X-ray radiation is generated during braking of accelerated electrons on the screen anode, made of heavy metal, the electrons used for the cathode.To accelerate the electrons to the cathode of the high voltage is applied.
In modern X-ray tubes, electrons are obtained by glowing of the cathode.The number of electrons can be changed by adjusting the current in the heater circuit.At low voltage, not all the electrons involved in the creation of the anode current, while at the cathode, the electron cloud that dissolves with increasing voltage.From a certain voltage, all the electrons reach the anode, while flowing through the tube the maximum current, it is called the saturation current.
Typically, anode X-ray tube is in the form of a massive cover of copper, in which the thickness of the tungsten plate is soldered, which is called the mirro
r of the anode.The anode facing the cathode of a beveled end, thus x exiting radiation perpendicular to the tube axis.
The cathode is a refractory filament, most often it is made of tungsten in the form of a flat or cylindrical helix.The thread is surrounded by metal cup designed to focus the electron beam on the mirror anode.Bifocal X-ray tube equipped with two filaments.
At the anode, a large amount of heat as a result of inhibition of electron flow, only a small amount of energy is transformed into X-ray radiation.In order to prevent overheating of the anode and increase the efficiency of the X-ray tube used for oil and water or air cooling, sometimes this purpose use radiation.
magnitude focus X-ray tube affects the sharpness of the image.Modern handsets focus a line from 10 to 40 mm, but the practical importance than its actual value, and the apparent projection in the direction of the beam.The modern diagnostic tubes effective focus area is about three times smaller than the actual area.The capacity of such tubes to 2 times greater than that of the device with a circular focus.
In X-ray tubes with rotating anode power even more.Solid tungsten anode has a line spectrum in their focus, stretched around the circumference.It rotates on bearings so that the cathode tube is displaced relative to its axis, so that the focused electron beam is always incident on beveled mirror surface of the anode.