electrode 5 of a high-density electron beam 6, a magnetic solenoid 7, a target 9, a deflection electrode 8 that precisely controls the electron beam to hit the specified position of the target 9, and for The X-ray source 13 is air-insulated from the housing 1 .

The focusing electrode is used for the first focusing of the electrons, and the magnetic solenoid is used for the second focusing of the electrons. The electrons emitted by the cathode strike the target after twice focusing, so that the target emits rays 11 .

The X-ray source innovatively adopts electronic scanning technology, so that the position of the focus of the rays can be precisely controlled, and the line array scanning of the focus of the X-ray source can be realized, which replaces the mechanical scanning in traditional CT and avoids errors caused by mechanical scanning; at the same time, the heat dissipation performance is also 1-2 times that of general X-ray sources.

In the above-mentioned X-ray source, the voltage of the deflection electrode 8 is precisely controlled by the control system, so that the position where the electron beam hits the X-ray target 9 is precisely controlled, and the X-ray micro-focus point is realized by time-sharing scanning of the electron beam. Scanning on the X-ray target 9, on the one hand, replaces the mechanical scanning in the traditional CT to avoid errors caused by the mechanical scanning; By controlling the time-sharing scanning of the electron beam, the electron beam hits different positions on the X-ray target 9 at different times, thereby improving the heat dissipation efficiency and reducing the impact of excessive temperature on the X-ray source.

Preferably, the deflection electrode 8 adopts a sawtooth wave voltage, as shown in FIG. 3 , and a continuous deflection voltage is applied to the electron beam, so that the electron beam continuously scans on the X-ray target 9 to realize continuous scanning of the X-ray focus on the X-ray target. First, a saw-tooth wave deflection voltage is applied to the deflection electrode 8, and then the cathode starts to emit electrons, thereby forming a continuous scanning electron beam, which continuously scans on the X-ray target to realize continuous scanning of the focus.

In some embodiments, the deflection electrode 8 can adopt a discontinuous method, and scan the fixed position on the X-ray target 9 by a fixed voltage to form a one-to-one correspondence. The specific steps are: first, adjust the voltage of the deflection electrode 8 to a voltage And maintain, then the cathode 2 emits electrons through acceleration, focusing, deflection, and hits the X-ray target 9 to generate X-rays 11 to image the object 10 to be detected. After the imaging is completed, the cathode 2 stops emitting electrons and adjusts the voltage of the deflection electrode 8 At the next fixed voltage value, the cathode 2 starts to emit electrons, and hits the position on the X-ray target 9 corresponding to the fixed voltage through the same process, and so on, until the focus imaging at all positions is completed, and the pulse scanning of the focus is realized.

In the above-mentioned X-ray source 13, the cathode 2 adopts a field electron emission cathode, such as a carbon nanometer cathode, a graphene cathode, etc., which overcomes many shortcomings of the traditional hot cathode, and at the same time greatly improves the emission density of the current, thereby producing High-intensity X-rays. In addition, the field electron emission source also has the advantages of low energy consumption and quick start.

Preferably, the cathode 2 emits electrons continuously to provide conditions for continuous scanning of the electron beam.

In some embodiments, cathode 2 may also employ pulsed emission.

In the above-mentioned X-ray source 13 , a voltage is applied between the grid 3 and the cathode 2 to accurately control and adjust the magnitude of the current between the cathode 2 and the anode 4 .

In the above-mentioned X-ray source 13, a high voltage is applied between the anode 4 and the cathode 2, between 20-160KV, to accelerate electrons to a high energy level, so that the electrons finally bombard the X-ray target 9 at high speed to generate X-rays.

In the above-mentioned X-ray source 13, the magnetic solenoid 7 adopts the principle of electromagnetic lens to focus electrons into a small-section, high-density electron beam, so that it can form micron or submicron-sized X-rays on the X-ray target focus.

In the above-mentioned X-ray source 13, the housing 1 is made of a material with good airtightness and not easily damaged, such as an alloy such as stainless steel.

In this embodiment, the structure of the target is shown in Figure 4. The target 9 includes a target base 15 and a dot-like serial target set on the target base. The dot-like serial target includes several dot-like targets. Target point 14, a number of point-shaped target points are arranged at certain intervals, and the point-shaped target array is a point-shaped tandem structure. focus. The ability of the target point to convert into X-rays is much greater than that of the target base. The function of the target base is to fix the target point while having sufficient strength to isolate the vacuum inside the X-ray tube.

The target point is in the shape of a cuboid, and its height H is 5-10 μm. The width d and length w are designed according to the size of the effective focal point of the radiation source, and can reach submicron level. The number of target points needs to be designed according to the number of effective focal points of the ray source, which can be 1, 2, or 1024 or more.

As a further optimization of this embodiment, the distance between the two target points is greater than 10 to 15 times the length w of the target points.

As a further optimization of this embodiment, the thickness D of the target base is 200-300 μm, which can also be designed according to the vacuum requirements of the radiation source, target size and other requirements.

As a further optimization of this embodiment, the aperture of the electron beam incident on the target surface may be 2 to 4 times larger than the length w of the target point.

The electron beam 3 in the X-ray source obtains a lot of kinetic energy under the action of the high-voltage electric field, and flies to the target surface at high speed. Due to the obstruction of the target surface, the electrons are suddenly decelerated, and most of the lost energy is converted into heat, and a small part is converted into heat. It is radiated in the form of X photons, that is, the bremsstrahlung effect of electrons, as shown in Figure 7. The bremsstrahlung intensity I _rad is approximately expressed as:

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; rad</span>}}<span\; class="notranslate">\; \&Proportional;</span>\frac{{\mathrm{<span\; class="notranslate">\; Z</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; z</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; 6</span>}}}{{\mathrm{<span\; class="notranslate">\; m</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the formula, Z is the atomic number of the target, z is the atomic number of the incident charged particle, electron z=-1, and e is the electric quantity of the electron. The formula (1) shows that when electrons are incident on the target surface, the X-photon conversion efficiency of the target is proportional to the target atomic number Z ² .

Therefore, target materials with high atomic number and high density are selected, such as tungsten, tantalum, molybdenum, gold, etc., to increase the X-ray yield. The target base is made of materials with low density and low atomic number, such as beryllium and diamond. Relative to the target point, the target base material generates X-rays 18 with very low intensity. As shown in Fig. 6, the X-ray 17 generated by the target point forms a strong peak, and the X-ray intensity generated by the target base material is relatively low. Therefore, the X-ray source is the width of the X-ray beam intensity peak produced by the effective focal point and the target point. Figure 8 is the simulation calculation result using the Monte Carlo simulation software EGSnrc. The figure shows that the X-ray intensity produced by 250 μm beryllium and 10 μm diamond is less than 10% of the X-ray intensity produced by the 10 μm tungsten target, and it is mainly low-energy X-rays. This X-ray photon is easily filtered out by the filter. Therefore, based on the above principles, the X-ray effective focus size generated by the point-like tandem target structure of the present invention can be approximately equal to the size of the target point.

The method for preparing the target 9 of this embodiment: the target layer is prepared by stamping, tape casting, sintering and other methods; the target point is prepared on the target layer material by printing, sintering or coating, and photolithography on the upper surface of the target layer.

In the target described in this embodiment, since the target material with high density and high atomic number is much more capable of converting X-rays than the target base material with low density and low atomic number, the effective focus size of the ray source is mainly determined by the target It is determined by the size of the electron beam, which is not directly related to the cross-sectional area of the electron beam. It is conducive to the formation of a stable, micro-nano-sized multi-focus array, which greatly reduces the requirements for the focus size of the electron beam and the control of scanning deflection precision. In order to achieve sub-micron or even The linear array multi-focus ray source with nanoscale focus size provides a feasible way. Optionally, by setting target structures and sizes of different sizes and correspondingly optimizing the energy of the electron beam, radiation sources with different focal spot sizes and different characteristic spectral lines can be realized to meet different radiation detection requirements.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations.

Claims (6)

1. The line array micro-nano focus X-ray source for micro-nano CT system is characterized in that: comprise cathode (2), grid (3), anode (4), focusing electrode (5), magnetic solenoid ( 7), a deflection electrode (8) and a target (9); the cathode is used to generate electrons, and the anode is used to accelerate electrons; the grid is arranged between the anode and the cathode to adjust the electrons emitted by the cathode Beam intensity; the focusing electrode is used to complete the first focusing of the accelerated electrons, the magnetic solenoid is used to complete the second focusing of the electrons, and the deflection electrode is used to control the position of the electrons hitting the target. 2. The line-array micro-nano focus X-ray source for a micro-nano CT system according to claim 1, characterized in that: the X-ray source is accommodated in a casing (1), and the casing is used to isolate air. 3. The array micro-focus X-ray source for micro-nano CT system according to claim 1, characterized in that: the voltage applied to the deflection electrode is a sawtooth wave voltage, and by adding a continuous deflection voltage to the electron beam, the electron beam The beam continuously scans on the X-ray target to realize the continuous scanning of the X-ray focus on the X-ray target. 4. The array micro-focus X-ray source for micro-nano CT system according to claim 1, characterized in that: the cathode uses a field electron emission material. 5. The array micro-focus X-ray source for micro-nano CT system according to claim 1, characterized in that: the cathode emits electrons in a continuous emission manner. 6. The array micro-focus X-ray source for micro-nano CT system according to claim 1, characterized in that: the voltage between the anode and the cathode is 20-160KV.