CT tubeIt is mainly composed of tube core, tube sleeve, radiator, insulating oil and some subordinate accessories. The tube core is the central part of the bulb, which is composed of anode and cathode.

One, the buffer tube (Expansion Bellow)

When the bulb works and heats up, the volume of the oil increases, which acts as a buffer.

2, Arm (Horn)

Contains sockets for connecting high voltage cables that supply power to X-ray generators.

3, Filaments\/Focal Spots

At present, X-ray tubes almost always use tungsten as the filament material. Because tungsten has a certain emission ability at high temperature; it has a high melting point (3370 degrees Celsius), and it is not easy to evaporate into a gas at high temperature; its ductility and tensile strength. It is better, easy to process, and can be drawn into filaments to make a certain shape; it is not easy to deform under the absorption of strong electric fields.

Due to the limitation of the specific capacity of the anode target surface (the power dissipated on the focal area of ​​1mm2), the filament cannot be made too small. Since the practical focal area of ​​the X-ray tube with fixed anode is very small, too small focus will cause emission The amount of X-rays is reduced. In order to obtain a large amount of X-rays, the filament must be thickened. Although the focus is increased, the geometric ambiguity is improved, but the increase in the amount of X-rays shortens the exposure time, preventing the movement of the projected object. cited ambiguity.

At present, many X-ray tubes are equipped with 2 filaments of different sizes on the same cathode to obtain large and small focal points.
, known as a dual focus X-ray tube. Its filament has 3 leads, one is a common lead, and the other two are large and small focus filament leads.

After the temperature of the filament rises to a certain value, it starts to emit electrons, and the number of emitted electrons depends on the temperature of the filament.

It can be seen from the figure that when the temperature of the filament is low, the current density of the emitted electrons is less, but when the temperature rises to a certain value (2600 degrees K), the emission current density increases very rapidly, so the current density of the X-ray tube should be adjusted when adjusting the current of the X-ray tube. Pay special attention to this characteristic, that is, when the filament voltage is increased to a large value, slightly changing the filament voltage will greatly change the tube current.

4,CT tubeWindow (Tube Port)

The outlet of X-ray, and the collimator of X-ray is also installed here.

5, glass core rod (Tube Insert)

Glass mandrel: The X-ray glass shell is used to support the cathode and anode and maintain the vacuum degree in the tube. Usually, hard boric acid glass with high temperature resistance, high dielectric strength and small shrinkage coefficient is used as the main component. In the X-ray tube The vacuum degree of the filament should be kept below 133.32210-7Pa (10-7mmHg) to ensure the normal heating of the filament and the speed of electrons flying to the anode.

6, Stator

The thick anode disc is firmly installed on the shaft rotating in the bearing, and a copper cylinder is also installed on the same shaft, which is used as the rotor for the induction of electron movement. The current of the stator winding establishes a rotating magnetic field, which drives the rotor to rotate, which also drives the anode to rotate. The cathode of the tube is equipped with a tungsten filament wound into a spiral tube, and its position is deviated from the central axis of the tube. Therefore, when the anode rotates, the actual focus is along the It rotates on its surface, and its trajectory is a ring, which makes the generated heat spread on a continuously moving annular surface. The heat and mass received per unit area at the focus become smaller, which significantly improves the X-ray. Although the actual focus area is large, the effective focus is small, which improves the clarity of the X-ray image.

Cathode: The cathode of the X-ray tube is composed of a filament, a focusing mask, etc. Its function is to emit electrons and focus the electrons to bombard the anode.

Anode end (plus)

Anode: The role of the anode target is to withstand electron bombardment radiation X-rays, and at the same time distribute heat. Generally, tungsten is used as the material of the anode target surface, which has the advantages of high atomic number, high melting point, and low vapor pressure at high temperature.

This end is part of the installation close to the cathode This is the part of the end of the rack close to the installation of the anode

8, Trunnion Area

Tube suppliers (such as Siemens, Picker, GE, etc.) provide a trunnion ring around the tube for the clamping frame. This ring enables the tube frame to be securely fixed on theCT tubePlacement.

9, Target

The role of the anode target is to withstand electron bombardment radiation X-rays, and at the same time distribute heat. Generally, tungsten is used as the material of the anode target surface, which has the advantages of high atomic number, high melting point, and low vapor pressure at high temperature.

The tungsten target surface is generally square or rectangular, with a thickness of 1.5mm3mm, and is embedded on an oxygen-free copper column with good thermal conductivity. This not only has high radiation performance, but also conducts heat in time.

The area of ​​the anode target bombarded by the electron beam is called the actual focus. In order to reduce the geometric ambiguity in order to obtain a clear image, it is required to reduce the effective focus of the X-ray, which can be achieved by reducing the inclination of the anode target. Of course, from the projection According to the required angle, the smaller the effective focus surface is, the better, which will inevitably require the actual focus area to be reduced. However, under a certain anode load power condition, the specific capacity of the target surface is improved, which is not conducive to heat diffusion, so the inclination angle should not be too small. .But it can't be too large, too large anode inclination will increase the effective focus area and make the image blurry.

The secondary electrons generated by the anode target surface not only harm the filament and the glass bulb, but also scatter in all directions, causing X-rays to be generated in the center outside the anode target surface. Such non-focus X-rays will affect the clarity of the image. A metal cover made of oxygen-free copper is added to the anode end, which is called a bounce cover. There is an opening in the axial direction of the cover to allow the cathode electrons to pass through quickly; the opening on the side is the X-ray outlet.

In this way, the copper cylinder on the tungsten target surface of the anode and the rebound cover are integrated, and they are connected to the outside of the tube after being sealed by the iron-nickel diamond alloy and the glass bulb with a similar shrinkage coefficient to the glass.