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A modern dental X-ray tube. The heated cathode is on the left. Centre is the anode which is made from tungsten and embedded in the copper sleeve. William Coolidge explains medical imaging and X-rays. An X-ray tube is a vacuum tube that converts electrical input power into X-rays. [1]
Both of these X-ray production processes are inefficient, with only about one percent of the electrical energy used by the tube converted into X-rays, and thus most of the electric power consumed by the tube is released as waste heat. When producing a usable flux of X-rays, the X-ray tube must be designed to dissipate the excess heat.
An X-ray generator generally contains an X-ray tube to produce the X-rays. Possibly, radioisotopes can also be used to generate X-rays. [1]An X-ray tube is a simple vacuum tube that contains a cathode, which directs a stream of electrons into a vacuum, and an anode, which collects the electrons and is made of tungsten to evacuate the heat generated by the collision.
X-ray generators produce X-rays by applying a high voltage between the cathode and the anode of an X-ray tube and in heating the tube filament to start the electron emission. The electrons are then accelerated in the resulting electric potential and collide with the anode, which is usually made of Tungsten .
X-ray tube, a vacuum tube that produces X-rays when current flows through it; X-ray laser; X-ray generator, any of various devices using X-ray tubes, lasers, or radioisotopes; Synchrotron, which produces X-rays as synchrotron radiation; Cyclotron, which produces X-rays as cyclotron radiation
The kinetic energy of the electrons is converted into heat and radiation (X-ray photons) due to these interactions. Most of the energy carried by the electrons is converted to heat (99%). Only 1% is converted into radiation or X-rays. In order to assist with the dissipation of such high heat, a larger focal spot or focal track is needed.
In early and basic X-ray equipment, the applied voltage varies cyclically, with one, two, or more pulses per mains AC power cycle. One standard way to measure pulsating DC is its peak amplitude, hence kVp. Most modern X-ray generators apply a constant potential across the X-ray tube; in such systems, the kVp and the steady-state kV are identical.
Crookes X-ray tube from around 1910 Another Crookes x-ray tube. The device attached to the neck of the tube (right) is an "osmotic softener". When the voltage applied to a Crookes tube is high enough, around 5,000 volts or greater, [16] it can accelerate the electrons to a high enough velocity to create X-rays when they hit the anode or the glass wall of the tube.