JPS6346952B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermionic emission structure using a heat-resistant metal strip for an X-ray tube.

FIG. 1 shows an example of an X-ray tube currently used for normal purposes. A cathode 1 and an anode 4 are disposed facing each other in a high vacuum glass bulb, and electrons emitted from the thermionic emission structure 3 of the cathode 1 are focused into an electron beam by a focusing groove 2 and applied between the cathode and anode. It is accelerated by the applied high voltage and collides with the target 5 of the anode 4, causing it to emit X-rays. The part where the electron beam collides with the target is called the focal point, and is important for use because it is an X-ray radiation source, but the focal area and electron flow density are determined by the focusing groove 2 and thermionic emission structure 3.
It is determined by the structural dimensions and mutual arrangement of the two, so that an appropriate focal point is formed depending on the application. Conventionally, most thermionic emission structures used coiled filaments of heat-resistant metals such as tungsten, but there is the possibility of reducing unnecessary sub-focal points and making the electron distribution at the focal point uniform. Due to its large size, it is desired to use a flat plate-like, band-like, or ribbon-like thermionic emission structure. However, while it has many advantages, it actually has many drawbacks, and it has not reached the point where it can replace conventional coiled filaments. One of its drawbacks is that the temperature distribution tends to become uneven during electrical heating. As a countermeasure against this problem, a thermionic emission structure having a flat thermionic emission part having a structure as shown in FIGS. 2a to 2e has been proposed. However, all of these methods are expensive because they use expensive materials inefficiently (the width of the thermionic emission part is narrowed, so a lot of parts are discarded), and because complicated processing is performed on materials that are difficult to process. Another problem is that even if the desired shape is achieved, the thermionic emission surface may become sagging or warped due to thermal expansion and deformation during high-temperature use, causing displacement with respect to the focusing groove 2 and changing the focal point.

An object of the present invention is to provide a thermionic emission structure for an X-ray tube that is free from the above-mentioned problems, provides a stable focal point with a sharp contour and uniform electron density, and is relatively inexpensive. There is a particular thing.

In order to achieve the above object, in the present invention,
Thin strip (ribbon) of heat-resistant metal with equal thickness and width.
The material was processed and formed into a U-shape, and the center part was used for thermionic emission and both ends were used for support. In this way, material loss is reduced and processing is easy. Since the support part that does not require thermionic emission needs to be at a low temperature and have sufficient rigidity so as not to emit thermionic electrons, it is supported and fixed with a backing plate made of a heat-resistant metal plate. Furthermore, in order to prevent the thermionic emission part, that is, the central part of the U-shape, from sagging or warping at high temperatures, a backing plate placed inside the U-shape is used as a spring material.
The U-shaped bent portion is pushed outward, and tension is applied so that the thermionic emission portion at the center of the U-shape is not deformed. In order to prevent this spring caul plate from becoming so hot that it loses its elasticity, the edge of the caul plate that contacts the U-shaped bent part should be shaped so that a large amount of heating current and heat will not be diverted to the caul plate, i.e., serrated or rough. A face, etc.

FIG. 3 is a diagram showing a first embodiment of the present invention. 6 is a thermoelectron emitting part in the center of a heat-resistant metal strip formed into a U-shape, 7 is a support fixing part at both ends of the U-shape, 8 is a backing plate, and 9 is a support plate at both ends of the U-shape. The anchor is supported and fixed together with the backing plate, and 9a is a groove in the anchor. In the case of X-ray tubes, a high voltage is applied between the cathode and anode, and there is no very effective protection against cation bombardment, so tungsten is used as the material for the U-shaped member that forms the thermionic emission section. is appropriate. The material of the U-shaped member according to the present invention can be relatively narrow, unlike the case shown in FIGS. As mentioned above, since the material is simply bent into a U-shape while keeping the same width, there is no part of the material that becomes scraps.

FIG. 4 shows a second embodiment of the present invention, in which a fixing plate 10 is used in place of the anchor 9 of the first embodiment.

Although the cost can be reduced in the first and second embodiments, if the backing plate and other supporting and fixing parts are not properly processed, there is a risk that thermal deformation will occur in the thermionic emission section 6. FIG. 5 is a diagram showing a third embodiment of the present invention, in which the U-shaped bent portion is pushed outward as shown by the arrow in the figure using a spring-duty backing plate 11 to apply tension to the electron emitting portion 6. Prevents thermal deformation. The caul plate used in this embodiment may be one of the shapes shown in FIGS. 6a to 6d that is easy to manufacture in actual manufacturing process (it is not necessarily constant depending on the equipment at the manufacturing site, technical tradition, etc.). End portion 12 where the backing plate 11 contacts the bent portion of the U-shaped material
If a large amount of heating current or heat is diverted to the patch plate 11, the elasticity of the patch plate 11 may weaken and become useless, so the plate is made serrated or has a rough surface to prevent the split flow.

As explained above, according to the present invention, a thermionic emission structure for an X-ray tube having a rectangular thermionic emission surface that produces a good focus can be manufactured at a low cost with a high material yield.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of an X-ray tube, FIGS. 2 a to e are examples of a thermionic emission structure having a conventional flat thermionic emission section, and FIGS. 3 to 5 are examples of different embodiments of the present invention. , and FIGS. 6 a to 6 d are views of the spring and backing plate according to the present invention. DESCRIPTION OF SYMBOLS 1... Cathode, 2... Focusing groove, 3... Thermionic emission structure, 4... Anode, 5... Target, 6... Thermionic emission part, 7... Support fixing part, 8... Backing plate, 11, 11
a, 11b, 11c, 11d... Spring-duty backing plates.

Claims (1)

[Scope of Claims] 1. A thin strip of heat-resistant metal suitable for thermionic emission with equal thickness and equal width cross section is bent into a U-shape, and the center part is used for thermionic emission and both ends are used for support. A thermionic emission structure for an X-ray tube, characterized in that both ends are supported and fixed together with heat-resistant metal backing plates disposed at least on the inside. 2 The backing plate applies tension to the central part of the U-shaped material by pushing the area near the bent part of the U-shaped material outward, and contacts the U-shaped material only at the support fixing part and the vicinity of the U-shaped bent part. 2. The thermionic emission structure for an X-ray tube according to claim 1, wherein the end of the backing plate at the contact point near the bent portion is in a state to suppress the shunt of heating current from the U-shaped member.