JP2004220975A - X-ray tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray tube emitting an X-ray by colliding electrons with a target. <P>SOLUTION: Ions i produced by ionizing argon gas are accelerated toward a filament 3. Even if many ions i of argon gas exist, since the voltage of a high potential electrode 11 is higher than that of the target 4 by 50 V or more, it acts as an ion barrier. Since the ions i of the ionized argon gas receive a deceleration electric field by the high potential electrode 11 they are pushed back to the target 4 to prevent discharging. Even if the electron beam incident to the target 4 emits secondary electrons s, by a same potential electrode having the same potential as the target 4, the secondary electrons s are pushed back to the target 4 due to potential degradation by the electron-beam b, and the secondary electrons s are prevented from flowing into the high potential electrode 11. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an X-ray tube that emits X-rays by colliding electrons with a target.
[0002]
[Prior art]
Conventionally, an X-ray tube emits an electron beam from a filament and collides the emitted electrons with a target serving as an anode to generate X-rays. Also, an electrode having the same potential as the target is provided between the filament and the target. Then, the space between the target and the electrode is made to be a space without an electromagnetic field, and the electron beam emitted from the filament collides with the target, and 99% or more becomes heat and X-rays are partially generated.
In addition, when the electron beam collides with the target in this way, ions are also generated, but since these ions are generated in a space without an electromagnetic field, only a few ions reach the filament, and the filament is It is prevented from being deteriorated by the impact of ions (for example, Patent Document 1).
[0003]
[Patent Document 1]
JP-A-8-287855 (page 4, FIG. 1)
[0004]
[Problems to be solved by the invention]
However, as described above, since 99% or more of the electron beam emitted from the filament is converted into heat, the temperature of the target increases as the amount of X-ray used increases. Then, the gas occluded locally in the target is released from the target due to a rise in temperature, and the released gas may collide with an electron beam to cause ionization and discharge.
[0005]
The gas released from the target is mainly an atmospheric gas such as argon (Ar) gas occluded in the target forging process, and this gas cannot be removed in the X-ray tube exhaust process or aging process.
[0006]
The present invention has been made in view of the above problems, and has as its object to provide an X-ray tube having a reduced probability of occurrence of discharge.
[0007]
[Means for Solving the Problems]
According to the present invention, a vacuum envelope having a vacuum inside, a filament for emitting electrons into the vacuum envelope, and electrons from the filament provided in the vacuum envelope collide with each other to emit X-rays And a high-potential electrode located between the filament and the target and having a potential higher than the target by 50 V or more and preventing discharge by gas released from the target, wherein the potential of the high-potential electrode is set to the potential of the target. By raising the voltage by 50 V or more, the gas generated from the target collides with electrons and is ionized to become ions. The ions are pushed back to the target because they receive a decelerating electric field due to the potential of the high potential electrode, so that discharge occurs due to the ions. To prevent that.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the X-ray tube of the present invention will be described with reference to the drawings.
[0009]
As shown in FIG. 1, reference numeral 1 denotes an X-ray tube used for, for example, a medical device. The X-ray tube 1 is a cylindrical vacuum envelope 2 having a vacuum sealed inside at both ends sealed with glass. Have. A filament 3 is disposed at one end of the vacuum envelope 2 at a position displaced from the center, and a rotating anode target 4 is disposed at the other end. The target 4 rotates the target 4. It is rotatably rotated by the rotor 5.
The target 4 is made of, for example, tungsten (W) or molybdenum (Mo) or an alloy thereof forged in an argon (Ar) gas atmosphere, and has a substantially umbrella-shaped cross section. A frusto-conical target surface 6 is formed which is inclined towards the filament 3 and faces the filament 3.
[0010]
A high-potential electrode 11 is provided between the filament 3 and the target 4 to which a voltage of 50 V or more and 300 V or less, preferably 100 V or less is applied and the potential of which is higher than the target 4 by 50 V or more and 300 V or less, preferably 100 V or less. An inclined surface 12 parallel to the target surface 6 is formed on a surface between the filament 3 of the high-potential electrode 11 and the target surface 6, and the inclined surface 12 of the high-potential electrode 11 is parallel to the target surface 6 regardless of the position. The electric fields are set so as to be equal at equal intervals, and an opening 14 for passing an electron beam is formed in a portion through which the electron beam from the filament 3 passes.
[0011]
Further, an equipotential electrode 15 having the same electric potential as the target 4 is disposed between the high electric potential electrode 11 and the target 4, and the portion of the inclined surface 12 of the high electric potential electrode 11 of the same electric potential electrode 15 is high. An inclined surface 16 parallel to the potential electrode 11 and the target surface 6 is formed, and the target surface 6, the inclined surface 12 of the high-potential electrode 11, and the inclined surface 16 of the same potential electrode 15 are parallel and are equally spaced regardless of the position. Are set to be equal, and an opening 17 for passing an electron beam is formed in a portion through which the electron beam from the filament 3 passes.
[0012]
Next, the operation of the above embodiment will be described.
[0013]
First, the target 4 is rotated by the rotator 5, and the rotating target surface 6 is irradiated with the electron beam b from the filament 3 to generate X-rays. At this time, since 99% or more of the energy of the electron beam b becomes heat, the temperature of the target 4 during the bombardment of X-rays becomes about 1000 ° C. to 1500 ° C. Further, when the temperature of the target 4 rises to, for example, 1500 ° C., a gas such as argon gas vapor of an atmospheric gas occluded at the time of manufacturing such as forging of the target 4 is released.
[0014]
This argon gas vapor is collided with an electron beam, ionized and ionized to become ions i, and discharge occurs. If the velocity distribution of the ions i follows Maxwell's velocity distribution law, the average velocity is 3055 m / s. The most probable speed is 856 m / s, and when converted to energy, they are 1.4 eV and 1.9 eV, respectively. Although the velocity distribution of Maxwell is distributed up to velocity 、, the energy of the argon gas vapor is considered to be several eV to several tens eV because the probability is very small.
[0015]
Further, the ion i ionized by the argon gas is accelerated to the filament 3, and when a large amount of the argon gas is present, a large amount of the ion i of the argon gas flows from the target 4 to the filament 3 to cause discharge. Since the potential is higher than the target by 50 V or more, it acts as an ion barrier. The ions i of the ionized argon gas receive a decelerating electric field by the high potential electrode 11 and are pushed back to the target 4 to prevent the discharge. Further, since the energy of the argon gas is several tens of eV, for example, 20 eV, regardless of the voltage of the filament 3, a deceleration effect is sufficient if about 50V is applied to push the argon gas back to the target 4. Furthermore, since the potential of the high potential electrode 11 is higher than the potential of the target 4 by 300 V or less, preferably 100 V or less, the potential of the filament 3 is considerably small, so that the effect of disturbing the electric field distribution between the filament 3 and the target 4 is minimal. Therefore, the trajectory of the electron beam can be appropriately corrected easily by slightly changing the arrangement of the electrodes.
[0016]
When the electron beam incident on the target 4 emits secondary electrons s, the high-potential electrode 11 to which a voltage of 50 V or more is applied from the target becomes an accelerating electrode for the secondary electrons s. Accelerates and heats the high potential electrode 11. When the recoil electrons are neglected, the energy of the secondary electrons s is almost 20 eV to 30 eV. Therefore, the electron beam b is applied between the high potential electrode 11 and the target 4 by the same potential electrode having the same potential as the target 4. The secondary electrons s can be prevented from flowing into the high-potential electrode 11 due to the Faraday cage effect in which the secondary electrons s are pushed back to the target 4 by a potential drop, that is, a so-called potential well.
[0017]
Therefore, even if the argon gas occluded during production is released from the target 4 due to long-term use and ionized by ionization, the high-potential electrode 11 can suppress the probability of discharge generation as an ion barrier to an extremely low level. Although the electrons s are accelerated by the high-potential electrode 11, they are pushed back by the same-potential electrode 15, thereby improving the reliability.
[0018]
Further, since both the high-potential electrode 11 and the same-potential electrode 15 have the inclined surface 12 and the inclined surface 16 parallel to the inclination of the target surface 6 of the target 4, their distances become constant, respectively. Since the electric field between the same potential electrode 15 and the target 4 can be prevented from being disturbed, the electric field is stabilized. Furthermore, since the electron beam b is irradiated through the openings 14 and 17 formed in the high-potential electrode 11 and the same-potential electrode 15, respectively, the electric field on the plane by the high-potential electrode 11 and the same-potential electrode 15 itself is increased. The distribution tends to be constant, and the disturbance of the electric field on the plane can be prevented. Therefore, it is possible to prevent the change in the electric field from affecting the electron beam b.
[0019]
Next, an X-ray tube according to another embodiment will be described with reference to FIG.
[0020]
The X-ray tube shown in FIG. 2 does not have the same potential electrode 15 of the embodiment shown in FIG.
[0021]
As described above, even if the same potential electrode 15 is eliminated, the high potential electrode 11 becomes an accelerating electrode for the secondary electrons s, but the high potential electrode 11 functions as an ion barrier, so that the discharge can be performed with a simple configuration. Can be suppressed.
[0022]
【The invention's effect】
According to the present invention, by setting the potential of the high-potential electrode higher than the potential of the target by 50 V or more, the ionized ions receive a decelerating electric field due to the potential of the high-potential electrode and are pushed back to the target. Can be prevented.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing one embodiment of an X-ray tube of the present invention.
FIG. 2 is an explanatory diagram showing another embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 X-ray tube 2 Vacuum envelope 3 Filament 4 Target 11 High potential electrode 14 Opening 15 Same potential electrode 17 Opening

Claims (6)

A vacuum envelope with a vacuum inside,
A filament for emitting electrons into the vacuum envelope;
A target provided in the vacuum envelope and emitting X-rays by collision of electrons from the filament;
An X-ray tube comprising: a high-potential electrode located between the filament and the target and having a potential higher than the target by 50 V or more and preventing discharge by a gas released from the target. 2. The X-ray tube according to claim 1, wherein the high potential electrode has a higher potential than the target at a height of 300 V or less. The X-ray tube according to claim 1, wherein the high potential electrode has a potential higher than the target at a height of 100 V or less. The X-ray tube according to any one of claims 1 to 3, wherein the high potential electrode has an opening through which electrons from the filament pass. The X-ray according to any one of claims 1 to 4, further comprising an equipotential electrode located between the high-potential electrode and the target and for pushing secondary electrons from the target to the target at the same potential as the target. tube. The X-ray tube according to claim 5, wherein the same potential electrode has an opening through which electrons from the filament pass.

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