Other Definitions
x ray tube (dict)
|
X-ray TubeAn X-Ray tube is a vacuum tube designed to produce man made X-Ray photons on demand. The development of X-Ray tubes was an important historical event which enabled the field of radiology, for both imaging and treatment applications. Over decades, the development and usefulness of internal imaging using X-Rays spread into development and use of other physical modalities, e.g. ultrasound, radioactive isotope decay (nuclear medicine), nuclear magnetic resonance (MRI), etc. X-Ray tube design As with any vacuum tube, there is a cathode to emit electrons into the vacuum and an anode to collect the electrons, thus establishing a flow of electrical current through the tube. A high voltage electrical current power source is connected across cathode and anode, e.g. 20-100 KV (Kilovolts), such that the voltage can be quickly turned on & off for precise amounts of time, e.g. 0.001 second, and the current flow, often in the 0.1 to 10.0 milliAmp range, once started, can be controlled. What is special about vacuum tubes designed to emit X-Rays is that the electron flow within the vacuum is - focused onto a very small spot on the anode,
- the anode is specially designed (often mechanically spun, occasionally external circulating oil radiator cooled) so as to dissipate the heat and wear resulting from this intense focused barrage of electrons,
- the anode is precisely angled at 1-20 degrees off perpendicular to the electron current so as to allow escape of some of the X-ray photons which are emitted essentially perpendicular to the direction of the electron current,
- the anode is usually made out of tungsten or molybdenum and
- the vacuum tube has a window designed for escape of the generated X-ray photons.
X-Ray tube function Electrons focused on the anode collide with and accelerate other electrons, ions and nuclei within the anode material and about 1% of the energy generated is emitted/radiated, perpendicular to the path of the electron current, as X-Ray photons. This X-Ray photon-generating effect is generally called the Bremsstrahlung effect, a contraction of the German brems for braking, and strahlung for radiation. The range of photonic energies emitted by the system can be adjusted by changing the applied voltage. The number of emitted X-Ray photons, dose, adjusted by controlling the current flow. Related topics
|
 |