Generation of X-rays for X-ray imaging
An electric current flows through the tungsten wire and heats it. As the heat increases, the energy allows the electrons to be released from the filament by thermionic emission. Electrons are attracted to the positively charged anode and hit the tungsten target at a maximum energy determined by the tube potential (voltage).When the electrons hit the target, they convert their energy into heat (99%) and X-ray photons (1%) through bremsstrahlung and characteristic interactions. X-ray photons are released from the beam as a beam of energy (X-ray spectrum) and form the basis for the formation of X-ray images equipment.
The cathode
The filament
Made of thin (0.2mm) tungsten filaments, because tungsten: high atomic number (A 184, Z 74) is A good hot electron emitter (good at emitting electrons) can be made into thin lines. The melting temperature is very high (3422° C). The size of the filament depends on the size of the focal point. Some cathodes have both wide focusing and fine focusing filaments.
Focusing cup
Made of molybdenum: a hot electron emitter with a high melting point and a poor melting point, so it does not release electrons to interfere with the negative charge of the electron beam from the filament, focusing the electrons to the anode and stopping the space-diffusion anode.
A target made of tungsten for the same reason that the filament is made with rhenium added to tungsten to prevent the anode from breaking under high temperature and in use and a molybdenum anode disc with a valve stem is positively charged to attract electrons and is set at an Angle so that the X-ray beam is directed to the patient. It's usually 5 to -15 definitions.
Focus: The position where the electron strikes the anode Actual focus: The physical area of the affected focus trajectory Focus trajectory: The anode portion of the electron bombardment. On the rotating anode, this is a circular path available.
Focus: The area of focus projected outside the tube.
Fixed Anodes: These are generally limited to dental radiology and radiotherapy systems. It consists of a fixed anode and an electron beam that flows continuously to a small area.
Rotating anode: Used in most radiography applications, including mobile devices and fluoroscopy. Includes a disk with a thin tungsten hypotenuse at the circumference of the circle and rotates at a frequency of 50 Hz. Over time, it overcomes the heating by being exposed to different areas of the electron stream. It includes:
Around the molybdenum disc molybdenum rod with thin tungsten target, it is a poor heat conductor, can prevent heat transfer to the metal bearing valve stem and the silver lubrication bearing between the rotor, has no effect on the heat transfer, but at low resistance to allow very fast rotation, to reduce the heat transfer of the rotor blackening, easy heat transfer.
