JPH04101339A - X-ray tube - Google Patents

Abstract

PURPOSE:To realize X-ray with brighter luminance by setting an emission rate of electron from the portion facing to a target of filament, larger than an emission rate from the other part. CONSTITUTION:An emission rate of electron from the portion facing to a target 30 of a filament 10 in coil shape is set larger than an emission rate from the other part. As the emission rate of electron from the portion other than that facing to the target 30 is smaller, an electron beam emitted from the other part is drawn to the target 30, being curved by bias voltage. As a result, electron density do not increase much even if the beam diameter gets smaller. Controlling of image formation portion of the electron beam can be thus simplified and the electron density of the electron beam increases.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an X-ray tube, particularly a coiled filament.

[Conventional technology]

Traditionally, X-ray tubes are XPS (X-ray photoelectron spectroscopy), EX
It is used as a basic product that utilizes physical phenomena such as AFS (X-ray absorption wide area fine structure) and total internal reflection fluorescence.

An example of a schematic diagram of this X-ray tube is shown in FIG.

In FIG. 6, a negative high voltage is applied to the coiled filament 10, while a Wehnelt electrode (control electrode)
A bias voltage is applied to 20, and target 3
0 is grounded. The electrons C emitted from the filament IO are accelerated by the potential difference between the filament IO and the target 30, and the Wehnelt electrode 2
With a bias voltage of 0, the center 32 of the target 30
and collides with target 30. The energy of this collision generates X-rays B.

[Problem to be solved by the invention]

By the way, in order to obtain high-luminance X-rays B, it is ideal that the distribution of the electrons e colliding with the target 30 be a Gaussian distribution (more preferably a rectangular distribution), as shown by the broken line in FIG. However, it has been difficult to realize such a Gaussian distribution for the following reasons.

In FIG. 6, a portion of the filament IO facing the Yuichi get 30 (hereinafter referred to as “opposing portion”) 1
Since the electron beam Ea emitted from the target 1 heads straight toward the center 32 of the target 30, as shown by the - dotted chain line, the beam diameter φ does not change. In contrast, other parts 12 of the filament 10, such as the lateral parts 1
As shown by the two-dot chain line, the electron beam Eb emitted from the electron beam Eb is pulled toward the target 30 while being bent by the bias voltage of the Wehnelt electrode 20, so the beam diameter φ is small, that is, the electron density per unit solid angle is small. becomes higher.

Therefore, it is difficult to control the imaging position of the electron beam Eb, and since the electron density of this electron beam Eb is high, when combined with the electron beam Ea from the opposing portion 11, the corner H Therefore, it is difficult to obtain X-rays with high brightness.

On the other hand, in order to concentrate the focus, it may be possible to increase the bias voltage.If you do this, the filament 10
Since the emission of electron e from is suppressed, the colliding electron e
density decreases. Therefore, it is still not possible to obtain X-rays with high brightness.

The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to make the distribution of electron density irradiated onto a target close to a rectangular or Gaussian distribution to obtain high-luminance X-rays.

[Means to solve the problem]

In order to achieve the above object, in the present invention, the electron emission rate from the portion of the coiled filament facing the target is set higher than the electron emission rate from other portions.

[Effect]

According to this invention, since the emission rate of electrons from other parts than the part facing the target is small, the electron beam emitted from the other parts is bent by the bias voltage and pulled toward the target. Even if the beam diameter becomes smaller, the electron density does not increase significantly, making it easier to control the imaging position of the electron beam. electron density increases.

〔Example〕

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

1 and 2 show a first embodiment of the invention.

In FIG. 1, the X-ray tube is equipped with a pressure vessel 40,
The interior is kept in a vacuum state. The pressure vessel 40 is provided with a beryllium window 41, and the X-rays B generated by the target 30 are transmitted through the beryllium window 41 and emitted to the outside.

FIG. 2 is a sectional view taken along the line ■--■ in FIG. 1, and shows the filament 10 and target 30 in an enlarged manner.

In this figure, a coiled filament 10 made of tungsten is wound in an oval shape in this embodiment, and a slightly pointed part of the oval shape is placed facing a target 30. That is, the curvature of the portion (opposed portion) 11 of the filament 10 that faces the target 30 is thicker (set) than the curvature of the other portion (non-opposed portion) 12.

Here, the filament 10 generates heat when energized, but the facing part 11 has a large curvature, so it does not cool easily (and reaches a high temperature), whereas the non-facing part 12 has a relatively small curvature, so it gets cold easily and becomes relatively hot. The temperature becomes low. Therefore, the emission rate of electrons e (
The amount of electron e emitted per unit surface area) is
This means that the rate is set higher than the electron emission rate from .

Note that on the opposite side of the target 30 from the filament 10, a passage 31 for cooling water W is provided.

The rest of the configuration is the same as that of the conventional example described above, and the same or corresponding parts are given the same reference numerals and detailed explanation thereof will be omitted.

Next, the operation of the above configuration will be explained.

As described above, the electron beam Eb emitted from the non-opposing portion 12 of the filament IO, for example, the side portion 13, has a small beam diameter φ, but since the emission rate of electrons e from the non-opposing portion 12 is small, , the electron density does not increase significantly. Therefore, it is relatively easy to control the imaging position of the electron beam Eb, and even if some error occurs in the control, the electron density is not that large, so the distribution of the electron density is changed as shown by the broken line. Close to rectangular or Gaussian distribution.

Moreover, the electron beam Eb emitted from the non-opposed portion Eb
Since the electron density is relatively low, the imaging position can be controlled without increasing the bias voltage of the Wehnelt electrode (control electrode) 20. Therefore, filament 1
Since the emission of electrons e from the opposing portion 11 of 0 and its vicinity is not suppressed, the density of electrons e that collide with the target 30 in a well-controlled manner increases. Therefore, X-rays with high brightness can be obtained.

In the first embodiment, the coiled filament 10 is formed into an egg shape, and the facing portion 11 of the filament 1o is
Although the emission rate of electrons e from the non-opposing portion 12 was set to be higher than the emission rate of electrons from the non-opposing portion 12, other embodiments will be described below. In the following embodiments, the same or equivalent parts as in the first embodiment are denoted by the same reference numerals, and detailed explanation thereof will be omitted.

FIG. 3 shows a second embodiment.

In this figure, the opposing portion 1 of the filament 10
1 and its vicinity are electrolytically polished or polished with a polishing stone, and the cross-sectional area of the coil is set smaller than that of the other portions 12. Therefore, the opposing portion 11 has a larger electrical resistance value than the other portions 12, so that the temperature increases easily and the emission rate of electrons e becomes higher than the other portions.

FIG. 4 shows a third embodiment.

In FIG. 4, the opposing portion 11 of the coiled filament 100 and its vicinity are made of metal having a higher electrical resistance value than the portion 14 on the opposite side. Therefore, since the temperature of the facing portion 11 becomes high, the electron emission rate becomes high.

As a method for manufacturing such filament 10,
First, a metal such as molybdenum is vapor-deposited onto a portion 14 of the filament 10 made of tungsten on the opposite side of the opposing portion 11 . The opposite portion 14 is then partially heated to diffuse the molybdenum. As a result of this treatment, the opposite portion 14 becomes an alloy of molybdenum and tungsten, and therefore has a low electrical resistance value.

FIG. 5 shows a fourth embodiment.

In FIG. 5, a material having a small work function, such as thorium, is provided in the form of a film on the surface of a facing portion 11 of a coiled filament made of tungsten. Here, the work function refers to the minimum energy required to extract one electron e from the metal crystal surface to just outside the surface. Therefore, in this embodiment as well, since the facing portion 11 of the filament 1o has a higher electron emission rate than the other portions 12, the same effect as in the first embodiment can be obtained.

Note that since thorium has low mechanical strength, thorium is provided in the form of a film after forming a filament made of tungsten into a coil shape.

〔Effect of the invention〕

As explained above, according to the present invention, the emission rate of electrons from the part of the filament facing the target is set higher than the emission rate from other parts, so that the electron emission rate from other parts is The electron density of the electron beam does not become significantly larger than that of the other electron beams, which makes it easier to control the imaging position of the electron beam, and increases the electron density of the electron beam from the opposing portion, which is originally easy to control. Therefore, since the distribution of the electron density colliding with the target becomes close to a rectangular or Gaussian distribution, X-rays with high brightness can be obtained.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an X-ray tube showing a first embodiment of the present invention;
2 is a sectional view taken along the line ■-■ in FIG. FIG. 5 is a sectional view of the section X showing the fourth embodiment.
FIG. 6 is a sectional view of the main part of the ray tube, FIG. 6 is a sectional view showing a conventional X-ray tube, and FIG. 7 is a characteristic diagram showing the distribution of electron density. 10... Filament, 11... Opposing part, 1
2...Other parts, 20...Control electrode (Wehnelt electrode), 30...Target,...Electron. Patent application: Human Science Denki Kogyo Co., Ltd.

Claims (1)

[Claims] (1) An X-ray tube comprising a coiled filament, a target that generates X-rays when electrons emitted from the filament collide with each other, and a control electrode that directs the electrons emitted from the filament toward the target. An X-ray tube, wherein the filament is set so that the electron emission rate from a portion facing the target is higher than the electron emission rate from other portions.